Optimisation of cement-sand mortar compositions modified with fine-grained rubber powder in relation to their mechanical performance

The article presents the results of a research study aimed at determining the optimum amount of 0/1 mm rubber powder additive for cement-sand mortars (CSM) used in asphalt-cement concretes (ACC), to meet the requirements for mineral-cement-emulsion mixtures (MCEM) due to the lack of regulations concerning these concretes. The study includes test results for indirect tensile strength (ITS) and stiffness modulus (IT-CY method) at 5°C, performed after 7 and 28 days of curing. The regression curves for ITS and IT-CY values in relation to rubber powder content after 7 days were well described by exponential functions, whereas the results after 28 days were best fitted by linear functions. It has been observed that compliance with ITS limit requirements excludes CSR mortars that meet IT-CY requirements, and vice versa. In order to clearly define the requirements for mortar mixtures, minimum and maximum ITS and IT-CY values were proposed so that the samples would meet both requirements simultaneously. Supplementary tests were also carried out to assess water resistance.