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  Subjects -> ENGINEERING (Total: 2298 journals)
    - CHEMICAL ENGINEERING (192 journals)
    - CIVIL ENGINEERING (192 journals)
    - ELECTRICAL ENGINEERING (104 journals)
    - ENGINEERING (1209 journals)
    - ENGINEERING MECHANICS AND MATERIALS (385 journals)
    - HYDRAULIC ENGINEERING (55 journals)
    - INDUSTRIAL ENGINEERING (69 journals)
    - MECHANICAL ENGINEERING (92 journals)

CIVIL ENGINEERING (192 journals)                     

Showing 1 - 192 of 192 Journals sorted alphabetically
ACI Structural Journal     Full-text available via subscription   (Followers: 17)
Acta Polytechnica : Journal of Advanced Engineering     Open Access   (Followers: 2)
Acta Structilia : Journal for the Physical and Development Sciences     Open Access   (Followers: 2)
Advances in Civil Engineering     Open Access   (Followers: 36)
Advances in Structural Engineering     Full-text available via subscription   (Followers: 28)
Agregat     Open Access  
Ambiente Construído     Open Access   (Followers: 1)
American Journal of Civil Engineering and Architecture     Open Access   (Followers: 31)
Architectural Engineering     Open Access   (Followers: 4)
Archives of Civil and Mechanical Engineering     Full-text available via subscription   (Followers: 1)
Archives of Civil Engineering     Open Access   (Followers: 10)
Archives of Hydro-Engineering and Environmental Mechanics     Open Access   (Followers: 2)
ATBU Journal of Environmental Technology     Open Access   (Followers: 4)
Australian Journal of Structural Engineering     Full-text available via subscription   (Followers: 6)
Baltic Journal of Road and Bridge Engineering     Full-text available via subscription   (Followers: 1)
BER : Building and Construction : Full Survey     Full-text available via subscription   (Followers: 10)
BER : Building Contractors' Survey     Full-text available via subscription   (Followers: 4)
BER : Building Sub-Contractors' Survey     Full-text available via subscription   (Followers: 3)
BER : Survey of Business Conditions in Building and Construction : An Executive Summary     Full-text available via subscription   (Followers: 4)
Bioinspired Materials     Open Access   (Followers: 5)
Bridge Structures : Assessment, Design and Construction     Hybrid Journal   (Followers: 16)
Building & Management     Open Access  
Building and Environment     Hybrid Journal   (Followers: 15)
Building Women     Full-text available via subscription  
Built Environment Project and Asset Management     Hybrid Journal   (Followers: 15)
Bulletin of Pridniprovsk State Academy of Civil Engineering and Architecture     Open Access   (Followers: 6)
Canadian Journal of Civil Engineering     Hybrid Journal   (Followers: 12)
Case Studies in Engineering Failure Analysis     Open Access   (Followers: 8)
Case Studies in Nondestructive Testing and Evaluation     Open Access   (Followers: 11)
Case Studies in Structural Engineering     Open Access   (Followers: 9)
Cement and Concrete Composites     Hybrid Journal   (Followers: 17)
Challenge Journal of Concrete Research Letters     Open Access   (Followers: 2)
Challenge Journal of Structural Mechanics     Open Access   (Followers: 5)
Change Over Time     Full-text available via subscription   (Followers: 2)
Civil and Environmental Engineering     Open Access   (Followers: 7)
Civil And Environmental Engineering Reports     Open Access   (Followers: 6)
Civil and Environmental Research     Open Access   (Followers: 19)
Civil Engineering = Siviele Ingenieurswese     Full-text available via subscription   (Followers: 4)
Civil Engineering and Architecture     Open Access   (Followers: 18)
Civil Engineering and Environmental Systems     Hybrid Journal   (Followers: 3)
Civil Engineering and Technology     Open Access   (Followers: 10)
Civil Engineering Dimension     Open Access   (Followers: 8)
Civil Engineering Infrastructures Journal     Open Access  
Cohesion and Structure     Full-text available via subscription   (Followers: 2)
Composite Structures     Hybrid Journal   (Followers: 268)
Computer-aided Civil and Infrastructure Engineering     Hybrid Journal   (Followers: 11)
Computers & Structures     Hybrid Journal   (Followers: 36)
Concrete Research Letters     Open Access   (Followers: 6)
Construction Economics and Building     Open Access   (Followers: 2)
Construction Engineering     Open Access   (Followers: 9)
Construction Management and Economics     Hybrid Journal   (Followers: 22)
Construction Science     Open Access   (Followers: 4)
Constructive Approximation     Hybrid Journal  
Curved and Layered Structures     Open Access   (Followers: 2)
DFI Journal : The Journal of the Deep Foundations Institute     Hybrid Journal   (Followers: 1)
Earthquake Engineering and Structural Dynamics     Hybrid Journal   (Followers: 17)
Enfoque UTE     Open Access   (Followers: 4)
Engineering Project Organization Journal     Hybrid Journal   (Followers: 7)
Engineering Structures     Hybrid Journal   (Followers: 13)
Engineering Structures and Technologies     Hybrid Journal   (Followers: 2)
Engineering, Construction and Architectural Management     Hybrid Journal   (Followers: 14)
Environmental Geotechnics     Hybrid Journal   (Followers: 5)
European Journal of Environmental and Civil Engineering     Hybrid Journal   (Followers: 9)
Fatigue & Fracture of Engineering Materials and Structures     Hybrid Journal   (Followers: 16)
Frattura ed Integrità Strutturale : Fracture and Structural Integrity     Open Access  
Frontiers in Built Environment     Open Access  
Frontiers of Structural and Civil Engineering     Hybrid Journal   (Followers: 6)
Geomaterials     Open Access   (Followers: 4)
Geosystem Engineering     Hybrid Journal   (Followers: 1)
Geotechnik     Hybrid Journal   (Followers: 3)
Géotechnique Letters     Hybrid Journal   (Followers: 7)
GISAP : Technical Sciences, Construction and Architecture     Open Access  
HBRC Journal     Open Access   (Followers: 2)
Hormigón y Acero     Full-text available via subscription  
HVAC&R Research     Hybrid Journal  
Indonesian Journal of Urban and Environmental Technology     Open Access  
Indoor and Built Environment     Hybrid Journal   (Followers: 2)
Infrastructure Asset Management     Hybrid Journal   (Followers: 2)
Infrastructures     Open Access  
Ingenio Magno     Open Access   (Followers: 1)
Insight - Non-Destructive Testing and Condition Monitoring     Full-text available via subscription   (Followers: 22)
International Journal for Service Learning in Engineering     Open Access  
International Journal of 3-D Information Modeling     Full-text available via subscription   (Followers: 3)
International Journal of Advanced Structural Engineering     Open Access   (Followers: 16)
International Journal of Civil, Mechanical and Energy Science     Open Access   (Followers: 1)
International Journal of Concrete Structures and Materials     Open Access   (Followers: 14)
International Journal of Condition Monitoring     Full-text available via subscription   (Followers: 2)
International Journal of Construction Engineering and Management     Open Access   (Followers: 9)
International Journal of Geo-Engineering     Open Access   (Followers: 3)
International Journal of Geosynthetics and Ground Engineering     Full-text available via subscription   (Followers: 4)
International Journal of Masonry Research and Innovation     Hybrid Journal   (Followers: 1)
International Journal of Pavement Research and Technology     Open Access   (Followers: 6)
International Journal of Protective Structures     Hybrid Journal   (Followers: 6)
International Journal of Steel Structures     Hybrid Journal   (Followers: 2)
International Journal of Structural Engineering     Hybrid Journal   (Followers: 10)
International Journal of Structural Integrity     Hybrid Journal   (Followers: 2)
International Journal of Structural Stability and Dynamics     Hybrid Journal   (Followers: 7)
International Journal of Sustainable Built Environment     Open Access   (Followers: 4)
International Journal of Sustainable Construction Engineering and Technology     Open Access   (Followers: 8)
International Journal on Pavement Engineering & Asphalt Technology     Open Access   (Followers: 7)
International Journal Sustainable Construction & Design     Open Access  
Journal of Bridge Engineering     Full-text available via subscription   (Followers: 15)
Journal of Building Engineering     Hybrid Journal   (Followers: 1)
Journal of Building Materials and Structures     Open Access   (Followers: 2)
Journal of Building Performance Simulation     Hybrid Journal   (Followers: 6)
Journal of Civil Engineering and Construction Technology     Open Access   (Followers: 12)
Journal of Civil Engineering and Management     Hybrid Journal   (Followers: 7)
Journal of Civil Engineering and Science     Open Access   (Followers: 8)
Journal of Civil Engineering Research     Open Access   (Followers: 6)
Journal of Civil Engineering, Science and Technology     Open Access  
Journal of Civil Society     Hybrid Journal   (Followers: 4)
Journal of Civil Structural Health Monitoring     Hybrid Journal   (Followers: 4)
Journal of Composites for Construction     Full-text available via subscription   (Followers: 13)
Journal of Computing in Civil Engineering     Full-text available via subscription   (Followers: 24)
Journal of Construction Engineering     Open Access   (Followers: 7)
Journal of Construction Engineering and Management     Full-text available via subscription   (Followers: 19)
Journal of Constructional Steel Research     Hybrid Journal   (Followers: 8)
Journal of Earth Sciences and Geotechnical Engineering     Open Access   (Followers: 4)
Journal of Fluids and Structures     Hybrid Journal   (Followers: 6)
Journal of Frontiers in Construction Engineering     Open Access   (Followers: 2)
Journal of Green Building     Full-text available via subscription   (Followers: 11)
Journal of Highway and Transportation Research and Development (English Edition)     Full-text available via subscription   (Followers: 14)
Journal of Infrastructure Systems     Full-text available via subscription   (Followers: 21)
Journal of Legal Affairs and Dispute Resolution in Engineering and Construction     Full-text available via subscription   (Followers: 5)
Journal of Marine Science and Engineering     Open Access   (Followers: 1)
Journal of Materials and Engineering Structures     Open Access   (Followers: 5)
Journal of Materials in Civil Engineering     Full-text available via subscription   (Followers: 10)
Journal of Nondestructive Evaluation     Hybrid Journal   (Followers: 11)
Journal of Performance of Constructed Facilities     Full-text available via subscription   (Followers: 4)
Journal of Pipeline Systems Engineering and Practice     Full-text available via subscription   (Followers: 7)
Journal of Rehabilitation in Civil Engineering     Open Access   (Followers: 3)
Journal of Solid Waste Technology and Management     Full-text available via subscription   (Followers: 1)
Journal of Structural Engineering     Full-text available via subscription   (Followers: 40)
Journal of Structural Fire Engineering     Full-text available via subscription   (Followers: 6)
Journal of Sustainable Architecture and Civil Engineering     Open Access   (Followers: 3)
Journal of Sustainable Design and Applied Research in Innovative Engineering of the Built Environment     Open Access   (Followers: 1)
Journal of the Civil Engineering Forum     Open Access  
Journal of the South African Institution of Civil Engineering     Open Access   (Followers: 4)
Journal of Water and Environmental Nanotechnology     Open Access  
Jurnal Spektran     Open Access   (Followers: 1)
Jurnal Teknik Sipil dan Perencanaan     Open Access   (Followers: 1)
Konstruksia     Open Access  
KSCE Journal of Civil Engineering     Hybrid Journal   (Followers: 2)
Latin American Journal of Solids and Structures     Open Access   (Followers: 4)
Materiales de Construcción     Open Access  
Mathematical Modelling in Civil Engineering     Open Access   (Followers: 3)
Nondestructive Testing And Evaluation     Hybrid Journal   (Followers: 17)
npj Materials Degradation     Open Access  
Obras y Proyectos     Open Access   (Followers: 1)
Open Journal of Civil Engineering     Open Access   (Followers: 7)
Photonics and Nanostructures - Fundamentals and Applications     Hybrid Journal   (Followers: 2)
Practice Periodical on Structural Design and Construction     Full-text available via subscription   (Followers: 4)
Proceedings of the Institution of Civil Engineers - Bridge Engineering     Hybrid Journal   (Followers: 8)
Proceedings of the Institution of Civil Engineers - Civil Engineering     Hybrid Journal   (Followers: 12)
Proceedings of the Institution of Civil Engineers - Management, Procurement and Law     Hybrid Journal   (Followers: 8)
Proceedings of the Institution of Civil Engineers - Municipal Engineer     Hybrid Journal   (Followers: 3)
Proceedings of the Institution of Civil Engineers - Structures and Buildings     Hybrid Journal   (Followers: 4)
Random Structures and Algorithms     Hybrid Journal   (Followers: 5)
Research in Nondestructive Evaluation     Hybrid Journal   (Followers: 7)
Revista IBRACON de Estruturas e Materiais     Open Access   (Followers: 1)
Road Materials and Pavement Design     Hybrid Journal   (Followers: 11)
Russian Journal of Nondestructive Testing     Hybrid Journal   (Followers: 6)
Science and Engineering of Composite Materials     Hybrid Journal   (Followers: 61)
Selected Scientific Papers - Journal of Civil Engineering     Open Access   (Followers: 3)
Slovak Journal of Civil Engineering     Open Access   (Followers: 2)
Soils and foundations     Full-text available via subscription   (Followers: 5)
Steel Construction - Design and Research     Hybrid Journal   (Followers: 3)
Structural and Multidisciplinary Optimization     Hybrid Journal   (Followers: 10)
Structural Concrete     Hybrid Journal   (Followers: 11)
Structural Control and Health Monitoring     Hybrid Journal   (Followers: 9)
Structural Engineering International     Full-text available via subscription   (Followers: 12)
Structural Mechanics of Engineering Constructions and Buildings     Open Access  
Structural Safety     Hybrid Journal   (Followers: 7)
Structural Survey     Hybrid Journal  
Structure     Full-text available via subscription   (Followers: 23)
Structure and Infrastructure Engineering: Maintenance, Management, Life-Cycle Design and Performance     Hybrid Journal   (Followers: 13)
Structures     Hybrid Journal   (Followers: 1)
Study of Civil Engineering and Architecture     Open Access   (Followers: 9)
Superlattices and Microstructures     Hybrid Journal   (Followers: 2)
Surface Innovations     Hybrid Journal  
Technical Report Civil and Architectural Engineering     Open Access  
Teknik     Open Access  
The IES Journal Part A: Civil & Structural Engineering     Hybrid Journal   (Followers: 6)
The Structural Design of Tall and Special Buildings     Hybrid Journal   (Followers: 6)
Thin Films and Nanostructures     Full-text available via subscription   (Followers: 2)
Thin-Walled Structures     Hybrid Journal   (Followers: 4)
Transactions of the VŠB - Technical University of Ostrava. Construction Series     Open Access   (Followers: 1)
Transportation Geotechnics     Full-text available via subscription   (Followers: 1)
Transportation Infrastructure Geotechnology     Hybrid Journal   (Followers: 8)
Underground Space     Open Access  
Water Science & Technology     Partially Free   (Followers: 25)
Water Science and Technology : Water Supply     Partially Free   (Followers: 22)

