Abstract
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 carbon dioxide 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. PSA-treated soil specimens were shown to perform well compared to lime-treated or cement-treated ones: (a) PSA considerably lowered 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 gave UCS at least twice as high compared to those obtained using commercial limes at equivalent dosages (> 1 MPa for the two expansive soils after 7 or 28 days of curing) and in the inspected cases also higher UCS than cement; and (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-treated or cement-treated soils. Overall the results give promise for a valorisation route of this waste material in the field of ground improvement.
Highlights
Introduction iewEngineers must provide infrastructure making better use of resources to minimise waste generation and the consumption of primary materials
The aim was to assess paper sludge ash (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
All stabilisers affected the plasticity characteristics; in particular lime and PSA favourably changed the plasticity characteristics of all clays mainly due to the higher plastic limit wP; the liquid limit wL of each soil was in most cases consistent between lime and PSA; for the expansive clay mixture cement increased both wL and Ip
Summary
Introduction iewEngineers must provide infrastructure making better use of resources to minimise waste generation and the consumption of primary materials. There is interest in finding alternative stabilisers from waste that can be used as a source of the required chemicals Examples of such alternatives to commercially supplied cement or lime include: cement or lime kiln dust (Petry and Little, 2002), other forms of by-product lime e.g. calcium carbide residue (Kampala and Horpibulsuk, 2013) or lime extracted from eggshells (Zaman et al, 2018). With an annual paper production of approximately 4.5 million tonnes in the UK and an increase in paper recycling rates, abundant volumes of waste paper sludge are produced, leading to steadily increasing amounts of PSA (in the UK 4 out of 40 paper mills generate 140 ktonnes of PSA annually, Spathi, 2015) This has caused environmental concerns and high costs to industry due to UK landfill tax. The potential use of PSA as soil stabiliser was studied in a limited amount of works, e.g. Bujulu et al (2007), who found that 18-month old field samples from lime-cement-PSA columns in a quick
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