Influence of limestone powder used as filler in SCC on hydration and microstructure of cement pastes

In recent years, self-compacting concrete (SCC) has gained wide application in the construction industry. As for high performance concrete (HPC) and traditional concrete (TC), the microstructural properties of SCC are the main factors, which determine the material properties, i.e. the mechanical properties, transport properties and the durability behaviour.In order to investigate the development of the microstructure of SCC, the microstructural parameters of the paste including porosity, pore size distribution and phase distribution are determined by means of mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). The thermogravimetric analysis (TGA) and the derivative thermogravimetric analysis (DTG) are used to identify the phase constituents. These parameters as studied for self-compacting concrete are compared with high performance concrete and traditional concrete. The specimens of self-compacting cement paste (SCCP) are made with water/binder ratio 0.41 and 0.48, the high performance cement paste (HPCP) with w/c 0.33 and traditional cement paste (TCP) with w/c 0.48. The measurements are performed at different hydration stages, i.e. at 1, 3, 7, 14, 28 and 56 days.The result of this research shows that the pore structure, including the total pore volume, pore size distribution and critical pore diameter, in the SCCP is very similar to that of HPCP. The fact that limestone powder does not participate in the chemical reaction was confirmed both from thermal analysis and BSE image analysis.