等强条件下混凝土收缩徐变试验研究与现场监测

Research on Shrinkage and Creep Tests of Concrete with Same Compressive Strength and Field Monitoring

采用自制的试验装置,研究了混凝土组分对7d等强条件下混凝土收缩徐变的影响规律和机理,以配制和优化高铁混凝土。通过现场监测在建预应力混凝土桥梁的应变,并与JTG D62-2004《公路钢筋混凝土及预应力混凝土桥涵设计规范》的计算值进行了比较。结果表明,双掺质量比2:1的粉煤灰和矿渣及掺用减缩剂(SRA)可以有效降低混凝土收缩徐变,其中以掺减缩剂效果最好;聚乙烯醇(PVA)纤维可以降低自收缩,但会增加干燥收缩和徐变,不宜用于配制高铁混凝土;排除弹性和温度应变的影响,现场监测的收缩和徐变应变在加载80d左右趋于稳定,保持在(165～200)×10-6之间,各跨中截面的下底板应变略高于上顶板值;计算值与监测值相差很大,计算值过于保守,不宜直接用于指导工程施工。

The influence law and mechanism of concrete constituents on shrinkage and creep of concrete with 7 days same compressive strength are studied by the self-made test device to produce and optimize concrete for high speed railway.The test strains of prestressed concrete bridge under construction by field monitoring are compared with the calculated values by use of the design specifications of prestressed concrete bridge and culvert and highway reinforced concrete（JTG D62-2004）.The results indicate that shrinkage reducing admixture（SRA） and the mass ratio 2：1 of fly ash and slag can reduce effectively shrinkage and creep of concrete,and the effect with SRA is best.Polyvinyl alcohol（PVA） fiber can decrease autogenous shrinkage,but increase dry shrinkage and creep,which is not suitable to produce concrete for high speed railway.The test shrinkage and creep strains by field monitoring tend to be stable after about 80 days＇ loading,which is keeping on（165～200）×10-6,and the bottom plate strains of mid-span sections are a little more than these of upper plate except elastic strains and temperature strains.The calculated values differ obviously from the test values,and the calculated values are over-conservative,which are not suitable to directly guide the engineering construction.