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Polypropylene fiber (PPF)-based concrete incorporating carbon nanotubes (CNTs) has garnered significant attention in recent literature. However, determining the optimal content of PPF and CNTs remains crucial. Therefore, this study employed response surface methodology (RSM) to systematically optimize the ideal content and interaction between PPF and CNTs, with the aim to achieve the highest concrete strength and impact resistance. Following the recommendation of the ACI committee 544, the drop-weight impact test procedure was refined and utilized to assess the concrete's impact resistance. The study findings revealed that concrete incorporating optimal proportions of PPF (0.3 %) and CNTs (0.1 %) exhibited significantly enhanced strength properties and impact resistance compared to the control sample. The enhancements in compressive, tensile, and flexural strengths were measured at 29 %, 75 %, and 64 %, respectively. Furthermore, the impact energy consumption at the first and failure cracks was significantly higher, i.e., 1433.82 J and 2016.32 J, respectively, compared to 89.61 J for the control concrete. Scanning electron microscopy analysis revealed ribbed calcium silicate hydrate structures with CNTs, which were identified as the primary factor fortifying the stiffness and strength of the concrete matrix. This suggests that the inclusion of both CNTs and PPF holds promise for advancing the development of sustainable concrete materials with improved strength and impact resistance in the future. • Response surface methodology effectively optimized polypropylene fiber and carbon nanotube content. • Concrete with 0.3% polypropylene fibers and 0.1% nanotubes showed remarkable strength and impact resistance. • Strength improvements recorded: 29% in compressive, 75% in tensile, and 64% in flexural. • Utilizing scanning electron microscopy, ribbed calcium silicate hydrate structures with carbon nanotubes were identified. [ABSTRACT FROM AUTHOR]

In this study, the bonding strengths of three different types of externally bonded composite systems were investigated under different environmental aging conditions at high temperatures, and the finite element model for a roof fire and concrete slab fire from above evaluated if the beams were externally reinforced with fiber-reinforced polymers (FRP). An FRP system is a structural reinforcement made of a type of fiber reinforcement fixed to a concrete surface through an epoxy adhesive. The bonding strength between the FRP and concrete substrates was measured using a pull-off test machine, as described in the EN 1542 standard. This study aims to determine the deterioration and negative effects of miscellaneous high temperatures on externally bonded FRPs used for strengthening civil structures. Epoxy-bonded carbon fiber-reinforced polymers (CFRP), glass fiber-reinforced polymers (GFRP), and basalt fiber-reinforced polymers (BFRP) were exposed to various temperatures of 23°C (control conditions), 70, 85, 100, 115, 130, and 150°C. Duratek® AV21 epoxy-based lamination system was used as an adhesive between the concrete and the FRP sheet. Three bonding failure modes (adhesive, cohesive, and substrate) were investigated for each test. The results were compared for three different types of FRPs under various temperatures, which is also significant research on the heat aging of the degradation process. The test results were also evaluated using finite element (FE) software modelling for roof and slab fires exposed from above, where the beams under the slab were reinforced with FRP systems. The test pull-off test results and FE model thermal analysis results were evaluated to obtain the temperature rise in the critical section of the concrete beam/slab in existing retrofitted buildings. The FE model results showed a critical temperature rise on the beam-slab corner connection as a result of the fire above the concrete slab. The duration of the FRP systems effectively bonded to the concrete beams located under different slab thicknesses and pull-off results were evaluated at elevated temperatures. • Pulloff testing was used for different FRP/Epoxy systems (CFRP, GFRP, BFRP) used for adhesion when exposed to elevated temperatures. • Experimental tests of pulloff tests conducted at temperatures from 23°C to 150°C. • ANSYS Finite Element modelling of fire above the RC slab with a beam strengthened with FRP system evaluted for a critical temperature and duration. • The critical temperature was found for pulloff strength 150°C at the critical section of beam/slab section. [ABSTRACT FROM AUTHOR]

