Waste Foundry Sand (WFS) as Aggregate Replacement for Green Concrete

Abstract

Globally, 113 million tonnes (Mt)/year of cast metal are produced, generating 10-20 Mt/year of waste foundry sand (WFS). In the UK alone, 200,000 tonnes of WFS are disposed via landfilling, challenging current efforts in tackling climate change and sustainable development (CO2 emissions due to transportation, extraction of natural resources, increase in landfill inputs). Concrete uses up to 90% of natural aggregate per tonne of concrete produced, including sand. The latter is the most extracted material in the world today. Approximately 40-50 billion tons of sands are mined around the globe for construction each year (UNEP2016). This work examines the use of waste foundry sand (WFS) as a replacement for fine aggregate (sand) in concrete. Two types of WFS supplied by Weir UK were used: quartz and chromite sand. After initial chemical and physical characterization, both types of sand were deemed suitable for use in construction. We compared the physical and chemical properties of both WFS types to river sand used for concrete production. Quartz and chromite WFS were finer and contained less silicon than conventional sand but richer in metallic ions. Leaching tests showed that WFS released metals, but their chloride, fluoride and sulphate content was less than river sand. WFS was then used in concrete at different fine aggregate replacement levels (30%, 50% and 100%). We investigated the mechanical performance at 28 days of curing, water transport and durability properties. Whilst the overall compressive strength decreased with increasing the WFS content, samples subjected to freeze/thaw cycles exhibited outstanding durability performance with respect to their water absorption capability. Preliminary results suggest that WFS is an environmentally sustainable solution both for the cast metal industry and the construction sector, as it repurposes a material otherwise disposed of into a raw material for durable concrete production.