Abstract:
Sri Lanka, being an island with well developed coastal areas, has a large number of
reinforced concrete (RC) structures in the coastal zone. Chloride attack on such concrete
structures has become a significant issue in the construction sector and it has become
necessary to curtail the adverse effects of chloride ions which lead to corrosion of
reinforcing steel and subsequent reduction in the strength, serviceability, and aesthetics of
structures and finally the failure of structures. The level of chloride ion penetration is related
to concrete permeability and with increasing permeability, an increase of chloride ion
penetration occurs. Studies have indicated that the addition of materials such as fly ash,
ground granulated blast furnace slag and silica fume in certain proportions in the mix
reduces the penetrability of concrete. Hence, a possibility exists for the retardation of
chloride ion penetration under such conditions. In this study, the chloride ion penetration
resistance of silica fume mix concrete was examined.
The physical properties of silica fume (fineness, specific gravity and water absorption) were
determined in the study. Concrete mix of Grade 25 was tested according to the BS Mix
Design Method. Specimens with Ordinary Portland Cement (OPC) concrete and specimens
with OPC replaced by silica fume at the levels of 5%, 10% and 15% by weight of cement
were tested. Compressive strength tests (according to BS 1881-116-1983) were carried
out on concrete cubes of size 150 mm x 150 mm x 150 mm. Workability was measured by
the slump test, compacting factor test and VB test. Chloride Ion Penetration test was carried
out according to the procedure given in ASTM C-1202. The results indicated that the
workability reduces with the increase of silica fume for Grade 25 concrete. The compressive
strength of silica fume mix concrete decreased with the increase of silica fume content in
the concrete. However, the results of Chloride Ion Penetration test revealed that the
addition of silica fume reduced the chloride ion penetration indicating a reduced level of
chlorine attack in concrete.