This study offers a thorough analysis of the efficiency of adhesively bonded Carbon Fiber-Reinforced Polymer (CFRP) patches in reinforcing concrete structures. In the dynamic field of civil engineering and infrastructure maintenance, utilizing modern materials and innovative techniques is crucial. Given the diverse stresses on concrete structures, sustainable reinforcement strategies like CFRP patching are vital. CFRP patches, with their high tensile strength and lightweight properties, reinforce concrete, enhancing its load-bearing capacity. The study reviews extensive literature on CFRP use, emphasizing its effectiveness in various environments. However, prevailing analyses often overlook shear-induced failures at the interface of bonded CFRP patches. To address this, the study introduces a novel fracture analytical technique, consolidating material parameters for assessing CFRP patch bonding efficiency. Experimental investigations compare epoxy, polyurethane, and silyl-modified polymers under mode-I loading conditions, revealing performance variations. The study underscores the importance of adhesive selection, advocating for a balance between strength and fracture energy absorption for optimal CFRP patch performance in concrete structures. It urges future design applications to consider these findings for enhanced selection and application of CFRP patches. [Display omitted] • Adhesive effectiveness varies among epoxy, polyurethane, and silyl-modified polymers. • Crack propagation in CFRP-patched concrete is influenced by adhesive choice. • Hybrid adhesive formulations show promise in enhancing patching performance. • Selecting the right adhesive is crucial for optimizing CFRP patching efficacy. • Future research should focus on exploring hybrid adhesive technologies for sustainable infrastructure development. [ABSTRACT FROM AUTHOR]

Reinforced concrete structures exposed to chemical attacks require special repair mortar with specific features to work in a corrosive environment and interact effectively with the damaged substrate concrete. In this study, various geopolymer mixtures containing nano-SiO 2 (0%, 1.0%, and 2.0% binder weight replacement) and polypropylene (PP) fibers (0%, 0.3%, and 0.6% volume fractions) were tested to evaluate bonding properties when exposed to 5% concentration of sulfate attack. The research analyzed diverse bond tests, such as the shear bond strength and tensile bond strength. The substrate layer chosen for the study was normal concrete, on which the geopolymer mixtures were used for repairing. These mixtures were then cured in an environment containing sodium sulfate. A comparison was made between the bond specimens cured in sulfate solutions and a reference mixture cured in a water tank. Although the mortar samples subjected to sulfate attack showed more shrinkage than samples cured in water, the normalized results revealed that sulfate solutions curing for geopolymer mixtures containing 1.0% nano-SiO 2 causes a higher bond strength (both tensile and shear) as compared to the reference mixture in water curing. • Experimental tests on the bonding of geopolymer repair materials in aggressive sodium sulfate environments. • Effects of NS and PP fiber on geopolymer repair mortar's fresh and hardened properties. • Effects of NS and PP on the shear and bond properties between geopolymer and normal concrete substrate. • The shrinkage of the samples cured in a sodium sulfate solution is more significant than in water. • The addition of 0.6% PP fibers and 2.0% NS nanomaterials improved the tensile bond strength. [ABSTRACT FROM AUTHOR]

The structural foundations in southern Iran face a formidable challenge due to extensive corrosion. To enhance concrete strength and durability, the construction industry in this region typically incorporates micro silica at a rate of 8% by weight of cement. Nonetheless, given that a significant amount, around 70%, of the concrete expenses in these projects can be attributed to micro silica, and the cost of natural pozzolan in proximity to project sites amounts to only 10% of the price of micro silica, the primary goal of this study is to investigate the durability of concrete incorporating both micro silica and natural pozzolan. The aim is to potentially replace a portion of the micro silica with natural pozzolan while maintaining the required durability and strength of the concrete as specified in the project requirements. To achieve this, eight different concrete mix designs were proposed and subjected them to assessments of compressive strength and various durability standard tests, including water absorption, resistance to rapid freezing and thawing, water permeability, chloride migration coefficient, electrical resistivity, and electron microscopy (Scanning Electron Microscopy (SEM)/Energy Dispersive X-ray Spectroscopy (EDS)/MAPPING). The obtained results indicated that the concrete sample containing 4% micro silica and 12.5% natural pozzolan exhibited similar characteristics to the project's mix design with 8% micro silica in terms of the durability and distribution of permeable spaces within the material. In addition, concerning the pozzolanic reaction, one kilogram of micro silica is nearly comparable to three kilograms of natural pozzolan. Moreover, despite the non-uniform nature of the concrete environment, the EDS and MAPPING results, obtained through random sampling of study points, closely mirrored trends observed in other controlled experiments. • Raising the proportion of natural pozzolan in the concrete up to 25% enhances the durability of reinforced concrete. • The mixture with 30% natural pozzolan displays the most significant reduction in compressive strength. • 4% micro silica + 12.5% pozzolan blend excels in durability and compressive strength compared other mixtures. [ABSTRACT FROM AUTHOR]

