Search

Using ultra‐high‐performance fiber‐reinforced concrete (UHPFRC) in profiled slabs, as opposed to normal strength concrete without fibers, has been shown experimentally to significantly increase both the bond between the profiled sheet and the concrete, and the tensile forces across cracked concrete. The consequence of these fiber benefits is to substantially increase the flexural rigidity leading to reduced deflections and also to substantially reduced crack widths leading to improved behavior under serviceability loads and to improved durability. To quantify these benefits so that they can be used in design, a rational partial‐interaction numerical model has been developed that can incorporate the material properties of any type of UHPFRC including time‐effects. This modeling should help in the development of simplified design rules for specific fiber types. [ABSTRACT FROM AUTHOR]

The objective of this paper is to present the methodology used to validate the threshold levels of durability indicators from data acquired from existing reinforced concrete structures that may present corrosion problems resulting from carbonation or chloride ingress. This study was conducted in the framework of the French National Project PERFDUB in close collaboration with the MODEVIE ANR project. Durability tests form the basis of a performance‐based approach for the durability of concrete structures, and in order to set the threshold level for each of these durability indicators, it is important to take into account the experience feedback that can be obtained from the actual behavior of existing structures. This paper presents the investigations carried out on eight reinforced concrete structures, all of them having an age well in excess of 50 years, and the main data gathered on some relevant durability and lifetime indicators. Based on all these data, predictive models of carbonation and chloride penetration are applied in order to validate the threshold levels to be adopted for the durability indicators, and several other conclusions are drawn. [ABSTRACT FROM AUTHOR]

The durability of reinforced concrete structures exposed to aggressive environments is affected by corrosion of carbon steel reinforcement. For this reason, it is of great practical interest to look for alternative solutions guaranteeing durability through the incorporation of corrosion‐resistant materials, such as stainless steel rebars. This type of steel is specially recommended for structures with a long lifespan, located in aggressive environments, with chlorides or de‐icing salts, and for structures where repair, inspection and rehabilitation is complicated. This solution presents a challenge from the point of view of the materials themselves, the mechanical design and their durability. This article presents the material properties of stainless steel and their influence on concrete structures. Furthermore, it is explained how these properties have been taken into account in the latest draft of the second‐generation Eurocode 2. [ABSTRACT FROM AUTHOR]

The rise in temperature due to the heat of hydration in the high‐strength mass concrete poses serious issues such as thermal cracking and delayed ettringite formation. The present experimental investigation is to optimize the proportions of SCMs like fly ash (FA) and ground granulated blast‐furnace slag (GGBS) for the same grade of high‐strength mass concrete with a focus on controlling the peak temperature rise and improving sustainability. For this purpose, one 100% ordinary Portland cement (OPC)‐based sample (T1) and five SCMs‐based samples viz. T2, T3, T4, T5, and T6 in which OPC was replaced by 20% FA, 35% FA, 50% GGBS, 70% GGBS, and 33%FA + 33% GGBS, respectively, were cast in the insulated blocks having one cubic meter volume. Analyzing critically, it is observed that for the same grade of concrete, the right blend of SCMs greatly reduces the peak core temperature (~33.2% and ~ 39.4% for T5 and T6 samples, respectively) than the sample prepared with 100% OPC. This is due to the reduction in the total heat of hydration in the SCMs‐based system than that of the OPC‐based system at early age. The amount of hydration products formed at early age varies for different percentages of SCMs, which is investigated by X‐ray diffraction (XRD), Fourier‐transform infrared spectroscopy (FTIR), and Field emission scanning electron microscopy (FESEM) analyses. Additionally, compressive strength analysis reveals that all the samples achieved almost similar strength (71.4, 74.6, 73.5, 71.5, 69.2, and 68.2 MPa, respectively, for T1 to T6 samples) at 56 days. Moreover, the rapid chloride permeability test (RCPT) values of the T2 to T5 samples are measured to be 597, 461, 672, 584, and 621 coulombs; while, the same is measured to be 2637, coulombs for the T1 sample, indicating higher durability of SCMs‐based samples. Finally, based on the analyses, a plausible model has been presented to explain the phenomenon, and industrial viability analysis is done to adjudge its suitability for an onsite application. [ABSTRACT FROM AUTHOR]

