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This study focuses on the role of low-quality calcined Fanja (FNJ) clay in enhancing the behavior of cured cement mortar (CM) and its resistivity to chloride and sulfuric acid attack. Ordinary Portland cement was replaced with different quantities (10%, 25%, 35%, and 50% by weight) of FNJ, which was calcined at different temperatures (620 °C, 760 °C, and 900 °C). After 28 days of curing, all the hardened mortars were immersed in 5% sulfuric acid for up to 12 weeks. Additionally, a rapid chloride permeability test was conducted on the 91-day cured CM and CM-FNJ samples to evaluate the affinity of calcined FNJs to retard the chloride diffusion into CM. The results showed that all samples containing FNJ900 showed better physical and mechanical properties than the control sample, while CM with NFJ760 recorded nearly similar performance as CM-NFJ900. In contrast, the CM-FNJ620 mixtures showed lower properties than those of other mixtures. In addition to the pozzolanic reactivity of the calcined clay, the presence of hematite in the calcined clay strongly contributed to increasing the mechanical properties of the hardened mortar through forming calcium ferrosilicate hydrate binding phase, as confirmed by X-ray diffraction. Moreover, the existence of hematite increased the resistivity of CM against sulfuric acid attack as it acts as a buffer for an acidic medium. Compared with CM-FNJ900, the CM-FNJ760 is recommended for use as it exhibited a higher strength activity index and comparable resistance to accelerated chloride diffusion and sulfuric acid accompanied by lower energy demand and lower CO2 emission, achieving the concept of 'sustainability'. [ABSTRACT FROM AUTHOR]

Abstract This study focuses on the role of low-quality calcined Fanja (FNJ) clay in enhancing the behavior of cured cement mortar (CM) and its resistivity to chloride and sulfuric acid attack. Ordinary Portland cement was replaced with different quantities (10%, 25%, 35%, and 50% by weight) of FNJ, which was calcined at different temperatures (620 °C, 760 °C, and 900 °C). After 28 days of curing, all the hardened mortars were immersed in 5% sulfuric acid for up to 12 weeks. Additionally, a rapid chloride permeability test was conducted on the 91-day cured CM and CM-FNJ samples to evaluate the affinity of calcined FNJs to retard the chloride diffusion into CM. The results showed that all samples containing FNJ900 showed better physical and mechanical properties than the control sample, while CM with NFJ760 recorded nearly similar performance as CM-NFJ900. In contrast, the CM-FNJ620 mixtures showed lower properties than those of other mixtures. In addition to the pozzolanic reactivity of the calcined clay, the presence of hematite in the calcined clay strongly contributed to increasing the mechanical properties of the hardened mortar through forming calcium ferrosilicate hydrate binding phase, as confirmed by X-ray diffraction. Moreover, the existence of hematite increased the resistivity of CM against sulfuric acid attack as it acts as a buffer for an acidic medium. Compared with CM-FNJ900, the CM-FNJ760 is recommended for use as it exhibited a higher strength activity index and comparable resistance to accelerated chloride diffusion and sulfuric acid accompanied by lower energy demand and lower CO2 emission, achieving the concept of ‘sustainability’.

In this study, the influence of nano silica, used in the production of construction materials in recent years, on the durability properties of cement-based mortar has been investigated. Mortars with nano silica additions at 1%, 2%, and 4% ratios were produced; workability, water absorption, compressive strength development, and chloride permeability were examined. Tests were repeated on the 28th and 90th days to reveal the time-dependent behavior of nano-silica-containing mixtures. As a result of the study, it was observed that nano silica adversely affected the workability properties but improved the hardened state properties of mortars. It was determined that with increasing nano silica content, the void ratio and chloride permeability decreased while the compressive strength increased. It was emphasized that with the condition of ensuring the homogeneous distribution of the nano material within the cement matrix, a high addition of nano silica such as 4% is possible and significantly improves the durability properties. [ABSTRACT FROM AUTHOR]

The number of fires in buildings and on bridges has increased worldwide in recent years. As a structural material, the strength of alkali-activated slag (AAS) concrete after exposure to high temperatures has been given much attention. However, research of its durability is still lacking, which limits the application of this type of concrete on a larger scale. In this context, as one of the most important aspects of durability, the chloride permeability of AAS concretes after exposure to high temperatures was examined in this study. The influence of the alkali concentration (Na2O%) and the modulus (Ms) of the activator, as well as the influence of heating regimes, including the heating rate, duration of exposure to the target temperature, and cooling method, was also discussed. The results show that the chloride permeability of the AAS concretes increased with temperature elevation. Due to the interference of pore solution conductivity, the influence of the Na2O% and the Ms of the activator on the chloride permeability of the AAS concretes was not made clear by using the ASTM C 1202 charge passed method; however, after exposure to high temperatures, AAS with a lower Na2O% and lower Ms has lower porosity and may have lower chloride permeability, which needs further investigation. Faster heating for a longer duration at the target temperature and water cooling reduced the resistance of the AAS concretes to chloride permeability as a result of their increased porosity. [ABSTRACT FROM AUTHOR]

Microbial-induced carbonate precipitation (MICP) technology can heal cracks in concrete materials. The development of this technology is conducive to improving the sustainability of concrete materials and alleviating the environmental burden of concrete production. In this paper, a two-component self-healing agent was prepared using porous volcanic rocks to adsorb microorganisms and mineralized substances under negative pressure conditions, and the cracks were healed under standard curing conditions. The effect of crack healing under different proportions was studied by keeping the same total dosage and modifying the proportion of the two-component self-healing agent. The results showed that the honeycomb-like pore structure of volcanic rock can adsorb a large number of microorganisms and effectively protect their activity. The maximum crack healing width was 335.4 μm after curing for 28 days. The ultimate effect of crack healing was positively correlated with the proportion of mineralized material components. The initial crack healing rate accelerated when the proportion of microbial components was increased. Nevertheless, the mineralization was constrained by the content of mineralized materials, and the maximum value of crack healing could not be achieved. The calcium carbonate precipitates produced by microbial mineralization were conducive to improving the recovery of compressive strength under pre-damage conditions and reducing the chloride penetration to a certain extent under the condition of applied current. [ABSTRACT FROM AUTHOR]

