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.
A one-day Nordic Concrete Research workshop on “Accelerated freeze-thaw testing of concrete” attracted approx. 30 participants. The workshop included presentations on various aspects, such as observed frost damage in the field and the importance of the temperature curve during testing as well as other interactions with the surroundings of the concrete. The workshop also included examples of recent research, which can improve our knowledge about the frost damage mechanism and therefore provide input to improving the standardised test methods. The present paper is a summary of the nine presentations and the discussion arising from the presentations.
It has been observed that storage of specimens with chloride gradients before determining the chloride profile can lead to changes in the shape of the chloride profile. An experimental study to quantify the influence of the duration of the storage period and the storage temperature has been carried out. It comprised three storage periods (7, 28 and 91 days) and two storage temperatures (+ 5 °C and + 20 °C). The specimens had previously been immersed in a 15% NaCl solution for 56 days and were sealed in plastics during storage. The results show that a temperature of + 5 °C diminishes the rate of redistribution considerably, compared to a storage carried out at + 20 °C, and the longer the storage period is, the more redistribution will take place. It is also shown that it is of importance to assure that the sealing of the specimens during storage is capable of maintaining the relative humidity at the surface, so that local redistribution of chlorides close to the surface will not take place.
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