Performance Concrete Research Articles

Research on the Variation law of Compressive Strength of Concrete under the Coupling Effect of Freeze-Thaw and Salt Corrosion

Due to its unique freeze-thaw and sulfate corrosion environment, the northwest region is an important factor causing the deterioration of concrete structures. Compressive strength is a key indicator of the macroscopic performance of concrete. Analyzing the changes in compressive strength of different water cement ratios under complex freeze-thaw environmental conditions is of great guiding significance for improving the service performance of concrete. Therefore, in order to obtain the variation law of compressive strength of concrete under freeze-thaw cycle conditions, this paper designs three water cement ratio concrete freeze-thaw cycle and sulfate solution freeze-corrosion coupling tests to analyze the compressive strength changes at different stages. The results show that in a water freezing and thawing environment, the compressive strength of concrete decreases continuously with the increase of experimental age, and the larger the water cement ratio, the greater the decrease in compressive strength. In sulfate solution freeze-thaw, in the early stage of the experiment, the decrease in compressive strength compared to water freeze-thaw decreased, and in the later stage of the experiment, the decrease increased. The larger the water cement ratio, the greater the impact of the above.

Experimental and numerical assessment of GFRP and synthetic fiber reinforced waste aggregate concrete members

Improper disposal of plastic waste (P-waste) poses significant pollution and health risks to the environment. Additionally, steel rebar corrosion in concrete structures reduces their strength and serviceability. To address these issues, this study explores using glass fiber-reinforced polymer (GFRP) rebars and replacing natural coarse aggregates with P-waste aggregates for sustainable and eco-friendly construction. This work investigates the axial performance of polypropylene structural fiber-reinforced P-waste aggregate concrete (SFPC) compressive components having GFRP-reinforcement (GSFPC) under various loading conditions. For comparison, steel-reinforced SFPC compressive components (SSFPC) were also fabricated. Eighteen circular components with 1200 mm height and 300 mm diameter were tested and compared under different loading conditions. SSFPC components exhibited up to 21.9 % higher axial strength but up to 27.4 % lower ductility compared to GSFPC components. Eccentric loading similarly reduced axial strength in both GSFPC and SSFPC components. A 3-D finite element analysis (FEA) of GSFPC components was proposed using a modified damaged plastic model for SFPC which showed deviations of 2.3 % in axial strength and 7.7 % in equivalent axial shortening, demonstrating a good accuracy of the FEA model.

Research and Development of New Polylactic Acid (PLA) Fiber Concrete Materials and Performance Research

Polylactic acid (PLA) fiber concrete has broad application prospects in the field of building materials. This article summarizes the current research status of fiber-reinforced concrete and its importance in improving the mechanical properties of cement-based materials. In view of the modification of the physical properties of PLA fiber, experimental research is conducted to improve its mechanical properties, solve the problem of natural degradation, and explore the application of anti-corrosion materials. In terms of concrete preparation technology, experiments were carried out to study uneven fiber distribution and compatibility with cement slurry to determine the optimal proportion and processing technology. Mechanical property tests and theoretical studies have shown that fiber type and length have a significant impact on the performance of concrete, and it is necessary to further explore the mechanical properties of the transition zone between the fiber and the concrete matrix. Aiming at the durability, fire resistance and other issues of PLA fiber concrete, relevant experimental research plans were proposed. Finally, the mechanical properties of ultra-high toughness PLA fiber concrete were optimized by improving the mix design, optimizing fiber type and dosage, and surface treatment technology. These research results provide an important reference for the wide application of ultra-high toughness PLA fiber concrete in building structures.

