Simulation on strength and thermal shrinkage property mechanisms of pre-cracked cement stabilized crushed stone
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摘要: 针对水泥稳定碎石材料易产生裂缝，从而降低路面使用寿命这一问题，基于粗集料预处治技术提出了一种预裂型水泥稳定碎石材料改良思路；通过对水泥稳定碎石中一定比例的粗集料进行预处治，使其表面裹附一层新的物质，从而形成新的界面，分散了收缩过程中降低开裂对材料整体均一性的影响，继而仿真分析了这种新型材料的强度特征和温度收缩裂缝发展的内部机理；基于离散单元法建立了预裂型水泥稳定碎石仿真模型，并分别开展了虚拟无侧限压缩试验和有限制梁温度收缩开裂试验。研究结果表明：在假设预处治粗集料仅影响粗集料界面强度的前提下，试件的无侧限抗压强度与界面强度比和预处治粗集料替换比这2个关键参数之间呈现出良好的线性相关性，可通过回归公式进行计算与预测；当界面强度比大于40%时，预处治粗集料替换比的增加仅会降低材料的强度而不能避免局部贯穿裂缝的产生；当界面强度比小于40%时，随着预处治粗集料占比的增加，试件在收缩过程中产生的裂缝由局部贯穿宽裂缝转变为均匀分布的微裂缝，从而保证了材料在收缩开裂后的整体均一性；当界面强度衰减至未处治材料的30%以下，且预处治粗集料替换比大于30%时，可有效减少试件内部贯穿裂缝的产生，从而缓解了水泥稳定碎石的温缩开裂。Abstract: For the problem that the cement stabilized crushed stone tends to develop cracks, thus reducing the service life of pavements, an idea based on the coarse aggregate pretreatment technology was proposed to improve the pre-cracked cement stabilized crushed stone material. Some coarse aggregates of the cement stabilized crushed stone were pretreated to make their surfaces coated with a layer of new material, and thus a new interface was formed, to alleviate the influence of reducing cracks on the overall uniformity of the material during the shrinkage process. Then, the strength properties and the internal mechanism of crack development under the thermal shrinkage of new material were analyzed through simulations. A simulation model of the pre-cracked cement stabilized crushed stone was built based on the discrete element method. The virtual unconfined compression tests and restrained thermal shrinkage and cracking beam tests were conducted, respectively. Research results show that under the premise that the pretreatment of coarse aggregates only affects the interface strength of coarse aggregates, there is a good linear correlation between the unconfined compressive strength of the specimen and the two key parameters including the interface strength ratio, as well as the pretreated coarse aggregate replacement ratio. The unconfined compressive strength can be calculated and predicted through the regression formulas. When the interface strength ratio is higher than 40%, the increase in the pretreated coarse aggregate replacement ratio will only reduce the material's strength and cannot avoid the locally transverse cracks. When the interface strength ratio is lower than 40%, the cracks appearing during the shrinkage process of the specimen will change from the locally transverse cracks to the evenly distributed micro-cracks as the pretreated coarse aggregate percentage increases, thus ensuring the overall uniformity of the material after the shrinkage cracking. When the interface strength is less than 30% of that of the untreated material, and the coarse aggregate replacement ratio is higher than 30%, the internally transverse cracks of the specimen will be effectively reduced, and the thermal shrinkage cracking of the cement stabilized crushed stone can be alleviated.
