Performance Regulation Mechanism Of Non-Steam Curing Ultra-High-Performance Concrete And Its Fatigue Assessment Of Reinforced Steel Bridge Deck

The combination of ultra-high performance concrete(UHPC)and orthotropic steel bridge deck(OSD)can solve the persistent problems of fatigue cracking and pavement damage in traditional steel bridge decks,and has broad prospects and enormous application value in the field of bridge engineering.Compared with new bridges,UHPC is more meaningful for the reinforcement and reconstruction of many old bridges on existing highways.In order to give full play to the activity of a large number of auxiliary cementitious materials used in the UHPC system and improve the early age strength,steam or autoclave mode is usually used for early curing,but it also indirectly increases the production cost and energy consumption of UHPC,which is unfavorable to its promotion and application in practical projects.And,for the reinforcement of existing old bridges,the temperature rise and temperature drop system of steam or autoclave curing is easy to have unpredictable adverse effects on the steel bridge deck system with long service life,so the preparation of non-steam curing UHPC bridge deck pavement is of great significance to the repair and reconstruction of existing bridges.However,the current research on the multi-objective optimization design of the mix ratio,key performance regulation mechanisms,and their application in bridge reinforcement of non-steam curing UHPC paving materials is not sufficient.Guided by the design and performance regulation requirements of the pavement materials for the old bridge reinforcement deck,this paper takes non-steam curing UHPC as the main research object,studies the key scientific problems existing in the regulation mechanism of key performance of non-steam curing UHPC and its fatigue assessment of reinforced steel bridge deck from multiple levels of materials,components,and structures.The main research methods and content are as follows:(1)Aiming at the design problem of the single objective of UHPC mix proportion optimization,a design method of multi-objective joint optimization of non-steam curing UHPC based on particle swarm optimization(PSO)algorithm was proposed,the accuracy of the prediction model established by PSO algorithm and artificial neural network(ANN)was compared.Meanwhile,the optimal ratio under multi-objective joint optimization of the PSO algorithm was obtained based on the ELECTRE-III method sorting,and then the accuracy of the optimal mix proportion was verified by the macro-micro experiment,and the optimized preparation of non-steam curing UHPC for multi-objective requirements was achieved.(2)Through macroscopic mechanical performance tests and microstructure analysis,the influence of mineral admixtures on the temperature-sensitive characteristics of early age mechanical properties of UHPC was explored.Meanwhile,the mechanism of temperature effect on the activity of mineral admixtures was revealed,the early age damage mechanism of UHPC under temperature effect was clarified.Moreover,the early age mechanical properties control mechanism of UHPC considering temperature effect was formed.(3)By using rheological performance tests,the effects of ambient temperature and mineral admixtures on the rheological properties of UHPC,such as plastic viscosity,yield stress,and rheological index,were clarified.Simultaneously,a calculation model for the rheological properties of UHPC considering the combined effects of ambient temperature and mineral admixtures was established,and a dynamic control method for the rheological behavior of UHPC was proposed,achieving a rational understanding of the rheological behavior of UHPC systems under different construction environments.(4)To solve the problem of large autogenous shrinkage deformation of UHPC at early age,a new idea of mixing multi-scale MgO expansion agent and superabsorbent polymer(SAP)to greatly reduce or even completely compensate the autogenous shrinkage of UHPC during the whole hydration process was proposed.Simultaneously,the synergetic reduction mechanism of multi-scale MgO and SAP on the early age autogenous shrinkage behavior of UHPC was revealed,and then the prediction model of early age autogenous shrinkage behavior of UHPC was constructed,forming an effective regulation mechanism of shrinkage deformation of non-steam curing UHPC.(5)By conducting fatigue tests on steel-UHPC composite plates,the fatigue characteristics of steel bridge deck reinforced by UHPC bridge deck pavement under different curing modes are investigated.And,the evolution rules of deformation,deflection and relative slip of non-steam curing UHPC deck pavement under fatigue load are clarified.Meanwhile,the fatigue damage mode and performance degradation mechanism of non-steam curing UHPC pavement are revealed,and the service safety characteristics of non-steam curing UHPC deck pavement during its full life cycle are ensured.(6)In order to study the reinforcement effect of non-steam curing UHPC on steel bridge decks,in-situ tests were conducted to investigate the stress reduction degree on the fatigue vulnerable details and overall structural stiffness reinforcement effect of steel bridge decks with of non-steam curing UHPC bridge deck pavement.Furthermore,the improvement mechanism of non-steam curing UHPC on the fatigue performance of existing long service steel bridge deck systems was revealed,providing theoretical and technical support for the application of non-steam curing UHPC in the maintenance and reinforcement of old bridges.