The aim of this research is to determine the effect of sodium hydroxide molarity 2M combined with variations in slag percentage, ratio of alkali activator to binder (Al/Bi), and ratio of sodium silicate to sodium hydroxide (SS/SH) on the transport properties of fly ash-slag-based GPC cured at ambient temperature. The result is increase in slag percentage and SS/SH ratio lead to a decrease in porosity, water absorption rate and chloride permeability. The alkali activator to binder (Al/Bi) ratio of 0.45 produces the lowest porosity, water absorption rate, and chloride permeability. The porosity, sorptivity, and chloride penetration depths of all GPC are lower than those of OPC. The recommended mix compositions for GPC that exhibit lower transport properties than OPC are GPC4 (slag 40%, SS/SH ratio 1.5, Al/Bi ratio 0.45); GPC5 (slag 50%, SS/SH ratio 1.5, Al/Bi ratio 0.45); and GPC7 (slag 30%, SS/SH ratio 2.0, Al/Bi ratio 0.45).

In the current study, the influence of substitution of ground granulated blast-furnace slag (GGBFS) on the characteristics of less active geopolymer binders, including pumice and the waste material produced during the washing process of sand in aggregate industries (waste soil), is investigated. The aforementioned materials were examined individually and in hybrid form. In the hybrid mixes, less-active materials (pumice and the waste soil) were replaced with GGBFS at levels of 25%, 50%, and 75%. The evaluated properties consisted of compressive strength, modulus of rupture, sorptivity, rapid chloride ion migration coefficient, and the content of water absorption. Moreover, the effects of different curing conditions on the properties were investigated. The results indicate that partial replacement of the waste soil and pumice with GGBFS leads to enhanced durability and mechanical characteristics owing to the higher reactivity of GGBFS. The mixture denoted as P25S75 (with 75% GGBFS and 25% pumice) exhibited the best durability properties, surpassing even the S100 mixture (with 100% GGBFS). Substituting the waste soil with GGBFS had a greater enhancing effect compared to the mixtures containing the pumice mixes. [ABSTRACT FROM AUTHOR]

Coal gangue has the characteristics of complex physical and chemical properties, low strength, loose and porous, which limit its extensive use in building materials. In this paper, coal gangue was modified by soaking in hydrophobic solution under uncalcining and non-prewetting conditions. The basic characteristics of coal gangue before and after modification was systematically studied, and hydrophobically modified coal gangue mass substitution rates of 0%, 30%, 50%, 70% and 100% were set. Contact angel, flexural strength, compressive strength, electric flux were used as characteristic parameters to evaluate the influence of modified coal gangue replacement rate on the basic properties of mortar under different substitution rates.Results showed that, by using the binary cooperative complementary method, when the replacement rate of modified coal gangue was lss than 50%, the hydrophobic state of the surface of coal gangue mortar could be achieved. As the replacement rate of modified coal gangue increases, the compressive strength showed a decreasing trend, the maximum decrease was 15.7% compared with none modified coal gangue added. The 28 d compressive strength was 58.5 MPa with 30% replacement rate of modified coal gangue. The electric flux was less than 250 C under different modified coal gangue replacement rate, which indicated excellent resistance to chloride permeability. When the modified coal gangue replacement rate is 30%, the electric flux was the smallest (130 C). The hydrophobic modification method could ensure good mechanical strength and resistance to chloride penetration under the condition of uncalcined and non-prewetted coal gangue, which fully utilizes coal gangue.

Numerous research has investigated the effects of blast furnace slag as a cementitious or substitute cementing material on the characteristics of concrete. Blast furnace slag cement (BFSC) shows promise in the concrete permeability domain, where this extra cementing ingredient enhances the chloride attack resistance of concrete. Four mixtures of BFSC concrete made with 0.5, and 0.6 water-to-cement ratios (w/c) were studied. The effect of using an air-entraining agent (AEA) and a change in the surface of tested samples (top, bottom, and side) on the chloride penetration and its diffusion coefficient has been investigated. The properties of fresh and hardened concrete were determined. This research has its novelty for the first time, where the chloride contents were determined through specimens' top, bottom, and side surfaces using potentiometric titration. The results indicated that the air-entraining agent and w/c ratio had inversely affected the invested concrete properties. The measured total and soluble chloride content at a depth of 20∼30 mm is less than the limits of the corrosion threshold for the three studied surfaces. Also, changes in the w/c ratio, cement content, and AEA affect the diffusion coefficient.

This research investigates the effective utilization of waste glass powder (WGP) in fly ash (FA)-ground granulated blast furnace slag (GGBS) based alkali-activated concrete (AAC) containing 100 % recycled concrete aggregate (RCA) cured at ambient temperature. FA substituted with WGP in the range of 0–25 %, and the percentage of GGBS was kept unaltered at 50 %. The influence of WGP on the strength, durability, and microstructural properties of FA-GGBS based AAC was evaluated. The experimental results showed that the strength and durability were enhanced with the increases of WGP of up to 20 %, and then started to decrease. The highest compressive strength (51.4 MPa) and ultrasonic pulse velosity (UPV) (4.35 km/s) were obtained for F30W20 (FA:GGBS:WGP - 30:50:20). In addition, sorptivity, chloride, and water permeability were reduced by 39.92 %, 56 %, and 64.13 %, respectively for optimized specimens as compared to a control sample (without WGP). Furthermore, the microstructural analysis was carried out to investigate the alteration in the mineralogical and morphology. On the basis of microstructural investigations, WGP notably enhanced the microstructure of FA-GGBS-based AAC by enhancing the formation of reaction products, including C-S-H and C-(N)-A-S-H gel. At last, this study found that CO 2 emissions, energy consumption, and cost analysis were lowered by approximately 60 %, 28 %, and 41 % compared to conventional concrete of the same quality. [Display omitted] • The co-effects of FA, GGBS, and WGP on 100 % RCA-based AAC were studied. • The highest performance was exhibited for optimized the proportion with FA: GGBS: WGP – 30:50:20. • Microstructural analyses showed densification of the matrix forming CSH, CASH, and NASH. • Environmental Impact of AAC lowered by about 60 % than conventional concrete. [ABSTRACT FROM AUTHOR]