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图 1 预处治粗集料水泥稳定碎石结构
Figure 1. Structure of cement stabilized crushed stone with pre-treated coarse aggregates
图 2 圆柱型水泥稳定碎石试件生成步骤
Figure 2. Generation steps of cylinder cement stabilized crushed stone specimen
图 3 不同预处治粗集料替换比的试件示意
Figure 3. Schematic of specimens with different pretreated coarse aggregate replacement ratios
图 4 不同预处治粗集料替换比的试件应力-应变曲线
Figure 4. Stress-strain curves of specimens with different pretreated coarse aggregate replacement ratios
图 5 不同界面强度比下强度衰减速率线性回归结果
Figure 5. Linear regression results of strength reduction rates with different interface strength ratios
图 6 水泥稳定碎石强度衰减速率与界面强度比的关系
Figure 6. Relationship between strength reduction rate of cement stabilized crushed stone and interface strength ratio
图 7 2D水泥稳定碎石梁仿真试件
Figure 7. Simulation specimen of 2D cement stabilized crushed stone beam
图 8 不同预处治粗集料替换比试件示意
Figure 8. Schematic of specimens with different pretreated coarse aggregate replacement ratios
图 10 不同计算步数下梁试件温度传导
Figure 10. Beam specimens' temperature transformation with different calculation spets
图 11 界面强度比为10%的梁试件收缩裂缝
Figure 11. Shrinkage cracks in beam specimens when interface strength ratio is 10%
图 12 界面强度比为10%的试件颗粒位移
Figure 12. Particle displacements of specimens when interface strength ratio is 10%
图 13 预处治粗集料替换比为50%时试件的裂缝分布
Figure 13. Crack distributions in specimens when pretreated coarse aggregate replacement ratio is 50%
图 14 预处治粗集料替换比为50%时试件的颗粒位移
Figure 14. Particle displacements of specimens when pretreated coarse aggregate replacement ratio is 50%
表 1 水泥稳定碎石试件级配
Table 1. Gradation of cement stabilized crushed stone specimen
级配类型 通过不同直径(mm)筛孔的质量百分率/% 31.5 19.0 9.5 4.75 2.36 0.6 0.075 悬浮密实型 100.0 93.5 67.0 39.0 26.0 15.0 3.5 
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表 2 接触模型力学参数
Table 2. Mechanical parameters of contact model
参数 取值 颗粒摩擦因数 0.40 颗粒密度/(kg·m-3) 2 650 容器-颗粒法向接触模量/GPa 40 容器-颗粒切向接触模量/GPa 26.67 颗粒-颗粒法向接触模量/GPa 30 颗粒-颗粒切向接触模量/GPa 20 拉伸强度/MPa 1 剪切强度/MPa 20
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表 3 不同试件无侧限抗压强度
Table 3. Uniaxial compressive strength of different specimens
界面强度比/% 不同预处治粗集料替换比(%)下试件的无侧限抗压强度/MPa 对照组 10 20 30 40 50 0 13.26 10.36 7.64 5.61 3.24 1.28 10 10.92 9.12 8.04 6.27 4.74 15 11.59 10.23 9.10 7.46 5.98 20 11.96 10.79 9.74 8.31 6.81 30 12.12 11.47 10.58 9.50 8.29 40 12.47 11.97 11.21 10.30 9.32 50 12.73 12.29 11.75 10.97 10.13 70 12.80 12.46 12.43 11.92 11.44
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表 4 不同界面强度比下试件强度衰减速率公式
Table 4. Strength reducttion rates formulas of specimens with different interface strength ratios
界面强度比/% 回归公式 决定系数R2 0 y=1.880 2x+1 0.991 6 10 y=1.328 2x+1 0.982 9 15 y=-1.095 4x+1 0.997 1 20 y=－0.945 0x+1 0.996 6 30 y=－0.722 7x+1 0.992 3 40 y=－0.564 1x+1 0.988 9 50 y=－0.436 9x+1 0.978 5 70 y=－0.264 1x+1 0.963 0
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表 5 PFC2D热接触模型参数取值
Table 5. Parameter values of thermal contact model in PFC2D
参数 取值 颗粒比热容(J·(kg·℃)-1) 800 水泥砂浆线性热膨胀系数 15.0×10-6 粗集料线性热膨胀系数 10.0×10-6 热导率 0.285
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表 6 界面强度比为10%时试件裂缝类型统计
Table 6. Statistics of crack types of specimens when interface strength ratio is 10%
裂缝类型 不同预处治粗集料替换比(%)下裂缝数目 0 10 20 30 40 50 60 Ⅰ类裂缝 156 44 42 31 26 11 1 Ⅱ类裂缝 0 211 465 648 873 1 011 1 043 总数 156 255 507 679 899 1 022 1 044
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表 7 预处治粗集料替换比为50%时试件的裂缝类型统计
Table 7. Statistics of crack types of specimens when pretreated coarse aggregate replacement ratio is 50%
接触类型 不同界面强度比(%)下接缝类型数据 10 20 30 40 50 100 未经预处治的粗集料表面 11 23 35 62 51 156 经预处治的粗集料表面 1 011 639 463 323 179 0 总数 1 022 662 498 385 230 156
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