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The construction industry continually seeks to optimize the materials used in building projects to balance structural integrity with economic and environmental concerns. Particularly in urban high-rise construction and seismic zones, the choice of material can significantly affect the project's feasibility and safety. This study investigated the mechanical response of regular and lightweight concrete to bending stresses, which are critical factors in the structural design process. By comparing the strain–stress relationships, densities, and deformation capacities of these two varieties of concrete, this research aimed to clarify their fundamental differences. Lightweight concrete, with its lower density of 1800 kg/m3, offers noticeable weight reductions, thus presenting a viable solution for structures where reduced mass is beneficial, such as in areas with load-bearing limitations or for components that require ease of transportation and assembly. However, this study found that the reduction in weight is accompanied by lower compressive and flexural strength compared to normal concrete, which, with a density of 2400 kg/m3, exhibited greater mechanical strength and resilience under bending stresses. Stress–strain graphs generated from the experimental data illustrated both types of concrete's elastic and plastic deformation behaviors, highlighting the material's transition from elasticity to plasticity at specific stress points. This nuanced understanding of the materials' behaviors is vital for construction professionals as it equips them with the information necessary to make informed decisions on material selection, ensuring safety, sustainability, and cost-effectiveness in construction projects. [ABSTRACT FROM AUTHOR]

In this study, we propose a model describing the mechanical behavior of basalt aggregate concrete under high temperatures. Basalt aggregate concrete is formulated. The bulk density, residual mechanical (compressive strength, tensile strength and elastic modulus) and microscopic properties of basalt aggregate concrete specimens are analyzed. The damage basalt aggregate concrete, the geometry and nonlinear behavior of the material is investigated. Based on Newton’s second law, the investigation is conducted on the simultaneous effects of mechanical loading and thermal treatment. The finite difference method is used for the numerical solution of the problem to determine the peak stress and strain of normal basalt aggregate concrete as a function of temperatures and time. It follows from the results obtained that, after [3–5 min] the critical temperature at which material damage, for both stress and strain, is observed to be 350 °C at the center, corresponding to a 30% reduction in peak stress on the value initially obtained experimentally; And 300 °C at the free and fixed end of basalt aggregate concrete specimen respectively, corresponding to a 38 and 30% reduction in stress in the z-axis direction. Beyond these temperatures, it is observed that the amplitude of the deformations continues to increase whatever the position announcing an imminent collapse of the material, probably due to the loss of stiffness of the cement paste which significantly reduces the mechanical performance of the normal basalt aggregate concrete observed experimentally.Article highlights: The model describing the thermomechanical behavior of basalt aggregate concrete at high temperatures has been established. Analogy between numerical and experimental studies, which show similar behavior; A drop-in strength of basalt aggregate concretes from 300°C onwards 300°C is the critical temperature at which the amplitude of internal stresses begins to decrease significantly, reflecting a progressive degradation of the material with increasing temperature, manifested by the appearance of macro cracks in the samples. [ABSTRACT FROM AUTHOR]

Abstract In this study, we propose a model describing the mechanical behavior of basalt aggregate concrete under high temperatures. Basalt aggregate concrete is formulated. The bulk density, residual mechanical (compressive strength, tensile strength and elastic modulus) and microscopic properties of basalt aggregate concrete specimens are analyzed. The damage basalt aggregate concrete, the geometry and nonlinear behavior of the material is investigated. Based on Newton’s second law, the investigation is conducted on the simultaneous effects of mechanical loading and thermal treatment. The finite difference method is used for the numerical solution of the problem to determine the peak stress and strain of normal basalt aggregate concrete as a function of temperatures and time. It follows from the results obtained that, after [3–5 min] the critical temperature at which material damage, for both stress and strain, is observed to be 350 °C at the center, corresponding to a 30% reduction in peak stress on the value initially obtained experimentally; And 300 °C at the free and fixed end of basalt aggregate concrete specimen respectively, corresponding to a 38 and 30% reduction in stress in the z-axis direction. Beyond these temperatures, it is observed that the amplitude of the deformations continues to increase whatever the position announcing an imminent collapse of the material, probably due to the loss of stiffness of the cement paste which significantly reduces the mechanical performance of the normal basalt aggregate concrete observed experimentally.

