基于分子动力学的硅烷偶联剂对铁尾矿沥青混合料改性的机理

Modification mechanism of iron tailings asphalt mixture by silane coupling agents based on molecular dynamics

为解决由铁尾矿与沥青黏附性差导致的铁尾矿沥青混合料路用性能不佳问题,提出采用硅烷偶联剂进行改性的方法。首先,基于分子动力学方法,通过“化学接枝”“叠加组合”方式构建沥青-硅烷偶联剂-铁尾矿三相界面体系,以模拟硅烷偶联剂的作用过程,并基于相互作用能优选硅烷偶联剂种类,验证其改性机理;然后设计铁尾矿沥青混合料,通过室内试验验证硅烷偶联剂对其路用性能的改良效果。研究结果表明:在分子动力学模拟中,在同一质量分数下,KH-550型硅烷偶联剂改性体系的相互作用能绝对值最大,表明其对沥青与铁尾矿界面黏附改善作用最强,因此,作为优选材料;KH-550通过亲无机端的乙氧基水解并与铁尾矿表面的羟基发生脱水缩合反应,形成稳定的化学键连接,通过亲有机端与沥青分子交联缠绕,产生较强的物理吸附作用,从而显著提高铁尾矿与沥青的黏附性;使用KH-550改性后,铁尾矿沥青混合料的冻融劈裂强度增加22.8%、冻融劈裂强度比增加21.3%、动稳定度增大16.3%,最大弯拉应变提高96.6%,水稳定性、高温稳定性以及低温抗裂性均有显著提高。铁尾矿代替传统集料用于沥青路面建设有益于交通基础设施可持续化发展。

In order to solve the problem of terrible road performance of iron tailings asphalt mixture caused by poor adhesion between iron tailings and asphalt,the method of modifying with silane coupling agents was proposed.Firstly,three-phase interface systems of asphalt-silane coupling agent-iron tailings were constructed by means of"chemical grafting"and"superimposed combination"to simulate the interaction process of silane coupling agents based on molecular dynamics simulation,and the type of silane coupling agents was optimized based on the interaction energy,and the modification mechanism was verified.Then,iron tailings asphalt mixture was designed,and the improvement effect of silane coupling agents on its road performance was verified through laboratory tests.The results show that the absolute value of interaction energy of KH-550 silane coupling agent modified system is the largest at the same dosage in molecular dynamics simulation,which indicates that it has the strongest effect on improving the interface adhesion between asphalt and iron tailings,so it can be used as the preferred material.KH-550 can significantly improve the adhesion between iron tailings and asphalt because the ethoxy groups at the inorganic end can hydrolyze,dehydrate and condense with hydroxyl groups on the surface of iron tailings to form stable chemical bond connections,while the organic end can form strong physical adsorption by crosslinking and winding with asphalt molecules.After modified with KH-550,the freeze-thaw splitting strength of iron tailings asphalt mixture increases by 22.8%,the freeze-thaw splitting strength ratio increases by 21.3%,the dynamic stability increases by 16.3%,and the maximum bending tensile strain increases by 96.6%.The water stability,high temperature stability and low temperature cracking resistance of the mixture are significantly improved.Replacing traditional aggregates with iron tailings in asphalt pavement construction is beneficial to the sustainable development of transportation infrastructure.