The application of CO2 curing on sludge ceramsite may improve its mechanical properties, and then increase the corresponding corrosion resistance. In this study, the influence of CO2-cured sludge ceramsite on the strength and long-term properties of cement concrete is investigated. CO2 curing time ranges from 0 h to 2 d. The cylinder compressive strength and water absorption rate of CO2-cured sludge ceramsite are first determined. Additionally, the flexural and compressive strengths, the chloride permeability and the freeze—thaw damage, as well as the corresponding thermal conductivity of cement concrete, are tested. Furthermore, the corrosion resistance of reinforcement inner-sludge-ceramsite cement concrete is measured. Finally, the scanning electron microscope photos of sludge ceramsite are obtained. Results show that the cylinder compressive strength of CO2-cured sludge ceramsite is 15.1, ~34.2% higher than that of sludge ceramsite. Meanwhile, the water absorption rate of CO2-cured sludge ceramsite is 39.6, ~82.4% higher than that of sludge ceramsite. The compressive strength and the flexural strength of cement concrete with CO2-cured sludge ceramsite are 11.4 and 18.7, ~21.6% and ~31.5% higher than the cement concrete with sludge ceramsite, respectively. The resistance of NaCl freeze—thaw cycles, determined by comparing the mass loss rate and the loss rates of mechanical strengths, is effectively improved by CO2 curing, while the thermal conductivity of cement concrete is decreased by CO2 curing. The corrosion resistance of inner reinforcement is improved by the application of CO2 curing on sludge ceramsite. [ABSTRACT FROM AUTHOR]

Low volume Coal Bottom Ash (CBA) was introduced as a substitute for Portland Cement (PC) and Fine Natural Aggregates (FNA) in concretes that were tested for permeation performance. Carbonation and chloride resistance was measured through accelerated carbonation tests and rapid chloride tests respectively while water penetration was evaluated through capillary water absorption tests for the aforesaid concretes. This paper particularly investigates the effectiveness of CBA in regard of permeation behaviour in concrete. The experimental investigation inferred that as level of CBA increases, the resistance towards carbonation, chloride penetration and water penetration decreases to some extent for low volume alterations while higher decrements were observed for higher replacements. The joint replacement of CBA as PC and FNA for the level of 10% and 25% respectively resulted in satisfactory behaviour comparing to control concrete demonstrating the efficacy and potential of CBA for its successful application in concrete. [ABSTRACT FROM AUTHOR]

This paper evaluates the effect of the addition of nanocalcium carbonate (NC) and nanosilica (NS) on chloride-induced corrosion, chloride diffusion, chloride permeability, and service life of high-volume slag (HVS) and high-volume slag–fly ash (HVS-FA) blended concretes containing more than 70% blast furnace slag (BFS) and combined BFS and FA as the partial replacement of ordinary Portland cement (OPC). Compared to the control OPC concrete, the HVS and HVS-FA concretes containing NC and NS exhibited superior compressive strengths in all curing ages up to 365 days. Superior performance against chloride permeability, chloride diffusion, and chloride-induced corrosion are also observed in both HVS and HVS-FA concretes due to the addition of both nanomaterials. Among NS and NC, the concretes containing NC performed much better than the concrete mixes with NS. Significant extension of service life is also observed in both HVS and HVS-FA concretes by the inclusion of both nanomaterials. [ABSTRACT FROM AUTHOR]

Bacteria-prompted calcite precipitation enhances concrete strength properties and durability performance by creating nuclei crystals in the concrete pore structure. In this paper, the effect of bacterially treated sugarcane bagasse ash (SCBA)-based concrete on concrete's mechanical and permeability properties has been comprehensively investigated. The SCBA was used in concrete as a partial replacement of normal portland cement at two different replacement levels of 10 and 20%, while bacteria content was kept constant at 105 cells/mL (2.96 x 106 cells/oz.). This study used two different types of bacteria, Sporosarcina pasteurii and Bacillus megaterium from the Bacillus subtilis family. After 28 days of curing in water, the blended cement concrete with 10% SCBA showed higher compressive strength compared to the control mixture. Incorporating B. megaterium and S. pasteurii further improved the compressive strength of concrete by 7 and 10% in SCBA 10% concrete. This compressive strength enhancement is due to the continuous hydration process of cement and the pozzolanic reaction of SCBA in concrete. The addition of bacteria further improves the strength by forming calcite crystals and filling the pore spaces in the concrete. Calcite deposition in the pores of concrete subsequently refines and enhances the microstructure of concrete. The deposition of calcite precipitation in the pores blocks the water permeability, which ultimately reduces the porosity and water absorption of bacteriaincorporated concrete. The incorporation of bacteria in concrete also reduces the penetration of chloride ions compared with the control mixture and the concrete treated with only SCBA. Based on the nuclear magnetic resonance (NMR) spectroscopy analysis, the average chain length of calcium-silicate-hydrate (C-S-H) gel was increased by incorporating SCBA in concrete up to a replacement level of 10%. Further addition of bacteria increases the chain length of C-S-H gel and the degree of cement hydration in concrete. [ABSTRACT FROM AUTHOR]

The utilization of waste foundry sand (WFS) has been widely explored in conventional concrete to evaluate strength and durability properties. In this study, durability properties of self‐compacting concrete (SCC) made with various percentages (0%–30%) of WFS as a partial replacement of river sand up to the age of 365 days are investigated. Annually, more than 60 million metric tons of WFS is produced worldwide from the casting industry, creating environmental problems. The scarcity of river sand is another major area of concern that can be addressed with the utilization of WFS in concrete. Tests were conducted for fresh properties, compressive strength, water absorption, sorptivity, rapid chloride permeability, and sulfate resistance. All the SCC mixes exhibited fresh‐state properties as per EFNARC. With the incorporation of WFS up to 30% increased volume of permeable pore space (13.43%–16.67%), water absorption (2.11–3.07 mm), chloride permeability (2119–3553 C), and decreased compressive strength of sulfate‐cured samples by nearly 5% compared to water‐cured samples at 28 days of curing were observed. The concrete samples showed better performance of pore structure, permeation, sulfate attack, and chloride permeability at 90 and 365 days of curing age. It was found that cost‐effective SCC with performance comparable to the control mix could be achieved by using WFS up to 10%. [ABSTRACT FROM AUTHOR]