Annually, engineers face many sustainability problems due to thousands of tons of concrete being manufactured for buildings and structures. So, alternatives to some construction materials are used. In this research, cement composites reinforced with steel mesh and cement composites reinforced with polypropylene fibers (PPFs) were used. For this purpose, 36 concrete slabs were poured with dimensions of 40 x 40 x 4 cm containing steel mesh, and PPF with dimensions (10 x 10, 15x15, 20x20, 25x25, and 40x40) cm in the center of the slab. The impact resistance of both types of concrete was examined, in addition to noting the initial cracking of the samples and examining the energy absorption at the initial cracking and the final failure of both types, through the results, it was found that the use of steel mesh 40x40 cm is the best in terms of its resistance to repeated impact loads as well as its energy absorption. [ABSTRACT FROM AUTHOR]

There are no sufficient researches into the umbrella arch method for highway tunnel reinforcement. Finding a way to ensure the lining has enough bearing capacity to meet the engineering requirements under the premise that the highway tunnel lining reinforcing structure is not thinned beyond its limit is now a high priority in the research into umbrella arch method. This paper proposes a new reinforcing method, where a composite structure built of ultra-high-performance concrete (UHPC) and normal concrete (NC) is used to reinforce the lining. The flexural test and numerical simulation of UHPC-NC composite beam member have been conducted, so as to investigate the flexural bearing capacity of the reinforcing structure from the aspect of members. According to the results, greater thickness of section results in greater bearing capacity of composite beam and greater flexural stiffness. Increasing the UHPC thickness will increase the bearing capacity of the specimens with 120 mm thickness of section, but will not significantly improve the bearing capacity of the specimen with 150 mm thickness of section. Greater roughness of composite material interface results in greater bearing capacity and better crack resistance of the specimens.

The construction industry continually seeks to optimize the materials used in building projects to balance structural integrity with economic and environmental concerns. Particularly in urban high-rise construction and seismic zones, the choice of material can significantly affect the project’s feasibility and safety. This study investigated the mechanical response of regular and lightweight concrete to bending stresses, which are critical factors in the structural design process. By comparing the strain–stress relationships, densities, and deformation capacities of these two varieties of concrete, this research aimed to clarify their fundamental differences. Lightweight concrete, with its lower density of 1800 kg/m3, offers noticeable weight reductions, thus presenting a viable solution for structures where reduced mass is beneficial, such as in areas with load-bearing limitations or for components that require ease of transportation and assembly. However, this study found that the reduction in weight is accompanied by lower compressive and flexural strength compared to normal concrete, which, with a density of 2400 kg/m3, exhibited greater mechanical strength and resilience under bending stresses. Stress–strain graphs generated from the experimental data illustrated both types of concrete’s elastic and plastic deformation behaviors, highlighting the material’s transition from elasticity to plasticity at specific stress points. This nuanced understanding of the materials’ behaviors is vital for construction professionals as it equips them with the information necessary to make informed decisions on material selection, ensuring safety, sustainability, and cost-effectiveness in construction projects.

Annually, engineers face many sustainability problems due to thousands of tons of concrete being manufactured for buildings and structures. So, alternatives to some construction materials are used. In this research, cement composites reinforced with steel mesh and cement composites reinforced with polypropylene fibers (PPFs) were used. For this purpose, 36 concrete slabs were poured with dimensions of 40 x 40 x 4 cm containing steel mesh, and PPF with dimensions (10 x 10, 15x15, 20x20, 25x25, and 40x40) cm in the center of the slab. The impact resistance of both types of concrete was examined, in addition to noting the initial cracking of the samples and examining the energy absorption at the initial cracking and the final failure of both types, through the results, it was found that the use of steel mesh 40x40 cm is the best in terms of its resistance to repeated impact loads as well as its energy absorption.

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

As a high-quality building material exhibiting excellent toughness and durability, ultrahigh-performance concrete (UHPC) is increasingly being used in the construction industry and as building reinforcement. During the reinforcement of existing concrete structures with UHPC, their interface is the weakest part of a structure. Interface bonding ensures the operation of two types of materials together. However, existing studies rarely report the bonding of the UHPC–normal concrete (NC) interface. Herein, the existing test methods and interface bonding mechanisms are summarized. Subsequently, the differences among relevant design codes are investigated by comparing different theoretical formulas. Important influencing factors of the reinforcement method, namely, interface roughness, fiber type and content, interface agent type and content, moisture content, existing concrete strength, cementitious material content, curing conditions, freeze–thaw cycles, and chloride ions, are also considered. Further, the enhancement mechanism of the characteristics of the UHPC–NC interface is clearly described. Finally, the shortcomings and application prospects of the interfacial bonding properties are highlighted. [ABSTRACT FROM AUTHOR]

