Effect of rice straw ash and palm leaf ash on the properties of ultrahigh-performance concrete

The global expansion of agricultural production has increased the amount of agricultural waste (AW). Accordingly, AW should be disposed of properly to preserve the environment. This study focuses on using rice straw ash (RSA) and palm leaf ash (PLA) as partial replacement for cement in the production of ultrahigh-performance concrete (UHPC). In particular, this research investigates the effect of using RSA and PLA as pozzolanic materials on the microstructure and the fresh, mechanical and physical properties of UHPC. Eleven UHPC mixtures are prepared as control mixtures without RSA and PLA. Five mixtures are used with 10%, 20%, 30%, 40% and 50% RSA, whilst five residual mixtures contain 10%, 20%, 30%, 40% and 50% PLA. Results indicate the efficiency of RSA or PLA as a partial substitute (i.e. 20% of cement weight), with mechanical properties and durability better than those of the reference mixture. The microstructure analysis shows that 20% RSA or PLA yields denser concrete than the control mixture. The UHPC samples with 20% RSA and 20% PLA achieve the best results of 188.5 MPa and 185 MPa by increasing compressive strength by about 13.2% and 11.1%, respectively, compared with the control mixture at a test age of 28 days. Important mechanical properties, such as splitting tensile strength, flexural strength and modulus of elasticity, exhibit a trend similar to that of the compressive strength results for all the UHPC mixtures. The average values of splitting tensile strength and flexural strength at 28 days are about 11% and 14% of the compressive strength of the same UHPC mixtures, respectively. The significance of the current study is the relatively high cement replacement percentages of up to 50% by weight and the use of AW as replacement materials.