Evaluating the effect of high fly ash content and low curing temperature on early hydration heat of blended cement based on isothermal calorimetric method

• Published in: Construction & building materials Vol. 430; p. 136110
• Main Authors: Li, Lin, Feng, Tengteng, Li, Yizheng, Zhang, Youwei, Sun, Wangwen, Liu, Zhuangzhuang
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 07.06.2024
• Subjects: Blended cement; Fly ash; Hydration heat; Isothermal calorimetric; Low temperature; Modeling; Isothermal calorimetric; Fly ash; Hydration heat; Modeling; Blended cement; Low temperature
• ISSN: 0950-0618; 1879-0526
• DOI: 10.1016/j.conbuildmat.2024.136110

Low temperatures environment in cold regions seriously affect the hydration reaction of cementitious materials. In this study, we specifically investigated the effect of low curing temperatures on the hydration heat of blended cement containing high fly ash (FA) content via isothermal calorimetry. The index of full-width at half-maximum (FWHM) value and the cementitious index (CMI) of FA were employed to assess the influence of low curing temperature and high FA content. Moreover, the different hydration stage was studied in detail. The decrease in curing temperature and the increase in FA content cause the end time of the induction period to be delayed, while the duration of the acceleration period and the arrival time of the exothermic peak increase. The CMI analysis reveals that the increase in temperature (10–20 °C) intensifies and advances the hindering effect of FA on cement hydration during the first 48 h of hydration. The FWHM value is related to the shape of the heat flow curve in acceleration and deceleration periods, which is mainly affected by the curing temperature, whereby a drop in curing temperature results in an increase in FWHM value. The FWHM values of samples cured at 5 °C, 10 °C, and 15 °C were 3.8%, 68.2%, and 154.8% higher than that of samples cured at 20 °C, respectively. This may be due to that the nucleation site effect of FA slows down the reduction rate of heat flow in the deceleration period, and the decrease in temperature makes the heat release curve gently. It is feasible to use a logarithmic function model to fit the hydration heat results of samples with FA content ranging from 0% to 42% and cured within the temperature range of 5–20 °C. Furthermore, this model can be utilized to predict the hydration heat for an extended age. [Display omitted] •The effect of FA content and low temperatures on the hydration heat was studied.•FA delays the induction period of hydration at 20 °C.•FA promotes the hydration reaction of blended cement paste at 5 °C.•The rise of curing temperature amplifies and advances the hindrance effect of FA.