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Rheology of Self-Compacting Concrete (SCC) containing selected silica fume dosages (0% (control mix), 5%, 10% and 15%) in a binary binder has been investigated using the flow-curve test protocol implemented on a co-axial cylinder rheometer. At each silica fume dosage, coarse recycled concrete aggregate volumetric replacement levels were 0%, 50% and 100%. Calibration of selected flow models with the measured flow data showed that rheology transitioned from shear thickening to shear thinning as the silica fume dosage increased from 0% to 15%, other mix constituents remaining unchanged. Similar flow behaviour was noted in the SCCs made with the recycled concrete aggregates (SCRACs) across all replacement levels though for a given silica fume dosage, degree of shear thinning decreased with increasing contents of the coarse recycled aggregates. The experimental results have been used to propose a workability box containing bounds for acceptable rheology of the SCCs and the SCRACs. [ABSTRACT FROM AUTHOR]

Polycarboxylate (PCE) superplasticizers are the most important additive in concrete, which can effectively improve the workability of cement slurry. Different from the traditional regarding of PCEs as dispersants, here, we understand the PCEs as nano‐lubricants. By employing the molecular dynamics simulation, a sophisticated model was used to evaluate the interfacial friction between the C–S–H particles. The results reveal that the PCEs can reduce the interfacial friction between the C–S–H particles, and thus increase the fluidity of cement slurry. Further analyses infer the role of PCE segments in lubrication. The carboxylates on PCEs ensure the anchoring and hinder the separation of Ca ions. The side chains are used to lubricate the C–S–H surface, due to the weak adsorption between the side chains and the C–S–H surface. Predictably, this study not only provides a method to directly evaluate the performance of PCEs but also suggests new insights into the colloid dispersion of the low‐water content system. [ABSTRACT FROM AUTHOR]

A circular economy based on symbiotic relationships among sectors, where the waste from one is resource to another, holds promise for cost-effective and sustainable production. This research explores such a model for the agriculture, energy, and construction sectors in California. Here, we develop new an understanding for the synergistic utilization mechanisms for rice hull, a byproduct from rice production, as a feedstock for electricity generation and rice hull ash (RHA) used as a supplementary cementitious material in concrete. A suite of methods including experimental analysis, techno-economic analysis (TEA), and life-cycle assessment (LCA) were applied to estimate the cost and environmental performance of the system. TEA results showed that the electricity price required for break even on expenses without selling RHA is $0.07/kWh, lower than the market price. As such, RHA may be available at little to no cost to concrete producers. Our experimental results showed the viability of RHA to be used as a supplementary cementitious material, meaning it can replace a portion of the cement used in concrete. LCA results showed that replacing 15% of cement with RHA in concrete can reduce carbon dioxide equivalent (CO2e) emissions by 15% while still meeting material performance targets. While the substitution rate of RHA for cement may be modest, RHA generated from California alone could mitigate 0.2% of total CO2e from the entire cement production sector in the United States and 1% in California. [ABSTRACT FROM AUTHOR]

This study investigated the suitability of recycled asphalt pavement and polyethylene wastes as coarse aggregate in asphaltic concrete by evaluating the impact of the use of polyethylene polymer wastes and recycled asphalt pavement composite as aggregates on the physical and mechanical properties of the asphaltic concrete. The physical characteristics of the aggregate and bitumen were determined using relevant parametric tests. Recycled asphalt pavement was used to make asphaltic concrete samples using LDPE at 5%, 10%, 15%, RAP at 5% and HDPE at 5%, 10%, 15%, and a mixture of LDPE + HDPE at 5+5%, 7.5+7.5% and 10+10% RAP at 5% as additives. Marshall Stability test was conducted to assess the mechanical strength of the asphaltic concrete, and the results included information on the aggregate's stability, flow, density, voids filled with bitumen, voids filled with air, and voids in mineral aggregate. In addition, the surface and crystal structure of the aggregates was studied by carrying out a microscopic examination with a Scanning Electron Microscope (SEM) and X-Ray diffraction (XRD). The results obtained from this study demonstrated that RAP, HDPE & LDPE are viable conventional aggregate substitute for asphalt concrete production. [ABSTRACT FROM AUTHOR]

A comparative evaluation of the single and combined effect of nanoparticles (NPs) on the static and impact properties of concrete is presented. Different NPs (silicon dioxide, aluminium oxide and ferric oxide) were used separately and in combination as partial replacements of cement at 0.5% and 1% by weight of cement. The effects of the NP additions on the unit weight, compressive strength, split tensile strength, flexural strength, toughness, fracture energy and impact performance of concrete were experimentally examined. The effects of the NPs on the microstructure of concrete was investigated using scanning electron microscopy (SEM). The cost effectiveness of the use of NPs in concrete was also assessed in order to evaluate the commercial production of NP-doped concretes. Desirability function analysis was also conducted to compare the overall performance of the concretes. The addition of NPs had a positive effect on improving the mechanical performance of the concrete, with the addition of NPs increasing the compressive strength, split tensile strength, flexural strength and energy absorption capacity. The NPs did not have any significant influence on the unit weight of the concrete. SEM analysis showed that the use of NPs improved the concrete microstructure, but the NPs did not have a good influence on the impact performance of the concrete. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) is one of the most widely used building materials. However, RC, especially in coastal seaside or humid environments, can suffer reinforcement corrosion with the result that the reinforcement fails to perform its function over time. The effect of a retarder additive used to eliminate loss of consistency in hot, windy and humid weather on the corrosion of RC elements was investigated in this work. Four different concrete types were assessed, with 0%, 1%, 1.5% and 2% additions of the chemical additive. Along with accelerated corrosion and pressure tests, physical properties such as electrical resistivity, water absorption, porosity, unit weight and capillary water absorption were also determined. The results of this work indicate that the use of up to 2% of the setting retarder did not pose a problem in terms of the physical and mechanical properties of the concrete. However, in terms of the frequently encountered corrosion problem, the use of 1.5% is more appropriate. Many chemical additives are used for different purposes in concrete and it is suggested that, alongside physical and mechanical properties, durability characteristics should also be examined when determining the suitable ratios of these additives. [ABSTRACT FROM AUTHOR]