Recycling of contaminated waste glass in ultra-high performance concrete: Impurities impact

The feasibility of recycling clean waste glass in construction products has been demonstrated. However, the direct utilization of contaminated waste glass from consumed beverage glass bottles may negatively affect the performance of concrete. This study aimed to investigate the effect of impurities in waste glass on the properties of ultra-high-performance concrete (UHPC). Washed and unwashed waste glass powder and sand were used as cement and river sand substitutes, respectively. Light particles, clay and fine silt, organic impurities and aluminium content in waste glass were determined. The results showed that the use of washed waste glass powder (W-WGP), washed waste glass sand (W-WGS) and unwashed waste glass powder (U-WGP) had a limited negative effect on the compressive strength of UHPC. In contrast, the use of unwashed U-WGS significantly decreased the compressive strength of UHPC due to the presence of impurities (e.g., paper and metallic aluminium). However, the impurities in the unwashed waste glass could positively reduce the autogenous and drying shrinkages of UHPC. The metallic impurities reacted with an alkaline solution to generate gases, resulting in the expansion of the matrix and reduction of autogenous shrinkage at the early stage. X-ray CT and microstructural images indicated that expansion resulting from the U-WGS caused cracks in the matrix and degraded the interfacial zone between the U-WGS and the paste. However, the incorporation of waste glass did not induce any alkali-silica reaction expansion in UHPC due to its low water-cement ratio and dense structure. The UHPC prepared with 30 % U-WGP as a replacement for cement was found to achieve satisfactory performance and lower carbon emissions.

Predicted Corrosion Performance of Organofunctional Silane Coated Steel Reinforcement for Concrete Structures: An Overview

This article provides a comprehensive overview of the potential use of organofunctional silane coatings in the corrosion protection of concrete reinforcement in close relation to other commercially used coating technologies—i.e., epoxy coatings and bath hot-dip galvanizing coatings. The application technology of the steel surface is described in detail, and the corrosion performance and bond strength in concrete are compared. The paper also points out the possibility of improving the durability of epoxy coatings by the addition of silanes and, in the case of application to the surface of hot-dip galvanized steel, they can prevent corrosion of the coating by hydrogen evolution. The application potential of organofunctional silanes is also presented in the form of hydrophobic coatings on concrete surfaces or as corrosion inhibitors in simulated concrete pore solutions. The use of a suitable type of modified silane coating on the surface of carbon steel reinforcement can increase the corrosion performance and can also increase the bond strength in concrete. However, these facts need to be experimentally verified.

Mechanical properties and microstructure of artificial sand concrete based on rock-powder content

The rock-powder content in artificial sand has a significant impact on the performance of concrete. In order to investigate the influence of rock-powder content on the physical and mechanical properties of artificial sand concrete, this study summarizes the current application status and background of artificial sand. Starting from the characteristics of artificial sand, different levels of rock-powder content in artificial sand are discussed. Scanning electron microscopy (SEM) tests are conducted on artificial sand products made from stone chips in Shangqiu, Henan Province. The research findings indicate that when the rock-powder content is between 6 % and 15 %, the workability of the concrete improves, and it exhibits higher strength and a larger strength-to-cementitious ratio. However, when the rock-powder content exceeds 20 %, although the workability still improves, the strength decreases, and the strength-to-cementitious ratio becomes smaller. Under a magnification of 2000X, the SEM images show a good bonding between artificial sand and the cementitious gel C-S-H in the concrete, with no cracks at the interface of artificial sand. These results demonstrate a favorable outcome. It is expected that the research findings will provide theoretical reference for the application of artificial sand in concrete structures.

Cyclic behavior of rubber-coated stud-UHPC shear connectors exposed to reversed cyclic loadings

Steel-ultra-high performance concrete (UHPC) composite structures that could maximize the benefits of two materials have gained ground in bridge structures for accelerating construction speed and reducing self-weight. However, the shear stiffness of ordinary stud connectors (OSCs) in UHPC might exceed the actual demand, leading to the insufficient deformation capacity of OSCs. Therefore, the flexible rubber-coated stud connectors (FRSCs) were developed to replace the OSCs for improving the ductility of shear connectors. The shear performance of FRSCs in UHPC subjected to reversed cyclic loadings has been not understood, which limits its application in the practical construction. The cyclic behavior of FRSCs was examined through modified push-pull test specimens, and the static loading tests were carried out to determine the characteristic slip capacity and shear strength. Numerical models were established to reveal the damage process and failure mechanism of FRSCs and employed to conduct detailed parametric studies. The results demonstrated the FRSCs exhibited high ductility and large energy absorption capacity than OSCs and possessed sufficient shear bearing capacity, indicating their potential application in steel-UHPC composite systems. Increasing the height and thickness of rubber sleeve could enhance the slip capacity of FRSCs under monotonic loadings, while having no effect on the cyclic ductility. Finally, an empirical equation was developed to accurately predict the FRSC shear strength.

