Mechanical Properities Of Alkali Activated Slag At Low Temperature

This thesis presents results of detailed investigations about the effects of low and subzero temperature on the mechanical properties of waterglass activated granulated blast furnace slag motars(AAS).The influence of waterglass modulus,w/b and Na2 O content of waterglass on early compressive strength was tested utilizing orthogonal design.The effects of curing condition on mechanical strength and mineral admixture on properties of AAS before and after exposure to different low temperature has been investigated.The early compressive strength of AAS using variety of waterglass modulus,w/b and Na2 O content was measured based GB/T.It could be shown that the effect of them on strength decreased in order of w/b,waterglass modulus and Na2 O content.The strength development of AAS placed in different low and subzero temperature were studied.A drop in temperature reduced the strength and reaction process,but different with cement,AAS could go on reacting in subzero environment.The experimrntal data shows that the strength reach to 20 Mpa when curing 28 d at-20?.Slag was partially replaced with OPC at levels of 0,2,6 and 10 %,by mass.The results indicated that the fluidity and the setting time of mortars and pastes decreased with the increase content of OPC.OPC admixture elevated the early strength but reduced the long-term strength at 20?.On the other hand,OPC always increased strength curing at subzero temperature.Slag was partially replaced with SF at levels of 0,10,15 and 20 %,by mass.The results indicated that SF increased the fluidity and the setting time of mortars with the increase content,but pastes is totally opposite.SF admixture elevated the very early strength but reduced the long-term strength at 20?.On the other hand,SF always increased strength curing at subzero temperature.The hydration proccess of AAS at different curing condition was analyzed utilizing non-evaporable water method.It was found that the non-evaporable water of OPC and SF admixture at subzero temperature is higher than neat slag,indicated that OPC and SF makes the reaction process faster.The results of non-evaporable water is in highly keeping with strength development.The hydration products of this cement at different temperature have been investigated by means of XRD,TG-DTA and TEM.The results showed that hardened cement paste was mostly consisted of C-S-H gel,maybe mixing with Na or Al,formed C-A-S-H and N-A-S-H gel,neither Ca(OH)2 nor AFt,which are usually present in the hardened Portland cement paste.