Andrew S. Smith1
1) Programme Leader, Cement, Clay & Concrete Technology
Mineral Products Centre, University of Derby, DE1 3LD United Kingdom

Keywords: Masonry Mortar, Porosity, Pore Structure, Durability, Freeze-thaw.

Abstract. The durability of masonry mortars is fundamentally linked to the physical properties of the mortar in its hardened state. One of these key properties is porosity and pore connectivity (capillary pore structure and permeability). The pore structure seen in hardened mortars can be formed by a number of processes including; air entrainment, air entrapment, free water evaporation or chemical dissolution. The resulting macro and micro pore structure has a significant impact upon the long term durability of the mortar, not least in relation to cyclical freeze-thaw action, cyclical salt crystallisation and the movement of moisture within the mortar and the masonry units. This paper explores the results of detailed studies of the pore structure of different mortars, using both 2D visual imagery (SEM Photomicrographs), surrogate porosity measurements such as water absorption and initial rate of water absorption results, along with results from laboratory testing of freeze-thaw durability testing, with the view of understanding the influence that the pore structure has on the durability of the mortar in service, and the pore size range that is most influential. Initial results indicate that the pore structure has an influence on the long term durability of the mortar, especially the resistance of the exposed mortar surface to progressive erosion, however careful choice of analytical techniques to measure the correct pore size range is critical, not least as the macro porosity, >100μm, and total porosity don’t necessarily directly correlate with observed durability.