Design of self-consolidating precast concrete using powdered limestone

Abstract

With their adoption into ASTM C595 and AASHTO M240 in 2012, Type IL cements which contain 15% interground limestone, have the potential to improve the environmental impact and workability of concrete, while meeting the need for cost-effective alternative supplementary cementitious materials to replace the diminishing supply of fly ash. In the precast industry, where limestone powder is blended with Type III cement, additional benefits have been recognized, including reduced abrasion leading to increased equipment longevity, as well as production of concrete with increased cohesion and improved surface finish. Although there is extensive research on the fresh and hardened properties of concretes produced with Type IL cement, there is limited research on how the amount and fineness of limestone powder blended with varying cement types can be best utilized to tailor concrete mix designs. This research compares self-consolidating concrete (SCC) mixes made with limestone powders of varying finenesses and varying limestone quantities of up to 25% cement replacement by mass. Limestone fillers from the same source were ground to finenesses ranging from 3 μm to 40 μm median particle size and blended with cements of the same base clinker but with varying fineness. These limestone blended cements were evaluated from early age hydration properties, to fresh concrete workability, and finally to long-term dimensional stability and durability. Results show that early age hydration kinetics and workability are more affected by the median particle size of the limestone powder and that later-age compressive strength, dimensional stability and durability are more affected by percent cement replacement. Existing drying shrinkage and creep models which use compressive strength to predict volume stability can be used with minor modifications to predict the long term dimensional stability of concrete mixes made with limestone blended cements. Finally, minutes long nanoindentation creep studies conducted on limestone blended cement pastes were shown to correlate with long-term creep rates of concretes made with matching cement pastes, providing a reliable and more rapid means for creep assessment.