Investigation into the structural, durability, and thermal behavior of paddy stubble ash as a cementitious replacement for sustainable concrete

In light of the increasing population leading to climatic changes across the globe, it has become imperative to dispose of waste materials, both organic and inorganic, bionic and non-bionic, to mitigate all aspects of environmental pollution, that is, land, water, and air. One method is to reuse such waste in the construction industry, which is also a major contributor to environmental pollution, in various forms, viz., admixture, additive, and reinforcement. In the present investigation, paddy stubble ash (PSA) was prepared by burning the stubble within an enclosure subjected to isothermal heating. The ash was found to comprise more than 60% silicon, aluminum, magnesium, and oxygen, confirming it as a pozzolanic material. The assay was followed by replacement of ordinary Portland cement (OPC) at 5%, 7.5%, and 10%. The structural properties of the lightweight concrete blocks, such as compressive strength and durability, were investigated following the IS 516:1959 (Reaffirmed 2018) and IS 456:2000 (Reaffirmed 2021) standards, respectively. At 7.5% replacement, the compressive strength had the highest value of 25.27 MPa, 30.61 MPa, and 34.28 MPa for 7 days, 28 days, and 56 days of curing, respectively, and that of the 10% replacement was the lowest. The scanning electron microscope (SEM) micrographs revealed uniformity in calcium silicate hydrate (C–S–H) gel formation during the hydration process for the concrete mix compositions. The energy-dispersive X-ray analysis (EDAX) and X-ray diffraction (XRD) elemental analysis showed dominance of calcium (Ca) and its compounds in PSA-incorporated concrete, as well as in the control concrete after 28 days and 56 days of curing. The thermogravimetric analysis (TGA) reveals significant mass loss for control concrete and 5% PSA-replaced concrete, whereas with the 7.5% and 10% PSA-incorporated concretes, the mass loss was found to be reduced because of better moisture absorption.