Investigation On Preparation Of Foamed Concrete With Special Steel Slag Powder

To utilizing the slag from special steel production,in the present study,the basic property of a special steel slag from BaoSteel was first examined,an optimal ratio to produce foamed concrete with this slag?and fly-ash?etc.to partially replace cement was then investigated,the mechanism which such slag exhibited in formation of foamed concrete was also explored.It was anticipated that the result to be achieved in this study might provide theoretical basis and technical support to handle 20,000 tons of steel slag Baosteel produces annually,and thereby find solution to its comprehensive utilization.The main results/findings are presented as follows.Study was first carried out to investigate the chemical&mineral composition of this special steel slag,along with its grindability,bulk density,apparent density,f-CaO,f-MgO and activity index.It was found that:?1?The primary chemical components in slag were CaO,Fe₂O₃ and SiO₂,with a certain amount of Al₂O₃,MgO and MnO etc.,contributed to the pre-treatment process,content of f-CaO and f-MgO was extremely low in this slag;its main mineral composition were calcium aluminosilicate and silicate?this silicate contains Pb,Mn and Cu heavy metal elements?.Other heavy metal elements such as Cd,Zn,Ni,As and Cr could be also found in slag,in particular,the contents of Pb,Ni and Cr exceeded the limit of leaching toxicity contents as specified by?National Leaching Toxicity Identification Standard?.?2?the grindability of this slag was poor?measured in an index at 99.43kwt/t?;it is therefore more difficult to grind than some conventional residue.In addition,its gel after hydration was low:its 28d mortar activity index was only 62%.?3?this steel slag should be collectively handled at a designated location in order to limit its heavy metal pollution to environment while minimizing capital investment;water-washing ball mill was recommended to grind this slag to separate its metal elements,a process to be realized with an aid of water shaker.A separation of metal elements from this slag fulfilled purpose of metal recycling,and provided feasibility of a comprehensive utilization of this slag.To reduce the portion of cement amount as required in preparation of foamed concrete,experiments were carried out with this special steel slag fine powder?and fly-ash?etc.additives as substitutes to partially replace cement;nonlinear regression model and BP neural network model were also employed to find an optimal ratio in such mixture.Uniform design experiment confirmed that foamed concrete could be produced with steel slag fine powder and fly ash to replace a portion of cement;the performance and mechanical property of the foamed concrete was affected in rank by the used portions of cement,foaming agent,special steel slag fine powder,water-cement ratio and fly ash.Both non-linear regression model and BP neural network model were useful tool;and were used in the present study to find a ratio of mixture by blending special steel slag fine powder fine powder to replace a certain portion of cement to produce foamed concrete.With nonlinear regression model,it was found that an optimal ratio of such mixture was:cement 3847g?61%?,steel tailings fine powder 1445g?23%?,fly ash 708g?11%?and the foaming agent 316.4g?5%?,with water-cement ratio in 0.46;the measured dry density and the 28d-compressive strength of thus prepared foamed concrete was 648.1kg/m³ and 2.7Mpa.With BP neural network model,a similar ratio of mixture was found:cement 3812 g?60%?,steel tailings fine powder 1537g?25%?,fly ash 651 g?10%?and the foaming agent 309.7g?5%?,with water-cement ratio in 0.46;the measured dry density and the 28d-compressive strength of thus prepared foamed concrete was 628.5 kg/m³ and 2.7 MPa.Results as obtained respectively based on non-linear regression model or BP neural network model were in good agreement.Mechanism which this special steel slag fine powder fine powder exhibited in formation of foamed concrete was explored in the present study,meanwhile,the performance and mechanical property of the foamed concrete as prepared by the optimized scheme?i.e.by either non-linear regression model or BP neural network model?were characterized and analyzed.The size distribution of pores as generated within the foamed concrete was modelled based on the fuzzy group theory.It was found that a small amount of C₃S in steel slag hydrated rapidly during formation foamed concrete,while the amount of C₂S and Ca₃Al₆Si2O₁₆ would only hydrated gradually in a later stage;the hydrated C-S-H gel and Ca?OH?₂ carbonated,contributing to mechanical properties of the foamed concrete,and effectively inhibiting at the same time the heavy metal elements from leaching by its chemical curing and physical encapsulation.Evaluation model based on the fuzzy group theory?or nonlinear fitting?also found that the size of pores distributed within the foamed concrete was in a range between 50?m-250?m,and mainly existed as in form of large-pore groups.The existence of large-pore groups in such foamed concrete might well lead to its lightness in its density?628.5 kg/m³?,while still retaining its strength in mechanical properties?28d-compressive strength at 2.7 MPa?.