Incorporation of basaltic aggregates from the Sibasa formation in shotcrete for potential use as support in underground mining

Abstract

The use of crushed basalt aggregates as an alternative to sand aggregates is gaining momentum. This is driven by efforts of ensuring sustainable developments in shotcrete production. The main objective of this study was to assess the suitability of basalt aggregates as sand replacement through aggregate physical characteristics tests. To this end, shotcrete mixes of proportions 0%, 25%, 50%, 75% and 100% replacement of sand by basalt aggregates were prepared. The shotcrete mixes were then tested for compressive and flexural strengths over curing ages 7, 14, 21 and 28 days. Basalt aggregates used for the purpose were collected from the Sibasa Formation in Limpopo Province. They were subjected to crushing, milling and sieving to size of 425 µm as well as physical characterisation for fineness, water absorption, moisture content, specific gravity, bulk density, petrographic and geochemical properties. In addition to this, fresh mixes were evaluated for workability while hardened sand-based and basalt-based shotcrete mixes were studied for hardened density, compressive and flexural strengths. Results indicated that basalt aggregates have favourable characteristics that influence the mechanical properties of shotcrete when compared to sand. Furthermore, fresh mixes with elevated basalt content exhibited higher consistency. Increased flexural and compressive strengths were also observed for shotcrete mixes at high basalt content. Conversely, lower compressive and flexural strengths were recorded for mixes at high sand content. Water immersion curing and curing age also contributed to a gain in strength for basalt-based shotcrete. Equally, basalt content and curing age were found to enhance shotcrete strength with notable interaction between the two parameters. Lastly, high deformations were observed for sand-based shotcrete compared to basalt-based mixes suggesting that basaltic aggregates lead to shotcrete of superior properties.