Evaluation of Portland-Limestone Cement Concretes Containing High Volume of Fly Ash

There is a global initiative aimed at reducing the impact of humans on the environment of which the concrete industry is a large part. In order to achieve this, current focus is being placed on the use of portland-limestone cements. U.S. standards currently allow for a replacement of portland cement clinker up to 10% and an increase to 15% is being considered. Canadian standards currently allow the use of 15% limestone and Europe the maximum allowed is 35%. This research compares the performance of concrete produced using portland-limestone cement with Type I/II portland cement. Additionally, high volumes of fly ash were incorporated in order to determine its effect on concretes made with portland-limestone cement. Six concrete mixtures were designed: one control mixture using Type I/II portland cement with a companion mixture incorporating portland-limestone cement, and four mixtures replacing portland-limestone cement with 30%, 40%, 50%, and 60% Class F fly ash. Testing of the fresh and hardened properties was conducted including slump, air content, unit weight, compressive strength, modulus of rupture, modulus of elasticity, and permeability. Both concretes containing 100% Type I/II cement and portland-limestone cement (PLC) performed similarly. Acceptable strengths at 56 days of age were found in mixtures with up to 50% portland-limestone cement replacement with strengths substantially decreasing at 60% fly ash. Permeability was found to decrease with increasing percentages of fly ash indicating that the use of High Volume Fly Ash (HVFA) in PLC concretes resulted in concrete mixtures that were more durable than the concrete mixtures containing no fly ash.