Abstracts Category : Other

Carbonation induced corrosion in integral and non-integral surface treated lightweight foam concrete

by Marlin Mubatapasango

ENGLISH ABSTRACT: Carbonation induced corrosion is a concern in reinforced lightweight foam concrete (R/LWFC) as a result of air entrainment. Concerns arise from whether the air voids increase diffusivity of carbon dioxide (CO2) into LWFC. The effect of carbonation is the destruction of the protective cover for the steel reinforcement.LWFC is a low density concrete in which at least 20 per cent air by volume is entrained in a base mix comprising water, cement and a filler. The air entrainment is achieved by adding stable foam to the base mix. LWFC is a versatile construction material whose density can be altered by using various amounts of entrained air to suit the required function, structural or non-structural. The significant amount of air entrainment give LWFC its advantages of high strength to weight ratio and improved insulating properties. While progress in LWFC on mix designs and suitable compressive strengths for structural use has been made, other properties such as durability have not been adequately explored. In normal weight concrete, surface treatment has been used to improve durability, little research has been conducted on the efficacy of surface treatment agent on the durability of LWFC. Surface treatments are applied either during mixing (integral) or after curing (non-integral).This study investigates the durability of R/LWFC with a particular focus on carbonation and whether surface treatment can be used to limit corrosion induced by carbonation. The influence of surface treatment on the lightweight foamed concrete is also characterised. In this investigation R/LWFC is used with a target casting density of 1400 kg/m3 for testing changes in microstructure via CT scans, compressive strength, penetration depth (carbonation front and silane) and half-cell potential corrosion measurement. Application of integral and non-integral surface treatment is done and the effects on the R/LWFC and evaluated against results from control samples. CT scanning is used for investigating the effect of surface treatment on the lightweight foam concrete. An accelerated carbonation set-up is used to investigate carbonation resistance. Phenolphthalein indicator solution is used to determine the depth of carbonation.Integral surface treatment affected the size and distribution of voids compared to non-integral treatment. Consequently, the compressive strengths observed for integral surface treatment were higher than for control and non-integral treatment. The shape of the voids in integral and non-integral surface treated concrete were similar. Integral surface treatment provided the highest resistance to carbonation followed by the non-integral surface treatment. High levels of carbonation and carbonation rates were observed for control samples.The observed half-cell potentials showed that integral treatment resulted in high carbonation resistance. Little difference was observed between control samples and non-integral treatment.This investigation concluded that surface treatment can be used in lightweightAdvisors/Committee Members: Van Rooyen, Algurnon Steve, Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering..