模拟地热环境下延迟钙矾石的形成探究

Study on the formation of delayed ettringite in simulated geothermal environment

随着“西部大开发”战略推进,我国基建工程逐渐延伸至藏南—川西—滇西地热带,工程中经常出现高温蒸汽喷出、隧洞岩壁高温等地热高温热害问题。而在蒸养、地热等高温环境下,混凝土水化硬化初期生成的钙矾石(AFt)会受热分解,转化为单硫型硫铝酸盐(AFm),随龄期增长易与未反应的硫酸根在孔隙或骨料界面处生成延迟钙矾石,从而导致混凝土膨胀开裂,为西部山脉中桥隧工程的安全服役埋下严重隐患。鉴于此,试验采用溶液法模拟水泥孔溶液中钙矾石生成的液相环境,通过高温蒸养模拟90℃地热环境,综合运用XRD、SEM、热重分析等测试技术,对地热环境中钙矾石的生成与温度、石膏掺量的关系进行了研究,得出了70~75℃为延迟钙矾石生成(DEF)的临界温度区间,地热环境服役混凝土中石膏的适宜掺量在4%左右的结论。

With the promotion of the “China's Western Development Policy”,China's infrastructure projects gradually extend to the subtropical zone of Southern Tibet-Western Sichuan-Western Yunnan.High temperature heat hazards such as high-temperature steam ejection and high temperature of tunnel rock wall often occur in the projects.Under the high-temperature environment such as steam curing and geothermal,the ettringite(AFt)generated at the initial stage of concrete hydration and hardening will be decomposed by heating and converted into single sulfur sulphoaluminate(AFm).With the increase of age,it is easy to form delayed ettringite with unreacted sulfate at the pore or aggregate interface,and result in concrete expansion and cracking,which posts a serious hidden danger for the safe service of the bridge and tunnel engineerings in the western mountains.In view of this,the test uses the solution method to simulate the liquid phase environment of ettringite formation in cement pore solution,simulates the geothermal environment of 90 ℃ through high-temperature steam curing,and comprehensively uses XRD,SEM,thermogravimetric analysis and other test technologies to explore the relationship between ettringite formation and the temperature and gypsum content in geothermal environment.It is concluded that the critical temperature range of delayed ettringite formation(DEF) is about 70~75 ℃,and 4% is the appropriate content of gypsum in concrete in geothermal environment.