           

Journal Cover Cement and Concrete Composites
  [SJR: 3.017]   [H-I: 83]   [17 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0958-9465
   Published by Elsevier Homepage  [3118 journals]
  • The effect of synthesis conditions on the efficiency of C-S-H seeds to
           accelerate cement hydration
    • Abstract: Publication date: March 2018
      Source:Cement and Concrete Composites, Volume 87
      Author(s): G. Land, D. Stephan
      C-S-H seeding is a promising approach to accelerate cement hydration in a very effective way. Until now little is known about the way the C-S-H seeds work and how they affect the properties of the hydrated cement paste. To be able to analyse this in detail it is necessary to have a preparation method for the C-S-H seeds, which is reproducible and able to prepare seeds with defined properties. The present work describes two methods for the synthesis of C-S-H seeds, a mechanochemical approach and a sol-gel synthesis. A factorial design of experiments setup was used to find those parameters, which affect the efficiency of the C-S-H seeds to accelerate cement hydration and to adjust these parameters in order to achieve the optimized seeds, which are very effective accelerators. Heat flow calorimetry shows that the dormant period of cement hydration can be eliminated by the use of the optimized C-S-H seeds and compressive strength tests show a multiplication of early compressive strength even at very low concentrations of seeds, indicating that an optimization of the synthesis by factorial design of experiments is a promising way for further studies on the mode of action of C-S-H seeds.

      PubDate: 2017-12-27T02:44:17Z
       
  • Design of SiO2/PMHS hybrid nanocomposite for surface treatment of
           cement-based materials
    • Abstract: Publication date: March 2018
      Source:Cement and Concrete Composites, Volume 87
      Author(s): Ran Li, Pengkun Hou, Ning Xie, Zhengmao Ye, Xin Cheng, Surendra P. Shah
      A silica-based hybrid nanocomposite, SiO2/polymethylhydrosiloxane (SiO2/PMHS), is synthesized by a sol-gel process and used for surface treatment of hardened cement-based materials. The advantages of both normal organic and inorganic silica-based treatment agents are explored. Results revealed a covalent chemical bonding of SiO2 and PMHS and the SiO2/PMHS showed hydrophobicity and pozzolanic reactivity when used for surface treatment. Greater reductions of the water absorption rate and gas permeability coefficient of cement-based materials were achieved by the hybrid nanocomposite compared to its individual components, showing synergistic effects of hydrophobicity and pore refinement characteristics as proved by the measurements of the contact angle, the mineralogy, the morphology and the porosity. The results showed promising advantages of using silica-based hybrid nanocomposite for surface treatment to achieve a higher surface quality. Moreover, it can be suggested that more functionalities of the cement-based materials can be tailored through the design and use of the silica-based hybrid materials.

      PubDate: 2017-12-27T02:44:17Z
       
  • Whether do nano-particles act as nucleation sites for C-S-H gel growth
           during cement hydration'
    • Abstract: Publication date: March 2018
      Source:Cement and Concrete Composites, Volume 87
      Author(s): Deyu Kong, Senle Huang, David Corr, Yang Yang, Surendra P. Shah
      In this study, three modelling experiments were designed to investigate whether nano-particles incorporated in the cement paste act as nucleation sites for CSH gel growth during cement hydration. The nano-particles with (nano-SiO2) and without (nano-TiO2) pozzolanic reactivity were used. In the first experiment, both the cement and nano-particles were dispersed in water to prepare dilute cement paste, in which the cement and nano-particles can contact each other. In the second one, the cement particles were laid inside a filter paper funnel and immersed in tap and ultrapure water with nano-particles dispersed, in order to separate the cement particles with nano-particles by using the filter paper. In the third one, large clinker particle was embedded in resin, surface-polished and then exposed upside down in ultrapure water with and without nano-particles dispersed. After hydration for 7 days, the hydration products in the paste or the nano-particle dispersion were observed by using TEM and the hydrated surface of the embedded clinkers were detected by using SEM. Based on the experimental results and the detailed discussions by using the classic nucleation theory, it was found that there may have no nucleus function of the nano-particles for the CSH gel precipitation during cement hydration, at least in the hydrating system with nano-silica and nano-TiO2 addition. It was proposed to more reasonably explain the observations in the three modelling experiments by using the topochemical reaction instead of the through-solution mechanism for the CSH gel formation.

