Study On Mix Design And Mechanical Properties Of Early Strength Wet-Joint Concrete

The splicing of new and existed bridges in expansion of expressway projects are of a difficulty in expansion projects,and the quality of wet-joints are critical issues of widen projects.The potential materials for casting wet joints require various specific demands.The core problem is to maintain the balance between early stage performance and long-term durability.This study based on a highway bridge widening,expansion project in Jiangsu Province.The main topic focused on the performance-based design and mechanical properties of high-performance cement-based composite materials for wet joint structures.The early stage hydration rate of Portland cement was accelerated by adding suitable content of Calcium Sulpholauminate(CSA).Furthermore,the effects of early stage traffic-induced vibration on the degradation of material properties under different conditions were experimental investigated.And the corresponding antidisturbance countermeasure were carried out.In summary,the main research contents and conclusions are listed as follows:(1)A series of paste and mortar experiments of combination of Portland cement and CSA cement were conducted.According to the setting time and early stage mechanical tests,it can be concluded that a low content(5%～15%)of CSA are beneficial to the early hydration of the compound system.However,the excessive CSA cement may result in adverse effects to the properties of mortar.(2)The effects of CSA content and volume fraction of steel fiber on the properties of high-performance concrete under various curing temperatures were studied.The test results show that the optimized high-performance concrete exhibit extraordinary mechanical strength,which compressive and flexural strength can reach up to 70.9 MPa and 7.1 MPa at 1d,and 122.3 MPa,17.4MPa at 28 d under standard curing.Moreover,the compounding system can improve the hydration speed of Portland cement at low temperature.Therefore,addition of a certain amount of CSA cement are suggested during winter construction.Based on the limited expansion test of concrete,the optimized expansion rate can reach 0.02% under sufficient curing conditions,which can effectively compensate the time-dependent shrinkage and deformation of the concrete;(3)The early age traffic-induced vibration test of concrete was carried out to investigate the influence of different traffic conditions on the mechanical properties of concrete.Experiment results demonstrated that the continuous vibration will shorten the setting time of concrete under certain conditions.Meanwhile,due to the nonnegligible impacts of CSA on the setting time of concrete,the addition of CSA should be selected carefully according to the environment temperature.(4)When the vibration is relatively low(less than 3mm),the traffic-induced vibration has little effect on the properties of concrete.While the high amplitude(5mm)vibration result in remarkable impacts on the material strength.Both steel fiber and CSA can improve the vibration resistance of the concrete.Considering the concrete pouring quality and minimum construction time,a certain amount of fiber are suggested for wet joint concrete during non-closure construction period.