This paper investigates the bond failure performance between precast normal concrete (NC) and cast-in situ ultra-high performance concrete (UHPC), emphasizing the influence of interfacial roughness. The interfacial bonding behavior under tension and under shear was investigated based on 72 groups of pull-off tests and 36 groups of bi-shear tests, considering six different interface treatment methods and two different NC strength levels. The results demonstrate that certain interfacial roughness is essential to gain a reliable bond connection between NC and UHPC. Its enhancement on the tensile bond performance could be described by the positive linear relationship between the mean roughness and the pull-off strength. However, further research is required to determine the characterization method of its influence on the shear bond performance. The higher strength of the base concrete is beneficial to the bond performance. Though this effect is evident in the pull-off tests under tension, the influence on the shear interfacial performance could be offset by that of the interface morphology in the case with high interfacial roughness. [ABSTRACT FROM AUTHOR]

Recycled rubber particles can be produced by using waste tires. Adding recycled rubber particles to concrete can form rubber concrete (RC). RC can not only reduce the amount of natural sand and reduce the cost of concrete but also improve the static compressive toughness of concrete. Adding steel fiber into RC can improve the strength of concrete. In order to study the compressive toughness of steel fiber rubber concrete (SFRC), rubber particles washed with NaOH are added to steel fiber reinforced concrete. This can enhance the bonding performance between the recycled rubber particles and concrete. The volume ratio of recycled rubber is 5, 10, and 15%. Prismatic and cubic test blocks were prepared and their compressive tests were carried out. The results show that the stress interaction between the rubber particles and steel fiber in concrete significantly improves the compressive strength, elastic modulus, and stress–strain relationship of concrete. The compressive toughness and ductility of concrete are improved. When the content of rubber particles is 15–20%, the compressive toughness of SFRC is improved most obviously. Through experiments, the toughness index and specific toughness of rubber steel fiber reinforced concrete are calculated, which explores a new way and method for studying the compressive toughness of similar recycled material concrete.

The main objective of this work was to adopt an environmentally friendly technology with enhanced results. The technology of magnetic water (MW) treatment system can be used in concrete mixture production instead of potable water (PW) to improve both workability and strength. Two types of concrete were adopted: normal concreter production with two grades 25 and 35 MPa and the self-compacted concrete (SCC) with 35 MPa grade. The concrete mixes containing MW instead of PW results showed that, for 25 MPa grade, an improvement in a compressive strength of 15.1, 14.8, and 10.2% was achieved for 7, 28, and 90 days, respectively. For 35 MPa grade, an improvement of 13.6, 11.5, and 9.1% was achieved for 7, 28, and 90 days, respectively. The mixture of SCC showed the highest improvement up to 16.2, 15.8, and 12.4% for 7, 28, and 90 days, respectively. The effect of MW is significant for 7 days compared to 28 and 90 days. An increase in the water content to cementitious material presents the more efficiency of MW, while the combined effect of MW and superplasticizer in SCC showed the best improvement with less water content for 35 MPa grade.

This study aims to investigate the adequacy of composite cellular beams with lightweight reinforced concrete deck slab as a structural unit for harmonic loaded buildings. The experimental program involved three fixed-ends supported beams throughout 2140 mm. Three concrete types were included: Normal Weight Concrete (NWC), Lightweight Aggregate Concrete (LWAC), and Lightweight Fiber Reinforced Aggregate Concrete (LWACF). The considered frequencies were (5, 10, 15, 20, 25, and 30) Hz. It was indicated that the harmonic load caused a significant influence on LWAC response (64% greater than NWC) and lattice cracks were observed, especially at 30 Hz. As for LWACF slab, no cracks appeared, and the harmonic load had a minor effect on the vibration amplitude. Adding fiber to LWAC improved its behavior and made the amplitude no more than 11.11%, corresponding to NWC. So, the response variance for the LWACF was approximately negligible compared with NWC. It is worth mentioning that the study produced a lightweight structure that resists harmonic vibrations with a small strength reduction by using LWACF as a deck-slab for cellular specimens and provides a structural element with a smaller density of about 27%, which presents an advantage for the cellular beam that is adopted for low-loaded structures.

Bond durability between fiber-reinforced polymer (FRP) bars and concrete is a significant point of concern with respect to structural integrity, performance, and retrofit purposes. This experimental study addresses the bond durability of glass-FRP (GFRP) bars embedded in different concretes after exposure to harsh environmental conditions (i.e., seawater and an alkaline solution at 60° C). A total of 54 beam specimens of self-compacting, fiber-reinforced, and normal concretes were constructed, conditioned, and tested under flexural pullout according to RILEM provisions, which simulate the reinforcement behavior as a structural element in buildings. Sand-coated GFRP bars and steel bars were used to reinforce concrete beams. The obtained results demonstrated that the bond strength of beams with sand-coated GFRP bars decreased less after exposure to seawater in comparison with alkaline solution. However, the converse outcome was found for beams with steel bars. In addition to the reinforcing bars, the type of concrete was found to be effective in the bond durability of beams with both GFRP and steel bars under aggressive environments. Generally, the higher the density and strength, and the lower the permeability, the greater the bond strength and less its reduction. [ABSTRACT FROM AUTHOR]

