Effects of pre-curing treatment and chemical accelerators on Portland cement mortars at low temperature (5 ℃)

摘要

Artificial heating and chemical admixtures are widespread solutions to keep and improve the early strength of cement concretes in cold weather. The research analyzed the performance of cement mortar at low temperature (5 degrees C) in combination with pre-curing treatment and the use of chemical accelerators, e.g., calcium chloride (CaCl2), sodium nitrite (NaNO2), potassium carbonate (K2CO3), and sodium sulfate (Na2SO4). The investigation comprised the mechanical behavior, setting time, released heat of hydration, and microstructures. The standard curing pretreatment at 20 degrees C, differently from curing at 5 degrees C, engendered a reduction in the mechanical strength of both untreated and chemically treated cement mortar samples. Although all chemicals accelerated the reactions of hydration, the achieved compressive strengths of the mortars were different. The specimens treated with calcium chloride (CaCl2) reached the highest compressive strength, followed by sodium nitrite (NaNO2) and sodium sulfate (Na2SO4). Specimens containing potassium carbonate (K2CO3) attained the lowest compressive strength. Further analyses highlighted the importance of the time interval between initial and final setting: a shorter time interval led to lower mechanical strength due to more cracks in the cement matrix. (C) 2019 Elsevier Ltd. All rights reserved.