Pozzolanic Potential and Mechanical Performance of Wheat Straw Ash Incorporated Sustainable Concrete

Abstract

The pozzolanic potential, mechanical strength, and stress-strain behavior of a locally available wheat straw ash (WSA) as a partial substitute of cement was evaluated in this study. Various samples of a locally available wheat straw were burnt to ashes at three distinct temperatures and characterized through X-ray powder diffraction and energy dispersive X-ray spectroscopy. The WSA obtained from burning at 550 °C was found highly amorphous and possessed suitable chemical composition to be used as pozzolanic material. The burned WSA was grounded to achieve the desired fineness and mortar cubes and concrete cylinders were cast by substituting 15%, 20%, 25%, and 30% cement with it. The strength of mortar and concrete decreased with increasing amounts of WSA except for those containing 15% WSA, where it slightly increased than the respective control samples at later ages, i.e., 28 and 91 days. Despite reduced strength at high replacements (20%, 25%, and 30%), the strength activity index values met ASTM C618 requirements for pozzolanic materials. Moreover, the compressive strength of concrete containing 20% WSA exceeded to that of control concrete at 91 days. The stress-strain relation of concrete containing 15% to 20% WSA also showed comparable stiffness and toughness to those of control samples at all ages. Particularly, the concrete containing 15% WSA showed significant improvement of strength, stiffness, toughness, and ductility at 91 days. Lastly, the results of mechanical strengths and pozzolanic reactivity were successfully validated indirectly by measuring the porosity of mortars and thermo-gravimetric analysis of cement pastes, respectively. Based on current findings and their validation, WSA can be used as a substitute of cement up to 20% in the production of sustainable normal strength concrete for their application in common domestic building projects.