沥青中蜡含量预测理论模型初步研究

Preliminary study on theoretical model for prediction of wax content in asphalt

【目的】蜡含量对沥青的路用性能影响大,准确测量和限制沥青中的蜡含量至关重要。常用试验方法存在误差和操作不便等问题,并难以揭示蜡结晶的本质。本文从理论角度构建了沥青中蜡结晶的预测模型。【方法】以SHRP(strategic highway research program)材料参考库的两种沥青为研究对象,将沥青视为固液两相系统,通过与变温傅里叶变换红外光谱(variable temperature Fourier transform infrared spectroscopy,VT-FTIR)试验结果进行比较,基于相平衡理论和正规溶液模型构建了蜡析出模型。【结果】用参数a考虑正构烷烃熔化热的分支效应,参数c考虑芳香分的影响,当参数a取0.3,c取0.6时,模型预测的蜡析出温度(wax precipitation temperature,WPT)和蜡析出曲线(wax precipitation curve,WPC)与试验结果基本吻合。正构烷烃的组成碳数越大,含量越多,蜡析出趋势越明显。芳香分含量的增加会导致蜡析出温度升高。【结论】通过将沥青组分划分为P(正构烷烃)、N(异构烷烃)、A(芳香分),使基于热力学和正规溶液理论构建蜡含量预测模型成为可能,熔点、熔化焓和溶解度等热力学参数的计算对预测结果有很大的影响。正构烷烃和芳香分通过影响沥青组分之间的相容性,从而对蜡析出产生影响。

[Purposes]The wax content has a great influence on the pavement performance of asphalt,and it is very important to accurately measure and limit the wax content.Commonly used test methods for wax content have problems such as large errors and complex procedures,and it is difficult to reveal the essence of wax crystallization.To solve issue,this paper constructed a prediction model of wax crystallization in asphalt from a theoretical point of view.[Methods]Taking two kinds of asphalts from SHRP(strategic highway research program)as the research objects,the asphalt was regarded as a solid‐liquid two‐phase system,and a wax precipitation model was constructed based on the phase equilibrium theory and the normal solution model.[Findings]A parameter ofawas used to consider the branching effect of the melting heat forn‐alkanes,and a parameter ofcwas used to consider the influence of aromatic content.When the parameterawas 0.3 andcwas 0.6,the wax precipitation temperature(wax precipitation temperature,WPT)and wax precipitation curve predicted by the model(wax precipitation curve,WPC)was generally consistent with the test results.A higher carbon number and content ofn‐alkanes resulted in,more obvious wax precipitation.The increase in aromatic content can lead to an increase in wax precipitation temperature.[Conclusions]By categorizing asphalt components into P(normal alkanes),N(isoalkanes),and A(aromatics),it is feasible to construct a wax content prediction model based on thermodynamics and regular solution theory.Calculations of thermodynamic parameters such as melting point,enthalpy of fusion,and solubility have a substantial influence on the predictive results.The compatibility between normal alkanes and aromatics affects asphalt component interaction,thus exerting an impact on wax precipitation.