Abstract: This study evaluates the workability and compressive strength properties of normal weight concrete (NWC) using high dosage of fly ash cement replacement. The goal is to find the suitable mix proportion of G40 NWC and to study the slump-loss at different interval time with fly ash replacement up to 60%. The strength properties of NWC were investigated using rebound hammer test as non-destructive and compressive strength test for verifying it. The acceptable mix proportion for fly ash replacement was then investigated using laboratory experiments. For strength properties of NWC, the samples were tested for 3, 7, 14 and 28 days. Results indicate that the inclusion of fly ash as partial cement replacement improves the workability of NWC concrete. The slump-loss of NWC with fly ash increases and it delays the setting time of fresh concrete. The strength of concrete reduces with an increment of fly ash. The strength measured using non-destructive test is lower when compared to compressive strength test. The results demonstrate that the replacement of cement with fly ash in concrete is beneficial and the targeted strength of concrete will achieve with time. PubDate: 2019-09-07 DOI: 10.1007/s41024-019-0065-5
Abstract: In this study, the effect of two water reducer polymers on the thermal stability, rheology, and compressive strength of Gasin Ordinary Cement (GC) was investigated. The behavior of cement in the liquid phase (slurry) and hardened phase modified with two types of polymer varied from 0 to 0.06% (%wt) were investigated. XRD and TGA tests were conducted to identify the effect of polymers on the behavior of GC. The compressive strength of cement mixed with polymers was tested from the early aged of 1 days to 28 days of curing. The shear stress versus shear strain rate of cement slurry was modeled and the results of prediction using Vipulanandan rheological model were compared to the Vocadlo model. High reduction in the total weight loss of the GC at 800 °C when the cement modified with 0.06% of polymers detected using TGA test. The rheological properties of the cement slurry such as viscosity, yield stress, and the compressive strength of GC were increased significantly with increasing the polymer contents. Addition of polymers reduced the required water to reach the desired fluidity by about 43% based on the type of polymer. The results showed that the Vipulanandan rheological model predicted the shear-thinning relationship between the shear stress and shear strain rate of the cement slurry modified polymers very well. Also, the Vipulanandan rheological model has a maximum shear stress limit were as the Vocadlo model did not have a limit on the maximum shear stress. Based on the Vipulanandan rheological model the maximum shear stress produced by the cement slurry modified with 0% and 0.06% of polymers at the temperature of 25 °C were increased from 38.7 to 171.3 Pa and to 184.8 Pa respectively due to the addition of polymers. Nonlinear models were used to separate the effect polymer quantity, water–cement ratio, and curing time on the rheological properties and compressive strength of cement. PubDate: 2019-08-26 DOI: 10.1007/s41024-019-0064-6
Abstract: The detonation of an explosive charge extremely near or above the ground could be devastating causing deformation to the structural frame of the building, cracking of walls, exploding huge areas of windows and shattering all kinds of life saving systems. Depending upon the type and size of explosive used, the possible structural collapse happens when the blast waves produced during explosion, impacting the structure over time. This paper presents to study the characteristics of blast waves and understanding the relationships between various parameters considered in blast loading such as incident overpressure, reflected overpressure, phase duration and scaled distance. Analysis and quantification of uncertainties of the TNT equivalency of different explosives with respect to pressure and impulse observed. Focus was given to formulate an empirical equation from the extracted experimental data considering the influential parameters affecting the blast resistant design that governs the modeling of blast loads. This equation could help in predicting the safe distances beyond which the blasting of different types of explosives would cause minimum impact on the structure. Thus for designing a structure to be resisting blast weight, the foremost important task is to have a realistic overview about the prediction of pressures impacting on a structure and this paper gives essential outline of the detonating effects due to various types of explosives on structures. PubDate: 2019-08-22 DOI: 10.1007/s41024-019-0063-7
Abstract: Worldwide, the concrete industry is consuming about one billion cubic meters of mixing and curing fresh water per year. A settled fact in the cement industry tells that excessive water content leads to a reduction in strength of cement mortar, however inadequate water content incurs poor workability. The need for research to study enhancing the utilization of the same amount of potable water in concrete to maintain higher ultimate compressive strength, workability, and durability is essential. The proposed plan of work introduced a technique for the addition of the mixing water through sprinkling the water in the mixer as compared with the pouring traditional method, this was investigated via compressive strength, tensile strength, X-ray diffraction (XRD), and Scanning electron microscope (SEM). The results revealed that the new technique showed to be a significant method that could reduce the mixing water content within the concrete mixes while keeping the strength and durability at their ultimate levels. The gain in compressive, and tensile strengths reached in some mixes about 31%, and 48% respectively, with an incomparable microstructure as it has been found employing the SEM micrographs, and XRD diagrams. Finally, it is highly recommended to study the application of the mixing water through sprinkling with Nano nozzles. PubDate: 2019-08-13 DOI: 10.1007/s41024-019-0062-8