      PubDate: 2017-12-27T02:44:17Z
       
  • Use of biochar as carbon sequestering additive in cement mortar
    • Abstract: Publication date: March 2018
      Source:Cement and Concrete Composites, Volume 87
      Author(s): Souradeep Gupta, Harn Wei Kua, Chin Yang Low
      Biochar is widely considered as effective way of sequestering carbon dioxide. The possibility of using it to enhance the mechanical strength and reduce permeability of cement mortar is explored in this study. The effect of fresh biochar and biochar saturated with carbon dioxide a priori on the setting time, mechanical strength and permeability of cement mortar was evaluated. The biochar was prepared from mixed wood saw dust at 300 °C and added to mortar during mixing at 2% by weight of cement. It was found that addition of fresh biochar and saturated biochar reduce initial setting time and significantly improve early compressive strength of mortar. The experimental results suggested that biochar addition can impart ductility to mortar under flexure, although flexural strength was not significantly influenced. Water penetration and sorptivity of mortar was significantly reduced due to addition of biochar, which indicate higher impermeability in biochar added mortar. However, it is found that addition of fresh biochar offers significantly higher mechanical strength and improved permeability compared to biochar saturated with carbon dioxide. These results suggest that biochar has the potential to be successfully deployed as a carbon sequestering admixture in concrete constructions that also provides a way to waste recycling.

      PubDate: 2017-12-27T02:44:17Z
       
  • Investigation of incorporating cinnamaldehyde into Lightweight Aggregate
           for potential corrosion reduction in cementitious materials
    • Abstract: Publication date: March 2018
      Source:Cement and Concrete Composites, Volume 87
      Author(s): Hajar Jafferji, Naser P. Sharifi, Emily M. Schneider, Aaron R. Sakulich
      Each year, corrosion of concrete results in billions of dollars' worth in damage. Cinnamaldehyde, a bioactive agent, can mitigate the corrosion of metals and potentially protect rebar within concrete. However, it cannot be incorporated into concrete during mixing since it negatively effects the hydration reaction between cement and water. To avoid these undesirable effects while keeping anti-corrosive properties in a cementitious mixture, an innovative approach through the use of Lightweight Aggregate (LWA) was taken. The experimental cinnamaldehyde-LWA mortar showed reduced compressive strength, heat evolution, and rebar pullout bond stress, but promising results regarding chloride threshold level and sorptivity.

      PubDate: 2017-12-12T19:16:56Z
       
  • Leaching effect on mechanical properties of cement-aggregate interface
    • Abstract: Publication date: March 2018
      Source:Cement and Concrete Composites, Volume 87
      Author(s): M. Jebli, F. Jamin, C. Pelissou, E. Malachanne, E. Garcia-Diaz, M.S. El Youssoufi
      This study concerns the characterization of the mechanical properties of the cement paste and of the cement-aggregate interface in the degraded state by a chemical leaching mechanism. This study is carried out within the framework of the MIST laboratory. The experimental tests were carried out on cement paste and composites consisting of aggregates bound by the same cement paste prepared with a water/cement ratio of 0.5. The particular experimental devices, designed and produced for the purposes of this study, made it possible to directy solicit the composites at the cement-aggregate interface. As the process of leaching with the deionized water occurs very slowly, the experimental study is accelerated in the laboratory by replacing water by ammonium nitrate solution. To quantify the development and kinetics of chemical degradation at the cemented bond, the concrete leaching fronts are characterized at different times of degradation by using phenolphthalein. The local mechanical tests (tensile and shear) are performed on cement paste and composite at different degradation rate. The experimental results show a fast drop in shear or tensile strength of about 45% at the beginning of degradation. These results confirm the effect of the cement paste-aggregate interface degradation on the mechanical properties.

      PubDate: 2017-12-12T19:16:56Z
       
  • Microstructure-guided numerical simulations to predict the thermal
           performance of a hierarchical cement-based composite material
    • Abstract: Publication date: March 2018
      Source:Cement and Concrete Composites, Volume 87
      Author(s): Sumanta Das, Matthew Aguayo, Subramaniam D. Rajan, Gaurav Sant, Narayanan Neithalath
      This paper presents a microstructure-guided numerical homogenization technique to predict the effective thermal conductivity of a hierarchical cement-based material containing phase change material (PCM)-impregnated lightweight aggregates (LWA). Porous inclusions such as LWAs embedded in a cementitious matrix are filled with multiple fluid phases including PCM to obtain desirable thermal properties for building and infrastructure applications. Simulations are carried out on realistic three-dimensional microstructures generated using pore structure information. An inverse analysis procedure is used to extract the intrinsic thermal properties of those microstructural components for which data is not available. The homogenized heat flux is predicted for an imposed temperature gradient from which the effective composite thermal conductivity is computed. The simulated effective composite thermal conductivities are found to correlate very well with experimental measurements for a family of LWA-PCM composites considered in the paper. Comparisons with commonly used analytical homogenization models show that the microstructure-guided simulation approach provides superior results for composites exhibiting large property contrast between phases. By linking the microstructure and thermal properties of hierarchical materials, an efficient framework is available for optimizing the material design to improve thermal efficiency of a wide variety of heterogeneous materials.

      PubDate: 2017-12-12T19:16:56Z
       
  • Enhancing the performance of calcium sulfoaluminate blended cements with
           shrinkage reducing admixture or lightweight sand
    • Abstract: Publication date: March 2018
      Source:Cement and Concrete Composites, Volume 87
      Author(s): Iman Mehdipour, Kamal H. Khayat
      This study investigates the effect of using shrinkage reducing admixture (SRA) or lightweight sand (LWS) on enhancing the performance of calcium sulfoaluminate (CSA) cement in combination with ordinary Portland cement (OPC). Of special interest is the efficacy of the SRA or LWS in modifying the expansion/shrinkage and compressive strength characteristics of OPC-CSA systems in the absence of adequate duration of water curing, which is critical for the expansive reaction of CSA cement and its ability to mitigate shrinkage. Hydration kinetics, autogenous and drying deformation, thermogravimetry, and scanning electron microscopy (SEM) are used to evaluate the effect of SRA or LWS on the performance of the OPC-CSA systems. Test results indicate that the OPC-CSA system can exhibit similar drying shrinkage to that of the plain OPC mixture when no moist curing is applied. In the presence of LWS or SRA, the OPC-CSA systems exhibited lower shrinkage or higher extent of expansion compared to the corresponding OPC-CSA mixture alone. This is attributed to delay of the drop in internal relative humidity and promoting hydration of the OPC-CSA system which can enhance the ettringite-generating potential of CSA cement. The use of LWS was found to be highly effective in enhancing compressive strength of OPC-CSA system. SEM results at 91 days confirm the higher density and lower porosity for the paste surrounding LWS particles compared to the corresponding mixture made without LWS. In the case of inadequate moist curing, the presence of LWS or SRA is shown to enhance the overall performance of OPC-CSA system. For a given overall desirability value of 0.65 determined by multi-objective optimization, the incorporation of 1% SRA or 10% LWS was found to enable the reduction the required period of moist curing from 6 days to 5 and 3 days, respectively.

      PubDate: 2017-12-12T19:16:56Z
       
  • Interfacial properties and structural performance of resin-coated natural
           fibre rebars within cementitious matrices
    • Abstract: Publication date: March 2018
      Source:Cement and Concrete Composites, Volume 87
      Author(s): Hassan Ahmad, Mizi Fan
      This paper investigates the interface and behaviour of continuous natural fibre rebar reinforced cementitious composites. Various resins were used to coat sisal fibres which were then used as reinforcement within the composites. Non-destructive tests (SEM, OM, FTIR) were employed to evaluate the interfacial bonding and interaction between the sisal, resin and cementitious matrix. The results showed that the uncoated fibre could not develop a compact interface due to the moisture absorption/desorption of the fibre, which caused low mechanical properties of the composite. The coating was able to improve the strength of the rebars and reduce the OH− concentration, which improved the interfacial bonding and integrity. The flexural stress-strain relation of the composites exhibited three regions with two clear dips, reflecting the progressive stress transfer and failure of the composite constituents and their interactions. The comparable mechanical properties to those of steel rebar reinforcement demonstrate the potential of the resin-coated sisal fibre rebar for structural applications.
      Graphical abstract image

      PubDate: 2017-12-12T19:16:56Z
       
  • Application of sensitivity analysis in the life cycle design for the
           durability of reinforced concrete structures in the case of XC4 exposure
           class
    • Abstract: Publication date: March 2018
      Source:Cement and Concrete Composites, Volume 87
      Author(s): T.A. Van-Loc, Tristan Senga Kiesse, Stéphanie Bonnet, Anne Ventura
      The aim of this study is to develop a new design procedure for the durability of the Reinforced Concrete (RC) structures in aggressive environments. The study approach developed here includes: (i) a qualitative analysis phase to characterize the design parameters and environmental exposure conditions of RC structures; (ii) a quantitative analysis phase, to establish the relationship between service life and design parameters and environmental exposure conditions using the service life prediction model firstly, and then to determine the most influential design parameters on service life using sensitivity analyses; and (iii) a final design phase, to design RC structures using some favorable values of the most influential design parameters firstly, and then to compare the service life thus obtained with that of RC structures designed using a standardized approach. An application is also proposed on simulated RC structure exposed to carbonation in Madrid (Spain). This RC structure follows the recommendations of the European standard EN 206–1 for XC4 exposure class. The sensitivity analysis results are discussed in detail including influence trends, importance ranking, non-monotonic effects and parameter interaction influences. The most influential design parameters obtained are cement strength class ( f c e m ), water-to-cement ratio ( W / C ) and cement type ( C E M ). By using W / C of about 0.4, f c e m of about 52.5 MPa and CEM I cement type instead of their limiting value as recommended by EN 206–1, the service life of the RC structure is significantly improved.