Conduct alkali silica reaction (ASR) tests on concrete by using cement with different alkali contents and according to different test standards. The influence of cement alkali content on the alkali-silica reaction of concrete was explored, and the effects of different test methods on the results of alkali-silica reaction tests were compared. The results indicate that: the type of cement and the testing method used have no significant impact on the experimental results of the alkali silica reaction. The rate of alkali silica reaction accelerates with the increase of cement alkali content. When the alkali content of cement is greater than 2.0 %, there is no potential harm of alkali silica reaction in the aggregate, which will cause harm of alkali silica reaction. The research conclusion can provide reference for the control value of alkali content in engineering cement. [ABSTRACT FROM AUTHOR]

The aim of this study is to promote the application of the excited zeolite powder (ZP)with aeolian sand powder (ASP) in the field of aeolian-sand concrete (ASC) production. This study utilises NaOH to treat composite cementitious materials containing aeolian sand and zeolite powders, which were used to replace 50% of the cement in aeolian-sand concrete (ASC). Production of alkali-inspired cement-based windswept concrete(AAZC).The mechanical properties of treated ASC considerably improved, especially when the NaOH dosage was 4% by mass. After curing this sample (denoted as AAZC-4) for 28 d, its compressive strength improved by 17.2%, and its split tensile increased by 16.3%. Potassium feldspar and montmorillonite in zeolite powder and SiO2 in the sand were decomposed by OH− and combined with other elements to generate various silicate gels and A-type potassium zeolite crystals inside the concrete. Microscopic examination showed that the gels and crystals intertwined to fill the pores, decreasing (increasing) the percentage of large (small) pores, thus optimising the pore structure. This substantially improved the mechanical properties of ASC. Freeze–thaw salt-intrusion tests showed that the extent of mass loss, degree of damage and loss of compressive strength of AAZC-4 were similar to those of ordinary concrete but were reduced by 36.8%, 19% and 52.1%, respectively, compared with those of ASC. Therefore, AAZC-4 has a sustainable working performance in chloride-ion permeable environments in cold and arid areas. [ABSTRACT FROM AUTHOR]

Externally bonded strengthening technique to the concrete has been widely used with epoxy adhesive. However, the adhesive is considerably weak against high temperatures, which has been regarded as the critical point in the loss of integrity of the strengthened system. Alternatively, geopolymer materials have shown an excellent performance at high temperatures, thus, their potential to be used as adhesive material has been investigated in this work. In experimentation, the composite specimens were developed using both types of adhesives, epoxy and geopolymer, and their performance was evaluated at three temperature levels (20, 60, and 120°C) by conducting pull‐off strength tests and classifying their failure modes. It was observed that the strength of concrete and epoxy was reduced with temperature. In contrast, the strength of geopolymer‐based adhesives strength was increased due to the reactivity of the precursor at high temperatures. Also, bond strength was reduced for both composite specimens at elevated temperatures. The highest bond strength was observed for the epoxy‐based adhesive system at 20°C, and about 70% loss in bond strength was observed when exposed to 120°C. The failure mode was also shifted from concrete to adhesive interface failure, that is, failure between the adhesive and the fiber fabric layer. The geopolymer‐based adhesive system has lower strength than its counterpart at all temperature levels, and the failure mode was adhesive interface failure. To enhance the bonding capacity at high temperatures, efforts are being made by adding different minerals has been employed. From the experimental results, it was found that there were some improvements, however, it was still less than that of epoxy‐based system. Further optimization of the geopolymer adhesive using minerals is required and then high‐thermal resistance geopolymer adhesive can be established. [ABSTRACT FROM AUTHOR]

Additive manufacturing with concrete – guidance for planning and implementation of projects This guideline, created by the DAfStb Working Group "Digital Concrete Construction through Additive Manufacturing," serves as a comprehensive resource to support the planning and implementation of additive manufacturing projects in concrete construction. It is intended for architects, planners, applicants, material manufacturers, construction companies, and other parties involved in construction. After a brief introduction to the classification, terminology, and methods of additive manufacturing, legal aspects and approval procedures are highlighted to ensure seamless integration of this technology into construction practice. The guide addresses the integration of additive manufacturing methods with concrete into construction law, explains the approval process, and offers assistance for coordinating responsibilities in projects. It addresses technical rules for the design and construction of structures, particularly for walls produced by additive manufacturing, and covers constructive aspects of reinforcement. An important component is concrete and component testing, including methods for sample preparation and testing procedures for fresh and hardened concrete, making the guide a useful tool for professionals in the field of digital concrete construction. [ABSTRACT FROM AUTHOR]

This study investigates the feasibility and effectiveness of employing waste ceramic (WC) in rigid pavement as a replacement for fine aggregate. WC was integrated into concrete; untreated and treated with a silane compound, where 30 wt.% and 50 wt.% sand was replaced with WC. The workability, compressive strength, water absorption, skid resistance, microstructural analysis, and surface chemistry of mixtures were evaluated. The results illustrated the positive impact of using treated WC on the water absorption of mixtures, where a maximum reduction of 19% was achieved in the mixture with 50% treated WC. Moreover, concrete with 30% treated WC attained a higher compressive strength of 43 MPa than its untreated counterpart, which achieved 29 MPa, when tested at 28 days. The integration of treated and untreated WC in concrete pavement reduced its skid resistance due to the presence of glaze in the untreated mixture and silane in the treated mixture. The morphological and surface chemistry analyses confirmed the development of C–S–H, CaCO3, and SiO2 in high contents in concrete with silane-treated WC. Also, a strong bonded interfacial transition zone was noticed in concrete with silane-treated WC, unlike concrete with untreated WC, which had a poor interfacial transition zone. [ABSTRACT FROM AUTHOR]