Abstract: Now a day’s concrete is the extreme broadly used construction material in civil engineering industry because of its extraordinary structural strength and stability. The overuse level of cement and natural sand for civil industry has several undesirable social and ecological consequences. As an answer for this, industrial wastes called as by-products (pozzolanic materials) such as fly ash, GGBFS, silica fume and metakolin can be used to interchange partially cement and natural sand by manufacturing sand (M-sand). This research aims to investigate the possibility of replacing natural sand by M-sand with 20% of above pozzolanic materials substitute in concrete. In this experimentation, natural sand was replaced by M-sand in various percentages (0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100%), with water–cement ratio of 0.45 and cement was partially substituted by 20% of pozzolanic materials. M30 grade of concrete mix proportions were designed as per IS 10262:2009 guidelines. The fresh concrete properties and compressive strength, tensile strength and flexural strength results were checked for the different concrete mix proportions and compared with conventional concrete. From this research work, it can be concluded that for replacement of 60% natural sand by M-sand and 20% cement by silica fume yields maximum compressive strength, tensile strength and flexural strength than conventional concrete. PubDate: 2019-07-23 DOI: 10.1007/s41024-019-0061-9
Abstract: The main purpose of this paper is the probabilistic safety analysis of the historical masonry arch bridges (HMAB) and to calculate its reliability index (RI) using the “probabilistic design system” of the ANSYS software. In evaluating the reliability of bridge, the load-resistance model has been used to express the bridge failure functions. Calculating the RI requires the definition of loads effects on the structure and structure resistance. The load and resistance implicit functions are evaluated by stochastic finite element method and the Monte Carlo method has been used for laboratory simulation. The sampling method is the Latin hypercube sampling. The innovations in this paper is to use the functions dependent on parameters, modulus of elasticity, Poisson ratio, density of materials, and traffic load of bridge deck. The number of random parameters is 19. These random parameters are defined by the Log-normal distribution function. In this paper, the reliability status of bridge is investigated in the ultimate limit state under gravitational loading. The constitutive law of the bridge material is considered to be linear elastic. Three types of compressive, tensile, and allowable deflection are considered as limit states of the present research. The case study of the Pole Kheshti Langroud HMAB showed that the required safety is not provided for the ultimate limit state and the bridge is at risk of failure. The RI of bridge in the tensile limit state is lower than the target RI. The sensitivity analysis of random variables of the load and resistance implicit functions to the deflection and tensile responses is investigated, and random parameters with more impact are specified. In the stress limit state and deflection limit state, the modulus of elasticity and weight per unit volume of the sidewalls have the greatest impact on safety, respectively. PubDate: 2019-07-12 DOI: 10.1007/s41024-019-0060-x
Abstract: Reinforced concrete structures are subjected to several degradation processes that often occur early, especially due to reinforcements corrosion. Therefore, the use of representative models for an accurate service-life prediction of reinforced concrete structures becomes indispensable. Thus, this study is aimed at evaluating the model proposed by Andrade to efficiently predict the chloride penetration in concrete structures. In addition, the input variables of this model, as well as the challenges in obtaining them are analyzed. Andrade’s model was applied in some case studies to verify their efficiency in predicting the chloride penetration in reinforced concrete structures in marine environments. The results indicate that for data with small exposure times, the model yielded similar responses to the chloride penetration in situ, with good results within an error range of 35%, associated with a maximum difference of only 4.6 mm between observed and calculated values. For the data with higher exposure times, the differences were significant, indicating the need for an alteration in order to best determine the increase in surface chloride concentration over time. Thus, it is suggested that the model undergoes modifications, mainly in relation to two fundamental aspects, (i) adopt the growth of the chloride surface concentration over time and (ii) consider the variability of the concrete characteristics and exposure conditions through a probabilistic approach. PubDate: 2019-07-10 DOI: 10.1007/s41024-019-0059-3
