Cement-based materials with oil shale fly ash additives

Abstract

Experimental studies on the influence of oil shale fly ash additives on thermal expansion, strength, shrinkage, and heat release of concrete were carried out. The addition of 30% fly ash over cement content increases the thermal expansion by 6 times. The addition of 40% fly ash increases the thermal expansion by 16 times. The expansion is due to the high free calcium oxide content (10%) in the fly ash and the high sulfuric acid anhydrite SO3 content (10.3%). The anhydrite forms a highly expanding calcium hydrosulfoaluminate upon reaction with tricalcium aluminate cement in an unlimited amount of water. The oil shale fly ash addition above cement content significantly reduces shrinkage. If the ash content is higher, then the shrinkage decreases more. Shrinkage is on average 1.3 times less at a 30% fly ash content, and shrinkage is 1.8 times less at a 40% fly ash content. The fly ash has a higher sorption capacity than cement. Samples with the oil shale fly ash addition absorb more moisture than mixes without fly ash. Oil shale fly ash increases the compressive strength. If the fly ash content is 30% by weight of cement, then the compressive strength is higher than if the fly ash content is 40% by weight of cement for all concrete hardening periods. The flexural strength of mixes containing the fly ash turned out to be lower than the flexural strength of the mix without fly ash in the initial period of up to 15-22 days. Mixes with fly ash content in the amount of 30% and 40% by weight of cement exceeded the flexural strength of the mix without fly ash, respectively, by 24 and 17%. The fly ash addition provides a calmer, extended in time heat release with low self-heating of concrete in the initial period from 1 to 3 days. That is especially valuable for the thermal crack resistance of concrete.