Multi-scale Research On The Mechanical Properties Of Steel Slag Pervious Cement Concrete

Because of the modernization and acceleration of urbanization,there are increasingly severe concerns including shortage of high quality natural aggregates,accumulation of industrial by-products like steel slag,and urban environmental problems like waterlogging and heat island effect.Steel slag aggregate(SSA)can improve the mechanical properties of pervious concrete as a potential substitute of natural aggregate.It makes great sense to research on SSA pervious concrete for reducing overexploitation of mines,improving urban environmental benefits and decreasing industrial waste accumulation and pollution.SSA has been used in the cement,cement treated base and concrete.However,limited by its changeable properties and volume stability,the conclusions are often different,and there are problems such as insufficient strength,poor workability and volume expansion.Therefore,more detailed analysis of the mechanism of SSA is needed.This paper researched on SSA pervious concrete from multiangle and multi-scale based on stability treatment,macro performance evaluation,numerical simulation and microscopic mechanism.Firstly,based on XRF and XRD test methods,high alkalinity SSA with good stability was selected to design SSA pervious concrete.The control test was carried out with steel slag replacement amount as variable.Through the change of mechanical strength and permeability of pervious concrete,this paper analysed the influence of SSA was and designed a practical SSA pervious concrete.Then steel slag with poor stability was selected to test volume expansion rate.This paper chose three additives to process SSA including silica,colloidal silica and composite aluminum silicate solution.The pervious concrete made with processed SSA was tested for mechanical properties to analyze the influence of treatment methods,and the most appropriate method was selected.Secondly,based on various micro-testing methods,the enhancement effect of steel slag on pervious concrete was studied from the perspective of micro morphology,chemical elements composition and micro-mechanical properties.Based on Backscattered Scanning Electron Microscope(BSEM)method,the morphology of SSA and natural aggregate were compared,and the hydration products in the ITZ and cement mortar were analyzed.Based on Energy Dispersive Spectroscopy(EDS)method,took spot scanning on the ITZ and cement mortar to evaluate the density of microstructure depending on the silicon over calcium ratio.Took line scanning on aggregate-ITZ-mortar region to evaluate the width of ITZ depending on the concentration curve of elements.Based on nano-indentation method,the indentation lattice was laid on the region.nano indentation lattice.through the load-depth curves,established contour maps of hardness and modulus.Furthermore,evaluated the width of ITZ and compared with EDS results,and synthetically analyzed the microscopic mechanism of SSA.Finally,based on microscopic damage mechanics and finite element model,the mesoheterogeneity and crack propagation mechanism of SSA pervious concrete were studied.Based on Digital Image Processing(DIP)and Cohesive Zone Model(CZM),Two-dimensional numerical models scanned from actual concrete specimens were build to simulate compressive strength test and splitting tensile strength test.The parameters of models were inversely analysed through the actual laboratory test results and the micro-mechanical test results.This paper focused on the interfacial transition zone(ITZ)to evaluate the influence of SSA in mesoscale.Meanwhile,based on Monte Carlo stochastic modeling method,models with simplified aggregates and pores were build to make calculation and analyze the applicability of such parameterization modeling method,which had same parameters as DIP models.