Hollowcore slab with alternative cementitious materials for winter conditions

The precast industry, due to its specific early-age strength requirements for hollowcore (HC) slab products, has been reluctant to introduce alternative cementitious materials such as ground granulated blast-furnace slag (GGBS) due to the slower strength development of such materials. This paper reports on a study undertaken at a precast production facility to examine how to overcome the consequences of strength loss due to the replacement of up to 50% of CEM I (42·5R), as usually used in cold weather conditions, with GGBS, for environmental or durability reasons. The GGBS concrete slabs were activated using thermal, chemical and mechanical means to enhance their early-age strength gain. The results were compared at early ages in terms of the temperature profile during curing, cube compressive strengths, load-carrying capacities for transportability requirements, ultimate load and short-term creep. In addition, 28 d densities and strengths were compared for in situ cubes and cores extracted from HC slab samples. The experimental results showed a favourable potential for replacing CEM I (42·5R) cement with up to 50% GGBS in winter without compromising on factory productivity.