Assessment of in-situ alkali-silica reaction (ASR) development of glass aggregate concrete prepared with dry-mix and conventional wet-mix methods by X-ray computed micro-tomography

Abstract

A recent study showed that concrete products prepared with the dry-mix method have better alkali-silica reaction (ASR) resistance than that prepared by the wet-mix method. But the mechanism of ASR in dry-mix glass concrete remains unclear. Meanwhile, the techniques such as Scanning Electron Microscopy (SEM) and Mercury Intrusion Porosimetry (MIP) cannot reflect the in-situ evolution of the microstructure with the progress of the ASR. In this study, two common casting methods, the wet-mix and dry-mix methods, were adopted to prepare the glass concrete. The non-destructive X-ray computed micro-tomography (X-ray μCT) technique was applied to observe the pore geometries of both the wet-mix and dry-mix glass concrete, to determine their porosities using 3D volumes and to investigate the generation of cracks during ASR development. This study firstly observed the irregular pore geometry of the glass concretes by quantitatively comparing the pore geometries using the sphericity developed by Wadell for both dry-mix and wet-mix glass concrete. The test results of the porosity measured by 3D volume showed that the porosity of the dry-mix glass concrete decreased after the ASR test. However, no obvious change was observed in the porosity of the wet-mix glass concrete. This change may be attributed to the large pores in the dry-mix glass concrete which can accommodate the ASR gel. Through the in-situ observation using 3D X-ray μCT, no new cracks were generated in the dry-mix glass concrete during the progressive development of ASR. On the contrary, new cracks which were filled with ASR gel were densely distributed in the wet-mix glass concrete, which led to failure of the concrete matrix. This is because the expansive ASR gel formed could not be accommodated by the limited pore space in the wet-mix glass concrete, and the swelling pressure of ASR gel induced new cracks in the wet-mix glass concrete.