      PubDate: 2017-12-12T19:16:56Z
       
  • Microstructural characteristics, porosity and strength development in
           ceramic-laterized concrete
    • Abstract: Publication date: February 2018
      Source:Cement and Concrete Composites, Volume 86
      Author(s): P.O. Awoyera, J.O. Akinmusuru, A.R. Dawson, J.M. Ndambuki, N.H. Thom
      Interfacial bonding between constituent materials and pore sizes in a concrete matrix are major contributors to enhancing the strength of concrete. In a bid to examine how this phenomenon affects a laterized concrete, this study explored the relationship between the morphological changes, porosity, phase change, compressive, and split tensile strength development in a ceramic-laterized concrete. Varying proportions of ceramic aggregates, sorted from construction and demolition wastes, and lateritic soil were used as substitutes for natural aggregates. Strength properties of the concrete specimens were evaluated after 7, 14, 28 and 91 days curing, but morphological features, using secondary electron mode, were examined only at 7 and 28 days on cured specimens, using Scanning electron microscope (SEM). From all the mixes, selected samples with higher 28 day crushing strength, and the reference mix, were further characterized with more advanced analysis techniques, using the mercury intrusion porosimetry (MIP), thermogravimetric analysis (TGA), X-ray Diffractometer, and SEM (backscatter electron mode-for assessment of the interfacial transition properties between aggregates and paste). The reference mix yielded higher mechanical properties than the concrete containing secondary aggregates, this was traced to be as a result of higher peaks of hydration minerals of the concrete, coupled with its low tortuosity and compactness. However, a laterized concrete mix containing both 90% of ceramic fine and 10% of laterite as fine aggregate provided the optimal strength out of all the modified mixes. Although, the strength reduction was about 9% when compared with the reference case, however, this reduction in strength is acceptable, and does not compromise the use of these alternative aggregates in structural concrete.

      PubDate: 2017-12-12T19:16:56Z
       
  • Healing cement mortar by immobilization of bacteria in biochar: An
           integrated approach of self-healing and carbon sequestration
    • Abstract: Publication date: February 2018
      Source:Cement and Concrete Composites, Volume 86
      Author(s): Souradeep Gupta, Harn Wei Kua, Sze Dai Pang
      Self-healing of cracks in concrete by bacterial carbonate precipitation is an effective mechanism to ensure better serviceability of civil infrastructure. This study explores biochar, derived from wood waste, as carrier for carbonate precipitating bacteria spores in cement mortar to seal cracks, and recover strength and permeability of healed samples. Superabsorbent polymer (SAP) and polypropylene microfibers (PP) were added to ensure moisture availability to bacteria and control crack propagation during damage of mortar. Samples were damaged by pre-loading to different levels – 50% and 70% of peak strength at 14-day. Experimental results show that biochar immobilized spores combined with SAP and PP precipitate copious amount of calcium carbonate, which completely sealed cracks up to 700 μm. This mix also showed highest recovery of impermeability and strength under both levels of preloading. Improvement in strength by 38% and reduction in water penetration and absorption by 65% and 70% was observed by immobilization of spores in biochar, compared to directly added spores. From comparison between samples, it was found that inclusion of PP fiber contributed to recovery of strength and impermeability, while SAP ensured higher precipitation of bacterial induced carbonate precipitation. The study suggests that spores immobilized in biochar has potential to offer excellent self-healing in cement composites. Using biochar is also a carbon sequestration strategy because of high volume of stable carbon stored in biochar particles during pyrolysis. Therefore, the proposed material combination would offer carbon storage in buildings, while also promoting waste recycling.

      PubDate: 2017-12-12T19:16:56Z
       
  • Multi-scale investigation of microstructure, fiber pullout behavior, and
           mechanical properties of ultra-high performance concrete with nano-CaCO3
           particles
    • Abstract: Publication date: February 2018
      Source:Cement and Concrete Composites, Volume 86
      Author(s): Zemei Wu, Caijun Shi, Kamal Henri Khayat
      The mechanical properties of a fiber-reinforced concrete are closely related to the properties of the matrix, fiber, and fiber-matrix interface. The fiber-matrix bond property is mainly governed by the adhesion between the fiber and surrounding cement materials, as well as the strength of materials at the interfacial transition zone. In this paper, the effect of nano-CaCO3 content, varying between 0 and 6.4%, by mass of cementitious materials, on microstructure development, fiber-matrix interfacial bond properties, and mechanical properties of ultra-high performance concrete (UHPC) reinforced with 2% steel fibers were investigated. The bond properties, including bond strength and pullout energy, were evaluated. Mercury intrusion porosimetry (MIP), backscattered electron microscopy (BSEM), optical microscopy, and micro-hardness testing were used to characterize the microstructure of matrix and/or interfacial transition zone (ITZ) around an embedded steel fiber. Test results indicated that the incorporation of 3.2% nano-CaCO3 significantly improved the fiber-matrix bond properties and the flexural properties of UHPC. This was attributed to densification and strength enhancement of ITZ as observed from micro-structural analyses. Beyond the nano-CaCO3 content of 3.2%, the fiber bond and mechanical properties of UHPC decreased due to increased porosity associated with agglomeration of the nano-CaCO3.

      PubDate: 2017-12-12T19:16:56Z
       
  • Mechanical and thermal properties of lightweight geopolymer composites
    • Abstract: Publication date: February 2018
      Source:Cement and Concrete Composites, Volume 86
      Author(s): F. Colangelo, G. Roviello, L. Ricciotti, V. Ferrándiz-Mas, F. Messina, C. Ferone, O. Tarallo, R. Cioffi, C.R. Cheeseman
      This research has investigated the properties of thermally insulating geopolymer composites that were prepared using waste expanded polystyrene as lightweight aggregate. The geopolymer matrix was synthetized using metakaolin and an alkaline activating solution. To improve its mechanical properties, this matrix was modified by the addition of an epoxy resin to form an organic-inorganic composite. Moreover, in order to reduce drying shrinkage marble powder was used as an inert filler. The materials obtained were characterized in terms of physico-mechanical properties, thermal performance and microstructure. The geopolymer expanded polystyrene composite have improved properties compared to Portland cement-based materials, with higher strengths and lower thermal conductivity. The research demonstrates the manufacture of sustainable lightweight thermally insulating geopolymer composites using waste expanded polystyrene.

      PubDate: 2017-12-12T19:16:56Z
       
  • Viscoelastic properties of self-consolidating concrete: Influence of the
           sustainable approach
    • Abstract: Publication date: February 2018
      Source:Cement and Concrete Composites, Volume 86
      Author(s): Hamza Samouh, Emmanuel Rozière, Ahmed Zakarya Bendimerad, Ahmed Loukili
      The service life of concrete structures is primarily affected by cracking. Concrete with a lower cracking potential is consequently more sustainable. In order to estimate the risk of shrinkage-induced cracking, at least four properties should be studied: shrinkage, Young's modulus, creep/relaxation and tensile strength. A mixed experimental and numerical approach, taking into account these properties is presented and used in this paper to improve our understanding of this complex phenomenon. The study is focused on restrained shrinkage of thin structures exposed to drying. Based on the viscoelastic and solidifying theories and on the experimental results from an adapted ring test some explanations of the observed cracking tendencies can be given. The efficiency of this method is shown when it is applied on two experimental studies linked with the sustainability issues. The first one concerns the greener mix-design which was found to have a positive effect on the cracking resistance, with two ways of reducing cement content. The reduction of the paste volume as well as the substitution of Portland cement by supplementary cementitious materials (SCMs) delayed cracking with different mechanisms. The second study aims to analyze the effect of the sealed curing duration on cracking, where the extracted aging-viscoelastic Young's modulus decreases with the curing duration and explains the observed results.

      PubDate: 2017-12-12T19:16:56Z
       
  • Distinguishing dynamic and static yield stress of fresh cement mortars
           through thixotropy
    • Abstract: Publication date: February 2018
      Source:Cement and Concrete Composites, Volume 86
      Author(s): Ye Qian, Shiho Kawashima
      The dynamic and static yield stress of fresh cement mortar were measured in a rotational rheometer with a vane geometry using shear rate and shear stress-controlled protocols, respectively. Through a shear rate-controlled steady-state protocol, the equilibrium flow curve is measured and fitted with the Bingham model to obtain dynamic yield stress. A negative slope in the equilibrium flow curve, shear banding and stick-slip phenomena are observed and discussed. Through a stress-controlled creep-recovery protocol, viscosity bifurcation behavior is captured and static yield stress is marked as the creep stress when the bifurcation occurs. Finally, the discrepancy between dynamic and static yield stress is tied to thixotropy.

      PubDate: 2017-12-12T19:16:56Z
       
  • Flexural strength reduction of cement pastes exposed to CaCl2 solutions
    • Abstract: Publication date: February 2018
      Source:Cement and Concrete Composites, Volume 86
      Author(s): Chunyu Qiao, Prannoy Suraneni, Jason Weiss
      Calcium chloride (CaCl2) can react with calcium hydroxide (Ca(OH)2) to form calcium oxychloride which can reduce flexural strength and damage concrete. This paper aims to characterize the reduction in flexural strength of cement pastes exposed to CaCl2 solutions using the ball-on-three-balls test. The amounts of Ca(OH)2 and calcium oxychloride in the cement paste are measured using thermogravimetric analysis and low-temperature differential scanning calorimetry, respectively. The volume change that occurs as a result of the reactions between the cement paste and CaCl2 is also measured. The reduction in flexural strength increases as the concentration of the CaCl2 solution increases and the exposure temperature decreases. The flexural strength reduction can be mitigated by increasing the amount of supplementary cementitious materials (fly ash) in the cement pastes. Lowering the water-cementitious materials ratio also reduces the flexural strength reduction. The flexural strength reduction is correlated with the amount of calcium oxychloride and the volume change in the cement pastes exposed to the CaCl2 solution. While the flexural strength reduction is believed to be primarily due to the formation of calcium oxychloride, the formation of Friedel's salt and Kuzel's salt also contributes to the flexural strength reduction.

      PubDate: 2017-12-12T19:16:56Z
       
  • Raman spectroscopic investigation of Friedel's salt
    • Abstract: Publication date: February 2018
      Source:Cement and Concrete Composites, Volume 86
      Author(s): Yanfei Yue, Jing Jing Wang, P.A. Muhammed Basheer, Yun Bai
      Friedel's salt (FS) forms upon chloride binding in monosulphoaluminate (AFm) phase. This removes chlorides from the pore solution, hence, delays the initiation of steel-bar corrosion. Apparently, characterising and, in particular, monitoring the formation and the status of FS facilitate the prediction of the service life of reinforced concrete structures. Raman spectroscopy offers a potential for investigating FS. The current work characterised FS, including the synthesised pure FS, and the FS formed in a Portland cement (PC) paste powder, using a bench-mounted Raman spectrometer. The results revealed the full Raman spectra of pure FS between 200 and 4000 cm−1, including the featured Raman bands at 534/568 cm−1 and 783 cm−1 which correspond to the Al-OH stretching and bending vibration of FS respectively. Furthermore, similar Raman bands of FS were identified in PC paste sample subjected to accelerated chloride attack, further confirming the potential of Raman spectroscopy for distinguishing FS in cementitious materials.

