Concrete structure exposed to marine environments is very susceptible to chloride ion ingress into the concrete, which in turn corrodes the steel reinforcing. The loss, in terms of repair of damaged structures and reduction in design life of structures, is very high. Therefore, this paper presents the laboratory investigations conducted to study the chloride permeability characteristics of admixed concrete specifically with Fly Ash (FA). The influence of various parameters such as water/cement (w/c) ratio, age of concrete and percentage of mineral admixture were undertaken. Rapid Chloride Permeability Test (RCPT) was used to study the chloride permeability characteristics of concrete. RCPT adopts a voltage of 60 V to measure the resistivity of concrete. This is the inherent disadvantage of RCPT. Because of this higher voltage, the specimen gets heated up, increasing the chances for encouraging chloride permeability. Hence, in the present work, experimental investigations for various voltages were performed. The outcome of this paper is to suggest an optimized percentage of FA suitable for concrete in an aggressive environment and to develop correlation between various parameters, which are responsible for chloride permeability.

Deterioration of concrete due to corrosion of reinforcement is the most serious durability problem faced by the construction industry, and it has reached alarming proportions in the past three decades, leading to very high repair costs, sometimes above the initial construction cost, or in extreme situations, to the final collapse of the structure. Corrosion of steel in concrete may occur due to chloride ingress, carbonation, loss of alkalinity, etc. Chloride ingress is one of the most serious causes, which is responsible for corrosion of steel. The harmful chloride ions may be present in concrete as a result of the use of contaminated ingredients in the manufacture of the mix, or as a result of an external contamination prior to construction. This situation arises from exposure of the structures to water and marine atmospheres, or to the use of deicing salts (NaCl, CaCl₂ and MgCl₂), a necessary practice in cold climates. The corrosion of steel can be minimized with the use of a properly designed concrete with lesser permeability, which depends on parameters such as cement type, water to cement (w/c) ratio, and pozzolanic admixtures (FA, silica fume, metakaolin, etc.). The use of finer FA reduces the average pore size of the cement paste and hence develops a dense interfacial zone between aggregate and the matrix which helps to improve the resistance of the concrete against the penetration of harmful ions like chlorides.

Hence it was proposed to study the performance of concrete containing different proportions of FA as a permeability reducing admixture. In addition to economic and ecological benefits, the use of FA in concrete improves the strength and enhances the chloride resistance. The pozzolanic activity of FA depends on the amount of glassy material in it, density and the fineness of the FA. FA reacts with calcium hydroxide liberated during hydration process, leading to the formation of CSH-gel, which results in increase of compressive strength of concrete. The pozzolanic reaction of the FA depends on the amount of SiO₂ present in it. Rapid Chloride Permeability Test (RCPT) (ASTM C1202, 2000) method was used to evaluate the influence of FA on the resistance of concrete to chloride ion penetration. This test quantifies the amount of electrical charges that passes through a concrete specimen for 6 h. A brief review of literature is discussed in the following paragraphs.

Structural Engineering Journal, Fly Ash Concrete, Rapid Chloride Permeability Test, Construction Industry, Hydration Process, Ordinary Portland Cement, Chloride Penetration, Hydration Process, Coulomb Values, Experimental Works, Pozzolanic Activities, Chloride Permeability.