Crack Initiation And Length Change In Modified Alkali Activated Slag Mortars

The aim of this paper was to quantify crack initiation and length change of ordinary Portland cement-based mortar and three types of alkali activated slag mortars: reference one that only slag was used as binder, the second one with same amount of slag and with shrinkage reducing admixture in amount 1 % weight of slag and the third one with 5 % weight of slag replaced by fluidized bed combustion fly ash. Czech standard sand consisting of three different fractions (fulfilling requirements of CSN EN 196-1) was used in all mixtures. The sand to binder ratio was 2: 1 and water to binder ratio was 0.40 in all mixtures. Curing and length change testing of the specimens were based on ASTM C596-07 and ASTM C490-7. After demolding and three days of water curing mortar prisms were placed in air storage for 24 days. During this period length change (shrinkage) was measured. After that the three point bending test was performed on these specimens at the age of 28 days to obtain the fracture parameters, which was determined via Double-K fracture model. The initiation of cracks during the fracture tests was also monitored by the acoustic emission method. For comparison, specimens cured in water until the age of 28 days were tested in the same manner.