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In this paper, the possibility of utilising coarse recycled concrete aggregate (CRCA) obtained from a construction and demolition waste (CDW) plant in Delhi to make 60 MPa self-compacted concrete (SCC) was evaluated. The CRCA was used in as-collected condition and was not processed any further. The aggregate packing (bulk) density (APD) method was adopted to prepare the SCC-CRCA mixture in order to obtain an aggregate mixture exhibiting maximum bulk density/least void content (45%). In addition, SCC was made using aggregate mixtures in which the natural coarse aggregate (NCA) was replaced with CRCA at 0%, 20% and 100% of the total coarse aggregate content by weight. The cement, fly ash, silica fume and water were kept constant for all SCC mixtures. The effects of CRCA on the flow behaviour, mechanical strength, shrinkage characteristics and microstructure properties of SCC mixtures were evaluated. The test results indicated that SCC mixtures made with up to 45% CRCA replacement can be used for structural concrete, which is higher than that recommended in Indian (20%) and international specifications (35%) for traditionally vibrated (conventional) concrete. [ABSTRACT FROM AUTHOR]

Beam-column joints are crucial load transmission zones because they face concentrated forces from both the beams and the columns. High shear and axial stresses caused by these concentrated forces in the area of the joint may result in decreased joint strength. This article proposes a new beam-to-column connection developed for precast concrete-resisting frames. Concrete mixtures are enhanced mechanically by adding nano silica as it increases compressive strength, flexural strength, and abrasion resistance. Within the concrete, it creates a solid, gel-like matrix that fills voids and strengthens the whole construction. In this study, three reinforced concrete beam-column joint specimens were cast with fly ash, the other three with nano-silica and fly ash, and one sample with nano-silica and a control mix without admixtures was cast. Specimen cast using fly ash and nano-silica is subjected to cyclic loading after 28 days of curing. A load capacity of 100 kN was imposed on the column during testing. It was observed that a gradual increase in fly ash decreased the compressive and flexural strength of the beam-column joints. This decrease in strength was addressed by adding 2.5% nano-silica. Nano silica acts as a nucleus to bond tightly with cement particles during hydration. The results showed that the flexural strength equivalent to that of a controlled specimen can be achieved by adding nano-silica at 2.5% and fly ash at 60%. The highest loading of 38.1 kN can be applied to the specimen with nano-silica without fly ash. Although a higher axial compression ratio can improve the bearing capacity and initial stiffness, it can also reduce deformation capacity and flexibility. [ABSTRACT FROM AUTHOR]

Ferrocement, a versatile building material, is becoming increasingly popular in structural and architectural applications. It is suitable for high degrees of prefabrication due to its durability, weather resistance, and relatively low cost. Additionally, there is the possibility to achieve considerable improvements in various properties of these thin structures by using some alternates. A study has been made on the behavior of ferrocement trough shaped panels (FCTSP) under static load using clay silica for partial replacement of cement and manufacturing sand for partial replacement of river sand. First, the strength characteristics of mortar cubes were determined by varying the percentage of cement with silica sand (0%, 5%, 10%, 15%, 20% and 25%). Incorporating the optimum percentage of clay silica replacement, a study on the flexural behavior of trough shaped panels reinforced with skeletal steel and wire mesh layers by replacing fine aggregates with manufacturing sand and varying the percentage of replacement was found. According to the findings, panels made with a combination of 10% clay silica sand (CSS) replaced for cement mix and 50% manufacturing sand (MS) replaced for the fine aggregate used in FCTSP showed better results in mechanical properties and microstructural bond behavior. [ABSTRACT FROM AUTHOR]

