Study On The Application Of Steel Slag Pervious Concrete Pavement In The Construction Of Sponge City

With the development and the construction of sponge city,the pervious pavements have been extensively used in the pavement structures.Aggregate is a major component of the pervious cement concrete.In the past,the natural aggregates mainly produced from bedrocks in stone quarries.However,Chinese government attaches more importance to environmental protection,and enacts the policies for protecting the natural environment,reducing the use of natural aggregates,increasing the use of recycled materials and industrial wastes.And China is the largest producer of crude steel in the world.A large amount of waste steel slags are inevitably generated from steel industry every year.A large amount of steel slag needs to occupy a lot of land resources,and the toxic chemicals in waste steel slags also cause environmental pollution.Fortunately,the steel slags can be recycled and utilized as a good road engineering material after removing toxic chemicals.As the steel slags have the characteristics of high porosity and high-strength,the mechanical and hydraulic properties of steel slag pervious concretes(SSPC)can meet the requirements at the same time,even better than that of ordinary pervious concretes.Therefore,it is necessary to study the appropriate basic requirements of raw materials,performance indexes and influencing factors of SSPC.The indexes and requirements of raw materials of SSPC were proposed.Then,the mix design methods and the preparation,molding,and curing methods of SSPC were investigated.And the variation laws of the mechanical and hydraulic properties of SSPC were analyzed under different influence factors.Besides,the performance sensitivities of SSPC were studied.At last,the engineering applications and construction technologies of SSPC pavements were introduced.Firstly,the raw material indexes and performance testing methods of SSPC were studied.The physical and mechanical properties and chemical compositions of the raw materials of SSPC were tested to ensure that they meet the requirements of the specifications.According to the characteristics of SSPC,the test methods of compressive and flexural strengths,permeability coefficients,and effective porosities of SSPC were determined.Secondly,the methods of proportioning SSPC mixes and the preparation,molding and curing methods of SSPC were studied.The performance-based SSPC mix design method were proposed on the basis of the volumetric mix design theory.The mix design parameters are water to cement ratio,aggregate to cement ratio,sand to aggregate ratio,and superplasticizer dosage.The mix design target is to balance the mechanical and hydraulic properties of SSPC.The SSPC mixtures were prepared using the cement paste encapsulating aggregate method.Compared with the tamping and vibration method,the vibration and rolling method can effectively improve the strengths of SSPC and better simulate the actual rolling and compaction processes in the field.Thirdly,the basic performances of SSPC were investigated.The variation laws of the mechanical and hydraulic properties of SSPC were analyzed under different influence factors,such as water to cement ratio,aggregate to cement ratio,and anti-crack additive(ACA)dosage.The microscopic morphologies and chemical compositions of SSPC with ACA were obtained to analyze the strengthening and modification mechanisms of ACA using X-ray diffractometer(XRD),Fourier infrared spectrometer(FTIR),and scanning electron microscope(SEM).The results show that both the strengths of SSPC increases but thereafter decreases with the increases of water to cement ratio,while decreases continuously with the increases of aggregate to cement ratio.Adding an appropriate amount of ACA can effectively enhance the mechanical properties of SSPC,while has little effect on the permeability of SSPC.The additions of ACA can produce more hydration products,which are beneficial to the strength growth,resulting in denser microstructures and higher strengths of SSPC.Fourthly,the performance sensitivities of SSPC were studied using the orthogonal experiments with five factors(the aggregate size of steel slag,the water to cement ratio,the aggregate to cement ratio,the ACA dosage,and the sand to aggregate ratio)and four levels.The influences of various factors on the performances of SSPC were analyzed to obtain the optimal formula of SSPC.Regression equations of the compressive and flexural strength,water permeability coefficient,and effective porosity on five factors were proposed to provide a reference for the performance prediction of SSPC.Finally,the construction technologies and key control indexes of SSPC pavements were studied.The construction processes of SSPC pavements were introduced in detail based on the dike reinforcement project of Suzhou section(Gusu district)of Beijing-Hangzhou Grand Canal.Compared with ordinary pervious concrete pavements,the social and economic benefits of these novel ecofriendly pavement materials were analyzed.Overall,the construction processes of SSPC pavement are simple and easy to operate.As a novel sustainable pavement materials,SSPC have many social and economic potentials for future developments.