Effect of fly ash chemical composition on the reinforcement corrosion, thermal diffusion and strength of blended cement concretes

- The chemical composition of fly ash plays a decisive role in the durability of concrete.
- The existence of clay minerals in fly ash causes concrete to swell and crack.
- Fly ash from Northern Greece improves the quality and consistency of concrete.
- Greek fly ash addition leads to anticorrosion protection of reinforcement steel.
- Fly ash concretes exhibit low values of thermal diffusion compared with OPC concrete.

This paper presents the results of an experimental study conducted to evaluate the influence of fly ash chemical composition on the physico-mechanical properties and the resistance of reinforced concrete against chloride penetration. The study examines cementitious composites prepared with two different types of fly ash, used at 5% w/w and 10% w/w as cement replacement, and compares them against reference specimens prepared without fly ash. Electrochemical (Half-cell potential, corrosion current) and mass loss of reinforcement steel measurements were performed, while the porosity, compressive/tensile strength and modulus of elasticity were measured to evaluate the quality of concrete; XRD patterns and SEM images coupled with EDX analysis were further recorded and used for mineral identification and microstructure observation respectively. The thermal properties of concrete samples were also estimated. Prior to testing, all specimens were partially immersed in 3.5% w/w NaCl solution. The experimental results indicate that the performance of hardened fly ash concrete depends not only on the CaO and SiO2 content of the additive, but also on its fineness, free lime and sulfate ions content. In particular, the durability properties of concrete containing fly ash with high SO3 and CaOf contents are improved, while concrete containing fly ash with significant amounts of clay minerals exhibits low chloride penetration resistance and strength; additionally, the composite concretes demonstrate low values of thermal diffusion comparing with the OPC concrete.