Evaluation of technical and gamma radiation shielding properties of sustainable ultra-high performance geopolymer concrete

This study proposed to use barite-enhanced ultra-high performance geopolymer concrete (UHPGC) as the composite matrix to develop high-strength, cement-free, and sustainable radiation shielding materials. The physical properties, γ ray attenuation capacity, microstructure, and environmental and economic impacts of prepared barite-enhanced radiation shielding UHPGC were determined and compared with normal concrete and ultra-high performance concrete (UHPC). The combination of steel fibers and barite aggregate increased the density of UHPGC, thereby enhancing its γ ray attenuation capacity. Multi-scale γ ray shielding simulation results demonstrated that although thickness was the more decisive factor of γ ray attenuation capacity of composites, the enhancement of the shielding capacity of the material helps reduce the floor area and the cost of radiation shielding structure. The micro-analysis results revealed that barite-enhanced UHPGC exhibited compact microstructure and excellent interfacial performance. Furthermore, life cycle assessment results demonstrated that UHPGC was more suitable as a composite matrix than UHPC to develop sustainable and low-cost radiation shielding materials.

Experimental investigation of the behavior of UHPCFST under repeated axial tension

A ultra-high performance concrete filled steel tube (UHPCFST) is a composite structural component that extends the performance of both steel and concrete. It is a promising component to be used in a diagrid structure to further reduce self-weight. Compared with the research on compressive performance of UHPCFST, there is a lack of knowledge on the mechanical behavior of UHPCFST under axial tension. This paper fills this knowledge gap by carrying out experiments on UHPCFST subjected to monotonic and repeated tension. The test parameters are steel tube thickness and volume fraction of ultra-high performance concrete (UHPC). The failure modes, load-strain curves, tensile strength and tensile stiffness are studied in detail. Stiffness degradation is also studied. The test results show that: (1) under axial tension load, a UHPCFST typically experiences fracture failure of the outer steel tube, followed by section fracture of the UHPC, and notable deformation before a final ductile failure; (2) tensile strength increases with the increase of the thickness of the steel tube, while it is less obvious in a UHPCFST with a higher steel ratio; (3) the force-strain curve of a UHPCFST under monotonical axial tension is close to that of the UHPCFST under repeated axial tension, suggesting that the accumulated damage during unloading and reloading is limited. An exponential decay formula is proposed to predict stiffness degradation observed in the repeated axial tensile tests. It is found that the design codes from Europe, USA, and China underestimate tensile strength and stiffness of UHPCFST. Finally, a three-phase empirical model is proposed for the load-strain curve of UHPCFST under tension.

Enhancing Concrete Performance through Sustainable Utilization of Class-C and Class-F Fly Ash: A Comprehensive Review

Integrating class-C and class-F fly ash (FA) as supplementary cementitious materials (SCMs) in concrete offers a promising pathway for sustainable construction practices. This study explores the pivotal role of FA in reducing carbon dioxide (CO2) emissions and improving concrete’s durability and mechanical properties through a comprehensive life cycle analysis (LCA). By blending FA with cement, significant reductions in CO2 emissions are achieved, alongside enhancements in the workability, compressive strength, and permeability resistance of the concrete matrix. This research elucidates the pozzolanic reaction between FA and calcium hydroxide (CH) during cement hydration, highlighting its contribution to concrete strength and durability. Through a range of comprehensive analysis techniques, including mechanical testing and environmental impact assessment, this study demonstrates the substantial benefits of prioritizing the utilization of class-C and class-F FA in sustainable construction. The findings underscore the industry’s commitment to environmentally conscious practices, promoting structural integrity and reducing ecological impacts. Overall, this research emphasizes class-C and class-F FA as critical components in achieving sustainable construction goals and advancing towards a more environmentally responsible built environment.

