Precast concrete materials, manufacture, properties and usage - Chapter 7

ACCELERATED CURING - Chương này tích hợp các kinh nghiệm của Laing R + D và Anh Liên đoàn Bê tông đúc sẵn (BPCF) về chủ đề bảo dưỡng nhiệt, mục đích là để tạo ra một nền tảng của hướng dẫn cho học viên có nhu cầu để sản xuất cao-đầu cường độ bê tông bằng cách sử dụng nhiệt nhưmáy gia tốc. Nó không phải là mục đích của tập thể dục để tóm tắt các báo cáo, dữ liệu đã được tóm tắt điểm đặc biệt cần được thực hiện. Khi tốc độ của phản ứng. | 7 ACCELERATED CURING This chapter integrates the experience of Laing R D and the British Precast Concrete Federation BPCF on the subject of heat curing the purpose is to produce a background of guidelines for the practitioner wishing to produce high-early-strength concrete using heat as the accelerator. It is not the purpose of the exercise to summarise each of the reports data has been abstracted where particular points need to be made. When cement hydrates its speed of reaction is mainly a function of the starting temperature of the system and the curing regime. Hydration is accompanied by exotherm so the concrete tends to warm up as hydration progresses. What this means is that a cold-starting concrete say 5 C warms up and gains strength slowly a warm-starting concrete say 25 C warms up and gains strength more quickly and a concrete starting at say 40 C can be handled within a few hours. Any method of accelerating the early strength of concrete is known to detract from the 28-day strength the usual specification age for concrete cube strength. However this decrease more often than not is within the range of the 10 variation one obtains. What is really significant is that heat curing is carried out to obtain a high early strength and 28 day strength specifications are generally exceeded by an excess one does not require. Research data obtained from both industrial and laboratory processes show that although there is a decrease in the 28 day cube strength at 36 months old the strength is equivalent to that of the normal-cured concrete. Flexural strength at 4-24 hours old is the practical consideration as concrete is subject to bending during demoulding and handling. If for example one aimed at and achieved a minimum 16 hour flexural strength of 3 N mm2 the cube strength at that time would be about 15 N mm2 and about 45 N mm2 at 28 days old. Copyright Applied Science Publishers Ltd 1982 Published data is rather sparse on the subject and the main references that .