Key Technology And Performance Enhancement Mechanisms Of The Semi-flexible Composite Materials

The semi-flexible composite material is a new type of pavement materials via pouring the cement grout into the large-void asphalt mixture,which has satisfactory cost performance and pavement properties.There is science significant and promotion value for researching the semi-flexible composite material.Based on the laboratory experiments,numerical simulation,and theoretical analysis,the objective of this study is to reveal the performance enhancement mechanisms of semi-flexbile composite material,so as to improve the engineering properties of the semi-flexbile composite material.The high-performance cement grout enhanced by nano-Si O₂（HCGM）was developed after the evaluation and optimization of the uncertainty using the multi-output support vector machine and Bayesian inference.The final formula of the HCGM was the cement-water ratio of 0.56 and the contents of water reducing agent,accelerating agent,expansion agent,and nano-Si O₂ of 1.0%,2.3%,9.0%,and 2.0%.The performance enhancement mechanisms of the HCGM and the effect of sulfate corrosion were revealed from a view of microscopic structure and hydration productions.Results showed that:（a）nano-Si O₂could accelerate the generation of CH crystals to reach saturation at a faster rate and urge the C-S-H gels to early generate coupled with the C₃S,while it was irrelevant to the C₂S,（b）the hydration products were not changed by the nano-Si O₂,and（c）the SO₄^2-in Na₂SO₄ solution formed the calcium sulfate gypsum crystal with the CH crystal at the initial corrosion stage,resulting in the increases of the strength of the HCGM;however,as the concentration of Na₂SO₄ solution and corrosion time increased,the conversion of the CH crystal into C-S-H gel was hindered by SO₄^2-,and a large number of the CH crystal were formed to stratiform structures and eroded by the SO₄^2-,resulting in the decrease of the flexbile strength of the HCGM.In the initial corrosion stage of the Mg SO₄solution,the magnesium hydroxide was generated causing by the magnesium ion and CH crystal,which would adhere to the surface of the HCGM to delay the entry of the SO₄^2-into the interior of the HCGM;however,as the concentration of Mg SO₄ solution and corrosion time increased,not only the generation of the C-S-H gel was hindered by the SO₄^2-,but also the magnesium hydroxide consumed a large number of the CH crystals to form unconsolidated M-S-H gel,resulting in the attenuation of the flexible strength of the HCGM.The effects of corrosion time and salt solution concentration on compressive strength is not significantThe testing system of aggregate structure strength and the corresponding DEM numerical simulation method were developed to analyze the effect of key aggregates on the porosity and aggregate structure strength of the large-void asphalt mixture（LVAM）,so as to put forward the strong-structure gradation of the LVAM based on the aggregate contact characteristics.Strengthening mechanisms of aggregate structure of the LVAM were revealed.Results showed that:（a）aggregate structure could be treated as a transmission system composed of strong contact forces and slight-strong contact forces,particularly the strong contact forces,while weak contact forces have less contribution on aggregate structure,and（b）the number of contact points in aggregate structure was not necessarily related to aggregate structure strength,and overmuch contacts only provided lots of weak contact forces.Moreover,the contribution of different aggregates to the aggregate structure strength was analyzed.Results showed that:（a）9.5～13.2 mm aggregates provided a large number of strong contact forces and were the main body of the aggregate structure,（b）4.75～9.5 mm aggregates had the faction of converting slightly-strong contact forces provided by 9.5～13.2 mm aggregates into strong contact forces,and（c）1.18～4.75 mm aggregates had less influence on the aggregate structure,because they mainly provided weak contact forces.The high-performance semi-flexible composite mixture（HSFCM）was developed based on the optimization technology of cement-asphalt interface between the HCGM and the LCAM using the cation emulsified asphalt.Results of pavement performance showed that:the HSFCM had satisfactory high-temperature stability,low-temperature crack resistance,water stability,and fatigue resistance(the dynamic stability exceeded 40000 times·mm^-1).Moreover,a precise fatigue prediction equation of the HSFCM was developed using the damage stable value obtained by the damage evolution of the HSFCM based on thepermanent deformation ratio.The coefficient of determination is larger than 0.99,which is better than the conventional fatigue equation.Afterwards,coupled with the existing standard,the effects of pavement structure thicknesses and material parameters on the mechanical responses of the HSFCM pavements were analyzed to provide the key control indexes of mechanical responses.Moreover,the recommended HSFCM pavement structure was proposed based on the mechanical response and economy.Moreover,according to the unique structural characteristics and material performance of the HSFCM,the construction technology and the quality control method of the HSFCM were put forward.The reliability was verified through the tracking observation of the experimental road at‘Hong-san’road in Jiaxing City,Zhejiang Provience,showing that the HSFCM could provide better pavement performance.