Mechanism, characterization and factors of reaction between basalt and alkali: Exploratory investigation for potential application in geopolymer concrete

This study aims to answer the question of how much one could leverage the alkali reactivity of basalt for geo-polymerization and thus benefit cementitious composites (e.g., concrete) that contain basalt aggregate (or fiber). This study investigated the reaction of basalt under alkaline conditions and characterized the microstructure, reaction type, and phases of alkali-activated product of basalt by scanning electron microscopy, Fourier trans -form infrared spectrometry, and X-ray diffraction, respectively. Furthermore, the reaction degree of basalt under different reaction conditions was analyzed by an acid-dissolution method. The effect of alkali fusion method on the reactivity of basalt was studied, and the effects of activator modulus, liquid/solid ratio, reactivity of basalt, and addition of metakaolin (MK) on the reaction degree and compressive strength of alkali-activated basalt were subsequently analyzed. The experimental results revealed that basalt with limited reactive aluminum can be activated by a highly alkaline solution and generate some geopolymer gels and the reactivity of basalt can be improved by alkali fusion. Hence, the treatment by alkali fusion with 50% NaOH increased the degree of geo-polymerization reaction of basalt from approximately 8%-38%, thereby improving the 7d compressive strength of the alkali-activated basalt paste from 2.4 to 12.1 MPa. The addition of MK also effectively improved the re-action degree of alkali-activated basalt. The present study produces new understanding of fundamentals that define the performance of geopolymer concrete incorporating rock aggregate (or fiber) with potential reactivity.