Volume changes, cracking and durability of cement grouts subjected to accelerated wetting and drying cycles

Abstract

Blended cements are specified for encapsulation of low level waste (LLW) and intermediate level radioactive waste (ILW) in the UK. These contain high level of replacement of OPC (up to 90% wt.) by blastfurnace slag (BFS). However, the behaviour of such grouts after long-term storage is not known and some accelerated tests may help in investigating the microstructure and properties of those composites on a short term. Alterations in the volume of cement pastes through wet/dry cycling may permanently change the microstructure and cause damage such as cracking. The penetration of rainwater and contact with groundwater are examples of this phenomenon. Therefore, accelerated wet/dry cycling may be a useful tool to predict volume changes, possible cracking and consequent durability of the grouts. This paper has studied two grout systems currently used for encapsulation, i.e. 9:1 BFS:OPC, 3:1 BFS:OPC, and another OPC replacement level (60%) with neat OPC as a reference grout. A novel system was also studied, a Na2SiO3 activated 9:1 BFS:OPC. The grouts were submitted to a new automatic accelerated wetting-drying test for 18 days, after curing at 20°C and 60°C. Length changes, weight changes, the depth of carbonation and changes in permeability were assessed due to the dry/wet cycles. Results of wet/dry cycles show that this test was effective in ageing the grouts and that the degree of expansion may be linked to the porosity, permeability of grouts and temperature of curing.