Issue 41

L. Zhang et alii, Frattura ed Integrità Strutturale, 41 (2017) 356-368; DOI: 10.3221/IGF-ESIS.41.47 360 The compressive strength of cement mortar with different dosages is obtained. As the accelerator dosage increases, the later strength loss tends to increase. However, if the dosage ranges from 1.5% to 4%, the later strength loss will not exceed 10%. Tab. 2 shows the compressive strength of cement mortar. Accelerator dosage/% Compressive strength/MPa 28d compressive strength ratio/% 1d 28d 0 7.8 47.8 100 1.5 13.6 46.9 98.1 2.0 13.9 46.1 96.4 2.5 14.5 45 94.1 3.0 15.1 44.6 93.3 3.5 15.8 43.7 91.4 4.0 14.2 43.1 90.2 Table 2 : Compressive strength of cement mortar. N UMERICAL CALCULATION Strength-time and elasticity modulus-time regression curve of shotcrete n the lab, the hardening characteristics of shotcrete are tested. Shotcrete adopts C25 mix proportion (selected from Changgang tunnel of Fushou Highway) of cement, sand, to stone as 469 : 912 : 912. Non-linear regression analysis is conducted on shotcrete strength and time, and then the change rules between the strength and age are obtained. Tab. 3 lists the uniaxial compressive strength of shotcrete added with the traditional accelerator. Tab. 4 lists the uniaxial compressive strength of shotcrete added with the new liquid accelerator. Age Specimen No. 8h/MPa 12h/MPa 1d/MPa 3d/MPa 7d/MPa 28d/MPa 1 4.35 6.80 9.52 14.6 21.89 25.4 2 5.05 7.22 10.25 15.40 20.76 26.38 3 4.92 6.95 9.80 14.88 22.12 27.10 4 4.36 6.50 9.30 15.72 23.30 26.70 5 4.8 7.10 10.64 16.20 21.66 25.89 6 4.45 6.83 9.13 14.67 23.20 27.80 7 4.82 7.25 10.37 15.60 21.37 28.31 8 6.15 7.64 11.28 16.38 22.50 29.25 9 5.20 7.30 9.95 14.68 21.86 27.97 Table 3 : Uniaxial compressive strength of shotcrete added with the traditional accelerator. Age Specimen No. 8h/MPa 12h/MPa 1d/MPa 3d/MPa 7d/MPa 28d/MPa 1 7.25 8.99 12.75 19.39 27.48 31.06 2 7.37 9.53 14.15 20.12 26.66 31.66 3 7.34 9.71 13.29 19.72 27.97 32.60 4 6.38 9.18 12.76 20.30 28.69 32.18 5 7.18 9.47 14.59 20.86 27.65 31.88 6 7.01 8.95 12.80 19.28 28.44 33.17 7 7.35 9.73 13.53 19.89 27.11 34.21 8 8.16 9.98 14.33 20.97 27.84 34.95 9 7.46 10.27 13.45 19.17 27.72 33.65 Table 4 : Uniaxial compressive strength of shotcrete added with the new liquid accelerator. I