Behaviour of mortar and concrete made with activated blast furnace slag cement

Activated blast furnace slag cement (ABFSC) was used as binder in mortar and concrete. A commercial pelletized slag, produced for use in the construction industry, was activated with sodium sulphate, sodium carbonate, or sodium silicate; and both normal curing and heat curing were used. Laboratory results of the effect on strength development of activator dosage, water-binder ratio, curing temperature, duration of heat curing, chemical admixtures, and the use of fly ash or silica fume in a slag replacement role are presented. It was found that there was an optimum dosage of sodium carbonate and sodium sulphate for maximum strength utilizing either curing regime, and this dosage was found to correspond approximately to the fully saturated activator solution concentration. However, for sodium silicate ABFSC, strength continued to increase well beyond this point and this activator proved to be the most effective. Although the strength of the ABFSC mixtures benefited from heat curing, the response depended mainly on the type of activator and the duration of curing; increased curing temperature had only a modest effect. With only one exception, chemical admixtures were found to be ineffective when used in ABFSC mixtures. Both fly ash and silica fume increased workability, and silica fume also increased medium term strength of the sodium sulphate activated mixtures. The results show that ABFSC mortar and concrete provide strengths comparable to, or better than, similar ordinary portland cement mixtures, given similar paste content, water content, and curing conditions. Compared with ordinary portland cement mixtures, the early volume stability of ABFSC mixtures was found to be lower, and both drying shrinkage and cracking due to hardening were found to be greater.