Design And Performance Study Of Silane Coupling Agent Modified Rubber Cement-based Material Based On Molecular Dynamics

Rubber cement-based material is a green building material with excellent impact resistance,freeze-thaw resistance and excellent toughness,which has a wide range of engineering application prospects in the field of solid waste building materials.The compatibility of waste rubber and cement-based materials is an important prerequisite for determining the mechanical properties and durability of the composite material.A large number of preliminary studies have shown that the interface defect between rubber and cement-based materials is a key bottleneck that limiting the improvement of material performance,and the material deterioration induced by the interface has always been a stubborn disease that plagues the engineering safety and long-life use of this material.In this paper,we propose a new research model for the modification of rubber cement-based materials with silane coupling agent(SCA)to address the weakness of the rubber-cement two-phase interface.The modification design of the composites was deepened to the nano-level,and the rubber-cement interface was modified by SCA based on the molecular dynamics method.The SCA model with better compatibility with rubber types was selected.And the salt solution transport properties in the capillary pore channels of the selected SCA-modified composites were also explored.At the micro-level,a series of modern testing techniques were used to characterize the interface structure and morphology of SCA-modified composites,and the modification mechanism of SCA on rubber-cement-based materials was proposed in combination with the pore structure of materials.A systematic experimental study of the mechanical and service properties of rubber cement-based materials before and after SCA modification was conducted under the guidance of micro-and nano-scale modulation.Finally,the SCA modified design and performance improvement of rubber cement-based materials within a multi-scale framework is realized.The main conclusions are as follows:(1)Based on molecular dynamics,the organic-inorganic model of the key interface of the rubber-cement two-phase material was constructed by introducing the cross-linked cis-rubber macromolecular structure in C-S-H for the first time.Based on the interface model,the nature of the weak intermolecular interaction between the butadiene group of the butadiene rubber and the calcium-silicon structure of C-S-H has been explored,and the mechanism of accelerating exfoliation of rubber and C-S-H by enrichment of water molecules and hydroxyl groups at the C-S-H interface was discovered.Considering the interfacial structure and mechanical properties of the modified material,the KH570 silane coupling agent with the best compatibility with cis-butadiene rubber was selected.After its modification,and its interfacial binding energy was increased by 66.5%,the interfacial friction performance was increased by 30.23%.(2)The higher the coverage of SCA on the modified pores,the better it is to inhibit the transmission of water molecules and corrosive ions.At the modified rubber cementbased interface,the amphiphilic SCA molecular chain structure has a different mechanism of action on water and ions.The tail alkyl chain acts as a hydrophobic "brush" and weakens the ion hydration membrane structure,greatly reducing the migration rate of water and ions in the pores of the composite material.The agglomeration of ions and the adsorption and solidification of ions by the interface are the essence of the nonsynchronous transport of water and ions.The wettability of the rubber interface is extremely low,and its strong hydrophobicity almost completely inhibits the water and ions transport behavior.(3)After SCA modification treatment,the X group in the SCA molecule(Y-R-SiX3)forms a tight connection with the cement-based material through chemical bonds,and the Y-R group is connected with the rubber through non-bonding interaction and mechanical interlocking.The amphiphilic SCA improves the weak bond between the two phases of rubber and hydration products,fills the interface gaps,and effectively repairs the interface defects between rubber and hydration products.The SCA modification treatment also reduces the proportion of pores that affect the strength of the material and refines the pore structure in the system.When the SCA modified rubber cement-based composite material is loaded,the stress is transferred from the brittle cement-based material to the rubber particles with excellent deformability,thereby enhancing the strength of the composite material.(4)Compared with the SCA content(0~3%),the rubber content(5%~25%)is the main factor affecting the mechanical properties of composite materials.Both flexural strength and compressive strength decrease with the increase of rubber content.Among the commonly used KH550,KH560,KH570,and A151 silane coupling agents,the mechanical properties of rubber cement-based materials were best improved after KH570 modification,and its flexural and compressive strengths were improved by 21.22% and15.23%,respectively.(5)When the SCA content ranges from 0 to 3%,the setting time of cement increase with the increase of SCA content,while the fluidity of the mixture gradually decreases.The SCA modification treatment reduced the capillary water absorption energy of rubbercement matrix composites,improved the freeze-thaw resistance and anti-carbonation performance of the composites,and greatly enhanced the chloride ion penetration resistance of the composites.