低温环境下粉煤灰漂珠改性沥青混合料施工期热量散失规律及有效碾压时间研究

Heat dissipation and effective compaction time of floating bead amended asphalt mixture during the construction stage of pavement under low-temperature conditions

漂珠作为一种高热阻材料,运用于多年冻土区沥青路面最初目的是减少运营期路面吸热,减缓冻土融沉。但其对施工期沥青路面温度散失规律及有效碾压时间的影响,则鲜有研究涉及。漂珠的加入改变了混合料自身的热物理性质,进而对沥青路面压实以及进入冻土路基的热量造成影响。本文首先通过室内试验,测试沥青胶浆热物理参数随漂珠掺量的变化规律。由于沥青混合料碾压过程中材料本身逐渐从松散状态转化为密实状态,该过程中材料孔隙率不断降低强度随之提高,因此施工期间沥青混合料热物理参数也处于动态变化之中。试验过程中,将添加漂珠后的沥青混合料视为一种复合材料,其主要由粗集料、沥青胶浆、空气三部分,通过室内试验测定漂珠沥青混合料中三种成分的热物理参数,并基于Williamson公式计算摊铺碾压过程中漂珠改性沥青混合料在密实和松铺两种状态下的热物理参数。之后建立摊铺碾压过程沥青路面温度场计算有限元模型,获取不同漂珠掺量和摊铺厚度下路面温度场变化规律,明确添加漂珠对施工期进入路基热流影响。最后基于数值计算结果,对施工期沥青路面温度影响因素进行多元回归分析,获得了施工期间沥青混合料温度预估方程。研究结果表明:添加15%沥青体积漂珠后混合料导热系数降低78%,比热容变化不大(小于1%)。外界气温为0℃、10℃、20℃、30℃工况下,添加15%漂珠可使密实状态下混合料有效碾压时间提升21.1%、20.2%、17.5%、16.8%;松散状态提升21.6%、21.2%、20.3%、18.7%。相同工况下,松铺状态有效碾压时间为密实状态下的1.7~2.1倍,因此,在低温工况下,初步碾压作业一旦开始,后续复压及终压应快速、连续开展,确保有效时间内使混合料达到规定压实度。此外,添加5%、10%、15%漂珠还可使密实状态下进入基层热量分别降低1.9%、3.1%、6.4%;松散状态下降低3.5%、7.3%、12.8%,说明添加漂珠对降低施工期热量对路基的扰动也有积极作用。

This paper investigates the impact of floating beads on temperature dissipation during the construction stage and their influence on the effective compaction time of asphalt pavements.As a high thermal resistance material,floating beads have been used in asphalt pavements in permafrost region to reduce heat absorption and mitigate thawing induced settlement during the operational stage.However,limited research has focused on the influence of floating beads on temperature dissipation during the construction stage and their impact on the effective compaction time of asphalt pavement.The addition of floating beads alters the thermo-physical properties of the asphalt mixture,thereby affecting pavement compaction and heat transfer to the frozen soil subgrade.During the compaction process of asphalt mixtures,the material undergoes a transition from a loose state to a dense state,resulting in decreased porosity and increased strength.Consequently,the thermo-physical parameters of the asphalt mixture dynamically change throughout the construction stage of asphalt pavement.This study considers the asphalt mixture modified with floating beads as a composite material comprising coarse aggregates,asphalt matrix,and air.Laboratory tests are carried out to measure the thermo-physical parameters of the three components in the modified asphalt mixture.The Williamson formula is utilized to calculate the thermo-physical parameters of the modified asphalt mixture in both dense and loose states.To analyze the temperature field in the asphalt pavement and the heat flux entering the soil subgrade,a finite element model is developed.The model takes into account different floating bead contents and paving thicknesses.Based on the numerical results,a multivariate regression analysis is performed to identify the key factors influencing temperature fields during construction stage of asphalt pavement.This analysis leads to the derivation of an empirical equation for estimating the temperature of the asphalt mixture.The research findings reveal that the inclusion of 15% volume of floating beads reduces the thermal conductivity of the asphalt mixture by 78%,while exhibiting negligible changes in specific heat capacity(i.e.,less than 1%).With an increase in air temperature 0℃,10℃,20℃,30℃,the addition of 15% floating beads enhances the effective compaction time by 21.1%,20.2%,17.5%,and 16.8% in the dense state,and by 21.6%,21.2%,20.3%,and 18.7% in the loose state.Compared to the dense state,the effective compaction time in the loose scenario is approximately 1.7 to 2.1 times longer.Hence,in low-temperature conditions,re-compaction and final compaction are crucial to be promptly and continuously completed to achieve the specified compaction level within the designated timeframe.Furthermore,the inclusion of 5%,10%,15% volume of floating leads to a reduction of 1.9%,3.1%,and 6.4% in heat flow to the subgrade in the dense state,and a reduction of 3.5%,7.3%,and 12.8% in the loose state.These results demonstrate the benefits of adding floating beads in mitigating heat disturbance to the soil subgrade during the construction stage.By minimizing heat flow,the potential adverse effects on the frozen soil subgrade are significantly reduced,contributing to the overall durability of the asphalt pavement.In conclusion,the addition of floating beads alters the thermo-physical properties of asphalt mixtures,thereby influencing the compaction process and heat transfer dynamics.The findings in this study provide valuable insights for optimizing construction practices of asphalt pavement,including adjusting compaction procedures and ensuring appropriate timeframes for effective compaction.Moreover,the benefits of floating beads in reducing heat flow to the subgrade indicate their potential for enhancing the long-term performance of asphalt pavements in challenging environmental conditions.Overall,this research contributes to the understanding of the thermo-physical behavior of asphalt mixtures containing floating beads and provides guidance for the design and construction of resilient asphalt pavement in permafrost regions.