The results of a research program conducted at the University of Mustansiriayah in Iraq to analyze the qualities of concrete created with crushed bricks and crush concrete are presented in this paper. To make a suitable aggregate, these materials were crushed. Some aggregates were treated, while others were not. The properties investigated were the workability and the density of fresh the aggregates of crushed bricks and crush concrete were treated in some mixtures and others were not treated. The properties investigated were the workability and the density of fresh concrete, and the compressive strength and tensile splitting strength behavior of hardened concrete. Different replacement ratios (0, 50%, and 100%) were investigated. The concrete rustles produced with recycled aggregates were compared with a reference concrete produced with natural coarse aggregates currently used in Iraq. Using surface treatment with silicate solution, when comparison to RCA50 and RCA100 samples, TRCA50 and TRCA100 compressive strength improved by roughly 5.05 percent and 5.9 percent after 28 days, respectively. And came closer to concrete with natural aggregate R, and improved 3.25% and 4.6% in TBR100 and TBR50, respectively compared. With the BR100 and BR50 respectively, they added a cross resistance of R for TRAC100% when silica fume was added, approaching R at TBR100%. Aggregates indicate that this type of concrete can be used in various precast applications.

Environmental problems are considered a serious situation in modern construction. Reusing and recycling glass wastes is the only method to decrease waste produced. There is growing environmental compression to decrease glass waste and to reprocess as much as possible. In this investigational work, the effect of partially substituting crushed waste glass in concrete is considered. The study investigates crushed waste glass used as a partial replacement of fine aggregate for new concrete. recycled glass waste was partially replaced as 5%, 10%, 15%, 20%, 25%, 30, 35, 40%, 45%, 45% and 50% and tested at 7, 14 and 28 days of curing at 20◦ for mechanical properties and compared with those of controlled mix. The compressive strength, splitting tensile strength and flexural forces and static elasticity modulus of specimens with 20% waste glass content was 30%, 19.41%, 9.13% and 10.12%, respectively, which is higher than the controlled mix at 28 days. The outcomes displayed that the maximum rise in strength of concrete occurred when 20% replacement with glass crush. It is found that crushed waste glass can be used as fine aggregate replacement material in concrete production.

Existing concrete structures often have difficulty reaching their design service life due to aging, increased loads, and natural disasters, and they need to be repaired and strengthened or replaced. Ultra-high-performance concrete (UHPC), known for its ultra-high strength and excellent toughness, offers a promising solution for repairing and strengthening normal concrete (NC) structures. It is expected to be a viable solution when applied to the repair and strengthening of NC structures. A reliable interfacial bonding between the two materials (NC substrate and UHPC) determines the overall performance of this composite structure. In this study, a data-driven approach is proposed to predict the bond performance at the UHPC-NC interface as accurately as possible. To overcome the problem of limited experimental data, a data augmentation model is introduced, combining kernel density estimation (KDE) and tabular generative adversarial networks (TGAN). The optimal model is determined from six decision tree-based ensemble learning models applied to two strategies: "synthetic training - real testing" and "real training - real testing." Finally, a parametric analysis is performed using SHapley Additive exPlanations (SHAP) to elucidate the importance and sensitivity of different features related to bond strength. The findings illustrate that the suggested KDE-TGAN model effectively captures the distribution of the original dataset, enhancing both the accuracy and robustness of the bond strength prediction models. Furthermore, the model's ability to explain the importance and sensitivity of different features provides valuable insights into bond strength prediction. Thus, the proposed data augmentation model provides a reliable approach for modeling experimental data with small samples in structural engineering applications. • Proposed a new solution—KDE-TGAN—for small sample machine learning modeling in structural engineering. • A review of factors affecting bond strength at the UHPC-NC interface was conducted. • The model developed to predict the bond strength under splitting tensile and slant shear tests has high accuracy and robustness. • The model explainability study conducted reveals the effect of the material and condition features on the bond strength. [ABSTRACT FROM AUTHOR]