Compared with the ground service environment, the evolution of concrete performance under a water pressure service environment is quite complex with variable conditions. Because of the coupling effect of load and pressure, water has a special impact on the strength and deformation of concrete. Meanwhile, harmful ions usually react with the cement matrix as pressure water seepages into concrete, resulting in the reduction of concrete durability. Based on this, this study provides a comprehensive review of the strength, deformation, and durability of concrete under water pressure environment. It is found that microcracks in concrete tend to propagate and connect after exposure to water pressure, leading to a decrease in strength and deformation performance. The average loss rate of strength and elastic modulus increased by 12.15% and 10.97%, respectively, when water pressure increased by 1 MPa. However, the loading process of water‐confining pressure makes concrete more compact, where the static and dynamic mechanical performance can be improved. Besides, due to the enhancement of excess pore water pressure, concrete strength under a high strain rate increases by 61.79% compared to static load. The effect of water pressure increases the ability of the liquid to penetrate concrete, and corrosive ions trapped within the liquid and freeze–thaw caused by external temperature changes would further reduce the concrete durability. This study points out that static and dynamic loading characteristics and durability of concrete under multi‐factor coupling in a water pressure environment will be the future research direction. The summarized contents can provide guidance for construction and research of concrete engineering under a water pressure environment. [ABSTRACT FROM AUTHOR]

Utilization of industrial by‐products in concrete is an effective way to reduce the exhaustion of raw materials for concrete production, but it can lead to degradation in concrete properties. Therefore, research efforts are required to achieve a balance between waste utilization and concrete performance. This study examined the strength and durability performance of geopolymer concrete (GPC) developed from fly ash (FA) and fine rice husk ash (FRHA) as main binders (50/50), with partial OPC substitution at different levels (0%–30%). Various properties like workability, compressive strength, water absorption, chloride penetration resistance, carbonation depth, electrical resistivity (ER), and acid attack resistance were experimentally investigated. Results indicated that there was a noticeable improvement in the workability with 20% OPC substitution, achieving the highest slump of 110 mm. The highest compressive strength (50 MPa) was attained with 15% OPC substitution after 90 days. Mix FR85C15 (15% OPC replacement) showed the highest durability performance at all ages through various indicators, that is, water absorption, charge passed, carbonation depth, and ER. Scanning electron microscopy and energy dispersive spectroscopy analyses also validated the enhanced microstructure of FR85C15 compared with other mixes. When exposed to sulfuric acid (H2SO4), Mix FR85C15 showed a minimal loss of 14% in compressive strength. It was concluded that GPC produced using FA and FRHA substituting OPC (up to 15%) can potentially be utilized for structural applications. [ABSTRACT FROM AUTHOR]

The fib Model Code 2020 (MC2020) is developed to serve as the basis for future international codes and standards for the design of concrete structures by summarizing international research and experience and converting this knowledge into a practical document. The chapter "Concretes" contained therein provides a clear set of application rules in combination with sufficient background information and related references. This paper gives a concise overview of the contents of the Chapter 14 "Concretes" in the 2nd draft of MC2020. Instead of presenting numerous details on changes in the text and equations compared with the previous MC2010, major fundamentals on modeling concrete behavior are indicated. New sections in MC2020 on non‐conventional concretes, durability specifications and environmental performance are covered. Extended state‐of‐the‐art chapters on concrete transport properties and durability design conclude this contribution. [ABSTRACT FROM AUTHOR]