Concrete is an important material for the construction of buildings, and highways. However, natural resources are being depleted by using natural coarse or fine aggregates for the production of concrete. The substitution of natural coarse aggregate (NCA) with recycled coarse aggregate (RCA) efficiently manages construction waste and preserves natural resources. In the present study, 50 and 100% NCA have been replaced with RCA for the preparation of recycled aggregate concrete (RAC) with blended hydrated-brick powder (RAC-HBr). Additionally, cement was replaced by 10 and 20% of blended HBr in the preparation of RAC mixes. To investigate the strength and durability properties of RCA-HBr mixtures, compressive strength, water permeability, chloride penetration test, and ultrasonic pulse velocity (UPV) tests were conducted. The outcomes indicate that the optimum percentage of blended HBr enhances the compressive strength of RCA mixes. However, blended HBr positively influenced the RCPT, water permeability, and ultrasonic pulse velocity of the RCA concrete mixes. Further, the RCPT outcomes show that the chance of corrosion was reduced by 20%, while the UPV value confirms that the density of the RAC-HBr mixes was enhanced by 28.7% at the age of 56 days. Furthermore, based on the FESEM and EDS analysis, the pozzolanic materials have densified the concrete matrix by reducing the pores and voids of RAC-HBr mixes. Thus, practically, 100% RCA with blended hydrated lime and brick powder can be used to create M35-grade concrete. The current paper investigates the effect of blended HBr on the properties of RAC. 10% HBr was an optimum percentage which has significantly enhanced the strength and durability characteristics of RAC mixes. CSH gel CH crystals densify the concrete matrix. CSH gel and CH crystals were confirmed from the microstructure analysis through FESEM and EDS analysis. [ABSTRACT FROM AUTHOR]

The advantages of using geopolymer materials instead of cement in concrete are not limited to high durability properties. geopolymer concrete was introduced to mitigate the environmental damages caused by CO2 emissions and the great level of fossil fuels consumption during cement manufacturing. In the present investigation, a number of experimental studies were conducted on slag-based geopolymer concrete. Accordingly, nano-silica particles were used to improve the geopolymer concrete structure's matrix. In the current study, slag-based geopolymer concrete was used with 0–2% polyolefin fibres and 0–8% nano-silica. They were subjected to water absorption and permeability tests to assess their durability. The addition of nano-silica enhanced the whole properties of the slag-based geopolymer concrete. By using the nano-silica, the concrete paste microstructure became denser and more homogeneous, and the pores decreased. The compressive strength and tensile strength of the concrete increased by up to 22% and 14% respectively. On the other hand, in terms of durability, the nano-silica lowered the water absorption and permeability coefficients by up to 24% and 44%, respectively, by filling the pores of the concrete. In the weight loss test, geopolymer concrete achieved superior results (up to 16%) compared to ordinary concrete. [ABSTRACT FROM AUTHOR]

Modern concrete technology places a strong emphasis on incorporating diverse resources, particularly industrial byproducts, into the concrete production process. The utilization of fly ash, a notable industrial waste, has gained increasing importance due to its potential to enhance concrete properties and provide economic advantages. In this study, we conducted experimental investigations on concrete, varying the concentrations of graphene oxide (ranging from 0.1% to 0.5%) and coal ash (at levels of 5%, 10%, and 15%). We evaluated the mechanical characteristics of concrete, including compressive strength, tensile strength, and flexural strength, by creating a total of 45 different mix specimens across 15 distinct mix formulations. Remarkably, the combination known as 4GOCA (Graphene Oxide and Coal Ash at 5%, 10%, and 15%) exhibited the highest strength, demonstrating a remarkable 65% increase compared to the reference mix. Similarly, both 2GOCA and 3GOCA demonstrated strength gains exceeding 50%. The unique aspect of this research lies in its innovative utilization of graphene oxide and coal ash in the concrete mix, showcasing the potential for sustainable and high-performance construction materials. [ABSTRACT FROM AUTHOR]

The application of recycled coarse aggregate (RA) in structural concrete can save non-renewable resources and reduce land occupation. Developing comprehensive knowledge of chloride penetration and service life modeling of recycled coarse aggregate concrete (RAC) is a prerequisite for practice. However, compared with the natural aggregate concrete (NAC), the inferior durability performance, especially chloride penetration resistance, of RAC hinders its application in structural concrete. Therefore, many RAC performance enhancement methods have been proposed. This paper presents a holistic review focused on the chloride penetration of RAC with/without enhancement methods and service life prediction. The current RAC performance enhancement methods are introduced. The improvement effect of the corresponding enhancement methods on the chloride penetration resistance of RAC are discussed and analyzed in turn. Based on the reviewed data on the chloride diffusion coefficient, the modification efficiencies of assorted enhancement methods are summarized. With the hope of promoting RAC application in structural concrete, the current literature on chloride-ingress-based service life prediction for RAC is also overviewed. In addition, the typical influencing factors on chloride transport properties are also discussed, i.e., RA quality. It can be concluded that enhancement techniques can effectively improve the chloride penetration resistance of RAC. The old mortar enhancement or removal methods can improve the chloride penetration resistance by 15–30%, depending on the specific treatment measures. The modification efficiency of the modifier material depends on the specific type and content of the incorporated substance, which ranges from approximately 5% to 95%. The estimated service life of RAC structures decreases with the increasing RA replacement ratio. Finally, concluding remarks are provided concerning future research on the chloride transport behavior of RAC. [ABSTRACT FROM AUTHOR]