In this work, novel calibration curves and calibration surfaces of Electromagnetic (EM) characteristics are modeled as a function of the water and chloride contents of concrete. An experimental campaign was carried out on cores extracted from two types of concretes: C1 (Ordinary Portland Concrete) and C3 (62% slag + 38% clinker). The cores were initially saturated at three sodium chloride (NaCl) concentrations and then oven-dried to attain different degrees of saturation. They were tested with the electromagnetic and electrical cell to determine the dielectric permittivity and electrical resistivity, respectively, at the targeted hydric and chloride ion contents. The calibration curves and calibration surfaces, which represent the resistivity and permittivity as a function of chloride content and/or degree of saturation, were adjusted and presented for both concretes. The calibration surfaces developed herein serve as an essential tool to study complex phenomena, such as the coupled water-chloride ingress. • Developing novel calibration curves and calibration surfaces that correlate the permittivity and resistivity of concrete to its chloride and water content. • Investigating the impact of slag on the permittivity and resistivity of concrete. • Proposing a non-destructive methodology to monitor chloride and water content for reinforced concrete structures exposed to a tidal zone. [ABSTRACT FROM AUTHOR]

Sulfur dioxide (SO 2) is the primary pollutant in industrial atmospheres, leading to significant damage to industrial buildings. The corrosion caused by SO 2 in concrete, including neutralization and solid phase volume expansion, poses particular concerns. However, there is a lack of research on the electrochemical behaviour and corrosion mechanisms of reinforcing bars embedded in concrete. This study conducted indoor simulations of reinforced concrete specimens exposed to industrial SO 2 corrosion utilizing an SO 2 testing chamber. The corrosion behavior of the reinforcing bars was monitored through half-cell potential, weak polarization, and electrochemical impedance spectroscopy (EIS). Additionally, the corrosion mechanisms of the reinforcing bars under SO 2 exposure were investigated using scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD), and Raman spectra. The results demonstrated a consistent correlation between variations in corrosion potential (E corr) and corrosion current density (i corr) of steel rebars in different types of concrete. The corrosion rates of the reinforcing steel in C1 (w/b=0.57), C2 (w/b=0.47), and C3 (w/b=0.37) concrete exceeds 0.1 μA/cm2 after 42, 72, and 90 days of SO 2 corrosion, respectively. At this time, the ratio of the depth of neutralization to the thickness of the protective layer is 0.51–0.65. The rust exhibits a layered structure with a presence of S elements adsorbed and deposited on the surface of the rust layer. Moreover, the research has identified the accumulation of S elements within corrosion pits, which can be attributed to localized acidification reactions. The rust products identified include iron hydroxide (FeOOH), and iron oxide (Fe 2 O 3), rozenite (FeSO 4 ·4 H 2 O). The formation of FeSO 4 ·4 H 2 O in corrosion pits suggests that significant localized corrosion on the surface of reinforcing bars in concrete under the impact of SO 2. ● Simulate typical industrial SO 2 corrosion environments. ● Surface analysis reveals the corrosion mechanism of steel rebars in concrete. ● Corrosion products contain ferrous sulphate hydrates. [ABSTRACT FROM AUTHOR]

