Impact of moisture curing conditions on mechanical properties of lime-cement mortars in early ages

Blended lime-cement mortars, which are frequently used in masonry construction, mature as a result of two different phenomena, namely lime carbonation and cement hydration. At any given temperature, these two processes require different moisture conditions for optimal contribution to the mechanical performance of mortar. Since mortars have an impact on the non-linear behavior of masonry from the time of application, it is necessary to optimize their performance with regard to composition and curing conditions. It is expected that a suitable choice of mortar in conjunction with the unit will provide better performance of masonry by reducing risk of cracking and facilitating durability of masonry. This work aims at studying the impact of environmental relative humidity (RH) in the curing process of lime-cement mortars, focusing on their early age behavior. Two mixes with 25% and 67% lime in the binder (by volume), binder-aggregate ratio of 1:3 and target workability of 175±10 mm were chosen for the study. Mechanical properties like compressive strength, flexural strength, open porosity and density have been studied at 2, 4 and 7 days of curing age. Temperature was kept constant at 20°C while three distinct environmental humidity conditions were tested: sealed environment, 90% RH, and 60% RH. Results have been explored to understand how the evolution of basic mechanical properties changed as a function of curing RH. Curing in sealed conditions and 90% RH did not result in similar values of strength, in either of the two blended mixes. For the mix with 25% lime - 3C1L12S (25%), hardening appeared to be guided by cement hydration. For the mix with 67% lime - 1C2L9S (67%), curing in RH of 60% and 90% resulted in almost the same strength at day 7, demonstrating that lime carbonation may be important earlier than 7 daysEuLA - European Lime Association, FCT PhD Grant of 1st Author. European Lime Association for funding this project. Funding provided by the Portuguese Foundation for Science and Technology (FCT) to the Research Project PTDC/ECMEST/1056/2014 (POCI-01-0145-FEDER-016841), Research Unit ISISE (POCI-01-0145-FEDER-007633), and scholarship SFRH/BD/137358/201