Main microscopic phase and microstructure in steel slag

 

A—metal iron particles, B-silicate phase, C-RO phase

 

Therefore, in the ordinary cement concrete system, the total amount of the phase contained in the steel slag which can be hydrated within 28 days and directly contributes to the strength of the concrete is negligibly small.

Fly ash, volcanic ash and some kinds of tailing fine powder in concrete, because of the secondary volcanic ash active reaction, will have a significant contribution to the strength growth of concrete. Therefore, in these areas where sufficient raw materials are available, there is no market for simply selling milled steel slag powder to cement plants or concrete mixing plants.

 

 

However, steel slag contains more than 70% of divalent oxides. In the system without cement clinker (or ultra-low cement clinker), these divalent oxides, under the synergistic action of gypsum, excite active silicon-rich materials. Good activators (they don't work in high cement clinker systems)

 

Chemical composition analysis (wt.%) of a hot smelting converter steel tail slag: the material basis of steel slag forming C-S-H gel is very weak

 

Main characteristics of water quenching blast furnace slag

 

The water-hardened blast furnace slag has a potential hydraulically active silicon (aluminum) oxygen tetrahedron that is 2-3 times that of cement clinker, but currently it is less than 30% silicon, either as a cement admixture or as a concrete admixture. The aluminum) oxygen tetrahedron plays a role. China's annual production of water quenching blast furnace slag nearly 300 million tons, the potential for further efficient use of it is still very large.

 

C-S-H gel is one of the most important phases for the strength of concrete. It is a chain structure silicate formed by connecting silicon (aluminum) oxygen tetrahedrons. The molar ratio of (SiO2+Al2O3)/(CaO+MgO) in the water-quenched blast furnace slag is above 0.9, and the molar ratio of (SiO2+Al2O3)/(CaO+MgO) in the cement clinker is about 0.3. Therefore, the water-quenched granulated blast furnace slag contributes 2-3 times more to the silicon oxytetrahedron and the aluminoxy tetrahedron in forming the C-S-H gel than the cement clinker.

 

Under alkaline conditions, ettringite is a double salt with very low solubility and its solubility product constant is 10-111.6.

 

Research progress in recent years:

 

A variety of solid waste synergies can be used to prepare zero clinker concrete

 

The latest all solid waste cementing materials ratio: steel slag micropowder 35%, slag micro-powder 40%, desulfurization gypsum 15%, fly ash + tailings fine powder 10%; currently has accumulated pouring floor and pavement concrete nearly 10,000 square meters.

 

100% of the research and development success uses the tailingand waste rock of magnetite quartzite iron ore as the aggregate to produce concrete prefabricated parts technology, and produces high-quality C60-C80 railway sleepers, pipe piles and other high-end products, and has been used in a large number of engineering applications. 2.1 million prestressed concrete sleepers complying with the TB/T2190-2002 standard. The proportion of cemented material of the newly developed C60 pre-stressed concrete sleeper is lower than 90% of the current C60 concrete sleeper cement.

 

The research succeeded in C40 extremely low cement clinker artificial reef concrete. The aggregate of the artificial reef concrete is still 100% using tailings and waste rock as aggregate, and almost all of the cementing material utilizes steel tailings, slag, and desulfurized gypsum. Using 1% cement clinker, 99% of the cementitious material is replaced by ultra-fine slag powder, steel slag powder and desulfurized gypsum. The content of heavy metals in concrete is lower than that of seafloor sediments. At present, it has invested 3,000m3 in the sea area of Zhangzidao, Dalian, and completed the "Ecosystem-based research and demonstration of marine pastures” of the major work and benefit project of the State Oceanic Administration, and passed the acceptance test.

 

4. Establish a tailing fine powder production line with an annual output of 600,000 tons/year and realize mass production and application.

 

The production technology of tailing micro-powder was successfully developed, and a tailing fine powder production line with an annual output of 600,000 tons was established to realize mass production. The produced tailing fine powder can not only be used for cement and concrete, but also has a significant effect on improving the fluidity and durability of concrete. The implementation enterprise was listed as the first batch of “Double Hundred Project” backbone enterprises by the National Development and Reform Commission.

 

 

The metallurgical slag solid waste cementitious material has the ability to cure heavy metals and dioxins more than 20 times that of ordinary Portland cement, and the ability to solidify chloride ions is more than 100 times that of ordinary Portland cement. The addition of 20% waste incineration fly ash to the metallurgical slag cementitious material can increase the strength of the cemented backfill by 20%-180%. After curing, the leaching concentration of various harmful substances can reach the drinking water level.

 

The economics of this technology:

 

(1) The production cost per ton of filling cement (including management cost) is 150 yuan/ton, the price is 220 yuan/ton, and the profit before tax is 30% or more.

 

(2) Additional income: A subsidy of 1600-3500 yuan can be obtained for every 1 ton of waste incineration fly ash in Beijing.

Environmental Protection Tax Law and Steel Slag: At present, most steel companies have some steel slag facing the environmental tax payment of 25 yuan / ton. In fact, this is not the most serious problem. The most serious problems are the following three aspects:

 

1. All steel slag stored in open storage will produce leachate during the rainy season. According to our experimental data, the leachate produced is subject to an environmental tax of about RMB 300/ton.

 

2. The solid waste environmental protection tax paid by any enterprise means that the enterprise has unconventional solid waste disposal, storage or comprehensive utilization. This will become a clear goal of national environmental supervision. According to the current general practice of national environmental protection supervision, if an enterprise violates regulations and causes pollution to the environment, it must issue a notice of rectification to the enterprise. If a rectification fails, it will be ordered to suspend production for rectification. If the rectification is still unqualified, the business license will be revoked.

 

3.Listed companies whose environmental protection issues have been publicly exposed also face huge financial risks.