• Development of structural concrete at low molarities 4 M and 6 M of NaOH. • The effect of different curing conditions on compressive strength is assessed. • Effect of composition on mechanical and durability properties is assessed. • The study results indicate the possibility of multi-parameter optimization. The present study explores the application of low molarity geopolymer concrete for structural applications. In this context, 35 compositions with 4 M and 6 M NaOH concentrations have been developed to yield compressive strength ranging from 10 to 40 MPa. The flow values at low water to binder (w/b) ratio are shown to be influenced by molarity of NaOH while it remains range bound at higher w/b ratio. The effect of curing conditions reveals low reactivity rate under ambient conditions with significant enhancements at elevated curing conditions. Three compositions with compressive strength of 30 ± 2 MPa have been further investigated for tensile strength, elastic modulus, plastic strain, sorptivity and chloride migration. The results reveal that despite similar compressive strength, the mix compositions have significant impact on the fresh and hardened properties indicating possibility of multiparameter optimization. The development of low molarity geopolymer concrete with possibility to optimize other structural/durability parameters in addition to compressive strength would enhance sustainability, economy and structural performance of geopolymer concrete. [ABSTRACT FROM AUTHOR]

• The adequacy of rapid chloride migration test (RCMT) of concrete was assessed. • Natural marine environment results were compared with RCMT results. • A chloride penetration resistance classification was proposed according to the RCMT. • A service life range was suggested for the RCMT classification. This paper analyses the use of the rapid chloride migration test (RCMT) in assessing the long-term chloride penetration resistance of concrete in real marine environment. Based on extensive experimental data, RCMT results were related to the diffusion and penetration properties of a wide range of normal weight and lightweight aggregate concretes, 5-year exposed under real submerged (XS2) and wetting and drying (XS3) conditions. Most usual structural concrete with different water/binder, types of aggregates and binders were covered. Concretes were ranked in terms of their chloride durability performance in real environment and a new classification was proposed to evaluate the durability of concrete to chloride attack. Classes were established based on service life prediction analysis. Overall, it is shown that the RCMT classification can distinguish the resistance to the chloride penetration of different concretes under distinct exposure environments, allowing for an expeditious method to evaluate the concrete quality. [ABSTRACT FROM AUTHOR]

• The mechanical properties of specified-density concrete under static and dynamic compression were studied. • Specified-density concrete had superior dynamic mechanical properties. • The differences in the failure modes and mechanisms of specified-density and ordinary concrete were analyzed. • The dynamic increase factor (DIF) and an energy absorption model of specified-density concrete were established. • A dynamic constitutive model of specified-density concrete was established. As a green alternative building material for aggregates and admixtures in concrete, domestic waste incineration tailings recently have gained increasing attention from the scientific community, and can improve the sustainability of building materials. This paper studies the performance and mechanism of the specified density concrete reinforced by waste incineration tailings under dynamic impact, focusing on the influence of the dosage (25, 50 and 75 wt%) and the intermediate strain rate (20–80 s-1) of the incineration tailings, and the feasibility of using them as the lightweight aggregate in the specified density concrete. The results show that the failure morphology of the static and dynamic mechanical properties of the specified density concrete (SDC) is similar, and the failure crack passes through the weak interface between the tailing lightweight aggregate and the ordinary aggregate mortar. The addition of incineration tailings is conducive to improving the anti-impact properties of specified density concrete under intermediate strain rate. Due to the internal and external interlocking structure effect of aggregate, the dynamic increase factor (DIF) and energy absorption (ω s) of three types of specified density concrete (SDC-25, SDC-50 and SDC-75) are 79.6%∼99.1% and 1.09 ∼ 1.79 times higher than that of ordinary concrete respectively, and the degree of fragmentation, peak stress and peak strain are significantly improved. The dynamic constitutive equation of specified density concrete with good applicability is proposed and successfully applied to numerical calculation. Considering the engineering performance and potential economic benefits of specified density concrete, incineration tailings can be used as a sustainable and cost-effective substitute for some cement-based materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nano-additives accelerated the self-healing of the textile reinforced concrete (TRC). • Decorating the textile surface with micro silica particles accelerated the self-healing process and enhanced TRC tensile strength and toughness. • Salt-cured TRC samples showed more fine cracks than tap-water-cured which promotes the self-healing process. Textile reinforced concrete (TRC) is an attractive alternative to the classic steel rebar reinforcement since the textile is stronger, more flexible, and non-corrosive compared to steel. Moreover, the TRC approach promotes the formation of multiple thin cracks pattern upon loading instead of a few wide cracks in rebar reinforcement. We found that the self-healing of these multiple thin cracks was accelerated by modifying the concrete matrix (addition of crystalline additive and alumina nanofibers) and by decorating the carbon-based textile with micro silica particles. Exposing the TRC samples to a saturated NaCl environment (as in coastal constructions) improved the bonding strength between the textile and the matrix, hence increasing the self-healing capability (compared to samples cured in tap water). [ABSTRACT FROM AUTHOR]