Abstract: The objective of this study is to identify and quantify the effect of silica fume content (SF), water–cement-ratio (w/c) and curing time (t) on the compressive and tensile strengths of concrete at different strength ranges varied from 4 to 100 MPa. In this study, over 1000 data were used to characterize the compressive and tensile strengths behavior. The range of w/c for modified concrete with different percentage of silica fume up to 40% (by dry weight of cement) was in the range of 0.17–0.80%, compressive and tensile strengths were in the range of 4–100 MPa, and 1–7 MPa, respectively. Vipulanandan model correlated the relationship between mechanical properties of concrete modified with SF with a varied range of w/c and curing time and the result were compared with the Hoek–Brown correlation model used in the literature. Based on the coefficient of determination (R2) and root mean square error (RMSE) the compressive strength (σc), tensile strength (σt) of concrete as a function of w/c, percentage of silica fume and curing time using nonlinear (NLM) relationship quantified very well. Based on the NLM parameters, the effect of SF was less than w/c and curing time on the compressive strength of modified concrete with SF in different strength range. According to the coefficient of determination (R2) and root mean square error (RMSE), the Vipulanandan correlation model and Hoek–Brown model both are very close in predicting the mechanical behavior of concrete modified with SF for normal and high strengths concrete (NSC and HSC). PubDate: 2019-07-10 DOI: 10.1007/s41024-019-0058-4
Abstract: The technique of X-ray fluorescence spectroscopy is a non-destructive method used in several applications in Civil Engineering for the qualitative and quantitative determination of chemical elements in different materials. This technique allows the analysis of materials by atomic excitations and identification of spectra obtained from defined wavelengths interpreted for each chemical element present in the material in a precise and fast quantification, optimizing characterization analysis in a laboratory. Although the benefits obtained from this technique are clear, problems regarding the quantification of chloride ion in concrete powder samples, obtained from real structures, end up, giving significant errors in relation to its quantification, which, in turn, overestimate the chloride concentration in the profiles more than 500%. In this way, this work presents a correlation between two methodologies using concrete powder samples from structures present in a marine environment for more than 40 years. These samples were analyzed by X-ray fluorescence spectroscopy and potentiometric titration techniques in order to establish a correlation between the methods. The obtained results showed that there is a relationship between both techniques with a determination coefficient close to 1. PubDate: 2019-06-15 DOI: 10.1007/s41024-019-0057-5
Abstract: Concrete is susceptible to attack in places considered aggressive, such as wastewater treatment stations. Sulfate ions attack is very common in these places, resulting in accelerated degradation of the concrete, which can compromise any reinforced concrete structure. In this context, the present research aims to evaluate the pathological manifestations caused by these ions, analyzing the sulfate content in concrete samples taken from a station and their porosity. The result obtained in the sulfate content analysis was an average of 7.84%, values well above the acceptable maximum limit that would be on average 0.5%. In relation to the porosity of the sample, an increase of 10% was observed, on average, considering a sample of reinforced concrete without attack. PubDate: 2019-06-12 DOI: 10.1007/s41024-019-0056-6
Abstract: We propose an artificial neural network (ANN) model to predict the CO2 diffusion through the concrete to determine the carbonation depth over time, analyzing the influence of some training algorithm and the network architecture in the ANN learning process. A reliable experimental test database of the non-accelerated test with 278 results of concrete carbonation depth was created from the published literature. It was used to train, test, and validate the model. Altogether, 120 networks had been trained with different characteristics, verifying its performance. In spite of the non-linearity and complexity of the concrete carbonation phenomenon, the proposed ANN model yielded accurate prediction. Results indicate the best training algorithm and the optimum number of neurons in the hidden layer that allows faster ANN training process and generates the most accurate mapping for the concrete carbonation phenomenon. The use of ANN appears as a robust tool easily applied to the study of the concrete carbonation, aiding in decision making in engineering projects focused on durability. PubDate: 2019-06-05 DOI: 10.1007/s41024-019-0054-8
Abstract: Reinforced concrete degradation processes, such as corrosion and carbonation, directly impact the service life of these structures. Therefore, non-destructive tests are an effective approach to evaluate its quality. In order to quantify the impact of the corrosion degree and the carbonation depth in this research, non-destructive tests were used. Reinforced and non-reinforced samples were molded and subjected to accelerated carbonation and corrosion experiments. Its behavior was monitored through electrical resistivity (ER), ultrasonic pulse velocity (UPV) and corrosion potential (CP) tests. The specimens were exposed to different levels of carbonation and corrosion to obtain different corrosion degrees, which was determined visually. The results of this research proved that the ER decreased as the corrosion degree increased, although this reduction was not very significant, mainly after 1 day of exposure. Also, it was concluded that immersing the samples in a chloride solution had great impact on the ER, and the ionic migration directly affected the visual corrosion degree. For carbonation, it was found that the longer the exposure, the greater the corrosion degree. Regarding the non-destructive tests, it could be seen that the presence of reinforcements reduced the ER. In addition, the longer the exposure in the carbonation chamber, the higher the ER. This behavior was due to reduction in porosity, caused by the carbonation reaction. In the UPV test, no relation was found with the corrosion degree. Finally, the CP was more electronegative during the accelerated corrosion test, especially after 7 days of testing. PubDate: 2019-05-28 DOI: 10.1007/s41024-019-0055-7
