A new generation of self-healing detectable grouts

Billions of tons of cement are injected into the ground world-wide each year to increase ground strength and to create barriers to water flow. Examples of its use in construction include building foundations, reservoir dams and tunnel walls. This activity is termed 'permeation grouting'. Use of permeation grouts are recorded as far back 1802, when cement grout was injected into holes in the ground beneath a sluice at Dieppe to stabilise the foundations, which were failing. More recently, £5M was spent injecting over 42,000 tonnes of cement grout into the ground to stabilise mine workings for the construction of the Emirates Arena and the Sir Chris Hoy Veladrome for the 2014 Commonwealth Games in Glasgow. Whilst technology has substantially improved over the last two centuries, the basic principles of cement grouting have remained largely the same.

A key aim of this project is to revolutionise the grouting industry by developing the first 'detectable' grout. A fundamental issue with all grout injection is the inability to detect where the grout has gone once it has been injected into the ground. This lack of knowledge can result in significant grout wastage, drilling of unnecessary wells, a lack of data for efficient injection and an inability to detect 'gaps' in grout walls where containment of water is critical; for example in dams and surrounding waste disposal sites.

The ability to detect the location of grout beneath the ground, both during and after grout injection will transform industry practice. It will allow for more efficient design of grout walls, will reduce the risk of un-grouted 'gaps' in the rock through which water can leak, and will minimise the volume of cement needed. Cement production accounts for 5% of the worlds CO2 emissions to the atmosphere each year, hence this research will have a positive impact on meeting global climate emission targets.

Grouting campaigns can represent a significant environmental and financial cost. Cement production globally is estimated to account for up to 5% of global CO2 emissions; 900 kg of CO2 are emitted for the fabrication of every ton of cement. For the 2014 Commonwealth Games, for example, 41,430 tonnes of cement grout was used to stabilise disused mine workings for construction of the Emirates Arena and the neighboring Sir Chris Hoy Veladrome in Glasgow, at a cost of over £5M and an environmental impact of >37 million tonnes of CO2 emissions. Both of the proposed new technologies have the potential to make a significant impact on the financial and environmental cost of grout curtains. The detectable grout will enable minimisation of cement use, as well as increasing the reliability of the grout curtain by identifying any rock volumes into which the grout has not penetrated. The strong, self-healing non-cementitious grout, combining microbially-induced mineral precipitation with silica sol, can lead to a more environmentally acceptable alternative to current ultra-fine cements. Both developments have the potential to secure a leading technological edge for UK-based industry if proof of concept can be achieved. In particular, the detectable grout has the potential to become commonplace within what is a global billion-pound construction industry.