The effective use of waste materials is one of the key drivers in ensuring sustainability within the construction industry. This paper investigates the viability and efficacy of sustainably incorporating a polylactic acid-type plastic (WP) as a 10 mm natural coarse aggregate (NA) replacement in geopolymer concrete. Two types of concrete (ordinary Portland cement—OPC and geopolymer) were produced for completeness using a concrete formulation ratio of 1:2:3. The ordinary concrete binder control was prepared using 100% OPC at a water/binder ratio of 0.55, while the geopolymer concrete control used an optimum alkaline activator/precursor—A/P ratio (0.5) and sodium silicate to sodium hydroxide—SS/SH volume ratio (1.2/0.8). Using the same binder quantity as the control, four concrete batches were developed by replacing 10 mm NA with WP at 30 and 70 wt% for ordinary and geopolymer concrete. The mechanical performance of the developed concrete was assessed according to their appropriate standards, while a microstructural investigation was employed after 28 days of curing to identify any morphological changes and hydrated phases. The results illustrate the viability of incorporating WP in geopolymer concrete production at up to 70 wt% replacement despite some negative impacts on concrete performance. From a mechanical perspective, geopolymer concrete indicated a 46.7–58.3% strength development superiority over ordinary concrete with or without WP. The sample composition and texture quantified using automated scanning electron microscopy indicated that adding WP reduced the presence of pores within the microstructure of both concrete types. However, this was detrimental to the ordinary concrete due to the low interfacial zone (ITZ) between calcium silicate hydrate (CSH) gel and WP, resulting in the formation of cracks. [ABSTRACT FROM AUTHOR]

In order to improve the mechanical properties and durability of lightweight aggregate concrete in extreme environments, this study utilized Inner Mongolia pumice as the coarse aggregate to formulate pumice lightweight aggregate concrete (P-LWAC) with a silica powder content of 0%, 2%, 4%, 6%, 8%, and 10%. Under sulfate dry–wet cycling conditions, this study mainly conducted a mass loss rate test, compressive strength test, NMR test, and SEM test to investigate the improvement effect of silica powder content on the corrosion resistance performance of P-LWAC. In addition, using grey prediction theory, the relationship between pore characteristic parameters and compressive strength was elucidated, and a grey prediction model GM (1,3) was established to predict the compressive strength of P-LWAC after cycling. Research indicates that under sulfate corrosion conditions, as the cycle times and silica powder content increased, the corrosion resistance of P-LWAC showed a trend of first increasing and then decreasing. At 60 cycles, P-LWAC with a content of 6% exhibited the lowest mass loss rate and the highest relative dynamic elastic modulus, compressive strength, and corrosion resistance coefficient. From the perspective of data distribution, various durability indicators showed a clear mirror symmetry towards both sides with a silica powder content of 6% as the symmetrical center. The addition of silica fume reduced the porosity and permeability of P-LWAC, enhanced the saturation degree of bound fluid, and facilitated internal structural development from harmful pores towards less harmful and harmless pores, a feature most prominent at the 6% silica fume mixing ratio. In addition, a bound fluid saturation and pore size of 0.02~0.05 μm/% exerted the most significant influence on the compressive strength of P-LWAC subjected to 90 dry–wet cycles. Based on these two factors, grey prediction model GM (1,3) was established. This model can accurately evaluate the durability of P-LWAC, improving the efficiency of curing decision-making and construction of concrete materials. [ABSTRACT FROM AUTHOR]

Context: Asphalt, a polymer mixture composed of various hydrocarbons, is extensively utilized due to its excellent performance. To evaluate the sensitivity of asphalt concrete to chloride salt damage at the nanoscale, considering the anisotropy of aggregate mineral crystal orientation, molecular dynamic simulations were employed to model the interface interactions between asphalt and aggregate mineral components (silica and calcite) under chloride salt exposure. The wetting processes of water droplets and chloride salt droplets on different crystal surfaces of silica and calcite were analyzed. Furthermore, the adhesive energy, decohesion energy, degradation ratio, and energy ratio of the interaction model between asphalt and aggregate mineral interfaces were analyzed to reveal the variations in the interfaces between the two components. The results demonstrated that the anisotropy of the minerals significantly affects the adhesion energy of asphalt and aggregate. Moreover, the surface hydrophilicity of calcite was larger than that of silica. The interfacial adhesion energy of asphalt-calcite was larger than that of asphalt-silica under dry condition and chloride salt attack, and the interfacial adhesion energy of both asphalt and mineral decreased with the increase of chloride salt concentration. The degradation ratio and energy ratio values of asphalt and calcite were larger than those of asphalt and silica, and the anisotropy of the mineral surface affected the degradation ratio and energy ratio values. This study provides a new method and theoretical basis for further research on the damage mechanism and strengthening measures of asphalt-aggregate under chloride salt attack. Methods: To investigate the interaction between asphalt and mineral aggregates under chloride salt erosion, models of asphalt, aggregate, and asphalt/aggregate composite systems were constructed using the Amorphous Cell module in Materials Studio 2020 software. Molecular dynamic simulations of the asphalt/aggregate composite system were then conducted using the Forcite module, employing the COMPASS II force field to describe atomic and molecular interactions. Initially, considering the crystal orientation and surface configuration of the aggregate minerals, the impact of mineral anisotropy on the asphalt-aggregate interface model was analyzed. Subsequently, by simulating the contact states of nano water droplets and chloride salt droplets with different mineral surfaces, the wetting characteristics of nano water droplets on silica and calcite surfaces were determined. Lastly, considering the corrosion effect of chloride solution at different concentrations, the adhesion energy, debonding energy, degradation ratio, and energy ratio of the asphalt-aggregate interface interaction model were analyzed. [ABSTRACT FROM AUTHOR]

