Utilization of high volumes of unprocessed lignite-coal fly ash and rice husk ash in self-consolidating concrete

• Unprocessed FA and RHA were combined as raw materials in the production of SCC.
• Portland cement was partially replaced with 0%, 20%, 40%, and 60% by volume FA.
• Fine aggregate was also replaced with 0%, 25%, 50%, 75%, and 100% by volume RHA.
• RHA could be used at a level of up to 25% and still main satisfactory workability.
• FA at 20% and RHA at 25% exhibited a compressive strength of SCC more than 40 MPa.

This paper describes a study undertaken to explore the use of a high volume of lignite coal fly ash (FA) as a replacement for Type I Portland cement (OPC) and a high volume of rice husk ash (RHA) as a replacement for fine aggregate in the production of self-consolidating concrete (SCC). OPC was partially replaced with 0%, 20%, 40%, and 60% FA by volume, and fine aggregate was replaced with 0%, 25%, 50%, 75%, and 100% RHA by volume. Mixtures were designed based on a slump flow diameter of 70 ± 2.5 cm. The workability properties (i.e. slump flow, T50 cm slump flow time, V-funnel flow time, and J-ring flow) and hardened properties (i.e. compressive strength and ultrasonic pulse velocity) of SCC were determined, and a blocking assessment was performed. Increasing the FA or RHA content beyond a certain level reduced the compressive strength and increased the water requirement of the SCC mixture. However, up to 60% FA could be used to produce SCC with a compressive strength of 40–50 MPa. In addition, RHA could comprise up to 25% of the SCC, which is an acceptable value of compressive strength according to the Building Code Requirements. Moreover, partial replacement of OPC by FA and fine aggregate by RHA can result in substantial cost savings and alleviate environmental problems.