Effects of using rice straw and cotton stalk ashes on the properties of lightweight self-compacting concrete

Abstract This paper presents the mechanical properties and microstructure of lightweight self-compacting concrete (LWSCC) incorporating rice straw ash (RSA) and cotton stalk ash (CSA) as a replacement ratio by weight of cement content. Seven concrete mixtures of LWSCC are prepared as a control mix without RSA and CSA. Three mixes are used with 5%, 10% and 20% RSA, and the three remaining mixes contain 5%, 10% and 20% CSA. The pumice lightweight coarse aggregate is used as a replacement for normal weight coarse aggregates with a ratio of 80%. The filling capability, segregation resistance and passing capability of fresh LWSCC are evaluated. Mechanical properties of hardened LWSCC, including compressive strength, splitting tensile strength, flexural strength, density and microstructural analysis, are measured for 28 days. Results show that the workability of LWSCC is decreased as the RSA and CSA ratios increased. By contrast, the hardened properties of LWSCC are increased as the percentages of RSA and CSA increased, except for 20% replacement ratio. The scanning electron microscope analysis shows that 10% of RSA yielded a denser concrete than the control mix.