Textile-reinforced mortar (or textile-reinforced concrete, TRC) may be used to repair and/or strengthen structural elements of existing construction works (buildings, bridges, etc.) or may be used as constituent elements of new structures. When structures are subjected to fire, they are simultaneously submitted to high temperatures (potentially up to 1200 °C) and mechanical loadings. The elevated temperature thermomechanical behaviour of TRC remains both poorly understood and poorly studied. This study describes the experimental identification, at the macroscale level, of the thermomechanical behaviour of two TRC composites. It shows that the thermomechanical behaviour of two TRC composites is nonlinear and progressively evolves with the increase of the temperature level. The evolution of certain characteristics (the ultimate stress, the stress corresponding to the loss of linearity of the first zone of the stress/strain curve, the stress corresponding to the start of the post cracking stage, the maximum thermomechanical strain, the initial stiffness, the stiffness of the post cracked composite) of the studied materials as a function of the temperature levels will be identified. When temperature levels vary from 100 °C to 300 °C, the main parameters (the ultimate stress, the stress corresponding to the loss of linearity of the first zone of the stress/strain curve, the stress corresponding to the start of the post cracking stage, the initial stiffness, the stiffness of the post cracked composite) of the studied materials are in general gradually decreased with the increase of the temperature level. The influence of a grid and chopped strand textile reinforcement on the cement based composite under thermomechanical loading is analysed and discussed. The experiments show a clear difference between the thermomechanical responses of two TRC composites. Additionally, the cracked specimens are examined. [ABSTRACT FROM AUTHOR]

• Concrete expansion due to expansive additives in reinforced concrete has been studied. • Expansions decrease in restrained directions but remain unchanged in the free direction. • Volumetric expansion decreases with an increase in the reinforcement ratio. • Expansion characteristics of expansive concrete have been compared with that of ASR and DEF. Expansive additives in higher dosages induce chemical prestress in concrete by imparting higher early-age expansion. However, induced stress and concrete expansion can vary significantly, depending on different restraint conditions. In addition, concrete expansion can be highly anisotropic depending on the nature of external restraints and boundary conditions. Experimentations have been performed to study the effect of uniaxial (anisotropic) restraint on the concrete expansion (in both restraint and stress-free directions) and induced prestress. A higher degree of restraint resulted in a substantial decrement in the longitudinal expansion. In contrast, expansion in the stress-free (lateral) direction was not much affected by the restraint in other direction. As a result, an overall decrement in the volumetric expansion was observed with an increase in the reinforcement ratios. Stress induced in concrete due to the restraint expansion in the longitudinal direction was found to be higher for a higher reinforcement ratio. Data provided from the current work can be used for the comprehensive modelling of expansive concrete under external restraints. [ABSTRACT FROM AUTHOR]

Highlights: [•] Corrosion inhibitors’ performance is assessed through a probabilistic calculus of the design service life of RC structures. [•] Two types of inhibitors are analyzed: added as an admixture to fresh concrete (AACI) and surface applied migrating (MCI). [•] All cases show an increase in the design service life values with the influence of corrosion inhibitors. [•] RC elements’ performance depends on: inhibitor type; surrounding environment; whether structures are new or existing. [ABSTRACT FROM AUTHOR]