Role of graphene oxide infusion in concrete to elevate strength and fire performance in construction concrete

The study is centered on optimizing graphene oxide (GO) concentration in M30 designer mix concrete, aiming to enhance its performance under elevated temperatures and fire conditions. The findings revealed a significant 40 % increase in compressive strength with the addition of 0.05 wt% GO to M30 grade concrete after 28 days of curing in water. GO played a crucial role in mitigating the impact of high temperatures under heating in furnace and fire exposure under flame, resulting in reduced crack formation and a delayed temperature rise during thermal loading. In heat resistance assessments, GO concrete exhibited a substantial delay in temperature rise compared to plain concrete under controlled furnace conditions, showcasing superior resistance to elevated temperatures. Thermogravimetric analysis and Differential TG analysis elucidated the superior retention of water and hydrated products in GO concrete, even after exposure to high temperatures. Fire exposure tests demonstrated that GO concrete exhibited a much lower surface temperature (less than 50 °C) opposite to the flame (flame temperature ∼ 700 °C) within a 15 cm width of concrete. Additionally, fewer and less severe cracks appeared in the GO concrete compared to plain concrete, showcasing its anti-spalling behavior. The altered matrix porosity of GO concrete, creating nano- and microscale channels, contributed to reduced vapor pressure and mitigated crack formation. This comprehensive study underscores the potential of GO as a versatile additive in concrete, offering enhancements in strength, heat resistance, and fire performance for sustainable and resilient infrastructure development.

Analysis of damage and fracture characteristics for concrete subjected to cryogenic freeze-thaw cycles: An acoustic emission and digital image correlation study

This study examines concrete's performance under cryogenic (−170 °C) freeze-thaw cycles (CFTCs), inspired by the development of all-concrete liquefied natural gas (ACLNG) tanks. Focusing on plain concrete (PC) and concrete with 3 % volume content steel fiber (SFRC3), the impact of fibers and moisture content on concrete's damage and failure characteristics pre and post cryogenic exposure is investigated. The compressive strength variation laws of concrete before and after 10 CFTCs were summarized in air-dried and water-saturated condition. Acoustic emission (AE) and digital image correlation (DIC) techniques were employed in the study to delineate the variances in failure process and fracture characteristics attributed to cryogenic exposure. Findings indicate a decline in the compressive strength of both PC and SFRC3 post exposure, more pronounced in water-saturated condition. Post-cryogenic exposure, AE signals exhibit decreased activities. The failure process of concrete is categorized into four stages based on the trends of severity index Sr and historical index Hs, both of which diminished, reflecting reduced signal strength and rate of change. AE frequency-amplitude characteristics differs between PC and SFRC3 during failure, with significant reduction in high frequency signals in SFRC3, suggesting weakened fiber-matrix bonding and increased fracture scale. The rise in the number of shear cracks nearing failure is discerned from variations in rise angle (RA) and average frequency (AF), proposing the ratio of RA to AF equal to 15 as a precursor of concrete failure. The DIC analysis shows increased crack width and numbers in both PC and SFRC3 post exposure, along with localized spalling. SFRC3 can still effectively maintain the integrity without complete breakage despite severe cracks are generated.

