EFFECT OF ADDITION OF CaO ON COMPRESSIVE STRENGTH OF HIGH-VOLUME FLY ASH CONCRETE

Abstract

When released into the environment as solid waste, the by-product of coal called fly ash (FA) produced by coal-based electric power plants is detrimental. A further 8% to 10% of the worldwide anthropogenic emissions are produced by cement manufacturers. These issues may be resolved with high-volume fly ash (HVFA) concrete. HVFA concrete technology refers to employing fly ash instead of cement in the concrete mix to reduce the manufacturing of cement. But when the amount of fly ash in the concrete mix increases, the concrete’s compressive strength gradually decreases. The objective of this research is to determine the mechanical properties such as the compressive strength of HVFA concrete and compare it to the strength of the control concrete by adding Calcium Oxide (CaO) as an activator. Besides this, this research has another objective to reduce the use of cement in construction by replacing it with fly ash and making an environmentally friendly form of emission of CO2 while producing cement for the cement industry. In this research, different percentages of FA such as 20, 40, 50, 60, 70, and 80 percent are adopted replacing cement in concrete mixes with and without CaO. For this, cylindrical molds with dimensions of 100 mm × 200 mm were used for preparing concrete specimens. For each percentage of HVFA concrete mixtures, 3 (three) molds were cast without the activator and the same with the activator (2% of the binding material). A total of 117 concrete specimens were cast for the compressive strength test. These molds were cured using the water-curing technique. For determining mechanical properties, the compressive strength tests after 7, 28 and 56 days were conducted. Comparisons were made between the compressive strengths of HVFA concrete with and without the activator. These outcomes were contrasted with the compressive strength of the molds of conventional concrete. The early results for the compressive strength of HVFA concrete are extremely poor. The HVFA concrete’s 28-day compressive strength test results demonstrate a much higher compressive strength than the 7-day strength. However, the HVFA concret’s 56-day compressive strength test results were more satisfactory. According to this research, long-term water curing effectively boosts the compressive strength of HVFA concrete. Additionally, the use of CaO as an activator in HVFA concrete results in a minimum of 2 MPa higher compressive strength compared to HVFA concrete without the use of an activator. This result was therefore satisfactory for concrete with the activator content for up to 60% HVFA.