Britpave: The British In-Situ Concrete Paving Association

New research on swell tests could further use of soil stabilisation

New research into test methods for assessing potential soil stabilisation swell could further the use of binders, such as lime, cement and GGBS (ground granulated blast-furnace slag), to improve weak and poor soil into a sound and stable construction material.

Comparison of 3 swell/stability tests on clay soils treated with lime, cement and GGBS.

Comparison of 3 swell/stability tests on clay soil treated with lime, cement or GGBS

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Comparison of 3 swell/stability tests on clay soil treated with lime, cement or GGBS


new research on swell tests could further use of soil stabilisation

New research into test methods for assessing potential soil stabilisation swell could further the use of binders, such as lime, cement and GGBS (ground granulated blast-furnace slag), to improve weak and poor soil into a sound and stable construction material.

Widely used for constructing highway pavements, car/lorry parks, floor slab foundations and for the remediation of contaminated land, stabilising soil with lime and/or cement is an effective method of converting weak soil into an useable construction material. In rare circumstances, the presence of sulfates in wet soil can potentially cause swell problems due to calcium (from the lime or cement binder) reacting with alumina (a primary constituent of clay) and sulfates to produce calcium-aluminate-sulfate-hydrate materials which have a very large expansion potential of up to 250 per cent.

The research was carried out by Balfour Beatty Construction Services and the Cementitious Slag Makers Association members of the Soil Stabilisation Task Group of Britpave, the insitu cementitious infrastructure group. It reviewed and evaluated three test methods used for assessing the potential for stabilised soils to swell due to the presence of sulfates or sulfides in the soil. The three tests included: California Bearing Ratio (CBR) swell test; accelerated, unconfined expansion test; loss-of-strength immersion test. They were each tested on three clay types stabilised with various combinations of line, cement and GGBS. The clay types included a highly plastic but ‘zero sulfate’ glacial clay, a Lias clay with medium sulphates and a London clay with low sulfate but high sulfide.

It was found that whilst all three tests detected potential problems with the medium sulfate soil there was no evidence that European accelerated test is any better at detecting the potential for swell than the CBR test. The loss-of -strength immersion test was the most severe of the tests and may be overly severe for evaluating mixtures with lower binder contents. All three test methods showed an enhanced resistance to sulfate disruption where the binder used included GGBS.

“There is a difference in opinion as to which is the most suitable test method to assess the swelling potential of stabilised soils”, said Al McDermid, Chairman of the Britpave Soil Stabilisation Task Group. “This research demonstrates the capabilities and limitations of the three main test methods thereby allowing an informed decision to be made. This will help to further develop the use of soil stabilisation which is increasingly gaining recognition as the way forward to treat weak or contaminated soils”.

A free copy of the report ‘A Comparison of 3 Swell/Stability Tests on Clay Soils Treated with Lime, Cement and GGBS’, may be downloaded from the Britpave website: www.britpave.org.uk/FreePublicationsSoilStab.ink