Title: Role of Alkalis in Natural Pozzolans on Alkali-Silica Reaction

Author(s): R. D. Kalina, S. Al-Shmaisani, S. Seraj, R. Cano, R. D. Ferron, and M. C. G. Juenger

Publication: Materials Journal

Volume: 118

Issue: 3

Appears on pages(s): 83-89

Keywords: accelerated testing; alkali content; alkali-silica reaction; fly ash; natural pozzolans; supplementary cementitious materials

DOI: 10.14359/51732598

Date: 5/1/2021

Abstract:
Fly ashes with high alkali contents have been observed to be less effective in controlling expansion due to alkali-silica reaction (ASR) in concrete than low-alkali fly ashes, a problem that can be hard to predict using accelerated testing. Many natural pozzolans have high alkali contents, and there is concern that these alkalis may likewise reduce their effectiveness in ASR control and affect accelerated test results. This study examines the performance of natural pozzolans in ASR testing. The mineralogies of the natural pozzolans were determined using Rietveld quantitative X-ray diffraction (XRD), and the compositions of the natural pozzolans were determined using X-ray fluorescence spectroscopy (XRF) and available alkali testing. The results suggest that the available alkalis from fly ashes and natural pozzolans are different, and high-alkali natural pozzolans perform well in both the accelerated mortar bar and concrete prism tests for ASR.