      PubDate: 2017-12-12T19:16:56Z
       
  • IFC - Editorial board
    • Abstract: Publication date: January 2018
      Source:Cement and Concrete Composites, Volume 85


      PubDate: 2017-12-12T19:16:56Z
       
  • Influence of substrate moisture state and roughness on interface
           microstructure and bond strength: Slant shear vs. pull-off testing
    • Abstract: Publication date: Available online 8 December 2017
      Source:Cement and Concrete Composites
      Author(s): Dale P. Bentz, Igor De la Varga, Jose F. Muñoz, Robert P. Spragg, Benjamin A. Graybeal, Daniel S. Hussey, David L. Jacobson, Scott Z. Jones, Jacob M. LaManna
      There are conflicting views in the literature concerning the optimum moisture state for an existing substrate prior to the application of a repair material. Both saturated-surface-dry (SSD) and dry substrates have been found to be preferable in a variety of studies. One confounding factor is that some studies evaluate bonding of the repair material to the substrate via pull-off (direct tension) testing, while others have employed some form of shear specimens as their preferred testing configuration. Available evidence suggests that dry substrate specimens usually perform equivalently or better in shear testing, while SSD ones generally exhibit higher bond strengths when a pull-off test is performed, although exceptions to these trends have been observed. This paper applies a variety of microstructural characterization tools to investigate the interfacial microstructure that develops when a fresh repair material is applied to either a dry or SSD substrate. Simultaneous neutron and X-ray radiography are employed to observe the dynamic microstructural rearrangements that occur at this interface during the first 4 h of curing. Based on the differences in water movement and densification (particle compaction) that occur for the dry and SSD specimens, respectively, a hypothesis is formulated as to why different bond tests may favor one moisture state over the other, also dependent on their surface roughness. It is suggested that the compaction of particles at a dry substrate surface may increase the frictional resistance when tested under slant shear loading, but contribute relatively little to the bonding when the interface is submitted to pull-off forces. For maximizing bond performance, the fluidity of the repair material and the roughness and moisture state of the substrate must all be given adequate consideration.

      PubDate: 2017-12-12T19:16:56Z
       
  • The long-term creep and shrinkage behaviors of green concrete designed for
           bridge girder using a densified mixture design algorithm
    • Abstract: Publication date: Available online 7 December 2017
      Source:Cement and Concrete Composites
      Author(s): Trong-Phuoc Huynh, Chao-Lung Hwang, Andrian H. Limongan
      Creep and shrinkage behaviors are critical factors in the precast/prestressed concrete industry because these factors allow engineers to assess the long-term performance of concrete and to develop life-cycle estimates for concrete structures. The current study presents the results of an experimental work that addresses creep and shrinkage behaviors as well as the development of compressive strength in ordinary Portland cement concrete (OPC), high-performance concrete (HPC), and self-consolidating concrete (SCC). The concrete mixtures created for the present study were used to fabricate prestressed bridge girders. A conventional method (ACI) was used to design the mixture proportion for OPC and a densified mixture design algorithm (DMDA) was used to design the mixture proportions for HPC and SCC. All concrete mixtures had the same target strength of 69 MPa (10000 psi) at 56 days. Additionally, a comparative performance in terms of strength development and creep and shrinkage behaviors of ACI and DMDA concrete is performed in the present study. Test results show that all of the samples attained the target strength after 28 days of curing and that the strengths of each continued to increase afterward. Importantly, the incorporation of pozzolanic materials into concrete mixtures affected the propagation of creep strain and shrinkage positively. Furthermore, the DMDA concrete sample delivered better long-term performance than ACI concrete in terms of compressive strength, creep strain, and shrinkage.

      PubDate: 2017-12-12T19:16:56Z
       
  • Synergy assessment in hybrid Ultra-High Performance Fiber-Reinforced
           Concrete (UHP-FRC)
    • Abstract: Publication date: February 2018
      Source:Cement and Concrete Composites, Volume 86
      Author(s): Alessandro P. Fantilli, Sukmin Kwon, Hirozo Mihashi, Tomoya Nishiwaki
      Ultra-High Performance Fiber-Reinforced Concretes (UHP-FRC) subjected to uniaxial tensile loads are investigated in the present paper. The study comprises a new procedure to assess the effectiveness of the hybridization, herein obtained by reinforcing UHP-FRC with micro and macro steel fibers. A comprehensive experimental campaign is also performed on monofiber and hybrid UHP-FRC. In all the concretes, the distance between the cracks and the minimum fiber volume fraction, which produces strain hardening response and multiple cracking, are theoretically and experimentally evaluated. If the bond parameter of the macro-fibers is properly calculated, the results of the analytical model, in terms of crack-spacing vs. fiber volume fraction, are in good agreement with the test data. Moreover, to increase the number of the cracks, and to reduce crack spacing, the hybridization is suitable only when the amount of macro-fibers is within a well-defined range.

      PubDate: 2017-11-15T15:21:52Z
       
  • How do recycled concrete aggregates modify the shrinkage and self-healing
           properties'
    • Abstract: Publication date: February 2018
      Source:Cement and Concrete Composites, Volume 86
      Author(s): Sonagnon Medjigbodo, Ahmed Z. Bendimerad, Emmanuel Rozière, Ahmed Loukili
      This paper presents the main results of a research carried out to analyze the mechanical properties, intrinsic permeability, drying shrinkage, carbonation, and the self-healing potential of concrete incorporating recycled concrete aggregates. The recycled concrete mixtures were designed by replacing natural aggregates with 0%, 30%, and 100% of recycled concrete gravel (RG) and 30% of recycled concrete sand (RS). The water to equivalent binder ratio was kept constant and recycled concrete aggregates were initially at saturated surface dried (SSD) state. The contribution of the porosity of natural and recycled aggregates to the porosity of concrete was estimated to understand the evolution of the intrinsic permeability and the open porosity. At long term, the maximum variation of drying shrinkage magnitude due to recycled concrete gravels did not exceed 15%. The correlation between drying shrinkage and mass-loss through “drying depth” concept showed that recycled concrete aggregates are affected by drying as soon as concrete is exposed to desiccation. A good correlation between 1-day compressive strength and 18-month carbonation depth was observed. The recycled concrete aggregates presented a good potential for self-healing as the relative recovery of cracks reached up to 60%.

      PubDate: 2017-11-15T15:21:52Z
       
  • Impact performances of steel tube-confined recycled aggregate concrete
           (STCRAC) after exposure to elevated temperatures
    • Abstract: Publication date: February 2018
      Source:Cement and Concrete Composites, Volume 86
      Author(s): Wengui Li, Zhiyu Luo, Chengqing Wu, Wen Hui Duan
      The impact behaviours of steel tube-confined recycled aggregate concrete (STCRAC) following exposure to elevated temperatures of 20 °C, 200 °C, 500 °C and 700 °C were experimentally investigated using a 100 mm-diameter split Hopkinson pressure bar (SHPB). The recycled coarse aggregate (RCA) replacement ratios were set as 0, 50% and 100%. The effect of RCA replacement ratio and exposure temperature on the impact properties of STCRAC were analysed in terms of failure modes, stress-strain time history curve and dynamic increase factor (DIF). The results show that the fire-damaged STCRAC can maintain its integrity during impact load. However, there were evident degradations in the dynamic behaviour of STCRAC after exposure to high temperatures of 500 °C and 700 °C. The ultimate impact strength, impact secant modulus and residual impact strength of STCRAC obviously decreased because of the damage due to high temperature exposure. But the degradations of both the ultimate impact strength and impact secant modulus of STCRAC under impact loading were less severe than those under quasi-static loading. The remaining strength factor and the DIF tended to increase with the raise of the elevated temperatures. Overall, during the impact loading, the fire-deteriorated STCRAC exhibited excellent impact behaviour.

      PubDate: 2017-11-15T15:21:52Z
       
  • Comparison of glass powder and pulverized fuel ash for improving the water
           resistance of magnesium oxychloride cement
    • Abstract: Publication date: February 2018
      Source:Cement and Concrete Composites, Volume 86
      Author(s): Pingping He, Chi Sun Poon, Daniel C.W. Tsang
      The water resistance of magnesium oxychloride cement (MOC) incorporating glass powder (GP) and pulverized fuel ash (PFA) with and without CO2 curing was investigated in terms of the strength retention coefficient and the volume stability. The microstructure was studied using quantitative X-ray diffraction (QXRD), thermogravimetry (TG), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the effect of incorporating GP on the water resistance is much lower than that of PFA due to the lower pozzolanic activity of GP generating a lower amount of magnesium silica hydrate gel (M-S-H gel). The MOC incorporated with GP or PFA showed high water resistance after CO2 curing due to the higher quantity of amorphous gel that formed a much denser interlocking network.

      PubDate: 2017-11-15T15:21:52Z
       
  • Sensitivity of the rapid chloride conductivity index test to concrete
           quality and changes in various test parameters
    • Abstract: Publication date: February 2018
      Source:Cement and Concrete Composites, Volume 86
      Author(s): Mike Otieno
      This study assessed the robustness of the chloride conductivity test with respect to the effect of concrete quality on its sensitivity to selected test parameters. Experiments were carried out to assess the sensitivity of the test to changes in the following parameters: (i) test duration (10, 40 and 120 s), (ii) concentration of the NaCl solution (3M and 5M), and (iii) variation of capillary voltage (7, 10 and 15 V). Concrete test specimens were made using three w/b ratios (0.40, 0.50 and 0.60) and three binder types (CEM I 52.5N (PC – Portland cement), 70/30 PC/FA (FA – fly ash) and 50/50 PC/GGCS (GGCS – ground granulated Corex slag)). One parameter was varied at a time. The results show that concretes with high chloride conductivity index (CCI) values (>∼0.8 mS/cm) are generally sensitive to changes in concentration of NaCl solution, capillary voltage across the test specimen, and test duration. For such concretes, the CCI increases with increase in capillary voltage, CCI decreases with decrease in salt concentration while the effect of a longer testing duration on CCI appears to be random. Even though it is not stipulated in the test standard, this study recommends that the test duration (i.e. the duration the capillary voltage is passed across the specimen once the electrical circuit of the test set-up is closed) is limited to <10 s.