The extreme demand for aggregate leads to the exploitation of riverbeds for fine aggregates, affecting the environment adversely. Therefore, a suitable alternative to natural river sand is essentially required. This study focuses on preventing environmental impact by developing polycarboxylate ether (PCE) sand to replace natural river sand (NRS). Development of polycarboxylate ether (PCE) sand by mixing high-volume fly ash, bottom ash, cement, natural river sand, and locally purchased high-solid-content polycarboxylate ether–based superplasticizer (HSPCE). All the physical and chemical properties of PCE sand were observed and satisfied the requirement of current standards. PCE sand yields a good specific gravity of 2.31 and is classified as Zone I sand with a satisfactory friction angle (37°) compared with NRS and geopolymer fly ash sand (GFS). Although the water absorption (6.83%) and pH (12.18) are slightly more than those of GFS and NRS, the alkali silica reaction and soundness are well within the permissible limit as per Indian standards. The chemical analysis by X-ray fluorescence showed the presence of high amounts of SiO2 and Al2O3 with magnitudes of 58.879%, and 26.77%, respectively. Finally, the compressive strength of M25 grade concrete using PCE sand and GFS was observed to be 87.51% and 83.82% with respect to NRS after 28 days, respectively. The results of this study indicate that PCE sand can be a good alternative to NRS for construction work because it not only reduces the environmental effect due to sand mining but also focuses on utilizing fly ash and bottom ash. [ABSTRACT FROM AUTHOR]

The abundant natural volcanic ash (NVA) in East Africa is a prospective supplementary cementitious material that may be used to produce green and economical railway concrete. To mitigate the shrinkage of concrete with NVA, internal curing using a superabsorbent polymer (SAP) is employed in this study. The compressive strength, autogenous shrinkage, and drying shrinkage of internally cured concrete with NVA were measured. In addition, the water loss and internal relative humidity of internally cured concrete with NVA were analyzed. The results indicate that the compressive strength of concrete with NVA shows a linear decreasing trend with SAP. In addition, SAP significantly reduces the autogenous shrinkage but slightly increases the drying shrinkage of concrete with NVA. The internal curing using SAP increases the water loss of concrete, whereas the water released from SAP still significantly improves the internal relative humidity (IRH) of concrete. The positive influence of internal curing on the autogenous shrinkage overwhelms the unexpected influence on the drying shrinkage, resulting in the mitigated shrinkage of concrete with NVA. [ABSTRACT FROM AUTHOR]

Premature degradation of concrete, caused by frost damage, has been associated with inadequate transport properties and poor resistance to deicing salt. In this study, transport properties and deicing salt resistance of various kinds of ultrahigh-performance concrete (UHPC) containing Type V portland cement, fly ash, and microsilica were investigated. Seven combinations of cementitious materials (one reference, three binary, and three ternary) were used to batch UHPCs using a water-to-cementitious material ratio (w/cm) of 0.21. The aggregate-to-cementitious material ratio (Va/Vcm) of 1.20 was kept constant for all mixtures. The investigated transport properties included water absorption, volume of permeable voids, water penetration, rapid chloride penetration, and surface resistivity. The transport properties of the plain UHPCs were also compared to those of the corresponding steel fiber–reinforced UHPCs. The test results showed that the transport properties and deicing salt resistance of the studied binary and ternary UHPCs improved with the inclusion and increases in microsilica, replacing a portion of cement. The addition of steel fiber had a minor effect on strength and transport properties and a moderate increase in deicing salt resistance of the studied UHPCs. While rapid chloride penetration and surface resistivity tests were found appropriate to assess chloride transport through the studied plain UHPCs, both tests were deemed unsuitable for the companion steel fiber–reinforced UHPCs. [ABSTRACT FROM AUTHOR]

Ultra-high-rise buildings require high concrete bearing capacity. Ordinary concrete often fails to meet the project requirements. Admixture of admixtures in concrete is a means of solution. Currently, studies on the incorporation of basalt fiber (BF) and fly ash (FA) in concrete are relatively mature. However, research on incorporating nano-Titanium Carbide (nano-TiC) in concrete is still relatively scarce, which has a lot of room for development. To further improve the mechanical properties of concrete, BF, and FA synergized with nano-TiC were incorporated into concrete to produce TBF concrete in this study. And Response Surface Methodology (RSM) was used to optimize the mechanical properties of concrete. The collapse and compressive deformation damage characteristics of concrete were analyzed. The microstructure of the cement matrix was analyzed by the SEM (Scanning Electron Microscope). An optimization model of the TBF concrete craving function was developed. Optimized ratios with compressive, split tensile, and flexural strengths as response objectives were obtained, and the accuracy of the optimized ratios was investigated using the same experimental conditions. The results of the study showed that FA increased the collapse of concrete, while nano-TiC and BF decreased the collapse of concrete. Under uniaxial compression, nano-TiC, FA, and BF together incorporated into concrete can improve its compressive damage state. Moderate amounts of nano-TiC, BF, and FA could improve the mechanical properties of concrete. Their optimal mixing ratio admixtures were 0.88%, 0.24%, and 5.49%, respectively. And the measured values under the same conditions were compared with the predicted values. The maximum difference in compressive strength was 6.09%. The maximum difference in split tensile strength was 7.14%. The maximum difference in flexural strength was 8.45%. This indicated that the accuracy of the RSM optimization model was good. A moderate amount of nano-TiC, FA, and BF could improve the densification of concrete. [ABSTRACT FROM AUTHOR]

As an internal curing substance for cementitious materials, superabsorbent polymer (SAP) is emerging as the most potential solution. Nanomaterials and their composites have wide applications in concrete mainly as crack sealants and viscosity modifiers. Silane, as a coupling agent, is utilized in cementitious materials for its effective particle dispersion and adhesion characteristics. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Thermogravimetry (TGA) analysis, and Scanning electron microscopy (SEM) are utilized to characterize the microstructures and phase compositions of nanoalumina, (3-aminopropyl) triethoxysilane (APTES) and polyacrylamide (PAM) SAP. The impacts of silane-functionalized nanoalumina combined polyacrylamide SAP in cementitious materials are carefully investigated in this work. Compared with plain SAP, the application of silane-functionalized SAP was found to exhibit increased compressive strength, flexural strength and split tensile strength of concrete. The chemical durability properties of cement mortar, rheological and mechanical properties of concrete under self-curing and water curing with cement replaced by the prepared composites at 0.1, 0.2, 0.3, 0.4 and 0.5% by weight of cement are studied experimentally. Results revealed that silane-functionalized nanoalumina modified SAP has good water holding capacity than those with individual SAPs contributing to the advancement of internal curing materials in concrete buildings. The weight loss measurements reveal that lower weight loss is observed for the concrete containing SAP/APTES/nanoalumina in chloride, acidic and sulphate media. This work contributes to the advancement in material technologies for the prevention of building fractures. [ABSTRACT FROM AUTHOR]

