Manufacture Of Steel Slag Water-permeable Pavement Brick Through Carbonation Curing

With the development of steel industry in China, the amount of steel slag increases quickly, which has brought great pressure to the sustainable development of ecological environment and economy. So more attention should be always paid on the resource utilization of steel slag in the society. But it is difficult because the the bad soundness of steel slag products, and the comprehensive utilization rate of steel slag is very low.CO₂ sequestration by aqueous mineral carbonation, namely greenhouse gas CO₂ reacting with non-carbonate minerals to geologically stable mineral carbonates, such as CaCO₃, MgCO₃, is carbonation. However, as an advanced technology, carbonation can be used to utilize the waste and save resources and energy; carbonation could be also a technique to tackle with steel slag effectively. It would not only solve the pollution problem of steel slag, but also ease the greenhouse effect caused by carbon dioxide.It has been found that steel slag contains calcium and magnesium and other elements can be carbonated, by means of permanent storage with carbonation curing of greenhouse gas carbon dioxide. Under reasonable mix design and optimum manufacture process, water-permeable brick could be made by steel slag. It not only solves the problem of pollution of steel slag, but also could produce green building materials for economic and social profits. Namely, turn wastes into treasures.The water-permeable brick was made by steel slag, sand and carpolite as raw materials in this paper. The optimum experimental conditions in the process of carbonation were researched, including Ca(OH)₂ emulsion, forming pressure, CO₂ partial pressure and carbonation curing time. The results show that Ca(OH)₂ emulsion is 10% in mass, forming pressure is 4 MPa keeping 1 min, CO₂ partial pressure and carbonation curing time are 0.15 MPa 0.5 h, 0.25 MPa 1 h, 0.35 MPa 0.5 h, 2 h in total.The mix design of raw materials on the structure and properties of steel slag brick plays a vital role in the characterization, and is also one of important indicators of pavement brick affecting the strength and water permeability and so on. So, the optimum particle distribution of steel slag was found up, and the preliminary theory of carbonation was expounded. The morphology of carbonated products and the compositions of mineral and thermodynamic properties were used to analyse and discuss through SEM, XRD, DTA-TG, MIP and other test methods.The experimental results show that the best particle size gradation of steel slag mixed with sand products is steel slag 80%, sand 20% and that of steel slag, mixed with sand and gravel products is steel slag 80%, sand 15%, and gravel 5%. Other performances respectively expressed as follows, the mass gain degree of carbonation of test sample is 8.2% and 8.4%, compressive strength is 46.5 MPa and 55.5 MPa, saturation strength is 46.2 MPa and 45.5 MPa, antiflex strength is 3.2 MPa and 3.5 MPa, freeze-thaw strength is 38.7 MPa and 47.3 MPa, hygroscopic coefficient is 10.3% and 7.2%, permeability coefficient is 1.35 mm/s and 1.48 mm/s. Soundness is conformity.On this basis, adjusted the process parameters and scaled up. According to the relevant standard provisions, the bricks are tested. The results show that steel slag pavement bricks mixed sand and gravel, its physical performances have been some optimization, but the permeability effects are not obvious, the relationships of the pore structure and distribution and the mass gain degree of carboantion and strength need further research.Compared with other bricks, carbonated steel slag pavement bricks have the advantages of simple preparation process, and low-carbon, waste recycling and environmental benefits, and so on. Its performances are consistent with the state standards of unfired brick and paving brick suitable for practical engineering applications, with extensive prospects of use.