Splitting Tensile Mechanical Performance and Mesoscopic Failure Mechanisms of High-Performance Concrete under 10-Year Corrosion from Salt Lake Brine

In regions characterized by the challenging combination of brine corrosion in the salt lakes and river sand with alkali silica reaction (ASR) activity in areas of the Northwest, high-performance concrete (HPC) formulated with high-volume composite mineral admixtures as ASR suppression measures has been preferred for civil engineering structures in the region. This study investigates the splitting tensile strength, corrosion products, microscopic structure characteristics, and mesoscopic mechanical mechanisms of splitting failure of such HPC under 10-year corrosion from salt lake brine. The relationship between mechanical properties and corrosion damage, as well as the characteristics of internal crack propagation paths and failure mechanisms of HPC under splitting load, are explored. The findings reveal that as the alkali content within HPC rises, corrosion damage intensifies, resulting in a reduction in splitting tensile strength. Moreover, a linear association between mechanical properties and corrosion damage is observed. Microscopic structural analysis and numerical simulation of the splitting failure process of HPC elucidate that while the substantial presence of mineral admixtures effectively suppresses the ASR risk associated with alkali-reactive aggregates in concrete, uneven ASR gel products persist. These discontinuous micro-fine interface cracks induced by the gel products and the cracks induced by the gel products around the selective alkali-active aggregate particles distributed in the local area are the initiation sources of mortar cracks in HPC splitting failure. In terms of the overall failure state observed during the concrete splitting process, mortar cracks manifest two distinct extension paths: along the coarse aggregate interface and directly through the aggregates themselves. Notably, a greater proportion of coarse aggregates are directly penetrated by mortar cracks, as opposed to the number of interface failures bypassing coarse aggregates. More importantly, the above work establishes a theoretical reference in three dimensions: macroscopic, mesoscopic, and microscopic, for studying concrete corrosion damage in complex environments such as salt lake brine corrosion and ASR inhibition.

Performance of concrete containing waste demolished concrete powder as a partial substitute for cement

PurposePresent work deals with the partial substitution of cement by waste demolished concrete powder (WDP) for reducing the carbon footprints of concrete.Design/methodology/approachControl specimens and the specimens with 20% WDP as fractional substitute of cement were prepared. The waste powder was thermally activated at 825 °C prior to its use in the mix. The prepared specimens were evaluated in terms of density, workability, mechanical strength, Ultrasonic pulse velocity (UPV) and rebound hammer (RH).FindingsThe results showed that with the substitution, the workability of the mix increased, while the density decreased. A decrement within a 20% limit was found in compressive strength. The UPV and RH results were closely linked to the other results as mentioned above.Research limitations/implicationsThe study deals with only M15 concrete and the substitution level of only 20% as a baseline.Practical implicationsThe concrete containing 20% WDP is lightweight and more workable. Moreover, its strength at 28 days is 14 MPa, only 1 MPa lesser than the characteristic strength.Social implicationsThe WDP can be recycled and the dumping in landfills can be reduced. This is an important effort towards the decarbonation of concrete.Originality/valuePrevious literature indicates that the WDP has been frequently used as a partial replacement of aggregates. However, some traces of secondary hydration were also reported. This work considers the effect of partial substitution of cement by the WDP.

Artificial neural network evaluation of concrete performance exposed to elevated temperature with destructive–non-destructive tests

In this study, it is aimed to predict the performance of concretes obtained by using supplementary cementitious materials (SCM) before and after high temperature using artificial neural network. Thus, in addition to contributing to sustainable development and circular economy by using waste materials in concrete production, predicting concrete strength using artificial neural network without the need for experimental studies will provide a great advantage in practice. In addition, it will also contribute to the literature in terms of determining the optimum amount of metakaolin to be used with fly ash in concrete production. Metakaolin, silica fume and fly ash were used as SCM in different proportions in concrete mixes. Accordingly, a total of 22 concrete series were prepared, one of which was the control series. Porosity, ultrasonic pulse velocity, pressure and tensile strength tests were applied to the series at the end of 7th, 28th and 90th curing periods before high temperature. In order to determine the strength losses after elevated temperature, porosity and compressive strength tests were applied at temperatures of 400, 600 and 800 °C. Mineral additive series showed positive mechanical properties up to 20%. However, it has been observed that the use of fly ash after a certain rate causes a decrease in strength. After elevated temperature, strength loss was observed in all series due to the increase in temperature, while it was observed that the rate of being affected by elevated temperature decreased as the percentage of metakaolin increased. Optimum mineral additive usage percentages were determined as 10% fly ash and 15% metakaolin. On the other hand, the use of mineral additives above the optimum level caused the performance of the concrete to decrease. Then, the concrete compression strengths obtained at 7th, 28th, and 90th days and at 400, 600 and 800 °C temperatures are taken as the outputs of the ANN. The artificial neural network provided the closest results to experimental data. Moreover, to prove the predictive performance of ANN, a comparative analysis was made with GPR, SVM and LR and the smallest value of the RMSE value is obtained with the ANN model. Finally, a fivefold cross-validation criteria was used to objectively present the performance of the model.

