Evaluation of chlorides in fly ash for use in concrete

Abstract

This paper investigates the use of fly ash with various levels of chlorides as a supplementary cementitious material for use in portland cement concrete. The varying levels of chlorides in the fly ashes originated from the air-quality control systems used during collection, rather than chlorides admixed into the fly ashes. Reducing mercury emissions of the thermoelectric power plant resulted in higher concentrations of chlorides in the fly ash. Three different concentrations of chloride (approximately 0.20%, 0.10%, and 0.01%) in fly ash were measured and incorporated into concrete at 25% and 50% replacement. Specimens cured for 7 days in a 73 °F (23 °C) 100% RH fog room followed by 21 days submerged in limewater in a 100 °F (38 °C) environmental chamber resulted in concrete that has similar maturity to concrete cured at ambient conditions for 1 year. Surface resistivity, chloride-ion penetration resistance, and impressed current testing were used to evaluate performance and durability. Acid and water-soluble chloride content were determined to elucidate the binding capacity of the concrete amended fly ashes with different chloride contents. The research clearly indicates that incorporating fly ash with varying levels of chlorides do not reduce the durability; it outweighed the performance as compared to concrete without fly ash. Additionally, increasing the fly ash replacement from 25% to 50% resulted in concretes exhibiting increased durability properties.

Keywords

• Fly ash
• Chlorides
• Durability
• Concrete
• Portland cement
• Chloride threshold limit