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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]

The interfacial transition zone (ITZ) has a major detrimental impact on the structural performance of concrete. This negative impact can be modulated by introducing mineral admixtures to a concrete mix, which fill the excessive voids within ITZ and react with portlandite to form more compact products. The approach described here, consisting of characterization of phases and micromechanical modeling, enabled assessment of the effect of silica fume, fly ash, and metakaolin on ITZ thickness and strength. The proposed model was based on the Mori-Tanaka scheme coupled with an estimation of deviatoric stress within ITZ. This study suggests that silica fume is efficient in reducing ITZ thickness, while the addition of fly ash more significantly contributes to ITZ strength. Moderate replacements of Portland cement for silica fume or fly ash, up to 20%, can positively influence concrete performance; in case of metakaolin, replacement up to 10% is recommended. [ABSTRACT FROM AUTHOR]

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]

• 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]