Environmental impact and inherit brittleness of conventional concrete can be reduced simultaneously by utilising recycled aggregates instead of natural ones and fiber-reinforcements. In this research, the effect of incorporating single steel fiber (SF) and polypropylene fibers (PPF) and hybrid SF-PPF was studied on the performance of recycled aggregate concrete (RC). Both single fibers and hybrid fibers were used at the volume fraction of 1%. Examined properties included compressive strength-fcm, flexural strength-fbm, ultrasonic pulse velocity-UPV, water absorption-WA, and rapid chloride permeability-RCP. The results revealed the use of single SF and hybrid SF-PPF in incredibly advanced the flexural performance of RC. Single SF-reinforced-RC or hybrid SF-PPF-reinforced RC showed markedly higher flexural strength than that of the conventional plain NC. The optimum compressive and flexural strength were obtained when plain NC and RC were reinforced with 0.85%SF-0.15%PPF. Flexural strength of RC reinforced with 0.85%SF-0.15%PPF was 26% higher compared to that of the plain-NC. The use of hybrid SF-PPF also reduced the water permeability capacity of RC better than the use of single SF or PPF. Hybrid fiber-reinforced RC has implications for cheaper and eco-friendly concrete than single SF-reinforced concrete.

The deterioration of reinforced concrete structures caused by chloride‐induced corrosion is a major threat to their service life. Previous studies show that defects in the steel–concrete interface have a significant impact on the corrosion process of steel bars. Study on the chloride permeability of steel–concrete interface is very important for revealing the mechanism. In this article, we devised a new experimental method named chloride penetration depth test which was used to evaluate the chloride permeability along the steel–concrete interface. Two types of fresh concretes, normal concrete (NC) and lightweight aggregate concrete (LWAC) with obviously different stability, were designed to obtain specimens of various defect sizes in the steel–concrete interface. The results show that the chloride penetration depth measured with the new method increased with the defect size in the steel–concrete interface determined by backscattered electron (BSE) imaging and nanoindentation technology, indicating that the chloride permeability of steel–concrete interface could be identified by the method we proposed. [ABSTRACT FROM AUTHOR]

Ultrapotent chemogenetics, including the chloride-permeable inhibitory PSAM4-GlyR receptor, were recently proposed as a powerful strategy to selectively control neuronal activity in awake, behaving animals. We aimed to validate the inhibitory function of PSAM4-GlyR in dopamine D1 receptor-expressing medium spiny neurons (D1-MSNs) in the ventral striatum. Activation of PSAM4-GlyR with the uPSEM792 ligand enhanced rather than suppressed the activity of D1-MSNs in vivo as indicated by increased c-fos expression in D1-MSNs and in vitro as indicated by cell-attached recordings from D1-MSNs in mouse brain slices. Whole-cell recordings showed that activation of PSAM4-GlyR depolarized D1-MSNs, attenuated GABAergic inhibition, and shifted the reversal potential of PSAM4-GlyR current to more depolarized potentials, perpetuating the depolarizing effect of receptor activation. These data show that ‘inhibitory’ PSAM4-GlyR chemogenetics may activate certain cell types and highlight the pitfalls of utilizing chloride conductances to inhibit neurons.

The goal of the current paper is to study the effect of natural pozzolana (NP) when ground to a micro and nano size on some concrete properties. Syria is rich in natural pozzolana with an estimated quantity of nearly 1 billion tonnes. Four properties, namely compressive strength, chloride permeability, chloride-induced reinforcement corrosion and acid attack on mortar, have been investigated. Six levels of micro-NP (from 0% to 50%), and nano-NP (from 0% to 5%) were added as cement replacement to produce the studied concrete/mortar mixtures. The results revealed that grinding NP to extremely fine particles has positive effects. The shortcoming related to the lower early compressive strength can be eliminated. Further, much lower chloride permeability and longer corrosion initiation times were clearly observed in the concrete containing nano-NP. The best results were obtained when NP was added at 30% or more at micro-scale and at 3–4% at nano scale. Furthermore, acid resistance particularly at the early ages of exposure was noticeably improved with such additives. SEM technique fitted with EDX analysis was employed in the current research to study the microstructure of the cement paste after being exposed to acid solutions. XRD and TGA techniques were used as well.

Cutting rock was used as the parent rock to prepare coarse aggregate for concrete, and the properties of this coarse aggregate were tested. Besides, the workability, compressive strength, elasticity modulus and chloride permeability of concrete prepared by cutting rock aggregate and conventional limestone aggregate were researched systematically. The results show that the cutting rock aggregate has high water absorption, and concrete mix prepared by cutting rock aggregate showed high slump-loss; the compressive strength of concrete prepared by two types coarse aggregate was basically the same at each age. Nevertheless, the elasticity modulus of cutting rock aggregate concrete was lower than that of conventional limestone aggregate concrete. Meanwhile, the chloride penetration resistance of concrete has little difference. It is feasible for cutting rock to be processed into bridge concrete aggregate, but it is unsuitable for preparing prestressed concrete. [ABSTRACT FROM AUTHOR]

The goal of the current paper is to study the effect of natural pozzolana (NP) when ground to a micro and nano size on some concrete properties. Syria is rich in natural pozzolana with an estimated quantity of nearly 1 billion tonnes. Four properties, namely compressive strength, chloride permeability, chloride-induced reinforcement corrosion and acid attack on mortar, have been investigated. Six levels of micro-NP (from 0% to 50%), and nano-NP (from 0% to 5%) were added as cement replacement to produce the studied concrete/mortar mixtures. The results revealed that grinding NP to extremely fine particles has positive effects. The shortcoming related to the lower early compressive strength can be eliminated. Further, much lower chloride permeability and longer corrosion initiation times were clearly observed in the concrete containing nano-NP. The best results were obtained when NP was added at 30% or more at micro-scale and at 3–4% at nano scale. Furthermore, acid resistance particularly at the early ages of exposure was noticeably improved with such additives. SEM technique fitted with EDX analysis was employed in the current research to study the microstructure of the cement paste after being exposed to acid solutions. XRD and TGA techniques were used as well. [ABSTRACT FROM AUTHOR]