With water scarcity posing an ever‐present worldwide crisis, treated wastewater usage as an alternative to fresh water could be a smart choice and contribute to a sustainable construction industry. Numerous studies have been conducted by using treated domestic or industrial wastewater in concrete production, providing a promising solution to the global water shortage and wastewater management. However, the effectiveness of wastewater on the concrete manufacturing in comparison to pure freshwater has been a concern due to its impurities and contaminants. The results derived from previously published studies on concrete manufacturing with wastewater vary as a consequence of considerate different additives, curing age, treatment method, or wastewater quality. This review compiles and compares the previous investigations on physical and mechanical properties, durability characteristics, and morphological assessments of manufactured concrete with treated wastewater, and discusses the reasons for similarities and differences. Research findings and conclusions from the literature are summarized, and future research directions based on the research gaps are also recommended. [ABSTRACT FROM AUTHOR]

Multiple initiatives advocate for reducing embodied carbon (i.e., greenhouse gas emissions) associated with concrete production. Even though readily implementable strategies exist, practitioners are concerned that reducing embodied carbon emissions may adversely affect concrete performance and durability, resulting in detrimental effects from a life cycle perspective. To address such concerns, this study investigated the correlations between embodied carbon of concrete mixtures, mixture design parameters, and experimentally measured mechanical and durability properties. The analyzed datasets included 145 mixtures, featuring a variety of mixture designs from laboratory and field studies. The results indicate that the cement content is the most significant predictor of global warming potential (GWP) and that considerable GWP savings can be achieved by reducing and replacing cement without compromising performance. Clear correlations of GWP with compressive strength were not identified, while the results demonstrated that reduced GWP and increased electrically based resistivity (the utilized durability indicator) often occur in synergy. [ABSTRACT FROM AUTHOR]

Deck caps of bridges—in Germany shortly known as "bridge caps"—are usually made of steel reinforced concrete to form the anchoring area for the guardrail of bridge deck edges on existing cantilever slabs. Combined with protective devices, the outside arranged deck caps provide safety against lateral breaking or crashes of vehicles. Due to their exposed position in the cross section of bridges and the particularly intensive stresses, the deck caps are considered as wear parts and have to be renewed several times during the service life of a bridge. The decisive factor here is the discrepancy between the frost resistance of the concrete and the crack width restriction. On the one hand, only very small cracks (<0.2 mm) can be accepted to prevent corrosion of the rebars under the strong exposure of these elements. To confine crack widths without applying an excessively high degree of reinforcement, a low concrete compressive strength is advantageous. On the other hand, a sufficient frost resistance requires a correspondingly high compressive strength. With carbon reinforcement, these contrary points could be defused and simultaneously the needed durability could be provided. Therefore, slightly modified deck cap concretes combined with a carbon reinforcement mesh were tested to examine the bond behavior with and without freeze–thaw attack. To prove the characteristics of this combined system, the crack formation and crack distribution were investigated experimentally. The test results were compared to calculated values from a mathematically tool to be able to develop different reinforcement concepts in future that can ensure an optimized crack formation and crack width for deck caps. [ABSTRACT FROM AUTHOR]

The disposal of waste from coal plants and waste glass (WG) is causing significant environmental problems all around the planet. Currently, the amount of discarding of these wastes is increased. One possible option is to utilize fly ash (FA) from coal plants as a partial substitute for the cement and EG as a fractional substitute for sand in concrete, respectively. Besides, fibers can improve the strength and durability of concrete; explicitly speaking, using coconut fibers (CFs) is in trend due to their highest toughness among natural fibers making it suitable material as fiber reinforcement in concrete. This research studies the concrete behavior with 15% FA as a partial substitute of cement with 2% CFs and waste beverage glass as sand at various replacement levels (14%, 15%, 16%, 17%, 18%, 19%, and 20%). Mechanical and durability characteristics of concrete were assessed, such as compression strength, water absorption, flexural strength, density, workability, and water absorption. The current study results show that adding FA, CFs, and WG improved microstructure quality at 16% replacement of sand. The study showed that the M4 mix has enhanced the properties of concrete samples as compressive and flexural strength was improved to 47.2 and 6.2 MPa and improved apparent density by 20%. Adding more WGP than the optimal proportion (16%) led to detrimental effects on void ratio, permeability, and water absorption. Therefore, 16% of sand with WG and 15% of FA with cement can be substituted with 2% CFs to develop sustainable concrete. [ABSTRACT FROM AUTHOR]

