Development of low-carbon recycled aggregate concrete using carbonation treatment and alccofine

Since the construction industry is one of the major sectors responsible for the overexploitation of natural resources and the production of greenhouse gases, there is an urgent need to adopt a sustainable and environmental friendly approach to mitigate climate degradation. Research has explored the potential of recycled aggregate (RA) as a viable alternative to natural aggregate in concrete production. Currently, several treatment methods are being employed to enhance the efficient incorporation of RA into concrete, aiming to address this issue. However, the effective utilization of RA in place of NA remains uncommon. In this study, an effort has been made to develop a low-carbon recycled aggregate concrete by utilizing 100% carbonation treated recycled coarse concrete aggregate (CRCCA) in place of natural coarse aggregate (NCA) and alccofine as mineral admixture. A comprehensive analysis was performed, comparing the properties of CRCCA to those of untreated recycled coarse concrete aggregate. This analysis covered changes in weight, bulk density, water absorption, crushing value, and microstructure. Furthermore, five different concrete mixes were prepared, each varying in the proportion of natural coarse aggregate (NCA), untreated RCCA, and CRCCA. These mixes also incorporated alccofine as a mineral admixture. The evaluation process involved assessing the effectiveness of carbonation treatment and alccofine addition through tests on the workability, water absorption, density, and compressive strength of the concrete mixes. The study demonstrated that carbonation treatment of RCCA resulted in substantial improvements in crushing value and water absorption of CRCCA, alongside enhanced workability, reduced water absorption, and increased density in CRCCA concrete. Moreover, CRCCA concrete exhibited notable compressive strength gains at both 28 and 90 days compared to untreated RCCA concrete. Furthermore, the use of CRCCA and alccofine contributed to reducing GHG emissions associated with cement production, emphasizing the environmentally friendly attributes of this low-carbon concrete formulation

Genetic affinities of the Jewish populations of India

Due to the lack of written records or inscription, the origin and affiliation of Indian Jewish populations with other world populations remain contentious. Previous genetic studies have found evidence for a minor shared ancestry of Indian Jewish with Middle Eastern (Jewish) populations. However, these studies (relied on limited individuals), haven’t explored the detailed temporal and spatial admixture process of Indian Jewish populations with the local Indian populations. Here, using large sample size with combination of high resolution biparental (autosomal) and uniparental markers (Y chromosome and mitochondrial DNA), we reconstructed genetic history of Indian Jewish by investigating the patterns of genetic diversity. Consistent with the previous observations, we detected minor Middle Eastern specific ancestry component among Indian Jewish communities, but virtually negligible in their local neighbouring Indian populations. The temporal test of admixture suggested that the first admixture of migrant Jewish populations from Middle East to South India (Cochin) occurred during fifth century. Overall, we concluded that the Jewish migration and admixture in India left a record in their genomes, which can link them to the ‘Jewish Diaspora’

Durability of ternary blended concrete incorporating rice husk ash and calcined clay

Research on the combined substitution of supplementary cementitious materials (SCMs) has already demonstrated that it might be one of the few viable options to produce low-carbon concrete at scale. This paper presents an experimental investigation on the performance and durability of rice husk ash (RHA) and calcined clay (CC) in ternary blended concrete exposed to chloride attacks under wet/dry cycles. Portland cement (PC) was replaced by RHA and CC up to 50% by weight to produce low-carbon concrete. Samples were subjected to wet/dry cycles in 3.5% NaCl water, with mineralogical composition and microstructure development before and after exposure analysed by TGA-DSC, MIP, XRD, and SEM. The durability of the concrete against wet/dry cycles was investigated in terms of compressive strength, water absorption, open porosity, density, thermal conductivity, and electrical resistivity. The results showed that concrete mixes with CC and RHA up to 60% exhibited an increase of 33% in compressive strength, followed by minimal changes in water absorption. While a decrease in electrical resistivity was measured in all samples with RHA and CC, increasing the CC content to 50% resulted in improved resistance to chloride penetration. Increasing the CC content resulted in a more refined microstructure, with an overall decrease in porosity of up to 32% compared to the control series. While RHA alone did not contribute to significant improvements after wet/dry cycles, the combined substitution of RHA and CC at SCM replacement levels of 60% showed an overall improvement in hardened properties and durability. This investigation provides valuable insights into the long-term performance and strength of innovative low-carbon concrete

Durability studies on conventional concrete and slag-based geopolymer concrete in aggressive sulphate environment

As a potential substitute to conventional concrete, slag-based geopolymer concrete can be a promising material towards green and low carbon building approach. However, the lack of understanding of its performance subjected to sulphate environment can prohibit its use to some extent. This study examines the properties of conventional concrete exposed to a severe sulphate environment in comparison with slag-based geopolymer (SGPC). Plain cement concrete (PCC) also known as conventional concrete was cast using ordinary Portland Cement (OPC) as a binder. The durability of both types of concrete was examined by immersing test specimens in sulphate solutions (for varied salt concentrations of 2 and 4 g/l) for different curing ages up to a year. The performance of both types of concrete was studied for both mechanical and durability properties. Mechanical properties included compressive, tensile and flexural strengths (FS), while durability consisted of sorptivity, chloride diffusion, corrosion, EDS and SEM studies. The outcomes of this study revealed that the compressive (CS) and split tensile strengths (STS) of both OPC and SGPC decreased with the increase in magnesium sulphate salt concentrations and curing age. After being exposed to a 4% sulphate solution for 365 days, a decrease in the compressive strength was observed by 36.53% in SGPC and 55.97% in OPC, and a similar trend was found for the FS and STS. Rapid chloride permeability (RCPT) and sorptivity test results showed an increased diffusion with age and thus supported the findings of the compressive strength. Micro-structural properties were also studied, and observations showed that the formation of Sodium alumino-silicate hydrate (N–A–S–H) and Calcium alumino-silicate hydrate (C–A–S–H) was more obvious with the curing age in SGPC. At the same time, C–S–H gel formation decreased in conventional concrete with an increase in sulphate salt concentration. The cumulative effect of all these factors led to a much higher corrosion rate of rebars embedded in conventional concrete than in SGPC. Therefore, slag-based geopolymer concrete performed better than conventional concrete in an aggressive sulphate environment for all curing periods

Mechanical and microstructural properties of fly ash-based engineered geopolymer mortar incorporating waste marble powder

The marble processing industry produces a large volume of unmanaged waste in the form of microfine marble particles, usually referred as waste marble powder (WMP). Unregulated and open disposal of WMP has adverse effects on the environment. Marble is usually rich in calcium content, which can be used in geopolymer technology, thereby enhancing its recycling value. This research sought to determine the viability of WMP as a supplementary binder and polymerisation potential of its high calcium content (55.96%). For this purpose, WMP was used as fly ash replacement by weight (0, 5, 10, 15 and 20%) in geopolymer mortar (GPM) while other mix proportions are kept the same. The results indicated that WMP substitution adversely affected the water absorption (WA), ultrasonic pulse velocity (UPV), compressive and flexural strengths of engineered GPM. The mechanical strength trends were supported by, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy tests, which revealed that the calcium content of WMP showed poor alkali activation. Marble particles remained unreacted in the GPM matrix and failed to form additional geopolymeric compounds as Ca/Si ratio was found to consistently decrease with higher WMP substitution. Accordingly, WMP can be used in geopolymers in combination with siliceous binder (fly ash) without significantly reducing the mortar mechanical properties and thus the resulting GPM can find broad applications in practice