The Effect of Superabsorbent Polymers on Performance of Fly Ash Cementitious Mortars Exposed to Accelerated Freezing/ Thawing Conditions

The paper is focused on identification of micro-structural and mechanical alterations in porous matrices of Portland fly ash cement mortar, during frost deterioration. An attempt is made to assess the efficiency of superabsorbent polymer (SAP) ‘protection’ based on analysis of three SAP types with different water absorption/desorption capacities. Two different exposure regimes have been adopted in the study; the exposure to freeze/thaw cycles and the exposure to freeze/thaw with de-icing solution. In order to eval- uate the effect of SAPs on the micro-structural features of deteriorating mortars comprehensive MIP and SEM analyses were performed. It has been found that SAPs with high water absorption capacities may prevent flexural strength reduction caused by frost action. The limitation in micro-cracks propagation by SAP additions can be attributed to the higher tensile strength of ‘SAP pores’ walls, resulting from densification of CSH gel. This is consistent with the finding of higher ‘breaking pressure’ for ‘SAP pores’. Nevertheless, it was shown that the additional exposure to salt ions reduces the initial resistance to less than one month. Desorption characteristics of SAPs may play a particularly important role in the case of very early exposure to F/T cycles. Too slow release of water does not sufficiently facilitate densification of structure prior frost action. Neither can it create a suitable network of air pockets for the expansion of ice and freezing water as in air-entrainers. This is particularly relevant to fly ash cementitious composites due to delayed pozzolanic reaction.