Nowadays, geopolymers, which are more environmentally friendly than cement due to the high energy requirements and high carbon dioxide (CO2) emissions of cement production, emerge as alternative binders. In this study, the mechanical and durability properties of geopolymer concrete (GC) based on ground granulated blast furnace slag (GGBS) (100GGBS), 50% fly ash (FA) and 50% GGBS (50FA50GGBS), and FA (100FA) with two different water/geopolymer solids ratios (W/GP) of 0.33 and 0.35 were investigated. Slump, compressive strength, splitting tensile strength, unit weight, water absorption, elevated temperature resistance, abrasion resistance, modulus of elasticity, and drying shrinkage tests were carried out. As the percentage of FA in the mixture increased, the slump of the concrete increased, while the cohesion of the concrete decreased and the setting time was delayed. The addition of GGBS increased the compressive strength and the splitting tensile strength of the GC by up to 377% and 278%, respectively. Under the effect of elevated temperature, the 100FA concrete showed less strength loss and weight loss than other concrete. After the abrasion test, 100GGBS concrete lost about 2.5 times less weight than 100FA concrete. The drying shrinkage of geopolymer mortar reached a maximum of 100 microstrains. Among all concrete, 50FA50GGBS‐0.33 showed the highest performance in terms of overall performance. [ABSTRACT FROM AUTHOR]

The present study is focused on the compressive strength, water retention, and workability by varying the percentage of poly ethylene glycol 200 and liquid paraffin wax from 0% to 1% by weight of cement for self‐compacting concrete and compares it with conventional SCC. Percentages of 0.1%, 0.5%, and 1% (in proportion to the weight of cement) were adopted in the study. The comparison was done in a grade concrete and with cases such as indoor curing and water‐based curing. Slump‐flow test and V‐funnel tests were carried out on the fresh concrete to evaluate the workability of concrete. Concrete weight loss with time is evaluated to determine the water retention capacity. Compressive strength of cube specimens was conducted at the end of 7 and 28 days of curing. The durability of the concrete was assessed by immersing the concrete specimens in acids. The fresh properties were satisfied according to EFNARC specifications. Based on the weight loss percentage and satisfaction of compressive strength, the dosage of a self‐curing compound was determined. XRD analysis of the concrete was also performed on the concrete specimens. [ABSTRACT FROM AUTHOR]

Steel corrosion is a significant problem of concrete‐based infrastructure, and it increases the repair costs of the damage to structures. Glass‐fiber‐reinforced polymer (GFRP) composite bars are corrosion‐proof and exhibit relatively higher strength than ordinary steel reinforcement. However, GFRP bars degrade when exposed to the highly alkaline environment of concrete over extended periods. This study focuses on the effect of the high alkalinity of concrete on the tensile strengths of several types of GFRP bars. Different accelerated aging techniques were employed to evaluate the effects of GFRP characteristics (fiber volume fraction, matrix composition, bar diameter, and presence of protective coating) on the alkali resistance. The test results indicated that the alkali attack significantly decreased the tensile strength of GFRP, increasing with age. The alkali resistance of the GFRP bars increased up to a fiber volume fraction of 50% but decreased when the fiber volume fraction increased to 60% and above. The effects of protective coating on alkali resistance were generally positive but not consistent, and the effects of the matrix type and bar diameter on the alkali resistance of GFRP bars were insignificant. Accelerated aging did not change the bond strength but altered the failure mechanism associated with the bond failure of the specimens. [ABSTRACT FROM AUTHOR]

