Characterization of Pore Space of Cement-Based Materials by Combined Mercury and Wood's Metal Intrusion

Analysis of the pore space is crucial for a profound understanding of the transport and mechanical properties of porous materials. Mercury intrusion porosimetry (MIP) is an easy and widely applied method to determine the pore size distribution of mesoporous materials, but a principal problem makes data interpretation difficult. Large ink-bottle pores may be accessed by the intruding mercury through smaller, so-called neck pores only. This leads to significant under estimaion of pore sizes and to hysteresis effects between intrusion and extrusion in materials with a broad pore size distribution such as cement-based materials. More accurate pore space information is obtained when ink-bottle pores in the measurement are excluded from analysis. This may be achieved by repeated intrusion cycles or by impregnating the ink-bottle pore space with Wood's metal. The combination of Wood's metal impregnation (WMI) and mercury intrusion in mortars and cement pastes as presented allows a characterization of the pore space independent of accessibility considerations. Different special pore types are defined, analyzed, and quantified. In a cement paste, 50% of all pores are found to be ink-bottle type, of which 60% are accessible through neck entrances larger than 20 nm in diameter. A further 30% of all pores are nonink-bottle type but are connected to the surface through such ink-bottle pores only. Furthermore, hysteresis and contact angle alternation effects between intrusion and extrusion were studied. A contact angle shift of 26° between intrusion and extrusion is proposed.