Published: 2023

Publication Name: Phase Evolution and Property Development of Alkali-Silica

Publication URL: https://par.nsf.gov/servlets/purl/10482853

Abstract:

TIDC Project 3.19

 

The formation and swelling of alkali-silica reaction (ASR) gels, products of the reaction between amorphous silica from aggregates and alkalis from cement capable of absorbing moisture, are considered the primary mechanism of ASR-induced deteriorations in concrete. To date, the ASR mitigation approaches mainly focus on the incorporation of supplementary cementitious materials and the use of lithium-based admixtures. These traditional approaches possess limitations in the extent of ASR suppression and might compromise concrete performance. Effective ASR mitigation under carbonation has been recently documented but the underlying mechanisms still remain unclear. To fill this knowledge gap, phase evolution and property development of ASR gels under carbonation are investigated in this study A synthetic ASR gel with a calcium-to-silica ratio of 0.3 and an alkali-to-silica ratio of 1.0 was synthesized and conditioned under 20% CO2 concentration, 75% relative humidity, and 25oC. The extent of carbonation and phase evolutions were characterized and quantified through X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The modulus of elasticity and hardness of the carbonated ASR gels were measured using nanoindentation, and the moisture uptake capacity was evaluated using dynamic vapor sorption in stepwise relative humidity levels. The results indicate complete conversion of ASR gels into stable carbonates (nahcolite, vaterite, calcite and silica gel) with increased mechanical properties and suppressed hygroscopicity.