Effects of environmental exposure on Portland cement Type IL

This study investigates the physico-chemical change in a Type IL cement prehydrated in the natural environment for 7, 14, and 21 days. A focus was made on the reaction kinetics, product formation, and strength development using calorimetry, XRF, QXRD, TGA and compressive testing. It was found that prehydration converted hemihydrate to gypsum and partially transformed the principal cement phases and inherent portlandite into carbonates, thus reducing C₃S and C₂S while increasing CaCO₃ and gypsum. Hydration was slowed down with a delay in the appearance of the aluminate peak and reduction in cumulative heat at 72 h. Consequently, more C₃S and C₂S remained at an early age. Less ettringite was formed while amorphous phases were initially reduced but promoted later on. A secondary decomposition peak linked to metastable CaCO₃ became more prominent in the prehydrated samples. The early-age strength was reduced with the exposure time, but the 28-day strength improved due to the continuing hydration.