Wpływ mikrokrzemionki na mikrostrukturę i odporność betonów na pękanie

Results of investigations into the effect of silica fume addition on the fracture toughness of dolomite concretes and their structure have been presented. Silica fame, in the amount of 10 % of the cement mass, was added to the concrete in two ways: on the aggregate side (by removing sand) and on the paste side (by substituting 10 % of the cement mass with silica fume). Fracture toughness tests were carried out according to Mode n (shearing). Silica fume added to the concrete caused the formation of a compact cement paste structure with a small number of structural defects, which resulted in obtaining higher values of stress intensity factors, as compared to concretes without a silica fume addition. A particularly evident increase in occurred in the concrete with silica fume added on the aggregate side (without removing the cement). Microstructural examinations showed that in concretes with silica fume added cracks developed through the aggregate grains - the so called transgranular fracture formed. Both the cement paste itself and the aggregate-cement paste interface had higher toughness than that of dolomite grains. In concretes with no silica fume added, cracks developed in the cement paste with passing round coarse dolomite grains - the over-grain fracture formed.