Foundry sand (FS) waste creates a serious solid waste management problem worldwide due to the high volumes produced, necessitating alternatives to landfilling. A possible route is its use in concrete; however, the current consensus is that FS can only be used for modest sand replacements, based mostly on evidence on concrete with clay-bound FS (greensand). Conversely, this study assessed salient properties of structural concrete with chemically bound FS (polymeric resin binder), for which there is very little information. Concrete mixes were prepared in which FS replaced regular concrete sand partially or fully. The results showed that unlike greensand, the tested chemically bound FS could replace regular concrete sand fully, giving highly workable mixes with good mechanical properties (compressive, splitting and flexural strengths and static modulus of elasticity) similar to those of mixes with regular concrete sand; the effect of FS content on these properties was not statistically significant. Durability in terms of water absorption, carbonation and alkali-silica reaction tests was not adversely affected. The possibility of using high contents of this type of FS in concrete (as opposed to greensand) gives promise for an additional outlet route for large quantities of this waste material with clear economic and environmental benefits.

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Chemical ground improvement of soils of poor quality for construction has been increasingly used as a means of promoting sustainable construction practices. The production of conventional soil stabilisers such as cement or lime involves non-renewable natural resource and energy consumption and high CO2 emissions; therefore alternative stabilisers are sought. This study used waste paper sludge ash (PSA) to treat three different clays. The aim was to assess PSA effectiveness as an alternative to lime or cement for clay stabilisation based on plasticity characteristics, unconfined compressive strength (UCS), water retention and volumetric stability. PSAtreated soil specimens were shown to perform well compared to lime or cement-treated ones: a) PSA considerably lowed the plasticity indices of the two expansive clays, in a similar way as lime; b) in most cases PSA dosages equal to or greater than the Initial Consumption of Lime (ICL) gave UCS at least twice as high compared to those obtained using commercial limes at equivalent dosages (>1MPa for the two expansive soils after 7 or 28 days of curing) and in the inspected cases also higher UCS than cement; c) consistently with the plasticity results PSA-treated specimens swelled less during wetting and had lower volumetric strains upon drying (better volumetric stability) compared to lime or cementtreated soils. Overall the results give promise for a valorisation route of this waste material in the field of ground improvement.

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