大流动性高强轻集料混凝土早期收缩特性研究

Study on early-age shrinkage characteristics of high workability and high strength lightweight aggregate concrete

【目的】探索大流动性高强轻集料混凝土(high workability and high strength lightweight aggregate concrete,HHLC)的收缩特性,以期为HHLC推广应用提供参考依据。【方法】采用高强页岩陶粒制备HHLC,通过室内试验测量其自生收缩应变及总收缩应变。【结果】HHLC的28 d自生收缩应变仅为57×10^(-6),总收缩应变为203×10^(-6),与相同强度等级的自密实混凝土(self-compacting concrete,SCC)及普通混凝土(normal concrete,NC)相比,HHLC的早期自生收缩应变及总收缩应变最小;HHLC收缩变形的发展规律与SCC、NC收缩变形的基本一致,但HHLC在前3 d出现微膨胀现象,膨胀值约为10×10^(-6);在HHLC的总收缩应变中,自生收缩应变占比较小,收缩应变主要表现为外干燥引起的干燥收缩应变,且水胶比越小,干燥收缩应变越大;粉煤灰对降低HHLC的早期收缩效果明显,但粉煤灰的掺量不宜超过25%;用混凝土收缩计算模型MC90计算NC的变形,适用性较好,但用来计算SCC、HHLC的变形,误差较大。考虑掺合料及骨料对HHLC收缩特性的影响,对现行规范中的MC90模型进行修正。【结论】采用低吸水率的高强页岩陶粒制备的HHLC具有良好的工作性能及体积稳定性,在结构工程中应用前景广阔;修正后的MC90模型对HHLC具有较好的适用性。

[Purposes]The shrinkage characteristics of high workability and high strength lightweight aggregate concrete(HHLC)were explored to provide reference for the popularization and application of HHLC.[Methods]HHLC was produced with high strength shale ceramsite,and the autogenous shrinkage and total shrinkage deformation were measured by laboratory test.[Findings]The 28 d autogenous shrinkage strain of HHLC is only 57×10^(-6),and the total shrinkage strain is 203×10^(-6).The early-age autogenous shrinkage strain and the total shrinkage strain of HHLC are the smallest compared with self-compacting concrete(SCC)and ordinary concrete(NC)of the same strength grade.The development law of HHLC shrinkage deformation is basically consistent with SCC and NC,but HHLC autogenous shrinkage appears micro expansion in the first three days,and the expansion value is about 10×10^(-6).In the total shrinkage strain of HHLC,autogenous shrinkage accounts for a relatively small proportion.The shrinkage strain is mainly the drying shrinkage caused by external drying,and the smaller the water binder ratio is,the greater the drying shrinkage is.Fly ash has obvious effect on reducing the early shrinkage of HHLC,but the content should not exceed 25%.MC90 model is suitable for ordinary concrete,but the model has large calculation errors for SCC and HHLC.Considering the influence of admixture and aggregate characteristics on shrinkage of HHLC,a modified MC90 model is proposed.[Conclusions]HHLC produced with high strength shale ceramsite with low water absorption has good workability and volume stability,and it has a broad application prospect in structural engineering.The modified concrete shrinkage calculation model MC90 adopted in the current code also has good applicability to HHLC.