      PubDate: 2017-11-15T15:21:52Z
       
  • Numerical modeling of mechanical regain due to self-healing in cement
           based composites
    • Abstract: Publication date: Available online 11 November 2017
      Source:Cement and Concrete Composites
      Author(s): Giovanni Di Luzio, Liberato Ferrara, Visar Krelani
      Recently there has been an increasing interest in self-healing materials which have the ability to retrieve their physico-mechanical properties once the material is damaged. This paper presents a numerical model on the self-healing capacity of cementitious composites capable of simulating the recovery of mechanical properties of the damaged (cracked) material. The recent SMM (Solidification-Microprestress-Microplane model M4) model for concrete, which makes use of a modified microplane model M4 and the solidification-microprestress theory, is able to reproduce the concrete time-dependent behavior, e.g. creep, shrinkage, thermal deformation, aging, and cracking from early age up to several years. The moisture and heat fields, as well as the hydration degree, are obtained from the solution of a hygro-thermo-chemical problem which is coupled with the SMM model. This numerical framework is extended to incorporate the self-healing effects and, in particular, the effect of delayed cement hydration, which is the main cause of the self-healing for young concrete. The new update model can also simulate the effects of cracking on the permeability and the opposite restoring effect of the self-healing on the mechanical constitutive law, i.e. the microplane model. A numerical example is presented to validate the proposed computational model employing experimental data from a recent test series undertaken at Politecnico di Milano. The experimental campaign has dealt with a normal strength concrete, in which (by means of three-point-bending tests performed up to controlled crack opening and up to failure, respectively before and after exposure to different conditioning environments) the recovery of stiffness and load bearing capacity has been evaluated.

      PubDate: 2017-11-15T15:21:52Z
       
  • Effects of fibers and conventional reinforcement contents on fibers
           scaterring in prismatic bars
    • Abstract: Publication date: Available online 11 November 2017
      Source:Cement and Concrete Composites
      Author(s): Yuri S. Karinski, Avraham N. Dancygier
      This paper presents results from a second stage of an experimental study of the dependence of steel fibers distribution along RFC prismatic specimens on the conventional reinforcement ratio and on the total amount of fibers in the concrete mix. The experimental program included two types of prismatic specimens with 30- and 60- kg/m3 of hooked-end steel fibers. Each specimen was sawed into equal segments and the numbers of fibers appearing at the cross-sections were counted and used for a further statistical analysis. This analysis comprised calculations of the average value and standard deviation of a non-dimensional variable, which represents the distribution of the total steel along the specimen. They were used to calibrate a theoretical model, which had been previously proposed by the authors. The test results showed reasonable to good agreement with the theoretical model. A comparison between the results of the 30- and 60-kg/m3 fibers shows that as the conventional reinforcement ratio increases, the standard deviations for the different mixtures approach each other.

      PubDate: 2017-11-15T15:21:52Z
       
  • Development of sandwich panels combining Sisal Fiber-Cement Composites and
           Fiber-Reinforced Lightweight Concrete
    • Abstract: Publication date: Available online 10 November 2017
      Source:Cement and Concrete Composites
      Author(s): Cristina Frazão, Joaquim Barros, Romildo Toledo Filho, Saulo Ferreira, Delfina Gonçalves
      This research proposes the development of an innovative structural panels based on the use of thin outer layers of Sisal Fiber-Cement Composites (SiFCC) together with a core layer of Polypropylene Fiber-Reinforced Lightweight Concrete (PFRLC). The influence of sisal fibers was studied in two different ways, short sisal fibers (50 mm) randomly distributed in the matrix, and long unidirectional aligned sisal fibers (700 mm) applied by a cast hand layup technique. Lightweight aggregates and polypropylene fibers were used in the concrete layer forming the panel's core in order to reduce its density and improve its post-cracking tensile strength and energy absorption capacity. The behavior of the sandwich panels in four-point bending test is described, and the various failure mechanisms are reported. Mechanical properties of both SiFCC and PFRLC were obtained, which were also used in the numerical simulations. Pull-off tests were performed to evaluate the bond strength between the outer SiFCC layers and the core PFRLC. The results revealed that the long sisal fibers were more effective in terms of providing to the panel higher flexural capacity than when using short sisal fibers, long fibers ensured the development of a deflection hardening behavior followed by the formation of multiple cracks, while short sisal fibers promoted a softening response after cracking.

      PubDate: 2017-11-15T15:21:52Z
       
  • Interfacial transition zone of cement composites with steel furnace slag
           aggregates
    • Abstract: Publication date: Available online 10 November 2017
      Source:Cement and Concrete Composites
      Author(s): Alexander S. Brand, Jeffery R. Roesler
      As previous studies of mortar and concrete with steel furnace slag (SFS) aggregates have shown increases or decreases in the bulk mechanical properties, this study investigated the microstructural cause of these opposing trends through characterization of the interfacial transition zone (ITZ) with quantitative image analysis of backscatter electron micrographs. Three SFS types – basic oxygen furnace (BOF), electric arc furnace (EAF), EAF/ladle metallurgy furnace (EAF/LMF) – were examined as aggregates in a portland cement mortar. The ITZ size for all SFS mortar mixtures was similar, with the ITZ of BOF and EAF/LMF being slightly more porous than mortar mixtures with EAF or dolomite. Microstructural examinations of the SFS particle revealed that BOF and EAF/LMF aggregates have different outer and interior compositions, with the outer composition consisting of a porous layer, which likely contributes to the reduced strength relative to EAF. The imaging results demonstrated that the type of SFS and its spatial composition greatly influences the bulk properties of mortar and concrete, mainly as a function of porosity content in the ITZ and the outer layer and interior porosity of the SFS aggregate.

      PubDate: 2017-11-15T15:21:52Z
       
  • Chemical and mineralogical alterations of concrete subjected to chemical
           attacks in complex underground tunnel environments during 20–36 years
    • Abstract: Publication date: Available online 9 November 2017
      Source:Cement and Concrete Composites
      Author(s): Chen Li, Mengxue Wu, Qing Chen, Zhengwu Jiang
      This paper investigates the chemical and mineralogical alterations of concrete in underground tunnel structures built from 1980 to 1996, located on the China's east seashore. The underground water around the tunnels had once been treated to be not or little aggressive. However, the complex environments in the tunnels had increased the aggressiveness of certain ingredients, thus causing chemical attacks. The chlorides in the leakage underground water cause chloride attack, and the NaCl crystallizations on the surface of the C50 pre-cast concrete segments induce a deeper chloride contamination. When the concrete suffers flowing leakage water, calcium leaching also occurs, leading to decalcification and magnesium incorporation. Under this circumstance, C50 pre-cast concrete shows a higher resistance compared with C30 cast-in-place concrete, mainly due to the low water to binder ratio. Within the C30 cast-in-place concrete facing concentrated leakage water and NaCl crystallization, a strong magnesium chloride attack is observed. Besides the materials factors, the environmental factors, including the high concentrations of both chloride and magnesium ions, the removal timing of calcium ion, and the water saturation, are believed to take responsibility for the magnesium chloride attack.

      PubDate: 2017-11-15T15:21:52Z
       
  • Application of 3D-DIC to characterize the effect of aggregate size and
           volume on non-uniform shrinkage strain distribution in concrete
    • Abstract: Publication date: Available online 7 November 2017
      Source:Cement and Concrete Composites
      Author(s): Yang Chen, Jiangxiong Wei, Haoliang Huang, Wen Jin, Qijun Yu
      To elucidate the effect of aggregate size and volume on the non-uniform strain distribution in concrete, drying shrinkage of mortar and concretes were determined with 3D digital image correlation (3D-DIC). The distribution of shrinkage displacements and strains in mortar and concrete were analyzed. The results show that 3D-DIC makes it possible to measure non-uniform displacement distributions initiated by shrinkage in mortar and concrete. The non-uniformity became more remarkable with drying time. The presence of aggregates larger than 5 mm in concrete have locally changed the displacement and strain fields. Aggregates within 5–25 mm make non-uniform strain of concrete more fluctuant, especially when the aggregate size is larger than 10 mm. The maximum and minimum principal strain distributions became more heterogeneous with decreasing volume of aggregates.

      PubDate: 2017-11-08T14:26:30Z
       
  • Effect of fiber geometric property on rate dependent flexural behavior of
           ultra-high-performance cementitious composite
    • Abstract: Publication date: Available online 6 November 2017
      Source:Cement and Concrete Composites
      Author(s): Doo-Yeol Yoo, Nemkumar Banthia, Jin-Young Lee, Young-Soo Yoon
      In order to examine the rate dependent flexural performance of ultra-high-performance cementitious composite (UHPCC), a number of UHPCC beams containing three straight steel fibers with different aspect ratios of 65, 97.5, and 100 and one twisted steel fiber with an aspect ratio of 100 were fabricated and tested under quasi-static and impact loadings. Test results indicated that the use of long straight and twisted steel fibers resulted in improved quasi-static flexural performance, and their effectiveness was higher at large deflections. The twisted steel fiber was most effective at improving the deflection capacity and the number of micro-cracks under quasi-static flexural loading. In contrast, long straight steel fibers were more favorable than twisted steel fibers in terms of impact resistance and residual performance after impact damage. A lower sensitivity of the strain rate to the dynamic increase factor (DIF) was obtained for the post-cracking flexural strength than for the first-cracking strength, and the use of twisted steel fibers led to lower sensitivity to the strain rate on the DIF of post-cracking strength than that of straight ones. Finally, the higher strength concrete was less sensitive to the strain rate than the lower strength concrete.