The by-products of wood sawdust and wood fiber are considered to be waste material. It is utilized in the construction of buildings in the form of sawdust concrete or wood fiber concrete. It is used to make lightweight concrete and possesses heat transfer of a long duration. In this study, wood concrete was made at eleven different mix proportions of cement to wood waste by weight, to produce a lightweight concrete aggregate that has the density 1508-2122 kg/m3. The experimental work consists of 330 concrete specimens as 99 cubes (150 * 150 * 150) mm, 165 cylinders (150 * 300) mm, 33 prisms (50 * 100 * 200) mm, and 33 prisms (100 * 100 * 500) mm. Mechanical and thermal properties such as stiffness, workability, compressive strength, static elasticity modulus, flexural forces, splitting tensile strength and density were examined in the specimens after 28 days of 20 oC curing. Also, compressive strength was investigated at 7 and 14 days of curing at 20 oC. The basic observation of the results shows the values with the limitations of ACI and ASTM. Moreover, it is the perfect way to reduce solid wood waste and produce lightweight concrete to be used in industrial construction. It was found that with the increase in the quantity of wood waste, the strength decreased; however, in terms of workability and concrete with a higher quantity of wood waste held very well. Lightweight concrete aggregate is around 25 percent lighter in dead load than standard concrete. Given all the physical and mechanical properties, the study finds that wood concrete can be used in the construction of buildings.

As a high-quality building material exhibiting excellent toughness and durability, ultrahigh-performance concrete (UHPC) is increasingly being used in the construction industry and as building reinforcement. During the reinforcement of existing concrete structures with UHPC, their interface is the weakest part of a structure. Interface bonding ensures the operation of two types of materials together. However, existing studies rarely report the bonding of the UHPC–normal concrete (NC) interface. Herein, the existing test methods and interface bonding mechanisms are summarized. Subsequently, the differences among relevant design codes are investigated by comparing different theoretical formulas. Important influencing factors of the reinforcement method, namely, interface roughness, fiber type and content, interface agent type and content, moisture content, existing concrete strength, cementitious material content, curing conditions, freeze–thaw cycles, and chloride ions, are also considered. Further, the enhancement mechanism of the characteristics of the UHPC–NC interface is clearly described. Finally, the shortcomings and application prospects of the interfacial bonding properties are highlighted.

The results of a research program conducted at the University of Mustansiriayah in Iraq to analyze the qualities of concrete created with crushed bricks and crush concrete are presented in this paper. To make a suitable aggregate, these materials were crushed. Some aggregates were treated, while others were not. The properties investigated were the workability and the density of fresh the aggregates of crushed bricks and crush concrete were treated in some mixtures and others were not treated. The properties investigated were the workability and the density of fresh concrete, and the compressive strength and tensile splitting strength behavior of hardened concrete. Different replacement ratios (0, 50%, and 100%) were investigated. The concrete rustles produced with recycled aggregates were compared with a reference concrete produced with natural coarse aggregates currently used in Iraq. Using surface treatment with silicate solution, when comparison to RCA50 and RCA100 samples, TRCA50 and TRCA100 compressive strength improved by roughly 5.05 percent and 5.9 percent after 28 days, respectively. And came closer to concrete with natural aggregate R, and improved 3.25% and 4.6% in TBR100 and TBR50, respectively compared. With the BR100 and BR50 respectively, they added a cross resistance of R for TRAC100% when silica fume was added, approaching R at TBR100%. Aggregates indicate that this type of concrete can be used in various precast applications. [ABSTRACT FROM AUTHOR]

Component‐specific compressive strength of reinforced concrete columns made of normal‐ and high‐strength concrete The applied concrete compressive strength for the design of reinforced concrete columns is multiplied in various codes (EC2, EC2+NA, MC10) by a coefficient αcc, which considers time‐dependent behaviour of concrete (αcc,m) as well as simple component‐specific effects (αcc,b). However, the component‐specific conditions in reinforced concrete columns (e.g. influence of longitudinal and stirrup reinforcement) cannot be captured adequately. Particularly for reinforced concrete columns with high strength concretes or high reinforcement ratios, there are concerns regarding safe design. For a more reliable consideration, a column database is presented, which can be used to identify a general reduction factor depending on the concrete compressive strength. Subsequently, the effects caused by geometry and reinforcement configuration on the component‐specific compressive strength are discussed in a more differentiated way. Using the findings, a multiplicative approach for the detailed determination of the component‐specific factor is proposed. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, the influence of using polyethylene terephthalate (PET) wastes as a partial replacement of natural sand is investigated to study the mechanical and physical properties of concrete. Fine aggregate (sand) is partially replaced by equivalent weight percentages of PET waste particles while maintaining all other proportions. Mechanical tests for compression, splitting, flexure, modulus of elasticity, energy absorption, and axial strain as well as physical tests for density, shrinkage, and absorption, are performed. In addition, the ultrasonic pulse velocity is presented. All specimens are observed for 7, 14, and 28 days. The tests results presented that the presence of PET particles changed the physical and mechanical properties of produced concretes. Physical properties (density and ultra sound velocity) gradually decreased as PET ratios increased, while an increase in absorption rate was observed. Furthermore, for strength-related properties, the results showed that the specimens containing partial substitution ratios ranging within 5 %–12.5 % displayed 26.8 %–43.64 %, 18.6 %–26.9 %, and 18.1 %–30.2 % increments in the compressive, tensile, and flexural strengths, respectively, compared with the reference specimens. The findings also revealed an increase in energy absorption and axial strain of the specimens with 5%–20 % replacement percentages, while the modulus of elasticity decreased as the PET content increased. The results further indicated that the strength parameters decrease when the PET content exceeds 15 %. In conclusion, replacing sand with waste PET particles positively affects the strength-related values of concrete specimens as long as the replacement ratio is less than 15 %.