Conformity control is applied in order to safeguard the quality of produced lots. Conformity criteria are characterized by an operating characteristic curve, quantifying the probability of acceptance in relation to a concrete lot with a specific quality. By applying conformity control, certain lots of concrete are accepted or rejected. This induces a filtering effect, which in case of conformity control of durability parameters leads to an effect on the design service life. For durability, limiting values for durability‐related properties can be proposed. Specifying conformity criteria for the durability parameters of concrete can enable to safeguard the quality of concrete products in relation to durability. This conformity control has a filtering effect on the distribution of these durability parameters. When, for example, considering the diffusion coefficient of concrete, this filtering effect results in a lower mean value and standard deviation, consequently (positively) influencing the service life. In this paper, conformity criteria for durability parameters are developed, and their effect on the design service life of reinforced concrete elements is quantified. [ABSTRACT FROM AUTHOR]

The durability of concrete material after exposure to elevated temperatures is important for the serviceability prediction of concrete structures in a fire disaster scenario. Existing researches show that an appropriate amount of basalt fiber can significantly improve the splitting tensile strength and chloride penetration resistance of concrete. However, the mechanical properties of basalt fiber concrete after elevated temperatures and its durability properties are still not clear. In this paper, the mechanical properties, carbonization law, and chloride ion penetration law of ordinary concrete and basalt fiber concrete under high temperatures are studied. The concept of a burnt layer for concrete exposed to elevated temperatures is proposed, and the thickness of this burnt layer for concrete under different temperatures was measured. The results show that the addition of basalt fiber can inhibit the carbonization of concrete at elevated temperatures, diminish the thickness of the burnt layer, and significantly improve the chloride penetration resistance of concrete. [ABSTRACT FROM AUTHOR]

The focus of this study is to investigate the effect of using coarse recycled concrete aggregates (RCAs) as an alternative material to natural coarse aggregate on the fresh, mechanical and durability behavior of concrete reinforced with steel fiber. Eighteen unique concrete mixes with RCA content of 0%, 50%, and 100% and steel fiber content of 0%, 1%, and 2% were prepared, and tests were performed to study slump, density, compressive and splitting tensile strengths, flexural behavior, surface hardness, surface abrasion resistance, water absorption, and sorptivity of each mix. It is shown that concrete containing RCA has a lower unit weight, compressive, splitting tensile and flexural strength, flexural toughness, surface hardness, and abrasion resistance, and a higher water absorption and sorptivity in comparison with conventional concrete. An increased compressive, splitting tensile and flexural strength, flexural toughness, surface hardness, and abrasion resistance, and a decreased water absorption and sorptivity of concrete with an increased steel fiber content from 1% to 2% is less significant compared to those from 0% to 1%. The results also show that, at RCA content of 50%, incorporating 1% steel fiber develops a concrete mix with similar or even better properties compared to unreinforced conventional concrete. At 100% RCA content, incorporating 2% steel fiber develops a concrete mix with similar properties to unreinforced conventional concrete having water to cement ratio of 0.3, but inferior properties to unreinforced conventional concrete having water to cement ratio of 0.5. These findings indicate that recycled aggregate concrete with similar or even better properties compared to concrete with natural aggregate can be developed through properly designing mixes, providing a great avenue toward the production of green construction material for structural applications. [ABSTRACT FROM AUTHOR]

