Research On System Desing And Application Technology Of Solid Waste-based Cementitious Materials

In recent years,China’s industrialization has developed rapidly,and large-scale industrial production has resulted in the generation of a large number of industrial solid wastes.In China,there are many types of industrial solid waste with high output,which will not only occupy a lot of land resources,seriously pollute the environment,but also restrict the sustainable development of basic industries such as electric power,metallurgy and construction.The building materials industry is an important basic industry for national economic and social development.China is in a critical period of high-quality economic and social development.Major infrastructure and large-scale urbanization have huge demand for building materials.Therefore,the utilization of industrial solid wastes to prepare building materials is the key to realizing the sustainable development of the basic industry and building materials industry,and it is also the dual strategic needs of environmental protection and resource recycling at the national level.With the overall advancement of the national ecological civilization construction,policies and regulations related to"green and waste-free mining"have been continuously implemented,the infrastructure upgrade of"rural revitalization"has continued to deepen.Key materials in the fields of underground cemented filling engineering and road engineering are in urgent need of upgrading.This research relies on the"13th Five-Year"National Key R&D Program Sub-project:System Design of Solid Waste Cementitious Materials for Road Engineering and Underground Filling(2019YFC1907103-02).This paper takes bulk solid wastes such as steel slag(SS),phosphogypsum(PG),fly ash(FA),and ground granulated blast-furnace slag(GGBS)as the research objects,explores their synergistic strengthening mechanism and performance optimization method,and proposes a design method of solid waste cementitious materials for road engineering and underground filling.The main research contents and conclusions of this paper are as follows:(1)In the application of underground filling,SS-PG-GGBS-ultrafine slag(UFS)all-solid waste cementitious materials were designed.The addition of UFS could significantly improve the mechanical properties of this system,promote the hydration process,and refine the pore structure.The hydration process of SS-PG-GGBS-UFS system could be split into three stages:initial stage,early hydration stage and late hydration stage.The role of UFS in this system was as follows:UFS exerted high hydration activity and was easier to dissolve in the intial stage,acting as nucleation inducing effect and excellent filling effect in SS-PG-GGBS-UFS system,with great contribution to the formation of hydration products in early hydration stage and the refined pore structure in late hydration stage.Iron tailings were cemented with SS-PG-GGBS-UFS binders,the prepared tailings concrete for filling met the requirements of C3(28 d compressive strength≥3.0 MPa),F1(expanded diameter>150 mm,<250 mm),and S1(28 d setting ratio≤3%).(2)In the application of inorganic binder,SS-PG-FA all-solid waste cementitious materials were designed.When the content of PG is high,the early strength of the system is high,and when the content of FA is high,the late strength of the system is high.SS-PG-FA inorganic binder was used to stabilize gravel and iron tailings.Compared with the 7 d unconfined compressive strength(UCS)standard of lime-FA stabilized materials(the strength requirement of low-grade highway base layer is≥0.7 MPa),the 7 d UCS of SS-PG-FA inorganic binder stabilized gravel and stabilized iron tailings could meet the specification requirements.(3)In the application of wear resistant and flexural pavement,Copper slag(CS)-SS-Portland cement(PC)system was designed and studied,and the content threshold of CS and SS was determined.When the content of CS and SS was within20%,the 28 d flexural strength of this system could reach 7.5 MPa,the 28 d abrasion loss was less than 3.0 kg/m~2.When the content of CS and SS was within 10%,the 28d compressive strength of this system could reach 42.5 MPa.CS was subjected to mechanical grinding for 1 h,2 h and 4 h,and it was found that the mechanical grinding could reduce the particle size of CS.But the CS after grinding has little effect on the mechanical properties of CS-SS-PC system.