Using admixtures to replace part of cement can effectively reduce environmental pollution. Many concrete gravity dams have been planned for Tibet, where the resource of fly ash (FA) is scarce but the resource of tuff is abundant. Compared with the more mature and widely used FA concrete in gravity dams, the application of tuff concrete is rare, and the hardening mechanism of the cement–tuff binary cementation system and the performance of tuff concrete still need to be further studied. In view of this, the hydration and hardening mechanism of the cement–tuff binary cementation system using varying percentages of tuff contents (0%, 25%, and 50%) are discussed, and the mechanical properties (e.g., strength, modulus) and durability performance (e.g., freeze-thaw, carbonization) of tuff normal concrete are investigated in this paper. The microstructure of the cement–tuff system shows that additional tuff powder promotes the hydration of clinker in cement, which increases the calcium hydroxide content [ Ca(OH)2 ] and leads to a higher porosity at early curing age. Results show that the amount of tuff content is almost positively correlated with porosity. The additional tuff in concrete increases the earlier splitting tensile strength, ultimate tensile value, and drying shrinkage, which also slightly reduces the frost resistance and little affects the compressive strength, tensile strength, elastic modulus, impermeability, and carbonation depth. Tuff normal concrete shows better performance than FA concrete in some aspects. The results show that tuff materials can be used to replace FA, and tuff normal concrete can be applied to the construction of concrete gravity dams in areas where fly ash is scarce and tuff is abundant. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to evaluate the mechanical properties of normal concrete (NC) containing polyethylene terephthalate waste fibers (PETWF). In addition to check the influence the waste has on the behavior of reinforced concrete beams, five mixtures of NC with 0.41 of w/c ratio were tested. The mixtures contain four NC mixtures with various percentages of PETWF in different shapes and lengths. After that, the behavior of four 150 × 200 × 1400 mm simply supported concrete beams, including different percentages of the wastes within the concrete mixture was investigated via the influence of the wastes on the strengths and serviceability of concrete beams. Suitable tests were carried out to assess mechanical characteristics of mixtures that contain the plastic waste and compared with that of the control mixture. The tests variables of reinforced concrete beams included load-deflection behavior, cracking investigation, ductility indices, and stiffness. Testing of reinforced concrete beams showed a little decrease in the ultimate failure load of the specimens and secant stiffness. Nevertheless, there was prominent improvement in ductility behavior for all beams, especially in the hybrid beam, and also increase in the initial stiffness.

The effect of rust of the reinforcement bars on the bond and slip behavior between the rebars and the surrounding concrete is still under research judgement. This paper, investigated the effect of ranges of rebar rusting (0, 30-50% and 70-90%) of the limits of losing in mass that specified in the ASTM standard (6% of bar nominal mass) combined with other main parameters that affect the bond and slip behavior. A number of 72 pullout prepared specimens were tested. The studied parameters were using normal and high strength concrete (31 MPa and 76 MPa), different bars diameters (12, 16 and 25 mm), the change of embedment length (150 and 300 mm) and the using of bond epoxy coating for embedded length of reinforcing bars. The results showed that the rust within certain amount of permissible losing of mass (about 50%) led to increase the bond strength and decrease the slip between reinforcement bars and concrete. However, increasing rusting above 50% but within the permissible losing in mass would slightly decrease the bond strength and increase the slip comparing with zero rusting case for all tested bar sizes with and without using the bond improvement factors. The main recommendation of the study is to use the same criterion of acceptance of losing in mass specified by ASTM as the acceptance criterion of the amount of rust in the reinforcement bars and using one of the studied improvement factors when the rust amount exceed 50% of the permissible limit of losing in mass.

