Alkali-silica reaction products and cracks: X-ray micro-tomography-based analysis of their spatial-temporal evolution at a mesoscale

TL;DR

This paper introduces a non-destructive, time-lapse X-ray micro-tomography method using caesium contrast to study the spatial-temporal evolution of alkali-silica reaction products and cracks in concrete at a mesoscale.

Contribution

It presents a novel laboratory methodology for analyzing ASR-related cracking and product evolution in concrete using non-destructive imaging techniques.

Findings

Cs slightly accelerates ASR kinetics

Crack patterns are statistically similar with or without Cs

ASR products originate in aggregates and flow into cracks

Abstract

In this study, we propose a laboratory-scale methodology, based on X-ray micro-tomography and caesium (Cs) as a contrast agent, to advance the understanding of cracking due to alkali-silica reaction (ASR) in concrete. The methodology allows achieving a completely non-destructive and time-lapse characterization of the spatial-temporal patterns of both the cracks and the ASR products. While Cs addition slightly accelerated the ASR kinetics, the crack pat-terns, with and without Cs addition, were statistically equivalent. Cracks with ASR products appeared first in the aggregates, close to the interface with the cement paste. They propagated afterwards towards the aggregates interior. Some products were then extruded for several mm into air voids and cracks in the cement paste. This process suggests that, in the early stage, the ASR products may be a low-viscosity gel that can flow away from the source aggregate and may settle later elsewhere as a rigid phase, upon calcium uptake.