This study examined low-binder ultrahigh-performance concrete (UHPC) when nanosilica (NS) and/or microsilica (MS) were incorporated in Portland cement (PC) in either binary or ternary blends. Two groups were created for this purpose, and they were divided based on the presence or absence of silica flume (SF). NS was used as a restricted substitute for cement by weight at five different percentages (0%, 0.5%, 1%, 2% and 3%). The total binder was 800 kg/m3, and the ratio of water to binder was 1:5. Results demonstrated that optimum resistance to chloride permeability, gas permeability, sorptivity, water absorption and water penetration came from the 3% UHPC sample. The ternary blends of NS, PC and SF yielded better results than binary PC and NS blends. A 1% NS replacement gave similar effects to the UHPC properties investigated as a 10% MS replacement. [ABSTRACT FROM AUTHOR]

The performance of cement-based composites in engineering applications can be effectively enhanced through the integration of polymers and the internal inclusion of CaCO 3. By incorporating nano-sized CaCO 3 , the permeability of the cement matrix is reduced, and the toughness of the high-strength cement matrix is enhanced with the addition of Styrene Acrylate Emulsion (SAE). However, the combined effect of SAE and CaCO 3 in the cement matrix is not fully understood. This research aims to shed light on the macroscopic properties, microstructures and microscopic phase compositions of SAE-modified high-strength cement-based composites (SMHCC) incorporating CaCO 3. The findings demonstrate that SAE integration markedly improves the composites' resistance to cracking and chloride ion penetration. Specifically, SAE integration increases the concentration and promotes the recrystallization of CaCO 3 , which in turn optimizes the pores in the cement matrix due to the filling capabilities of both CaCO 3 and SAE. Conversely, SAE presence slows down the cement hydration process and its role in generating CH renders the matrix more prone to damage, leading to a reduction in mechanical strength with higher SAE concentrations. [Display omitted] • The toughness and resistance to chloride permeability of SMHCC are improved. • The encapsulation effect of SAE within the cement matrix is mainly on C 2 S. • SAE can act as a nucleation site for the crystallization of CH and CaCO 3. • The pore structure is refined in the cement matrix by adding SAE. [ABSTRACT FROM AUTHOR]

To study the effect of CaO/SiO 2 and Al 2 O 3 /SiO 2 ratios on the chloride permeability of one-part alkali-activated nickel slag (AANS) concrete, the chloride ion electromigration coefficient and the distribution of total chlorine concentration at different permeability depths of the one-part AANS concrete were investigated. The ratio of CaO/SiO 2 and Al 2 O 3 /SiO 2 of cement were designed in the range of 0.85–1.3 and 0.3–0.75, respectively. The reaction product and pore structure of paste were analyzed. The Results showed that the total chloride ion concentration in concrete first decreased and then increased with CaO/SiO 2 and Al 2 O 3 /SiO 2 ratios increasing. The chloride permeability of the concrete with CaO/SiO 2 of 1.0 and Al 2 O 3 /SiO 2 of 0.45 was the lowest, as the hydration degree of the concrete was the highest, which effectively optimized the pore structure. The chloride ion migration coefficient of concrete decreased with porosity, and an exponential relationship was observed between the chloride ion migration coefficient with porosity. • The effect of CaO/SiO 2 and Al 2 O 3 /SiO 2 ratios on the chloride penetration resistance of concrete were investigated. • The chloride concentration of concrete decreased sharply along the depth, and and then the trend slowed down. • The best resistance to chloride permeability was achieved for a CaO/SiO 2 ratio of 1.0 and a Al 2 O 3 /SiO 2 ratio of 0.45. • The compressive strength and resistance to chloride permeability of concrete mainly depended on its pore structure. [ABSTRACT FROM AUTHOR]

The potential use of the electrical resistivity (p) and the saturated electrical resistivity (pS) for the durability design of new concrete structures and the forecasting for in-service concrete structures has been increasing in the past three decades. Many investigations have proven the ease of the method and the possibility of it being a quality control/assurance tool during construction of new concrete infrastructure. Some previous investigations even consider the pS test a feasible one to remove other, more complicated and expensive tests used in cement-based materials as durability indicators; a few of them defined correlations between pS and the other indexes. The present investigation uses published data to determine if empirical correlations exist between pS and rapid chloride permeability (RCP), and between pS and the apparent chloride diffusion coefficient (DAP). A literature search was done on the three durability indexes in question (pS, RCP, and DAP) and some empirical equations were derived. Good empirical correlations were observed for pS versus RCP and pS versus DAP. The latter correlation, obtained from data of different sources, supported that pS and chloride diffusivity follows the well-defined Einstein law of diffusion with minor modifications for cement-based materials. [ABSTRACT FROM AUTHOR]

• Natural antioxidants are potential 'green' mixed-type corrosion inhibitors. • Green tea is rich in natural antioxidants and was chosen as the antioxidant source. • Green tea extract formed protective layer on rebar (mixed-type corrosion inhibitor). • Protective layer formation was confirmed visually and with microscopic methods. • The layer reduced rebar weight loss and was enriched with calcium carbonate. In our previous work, we have demonstrated that at equal volume, green tea extract (GT) exhibited a higher inhibition efficiency (IE) than commercial calcium nitrite corrosion inhibitor, on corrosion of steel reinforcing bar (rebar) embedded in mortar (75–80 vs. 14–24%). GT behaved as a mixed-type corrosion inhibitor which increased rebar polarization resistance (Rp); indicating that it formed a protective layer on rebar surface. In this paper, the formation of a protective layer was confirmed with visual inspection and microscopic examinations. In presence of this layer, rebar corrosion was reduced. This is evidenced by a reduced rebar weight loss and further indicated by a similar chloride permeability between control and GT concrete, and a similar corrosion rate (CR) between control reinforced mortar and reinforced mortar incorporating solely the residual solid of GT. The similarities ruled out the plausible higher IE of GT due to an improved physical barrier of mortar/concrete against corrosion. Analyses with energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction spectroscopy (XRD), and Fourier-transform infrared spectroscopy (FTIR) suggested that the layer was enriched with calcium, specifically the calcium carbonate polymorphs. Although the formation of protective layer and increase in Rp were influenced by the magnitude of antioxidant activity, in this study GT has shown a better IE than CI. This should encourage more studies on the IE of sustainable 'green' corrosion inhibitors in concrete. [ABSTRACT FROM AUTHOR]

