刘 竞
引气剂与凹凸棒土对新拌混凝土触变性能的影响研究
刘 竞
摘 要:高速铁路曲线段超高混凝土底座板的形态控制是无砟轨道底座混凝土施工控制难点,针对曲线段超高底座板混凝土在凝结前无法有效保持与定型,导致超高不满足要求及排水坡度不能顺利实现等难题,以混凝土动态处理时(如:泵送、浇筑、振捣)具有良好流变性能,静态放置时(如:抹坡、收坡后)具有良好形态保持能力为目标,通过新拌混凝土坍落度、含气量、屈服应力、坡度保持能力等室内试验以及现场工程试用,研究了引气剂、凹凸棒土等矿物掺合料对混凝土触变性能的影响。结果表明,引气剂与凹凸棒土双掺加入,充分发挥了引气剂在浆体引入大量微型气泡的滚珠、润滑作用与凹凸棒土凝胶在浆体中的纤维状结构与取向网络分布的束缚、托举的复合作用,提高新拌混凝土静态屈服应力至10.28N·m、降低动态屈服应力至5.47N·m,增加静/动态屈服力矩比至1.9,改善混凝土坡度保持能力至95.6%。现场试用情况表明,在泵送压力无明显增加情况下,引气剂与凹凸棒土双掺混凝土硬化后底座超高坡度保持率93%以上,明显优于单掺引气剂的混凝土。
Abstract: The elevation control of concrete bottom slab in curve line section of high-speed railway is difficult because fresh concrete cannot hold its shape and the slope of fresh concrete cannot maintain effectively before concrete hardening. To solve this problem, air-entraining agent and attapulgite clay were used to improve the thixotropy of fresh concrete. Results indicated when air-entraining agent and attapulgite clay incorporated simultaneously, the static yield stress of fresh concrete increased (10.28N·m), the dynamic yield stress decreased (5.47N·m), the ratio between the static and dynamic yield stress increased (1.9), and the ability of holding the shape and slope was improved (95.5%). Moreover, the pumping pressure was not increased obviously. The slope-holding rate of concrete bottom slab in curve line section on site reached more than 93% with air-entraining agent and attapulgite clay simultaneously added which was significantly better than that of fly ash concrete. This is mainly due to fibrous gel structure and orientation distribution of attapulgite clay and spherical air bubbles incorporated by air-entraining agent in fresh cement paste. These will provide valuable and useful references for quality control of concrete bottom slab in curve line section of ballastless track.
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