The chemical compatibility of cement–bentonite cut-off wall material

Containment techniques are amongst the most common methods of remediating land contaminated by previous industrial use. An important part of the containment process is the placing of vertical in-ground barriers to minimise the movement of contamination from site. Self-hardening slurry trench cut-off walls of cement–bentonite are barriers that are increasingly being used in the United Kingdom. The use of cement–bentonite slurry trench cut-off walls, particularly in highly aggressive environments, raises concerns over durability and long-term performance. The relatively recent use of such barriers means that there is little information on their long-term performance. This paper describes research being undertaken to investigate the properties of cement–bentonite cut-off walls and to examine potential durability problems. Laboratory immersion tests have been used to assess the chemical resistance of typical cement–bentonite mixes containing ordinary Portland cement, ground granulated blast-furnace slag and pulverised fuel ash. These mixes showed varying degrees of resistance to chemical attack with pulverised fuel ash mixes more resistant than those with ground granulated blast-furnace slag. The advantages and limitations of such tests are discussed.