# Characterization of Carbonation Curing Influence on Nonlinear Ultrasonic Response and Mechanical Performance of Mortar

## TL;DR

This study explores how carbonation curing affects mortar using ultrasonic methods and mechanical tests, showing improved strength and CO2 capture.

## Contribution

The study introduces nonlinear ultrasonic sensing as a sensitive, nondestructive method to monitor carbonation curing and its effects on mortar properties.

## Key findings

- Nonlinear ultrasonic response (SPC-I) captured distinct matrix evolution during carbonation curing.
- Compressive strength increased by up to 38.9% after 28 days of carbonation.
- Gravimetric analysis showed average CO2 sequestration with 2.62% mass gain in specimens.

## Abstract

The cement industry is a major contributor to global CO2 emissions, creating a need for monitoring techniques that support carbon capture strategies while assessing material performance. This study investigates the accelerated carbonation curing of cement mortar using linear and nonlinear ultrasonic sensing methods, alongside mechanical and gravimetric measurements. Mortar specimens were carbonated for 1–28 days and evaluated using ultrasonic pulse velocity (UPV), the Sideband Peak Count Index (SPC-I) for nonlinear ultrasonic response, compressive strength testing, and mass-based CO2 uptake analysis. UPV showed sensitivity primarily to bulk material changes, with comparatively less distinction among the observed responses during carbonation curing. In contrast, the SPC-I captured distinct nonlinear responses associated with matrix evolution. Early-age carbonation (<7 days) produced increased nonlinearity, attributed to shrinkage-induced microcracking, whereas extended curing led to reduced SPC-I values, consistent with carbonation curing age. These trends exhibited an inverse correlation with compressive strength, which increased by up to 38.9% on the 28th day compared to the control specimens. Gravimetric analysis confirmed effective CO2 sequestration, with average specimen mass gains reaching 2.62%. The findings demonstrate that nonlinear ultrasonic sensing provides a sensitive, nondestructive approach for monitoring carbonation curing and linking acoustic signatures to mechanical performance and carbon uptake in cement-based materials.