Polycarboxylic superplasticizers (PCEs) exhibit numerous advantages as concrete additives, effectively improving the stability and strength of concrete. However, competitive adsorption of PCEs occurs in the presence of clay, which may affect the cement dispersion and water-reducing performance. Extensive research has been conducted on the physical and mechanical properties of PCEs; however, the effect of the diverse structures of PCEs on the competitive adsorption on clay and cement hydration products has been rarely studied. This study employs Ca-montmorillonite (CaMMT) as a clay representative, by constructing adsorption models of PCEs on CaMMT and cement hydration products. A comparison of the adsorption energies considering different side-chain lengths of PCEs is included. Typically, the adsorption energy on CaMMT is lower than that on hydration products, leading PCEs to preferentially adsorb on the clay, thereby reducing its effective dosage in the cement particles. The challenge of PCE adsorption on CaMMT increases with the polymerization degree, and methylallyl polyoxyethylene ether (HPEG) exhibits lower adsorption energies on CaMMT. The density of states (DOS) analysis indicated the highest peak values of allyl polyethylene ether (APEG) as well as the peak area at n (polymerization degree) = 1. The total number of transferred electrons for APEG was 0.648, surpassing those of other PCEs. The interaction mechanism of PCEs with clay and hydration products is further elucidated through electronic gain/loss analysis, also providing a basis for the theoretical analysis on how to reduce the adsorption of PCEs on clay and the structural design of mud-resistant PCEs. [ABSTRACT FROM AUTHOR]

In this study, basalt fibers (BFs) and nano-silica (NS) were innovatively combined to reinforce recycled aggregate concrete (RAC) to prepare recycled aggregate concrete (named NBRAC) with better mechanical and microstructural properties as an alternative to ordinary concrete. Different NBRAC specimens were prepared by adjusting the contents of NS and BF; the damage mechanism and mechanical properties of NBRAC were investigated; and the compressive, split tensile, and flexural strengths of NBRAC were evaluated. The microstructure of NBRAC was analyzed by scanning electron microscopy observation. The results showed that the densification of NBRAC was improved under the condition of 50% RA substitution rate and that its compressive, split tensile, and flexural strengths were increased by 6.8%, 16.3%, and 32.7%, respectively, compared with that of natural concrete, which proved that the method was feasible for the preparation of high-performance RAC. Scanning electron microscope image analysis confirmed the improvement effects of NS and BF on RAC, and combined with the experimental data, a composite explanation for the improvement effects of NS and BF on RAC was proposed for the first time. [ABSTRACT FROM AUTHOR]

Today, the use of fibers in concrete is one of the best methods to improve weaknesses such as low tensile strength and brittleness. Polyvinyl alcohol fibers are one of the best fibers to improve the mechanical properties of fiber concrete. These fibers improve the mechanical strength and performance of concrete by the connection between the micro-cracks, which is due to its excellent adhesion, tensile strength and high modulus of elasticity. The main purpose of this research is to analyze and evaluate the effect of polyvinyl alcohol fibers with a diameter of 0.014 mm and lengths of 6 and 12 mm in combination in high strength concrete containing microsilica. Accordingly, four mixtures with different amounts of polyvinyl alcohol fibers (0, 0.15, 0.3 and 0.6% of the total volume of concrete) were evaluated due to their effect on the fresh and hardened properties of high strength concrete. 10% microsilica was used as a substitute for Portland cement in all mixtures. A series of experiments (compressive strength, indirect tensile strength) showed that the low volume of polyvinyl alcohol fibers significantly increases the mechanical properties of concrete. The results of this research show that the use of volume ratio of 0.15% of polyvinyl alcohol fibers increases the compressive strength by 10.29% and tensile strength by 10.43%. [ABSTRACT FROM AUTHOR]

The present paper highlight upon research work is that curing is one of most important aspect of construction. The life of concrete and its serviceability depends heavily on curing. The method of curing applied on concrete will affect its final strength and durability. Owing to this fact this paper contains the research done on concrete under various curing methods. The standard method of curing concrete is done by water and results wastage of a lot of water. With the increase in the deficiency of availability of water, curing becomes a problem. Hence this research aims at providing better methods of curing which will not only improve the strength and durability of concrete but will also save water. The various methods that have been researched upon are plastic covered curing, addition of sodium silicate to curing water, and addition of curing compounds to curing water. The tests are carried on concrete with desirable strengths of M15 and M20. In this research the fine aggregate used in making of M15 and M20 concrete consists of a mixture of sand and crusher dust. Two mixes of ratio 50:50 and 60:40, sand to crusher dust have been taken and the effects of curing on these mixes are considered. Plastic curing is done by covering the concrete with plastic soon after demolding. Hence minimum water is required. The curing done by sodium silicate is done by adding 2% by weight of sodium silicate to curing water. Concrete is submerged in water containing sodium silicate. Once the concrete is cured, this water mix can be reused to cure freshly cast concrete, thereby saving more water. Curing by curing compounds is done in a similar way as that of curing with sodium silicate, only that instead of sodium silicate, curing compounds are used. The effect of these three methods on concrete is studied and discussions are made. [ABSTRACT FROM AUTHOR]

