| China's steel production is about 780 million tons in 2015,which is a huge amount in the world.Steel slag and blast furnace slag are by-products of iron and steel smelting.At present,100~200 kg steel slag can be gotten by producing 1 t steel and about 300 kg blast furnace slag can be gotten by producing 1 t pig iron.Blast furnace has a high activity,which can be applied in the field of cement and concrete.And the utilization percentage of slag can reach above 85% in China now.However,with high hardness and low activity,the utilization percentage of steel slag is only about 20%.Since tricalcium silicate is in the mineral composition of high alkalinity steel slag,ways can be done to activate its cementitious properties.Aerated concrete is a kind of thermal insulation material,which can be used as new-type wall material.In this study,two dry density levels of non-autoclaved aretaed concrete was prepared by alkali activated high alkalinity steel slag and blast furnace slag with hydrogen peroxide as air entraining agent.Effects of two different non-autoclave curing methods on compressive strength were studied in this research.Physical property,drying shrinkage,durability,thermal performance,radioactivity of the products were also tested according to the Chinese standard.The microstructure,hydration products and reaction mechanism were characterized by using XRD,SEM,FT-IR and DSC-TG.Result showed that to produce non-autoclaved aerated concrete with optimum properties,the weight ratio of steel slag was 40% with blast furnace slag of 60%,and molar ratio of water glass was 1.6.The alkali content was 6%,and water to binder ratio was 0.42.The alkali solution temperature should be at 30°C.When the hydrogen peroxide content was 4% and 8%,products of B05 and B06 could be produced,respectively.The compressive strength increased with the increase of curing temperature under steam curing.The compressive strength increased with the increase of curing time under standard curing.And it showed that the compressive strength of products could reach the Chinese standard no matter which non-autoclave curing method we used in this study.Pore size for B06 and B05 products were ranging from 0.3 to 0.6 mm and from 0.5 to1 mm,respectively.Porosity for B06 and B05 products were 69.8% and 74.6%,respectively.Moisture content for B06 and B05 products were 33.9% and 36.7%,respectively.Water absorption for B06 and B05 products were 79.1% and 96.8%,respectively.The drying shrinkage for B06 and B05 products could reach the Chinese standard which requires that drying shrinkage value ? 0.50 mm/m.Frost resistance for B06 products could meet the requirement of Standard GB/T 11969-2008 while B05 products could not.Thermal insulation properties for B06 and B05 products were also pretty good.Thermal conductivity for B06 products was 0.1429 W/(m·K)? standard requirement 0.16 W/(m·K).Thermal conductivity for B05 products was 0.1264 W/(m·K)? standard requirement 0.14 W/(m·K).Curing methods had no obvious influence on the hydration products.Microstructure analysis showed that the mineral composition of hydration sample was consisted of RO phase,CaCO3,C-S-H gel and C-A-S-H gel.Results of FT-IR indicated that the process of alkali-activated hydration of steel slag and blast furnace slag was dissolution and polymerization,namely silicon-oxygen bond and aluminum-oxygen bond parted,dissolved and then polymerized. |
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