大体积混凝土低热水泥与普通水泥基胶凝材料热学及力学性能对比研究

胶凝材料水化热是造成大体积混凝土温度裂缝的主因,工程中多采用低热水泥或掺加矿物掺合料的普通水泥基胶凝材料降低水化热,目前关于二者水化热降低机制及力学、热学综合性能的对比研究较少。系统测定不同粉煤灰、矿渣掺量下低热水泥和普通水泥基胶凝体系的水化热和抗压强度,对比分析二者在3、7 d水化热条件下的热学、力学性能发展规律,建立热学、力学综合性能等值线图,为大体积混凝土胶凝材料选择提供参考。研究表明,在相同3、7 d水化热条件下,掺加掺合料的普通水泥基胶凝材料早期水化热及放热速率低于纯低热水泥,适用于对早期强度要求较高的工民建大体积混凝土;低热水泥最终水化热低,后期强度增长率大,适用于设计龄期较长的水工大体积混凝土;根据温度控制或强度要求,通过综合性能等值线图,可直接确定水泥基胶凝材料的力学、热学最优性能及其组成,为大体积混凝土胶凝材料选择提供参考。

Comparative Study on Thermal and Mechanical Properties of Low Heat Cement and Ordinary Portland Cement-based Cementitious Materials in Mass Concrete

The primary cause of temperature cracks in mass concrete is the hydration heat of cementitious materials. Using low heat cement or an ordinary cementitious material with mineral admixtures is the main approach to reduce the hydration heat. However, only a few comparative studies have investigated the mechanisms due to which the hydration heat is reduced and the comprehensive properties of materials, including their strength and hydration heat. The hydration heat and compressive strength of systems based on low heat cement and ordinary cement with different contents of fly ash and slag are measured in a systematic manner. To understand the mechanical and thermal properties, two cementitious materials exhibiting identical 3 d and 7 d hydration heat are compared. A contour diagram of the comprehensive performance of the two cementitious materials is sketched to provide a reference for the selection of a mass concrete cementitious material. The research results exhibit that under identical 3 d and 7 d hydration heat conditions, ordinary cement with an admixture exhibits a lower hydration heat and exothermic rate than those exhibited by pure low heat cement at an early stage. Therefore, ordinary cement is suitable to manufacture mass concrete, which is required in the fields of civil engineering and construction that demand high early strength. In case of low heat cement, the final hydration heat is low and the increase in late strength is large, which makes it suitable to be utilized in long term hydraulic mass concrete. According to the temperature control or strength requirements, the composition of cementitious materials and optimal mechanical and thermal properties can be directly determined using the comprehensive performance contour map, which further serves as a reference for the future selection of mass concrete cementitious materials.