Effect of preconditioning on the freeze-thaw resistance of concrete

The pore system in concrete, consisting of gel and capillary pores, influences its water absorption capacity and thus directly also the freeze-thaw resistance Different exposure conditions in the young age of concrete have a significant influence on the formation of the pore system. To clarify the role of preconditioning on the forming pore structure and thus the freeze-thaw resistance of concrete, specimens were preconditioned at different relative humidities and then tested according to the CDF test It was found that the freeze-thaw resistance of specimens with a water-cement ratio of 0.40 depended significantly on the degree of hydration near the surface. This varied due to the different humidities during preconditioning. The decisive criterion for the freeze-thaw resistance of the specimens with a water-cement ratio of 0.55 is the degree of water saturation due to the distinctive capillary pore system of this w/c. The degree of water saturation of the specimens with a water-cement ratio of 0.55 is also a decisive criterion for the freeze-thaw resistance. Specimens with a particularly distinct capillary pore system possessed very high amounts of weathering. Finally, a prediction model based on an artificial neural network is presented. This model is able to predict the weathering of mortar samples in the CDF test on the basis of moisture measurements before freeze-thaw exposure.