粗骨料体积分数对模袋混凝土干燥收缩的影响研究

粗骨料体积分数是模袋混凝土配合比设计的关键指标。开展了粗骨料体积分数在0.30～0.36的范围内对模袋混凝土扩展度、抗压强度和干燥收缩的影响研究，以期为模袋混凝土衬砌渠道的抗裂性设计提供参考。结果表明：在相同水胶比条件下随着粗骨料体积分数的增大，模袋混凝土的扩展度总体呈现波动上升再平稳的趋势，而低水胶比会使得扩展度更大；在相同水胶比下，随着粗骨料体积分数的增大，模袋混凝土的28 d抗压强度总体呈先减小后增大的趋势，而水胶比的降低会显著增大28 d抗压强度；随着粗骨料体积分数的增大，模袋混凝土的28 d干燥收缩率呈先减小后增加的趋势，在粗骨料体积分数为0.32时有最小值，而粗骨料体积分数分别为0.30、0.34、0.36时所对应的前7 d干燥收缩率均可达28 d总干燥收缩率的50%以上，说明模袋混凝土的干燥收缩在早期增长较快。

Effect of volume fraction of coarse aggregate on drying shrinkage of mold bag concrete

The volume fraction of coarse aggregate is a key index for the mix ratio design of mold bag concrete. In order to provide some reference for the crack resistance design of mold bag concrete lined channels, the influence of coarse aggregate on the slump flow, compressive strength and drying shrinkage of mold bag concrete is studied when the volume fraction of the aggregate falls in the range of 0.30-0.36. The results show that under the the same water-binder ratio, the overall slump flow of mold bag concrete rises with fluctuations and then stabilizes with the increase of the volume fraction of the coarse aggregate, and the lower the water-binder ratio the larger the slump flow. Under the same water-binder ratio, the volume fraction of coarse aggregate decreases first and then increases the 28 d compressive strength of mold bag concrete, whereas the decrease of water-binder ratio significantly increases the 28 d compressive strength. With the increase of the volume fraction of coarse aggregate, the 28 d drying shrinkage rate of mold bag concrete decreases first and then increases, and the minimum value is reached when the volume fraction is 0.32. The corresponding drying shrinkage rate of the first 7 days can reach more than 50% of the total drying shrinkage rate of 28 d when the volume fraction of coarse aggregate is 0.30,0.34 and 0.36, indicating that the drying shrinkage of the mold bag concrete increases rapidly at the early stage.