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New tests could swell the opportunities for soil stabilisation

New research into test methods to assess potential soil stabilisation swell could help widen the use of binders to improve weak and poor soil, according to a report.

The research, carried out by Balfour Beatty Construction Services and the Cementitious Slag Makers Association members of the Soil Stabilisation Task Group of Britpave, reviewed test methods used to evaluate sulfates or sulfides in the soil.

“There is a difference in opinion as to which is the most suitable test method to assess the swelling potential of stabilised soils,” said Britpave Soil Stabilisation Task Group chairman Al McDermid. “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”.

According to the research, the presences of sulfates or sulphides can react with calcium from a lime or cement binder and alumina in clay materials to result in swelling effects of up to 250%.

The review looked at the California Bearing Ratio (CBR) swell test; the accelerated, unconfined expansion test; and the loss-of-strength immersion test.

They were each tested on three clay types stabilised with various combinations of binders formed from lime, cement and ground granulated blast-furnace slag (GGBS).  The clay types included a highly plastic but “zero sulphate” glacial clay, a Lias clay with medium sulphates and a London clay with low sulfate but high sulfide.

It was found that while 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.

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