Synergistic Effects Of Freeze/Thaw Cycles And Alkali-Silica Reaction On Deterioration Of High Performance Cement Based Materials

With the development of lots of researches on the durability of concrete, more and more investigators become aware of that deterioration of concrete is seldom caused by a single factor. Usually, at advanced stage of material degradation more than one deleterious phenomenon are found in practice. Therefore, it is necessary to study the interactions when several deteriorative factors are present simultaneously. Durability of concrete involves freezing/thawing, Alkali Aggregate Reaction (AAR), carbonation, sulfate attack and corrosion etc. In the present work the behavior of concrete attacked by the combination of freezing/thawing cycles and Alkali-Silica Reaction (ASR) is explored, and the degradation features and mechanisms are discussed.The mix proportion of the concrete was fixed, whereas the alkali content was set to be 0.5%, 1.0% and 1.5% equivalent Na₂O in the present investigation. The influence of coal gangue on the synergistic effect of freezing/thawing cycles and ASR was taken into consideration.Three modes of damaging actions were selected for studying degradation process of concrete. For mode 1, ASR is to be carried out after freezing/thawing cycles. For mode 2, Freeze/thaw cycles are to be accomplished after ASR. For mode 3, 1 week ASR and subsequent 10 cycles of freeze/thaw are repeated. For mode 1, results showed that with increasing freeze/thaw cycles, the expansion and the loss of relative dynamic modulus of elasticity are incresed. The degradation degree of concrete is augmented with incresing freeze/thaw cycles. At early stage, freeze/thaw cycles accelerate ASR slightly, but at later stage, ASR is almost not affected by freeze/thaw cycles. For mode 2, it was discovered that alkali-aggregate reaction accelerates the damage caused by freeze/thaw cycles, concrete being cracked more seriously. Compared with the single factor of freeze/thaw cycle, the frost resistance of concrete is appreciably improved, due to improved pore structure by ASR. At the same time, the results indicat that after 1, 2 or 3 weeks ASR pretreatment, the frost resistance of the concrete subjected to subsequent freeze/thaw cycles does not improve much. For mode 3, it was shown that compared to single ASR or single freeze/thaw cycles, the rate and degree of degradation of the concrete subjected to alternative ASR and freeze/thaw cycles is lower, the frost resistance being escalated. Compared with the normal concrete, ASR expansion of the concrete containing 40% coal gangue is effectively suppressed and the frost resistance of concrete is improved, which is also true for synergistic effect of ASR and freeze/thaw cycles.