Abstract

Abstract

The use of metakaolins has been shown to be effective in modifying the properties of cementitious materials related to durability, highlighting the very positive impact in terms of increasing the electrical resistivity of concrete and reducing ionic transport in this porous medium. In this sense, the present work aims to evaluate the efficiency of different metakaolins in terms of pozzolanic activity, linking the efficiency to various characteristics of the metakaolin. Five samples of different Brazilian commercial metakaolins were then characterized, using the following methods: BET specific surface area, X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, thermal analysis (TA/DTA), thermogravimetric analysis (TG/DTG) and determination of pozzolanic activity by the modified Chapèlle method. As the main results, it was found that the BET specific surface area and the Al2O3 content, obtained by XRF, better explain the pozzolanic activity of metakaolins (Pearson correlation coefficients equal to 0.89 and 0.94, respectively). The amorphous content (quantified by Rietveld in the XRD) showed only a reasonable correlation with the pozzolanic activity determined by the modified Chapèlle method. In general, the chemical-mineralogical characteristics that indicate purity and amorphism of metakaolin, expressed by the Al2O3 content, Al2O3/SiO2 ratio, SiO2+Al2O3 sum, and amorphous content, represent important performance parameters of metakaolins. The specific surface area compensates for lower purity or chemical reactivity and significantly influences pozzolanic activity.

Abstract

Abstract

Alkali-silica reaction (ASR) is a major concrete durability problem. The occurrence of ASR results in significant maintenance and reconstruction costs to concrete infrastructures all over the world. Ever since Stanton (1940) discovered the expansive characteristics of ASR in 1940, there has been much speculation as to the cause and actual mechanism of expansion. Current market solutions are not always sustainable, such as hauling non-reactive aggregates or fly ash from long distance; or use of Li-based chemical admixture that is facing challenge of raw material‘s availability. The current article will present a patent pending technology which provides a commercial solution for mitigating the ASR. The ASR mitigating effect of this technology is compared with lithium, calcium, and aluminum salts, and densified silica fume.