      PubDate: 2017-11-08T14:26:30Z
       
  • Hot-pressed geopolymer: Dual effects of heat and curing time
    • Abstract: Publication date: Available online 6 November 2017
      Source:Cement and Concrete Composites
      Author(s): Navid Ranjbar, Amin Kashefi, Mahmoud R. Maheri
      Hot-pressed curing of geopolymers introduces an efficient fabrication of almost pore-less and high strength binders with a minimum usage of alkali activator in an extremely short time. This study presents the dual effects of temperature and curing time on kinetics and mechanical properties of VA-based hot-pressing geopolymer. Moreover, the effects of elevated temperature on the aluminosilicate precursors dissolution and the pressure loss of the hot-pressed geopolymer are investigated. It is observed that increment in temperatures and time improves the dissolving trends of the aluminosilicates. Furthermore, pressure loss of the hot-pressing system is associated with the liquid phase removal and gelation of particles; and, a successive repressing of mixture to the initial condition reduces the porosity of the matrix significantly. The increase in curing temperature of the hot-pressing system is the key point in acceleration of the geopolymerization kinetic, however, curing time is essential in stabilization of the reaction.

      PubDate: 2017-11-08T14:26:30Z
       
  • Applying a biodeposition layer to increase the bond of a repair mortar on
           a mortar substrate
    • Abstract: Publication date: Available online 4 November 2017
      Source:Cement and Concrete Composites
      Author(s): D. Snoeck, J. Wang, D.P. Bentz, N. De Belie
      One of the major concerns in infrastructure repair is a sufficient bond between the substrate and the repair material, especially for the long-term performance and durability of the repaired structure. In this study, the bond of the repair material on the mortar substrate is promoted via the biodeposition of a calcium carbonate layer by a ureolytic bacterium. X-ray diffraction and scanning electron microscopy were used to examine the interfaces between the repair material and the substrate, as well as the polymorph of the deposited calcium carbonate. The approximately 50 μm thick biodeposition film on the mortar surface mostly consisted of calcite and vaterite. Both the repair material and the substrate tended to show a good adherence to that layer. The bond, as assessed by slant shear specimen testing, was improved by the presence of the biodeposition layer. A further increase was found when engineering the substrate surface using a structured pattern layer of biodeposition.

      PubDate: 2017-11-08T14:26:30Z
       
  • Compressive strength and microstructure of alkali-activated fly ash/slag
           binders at high temperature
    • Abstract: Publication date: Available online 31 October 2017
      Source:Cement and Concrete Composites
      Author(s): Z. Pan, Z. Tao, Y.F. Cao, R. Wuhrer, T. Murphy
      This paper reports the results of the compressive strength and microstructure of various alkali-activated binders at elevated temperatures of 300 and 600 °C. The binders were prepared by alkali-activated low calcium fly ash/ground granulated blast-furnace slag at ratios of 100/0, 50/50, 10/90 and 0/100 wt.%. Specimens free of loading were heated to a pre-fixed temperature by keeping the furnace temperature constant until the specimens reached a steady state. Then the specimen was loaded to failure while hot. XRD, SEM and FTIR techniques were used to investigate the microstructural changes after the thermal exposure. The fly ash-based specimen shows an increase in strength at 600 °C. On the other hand, the slag-based specimen gives the worst high-temperature performance particularly at a temperature of 300 °C as compared to ordinary Portland cement binder. This contrasting behaviour of binders is due to their different binder formulation which gives rise to various phase transformations at elevated temperatures. The effects of these transformations on the compressive strength are discussed on the basis of experimental results.

      PubDate: 2017-11-02T13:58:14Z
       
  • A maturity approach to estimate compressive strength development of
           CO2-cured concrete blocks
    • Abstract: Publication date: Available online 28 October 2017
      Source:Cement and Concrete Composites
      Author(s): Dongxing Xuan, Baojian Zhan, Chi Sun Poon
      An alternative CO2 curing method for precast concrete products has been proposed in order to achieve rapid strength development at early age, as well as to capture and store greenhouse gas (CO2). In this paper, an experimental study for the development of a maturity approach is presented to estimate the strength development of carbonated concrete blocks. In order to promote the use of industrial flue gas containing CO2, a flow-through CO2 curing regime at ambient pressure and temperature was employed using different atmospheric conditions, such as various CO2 concentrations, RH values and gas flow rates. The experimental results showed that the compressive strength or maturity of the carbonated concrete blocks was affected by two factors: accelerated cement hydration and carbonation extent. A high CO2 concentration, a fast gas flow rate and a moderate relative humidity are essential for enhancing the maturity and the strength development. The developed model based on the maturity approach may accurately predict the strength development of the carbonated concrete blocks.

      PubDate: 2017-11-02T13:58:14Z
       
  • Mechanical properties of ambient cured high strength hybrid steel and
           synthetic fibers reinforced geopolymer composites
    • Abstract: Publication date: Available online 27 October 2017
      Source:Cement and Concrete Composites
      Author(s): Musaad Zaheer Nazir Khan, Yifei Hao, Hong Hao, Faiz Uddin Ahmed Shaikh
      Ambient cured geopolymer offers significant promise to the construction world as a possible alternative to ordinary Portland cement (OPC). However, as a member of the ceramic family, geopolymers exhibit extremely brittle behaviour. The inclusion of short discrete fibers is an effective way to enhance their ductility. In this research, a series of fiber combinations and volume fractions between steel fibers with end-hooked or spiraled and synthetic fibers (made of high strength polyethylene (HSPE)) were incorporated in a high strength ambient cured geopolymer matrix. The performance of synthesized geopolymer composites was compared in terms of fresh and hardened state properties, such as workability, uniaxial compressive strength, modulus of elasticity, Poisson's ratio, flexural tensile strength, energy absorption capacity and post-peak residual strength etc. The interfacial bond between the spiral steel fiber and the geopolymer matrix as well as fiber distribution in the composites were assessed through individual fiber-pull out tests and physical examination of the cast samples, respectively. The test results show that the addition of fibers significantly improved the load carrying capacity of the composites under flexure load, i.e. increased from 3.89 MPa to 11.30 MPa together with an improved behaviour in compression. In general, all fiber reinforced composites displayed a stable deflection hardening response and multiple-cracking failure mode. Moreover, among composites with different fiber volume fractions, the composite having 1.60% steel+0.40% HSPE showed the highest ultimate flexure strength, correspondingly the highest energy absorption capacity. The individual fiber pull-out test curves ascertained a strong bonding between the geopolymer mortar and spiral-steel fiber.

      PubDate: 2017-11-02T13:58:14Z
       
  • Influential factors in volume change measurements for cementitious
           materials at early ages and in isothermal conditions
    • Abstract: Publication date: Available online 25 October 2017
      Source:Cement and Concrete Composites
      Author(s): Lavinia Stefan, Claude Boulay, Jean-Michel Torrenti, Benoît Bissonnette, Farid Benboudjema
      Early age deformations, when restrained, lead to an increase of cracking risk of the material, especially in the case of high strength materials to which we apply modern high energy mixing techniques which accelerate initial hydration rate. The experimental campaign aims to investigate and understand the differences not yet explained between several autogenous measurement techniques, such as the initial swelling measured by the linear devices that is not observed in the case of volumetric measurements. The differences between the results obtained by means of devices when values are zeroed at setting time can be imputed to the intrinsic behaviour of the material within the well-defined boundary conditions imposed by the molds, and not only to the measurement artefact.

      PubDate: 2017-10-25T22:15:36Z
       
  • Decoupling the autogenous swelling from the self-desiccation deformation
           in early age concrete with mineral additions: Micro-macro observations and
           unified modelling
    • Abstract: Publication date: Available online 23 October 2017
      Source:Cement and Concrete Composites
      Author(s): Jérôme Carette, Shiju Joseph, Özlem Cizer, Stéphanie Staquet


      PubDate: 2017-10-25T22:15:36Z
       
  • Model for practical prediction of natural carbonation in reinforced
           concrete: Part 1-formulation
    • Abstract: Publication date: Available online 20 October 2017
      Source:Cement and Concrete Composites
      Author(s): Stephen O. Ekolu
      A model is proposed for prediction of natural carbonation in reinforced concrete (RC) structures, and is potentially applicable to existing and new RC structures. The major components of the model comprise mathematical functions applied to predict the influence of concrete composition, and environmental factors on natural carbonation. This paper introduces the model concept and explains its structure including derivation, optimization and calibration. Over 163 data sets taken from a 10-year carbonation study were used in the model development and calibration. Only the experimental data that were based on outdoor natural exposure environment were employed in this research. Also in this study, the proposed model is compared with fib-Model Code 2010 using carbonation predictions generated from 346 data sets involving real world, highway structures. It is shown that the proposed model is comparably accurate and involves mainly basic tests with no major anticipated costs.

      PubDate: 2017-10-25T22:15:36Z
       
  • Age-dependent size effect and fracture characteristics of ultra-high
           performance concrete
    • Abstract: Publication date: January 2018
      Source:Cement and Concrete Composites, Volume 85
      Author(s): Lin Wan-Wendner, Roman Wan-Wendner, Gianluca Cusatis
      This paper presents an investigation of the age-dependent size effect and fracture characteristics of ultra-high performance concrete (UHPC). The study is based on a unique set of experimental data connecting aging tests for two curing protocols of one size and size effect tests of one age. Both aging and size effect studies are performed on notched three-point bending tests. Experimental data are augmented by state-of-the-art simulations employing a recently developed discrete early-age computational framework. The framework is constructed by coupling a hygro-thermo-chemical (HTC) model and the Lattice Discrete Particle Model (LDPM) through a set of aging functions. The HTC component allows taking into account variable curing conditions and predicts the maturity of concrete. The mechanical component, LDPM, simulates the failure behavior of concrete at the length scale of major heterogeneities. After careful calibration and validation, the mesoscale HTC-LDPM model is uniquely posed to perform predictive simulations. The ultimate flexural strengths from experiments and simulations are analyzed by the cohesive size effect curves (CSEC) method, and the classical size effect law (SEL). The fracture energies obtained by LDPM, CSEC, SEL, and cohesive crack analyses are compared, and an aging formulation for fracture properties is proposed. Based on experiments, simulations, and size-effect analyses, the age-dependence of size effect and the robustness of analytical-size effect methods are evaluated.