As global urbanization flourishes, the adverse effects on the environment also incredibly increase. This urbanization leads to the evolution of construction and building materials. To meet the requirements of eco-balanced construction materials without compromising their original properties, many evolutions of concrete are in practice nowadays. One such evolution of concrete is geopolymer concrete. The objective of the current study is to produce high-strength geopolymer concrete using ground granulated blast furnace slag (GGBS), metakaolin (MK), and nano-silica (NS) in ambient-cured conditions. The influence of nano-silica in the geopolymer concrete is evaluated by workability, setting time, mechanical strength, durability properties, and microstructural analyses, which include scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and correlation analysis. In this research, the effect of nano-silica on formulating the equation for modulus of elasticity was determined. Nano-silica was replaced at a percentage of 1, 2, and 3% of the binder material. It is summarized that the molar ratios and properties of the precursor materials are the defining factors in altering the systems of geopolymer concrete. The highest strength of 89.4 MPa at 28 days of ambient-cured concrete with outstanding durability performance was achieved. [ABSTRACT FROM AUTHOR]

The current study presents an investigation into the optimal content determination of the mix parameters in their acceptable ranges through fresh, mechanical, and durability characteristics in ground granulated blast furnace slag (GGBFS) based self-compacting geopolymer concrete (SCGC) cured under ambient temperature. Ordinary portland cement (OPC) based self-compacting concrete (SCC) was prepared as a control concrete. Both the M25 SCGC and SCC were characterized through fresh property tests satisfying the flowability, passing ability, and segregation resistance; mechanical tests by both nondestructive and destructive tests; and durability tests through water absorption, sorptivity, acid attack, sulfate attack; and rapid chloride permeability test (RCPT). The prime mix parameters considered in SCGC with their variation ranges were molar concentration of sodium hydroxide (10M, 12M, 14M, 16M), sodium silicate to hydroxide ratio (1.5, 2.0, 2.5, 3.0), superplasticizer (SP) dosage (5%, 6%, 7%, 8%), and percentage of extra water (EW) (15%, 18%, 21%, 24%). The results of SCGC were compared with the control SCC and discussed. The mix parameter optimal values derived from all the fresh and hardened concrete properties were a 12M concentration of sodium hydroxide, sodium silicate to hydroxide ratio of 2.5, SP dose of 7%, and EW percentage of 21%. SCGC thus prepared is stable, workable, and exhibits superior properties to OPC-based concrete to promote sustainable development. The current study estimates the optimal quantity of mix parameters, i.e., 12M NaOH, AAS ratio of 2.5, 7% SP, and 21% EW to produce ground granulated blast furnace slag (GGBFS)-based self-compacting geopolymer concrete (SCGC) cured under ambient temperature. The SCGC-optimized mix-parametric values are evaluated based on the mix materials whose physical and chemical properties are declared in the manuscript. The cementless concrete thus prepared is GGBFS based, which is an industrial byproduct, yielding sustainable concrete. Under ambient temperature, the SCGC can be cured, which is practically beneficial for the in situ construction work. The self-compacting capability of SCGC involves minimal energy in producing a dense, smooth concrete surface, reducing both the construction period and cost involvement. Being a stable workable concrete, its nonsegregation nature makes it homogeneous with minimal entrapped air. The reduced permeability nature renders it a larger insulating potential. Concerning OPC-based concrete, SCGC has larger mechanical and durability characteristics, making it a better choice. Thus, the SCGC has a huge potential in the global construction sector and is practically applicable. [ABSTRACT FROM AUTHOR]

Manganese slag (MS) is a kind of chemical waste, which may pollute the environment if conventional handling methods (stacking and landfill) are applied. Ultra-high-performance concrete (UHPC)—with considerably high compactness and strength—can be used not only as a special concrete material, but also to solidify the toxic substances in solid waste. This study proposes the addition of MS to UHPC, where the mass ratio of MS varies from 0% to 40% in the total mass of MS and silica fume. The effects of MS on the fluidity, plastic viscosity, and yield shear stress are investigated, and the flexural strength, compressive strength, and dry shrinkage rate of UHPC with MS are measured. X-ray diffraction (XRD) spectrum and energy spectrum analysis (EDS) diagrams are obtained to analyze the performance mechanism of the UHPC. A rheological study confirms that the slump flow increases with the increasing rate of 0–14.3%, while the yield shear stress and plastic viscosity decrease with the rates of 0–29.6% and 0–22.2%, respectively. The initial setting time increases with the mass ratio of MS by 0–14.3%, and MS has a positive effect on the flexural and compressive strengths of UHPC. In the early curing stage (less than 14 days), the increasing rate in the specimens increases with the curing age; meanwhile, when the curing age reaches 14 days or higher, the increasing rate decreases with increasing curing age. The compactness of UHPC is increased by adding MS. Furthermore, MS can increase the elements of Al and decrease crystals of Ca(OH)2 and calcium silicate hydrate in UHPC. [ABSTRACT FROM AUTHOR]

Construction and demolition waste (CDW) management and recycling practices are crucial for transitioning to a circular economy. The focus of this study was on the detailed characterisation of different CDWs (hollow brick (HB), red clay brick (RCB), roof tile (RT), concrete and glass) collected from seven different demolition sites in Turkey. The CDWs were characterised based on particle size distribution, chemical composition and crystalline nature. Pozzolanic activity was evaluated through compressive strength measurements of cement mortars made with 20% cement replacement by CDWs at 7, 28 and 90 days. The results showed that the clayey CDWs exhibited similar physical/chemical properties and crystalline structures. The compositions of the waste concretes varied significantly based on their original materials. All the CDWs satisfied the minimum strength activity index (SAI) for supplementary cementitious materials, with pozzolanic activity influenced by the fineness and silica + alumina contents. The average SAIs for the HB, RCB, RT, concrete and glass were, respectively, 84.5%, 86.3%, 83.4%, 80.7% and 75.8%. Clayey CDWs contributed to mechanical strength development, while the contribution of concretes was related to the hydration of unreacted cementitious particles. Glass exhibited the weakest pozzolanic activity due to its coarser particle size. Overall, the CDWs demonstrated suitable properties for use as supplementary cementitious materials in Portland cement based systems. [ABSTRACT FROM AUTHOR]