Highlights: [•] The anticorrosion behavior of modified hydrotalcites (MHTs) was evaluated. [•] MHTs have a twofold beneficial effect against chloride-induced corrosion. [•] Ion-exchange between chloride and aminobenzoate reduced free chloride concentration. [•] Critical chloride concentration for initiating corrosion was increased by MHTs. [•] MHTs could be a promising additive of concrete for improved corrosion protection. [Copyright &y& Elsevier]

• - Reducing cement content of concrete, while keeping its mechanical performance by using nano additives. • - Increasing the activity and surface area of NC through chemical exfoliation in addition to thermal activation. • - The enhancement ratios in compressive, splitting and flexural strengths of concrete reached to 33%, 13% and 70% respectively. • - The highest gain in the mechanical performance was obtained from NC modified concrete. It is known that nanomaterials have been broadly employed worldwide as reinforcements for the production of high-strength and high mechanical performance concrete-based structures. Hereinafter, high-performance concrete (HPC) modified with three types of additives were synthesized: exfoliated nano clay (NC), nano-silica (NS), and hybrid particles [silica fume (SF) & limestone (LS)]. The compressive, splitting tensile and flexural strengths, were investigated at 28 days of hydration. The exfoliated NC was simply prepared via exfoliating the thermally activated ordinary clay with the aid of organic ammonium chloride. The results revealed that all types of the employed additives provided an augmentation in the mechanical properties of the hardened concrete mixes especially the mixes with a cement content of 350 kg/m3. Furthermore, the addition of 6% NC has improved the compressive strength of concrete with 350 kg/m3 by 17.06%, the splitting tensile strength by 7.32%, and the flexural strength by 13.21%. Furthermore, the compressive, splitting tensile and flexural strengths of the same concrete were enhanced by 9.57%, 12.1%, and 32.87% respectively, by adding 3% NS. Finally, incorporating (7.5% SF + 2.5% LS) led to an increase in the compressive, splitting tensile and flexural strengths of concrete by 10%, 2.64%, and 51.14%, correspondingly. [ABSTRACT FROM AUTHOR]

Abstract: It has been widely reported that self-compacting concrete mixtures usually show improved durability characteristics as compared with normally vibrated concretes with the same cement content and the same w/c ratio. The main target of this research is the evaluation of the durability properties of medium strength self-compacting concretes and their comparison with those measured on reference normally vibrated concretes. Eight different self-compacting mixtures were produced using different types of cements and aggregates. The durability properties assessed were the water absorption, the carbonation resistance and the chloride induced corrosion resistance. These were compared with the relevant properties measured on normally vibrated concretes of the same strength class. The coefficients calculated were used to estimate the service life of reinforced concrete structures. The results indicated that self-compacting mixtures have a significant impact on the extension of the service life of concrete structures, especially when carbonation is considered as the main aggressive factor. [Copyright &y& Elsevier]

Abstract: This work aims to validate the design assumptions by the California Department of Transportation in order to better define the strategies used to design concrete structures with adequate corrosion mitigation and thus a “maintenance-free” service life. To this end, various laboratory tests were conducted to investigate the compressive strength of and chloride diffusivity in mortar and concrete samples with cement partially replaced by various minerals (class F and class N fly ash, ultra-fine fly ash, silica fume, metakaolin, and ground granulated blast-furnace slag), the porosity of mineral concretes, the freeze–thaw resistance of mineral mortars in the presence of deicers, and the effect of supplementary cementitious materials on the chloride binding and chemistry of the pore solution in mortar. [Copyright &y& Elsevier]

Abstract: Sodium leak in fast breeder reactor, either from pipe in inert equipment cells or inside the reactor cavity may come in contact with the limestone sacrificial layer on structural concrete. Experimental studies are carried out to investigate thermal and chemical impact of sodium on the limestone concrete under different test conditions. Sodium pool is maintained at different temperature on the test blocks placed in leak tight test chamber. The temperatures at different locations, pressure, release of hydrogen and oxygen gas are monitored online during the experiments. On-set time and residence period for energetic thermal transients (ETT) along with peak and average heat generation rates are evaluated. Chemical parameters such as rate and extent of water release from concrete, sodium consumption, sodium hydroxide production and sodium emission into argon atmosphere are also elucidated. Preliminary analysis of test results revealed that when hot sodium at 500°C reacts on cold concrete block, it monotonically cools down with low degree of interaction. However, supply of external heat to sodium pool triggers considerable reaction with or without occurrence of ETT phase. [Copyright &y& Elsevier]

