Novel application of potassium methylsiliconate in cement-based materials: Retarding of hydration process and improvement of compressive strength

The presented research investigates the application of the organosilicon compound named potassium methylsiliconate (MESI) as a set-retarding admixture for cement-based materials which also provides the strengthening effect. The study concerns the impact of three dosages of MESI (1%, 2% and 3% per cement mass) on the properties of the cement paste, mortar and concrete. The greatest delay of the setting time of cement CEM I 42.5 R and retardation effect, examined by manual Vicat apparatus, was observed for addition of 1% methylsiliconate. The beginning of the setting was prolonged to 23 h. The influence of potassium methylsiliconate on the kinetics of cement hydration was investigated by isothermal calorimetry. The calorimetric results disclosed significant extension of induction period during Portland cement hydration with addition of potassium methylsiliconate as an admixture. It is especially visible in case of addition of 1% of MESI. Moreover, tests performed at 30 °C, 40 °C and 50 °C showed that MESI can also delay the cement hydration at higher temperatures. The influence of potassium methylsiliconate on the compressive strength of cement mortar and concrete after 1, 2, 7, 28 days and72 days was also investigated. In the first days of hydration, the compressive strength of the materials was reduced, but after 28 days of curing the compressive strength was increased by 21% and 16% for cement mortar and concrete, respectively. The impact of MESI on the microstructure and pore size distribution of cement pastes in 2nd, 7th and 28th of hydration was examined by mercury intrusion porosimetry (MIP). The result showed significant delay in the development of the cement pastes microstructure during the first days of hydration. The XRD and DTA/TG analysis provided the knowledge about impact of siliconate on the composition and formation of the cement phases. Both, the XRD and DTGA/TG analyze showed noticeable changes in portlandite formation during the first days of hydration. The conducted research and obtained results reveal the innovative and novel application of potassium methylsiliconate as retarders, which prolongs the workability of fresh mixture and improves the compressive strength of matured concrete and mortar. This admixtures can be a competitive alternative to traditional retarders.