One of the primary approaches being explored to produce more sustainable concretes consists of replacing a significant portion of the portland cement with industrial by-products. In high volume fly ash (HVFA) concretes, for example, the nominal goal is to replace 50 % of the portland cement in a conventional concrete with fly ash. While these mixtures typically perform admirably in the long term, often exceeding the strength and durability of their pure portland cement concrete counterparts, they sometimes suffer from early-age performance issues including binder/admixture incompatibilities, delayed setting times, low early-age strengths, and a heightened sensitivity to curing conditions. Recently, investigations have indicated that the replacement of a portion of the fly ash in these concrete mixtures by a suitably fine limestone powder can mitigate many of these early-age problems, specifically the undesirable delays in setting times. This paper will present the results of a recent study that investigated the production of concrete mixtures where either 40 % or 60 % of the portland cement is replaced by fly ash and limestone powder, on a volumetric basis. Mixtures based on both Class C and Class F fly ashes have been investigated. The mixtures are characterized based on measurement of their fresh properties, heat release, setting times, strength development, rapid chloride permeability metrics and surface resistivity. The limestone powder not only accelerates the early age reactions of the cement and fly ash, but also provides significant benefits at ages of 28 d and beyond for both mechanical and transport properties. These ternary blends exhibit a high degree of potential as the binder phase for the sustainable infrastructure concretes of our future.
Proceedings Title: Green Cements
Conference Dates: April 14-18, 2013
Conference Location: Minneapolis, MN
Conference Title: American Concrete Institute Spring Meeting
Pub Type: Conferences
Constructability, fine limestone powder, high volume fly ash concrete, setting, sustainability.