Investigation of shrinkage and compressive strength developments of concretes made with type GB cements

This paper presents the results of an ASA sponsored experimental program conducted at Monash University to study the shrinkages of concrete containing blended cements (Type GB) and their compressive strength developments. The mixtures were based on a typical Grade 40 concrete with 80 mm slump. The mixtures included two types of cements (Type GP and SL) and four types of supplementary cementitious materials, namely, three types of slag and one type of fly ash. Type GB cements with slag/Portland cement ratios of 35/65, 50/50 and 65/35, slag/flyash/Portland cement ratio of 35/20/45, fly ash/Portland cements ratio of 20/80 and 100% Portland cements were tested. Altogether 28 concrete mixtures were tested up to 182 days for drying shrinkage and compressive strengths. In addition to the standard tests, a modified shrinkage test was carried out to measure the shrinkages between 0, 1, 3 and 7 days. Concretes containing slag-blended cements exhibited expansion strains between 1 and 7 days. No appreciable expansions were observed in concretes made with 100% Type GP cement or GP/fly ash blends. The mixtures containing 65% slag demonstrated lower shrinkages than the 35% and 50% blends. Addition of 20% fly ash made little difference to the shrinkage or compressive strength developments. When shrinkages are measured from 1-day, rather than 7-days according to the current standard, the concretes made with slag-blended cements demonstrated lower shrinkages. This is due to the expansions of these concretes during the 1 to 7 days period, which are not registered in the standard shrinkage tests.