Calcined Aerated Concrete Block By Partly Replacing Lime With Calcium Carbide Slag

Fly ash and calcium carbide slag,as bulk industrial wastes,have potential cementing activity.Such industrial wastes can be used to produce silicate concrete products with the advantages of waste utilization,energy saving,environmental protection and saving natural resources.In this paper,some lime is replaced by calcium carbide slag to prepare autoclaved aerated concrete blocks,which are designed to reduce costs and make the best use of solid waste.Firstly,the calcium carbide slag was applied to produce autoclaved aerated concrete Grade B06.The heat loss due to the reduction of lime was compensated by‘external heating'measure to ensure the gas generation efficiency of aluminum powder.The process conditions affecting the stability of concrete were determined,the admixture was determined:NaOH 0.4%,sodium silicate 0.4%,silica fume 0.7%.The material ratio of B06 grade concrete was determined by orthogonal test:fly ash 65%,calcium carbide slag9%,lime 15%,gypsum 3%,cement 8%.In this case,the density of aerated concrete is590.2kg/m³ and compressive strength 5.73MPa..Secondly,the autoclaved aerated concrete block Grade B05 was prepared by using the synergistic effect of the admixture and the material,and the suitable‘external heat'process conditions of the aerated block were determined.And the ratio of B05 grade concrete admixture was determined by orthogonal test:NaOH 0.5%,sodium silicate 0.1%,silica fume 0.5%.On this basis,the amount of calcium carbide slag was further adjusted,and the initial strength of the block was improved by using the waste aerated block.The final material ratio of B05 grade aerated concrete is obtained:fly ash 59%,calcium carbide slag21%,lime 3%,gypsum 3%,cement 8%,waste aerated block 6%.In this case,the density of aerated concrete is 518.6kg/m³ and compressive strength 3.52MPa.Thirdly,the two kinds of hydration products were analyzed by XRD.The hydration products after pre-curing are mainly hydrated calcium silicate gel?C-S-H?and AFt.Especially for B05 block,the amount of Aft,calcium silicate hydrate?C-S-H?and tobermorite in the hydration products increased significantly at this stage.As the temperature increases in the autoclaved stage,the crystallinity of the hydrated calcium silicate increases,forming more tobermorite,which is the key to the compressive strength of the block.Feasibility and environmental impact analysis of the two grades of autoclaved aerated concrete blocks was carried out with the production scale of 300,000 m³/a.From the technical point,the performance of the two grades of autoclaved aerated concrete blocks are better than the requirement of China national standards.The lime consumption is significantly lower than that of ordinary aerated concrete and easy to implement.From economic point,the production cost of the modified aerated concrete is relatively low,and it has better economic benefits.From the environmental impact point,the modified concrete block can consume a large amount of solid waste,significantly reducing CO₂emission,and the environmental benefits are obvious.