Issue 35

L. Chunjiang et alii, Frattura ed Integrità Strutturale, 35 (2016) 500-508; DOI: 10.3221/IGF-ESIS.35.56 504 I NFLUENCE OF CRACK - DEPTH RATIO ON CONCRETE FRACTURE STIFFNESS edge splitting specimens (crack-depth ratio: 0.3:0.4:0.5:0. 6 and size: 150 mm × 150 mm × 150 mm) are selected for studying influence of a/h on double-K fracture parameter and crack mouth opening displacement (CMODc) and influence rule of crack-depth ratio in concrete fracture process and fracture strength. Test Design Tap water, 32.5 ordinary Portland cement, fly ash (level II), natural medium sand with particle size of over 5mm, macadam with maximum particle size of 20 mm (level I) and high efficiency slushing agent suitable for mass concrete are used in the test and their mix proportions are shown in Tab. 4. Material Tap water Cement Fly ash Sand Stones Additives RCC [kg/m 3 ] 130 134 90 805 1280 0.75% Ordinary concrete [kg/m 3 ] 203.5 407.5 0 535 1245 0 Table 4 : Mix proportions of RCC and ordinary concrete. Wedge splitting specimen is applied in the trial, containing two categories (12 kinds of working conditions), and quantity of specimen in each working condition is shown in Tab. 5. Categories Serial number Quantity Size 1×h×t [mm 3 ] Crack-depth ratio Depth of cracks [mm] Thickness of cracks [mm] RCC RCC1504 6 150×150×150 0.4 60 3 RCC1505 4 150×150×150 0.5 75 3 RCC1506 4 150×150×150 0.6 90 3 Ordinary concrete PC1504 6 150×150×150 0.4 60 3 PC1505 2 150×150×150 0.5 75 3 PC1506 3 150×150×150 0.6 90 3 Table 5 : Working conditions of specimen. Phenomenological Analysis of Wedge Splitting Test This test is carried out on a 200kN compression-testing machine and adopts formula to calculate valid crack growth quantity. From cracks in damaged trial (Figs. 3, 4), effective subcritical growth quantity can be obviously found in figures, and direction of crack growth is not smooth, which is mainly caused by reasons of concrete itself, as well as various construction aggregates. Cracks will bypass and keep on growing when encountering construction aggregates with large particle size. Figure 3 : Damaged cracks of RCC specimen. Figure 4 : Damaged cracks of concrete specimen (type 150). W