Abstract
This paper assesses comparatively the performance of a number of innovative soil stabilisers for the treatment of a highly swelling-shrinking soil, against that of commercial calcium lime. The production of lime, a most common soil stabiliser, involves high energy consumption, carbon dioxide emissions and the depletion of natural raw materials. Alternatives are actively sought, in particular industrial wastes and by-product materials or lower energy demand cements e.g. reactive magnesia (MgO) cements. In this paper calcium lime, reactive magnesia, industrial wastes and mixes of these with lime are comparatively assessed, based on a number of conventional measures of the propensity of a soil to swell, i.e. plasticity characteristics and swelling characteristics (swelling strains, swelling pressures, swelling indices). Furthermore, as expansive soils are typically in an unsaturated state hence sensitive to both changes in water content and suction, filter paper testing was performed to provide additional evidence of the effect of the treatments on the swelling/shrinking soil. According to the main findings, for the treatment of swelling shrinking soils, binders coming from the paper recycling industry show most promise as alternatives to lime; reactive magnesia cement had a smaller effect than calcium based stabilisers in improving the swelling-shrinking of the soil, yet it also suppressed swelling and shrinkage considerably; it thus shows potential for use as an alternative to common soil stabilisers (Portland cement and calcium lime) to alleviate the environmental impact of the latter.
Highlights
Soils that experience very considerable volume changes upon changes in moisture content are classified as swelling-shrinking soils
From the table and the figure it can be seen that all chemical stabilisers have improved considerably these parameters in comparison to the respective ones of the untreated soil, and overall consistently with the plasticity results: namely lime is best to reduce swelling followed closely by Paper Sludge Ash (PSA); MgO appears to have the lesser effect which is still considerable as it has reduced swelling strains by 17%
Compared on the considerable effect of the stabilisers on the volumetric stability of the filter paper specimens during drying, their effect on rates of drying and the suction capacity C = Dw/Dlog(suction) based on the filter paper results as shown in Fig 7 is less clear; according to the results the lowest suction capacity C of 24-25% is found for the PSA treated soils (9% PSA and 2%-7% PSA respectively); this could be partly due to the coarser texture of the soil when PSA is added [27]
Summary
Soils that experience very considerable volume changes upon changes in moisture content are classified as swelling-shrinking soils ( known as expansive soils). These soils cause major damages to lightweight structures, pavements, slopes and utilities and financial losses reported to exceed those caused by other natural disasters such as such as earthquakes or tornadoes [1]. Due to the severity of the problem, this type of soil has been the focus of considerable research Part of this concerns stabilisation with chemical agents such as lime, successfully used to improve the engineering properties of expansive clayey soils by changing their mineralogy and reducing their propensity for volume changes upon moisture changes. This paper assesses the potential of treating a highly expansive soil using (a) the latter type of cement; (b) one industrial by-product (of steel production) namely Ground Granulated Blast Furnace
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