The coronavirus (COVID-19) pandemic has not only had a severe impact on global health but also poses a threat to the environment. This research aims to explore an innovative approach to address the issue of increased waste generated by the pandemic. Specifically, the study investigates the utilization of discarded face masks in combination with recycled concrete aggregate (RCA) and Silica Fume (SFM) in civil construction projects. The disposable face masks were processed by removing the ear loops and nose strips, and then cutting them into small fibers measuring 20 mm in length, 5 mm in width, and 0.46 mm in thickness, resulting in an aspect ratio of 24. Various proportions of SFM and RCA were incorporated into the concrete mix, with a focus on evaluating the compressive strength, split tensile strength, and durability of the resulting material. The findings indicate that the addition of SFM led to improvements in both compressive and split tensile strength, while no significant impact on durability was observed. [ABSTRACT FROM AUTHOR]

Using nano-silica and steel micro-fibers in high-strength concrete has gained attention due to their potential to reduce solid waste and environmental pollution. In this study, the impact of nano-silica inclusions on the mechanical properties of steel fiber-reinforced concrete, referred to as “Micro-Concrete Reinforced with Steel Fibers Embedding Nano-Silica” (MRSFEN), was assessed. MRSFEN mixtures were prepared with 0%, 1%, and 2% nano-silica content and 0.5%, 1%, 2%, and 3% steel micro-fiber content. Tests showed a 17%-32% increase in compressive strength and a 12%-29% increase in tensile strength by adding 1%-2% nano-silica across all fiber contents. Incorporating 1%-3% steel micro-fibers resulted in 18–25 MPa higher compressive strength, 6–12 MPa higher tensile strength, and 10%-35% higher flexural strength relative to non-fiber concrete. However, workability reduced by 15%-30% with 3% fiber content. The combined use of nano-silica and steel micro-fibers enhanced strength and ductility, with the optimum composition identified as 1% nano-silica with 2% steel micro-fibers based on the mechanical performance. The results indicate the potential of tailored MRSFEN mixtures to improve the mechanical properties of steel fiber-reinforced concrete, with benefits in reducing solid waste and mitigating environmental contamination. [ABSTRACT FROM AUTHOR]

This study explores the possibility of partially replacing cement with crushed brick powder (CBP) and 6% hydrated lime (HL) in concrete. The results showed an increase in compressive strength compared with the control at the intermediate age of 56 days. Adding HL to the cement and CBP paste samples resulted in a 22% reduction in capillary pores and a 23% increase in gel pores. Although the control samples had less carbonation penetration, the corrosion rate was higher than that of blended cement concrete with HL. The half-cell potential measurement on carbonated samples indicated that, unlike chloride-induced corrosion, the depassivation of steel could not be identified by a stable demarcating half-cell potential value. Moreover, blended cement concrete with HL exhibited higher resistivity. Visual inspection of corroded bars revealed that the assumption of uniform corrosion by carbonation might not be entirely accurate. The use of HL with a cement-CBP binder improved the concrete's characteristics and reduced the risk of carbonation-induced corrosion. The study provides supplementary information on the feasibility of using a blend of crushed brick powder and hydrated lime as sustainable alternatives in the field of concrete construction with environmental considerations. [ABSTRACT FROM AUTHOR]

Soy methyl ester-polystyrene (SME-PS) is a biodegradable and nontoxic blend of soybean oil and waste polystyrene that can be used as a surface treatment to improve concrete deterioration and rebar corrosion caused by freeze–thaw cycles and chloride salt exposures. Although SME-PS has shown promising results for concrete protection, the mechanism by which it protects concrete is relatively unknown. The current study utilizes thermal analysis techniques to explore the physical and chemical protecting mechanism of SME-PS. The potential chemical reaction, reaction rate, and reaction products among SME-PS, hydrated cement paste, and cement hydration products are investigated using isothermal calorimetry and thermogravimetric analysis. Dynamic vapor sorption analysis is conducted to physically evaluate the effect of SME-PS on the pore structure of concrete. The results indicated that the SME-PS can occupy the pores with sizes smaller than 50 nm, physically preventing the ingress of detrimental ions and water into the concrete porous structure. It was also found that SME-PS can chemically interact with cement paste products rapidly occurring at the first 12 min of blending of cement paste powder with SME-PS. The thermogravimetric results indicated the SME-PS reaction mainly occurs among calcium hydroxide, pore solution, and gypsum. Additionally, the hydrophobic nature of SME-PS is beneficial in terms of protecting the cementitious material surface from aggressive chemicals. [ABSTRACT FROM AUTHOR]

This study investigates the performance of asphalt concrete containing recycled plastics as synthetic aggregates in the dry mixing process. Two types of recycled plastics were used, namely, acrylonitrile butadiene styrene (RABS) and Polyethylene Terephthalate (RPET), based on the high-temperature properties of the plastics that make them suitable to be treated as synthetic aggregates (i.e. do not melt during the asphalt mixing phase). The proportions of recycled plastics were chosen at 0.5%, 1%, 2% and 4% of the mix mass. The laboratory testing programme includes the evaluation of compactability properties, moisture resistance, cracking resistance via IDEAL-CT test, fatigue resistance via four-point bending beam test and rutting resistance via Hamburg wheel tracking (wet) test. It was found that the inclusion of recycled plastics did affect the compactability of the mixes depending on their relative size and shape. On the other hand, the inclusion of recycled plastics did not significantly vary the moisture resistance of asphalt mixes. The cracking and rutting behaviour of asphalt mixes that incorporated recycled plastics were also modified and some benefits were observed depending on the plastic content and size. [ABSTRACT FROM AUTHOR]