基于沥青混合料接触应力测试的旋转压实嵌锁点判定

A Method for Determining Gyratory Compaction Locking Point of Asphalt Mixture Based on Inter-Particle Contact Stresses

摘要:

基于智能颗粒传感器测试旋转压实过程中沥青混合料内部颗粒接触应力，提出了应力变化率指标R_s以及应力嵌锁点（LPS）判定方法。选取AC-13、AC-20与SMA-13这3种沥青混合料，进行旋转压实成型，测试粗集料接触应力，从细观力学角度识别混合料宏观力学嵌锁状态，并与传统基于旋转压实高度变化识别嵌锁点的结果进行对比。结果表明：① 位于试件上部与底部智能颗粒的测试信号存在频谱混叠和谐波干扰，建议将智能颗粒布置于受干扰小的试件中部进行测试；② 对于AC悬浮密实型沥青混合料，存在3个压实阶段：压实初始粗细集料相互接触挤压，R_s快速增大，进入快速压实阶段；随着悬浮在粗骨料周围的细集料与沥青胶结料开始承担荷载，R_s相对减小，进入蠕变阶段；当各组分间形成稳定内部结构，应力达到嵌锁状态；③对于SMA骨架密实型沥青混合料，可分为2个压实阶段：粗集料在初始压实作用下快速形成咬合骨架，并在外荷载作用下接触应力不断增强，进入紧固压实阶段，应力幅值与R_s呈增长趋势；当集料形成稳定骨架受荷结构时，达到应力嵌锁状态；④ SMA-13混合料压实可能会受温度离析影响，在拌和温度170℃条件下，颗粒应力幅值在紧固压实阶段产生波动，并非线性增加；⑤ 与传统基于试件高度变化的嵌锁点判定结果对比，基于R_s判定的LPS均滞后于体积嵌锁点。

Abstract:

This paper proposed a novel method for determining the stress change rate index R_s and the locking point of stress （LPS） based on a new granular sensor （SmartRock） to test the contact stress of particles inside the asphalt mixtures during rotary compaction. Three asphalt mixtures， AC-13， AC-20， and SMA-13， were selected for rotational compaction to test the contact stress of coarse aggregates. The interlocking state of mixture samples was investigated and identified from the perspective of micro-mechanics. In addition， the results of the identifications were compared with those from the traditional rotary compaction method. The results indicate that the test signals of the SmartRocks located at the top and bottom of the specimen have a spectral aliasing and harmonic interference. It is recommended to arrange the smart sensors in the middle of the specimen with less interference. For the AC-13 mixture， three compaction stages could be found. In the initial compaction stage， the coarse and fine aggregates contact and squeeze each other， and the stress and R_s of the coarse aggregates increase rapidly. As the fine aggregate and asphalt binder suspend around， the coarse aggregate begin to bear the load， and the stress of the coarse aggregate and R_s decrease and enter the creeping stage. When a stable internal structure is formed between the aggregate and the asphalt binder， the stress reaches an interlocking state. For the AC-20 mixture， the coarse aggregates quickly form an occlusal skeleton and the contact stress continues to increase under the action of external load to enter the tightening stage， resulting in the increase of stress and R_s. When the aggregates form a stable skeleton load-bearing structure， the interlocking state is reached. For the SMA-13 mixture， it would segregate due to the improper temperature. At a mixing temperature of 170°C， the particle stress amplitude fluctuates and increases non-linearly during the tightening compaction phase. Compared with the interlocking points results from the traditional method， the LPS determined based on R_s all lags behind the volume interlocking point.