Shrinkage Compensation And Crack Repair Of Concrete Pavement Structure

Due to the complexity of the generation mechanism and the developing evolution of cracks inconcrete pavement and their significant influence on the availability, safety and durability of thepavement, crack control and repair in concrete pavement are systematic engineering challenges.Based on the inherent characteristics of hydration, setting and hardening in concrete and the theory ofcompensating shrinkage with expansion in different periods, environment-friendly high-performancecomposite expansive materials with stable expansion in early, mid and late age were prepared withwasted industrial tailings as raw materials. The relationships of the constitute, the structure and theperformance of the materials were studied to reveal its hydration kinetic characteristics and expansionmechanism and also to enhance the cracking resistance of concrete pavement. For fine cracks in theconcrete pavement in service, an acrylic and epoxy resin copolymerized high-performance repairmaterial was used to hinder the invasion of the harmful mass. The performance characteristics andrepair mechanism of the materials were clarified. Therefore, the defense capability of concretepavement can be improved. The investigation in the dissertation is conducive to control the generationand the development of cracks, and to weaken the deterioration of the structural performance aftercracking. Consequently, the durability and service life of concrete pavement structures can beenhanced, which is of significance in theory and engineering practice.（1）Considering the disadvantages of traditional expansive agents, through the design ofcompatibility and calcining procedure for industrial tailings of dolomite and magnetite, the influencecharacteristics of the components, calcination temperature, soaking time and other relative factors onthe structures and the properties of high-performance composite expansion materials were discussedto determine a suitable preparation process and also different expansive components. Experimentalstudy on the basic properties of paste with high-performance composite expansion materials wasadopted. The effects of types and amounts of expansive components on the setting time, waterrequirement of normal consistency and strength were analyzed. It is shown that as the waterrequirement of normal consistency and setting time increased slightly, and there was a6%to15%improvement in the flexural strength of paste as well as the compressive strength. The influences ofthe type and dosage of expansive components, and curing temperature on the deformation properties of the paste and mortar were explored experimentally. The characteristics of the free，shrinkage andrestrained deformation of the mortar during different hydration periods were tested. It is found that thecomposite expansion component exhibited its compensation for shrinkage at early, mid and late age.Meanwhile the expansion rate and the total expansion amount can be controlled. It is discovered thathigher curing temperature and humidity as well as a suitable calcining procedure were conductive tothe expansion and the restrained shrinkage at high temperature could be multiple times of that onecuring in room temperature.（2）The stability and deformation development of the concrete with the expansion materials wasinvestigated based on the experiments. The effects of the autoclave procedure on the concreteexpansion rate were studied and the variation law for the flexural strength and the compressivestrength of the concrete before and after the autoclave were summarized. The effects of the type anddosage of expansive components, and the curing temperature on the growth rate of the free, restrainedand autogenous deformation of the concrete for different hydration periods were discussed. Thenumerical method was adopted to fit the expansive rate with time. The expansive index of thehigh-performance composite expansive component was calculated as well as its variation feature withthe dosage and the curing temperature of the expansive component was studied. Simulation wasapplied to the distribution feature of internal stress field of the expansion concrete under differentexpansion rates and different restrained conditions, through which the reasonable basis for theapplication of the composite expansive component can be expected.（3）The basic theory of concrete shrinkage compensation and the relation of deformations in thetwo stages-expansion or shrinkage were discussed. The microstructure, grain growth and porestructure characteristics for different composite expansion component types as well as differenthydration time were studied. Experimental results demonstrated the effect of the calcinationtemperature, heat preservation time and particle fineness of the expansive component on the hydrationactivity. The hydration degree of MgO in the expansion materials at different hydration temperaturesand pHs were also tested. With the aid of the hydration kinetic equation, the hydration reaction rateconstant and the apparent activation energy of the expansive component were computed. Through theanalysis of the evolution of hydration dynamics of the expansion materials, a physical expansionmodel for MgO hydrated into Mg(OH)2as well as CaO hydrated into Ca(OH)2was established.（4）The fine cracks in the concrete pavement were treated as the critical repair object and theinitial viscosity of the repairing material was set as a control start. Methyl methacrylate and epoxy resin were adopted as the main reactive monomers for the bulk polymerization according to synthesisdesign to determine the rational preparation methods. The orthogonal test was employed to analyzethe effects of the repairing component and the reaction time on the initial viscosity. The time-varyingcharacteristics of the initial viscosity were tested and the quantitative relation of the characteristicswith the groutability and the shrinkage of the repairing material were set up. Based on the orthogonaltest, the effects of the reactive monomer, the initiator, the plasticizer, and the curing agent on the bondstrength, the tensile strength and the elongation at break of high-performance repairing material wereinvestigated. It presented the best proportion of the high-performance repairing matrix. After modifiedwith silicone or inorganic mineral powders, the performances regarding to mechanics, deformationand thermal stability of the repairing material were studied. Due to organic optimization (OMM) andcomposite optimization (CMM), the high-performance repairing material, of which the overallperformance was improved remarkably even exceeding the requirements in the relevant nationalstandard, was prepared.（5）The time-vary law of the mortar bonding efficiency with the different types of highperformance repair materials distinguished by RM, OMM and CMM was discussed experimentally.The changes of the bonding properties of the repair materials in the salt solution and in rapidfreeze-thaw cycles were analyzed. It can be found that the mortar after repair did not break again atthe repair area, and the repaired part regained the bond strength as much as the mortar itself in7hoursafter repair. A comparative study of several repair materials was adopted to evaluate their repairefficiency to the compressive strength and the flexural strength of the concrete with prefabricatedcracks before and after repair. The experiments were also carried out to analyze the sectional failuremodes and interfacial adhesion characteristics. The change of stress intensity factor of concrete crackrepaired under different states was calculated by using finite element method. With the help of SEMand FT-IR tests, the microstructure of the fracture surfaces and the characteristic functional groups inthe structures of the concrete repaired with the high-performance repair materials were investigated.Based on the theory of polymer chemistry, the principles of epoxy resin polymerized with methylmethacrylate and silicone modifier polymerized with modified inorganic mineral powder wereexplained. For high-performance repair material, the correlation of the deformation and themechanical performance with the microstructures was revealed. The bonding repairing mechanism ofthe high-performance repair materials to the cracks in concrete was interpreted in two views of thephysical force and the chemical bonding force.