Investigating the Influence of Entrained Air and Fly Ash on Chloride Ingress in Concrete Pavements

Chloride-loaded brine accelerates erosion and reinforcement corrosion in concrete pavements. The extent and severity of these failures depend on the timing and mechanisms of chloride ingress - the infiltration of chloride ions - into concrete pores. The intricacies of chloride ingress remain incompletely understood. This study assesses the effectiveness of entrained air and fly ash as inhibitors of chloride ingress. Surface electrical resistivity serves as a metric, enabling an examination of chloride ingress potential across diverse exposure conditions. Over a three-year period, ponding tests were conducted on concrete samples (100 mm diameter; 200 mm tall cylinders) cast at various entrained air contents (0 to 10.0 percent by volume of concrete) with two fly ash classes (C and F) and Type I Portland cement. Two sets of concrete samples were subjected to disparate environmental conditions: one group underwent moisture curing in temperature-controlled water, while the other was immersed in salt brine consisting of 23.3 percent NaCl by weight of water, blended with CaCl2 at six different concentrations (0, 5, 10, 15, 20, and 25 percent by weight of water) to simulate multiple scenarios of chloride ingress at outdoor temperatures. Concrete resistivity increased as concrete pores developed and refined in water, signifying heightened resistance to chloride ingress grows in a chloride-free environment. Data revealed faster gains in concrete resistivity can be attained with reduced entrained air content. In chloride-rich environments, chloride ingress was affected not only by chloride concentrations but also by the species of cations (Ca++ versus Na+). Concrete resistivity exhibited a gradual decline as chloride concentration increased in blends of NaCl and CaCl2 but remained unchanged in pure salt brine, confirming the greater affinity of chloride binding for Ca++. The rate of resistivity loss increased with increased amount of entrained air. Class F fly ash demonstrated effective mitigation of chloride ingress in pure salt brine, its influence was inconsequential when exposed to blends of NaCl and CaCl2. Lastly, the findings were incorporated into the electrical resistivity model parameters to predict the initiation of reinforcement corrosion in concrete pavements.