回弹抑制剂对湿喷混凝土性能影响规律

Influence of Rebound Inhibitor on Performance of Wet Spraying Concrete

隧道工程中湿喷混凝土回弹率过大是影响工程质量和施工安全的主要问题之一。为了降低湿喷混凝土回弹率并满足混凝土综合性能的要求,根据混凝土工作性能和强度需求确定了混凝土的基准配合比和减水剂的类型及掺量,再采用试验对比法研究了纤维素醚与聚丙烯酰胺2种回弹抑制剂对湿喷混凝土性能的影响。揭示了回弹抑制剂在不同掺量下,喷射混凝土的坍落度、抗压强度、黏结强度和回弹率的变化规律,并结合规范对喷射混凝土性能的综合要求确定了2种回弹抑制剂的掺量范围。结果表明:随着纤维素醚掺量从0‰增加到3‰,坍落度呈现先增长后降低的趋势,坍落度峰值出现在掺量1‰附近;随着聚丙烯酰胺掺量从0‰增加到0.3‰,坍落度降低;随着纤维素醚掺量从0‰增加到3‰或聚丙烯酰胺掺量从0‰增加到0.3‰,混凝土抗压强度出现不同程度的下降,但仍能满足喷射混凝土的抗压强度要求;随着回弹抑制剂的掺入,混凝土黏结强度不断增长,且黏结强度均大于1.0 MPa;未掺入回弹抑制剂时,混凝土回弹率未满足规范需求;掺入纤维素醚2.0‰~3.0‰或掺入聚丙烯酰胺0.15‰~0.25‰后回弹率有明显降低;为满足喷射混凝土综合性能需求,建议纤维素醚适用掺量控制在2‰~3‰范围内,或聚丙烯酰胺适用掺量控制在0.15‰~0.25‰范围内。

The excessive rebound rate of wet spraying concrete in tunnel engineering is one of the main problems affecting project quality and construction safety.In order to reduce the rebound rate of wet spraying concrete and meet the requirements of comprehensive performance of concrete,based on the working performance and strength requirements of concrete,the benchmark mix proportion of concrete and the type and dosage of water reducing agent are determined,and the influences of 2 rebound inhibitors,cellulose ether and polyacrylamide,on the performance of wet spraying concrete are studied by using experimental comparison method.The variation rules of slump,compressive strength,bonding strength,and rebound rate of spraying concrete under different dosages of rebound inhibitors are revealed,and the dosage ranges of 2 rebound inhibitors are determined combining with the comprehensive requirements of spraying concrete performance in specifications.The result shows that(1)with the increase of the dosage of cellulose ether from 0‰to 3‰,the slump decreases after increases,and the peak value of slump appears around the dosage of 1‰;(2)with the increase of the dosage of polyacrylamide from 0‰to 0.3‰,the slump decreases;(3)with the increase of dosage of cellulose ether from 0‰to 3‰,or the increase of dosage of polyacrylamide from 0‰to 0.3‰,the compressive strength of concrete emerges varying degrees of decline,but still meeting the requirements on compressive strength of spraying concrete;(4)with the mixing of rebound inhibitors,the bond strength of concrete is growing,and the bond strength is greater than 1.0 MPa;(5)the rebound rate of concrete does not meet the requirement without mixing rebound inhibitors;(6)the rebound rate decreases significantly after mixing 2.0‰-3.0‰of cellulose ether or 0.15‰-0.25‰of polyacrylamide;(7)in order to meet the comprehensive performance requirements of spraying concrete,it is recommended to control the dosage of cellulose ether within 2‰-3‰or the dosage of polyacrylamide within 0.15‰-0.25‰.