Solidification/Stabilisation a New Way of Remediation

The Concrete Centre claim that if future housing accommodation required by an increase in population from 61 million to 71.6 million by 2033 then land originally thought of as being too highly contaminated to redevelop must be brought back into use.

To achieve this, cutting-edge and cost-effective remediation techniques will have to be employed. One such technique is solidification/stabilisation (S/S). Hailed as environmentally friendly, cost effective and fast, S/S is a process of mixing binding agents such as cement to contaminated material and chemically and physically fixing contaminants Improvements in the engineering properties material can also be gained.

The process involves two;
• Stabilisation – the chemical treatment of contaminants to produce a form that is less toxic and less available to the surrounding environment.
• Solidification – the products of hydration harden which physically ‘traps’ contaminants and improves the physical properties of the stabilised medium to form a solid, stable engineered fill or monolith.

Bulk densities between of 700-2200 kg/m3 and compressive strengths up to 20 Mpa can be rapidly achieved.

S/S most effectively treats heavy metals and other inorganic contaminants. It has also proved an effective treatment for some organic contaminants. The cost of treatment is approximately £20-£50 per tonne which compares favourably to other techniques such as bioremediation, £15-60 per tonne, and soil washing, £50-£150 per tonne.

The contaminated material can be treated on-site and both in- or ex-situ depending on practical constraints and site characteristics. In-situ S/S is usually carried out as a shallow treatment (0m to 0.5m), intermediate (0.5m to 5m) or a deep treatment (over 5m). Treatment at all depth ranges use commonly available civil engineering techniques and machinery such as rotovating plant for shallow treatment and hollow stem augers for deeper treatment.

With ex-situ S/S, the contaminated ground is excavated and mixed with the binder at the surface. Ex-situ S/S is advantageous on sites where heterogeneous ground and buried foundations are an issue, and where the treated materials are to be reused as an engineered fill elsewhere on site.

S/S can be a sustainable remediation option and contribute to sustainable construction practice. S/S techniques can reduce both the volume of materials leaving the site, as waste, and the volumes entering the site, such as engineered fill, with a subsequent reduction in associated traffic movements, noise and dust.

Although S/S has many economic, environmental and social benefits, the applicability and sustainability of the technique has to be assessed on a site-specific basis and against other viable remediation options.

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