Effects of various additives on the crumb rubber integrated geopolymer concrete

The use of scrap tyres in construction materials has been promoted to curb the environmental exploitation caused by the open disposal of non-biodegradable waste rubber. Tyre grinds as aggregates in geopolymer concrete (GPC) would increase its sustainability value by reducing the consumption of natural aggregates. Although there is limited literature addressing the damage to GPC characteristics caused by rubber aggregates, this investigation was designed to determine the extent of possible side effects of using crumb rubber (CR) in GPC. Additionally, this investigation aims to address any resulting reduction in strength and durability using additives such as cement and fibres. Geopolymer specimens with CR replacement of fine aggregates by volume (0, 5, 10 and 15%) showed a compressive strength reduction of up to 17% when tested according to ASTM standards. Substituting the total binder by weight with Ordinary Portland cement (OPC) (0%, 5%, 10%, 15%, and 20%) improved the microstructural integrity of the rubberised geopolymer mix with the highest percentage of OPC. Despite producing new and additional binding products (CSH and CASH gels), the GPC surface readily disintegrated under acid exposure. Optimum glass fibres (GF) reinforcement (0.30%) effectively disrupted the GPC pore network, consequently reducing the acid permeability of the matrix. Further addition of steel fibres (SF) enhanced the GPC specimen's compressive and flexural strength. To analyse the cumulative effect of these additives on GPC microstructure, supporting tests such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy were carried out. Although these additives enhanced the overall performance of rubberised geopolymer, it might somewhat reduce its green aspect

Enhancing the Durability Properties of Sustainable Geopolymer Concrete Using Recycled Coarse Aggregate and Ultrafine Slag at Ambient Curing

This study aimed at investigating the durability characteristics of the ambient-cured geopolymer concrete (GPC) developed using recycled coarse aggregate (RCA) and ultrafine slag (UFS). Two series of mixes were prepared. Natural aggregates (NAs) were replaced by RCA at different volume levels of 0, 25, 50 and 100% in both series. Meanwhile, UFS was added as a replacement by volume of fly ash at varying levels of 0, 15, and 30% in the first series, while UFS was used in addition to fly ash by percentage weight of fly ash at the levels of 0, 15, and 30% in the second series. The compressive strength, water absorption, chloride ion penetration, and carbonation depth of the developed ambient-cured GPC were studied. In addition, creep and drying shrinkage of the specimens were also examined. It was found that the compressive strength increased with the UFS content, while the opposite trend was observed with increasing RCA%. The highest compressive strength obtained with 100% RCA was 40.21 MPa (at 90 days), when 30% UFS was used in addition to fly ash. The addition of UFS not only helped in improving the strength characteristics but also provided an alternative to heat curing, which is a major drawback of GPC. Furthermore, the negative effects of RCA can also be minimised by adding UFS, which can be used as a compensator to RCA to improve the durability characteristics. The experimental results prove that susceptibility to chemical, water and chloride attacks can be mitigated by incorporation of UFS, and durable GPC can be produced by using RCA and UFS

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

Quantitative Assessment of Soil Salinity Using Electromagnetic Induction Technique and Geostatistical Approach

Not AvailableAssessment and monitoring of soil salinity is prerequisite for proper and timely decisions on reclamation and management of saline soil. Electromagnetic induction (EMI) method could be a cost effective and rapid method for assessment of soil salinity at large scale. EM-38, an instrument works on electromagnetic induction methods, was used for assessing spatial variation of soil salinity. Survey was carried out in vertical (EMV) and horizontal (EMH) modes at 200 m × 200 m grid spacing over 48 ha area of subsurface drainage site at village Mokhrakheri located in Rohtak district in Haryana, India. Based on the survey readings of high, moderate and low apparent conductivity, soil samples were collected from 8 sampling location points in field at 15 cm depth increment up to 90 cm depth for calibrating EM-38 observations. The soil samples were analyzed for soil salinity (ECe), cations (Ca2+, Mg2+ and Na+), anions (CO3 2-, HCO3 - and Cl-) and SAR using standard procedures. Sodium (Na+) and chloride (Cl-) ions were strongly correlated with apparent conductivity (EMV and EMH) measured by EM -38 as well as soil salinity (ECe). Therefore, Na+ and Cl- ions were mainly responsible for observed salinity in the field. Multiple regression analysis model based apparent conductivity (EMV and EMH) strongly predicted soil salinity (ECe). Quantitative evaluation of soil salinity for 0-90 cm profile indicated that more than 91% area of the field had salinity levels (ECe) above 4 dS m-1. It has been concluded that EM instrument is a reliable and rapid method for characterizing soil salinity at large scale for employing proper and precise reclamation measures for its effective utilization.Not Availabl

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