索塔锚固区泵送高性能钢纤维混凝土的研制

DEVELOPMENT OF PUMPING HPSFRC FOR ANCHORAGE ZONE BETWEEN STEEL ANCHORAGE BOX AND CABLE IN BRIDGE TOWER

普通纤维混凝土因可泵送性差很少用于索塔锚固区。采用多重复合技术,优选纤维混凝土配合比,并研究了各配合比的泵送性能;模拟干热环境,对优选的高性能混凝土(HPC)和钢锚箱锚固区专用高性能钢纤维混凝土(HPSFRC)进行了塑性收缩试验;研究了纤维掺量和减缩剂对塑性收缩和干燥收缩性能的影响,并对其机理进行了探讨。研究表明,经优化的高性能钢纤维混凝土2h内泵送性能优良。随着纤维掺量的增加,塑性收缩的开裂总面积下降,混凝土的抗裂等级提高。当钢纤维的体积掺量为0.8%时,高性能钢纤维混凝土自由干燥90d的收缩值同高性能混凝土相比下降了50%;有约束的干燥收缩66d试验环未见开裂,从而减少混凝土开裂的风湿,提高混凝土结构的耐久性。与同强度等级的高性能混凝土相比,钢纤维的加入也改善了混凝土的力学性能,高性能钢纤维混凝土的抗弯强度和劈拉强度提高了近30%。试验结果还表明,纤维体积率为0.6%的钢纤维与减缩剂复合后,对抑制塑性收缩和干燥收缩效果显著。

The usual fiber concrete is not widely used in high bridge tower due to bad pumping performance. Experiments were concentrated on pumpability, plastic shrinkage and drying shrinkage of the anchorage concrete. Based on the advanced multi-compound technique, the fiber concrete mix design was modified to ensure good pumpability. The effect of hot weather conditions on plastic shrinkage cracking of high performance concrete （ HPC ） and special high performance steel fiber- reinforced concrete （HPSFRC） have been analysised by the method of artificial imitation in the lab. The effect of fiber content and shrinkage-reducing agent （SRA） on plastic shrinkage cracking and drying shrinkage of HPC was also investigated. In the end, influence mechanisms have been explained. After 2 hours out of the machine, HPSFRC with the optimal mix proportion has good pumpability. The experimental results show that with the increase of content of fiber used in HPC, the total areas of plastic cracking decrease and the concrete anti-cracking grade improves. For HPC in which volume fraction of steel fibers is 0.8 %, the free drying shrinkage could be diminished by about 50 % in 90 days and the restrained drying shrinkage cracking could be avioded thoroughly within 66 days after casting, and accordingly reduce the cracking risk of concrete, and result in higher durability in anchorage zone. The test results also show that when 0.6% volume fraction of steel fibers together 1.5% SRA（by weight of eementitious material） are added into HPC, plastic shrinkage cracking and free drying shrinkage diminished obviously at early age. Furthermore, compared with the same strength of HPC, the experimental results indicate the addition of steel fiber improves the long term mechanical properties of HPC, especially the bending strength and splitting strength improve by 30 %.