Industrial waste has rapidly increased day by day due to the fast‐growing population and usage of products, which dumps unscrupulously, resulting in environmental pollutions. Waste foundry sand (WFS) is one of the industrial solid wastes. River sand is generally used in concrete as a fine aggregate, which is limited (scant), and river excavation for sand leads to environmental deterioration. To resolve these problems, a study was performed on WFS as a partial substitution instead of natural sand in concrete. The effects of WFS on concrete performance were assessed through durability and mechanical performance. The results from experimental tests show that, compared to concrete blends with WFS up to 30% substitution, the control mix strength was only 7.6% (28 days) higher, and this improvement is not too high. In the same manner, concrete mixtures that contain WFS up to 30%, and their durability properties were somewhat same to blank max (control). Test results showed that WFS with a substitutions ratio up to 30% can be successfully used in concrete without disturbing its durability and strength properties. [ABSTRACT FROM AUTHOR]

This study investigated the influence of nano silica (NS) addition on the early‐ and later‐age compressive strengths and durability properties such as sorptivity, drying shrinkage, volume of permeable voids, and rapid chloride permeability, along with microstructural changes, of high‐volume slag (HVS) and high‐volume slag–fly ash (HVS‐FA) blended concrete. The results showed that the addition of NS improved the early‐age (3 days) compressive strength of HVS and HVS‐FA concretes significantly by 34 and 45%, respectively. In addition, the HVS concrete containing 78% blast furnace slag (BFS) gained considerable compressive strengths at later age due to the addition of 2% NS than the control HVS concrete with 80% BFS and showed comparable compressive strengths to ordinary Portland cement (OPC) concrete. On the other hand, the compressive strengths of HVS‐FA concrete containing 67% BFS‐FA blend and 3% NS surpassed OPC concrete at 28 days and exhibited superior strengths at later ages than the OPC concrete. Significant reduction in sorptivity of both HVS and HVS‐FA concretes is observed at 28 and 91 days, respectively, due to the addition of NS. Similar substantial reduction of drying shrinkage, chloride ion permeability, and volume of permeable voids are also witnessed in both HVS and HVS‐FA concretes due to the inclusion of NS than their respective control concretes without NS, and these exhibited better performance than control OPC concrete on most occasions. A denser and compacted interfacial transition zone (ITZ) is also found in the HVS and HVS‐FA concretes due to the addition of a small amount of NS. [ABSTRACT FROM AUTHOR]

Recycled aggregate (RA) acknowledge with its inferior quality due to high water absorption and lower strength which is mainly due to presence of attached adherent mortar. Concrete made with RA have lower strength and durability properties when compared with natural aggregate concrete (NAC), recorded by many previous researches in past. In order to overcome these difficulties, two‐stage mixing approach (TSMA) is a good tool to improve the properties of recycled aggregate concrete when compared with normal mixing approach (NMA). The main objective of present research work is to study the influence of mixing approaches on concrete made with treated recycled aggregate (TRA). Basically the workability, mechanical and durability properties of concrete have been studied at fresh and hardened state. In this work, four different types of mixing approaches (viz. NMA, TSMA, TSMA1, and TSMA2) were used. In all types of mixing approaches, the natural aggregate was replaced with TRA at different replacement levels viz.: 0, 25, 50, 75, and 100% in a control mix of M40 grade. Based on the experimental results the workability, strength, and durability properties of concrete made with TRA were improved in TSMA2 when compared with all other mixing approaches. [ABSTRACT FROM AUTHOR]

Carbonation resistance of fly ash concrete (FAC) and recycled aggregate concrete (RAC) has been extensively tested in the past decade, but there are still no recommendations for their application in codes of practice. Therefore, the main objective of this study was to determine the minimum concrete cover depth of RAC and FAC exposed to carbonation to satisfy the required service life. In this study, the relationship between concrete compressive strength at 28 days (fcm) and inverse effective carbonation resistance (R−1ACC) was established. The analysis was carried out on all data available in the literature in order to establish this relationship for FAC and RAC made with different replacement percentages. After establishing a relationship between R−1ACC and fcm, a prediction of the service life was made using the fib‐Bulletin 34 (2006, Model code for service life design (1st ed.). Lausanne: International Federation for Structural Concrete (fib)) prediction model for all exposure classes to carbonation. For same concrete class, it can be concluded that in the case of RAC there was no significant difference in the duration of the service life compared with natural aggregate concrete, even at 100% replacement of natural aggregate with recycled ones. For concrete up to 35% of fly ash in total cementitious materials, concrete cover for satisfying the required service life of 50 years was 40% higher compared with Portland cement concrete, and more than two times higher in case of concrete with 40–70% fly ash. [ABSTRACT FROM AUTHOR]