      PubDate: 2017-10-18T21:36:04Z
       
  • Chemical self-healing system with novel microcapsules for corrosion
           inhibition of rebar in concrete
    • Abstract: Publication date: January 2018
      Source:Cement and Concrete Composites, Volume 85
      Author(s): Biqin Dong, Weijian Ding, Shaofeng Qin, Ningxu Han, Guohao Fang, Yuqing Liu, Feng Xing, Shuxian Hong
      Two kinds of chemically-triggered self-healing systems with novel microcapsules are designed to protect rebar from corrosion in concrete. X-ray micro-computed tomography (XCT) method is employed to non-destructively visualize the protection performance and quantitatively evaluate the efficacy of the self-healing system in a wet-dry cyclic accelerating corrosion test. Environmental scanning electron microscopy (ESEM) system equipped with texture element analysis microscopy (TEAM) is used to verify the results of XCT imaging analysis. The results reveal that the self-healing system-high efficiency is achieved by delaying the depassivation of the rebar and reducing the corrosion rate.

      PubDate: 2017-10-18T21:36:04Z
       
  • Pore-scale modeling of chloride ion diffusion in cement microstructures
    • Abstract: Publication date: January 2018
      Source:Cement and Concrete Composites, Volume 85
      Author(s): Yuankai Yang, Moran Wang
      Understanding the mechanism of chloride ion diffusion in cement is significant to improve the reliability of offshore reinforced concrete structures. The chloride ionic diffusivity in cement-based microstructures is predicted by pore-scale modeling using a modified lattice Boltzmann method. Both the Nernst-Planck equation for ion diffusion and the Poisson equation for electrodynamic effect are fully solved. The predicted effective diffusivities in cement-based microstructures with different porosities are in good agreements with the experiment data. The results show that the pore size distribution and Zeta potential of cement-based microstructures directly influence the effective diffusivities of chloride ions. The cement-based microstructure with smaller pore size and higher negative Zeta potential hinders chloride ions corrosion more effectively. The electrokinetic effect on the chloride ionic transport is negligible when the ratio of the maximum-probability pore size and the Debye length is higher than 32 in the cement-based microstructure. For engineering applications, we provide a predictive and easy-to-use formula by up-scaling to correlate the effective chloride ion diffusivity with electrokinetic effect in cement paste.

      PubDate: 2017-10-18T21:36:04Z
       
  • Alkali-activated slag concrete: Fresh and hardened behaviour
    • Abstract: Publication date: January 2018
      Source:Cement and Concrete Composites, Volume 85
      Author(s): F. Puertas, B. González-Fonteboa, I. González-Taboada, M.M. Alonso, M. Torres-Carrasco, G. Rojo, F. Martínez-Abella
      The behaviour of fresh and hardened alkali-activated slag (AAS) and OPC concretes was compared and the effect of mixing time assessed. OPC and AAS concrete slump and rheological results proved to differ, particularly when the slag was activated with waterglass (WG). The nature of the alkaline activator was the key determinant in AAS concrete rheology. Bingham models afforded a good fit to all the OPC and AAS concretes. In OPC and NaOH-activated AAS concretes, longer mixing had an adverse effect on rheology while improving hardened performance only slightly. In WG-AAS concrete, longer mixing times, improved mechanical properties and also rheological behaviour was enhanced, in which those conditions were required to break down the microstructure. Longer mixing raised thixotropy in OPC and NaOH-activated AAS concretes, but lowered the value of this parameter in waterglass-activated slag concrete.

      PubDate: 2017-10-11T06:59:00Z
       
  • Susceptibility of Portland cement and blended cement concretes to plastic
           shrinkage cracking
    • Abstract: Publication date: Available online 4 October 2017
      Source:Cement and Concrete Composites
      Author(s): Sadegh Ghourchian, Mateusz Wyrzykowski, Luis Baquerizo, Pietro Lura
      The market share of different types of blended cements is increasing year by year. Generally, blended cements are ground to higher fineness and exhibit a slower development of mechanical properties compared to Ordinary Portland Cement (OPC), which might affect the concrete performance in terms of shrinkage cracking at early ages. In this paper, the performance of concretes made with different cement types are compared according to the ASTM C1579-13 standard for plastic shrinkage cracking. The cracking behavior was further correlated to the deformations of both unrestrained and restrained specimens measured by a 3D image correlation system. The main factors influencing the cracking behavior were discussed based on poromechanics. It is concluded that the bulk modulus evolution has a dominant effect on controlling the plastic shrinkage cracking. Concretes made of more reactive cements, in particular with higher clinker content, are less susceptible to plastic shrinkage cracking. For cements with the same clinker content, increasing the cement fineness reduces the risk of plastic shrinkage cracking.

      PubDate: 2017-10-11T06:59:00Z
       
  • Passivity of embedded reinforcement in carbonated low-calcium fly
           ash-based geopolymer concrete
    • Abstract: Publication date: Available online 4 October 2017
      Source:Cement and Concrete Composites
      Author(s): Mahdi Babaee, M.S.H. Khan, Arnaud Castel
      This paper investigates the carbonation of two low-calcium fly ash-based geopolymer concretes to assess the effect of alkali concentration in the activator, and the carbon dioxide concentration on the pH drop and passivity of the reinforcement. Chemical adsorption of carbon dioxide at different concentrations into an aqueous NaOH solution, as representative of the pore solution, is studied to predict the distribution of carbonate species and pH drop. pH profiles were obtained during the exposure period. X-ray diffraction (XRD) was conducted to identify the carbonate phases. Half-cell potential and polarization resistance of reinforced concrete samples were monitored to assess the passivity of embedded reinforcement. The carbonated binders remained rather highly alkaline during the accelerated carbonation test which was in agreement with the predicted values. No sign of depassivation of reinforcement was observed, even for the lower strength grade concrete, during the long exposure time of 500 days to 1% carbon dioxide.

      PubDate: 2017-10-11T06:59:00Z
       
  • Effect of internal water content on carbonation progress in cement-treated
           sand and effect of carbonation on compressive strength
    • Abstract: Publication date: Available online 3 October 2017
      Source:Cement and Concrete Composites
      Author(s): Lanh Si Ho, Kenichiro Nakarai, Yuko Ogawa, Takashi Sasaki, Minoru Morioka
      This study investigates the effect of internal water content in cement-treated sand on carbonation progress and the effect of carbonation on compressive strength. To alter the internal water content, specimens were cured under three conditions: sealed, drying, and water sprayed. The carbonation coefficient, which was determined by a phenolphthalein spray test, decreased as the internal water content increased because of water sprayed. However, a thermal analysis revealed that the amounts of portlandite consumed and calcium carbonate generated by carbonation exhibited dissimilar trends: the amount of generated calcium carbonate was the maximum when there was a small increase in water content by water sprayed. Further increments in water content significantly lowered the amount of generated calcium carbonate. The measured compressive strength increased linearly with the amount of calcium carbonate. This implies that the amount of calcium carbonate is a good indicator of the effect of carbonation on the strength development of cement-treated sand and that both these quantities are affected by the internal water content.

      PubDate: 2017-10-03T17:48:26Z
       
  • Nanoindentation study of the interfacial zone between cellulose fiber and
           cement matrix in extruded composites
    • Abstract: Publication date: Available online 3 October 2017
      Source:Cement and Concrete Composites
      Author(s): R.S. Teixeira, G.H.D. Tonoli, S.F. Santos, E. Rayon, V. Amigó, H. Savastano, F.A. Rocco Lahr
      The present study shows the application of the nanoindentation technique to evaluate the properties of the cellulose fiber-cement matrix interfacial zone in composites prepared with an auger extruder. The degree of strength of the bond between fiber and matrix is recognized as important variable that influences macro-mechanical properties, such as modulus of rupture and toughness of cement based composites. The nanoindentation measurements showed the highest hardness and elastic modulus in the part inner of the cellulosic fiber after hydration process due to precipitation and re-precipitation of cement hydration products. These results indicate that mineralization of the cellulosic fibers can affect the stress distribution and interfacial bond strength in the cement based composite.

      PubDate: 2017-10-03T17:48:26Z
       
  • A combined SPM/NI/EDS method to quantify properties of inner and outer
           C-S-H in OPC and slag-blended cement pastes
    • Abstract: Publication date: Available online 3 October 2017
      Source:Cement and Concrete Composites
      Author(s): Y. Wei, X. Gao, S. Liang
      To identify the distinct microstructural features and to provide insight into the mechanism by which the phases in hardened paste possess, this study adopts the coupled techniques of quantitative modulus mapping in the form of Scanning Probe Microscopy (SPM) images, nanoindentation (NI), and energy-dispersive X-ray spectroscopy (EDS) for comprehensive investigation on the chemical-mechanical-morphological properties of C-S-H gel in both ordinary Portland cement (OPC) and slag-blended cement pastes. The thickness of the inner C-S-H (IP) layer is precisely measured for the first time by modulus mapping, it varies with the types of unreacted cores as well as the addition of the supplementary cementitious materials. An interface transition zone (ITZ) is found between the unreacted C3S grain and the surrounding inner C-S-H layer. The mechanical properties of the five types of C-S-H in OPC and the slag-blended pastes are not significantly affected by their chemical compositions. A good correlation between the storage modulus and the indentation modulus of the individual phases is found. The results indicate the significance of SPM-based modulus mapping technique as a powerful tool to characterize the phase in cementitious materials with more attractive features of higher spatial resolution.

      PubDate: 2017-10-03T17:48:26Z
       
 
 
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