Abstract
The purpose of the study is to understand how the cyclic water freezing (0, 25, 50, 75, 100 and 150 freeze-thaw cycles) impacts microstructure and transport properties of cement-based materials. Tests were conducted on cement mortars with different water/cement ratios (w/c=0.45 and 0.40) and on two types of cement (CEM I and CEM III) without air-entraining admixtures. The changes of pore size distribution and open porosity were investigated by means of mercury intrusion porosimetry. Additionally, the relationship between intrinsic permeability and the water absorption coefficient of cement mortar samples was analysed. The water absorption coefficient and gas permeability were determined using capillary absorption test and the modified RILEMCembureau method. The evolution of transport coefficients with growing number of freeze-thaw cycles were determined on the same sample. It was also established that change of pore structure (a decrease of small pore volume <100nm and increase of larger pores >100nm) induces an increase of water transport parameters such as permeability and water absorption coefficient. The higher gas permeability corresponds to the higher internal damage. In particular, it is associated with the change of cement mortar microstructure, which indicates damage of narrow channels in the pore structure of cement mortars.
Highlights
A complex pore microstructure is characteristic for the cement-based materials
The comparison of the averaged cumulative pore volume, pore size distribution is presented in Fig.1 and Fig. 2, respectively
The samples made of Z_4 mortar are more resistant to cyclic water freezing, no structure deterioration can be noticed until 150 frost cycle
Summary
A complex pore microstructure is characteristic for the cement-based materials. The total porosity consists of the closed pores, which do not contribute significantly to the permeability of the material, and open pores. The evolution of transport properties of cement-based materials due to the environmental loading is essential for a profound understanding of damage phenomena. The relationship between microstructure, transport properties and durability of cement-based materials is of particular importance when the ice-induced deterioration is considered. Since the parameters characterizing the inner structure of the cement-based materials, such as porosity or permeability, determine their strength, and risk of degradation of cement matrix due to aggressive environment [2,3]
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