Preparation and performance of steel slag and recycled brick aggregate modified concrete under the background of solid waste application

Permeable concrete has the characteristics of breathability, permeability, and high heat dissipation. To improve its mechanical and frost resistance properties, this study optimized the preparation and performance of permeable concrete by adding materials to improve its performance. The performance analysis validate that epoxy resin owns a filling effect on the pores of permeable concrete. The internal curing agent, high water absorbent resin, has a good water absorption effect. The synergistic effect of these two increases the density and compressive strength of permeable concrete. When the two contents are 0.5%, the maximum compressive strength of modified permeable concrete at 7 and 28 days was 15.62 and 17.97 MPa, respectively. Under the action of freeze-thaw cycles, its mass loss rate show an upward trend By comparison, epoxy resin and high water absorbent resin are beneficial for improving the frost resistance of permeable concrete. The minimum value of relative dynamic modulus of elasticity remains stable at over 80%, and the loss rate of dynamic modulus of elasticity is all below 0.4. However, the influence of epoxy resin and SAP on the mass loss rate is relatively small, and the mass loss of all experimental groups is controlled below 2.5%. The binomial Fourier function model is the best predictive model for permeable concrete under freeze-thaw cycles. This study has positive significance for improving the performance of permeable concrete and maintaining the sustainable development of ecological cities.

Enhancing mix proportion design of low carbon concrete for shield segment using a combination of Bayesian optimization-NGBoost and NSGA-III algorithm

The demand for segment concrete increases rapidly with the expansion of urban rail transit and underground space, which may lead to carbon emissions (CE). In the production of segment concrete, using supplement cementitious materials (SCM) can be used to reduce CE instead of cement. However, SCM contents are usually determined by many orthogonal experiments, which are often time-consuming and only consider the limited experimental variables. Therefore, a novel hybrid intelligent algorithm combining Bayesian optimization (BO), natural gradient boosting (NGBoost) and non-dominated sorting genetic algorithm (NSGA)-III is proposed, which overcomes these disadvantages. Firstly, NGBoost model after hyperparameter optimization using BO is used to establish a nonlinear mapping relationship between segment concrete mix proportion and performance, which was used as the fitness function of the non-dominated sorting genetic algorithm (NSGA-III). Secondly, the optimal Pareto solutions were obtained through NSGA-III, and the reasonable range of segment concrete mixing proportion was obtained. Finally, a segment concrete production case was used to verify the effectiveness of the proposed algorithm. The results showed that the proposed hybrid algorithm combining proposed scheme decision strategy can obtain an optimal design scheme for concrete mix proportion. In addition, the comprehensive optimization rate of the obtained optimal scheme compared to the experimental optimal group was 11.5%. Moreover, the amount of phosphorous slag (PS) and granulated blast furnace slag (GBFS) in the optimal scheme was 26%, with a mass ratio of 1:2. Compared to the experimental optimal group, the optimal scheme can reduce the cost and CE per cubic meter by 31.64 yuan and 31.04 kg, respectively. Furthermore, the hybrid algorithm proposed can accurately obtains an optimal amount of SCM, which could be used as a supporting tool to reduce the production cost and CE of segment concrete. Overall, this research contributes to combining machine learning algorithms with actual production processes, which overcomes the data limitations of traditional experiments. It also provides a new intelligent approach and reference cases for the low-carbon design and sustainable development of building materials such as concrete.

