青藏铁路西格二线混凝土冻融试验研究

研究目的：由于工期的要求，青藏铁路新增西宁至格尔木段必须进行冬期施工。为了保证西格线的施工质量，需要对冬期混凝土施工进行可行性研究。研究方法：本文从分析混凝土冻融机理开始，先进行基础试验，然后通过调整引气剂掺量、调整水胶比大小、砂率大小、粉煤灰掺量大小、粗集料的级配、细集料细度模数大小、混凝土搅拌温度、静停时间、以及其它影响因素来研究含气量对混凝土耐久性的影响而进行了大量的试验。研究结论：混凝土含气量随引气剂掺量的增加而增大，随水灰比的减小而减少，随砂率的提高，含气量逐渐增多，随粉煤灰掺量的增加，混凝土含气量急剧变小，随石子粒径变大，含气量变小，单粒级骨料混凝土含气量比连续级配骨料混凝土含气量低，用中砂的混凝土含气量高而且比较稳定，随温度升高而降低，振捣时间越长，含气量损失越大，搅拌时间太短会导致引气数量不够，时间太长会导致气泡的损失。然而随着含气量的增加混凝土强度呈递减趋势。因此，选择适宜的混凝土含气量是保证混凝土耐久性的关键。

Research on Concrete Freeze- thawing Test for the Second Line from Tibet to Golmud of Qinghai- Tibet Railway

Research purposes: According to the construction schedule,the second line from Tibet to Golmud of Qingghai-Tibet Railway should be constructed in winter season,so it is necessary to do research on feasibility of concrete construction in winter season for the purposes of guaranteeing construction quality.Research methods:First,the base test is done from beginning with analysis of the concrete freeze-thawing mechanism,then the researches are done on the influence on the concrete durability by the air content through adjustments of air entrainment,ratio of water and glue,sand ratio,mixture ratio of fly-ash,coarse aggregate grading,fine aggregate modulus,mixture temperature of concrete,static time and the other factors.Research conclusions:The air content of concrete increases with increment of air entrainment and the air content of concrete reduces with reduction of the ratio of water and fly-ash.The air content of concrete reduces seriously with increments of sand ratio,air content and mixture ratio of fly-ash.The air content reduces with increment of grain size of stone and the air content of concrete mixed with single particle grade is less than that of the concrete mixed with continuous grading aggregate.The air content of concrete mixed with medium-sized sand is high and stable and to this concrete,the tamping time is longer and the lose of air content is more,but if the tamping time is short,the quantity of air entrainment is not enough and if too long,the air bubble will lose.The strength of concrete will reduce with increment of air content,so national selection of air content of concrete is the key point of guaranteeing concrete durability.