Testing sprayed waterproofing membranes for composite action
Rosa Diez, Project Director, Mott MacDonald Testing sprayed waterproofing membranes for composite action
Sprayed waterproofing membranes have been used widely in the construction of sprayed concrete lined tunnels. However, it is increasingly being claimed that they can allow full composite action to occur between primary and secondary linings. Adequate characterisation of the properties and behaviour of these products under the conditions to which they will be subjected in the tunnels, is crucial to the demonstration of the composite behaviour. It is therefore the performance of the waterproofing materials under realistic moisture exposure conditions and sustained loading that would need to be investigated to replicate the expected tunnel environment during its design life.
This paper reviews the previously published material properties for EVA-powder and reactive resin based waterproofing membranes and presents the results of a testing programme that was carried out as part of the Crossrail project in London. ‘Wet conditioned’ samples were subjected to rapid tensile testing, displacement controlled testing and sustained load testing and the results, in terms of bond strength, stiffness and modes of failure of the waterproofing materials are compared with tests carried out on “dry” samples.
Despite the limitations of the testing programme undertaken, the significant creep behaviour exhibited by these materials under testing and their sensitivity to water raises concerns in terms of whether they are suitable for maintaining composite action in the long term.