Abstract: Existing masonry constructions are highly vulnerable to seismic actions, as demonstrated by the severe earthquakes which stroke the Italian territory in recent years, causing great damages, especially in old masonry buildings. Therefore, restoring damaged buildings, with the aim to recover or improve their structural capacity, is a key aspect in the post-seismic interventions. Fiber reinforced composite materials could be effectively used to this purpose. One aspect which is worth to investigate is the application of these reinforcement typologies on damaged structural elements. Even though many experimental campaigns are available concerning the mechanical improvement given by composite materials applied on undamaged structural elements, only few can be found considering strengthening of already damaged masonry walls. The objective of the work here presented is to evaluate the shear response of damaged masonry panels strengthened using fiber reinforced cementitious matrix (FRCM). Two unreinforced brick masonry walls were subjected to diagonal compression tests, producing an extended state of damage. Afterwards, the same walls were strengthened with FRCM and diagonal compression tests were again performed. Comparisons were done between the results of the unreinforced samples and the pre-damaged strengthened ones, in terms of shear strength and post-peak behavior. The FRCM retrofitting system was also used to strengthen an undamaged masonry panel, which was tested in order to analyze similarities and differences with respect to results obtained for pre-damaged samples. The experimental campaign allowed to study the sole contribution of the reinforcement to the shear capacity of the wall panels. Results showed that the presence of FRCM reinforcements on damaged masonry panels influenced the shear behavior of the samples, which experienced a more ductile failure. PubDate: 2019-05-23 DOI: 10.1007/s41024-019-0053-9
Abstract: This paper presents an experimental investigation into product based research, in preparation of stabilized adobe blocks (SAB) by attempting to utilize construction and demolition waste (CDW) in the form of excavated natural soil (NS) and crushed demolished brick masonry. SAB are energy efficient sustainable variety of masonry units. A detailed study on strength, durability and elastic properties of SAB produced in different combinations were carried out, to determine the optimum combination and gradation, to achieve the required engineering properties. The experimental results were evidenced at a micro-level through microstructure analysis using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). When excavated natural soil was replaced in the order of 60–80% by crushed demolition brick masonry waste, the test results indicated better strength and durability characteristics. The experimental program indicates suitability and potential of utilizing crushed demolished brick masonry waste as partial replacement to excavated natural soil in preparation of stabilized adobe blocks. This attempt of experimental research studying performance of masonry units is one of the ways to address the disposal of construction and demolition waste. PubDate: 2019-05-10 DOI: 10.1007/s41024-019-0052-x
Abstract: Corrosion of concrete sanitary sewers has become a major problem around the world. Concrete durability in sewerage systems is mainly related to the presence of effluents containing sulfur-rich compounds that lead to an acid attack and expansion reactions. This paper presents a microstructural analysis of concretes (two case studies) taken from corroded sewer pipes. The objective of this investigation is to highlight and identify the pathologies of cementitious materials in sanitation networks. A scanning electron microscope equipped with energy dispersive X- ray analysis (SEM–EDS) was performed on fragments of concrete samples taken at different areas. In addition to these microstructural analysis, bulk density and water-accessible porosity tests are performed, the results obtained were compared with those of a reference concrete (new pipe). The results of the analysis showed a deterioration of the pipes in both faces (internal and external) with the presence of products prejudicial for their durability. PubDate: 2019-04-30 DOI: 10.1007/s41024-019-0051-y
Abstract: Due to several reasons as the low resistance of constructed concrete and also change in codes or application of structures, some concrete frames need to be retrofitted. By adding the steel brace to the reinforced concrete, many seismic parameters such as resistance, ductility, stiffness and the resistance reduction coefficient change. This study experimentally investigates the impact of adding the prop, the convergent steel brace and also the convergent steel brace with a ductile ring on resistance, stiffness, ductility and energy dissipation of RC frames. Four samples of RC frames with one span and one story with the same characteristics were constructed and retrofitted by different methods. All frames were subjected to the cyclic loading, and the hysteresis and pushover-displacement graphs of them were plotted. The novelty of the work was using such braces in RC frames. The results obtained from the tests showed that although the frame retrofitted by the X-brace showed a better performance in terms of resistance and stiffness, but the retrofitted frame with a ring also showed a better behavior in terms of resistance and stiffness compared to the RC frame and the sample with the jacket as well as compared to the sample with the X-brace showed more ductility and energy dissipation (with a slight reduction in resistance). PubDate: 2019-04-22 DOI: 10.1007/s41024-019-0050-z
