钢管高强混凝土自收缩规律的研究

本文从理论上分析了钢管核心混凝土的变形机理,指出在水化过程中存在收缩变形和膨胀变形两种变形趋势,最终的变形表现为收缩还是膨胀取决于两种变形趋势谁占优势。并通过对7组钢管混凝土构件的变形测定来分析水胶比、外掺料、截面尺寸等因素对核心混凝土自收缩的影响以及钢管混凝土作为一种组合构件自身的一些特点。通过试验发现核心混凝土的自收缩随着水胶比的增大而减小,水胶比大的普通混凝土会表现为膨胀;掺硅粉可增大自收缩,掺粉煤灰可减小自收缩;自收缩值与构件尺寸关系不大。核心混凝土的收缩是在外围钢管约束下的收缩,收缩会使钢管产生压应力,混凝土产生拉应力,由于粘结强度较小,收缩引起的应力达到一定值后会使钢管与混凝土脱离,但一般会保持一定的应力余量,说明钢管与混凝土没有完全脱离。最终混凝土收缩的影响表现为使钢管与混凝土产生初应力,同时使混凝土与钢管有相对位移,纵向的相对位移使核心混凝土上表面低于钢管的上表面。

Research on the Regularity of Autogenous Shrinkage ofHigh Strength Concrete Filled Steel Tube

This paper analyzes the deformation mechanism of concrete in theory and points out that there are two kinds of deformation,shrinkage and expansion,in hydration and the final deformation depends on which deformation is predominate,shrinkage or expansion? The deformation of 7 sets of high strength concrete filled steel tube(CFST)specimens have been measured for analyzing the influences of water binder ratio, mineral admixture and specimen size on autogenous shrinkage of core concrete,and the deformation properties of CFST as a kind of composite material . The examination results show that the autogenous shrinkage of core concrete decreases while water binder ratio increases and the deformation of concrete with high water binder ratio turns to expansion; concrete mixed with silicon powder may increase autogenous shrinkage while mixed with pulverized fuel ash may decrease it,and there are little relationship between the value of autogenous shrinkage and the specimen size . As the shrinkage of core concrete being restricted by steel , in the process of shrinkage tensile stress will be produced in core concrete with compressive stress produced in steel. These two materials will be separated when the stress between them reach a certain value higher than the low adhesive strength, But usually certain stress will be remained indicating that concrete are still partially connected with steel. The shrinkage of core concrete finally results as initial stress and relative displacement between concrete and steel . Lengthwise displacement will cause the surface of core concrete lower than that of the steel tube.