Environmental degradation of macrodefect-free cements

The effect of different environments on the flexural strength of a range of macrodefect-free (MDFs) cements was studied. The results showed significant differences in behaviour of the MDFs. These differences were found to be clearly related to the cement system the MDF was made from.Initial measurements clearly established that high alumina cement (HAC) based MDFs were significantly stronger than ordinary Portland cement (OPC) based ones.Upon immersion in water the flexural strengths were observed to drop initially. In the OPC MDFs some recovery in strength was subsequently observed. No such behaviour was found in the HAC MDFs. One of the MDFs studied had had the polymer removed prior to testing. This showed no sign of loss of strength on immersion in water but this could be due to the processing rate used to prepare it.Gamma irradiation was more damaging to HAC MDFs than OPC MDFs. Gas analysis suggested that polymer degradation was occurring and it is proposed that the polymer matrix in HAC MDFs may be responsible to a degree for the high strength of these materials.