Ultrasonic monitoring of carbonation in Portland cements

TL;DR

This study develops non-destructive ultrasonic indexes to measure carbonation in Portland cement pastes, offering a faster alternative to traditional testing methods, with high correlation to carbonation levels validated by FTIR.

Contribution

Introduces ultrasonic-based indexes derived from linear and non-linear analysis for assessing cement carbonation non-destructively.

Findings

High correlation between ultrasonic indexes and carbonation levels

Indexes accurately estimate carbonation as a function of exposure time

Potential for rapid, non-destructive carbonation assessment

Abstract

Chemical reactions resulting from the ingress of carbonates into the cement matrix modify the properties of its pore solution, as well as its pore distribution and size. These changes lead to corrosion of the steel in reinforced concrete. The nature of conventional testing for the estimation of carbonation in cement-based materials is time-consuming and destructive. This paper presents a set of non-destructive ultrasound-based indexes, obtained solely from non-linear and linear analyses of ultrasonic signals, for measuring the carbonation of Portland cement pastes. Class 30RS cement pastes with three water/cement ratios by weight (0.4, 0.5, and 0.6) were considered. Carbonation was carried out for 120 days with a constant CO2 level of 4% by volume under controlled temperature and humidity, considering a unidirectional carbonation, parallel to the longitudinal axis of the samples. The level of carbonation was validated by FTIR measurements. From these analyses, different indexes with high correlation were obtained, estimated only from the ultrasonic signals and as a function of the days of exposure to carbonation, as well as of the percentage of carbonation. Further study is required for the evaluation of the reliability of these promising indexes for the determination of carbonation in cement-based materials.