In this research, different amounts of nano-MgO were added to normal concrete samples, and the effect of these particles on the durability of the samples under freeze and thaw conditions was investigated. The compressive and tensile strength as well as the permeability of concrete containing nanoparticles were measured and compared to those of plain samples (without nanoparticles). The age of concrete samples, percentage of nanoparticles, and water-to-binder ratio are the variables of the current research. Based on the results, the addition of 1% nano-MgO to the normal concrete with a water-to-binder ratio of 0.44 can reduce the permeability up to 63% and improve the compressive and tensile strengths by 9.12% and 10.6%, respectively. Gene Expression Programming (GEP) is applied, and three formulations are derived for the prediction of mechanical properties of concrete containing nano-MgO. In this method, 80% of the dataset is used randomly for the training process and 20% is utilized for testing the formulation. The results obtained by GEP showed acceptable accuracy. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Ultrahigh-performance concrete (UHPC) is increasingly recognized as being a better material in girders, and a composite prestressed UHPC-normal concrete (NC) girder is a better choice to be used for strengthening existing members and precast concrete constructions. In this study, 10 composite girders and 1 pure NC girder were fabricated and tested to investigate the effect of UHPC heights, prestress levels, and NC compressive strengths on the flexural properties of composite girders. The test results show that increasing the prestress level and UHPC height both delayed the formation and propagation of cracks. Compared with the pure NC girder, the mean crack spacing of composite girders decreased, and the number of cracks was considerably higher for the incorporation of UHPC. Adding UHPC into girders can considerably increase the stiffness and ductility of members. An analytical model based on the finite strip method was developed by considering the constitutive models of materials. The agreement between the predicted results and the experimental data is sufficient, indicating that the analytical model is suitable for analyzing composite girders. Additionally, the influencing factors of composite UHPC-NC girders were comprehensively investigated using the theoretical model. Finally, the reasonable range of the UHPC height is determined by the analytical results. The experimental results revealed the flexural behavior of large-scale composite prestressed UHPC-NC girders, including the failure modes, the load–deflection relationship, the concrete strain, and the crack pattern. The analytical model provides a powerful tool for the prediction of flexural behavior of composite girders, which would be helpful for the design analysis of composite girders. [ABSTRACT FROM AUTHOR]

Sustained load behaviour of normal‐strength concrete Reinforced and prestressed concrete structures must have adequate resistance to sustained stresses. Experiments in the technical literature show a reduction of effective compressive strength of concrete under high sustained loads. This effect is taken into account in standards and regulations (for instance EC2, EC2+NA und MC10) for the determination of design compressive strength using a constant coefficient αcc. However; it is unclear for practical applications, how different load conditions or load durations (early loading in case of construction loads or sustained loads at higher concrete age) should be considered. With regard to this problem a sustained load database was compiled at iBMB, Division of Concrete Construction of TU Braunschweig and the normative αcc‐coefficients were analyzed. Based on the results, a modified approach is proposed based on MC10, which considers the sustained load effects under consideration of loading age and load duration. [ABSTRACT FROM AUTHOR]

Developments in the concrete industry have allowed for the use of concrete types other than conventional concrete, such as self-compacting and high-strength concrete. Conventional concrete beams exhibit a significant reduction in strength following fire exposure. This study includes experimental and theoretical components. An experimental program was designed to investigate the effects of different elevated temperature levels on the most common concrete types. A total of 15 beams were cast using normal, self-compacting, and high-strength concrete beams. Moreover, 12 beams were subjected to temperatures of 400 °C and 600 °C for 1 and 2 h to study the beam behavior under indirect fire conditions. The exposure time had a significant effect on the behaviour of the different beams, particularly the normal concrete, which exhibited a dramatic strength reduction after being subjected to a temperature of 600 °C for 2 h. The selfcompacting concrete beam demonstrated acceptable behavior under elevated temperature conditions up to 600 °C. Strong agreements were observed between the experimental results and theoretical analysis, which was performed by the finite element program ANSYS. [ABSTRACT FROM AUTHOR]

This paper presents findings of research conducted on the improvement of radiation shielding in concrete, using barite as fine aggregate. Barite is a heavy mineral, having specific gravity in range of 3.5 to 4.5, and is abundantly available in different parts of Pakistan. Radiation shielding of barite concrete was studied experimentally for use in optimization of the thickness of radiation therapy bunkers. The Influence of barite on mechanical properties of concrete was also studied for a range of water-to-cement ratios from 0.30 to 0.45. ASTM standards were used to compute compressive and tensile strengths of concrete, whereas thermogravimetric analysis was carried out to determine percentage weight loss at elevated temperature. Radiation shielding potential of concrete was studied by subjecting concrete sections to gamma-ray source (Cobalt-60). Experimental results showed that the use of barite mineral as fine aggregate increases shielding ability of concrete. Linear attenuation coefficient was found to increase by 28.4% and varied proportionally with the variation in density of concrete. However, a slight decrease in compressive and tensile strengths was noted with the addition of barite as fine aggregate concrete. Due to high absorption capacity of barite, the problem of workability was overcome through the use of admixtures within allowable limit of ASTM (i.e., less than 3%). Finally, an optimum water-to-cement ratio of 0.45 for barite mineral infused concrete is recommended for the least reduction in mechanical properties and with significantly improved level of radiation shielding. [ABSTRACT FROM AUTHOR]

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In the harsh environment of extreme salt-freezing conditions, concrete structures face secondary durability issues after undergoing repairs, making it a critical yet challenging topic. This paper employs a novel ex-situ X-ray computed tomography approach to explore the mechanism of damage evolution in normal concrete (NC) to ultra-high performance concrete (UHPC) composites under salt-freezing conditions. For the first time, we consider evolution in both external and internal pores to quantitatively assess the damage. Additionally, slant shear tests, Mercury Intrusion Porosimetry (MIP) were also employed to validate the damage mechanism of NC-UHPC. Finally, empirical formulas summarizing the bond strength and pore changes in NC-UHPC were derived. The results reveal a crucial factor influencing the progression of damage in the NC-UHPC composite: the presence of external pores that directly interact with the salty solution. Damage initiation primarily occurs within the NC-UHPC composite due to these external pores located in the NC region, subsequently extending into the overlay transition zone (OTZ) and UHPC sections. Remarkably, the resistance of the OTZ, previously identified as the weakest zone in the NC-UHPC composite, surpasses that of the NC. This exceptional performance can be attributed to the higher porosity of the OTZ, offering additional space for the dissipation of pressure caused by freezing. What's even more important is that this highlights the consistent origin of damage in the NC-UHPC composite, emphasizing that it always begins within the NC. Considering this perspective prompts the question of whether the exceptionally high strength and durability of UHPC may lead to an excess of repair capabilities? • Novel ex-situ X-ray CT explores damage in NC-UHPC under salt-freezing. • Study highlights role of external pores in NC-UHPC damage progression. • UHPC's strength questioned as a repair material due to NC deterioration. [ABSTRACT FROM AUTHOR]

In this research, different amounts of nano-MgO were added to normal concrete samples, and the effect of these particles on the durability of the samples under freeze and thaw conditions was investigated. The compressive and tensile strength as well as the permeability of concrete containing nanoparticles were measured and compared to those of plain samples (without nanoparticles). The age of concrete samples, percentage of nanoparticles, and water-to-binder ratio are the variables of the current research. Based on the results, the addition of 1% nano-MgO to the normal concrete with a water-to-binder ratio of 0.44 can reduce the permeability up to 63% and improve the compressive and tensile strengths by 9.12% and 10.6%, respectively. Gene Expression Programming (GEP) is applied, and three formulations are derived for the prediction of mechanical properties of concrete containing nano-MgO. In this method, 80% of the dataset is used randomly for the training process and 20% is utilized for testing the formulation. The results obtained by GEP showed acceptable accuracy.

Seawater and sea sand concrete (SWSSC) is a highly attractive alternative to normal concrete (NC) that requires huge amounts of fresh water and river sand. However, reinforcements of stainless steel (instead of mild steel that is used in NC) may be required for SWSSC. This article reports investigation of stress corrosion cracking (SCC) of AISI 316 stainless steel (SS) in simulated SWSSC and NC environments, with and without addition of silica to SWSSC and NC, employing slow strain rate testing (SSRT) at 25 and 60 °C. For the purpose of comparison, SCC of SS was also investigated in simulated seawater (SW) solution. SS showed no SCC at 25 °C in any of the test solutions. Indications of SCC were seen in SW at 60 °C, but no features of SCC in SWSSC and NC at 60 °C, as suggested by scanning electron microscopy (SEM) fractographs. While the absence of SCC in SWSSC and NC is attributed to the highly passivating alkaline condition, its absence in SWSSC also indicates the role of alkalinity to predominate the deleterious role of chloride content of SWSSC. However, the addition of silicate to SWSSC or NC triggers transgranular SCC to SS at 60 °C, as evidenced by the fractography.

An experimental investigation was carried out to study the durability properties of Coconut Shell (CS) aggregate concrete. Effect of mineral admixtures such as fly ash and ground granulated blast furnace slag (GGBFS) as partial replacement of cement on durability properties of CS aggregate concrete was also verified. Specimens were cast and tested for durability characteristics such as water absorption, volume of pore voids, sorptivity, bulk diffusion, rapid chloride penetration, abrasion resistance and chemical attack tests. Four concrete mixes were considered for the study. Control mix, mix with18.5% coarse aggregate replaced by CS by weight, mix with 18.5% CS and 30% cement replaced by fly ash, and mix with 18.5% CS and 15% cement replaced by GGBFS. Test results showed that durability properties of all the mixes were comparable to normal concrete and some durability properties were enhanced by the addition of mineral admixtures. [ABSTRACT FROM AUTHOR]