• Biochar collected from a wood waste pyro-gasification plant for energy generation. • Biochar addition in structural concrete in 4 percentages, up to 10 % by wt. of cem. • Influence of biochar on microstructure of the cement-based composite. • Experimental evaluation of fresh and hardened physical and mechanical properties. • Improvement of concrete mechanical properties for additions up to 5%. The environmental impacts of cement and concrete industries are increasingly taken into consideration by regulatory agencies and new solutions must be found to turn into more sustainable productions. The use of waste materials as partial replacement of cement and/or aggregates or also as fillers into cement-based admixtures is a possible way to reduce the related negative impacts, such as carbon dioxide emissions and raw materials consumption. This work explores the possibility of using biochar, a carbon-rich and porous solid by-product resulting from thermochemical conversion of residual biomass under controlled conditions, as filler in concrete for structural use. The biochar used in this study derives from a commercial plant, which produces energy from pyro-gasification of woodchips. Biochar is at first chemically and morphologically characterized, then it is added as filler in concrete in different percentages, up to 10% by weight of cement. The effects of its introduction on fresh and hardened physical and mechanical properties of concrete, as well as on the internal matrix microstructure, are evaluated and compared to a reference concrete. Different curing conditions (wet and dry) and curing times (up to 365 days) are processed, also in order to evaluate biochar effect on concrete in terms of internal curing action and long-term behavior. [ABSTRACT FROM AUTHOR]

• The exposure data of concrete placed on both sides of the deicing salt highway for 20 years were obtained. • The long-term performance of concrete exposed to the high-cold environment has been explored. • The mechanism of concrete resisting the diffusion of iodine ions under different water-cement ratios was studied. • The influence of different mineral admixtures on the concrete resistance to the iodine ions diffusion was conducted. • The microstructures and hydration products of concrete at different impact factors were investigated by XRD and SEM-EDS. The low temperature of ice and snow all year round in Sweden leads to the common use of deicing salt to melt the roads, but the splash of the deicing salt on the reinforced concrete (RC) on both sides of the roads brings about the deterioration of the durability of RC components. The chloride ions diffusion coefficient is an important parameter to evaluate the durability of RC. By adopting the rapid chloride migration method (RCM) and replacing chloride ions with iodide ions, the samples of concrete blocks exposed on the side of the highway for 20 years were taken. This is directly beneficial to study the influence of the type, content, and water-cement ratio of mineral additions on the diffusion and distribution of iodide ions in concrete and analyze the surface environmental effect depth of concrete. The influence of chloride ions on the pore structure and microscopic morphology of concrete also were studied by scanning electron microscope-energy dispersive spectrum and X-ray diffractometer. The results show that as the water-cement ratio increases, the surface environmental effect depth of concrete and the diffusion area of iodide ions gradually increase. Silica fume and ground granulated blast furnace slag (GGBF slag) have an impediment to the diffusion of iodide ions, especially with the high volume of the GGBF slag (about 50%), the diffusion of iodide ions is very low. In general, this research is helpful to provide some empirical ideas and suggestions for the manufacturing and durability design of concrete structures in marine environments or deicing salt road environments. [ABSTRACT FROM AUTHOR]

