Salt-Frost Scaling of Concrete with Slag and Fly Ash - Influence of Carbonation and Prolonged Conditioning on Test Results

According to Swedish experience the slab method in CEN/TS 12390-9 is successful in predicting the salt-frost resistance of Portland cement concrete. However, doubts have been raised whether the same can be said when used on concrete with supplementary cementitious material, e.g. fly ash or ground granulated blast furnace slag (GGBS). Test results from concrete mixes with up to 35 % fly ash 65 % GGBS, with two different Portland cements and a water-to-binder ratio of 0.45 are presented in this paper. The tests were carried out with the standard method and with five modifications concerning the pre-conditioning of the specimens before freeze-thaw cycling. The age of the specimens at sawing was increased, the time in 65 % RH was prolonged and exposure to 1 % CO₂-environment was used. The results show that for air-entrained concrete with fly ash or GGBS both prolonging the exposure to 65 % RH and exposure to CO₂ diminishes the salt-frost resistance. The influence increases with increasing amount of fly ash or GGBS. However, the type of cement also has a certain influence. The influence of exposure to CO₂ on the salt-frost resistance of concrete without entrained air was totally different from the influence on concrete with entrained air.