One of the main problems with hydraulic structures is that floating silt, gravel, ice sand, boulders, and other materials circulating over a concrete surface have an abrasive effect that causes hydraulic structures to abrade. Abrasion causes concrete to degrade, which could eventually expose the reinforcing to corrosion. In addition to section loss, reinforced concrete hydraulic structures' endurance may also be a problem. Repair mortars are used to restore surfaces that have been abraded. The suitability of various repair materials for use as a repair layer on concrete surfaces is examined in this study. In order to apply different repair mortars to concrete specimens and subject them to abrasive forces, this work employs an experimental methodology. The ASTM C 1138 standard was followed for testing the abrasion resistance of the samples repaired using repair mortars underwater. Both silica fume mortar and polymer-modified mortar were employed in the study as forms of repair mortar. For each type of repair mortar, three cylindrical concrete specimens were cast, along with control specimens. Hence, nine cylindrical concrete samples in total were employed in this study. In order to quantify the effect of abrasion and, consequently, to assess the efficacy of various repair materials, abrasion volume loss was measured. Important findings about each type of repair material's resistance to underwater abrasion are included in the study. The findings show that in terms of abrasion resistance underwater, the polymer-modified mortar performs better than the silica fume mortar. [ABSTRACT FROM AUTHOR]

This paper introduced a new concrete composites made by quaternary binder by partially replacing ordinary Portland cement (OPC) with different percentages of supplementary cementitious materials (SCMs). The motivation is to reduce our dependency on OPC to reduce CO2 emission and carbon foot print. As the main substitute for the OPC, siliceous fly ash was used (FA). Moreover, silica fume (SF) and nanosilica (nS) were also used. This study utilized the following contents of SCMs used: 5% of nS; 10% of SF; 0, 15, and 25% of FA. During examinations the main mechanical properties of concrete composites, i.e. compressive strength (fcm) and splitting tensile strength (fctm) were assed. The brittleness of these materials was also analysed. Based on the conducted studies, it was found that concrete composite based on quaternary blended cements, of series Mix3, has shown the best results in terms of good strength parameters, whereas the worst mechanical parameters were characterized by concrete of series Mix4. On the other hand, concrete including only SF and nS (Mix2 series) were characterized by the greatest brittleness. It was observed that fcm of concrete composites for series Mix2, Mix3, and Mix4 increase of 41%, 48%, and 31% respectively compared with the concrete without additives, i.e. series Mix1. In addition, fctm also increase of 39%, 47%, and 30%, respectively, for the three series mentioned above, compared with the control concrete. Concrete of series Mix3, with high mechanical properties and demonstrating the features of quasi-plastic material, i.e. having lower brittleness, can be used in concrete and reinforced concrete structures subjected mainly to dynamic and cyclic loads. Therefore, it can be used, in the construction of foundation structures for machines and other types of structures in which the above-mentioned loads are dominant. [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]

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]

The paper describes the mechanical behavior of fine recycled concrete aggregate (FRCA) concrete according to the mineral admixtures. Three types of the mineral admixtures, i.e., fly ash (FA), ground-granulated blast-furnace slag (GGBS), and silica fume (SF), are used and the replacement ratios of FRCA are 50% and 100%. The dosages of the admixtures of FA, GGBS, and SF are determined with the normal dosage (30%, 40%, and 5.0%, respectively) based on the ACI committee reports (No. 232, 233, and 234) and half-normal dosage. The mechanical performance is investigated with the compressive and splitting tensile strength, and elastic modulus. Additionally, the total porosity is measured in natural fine aggregate (NFA) and FRCA 100% replaced specimens by mercury intrusion porosimetry (MIP) for investigating the relationship with the compressive strength. Based on the experimental test results, the mineral admixtures improve the mechanical performance of FRCA concrete. The effective dosages of FA, GGBS, and SF for FRCA concrete are investigated according to the replacement ratio of the FRCA. In particular, FRCA 100% replaced concrete may be possible to be used for the structural concrete members with the specific dosage of the mineral admixtures. The prediction of the splitting tensile strength and the elastic modulus by the codes or previous formulas exhibits underestimated and overestimated results, respectively. The relationship between the total porosity and the compressive strength of the FRCA concrete should be modified with more experimental tests. [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]