Effects of basalt fibre and rubber particles on the mechanical properties and impact resistance of concrete

The application of waste rubber particles and basalt fibre (BF) in concrete can not only improve the performance of the resulting concrete but also alleviate the environmental pressures related to waste tire disposal. In this study, the impacts of rubber particles and BF on the mechanical and impact performance of concrete are experimentally investigated. Additionally, the macroscopic test phenomenon is explained based on the appearance of the microstructure. The results show that for basalt fibre-reinforced concrete (BFC), when the BF content increases from 0 to 0.4 %, the cube compressive strength and elastic modulus decrease from 71.5 MPa to 62.5 MPa and 44.5 GPa to 41.0 GPa, respectively, while the bending strength increases from 5.9 MPa to 6.6 MPa and then decreases to 6.3 MPa. A BF content of 0.3 % is selected to prepare basalt fibre-reinforced rubber concrete (BFRC). As the rubber particle content of BFRC increases from 0 to 20 %, the cube compressive strength, elastic modulus and bending strength decrease from 64.3 MPa to 51.5 MPa, 41.9 GPa to 33.5 GPa and 6.6 MPa to 5.9 MPa, respectively. However, the reduction rate of the mechanical properties of BFRC is approximately half that of fibre-free rubber concrete at the same rubber content. The shapes of the stressstrain curves of the BFC and normal concrete (NC) are similar, whereas the descending stage of the stressstrain curve of the BFRC is obviously gentler, and the whole BFRC stressstrain curve is much fuller, reflecting typical ductile failure. Both the BF and rubber particles contribute to impact performance improvement, but the effect of the rubber particles is much greater than that of the BF. Compared with that of the NC, the incorporation of 0.3 % BF increases the initial crack impact energy (W1) and final crack impact energy (W2) by 71 % and 79 %, respectively, but when 20 % rubber particles are additionally added, the increase rates of W1 and W2 reach 668 % and 686 %, respectively. The impact life evolutions of BFC and BFRC can be described effectively by a two-parameter Weibull distribution function.

EXPERIMENTAL INVESTIGATION OF MECHANICAL PROPERTIES OF FLY ASH BASED GEO-POLYMER CONCRETE USED AS PAVER BLOCKS

The main objective of the present study is to find out a suitable, effective and alternative material for partial replacement of cement and fine aggregate, to find out possible utilization of waste materials in construction industry that in turn considerably minimize the usage of cement and coarse aggregate and ultimately reduce construction cost, to explore possibilities of improving mechanical properties of concrete using copper slag & pond ash instead of fine aggregate partially, to evaluate the effect of using fly ash and GGBS in concrete and to investigate the strength of replaced concrete with that of conventional concrete. This project is mainly undertaken to study the behavior and performance of concrete using waste materials such as fly ash and GGBS. This type of use of a waste material can solve problems of lack of aggregate in various construction sites and reduce environmental problems related to sand mining and waste disposal. The use of fly ash and GGBS can also reduce the cost of the concrete production and increase the workability. Keywords Cement Concrete, flexural strength, fly ash and GGBS, Strength parameters, water absorption, Workability.

Changes in air permeability of restrained expansive concrete under drying condition: contribution of expansive strain

Restraining the expansion of expansive concrete with embedded rebars can exert chemical prestressing, which may affect the durability of concrete structures. This study aims to investigate the durability performance of expansive concrete by understanding the mechanism of air permeability changes while considering the variations in reinforcement arrangements and concrete dimensions. The Torrent’s air permeability test was used to non-destructively evaluate the disparity in air permeability changes of expansive and normal concrete during the drying processes from 28 to 182 days. Additionally, expansive strain changes were continuously monitored to investigate chemical prestress. The experimental test results suggest the immense effect of the change in expansive strain on the air permeability of concrete. This study proposes that the change in microstructure owing to the loss of expansive strain may cause an increase in air permeability. The loss of expansive strain is a distinguished feature that differentiates the mechanism of air permeability changes in expansive and normal concrete. These findings suggest the possible improvement in the durability performance of expansive concrete in cases where the loss of its expansive strain can be controlled.