• Investigating chloride permeability and steel corrosion of concrete with carbonated recycled aggregate. • Chloride permeability of concrete with various qualities of carbonated recycled aggregate. • Establishing the relationship between chloride permeability and steel corrosion risk. Carbonation treatment was recently developed to enhance the properties of recycle concrete aggregate and prepared concrete, but the durability of concrete with carbonated recycled aggregate have received little consideration in the previous studies. This study investigates the chloride permeability and the resulting steel corrosion of concrete with carbonated recycled fine and coarse aggregates, and the effects of recycled aggregate quality on chloride permeability are presented. The carbonization treatment was first applied to recycled aggregate to prepare carbonated recycled aggregate; then, the chloride permeability and steel corrosion experiments were conducted on concrete with carbonated recycled aggregate. The results exhibit that carbonation treatment improves the physical performance of recycled aggregate, which results in an increase in the compressive strength of preparing recycled concrete. Concrete with carbonated recycled aggregate has a lower chloride permeability than that with non-carbonated recycled aggregate, and the improvement in the chloride permeability resistance is more obvious for concrete with carbonated recycled fine and coarse aggregates. In particular, the improvement of chloride permeability resistance becomes more distinct with the reduction of recycled aggregate quality. The addition of carbonated recycled aggregate reduces the steel corrosion risk of reinforced recycled aggregate concrete, and the chloride permeability and steel corrosion risk follow a linear trend. [ABSTRACT FROM AUTHOR]

Deicing chemical solutions can profoundly affect concrete's physical and chemical properties. It is a known fact that salt solutions are highly conductive in comparison with pure water and are expected to alter concrete's electrical resistivity as well as other transport properties. In this study, the influence of NaCl, CaCl2, and MgCl2 on transport properties of cementitious materials was investigated. The first part of the project evaluated the continuous exposure for 1 year, while the second part evaluated the wetting-drying cyclic exposure for 6 months (27 cycles). This paper presents the results of the cyclic exposure. Results obtained with standard testing methodologies can be misleading and should be interpreted with caution because transport properties were influenced by different factors, especially the exposure history. In addition, each salt affected each individual transport property differently. Cyclic exposed samples presented similar results as those subjected to 1 year of continuous exposure. [ABSTRACT FROM AUTHOR]

• Using pozzolanic materials such as RHA and TiO 2 in concrete reduce clinker consumption and the CO 2 generated. • The combination of 10%RHA and various amounts of TiO 2 improved strength and durability performances of concrete. • 3% TiO 2 nanoparticles was found to be the optimum replacement level. Sustainable development, climate change and the extensive extraction and consumption of non-renewable mineral resources are the greatest contemporary challenges facing humankind, especially construction industry. Reducing the mining and consumption of raw materials, and CO 2 emission generated by the production of Portland cement clinker as well as improving concrete performance are now achievable targets even with the use of various recycled and by-product materials in a partial replacement of virgin materials. In the present study, concrete designed with Titanium dioxide (TiO 2) Nanoparticles and rice husk ash (RHA) as pozzolanic materials used in a partial replacement of Portland cement (PC) has been investigated. RHA was used in a single amount of 10% while TiO 2 nanoparticles was incorporated at different replacement levels varying from 0 to 5% as a partial replacement of PC. The morphological and mineralogical characteristics of TiO 2 Nanoparticles were analysed using Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD), respectively. The blended cement concrete mixes have been assessed in terms of mechanical and durability performances including compressive, Flexural and Splitting Tensile strengths, resistance to Acid attack and Chloride Penetration. The results revealed that concrete mixes with a combination of 10%RHA and 3% TiO 2 Nanoparticles as a partial replacement of PC showed the highest strengths and durability performances. Increasing the TiO 2 Nanoparticles beyond 3% has resulted in a drop in strengths and durability properties. Thus, this replacement of 3% nano-TiO 2 might be considered as the optimum replacement level. [ABSTRACT FROM AUTHOR]

• Cement was partially replaced by ground granite powder (GGP) to prepare UHPC. • Strength and anti-permeability first grew then dropped with GGP replacing cement. • Autoclaved curing (AC) improved the macro performance of UHPC prepared with GGP. • GGP replacement and curing induced changes in hydration products and pore structures. • Pore structure parameters are key to determining the macro strength and permeability. Properties of ultra-high performance concrete (UHPC) which used ground granite powder (GGP) to replace cement by different ratios (from 0 to 25%) are experimentally investigated. The hydration products and pore structure on the micro scale, and the compressive and flexural strength as well as chloride permeability on the macro scale, were studied. Influence of curing conditions, i.e., standard curing (SC), warm water curing (WWC), and autoclaved curing (AC), was also explored. It was found that though the replacement of cement by GGP did not influence the morphology and chemical compositions of hydration products, however, the pore structure changed significantly over the replacement ratio, i.e., ω GGP. Compared to SC and WWC, AC can significantly improve the hydration degree of cement and promote the polymerization degree of hydration products. WWC and AC also improved the pore structure of UHPC prepared with GGP. Compressive and flexural strength as well as the anti-permeability were found to first increase and then decrease with the growth of ω GGP ; the optimal ω GGP were 5%, 10%, and 15% for UHPC specimens cured under SC, WWC, and AC, respectively. It was also found that the compressive and flexural strength are linearly related to the total porosity, while the chloride permeability is linearly related to the contents of harmful and more-harmful pores. [ABSTRACT FROM AUTHOR]