Investigation of mechanical properties and thermal behavior of expanded polystyrene concrete (EPS) and exfoliated vermiculite (EV) concrete has been accomplished in this research. It includes how EPS concrete is prepared by substituting the coarse aggregate with 0, 10, 15, and 20% with EPS aggregates. Similarly, EV concrete is prepared by replacing the fine aggregates with 0, 15, 45, and 60% with EV aggregates. The influence of EPS and EV proportion on mechanical and thermal properties was detected. Thermal properties were studied with an adiabatic box technique. Clear improvement in thermal behavior was observed in comparison with normal concrete and reduction in compressive strength was observed for an appreciable increase in the amount of EPS and EV. Also, the properties like split tensile strength, load–deflection curves, and durability properties of the EPS and EV concretes were experimented. [ABSTRACT FROM AUTHOR]

The performance of the conventional concrete skin was promoted by ultrasonic surface treatment (UST) in this study, and the newly formed dense and hard concrete skin was termed as ultrasonic hardening layer (UHL). The microstructure of UHL was scanned and analyzed, several durability‐related indicators, such as water vapor penetration rate, surface, and interface hardness, were measured, and it was found that UHL could effectively improve the durability of concretes. The light reflectance of the UHL concrete surface was measured in the spectrum range of UV (200 nm) to NIR (2,500 nm), and it manifested 24.17% less mean reflectance than the conventional concrete skin. Therefore, UHL could serve as a promising road material due to its better melting capacity in cold‐temperate zones. [ABSTRACT FROM AUTHOR]

This study investigated the effect of adding fly ash on the mechanical and durability characteristics of coconut shell (CS) concrete. Two different mixes were developed, one with CS and the other with conventional aggregate and CS as coarse aggregate. Cement was replaced with Class F fly ash in terms of weight at 0, 10, 20, and 30% in both mixes. Test result showed that the CS concrete with 10% fly ash replacement level exhibited the highest compressive and tensile strength. The addition of fly ash decreased the porosity of CS concrete due to its fineness and increased hydration products in the matrix at later ages. Additionally, it also improved the weak aggregate interfacial transition zone of CS lightweight concrete. Thus, the fly ash addition in CS concrete showed lower values of water absorption, permeable voids, sorptivity, and chloride permeability. Furthermore, the increasing content of fly ash addition improved the durability characteristics of CS concrete considerably. [ABSTRACT FROM AUTHOR]

This paper highlights the strength and durability characteristics of geopolymer concrete (GPC) developed with ground‐granulated blast furnace slag (GGBS) and metakaolin (MK) as binders. Sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) were used as alkaline activators of GPC. The variable parameters considered in this research work were proportions of GGBS and MK. The optimum mix was obtained by varying the proportions in the binder content of GPC. The influence of recycled coarse aggregates (RCAs) was also assessed on the arrived optimum GPC mix and compared with natural coarse aggregates. The replacement of RCA was done at 25, 50, and 100%. The durability studies were performed on the arrived optimum mix for natural and RCA concrete. The durability properties of GPC were studied by exposing the concrete specimens to HCl and H2SO4 at 5% concentration for 7, 28, and 56 days. Acid mass loss factor and acid strength loss factor were determined at all ages. From the results, it is observed that the usage of supplementary cementitious material as a partial replacement of GGBS in GPC is improving the strength as well as durability properties of blended GPC. The comparisons of these parameters were examined for the usage of RCA proportions also. The results indicated that the inclusion of RCA up to certain proportions is showing satisfactory results compared to that of GPC with natural aggregates. [ABSTRACT FROM AUTHOR]

