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Fracture properties of rubber concrete under three-point bending
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摘要: 通过橡胶混凝土三点弯曲梁断裂试验，测取橡胶混凝土的荷载、挠度和裂缝开口位移值，并绘制荷载-挠度曲线和荷载-裂缝开口位移曲线；根据《水工混凝土断裂试验规程》和ASTM规范计算断裂韧度与断裂能，研究不同橡胶掺量对混凝土断裂性能的影响，以及声发射累积能量和断裂能之间的关系，并对比分析两部规范中给出的不同断裂韧度计算公式的计算结果。研究表明：掺入橡胶后混凝土能承受的最大荷载降低，起裂断裂韧度、失稳断裂韧度、断裂韧度、断裂能和声发射累积能量均降低；混凝土梁的有效裂缝长度和最大挠度在橡胶掺量为10%时最小，在橡胶掺量为20%和30%时增大；延性指数随橡胶掺量的增加逐渐增大，最大提高了41%；通过拟合混凝土的断裂能和声发射累积能量曲线，可得出
$y=a+b{{\rm{e}}}^{cx}$ 形式的经验式。掺入橡胶后混凝土韧性和变形能力提高，脆性得到了改善，并可利用经验式推断达到某一声发射能量值时混凝土的破坏程度。Abstract: Through the rubber concrete three-point bending beam fracture test, the load, deflection and crack opening displacement values of the rubber concrete are measured, and the load-deflection curve and the load-crack opening displacement curve are drawn; according to "Hydraulic Concrete Fracture Test Regulations" and ASTM specifications, the fracture toughness and fracture energy are calculated, and the effect of different rubber contents on the fracture performance of concrete and the relationship between the cumulative energy of acoustic emission and fracture energy are studied; and the calculation results of the different fracture toughness calculation formulas given in the two codes are compared and analyzed. The test results show that the maximum load that the concrete can withstand after mixing with rubber is reduced, and the crack initiation toughness, unstable fracture toughness, fracture toughness, fracture energy and cumulative energy of acoustic emission are all reduced; the effective crack length and maximum deflection are the smallest when the rubber content is 10%, and increase when the rubber content is 20% and 30%; the ductility index gradually increases with the increase of the rubber content, and the maximum increase is 41%; and by fitting the fracture energy of concrete harmonic emission cumulative energy curve, the empirical formula in the form of$y=a+b{{\rm{e}}}^{cx}$ can be obtained. The ductility and deformability of the concrete are improved with the incorporation of rubber, the brittleness is improved and an empirical formula can be used to deduce the degree of damage to the concrete when a certain value of emitted energy is reached. -
图 1 橡胶掺量 20% 的三点弯曲试件断面
Figure 1. Cross section of three-point bending specimen with 20% rubber content
图 2 荷载P-裂缝口张开位移dCMOD
Figure 2. Curves of force P and crack mouth opening displacement dCMOD
图 4 橡胶掺量对混凝土断裂韧度和有效裂缝长度的影响
Figure 4. Effect of rubber content on fracture toughness and effective crack length of concrete
图 5 橡胶掺量对挠度和延性指数的影响
Figure 5. Effect of rubber content on deflection and ductility index
图 6 橡胶掺量对声发射累积能量的影响
Figure 6. Cumulative energy of acoustic emission under different rubber contents
图 8 不同橡胶掺量下断裂能-声发射累积能量
Figure 8. Fracture energy-acoustic emission cumulative energy at different rubber contents
表 1 每立方米混凝土材料组成
Table 1. Material composition per cubic metre of concrete
橡胶替代比例/% 水泥/kg 粉煤灰/kg 硅灰/kg 水/kg 减水剂/kg 橡胶+砂（总质量1 018 kg) 石/kg 0 385 139 26 200 7.5 橡胶0+砂100% 800 10 385 139 26 200 7.5 橡胶10%+砂90% 800 20 385 139 26 200 7.5 橡胶20%+砂80% 800 30 385 139 26 200 7.5 橡胶30%+砂70% 800 
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表 2 橡胶混凝土断裂参数
Table 2. Fracture parameters of rubber concrete
橡胶替代比例/% Pmax/kN E/GPa ac/m ${k_\beta } $ ${K}_{\mathrm{I}\mathrm{C} }^{\mathrm{i}\mathrm{n}\mathrm{i} }/(\mathrm{M}\mathrm{P}\mathrm{a}\cdot {\mathrm{m} }^{\frac{1}{2}})$ ${K}_{\mathrm{I}\mathrm{C} }^{\mathrm{u}\mathrm{n} }/(\mathrm{M}\mathrm{P}\mathrm{a}\cdot {\mathrm{m} }^{\frac{1}{2} })$ ${K}_{\mathrm{I}\mathrm{C} }/(\mathrm{M}\mathrm{P}\mathrm{a}\cdot {\mathrm{m} }^{\frac{1}{2} })$ 0 6.932 38.81 0.038 0.991 0.312 1.925 0.869 7.301 50.00 0.044 0.297 2.184 0.916 7.160 48.01 0.046 0.304 2.179 0.898 7.131* 45.60* 0.043* 0.304* 2.096* 0.894* 10 6.084 30.22 0.042 0.991 0.274 1.770 0.763 5.723 39.00 0.042 0.266 1.675 0.718 5.780 42.24 0.040 0.235 1.636 0.725 5.862* 37.15* 0.041* 0.258* 1.694* 0.735* 20 4.889 24.81 0.041 0.991 0.188 1.417 0.613 4.556 27.50 0.043 0.227 1.339 0.571 4.965 30.98 0.041 0.257 1.432 0.623 4.803* 27.76* 0.042* 0.224* 1.396* 0.602* 30 4.321 25.15 0.045 0.991 0.185 1.31 0.542 3.975 26.02 0.050 0.183 1.263 0.499 4.284 30.66 0.048 0.173 1.335 0.537 4.193* 27.27* 0.048* 0.180* 1.303* 0.526* 注：带*的数值为对应组的平均值。
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表 3 橡胶混凝土断裂能
Table 3. Fracture energy of rubber concrete
橡胶替代
比例/%试件重量/
kNPmax/
kNδmax/
mm断裂能/
(N·m−1)延性指数/
m−10 0.088 2 6.932 0.508 147.8 0.018 8 7.301 0.479 171.8 0.023 5 7.160 0.625 209.9 0.029 3 7.131* 0.537* 176.6* 0.023 9* 10 0.087 2 6.084 0.645 185.8 0.035 7 5.723 0.430 131.3 0.025 2 5.780 0.456 125.3 0.024 7 5.862* 0.510* 147.5* 0.028 5* 20 0.853 0 4.889 0.553 131.4 0.031 2 4.556 0.621 117.9 0.031 3 4.965 0.522 121.8 0.029 0 4.803* 0.562* 123.7* 0.030 5* 30 0.081 3 4.321 0.569 115.9 0.031 8 3.975 0.696 129.3 0.040 0 4.284 0.544 104.2 0.029 4 4.193* 0.603* 143.3* 0.033 7* 注：带*的数值为对应组的平均值。
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