Self-compacting concrete is one of the special concretes that flow in its own weight, which is used in the densely reinforced concrete structures. This concrete requires higher binder content. Higher cement content leads to uneconomical design, higher heat of hydration, higher shrinkage, etc. These factors can be counteracted by addition of mineral admixtures. Hence, Fly ash (30%) and micro silica fume (10%) are mineral admixtures replaced with cement. Concrete is having a poor flexural properties; this can be enhanced by using fibrous materials. Addition of steel fibres improves the strain softening property of composite system. Hence hooked ended micro steel fibres are used in this study. In order, to study the fresh and mechanical properties of SCC, totally eight mix (M1 to M8) designs are developed using Nan Su proposed method of mix design, with varying steel fibres (0.0%, 0.25%, 0.50% and 0.75%) and varying binder content. To evaluate the impact of steel fibres in reinforced concrete; four mixes (C-1 to C-4) of prism dimension 0.1 m × 0.15 m × 1 m were cast with optimized steel fibres and mineral admixtures content and tested using standard UTM. The key properties such as deflection, strain softening and effect of orienting the steel fibres along the direction of flow of concrete were studied. Later the experimental work was virtually modeled and analyzed using ABAQUS. In rheological study, the mix containing mineral admixtures showed better fresh concrete properties. Addition of fibres reduced the flowing ability of SCC. There is no significant change in compression strength due to addition of steel fibres. Flexural strength increased by 63% by addition of 0.75% of steel fibres. The SEM analysis helped to study the hydration process and morphological behaviors in concrete structures. The statistical analysis were carried out and regression equations have been developed for the better understanding in the field of micro steel fibre-reinforced self-compacting concrete containing admixtures. Stress-Strain behavior of mix C3 and C4 is more linear compared to C1 and C2, due to presence of micro steel fibres, which is arrested the development of micro-cracks. C4 shows better strength compared to C3, showing steel fibres are aligned align the direction of flow of concrete in between the reinforced structures. The analyzed theoretical model, developed used ABAQUS showed similar displacement results. [ABSTRACT FROM AUTHOR]

• Wood based biochar is explored as admixture in concrete under normal and elevated temperature. • Biochar-concrete exhibits improved water tightness and mechanical strength than control. • Addition of biochar minimize internal damage to concrete micro-structure than control and concrete with 10% silica fume. • Biochar-concrete shows higher strength restoration and lower water intrusion, by 22–25%, compared to control mixes. Although many inorganic fillers have been explored as supplementary cementitious admixtures, there is limited exploration into role of porous biochar, prepared from lignocellulosic biomass, in modifying mechanical and durability performance of structural grade concrete exposed to elevated temperature. This study investigates the effect of biochar particles, prepared by pyrolysis of woody biomass at 500 °C (BC 500), on mechanical strength (compressive, flexural and split-tensile strength) and permeability properties of concrete under normal condition (only wet-curing) and after exposure to high temperature (300 °C and 550 °C in this study) at 28-day age. Biochar was added at 0.50%, 1% and 2% by weight of cement in concrete. Thermal damage was inflicted to 28-day wet-cured concrete samples by placing in an electric kiln with residence time of 1 h (at steady state) and ramp rate of 5 °C/min. The strength and permeability performance of biochar-concrete composite were compared with plain concrete and concrete with 10 wt% silica fume (SF 10%) exposed to similar conditions. The findings show that addition of 0.50 wt% and 2 wt% of BC 500 increase 28-day compressive strength of concrete by 16% and 9% respectively compared to control mix, while 2 wt% addition led to reduction in permeability by 40%, measured by water sorptivity and water penetration test. After exposure to elevated temperature, addition of 1–2 wt% BC 500 to concrete is found to minimize thermal damage and retain 20% and 11% higher strength compared to control and concrete with silica fume respectively. Investigations show that biochar addition leads to lower damage to microstructure of concrete during thermal treatment, leading to 22–25% higher water tightness compared to control mix. The findings suggest that biochar from wood waste can be applied as a sustainable admixture and alternative to silica fume in order to improve compressive strength and durability of structure exposed to high temperature. Nevertheless, this can be also be an effective means to valorize lignocellulosic waste for high value construction applications. [ABSTRACT FROM AUTHOR]

Abstract: This discussion focuses on the feasibility of using non-hydrophilized and hydrophilized carbon, polypropene, basalt and kaoline fiber to reinforce the aerated autoclave concrete (AAC). It is shown that the four kinds of fibers are not appropriate for reinforcing AAC on the account of high thermal conductivity, no resisting alkali or high temperature, although they are appropriate for reinforcing concrete. [ABSTRACT FROM AUTHOR]