Abstract: Historical centres are often constituted of a series of masonry building compounds very vulnerable to earthquakes, whose static non-linear behaviour is not predicted by building codes. This paper propose a simplified modelling approach to predict the seismic response of structural units into masonry building compounds. This approach is based on the equivalent frame method modelling, a technique easy to be implemented within finite element method calculation programs. The modelling technique has been applied to investigate constructions representative of Southern Italy building aggregates erected during the past decades. Firstly, the whole aggregates have been modelled and analysed in order to evaluate the seismic behaviour of structural units having intermediate, heading and corner positions. Later on, the seismic response of these structural units has been assessed by modelling the single units as isolated structures with appropriate boundary conditions to consider, in a simplified way, their position in the aggregate and, therefore, the influence of other constructions. Finally, comparison of the achieved results has been carried out in order to confirm the effectiveness of the proposed analysis approach. PubDate: 2019-04-08 DOI: 10.1007/s41024-019-0049-5
Abstract: The materials used in this work were blended OPC limestone (24%), nano metakaolin. This thesis aims to study the effect of some nano materials such as nano metakaolin (NMK) on the hydration characteristics of blended cement pastes up to 90 days of hydration. Blended cements containing 0, 5 and 10 wt% nano MK, were also studied. The hydration and the physico-mechanical characteristics of cement pastes were investigated by the determination of water of consistency (W/C, %), setting times (STs), combined water (Wn), free lime (FL), penetration of chloride (PC), and compressive strength (CS). Some selected cement pastes were identified using XRD, TG and DTA techniques to show the hydration products with curing time. PubDate: 2019-03-25 DOI: 10.1007/s41024-019-0048-6
Abstract: An experimental program was undertaken to assess the effectiveness of a new retrofit concept to improve the in-plane behavior of unreinforced clay brick walls by means of full-scale static-cyclic in-plane tests. The proposed seismic retrofit system combines two standalone retrofit measures for in-plane and out-of-plane strengthening of masonry walls. The in-plane reinforcement consists of a single-sided carbon Fabric-Reinforced Cementitious Matrix (FRCM) overlay, and anchors embedded with a flexible adhesive in the masonry. The out-of-plane reinforcement, which consisted of deep mounted Carbon Fibre Reinforced Polymer (CFRP) strips embedded with a flexible adhesive in the masonry, was included in the study to investigate the possible degrading effects of the deep groove on the in-plane behavior. A total of nine full-scale reinforced masonry walls with three different geometries were tested under three different axial loads. None of the specimens showed shear failure at both the reinforced and the as-built side. Cracking predominantly occurred at the interface between the bottommost bed-joint and the foundation beam. The out-of-plane reinforcement did not affect the in-plane strength, as no vertical shear cracks occurred. Moreover, it was found that the anchors increased both the rocking and sliding resistance of the walls. An analytical model was proposed covering the rocking and sliding resistance of the reinforced walls, providing a good approximation of the experimentally obtained in-plane strengths. Additional pull-out experiments showed that the testing scenario where the tensile forces in the anchor were transferred to CFRP strip, provided a good approximation of the analytically determined anchorage strength. PubDate: 2019-03-22 DOI: 10.1007/s41024-019-0043-y
Abstract: Concrete is the most commonly used building material as well as one of the main construction material, the cracks in concrete create problems. Cracks in concrete occur due to various mechanisms such as shrinkage, freeze–thaw reactions, and mechanical compressive and tensile forces. Concrete structures are often reinforced with steel. In order for the reinforcement to take over tensile forces, concrete has to crack. Through such cracks, water and compounds that are harmful to concrete can enter. Therefore, a novel technique has been developed by using a selective microbial plugging process. The technology of Self-healing concrete based on calcium carbonate precipitation induced through bacterial activity has been investigated in recent years by teams around the world. One such thought has led to the development of a very special concrete known as Bacterial Concrete where bacteria is induced in the mortars and concrete to heal up the faults. Self-healing approaches are promising techniques for the remediation of micro-cracks in concrete. The autogenous self-healing techniques show better results in healing of micro cracks on the surface of the concrete. Bacterial concrete refers to a new generation of concrete in which selective cementation by microbiologically-induced CaCO3 precipitation has been introduced for remediation of micro cracks. In several follow up studies there is a possibility is to use viable bacteria is sustainable and concrete embedded self-healing agent was explored. PubDate: 2019-03-20 DOI: 10.1007/s41024-019-0045-9
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