The effect of presoaking of recycled coarse aggregate (RCA) in nano silica (NS) solution on the properties of recycled aggregates concrete is compared with the direct mixing of NS in concrete. In this study, four series of concrete are considered. The first and second series are control series containing 100% natural coarse aggregate (NCA) and 100% RCA, respectively. The third and fourth series are similar to the second series in every aspect except that 2 wt% NS is added through direct mixing in concrete and presoaking of RCA in 2 wt% NS solution of 24 hr, respectively. Results show that the measured 28‐day compressive strength of recycled aggregate concrete containing presoaked RCA is higher than that containing direct mixing of NS in concrete. The volume of permeable voids, water sorptivity, and chloride ion penetration measured after 28 days curing is also reduced in recycled aggregate concrete containing presoaked RCA in NS solution than that containing direct mixing of NS in concrete. The total porosity of mortar adjacent to presoaked RCA is also found to be significantly lower than the same, where NS is mixed directly. The concentration of pores in the matrix adjacent to presoaked RCA is also shifted to medium capillary pores from the large capillary pores of matrix adjacent to RCA containing no NS. The volume of medium capillary pores reduced significantly in the matrix adjacent to presoaked RCA compared to the same, where NS is mixed directly. The scanning electron microscopic image analysis also supports this observation. [ABSTRACT FROM AUTHOR]

Blended Portland cement-ceramic powder binder containing up to 60 % fine-ground waste ceramics from a brick factory is used in concrete mix design as an environmentally friendly alternative to the commonly used Portland cement. The experimental analysis of basic physical characteristics, mechanical and fracture-mechanical properties, durability properties and hygrothermal characteristics shows that the optimal amount of ceramic powder in the mix is 20 % of the mass of blended cement. The decisive parameters in that respect are compressive strength, liquid water transport parameters and resistance to de-icing salts, which are not satisfactory for higher ceramics dosage in the blends. In the case of other parameters studied, the limits for the effective use of ceramic powder are higher: 40 % for effective fracture toughness and specific fracture energy, 60 % for frost resistance and chemical resistance to MgCl2, NH4Cl, Na2SO4, HCl and CO2. The water vapour diffusion coefficient is found to increase with increasing ceramics content, which for wet envelopes can be considered as a positive feature, but may have a negative effect for dry envelopes. The thermal conductivity of all mixes increases fast with growing moisture content; differences of up to 50 % between the dry and water-saturated state values are observed. This has to be taken into account in energy-related calculations. [ABSTRACT FROM AUTHOR]

The transport mechanism of chloride ions in concrete during wetting and drying cycles of varying duration is evaluated in this paper. The experimental test results were used to validate a numerical simulation model in order to assess the influence of diffusion coefficient, surface chloride ion concentration and ratio of dry-wet cycle durations on the transport mechanism of chloride ions in concrete. Experimental and numerical analysis results indicate that the maximum transmission depth of chloride ions in concrete depends on the diffusion coefficient and the dry-wet cycle regime but has little relationship with the surface concentration of chloride. The chloride ion transmission in the surface zone accelerates only if the dry-wet ratio is > 1. As the dry-wet ratio increases, so the chloride ion transmission accelerates. It tends to become stable when the dry-wet ratio reaches 5:1. The dry-wet cycles accelerate the transport process of chloride ions within a certain distance from the surface; beyond this distance, chloride ions in the complete immersion specimen migrate more rapidly than those under dry-wet cycles. The peak concentration of chloride ions within the convection zone has a relationship with the diffusion coefficient, the surface chloride ion concentration and the dry-wet regime. The smaller the diffusion coefficient, the higher the surface chloride concentration; the greater the dry-wet ratio, the higher the peak of convection can be. [ABSTRACT FROM AUTHOR]