The pore structure of cement paste blended with fly ash

• Under long-term curing age up to 2 years, the pore structure of cement paste blended with fly ash is discussed.
• Linear relationships between total porosity and curing age are found.
• The linear relationships can be used to predict the total porosity in practice project.
• Compared with total porosity, pore size and pore connectivity play a significant role in studying transport properties.

To make full use of solid by-products and to improve the durability properties of concrete, fly ash is normally used as partially replacement of cement in the field of concrete. However, the addition of fly ash influences the pore structure of blended cement paste, which is one of the most important factors that influence the transport properties of concrete. The objective of this paper is to investigate the influence of fly ash on pore structure in blended cement paste at long-term curing age up to 2 years. Mercury intrusion porosimetry (MIP) test method was used to evaluate total porosity, pore size distribution (PSD) and critical pore size. The test specimens were sealed cured prior to testing. The influences of different water to binder (w/b) ratio and dosage of fly ash on the pore structure of blended cement paste were investigated. The results indicate that the addition of fly ash contributes to higher total porosity in blended cement paste regardless of w/b ratio and dosage. The critical pore size and PSD of each sample is variable, although the test samples have similar total porosity. At later curing age, blended cement pastes have the smaller critical pore size than reference sample.