Reuse of Waste from the South West of England in Alkali-Activated Cement Concrete

Abstract

The extraction of china clay in the South West of the UK generates waste in a mass ratio of 1:9 for china clay: waste. Currently, part of the coarser waste, “stent” and sand named “china clay sand” (CCS) in this study, is used as building stone or secondary aggregate in concrete and asphalt but the finest waste fraction, called “mica” waste, is used only for the restoration of old quarries. Looking for innovative solutions for the needs of a new Eco-town in the UK, and with regard to uses commercially applicable to construction and of low environmental impact, the china clay waste is being studied as an aggregate in alkali-activated cements (AAC). Aiming to replace primary aggregates with wastes in low risk construction materials, a series of AAC concrete based on a 50% GGBS and 50% fly ash (FA) blend and an equivalent Portland concrete series were produced. In the mixes the primary aggregate was steadily replaced by forms of the waste and tests in compression showed a decreasing trend in strength accordingly. The two series of concrete follow approximately the same ratios of decrease although in absolute values the AAC series reached higher range of strengths on the 28 day compared to the Portland series. While the use of CCS did not have any negative impact, the addition of mica decreased the strength up to 25% more.