Chemical Rock Grouting. An Experimental Study on Polyurethane Foams
Grouting is used to change the physical characteristics of concrete, soil and rock. The changes are usually related to permeability and/or strength. Although the most widely used grout for sealing of rock masses is cement suspension, there are certain conditions where polyurethane grout is used as a complement. The most favourable property in this respect is that such grouts react with water and expand due to exertion of carbon dioxide gas (CO2). Other important features of these grouts are the time dependency, the flow behaviour of unreacted as well as reacting polyurethane, and the physical influence of the carbon dioxide.
The scope of this research was to study the typical behaviour of polyurethane grouts in order to explain why the grouting result has been unsatisfactory at times, while mostly successful where other grouts have failed.
A comprehensive laboratory test programme was performed, including simple expansion tests, where the general characteristics of polyurethane grouts were studied, as well as a series of pipe flow tests. The latter tests comprised grouting of polyurethane against static groundwater pressure and into flowing water. The performance of polyurethane grouting in a field situation was also investigated with a test at the Röda Sten Rock Laboratory in Göteborg.
The study resulted in conclusions and recommendations for the application of polyurethane for rock grouting. The main conclusion regarding the practical use of such grouts is that a volume criterion, in combination with an awareness of the time dependency of the gelling of the material, is useful for achieving an optimal sealing result. When grouting into flowing groundwater, a sufficiently high grouting pressure should be used in order to cut off the water flow and facilitate grout penetration upstream. The CO2 gas generated in the reaction between polyurethane and water, contributes to the grout penetration in two ways: (i) by causing a volume expansion, and (ii) by increasing the pressure behind the front of the reacting polyurethane grout.