早龄期冻结土压力与负温耦合作用的井壁混凝土性能

研究了早龄期冻结压力等荷载、负温及早龄期荷载和负温耦合作用对冻结竖井井壁C60混凝土抗压强度、氯离子扩散系数和声发射特征的影响，并通过扫描电镜分析其内部微裂缝.结果表明:早龄期荷载加载时间越早对混凝土28d抗压强度的影响越大，当外部荷载作用时间在3d以后且荷载水平在混凝土当天强度40%以内时，混凝土28d强度几乎不受影响；冻结井井帮负温环境会延缓井壁混凝土早期水化，防冻剂的加入利于加快混凝土水化和强度的发展；在早龄期荷载及负温耦合作用下，混凝土28d抗压强度降低明显，氯离子扩散系数大大增加，混凝土的渗透性由"中"变为"高"，内部产生了缺陷和微裂缝导致声发射"活跃阶段"提前，且混凝土呈现明显的塑性变形. 

Performance of shaft lining concrete under the coupling effect of early-age frozen soil pressure and negative temperature

The effects of early-age frozen pressure,negative temperature,and early-age load and negative temperature coupling on the strength,chloride diffusion and acoustic emission characteristic of freezing shaft wall C60 concrete were studied,and the internal microcracks were analyzed by scanning electron microscopy(SEM). It is found that the earlier the early-age load applies,the greater effect it has on the 28 d compressive strength of the concrete. But when the external load is applied 3 d later and the load level is less than 40% of the day's strength,the 28 d compressive strength of the concrete is almost not affected. A negative temperature environment of the freezing shaft wall can delay early concrete hydration,and antifreeze speeds up the development of concrete hydration and strength. Under the early-age load and negative temperature coupling effect,the 28 d compressive strength and durability of the concrete decrease,the chloride diffusion coefficient increases apparently,the concrete permeability changes from middle to high,the internal microcracks and deficiencies lead to advancing the active phase of acoustic emission,and the concrete presents apparent plastic deformation.