EFFECT OF ACTIVE SILICEOUS MATERIALS ON THE RESISTANCE OF HARDENED CONCRETE TOWARDS ALKALI-AGGREGATE REACTION

Abstract

This investigation aims to study the effect of silica having different sizes on the properties of types of concretes containing dolomite and gravel as coarse aggregates (DC & GC). DC and GC, in which OPC is partially replaced by 2 and 5 wt.,% silica fume(SF) as well as 1, 2, and 4 wt., % nano silica( NS). The results showed that the increase of SF up to 5wt.,% led to enhance the mechanical properties of DC and GC up to 180 days of curing in tap water. On the other hand, NS with desirable content up to 2 wt., % showed the highest physico-mechanical properties of both concretes. 4 wt., % NS led to reduce the mechanical properties but still higher than those of control sample. X-Ray diffraction (XRD) proved that SF and NS acts as pozzolanic materials. The SEM-photographs, showed that the interfacial transition zone (ITZ) in case of DC and GC with SF and NS is more compact than those of control sample. The resistivity of DC and GC in IN NaOH up to 6 months of immersion has been carried out. The results also showed that all concrete mixes presented high resistivity towards NaOH up to 6 months of immersion. The compressive strength development rate of DC and GC containing NS and SF is higher than those of control sample. The aggregate type plays an important role on the mechanical properties of concrete. The DC gave the higher mechanical properties as compared with GC. Key words: Dolomite concrete, compressive strength, Total porosity, Pozzolanic reaction, calcium silicate hydrate.