青藏高原多年冻土地段灌注桩混凝土的研究和对策

研究目的:针对青藏高原多年冻土地段建设铁路、公路遇到桥跨结构混凝土灌注桩基强度的发展,耐久性和热传递对冻土结构扰动的技术难题等情况,提出相应对策。研究方法:对青藏公路桥基混凝土的耐久性破坏进行调研、室内模拟试验、现场暴露试验及清水河、昆仑山口桩基试验。研究结果:青藏公路冻土地段桩基混凝土长期处于恒负温下,硬化强度达不到设计等级;耐久性破坏主因是正、负温频繁交替引发冻融破坏,未发现有硫酸盐侵蚀破坏迹象;混凝土初温和水化热使界面冻土结构破坏,较长时间后,界面冻土才能回复到原始冻结状态。研究结论:掺用引气减水剂或早强引气减水剂拌制低温早强耐久混凝土可以满足对于混凝土灌注桩强度、耐久性和冻土结构稳定性的要求。若采用负温(-5~-20℃)混凝土方案时,须注意抗冻剂可能产生对界面冻土结构稳定性和环保的负面影响。

Research on Concrete of Cast-in-place Pile for Permafrost Zone in Qinghai- Tibet Plateau and Its Countermeasures

Research purposes: The countermeasures were proposed to the technical difficulties in strength and durability of concrete,and disturbance on frozen-soil structure by thermal transmission while building bridge span structure by adopting cast-in-place concrete pile in construction of railway and highway in permafrost zone in Qinghai-Tibet Plateau.Research methods: The research,indoor simulation test,site exposure test and tests for the pile foundations in Qingshui River and Kunlun Mountain's port were done for the durability's damage of concrete of bridge foundation on Qinghai-Tibet Highway.Research results: The hardening strength of concrete of pile foundation in permafrost on Qinghai-Tibet Highway couldn't arrive at the design grade because the concrete had been in negative temperature for long term.The main reason for durability damage was freezing-thawing damage caused by alternation of positive and negative temperatures frequently,and it was found no corruption damage by surfate.The start temperature of concrete and heat of hydration made frozen-soil structure damaged in interface.The frozen soil could return to its original frozen status for long time later.Research conclusions: The moderate-heat early-strength concrete made from air-leading water-reducing agent or early-strength air-leading water-reducing agent could meet the requirements for the strength and durability of cast-in-place concrete pile and the stability of frozen soil structure.It was necessary to note the anti-freezing agent probably had negative effect on the stability of frozen soil structure in interface and environment protection.