microsilica (Figure 5). It appears that chipping of the concrete specimens occurs when
there is an irregular expansion in the concrete due to ettringite formation.
On carrying out the destructive test by longitudinally cracking the concrete specimens
exposed to 5% NaCl or seawater for different durations, it was observed that the steel
bars in OPC cement blended with microsilica get more corroded when immersed in
seawater as compared to that in 5% NaCl solution environment (Table 7 and Figures 6
and 7). Table 7 reveals that SRC concrete are not very protective to rebars in 5% NaCl
solution, however, blending of this cement with microsilica does improve its corrosion
resistance.
4.4 Sulfate Resistance Test
The data on expansion in OPC cement mortar specimens with and without microsilica
are plotted in Figure 8. The expansion in specimens of OPC immersed in the sulfate
solution was 0.020% after an exposure period of 336 days, compared with a value of
0.024% noted in specimens with undensified microsilica and 0.017% in specimens
blended with densified microsilica. The expansion data for specimens made with SRC
concrete are shown in Figure 9. These data indicate a trend similar to that exhibited by
the specimens made with OPC. But the major difference between the data of (Figures 8
and 9) is that SRC blending with DMS suppressed considerably the expansion,
however, OPC blending with the same grade of microsilica shows initially a slight
enhancement in expansion followed by virtually no change in expansion. Furthermore,
the expansion of blended OPC becomes lower C after 125 hours immersion. The
OPC blending with UDMS show clearly the enhancement of expansion on immersion in
sulfate solution.
4.5 Chloride Ion Ingress and Rapid Chloride Permeability (RCP) Tests
Table 6 summarizes chloride ingress data in OPC and SRC concretes with and without
microsilica blending during Salt Ingress tests. Figure 10 shows kinetic of chloride
ingress in different types of concrete samples. Figures11 and 12 are bar diagrams
representing the effect of microsilica addition on the chloride ingress in different types
of concrete during Rapid Chloride Permeability tests. As it is evident from (Figures 10
and 11), chloride ion ingress measurement in all the five types of concrete mixes shows
the following behavior: