组成材料对混凝土早期塑性开裂分形特征的影响

Effect of Material Composition on the Fractal Characteristics of the Plastic Shrinkage Cracking in Concrete at Early Age

目的应用分形几何理论,探索了混凝土早期塑性开裂的分形特征,为定量描述混凝土早期塑性开裂提供有力的工具.方法试验采用平板约束法,对多种因素(水泥用量、砂率、硅灰掺量、粉煤灰掺量)下混凝土早期塑性开裂进行跟踪测试,并计算了各因素下混凝土塑性开裂的分形维数,探索了各因素对分形维数的影响.结果水泥用量的增加、砂率的增大及硅灰掺量的增加都会使裂缝的分形维数增加,裂缝复杂化趋势加剧;粉煤灰掺量的增加减小了裂缝的分形维数,裂缝复杂化趋势减缓.结论水泥用量、砂率、硅灰掺量、粉煤灰掺量影响着塑性裂缝分形特征的变化,并且与6 h时开裂总长度、最大裂缝宽度的变化规律一致;应用分形理论分析评价混凝土早期塑性开裂特征是十分有效的.

Appling the fractal theory, the paper explores the fractal characteristic of the plastic shrinkage cracking in concrete at early age, providing the useful instrument for describing the plastic shrinkage cracking in concrete at early age quantitatively. The tracking experiment tests the plastic shrinkage cracking in concrete at early age under various factors（the quantity of cement, sand percentage, microsilica and fly ash） by the method which is called flat restraint, calculates the fractal dimension of plastic shrinkage cracking in concrete under every factor, and explores the influence of every factor on fractal dimension. The result shows that the increasing quantity of cement, sand proportion and microsilica can increase the cracking fractal dimension and aggravate the tendency of cracking complication. The increase of fly ash content reduces the fractal dimension of the cracks, and decreases the tendency of cracking complication. The variety of the fractal characteristic of the plastic shrinkage cracking was influenced by the quantity of cement, sand proportion, microsilica and fly ash. Moreover, it is consistent with the varying regularity of the total cracking length in 6h and the maximum cracking width. It is efficient to apply fractal theory to analyze and evaluate the fractal characteristics of the plastic shrinkage cracking in concrete at early age.