Highlights • The production of green sustainable concrete utilising ultrafine palm oil fuel ash (UPOFA) and waste plastic Polyethylene Terephthalate (PET) fibres was presented in this study. • The proportions of UPOFA were (20% and 40%) as a partial replacement of the total cement binder combined with 1% PET fibres. • The combination of UPOFA and PET fibres enhanced strength and transport properties of Ultra-High-Performance PET Green Concrete (UHPPGC). Abstract The production of green sustainable concrete with enhanced performance against severe environmental conditions by using recycle waste materials has been a primary concern for recent studies. This article reports a study on investigating the effect of incorporating ultra-fine palm oil fuel ash (UPOFA) with shredded recycled waste bottle in form of Polyethylene Terephthalate (PET) on the engineering and transport properties of ultra-high-performance concrete. UPOFA was used as a partial replacement binder in varied proportions (20% and 40%) of the total cement binder, whereas shredded recycled PET bottles were added as reinforced fibre by 1% of the total mix volume. The greatest compressive strength was registered by a combination of 20% UPOFA and PET fibre in U 20 -UHPPGC. The combination of 40% UPOFA and PET fibres in U 40 -UHPPGC mix demonstrated a superior enhancement in terms of transport properties at the age of 28 days, such as porosity, initial surface absorption, gas permeability, water permeability and rapid chloride permeability. Thus, pozzolanic UPOFA can improve the engineering and transport properties of ultra-high-strength concrete. The overall results indicated that the PET fibre reinforced with UPOFA can produce UHPPGC with promising improvements in engineering and transport properties. The incorporation of waste materials into concrete constructions can reduce cement consumption and prevent the environmental pollution with save energy at the same time. [ABSTRACT FROM AUTHOR]

Highlights • High cycle fatigue behaviors and chloride permeability of RC beams are investigated. • Chloride content at steel bar surface markedly increases at loading levels >0.3. • Fatigue loading level of 0.4, 0.45 combined with chloride corrosion reduce total fatigue life by at least 13%. Abstract High cycle fatigue behaviors (crack widths, deflections and fatigue life) and chloride permeability of RC beams were experimentally investigated. The experiment processes included initial fatigue loading followed by 3 months of NaCl solution wet-dry cycles without loading, and then fatigue life tests before chloride content measurement. The loading levels (ratio of the maximum fatigue loads over the ultimate static strength) and initial fatigue loading cycles are taken as parameters in this study. Results show that: (1) the fatigue behaviors of RC beams are greatly affected by the loading level and chloride corrosion, but they are rarely influenced by the initial fatigue loading cycles; (2) chloride content markedly increase when the loading levels exceed 0.3; (3) at the loading levels of 0.4 and 0.45, combined actions of initial fatigue damage and chloride corrosion cause at least 13% decrease of the total fatigue life; (4) initial fatigue loading cycles barely affect the residual fatigue life of RC beams when initial fatigue damage of RC beams are in the slow variation stage of damage development. [ABSTRACT FROM AUTHOR]

Highlights • Replacing cement partially by RP obtained from C&D waste to prepare RPC. • Investigating the hydration activity, compound composition and strengths of concrete with various RP contents. • Chloride permeability of RPC with and without imposed damage are determined. Abstract Some studies were developed to investigate the potential of using recycled powder (RP), obtained from the construction and demolition (C&D) wastes, to partially replace the cement in concrete, whereas the chloride permeability of preparing recycled powder concrete (RPC) has not been investigated. This paper shows a comprehensive experiment to study the fundamental characteristics and chloride permeability of RPC. The capillary salt absorption, chloride diffusion and wet-dry cycles tests were carried out on the RPC, respectively, and the chloride permeability with the coupling of freeze-thaw damage was also investigated. The results highlight the addition of RP, with a high fineness and activity, improves the hydration reaction and reduces the concrete's porosity, and the concrete compressive strength slightly increases when the RP replacement ratio is 15%. The addition of RP results in the decrease in the chloride permeability, and the concrete with 30% RP replacement ratio possesses the lowest chloride permeability. Replacing the cement by RP reduces the freeze-thaw resistance of concrete, and the imposed freeze-thaw damage further boosts the chloride permeability of RPC. Particularly, the chloride diffusion coefficient of RPC increases linearly with the decreasing of relative dynamic elastic modulus. Basing on the testing results of fundamental characteristics and chloride permeability, the suggested RP replacement ratio in concrete should be below 30%. [ABSTRACT FROM AUTHOR]

Highlights • Use of natural pozzolan as partial replacement of cement and microsilica in UHPC mixtures. • No negative impact on the key properties of UHPC due to addition of natural pozzolan. • Significant saving of microsilica and cement due to use of natural pozzolan. Abstract Ultra-high performance concrete (UHPC), comprising of high amounts of cement and microsilica as binder and micro filler, is a new generation of concrete possessing highly dense microstructure with excellent mechanical properties, durability characteristics and ductility (fracture toughness). However, the use of high amounts of cement and microsilica makes UHPC costly and environment-unfriendly. In the present study, an effort is made to study the effects on properties of UHPC mixtures due to incorporation of natural pozzolan (NP) as a partial replacement of cement and microsilica. Targeting a significant reduction in consumption of cement and microsilica without compromising the required workability, six UHPC mixtures were considered. The first mixture was taken as control mixture without replacement of cement and microsilica by NP. In the second and third mixtures, 25 and 50% microsilica was replaced by NP, respectively. In fourth, fifth and sixth mixtures, 10, 20 and 30% of cement was replaced by NP, respectively. Specimens were moist-cured for 14 days before exposing them to air in the laboratory conditions. All the six UHPC mixtures were tested to determine the mechanical properties (compressive and tensile strengths, modulus of elasticity, and fracture toughness), drying shrinkage, and chloride permeability. Test results indicate that the replacement of cement (up to 30%) and microsilica (up to 50%) by NP did not significantly affect the fresh and hardened properties of UHPC mixtures confirming the potential of using NP for producing cost-effective and environment-friendly UHPC mixtures. [ABSTRACT FROM AUTHOR]

The evolution of electrical resistivity, chemical shrinkage ？ physical and mechanical properties and chloride permeability of the Portland cement pastes with air entraining agent were studied. The results show that the air entraining agent is added to increase the fluidity of the cement pastes and prolong the setting time？ the early hydration rate and chemical shrinkage increases. With the increase of dosage of air entraining agent？ the electrical resistivity of the cement pastes increases before setting and decreases after hardened. At 28 d, the dosages of air entraining agent have a little effect on the compressive strength of the hardened pastes within 0. 04%, and its loss rate is less than 5 % ？ the chloride diffusion coefficient decreases as its dosage increases. With the change of the dosage of air entraining agent, the electrical resistivity of cement pastes has a good quantitative relationship with chemical shrinkage, compressive strength and chloride diffusion coefficient. The variation of the chemical shrinkage？ strength and chloride permeability can be predicted by the electrical resistivity development curve of the cement pastes. [ABSTRACT FROM AUTHOR]

