Hardened cement paste microstructure as the main factor of concrete durability

摘要

When studying durability of concrete the main emphasis is put on its resistance to frost, water and sulphate, which depends on type, dispersion and stability of cement hydration products. The paper focuses on interrelation between strength, open porosity and peculiarities of microstructure of hydrated phases and their crystallization tendency under cyclic and chemical actions. In order to find out these dependences, the following parameters were defined in compliance with standards: open porosity of concrete by water absorption, compressive and tensile strength in bending, frost resistance and sulphate resistance. Methods applied in the research are X-ray diffraction analysis and scanning electron microscopy. The most promising structure of hardened cement paste for obtaining modern paving concrete is the one formed by weakly crystallized gel phases of type C-S-H(I) which are resistant to crystallization and provide stability and durability of concrete. One of the most used methods to obtain such structure is addition of compounds containing activated pozzolanic materials and superplasticizers.