Chloride resistance of high volume fly ash concretes

Costly reinforced concrete structures serve as foundations for the economic prosperity of a nation The continued deterioration of concrete structures, due to corrosion of steel reinforcing rebar, requires the implementation of vast multi-million dollar rehabilitation projects to maintain an adequate level of service in these systems. The process of corrosion in reinforced concrete is largely due to the ingress and build-up of chloride ions in the capillary pores of concrete caused by the use of road salts and from contact/spray from seawater. Lowering the water to cement ratio and incorporating Supplementary Cementing Material's (SCM's) are effective methods of lowering the permeability of concrete to harmful chloride ions. Fly ash is used commonly because it is environmental and economical. However, the amount of fly ash which can be used in concrete is limited, because there are concerns (controversy) over the long-term durability of such structures when fly ash is used in high volumes. This thesis will investigate the chloride resistance of two types of Portland cements and two silica fume blended Portland cement concretes. Each of the four cement types was replaced with two Type CI fly ashes, with coal sources from Sundance, Alberta and from Rockport, Indiana, at 0, 20, 40, 60, and 80 replacement percentages. The chloride resistance was determined by the Rapid Chloride Permeability Test (ASTM C 1202-08) for each combination made. The Sundance fly ash showed greater resistance to chloride permeability than the Rockport fly ash, assumingly because of its lower carbon content, higher fineness, and increased pozzolanic activity