• Inert granite powder and active mineral admixtures were introduced to prepare sustainable manufactured sand mortar. • Inert granite powder and active mineral admixtures showed synergistic effects on performance of manufactured sand mortar. • Granite powder can refine the microstructure of mortar owing to the hydration promotion and the pore filling effect. • The chloride diffusion coefficient is highly correlated with capillary pore characteristics. Granite powder (GP) and active mineral admixture including ground granulated blast furnace slag (GGBFS), metakaolin (MK) and fly ash (FA) were used to partially replace granite manufactured sand (GMS) and cement to prepare manufactured sand mortar (MSM). Synergistic effect of four mineral admixtures in MSM on mechanical properties, water absorption properties and chloride permeability was studied. Combined with the analysis of cementitious materials hydration and pore characteristics, the synergistic mechanism of four mineral admixtures was comprehensively expounded. The results show that although the synergy of GP can improve the performance of MSM, the replacement of cement by GGBFS and FA leads to the increase of water absorption and chloride diffusion coefficient and the decrease of mechanical properties. Synergistic effect of GP, GGBFS, FA and MK is greater than that of the three of them due to the complementarity of particle size and chemical composition of the four materials, which ends the situation of MSM performance reduction. [ABSTRACT FROM AUTHOR]

Durability of concrete designed for radiation shielding structures is an important issue in nuclear power plant safety. An investigation of the permeability of concrete containing heavyweight aggregates and water-bearing aggregates was performed with respect to gaseous and liquid media. Mix design was developed using Portland and slag cement, crushed magnetite and serpentine aggregate. The use of slag cement in concrete containing magnetite and serpentine aggregates resulted in the substantial improvement of the compressive strength in comparison with Portland cement concrete. The application of slag cement was found to reduce the chloride ingress, regardless of the special aggregate use. The coefficient of chloride migration was within the range 5 ÷ 8 × 10−12 m2/s and 17 ÷ 25 × 10−12 m2/s for slag cement concrete and Portland cement concrete, respectively. At the same time, the carbonation depth was increased twice for slag cement concrete in comparison to Portland cement concrete. However, the maximum carbonation depth after one year of exposure to 1% CO2 was only 14 mm for slag cement concrete, and 7 mm for reference concrete. The total pore volume evaluated using mercury intrusion porosimetry was influenced by the type of special aggregate used. It was shown that concrete with various contents of magnetite aggregate and slag cement achieved the smallest total pore volume. While serpentine coarse aggregate caused an increase in total pore volume in comparison to concrete with magnetite aggregate.

Abstract The paper presents the utilization of industrial by-products such as ground granulated blast furnace slag (GGBS) and rice husk ash (RHA) for the development of sustainable geopolymer concrete. GGBS-based geopolymer concrete mixture was prepared and the effect of adding RHA as partial replacement of GGBS, on compressive strength, split tensile strength, chloride permeability and sorptivity were investigated up to the age of 90 days. In addition, SEM, EDS and XRD tests were also performed to observe the microstructure. The results indicate the development of geopolymer concrete using GGBS and RHA with high 3-day compressive strength of approximately 60 MPa, which can replace the conventional cement concrete and thus reduce carbon dioxide emissions. Also, the increase in compressive and split tensile strength, and reduction in chloride permeability and sorptivity was observed with the inclusion of RHA up to 15% at all ages. Beyond this optimum content of 15%, RHA inclusion showed negative results. In addition, the results of microstructure analysis showed more compact and dense micrograph of geopolymer concrete with 15% RHA, due to the coexistence of polymerization products with the additional calcium based hydration products. [ABSTRACT FROM AUTHOR]

The current study investigates the effect of different percentages of steel and glass fibers on the durability of lightweight aggregate concrete. Pumice aggregates were used to reduce the density of concrete. In total, 15 concrete mix proportions were produced, for which the parameters like water absorption and chloride permeability were evaluated. In addition to this, these mixtures were exposed to hydrochloric acid, sulphuric acid, sodium sulphate solution and sea water solution to evaluate the percentage loss of weight and strength after 7, 28, 60 and 90 days. The replacement of normal aggregates with light weight aggregates in concrete decreased the strength due to higher porosity of light weight aggregates. However, inclusion of fiber increases the durability characteristics of lightweight aggregate concrete. [ABSTRACT FROM AUTHOR]

The integration and permeability of the interface between concrete layers of a dam considerably affect its structural functionality and safety. To understand the interface properties, several tests were conducted to examine the various characteristics of specimens with different layer interfaces. The mechanical property in terms of bond strength was assessed using the splitting tensile test, which was affected by interval time. On the other hand, the ultrasonic pulse test was used to confirm the influence of the interface on ultrasonic attenuation. The chloride and water permeability were also investigated by means of the rapid chloride permeability, alternating current resistance, and water permeability tests. The results of these tests proved that longer interval times lead to a weaker bond strength and higher permeability, which are harmful to layer structures. The change rules of mechanical and permeability properties were confirmed by the optical micrograph and hardness distribution of the overlay transition zone. Finally, the relationships among these tests were analyzed, and strong correlations demonstrated that the non-destructive ultrasonic pulse test and rapid electrical test could be employed to predict and evaluate the bond strength and permeability of a layered interface. [ABSTRACT FROM AUTHOR]

This paper discusses the feasibility of utilizing sugarcane bagasse ash as a pozzolanic material in the production of Ultra High Strength Concrete (UHSC). Ordinary Portland Cement was replaced with Treated Bagasse Ash (TBA) in this investigation. The replacement dosage varied from 5% to 20% by weight of cement. The effect of bagasse ash on workability, compressive strength, chloride penetration resistance and sorptivity was examined. In addition to this, the effect of different curing regimens on hardened properties of UHSC was carried out. The results proved that it is possible to produce UHSC with cylinder compressive strength more than 160 MPa by incorporating bagasse ash. Optimum replacement ratio of 15% yielded better performance in all the tests, without having any adverse effects on hardened concrete. Convincingly, 20% substitution of sugarcane bagasse ash is good enough for producing UHSC. [ABSTRACT FROM AUTHOR]