自密实混凝土早龄期孔结构演化及其强度形成规律研究

Pore Structure Evolution and Strength Formation Law of Self-compacting Concrete at Early Age

为保证水工混凝土构筑物在早龄期阶段的服役安全性,进行早龄期自密实混凝土力学性能和细观结构试验。制作100 mm×100 mm×100 mm的自密实混凝土试件,研究不同龄期(1 d、3 d、7 d、14 d、28 d)自密实混凝土立方体抗压强度的发展规律;分析龄期与自密实混凝土孔隙率、孔径分布之间的关系;构建龄期影响下抗压强度与孔隙率和T_(2)谱面积之间的数学模型。结果表明:自密实混凝土立方体抗压强度随龄期呈现非线性增长,且主要增长期为前7 d;随龄期发展,1号峰面积逐渐增大、2号和3号峰面积逐渐减小,自密实混凝土内部小孔隙(毛细孔)数量逐步增多且中、大孔隙数量逐步减少;1号峰面积和毛细孔孔隙率均与自密实混凝土立方体抗压强度呈正相关,且能更好地反映自密实混凝土强度的发展。随龄期增长,7 d之前毛细孔占比增长迅速,中孔和大孔占比减幅巨大,中、大孔均向毛细孔转变,28 d时内部结构中毛细孔占比达80%以上;毛细孔分形维数介于0.189~0.865,中孔分形维数位于2.881~2.977之间,大孔分形维数在2.906~2.998区间变化,整体上大孔分形维数明显大于中孔及毛细孔分形维数。

In order to ensure the service safety of hydraulic concrete structures at early age,the mechanical properties and meso-structure tests of self-compacting concrete(SCC)at early age are carried out,which has theoretical and practical significance for exploring the early-age strength development of rock filled concrete(RFC).In this paper,the SCC specimens with dimensions of 100 mm×100 mm×100 mm were made,and the development pattern of cubic compressive strength of SCC at different ages(1,3,7,14,28 days)was investigated.The relationship between age and porosity,pore size distribution of SCC was analyzed.A mathematical model was constructed to investigate the relationship between compressive strength and microscopic parameters(porosity and T_(2) spectral area)under the influence of age.The results are as follows.The cubic compressive strength of SCC increased nonlinearly with age,and the main growth period was within the first 7 days.The area of the first peak gradually increased,while the areas of the second and third peaks decreased.The number of small pores(micropores)inside SCC increased gradually,and the number of medium and large pores decreased.The area of the first peak and the porosity of micropores were positively correlated with the cubic compressive strength of SCC and can better reflect the development of self-compacting concrete strength.The fractal dimension of micropores increases first and then decreases,and the fractal dimension of mesopores and macropores increases gradually.And the fractal dimension of macropores is obviously larger than that of mesopores and micropores.The proportion of micropores increased rapidly before 7 days,and the proportions of mesopores and macropores decreased significantly,and both mesopores and macropores transform into micropores.By 28 days,micropores accounted for more than 80%of the internal structure.In the early age stage,the fractal dimensions of micropores ranged from 0.189 to 0.865,the fractal dimensions of mesopores was between 2.881 and 2.977,and the fractal dimensions of macropores varied between 2.906 and 2.998.Overall,the fractal dimension of macropores was significantly larger than that of mesopores and micropores.