Durability of High-Performance Concretes with Pozzolanic and Composite Cements

Abstract

Pozzolanic cements with 50% fly ash, and composite cements with 25% fly ash and 25% ground granulated blast furnace slag were produced to manufacture high performance concretes. These binders are in agreement with the European standard (EN 197/1) for cements type IV/B and V/A, respectively. Unground and ground fly ash was used for pozzolanic and composite cements. Ground slag was used for composite cements. Eight different blended cements were produced and characterized by strength measurements on standard mortar bars. High performance concrete mixtures were all manufactured with a water-to cementitious material ratio as low as 0.32, a portland cement factor of 235 kg/m3, and a fly ash or slag plus fly ash content of 235 kg/m3. A naphthalene-based superplasticizer was used to produce flowing concretes with a slump in the range of 190-220 mm. A slightly higher dosage of superplasticizer was needed to compensate the slump reduction caused by the fineness increase of the blended cements. Cube concrete specimens were cured at 5 degrees C and 20 degrees C. Compressive strength was measured at 3, 7, 28, and 90 days. The 28-day compressive strength at 20 degrees C was in the range of 60-80 MPa. Early compressive strength (at 3 days) was as high as 30-40 MPa even at the lower curing temperature (5 degrees C). Carbonation and chloride penetration tests were carried out to assess the influence of the cement fineness on the durability behavior. In general, the durability of these concretes in terms of carbonation and chloride penetration is excellent. However, there is no significant improvement related to higher fineness of the cementitious materials.