Contribution of pore structure analysis in short-term mechanical performance of lake sediments-based mortars

Abstract The study focuses on the analysis of the microstructure on the short-term mechanical performance of sediment-based mortars, prepared with the sandy and clayey San Giuliano and Camastra reservoirs sediments, to minimize the use of natural resources and to reduce the cement quantity. The workability of mortars was first investigated according to the rate of incorporation of sandy and/or clayey sediments, with a mass ratio of 0.5 as a standardized mortar. This ratio increases to 0.64 when clayey sediment is incorporated in place of cement, if the clayey sediment is not considered as a binder. The influence of water quantity and of sandy and/or clayey lake sediment substitutions on the microstructure of these mortar mixes was analyzed by measuring the specific surface area, pore size, and volume for specimens. Different samples have been compared regarding adsorption/desorption hysteresis and pores network. It was found that mortars absorb more water than normalized mortar (MN), due to a larger specific surface area. MN is the reference cementitious mortar, manufactured with river sand, common used in constructions. The mechanical strengths are about half that of MN, except mortars E10 and E12. The replacement of part of the binder with the upstream clay material significantly affects mechanical strengths, unlike pore size distribution, pore volume and adsorbed volume, on which the impact is less pronounced. The relationship between mortars’ mechanical properties and microstructural characteristics shows that specific surface area is not a significant parameter. On the contrary, the pore size distribution is a key parameter for predicting the in situ mortars’ behavior: higher pore size values (> 25 Å) correspond to better workability and to higher mechanical strength, so that their use, with nonstructural functions, can be hypothesized for applications on site.