C40大体积自密实混凝土在盾构井侧墙中的应用研究

Study on the Application of C40 Large Volume Self-compacting Concrete in Side Wall of Shield Tunnel

自密实混凝土具有良好的流动性和粘聚性,能自行流淌到无法振捣施工的复杂混凝土结构中,近年来获得了大量的工程应用。本工程是北京六环入地盾构井主体结构,其侧墙属于重要防渗抗裂永久结构,结构尺寸大于1m,属于大体积混凝土;混凝土施工时受现场环框梁限制无法正常振捣。经沟通,确定在环框梁中预设PVC管作为浇筑孔和辅助振捣孔,按照大体积防裂混凝土技术路线和自密实混凝土技术路线有机结合,通过采用大掺量优质I级粉煤灰和S95矿渣粉、多级配砂石和复配专用自密实外加剂设计出C40大体积自密实混凝土,实现了良好的自密实性能,同时降低了水化热,成功解决了工程施工难题;自密实混凝土因为考虑施工进度的要求需保持2h自密实流动状态,经过4次精心组织施工,现场采取科技手段控制温度变化,采用新型水养护膜进行结构补水养护,工程结构外观达到清水混凝土效果,无可见裂缝和施工缺陷;60d实体强度检测结果和标准养护强度都满足设计要求。

Self-compacting concrete has good fluidity and cohesiveness,it can flow into the complex concrete structure which can not be vibrated.It has been widely used in recent years.The side wall of the main structure of the six-ring-in-the-ground shield shaft is an important anti-seepage and anti-crack permanent structure,which is more than 1m in size and belongs to mass concrete structure.Through consultation and communication,this paper determines that the preset PVC pipe in the ring-frame beam is used as pouring hole and auxiliary vibrating hole,which is combined organically according to the technical route of mass anti-cracking concrete and self-compacting concrete,C40 large volume self-compacting concrete is designed by using large quantity of high quality grade I fly ash and S95 slag powder,multi-grade sand stone and special self-compacting admixture,which realizes good self-compacting performance and reduces hydration heat,because the construction schedule is taken into consideration,the self-compacting concrete is required to maintain the state of self-compacting flow for 2 hours.After four times of careful construction,scientific and technological measures are adopted to control the temperature change on site,the new water-curing membrane is adopted to make up the water in the structure,and the engineering structure appearance achieves the effect of fair-faced concrete,without visible cracks and construction defects.