13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- Fig. 4 shows WST experimental setup, where the rotational joints are used to prevent unwanted restrained. The rotational joint (a rectangular bar) was placed below specimen combined with roller bearing above the wedge. Loading is controlled by displacement measurements from a clip gage inserted into the groove of the WST specimen to measure the CMOD. Distance b = 83.5mm describes contact position of the clip gage. The clip gage was modified by using brass feet to contact the side of the groove. The vertical load was recorded by the testing machine, and subsequently used for calculation of the splitting load. The wedge angle from the vertical axis was used 15°. The constant displacement rate of the wedge was kept initially of 0.05 mm/s to a CMOD of 0.5mm. After reaching a CMOD of 0.5mm, the displacement rate was increased to 0.10mm/s to minimize testing time. Table 1 – Mix designs (kg/m3) Mix Contec DTUI DTUII Contec-F DTUIF DTUIIF Cement (CEM I 52.5 R) / 495 460 / 495 460 Binder Contop S 105-2 582.3 / / 582.3 / / CA, granite, 02-05 mm 832.3 868.4 1015.6 832.3 868.4 1015.6 FA, sea gravel, 0.1-1.5 mm FA, bauxite sand, 0-1 mm 763.7 / 781.6 / / 609.4 763.7 / 781.6 / / 609.4 Silica fume Fly ash Superplasticizer Glass fibers Polypropylene fibers Total dry mass / / / / / 2178.3 55 / 11 / / 2200 57.5 57.5 25.9 / / 2200 / / / 4.04 2.02 2184.4 55 / 11 4.0 2.0 2206 57.5 57.5 25.9 3.5 1.78 2205.3 Water-cementitious material ratio 0.304 0.25 0.25 0.304 0.25 0.25 Water-cementitious material ratio* / 0.27 0.295 / 0.27 0.295 * including the water content of the superplasticizer 4. Results and discussion Fig. 5a shows the load-CMOD curves demonstrate the performance of the model and of the inverse analysis (Example for DTUIF at 28 day maturity). It is visible that computation based on softening curve for N = 3 provide better approximation compared to the bi-linear curve. The computational time was approximately 15 minutes with softening curve for N = 2 and approximately 25 minutes with softening curve for N = 3. The increase in computational time is compensated with increase in accuracy of the model. Splitting force [N] 4500 4000 3500 N=2 N=3 Measured 3000 2500 2000 1500 1000 500 0 0 0.2 0.4 0.6 0.8 1 1.2 Crack Mouth Opening Displacement [mm] 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0 1 2 3 4 5 6 7 w [mm] σ(w) [MPa] 672h 168h 72h 24h Figure 5. Example of comparison of the measured and the computed load-CMOD curves for DTUIF at 28 day maturity (a) and stress-crack opening relationships for DTUIF for different ages (b). (a) (b) 4500 4000 3500 3000 2500 2000 1500 1000 0 0.05 0.1 0.15
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