Production Of Autoclaved Foamed Concrete Block From Fly Ash And Carbide Slag

Foamed concrete is widely used for building engineering due to its excellent properties of thermal insulation,lightweight earthquake resistance,sound absorption and sound insulation.The raw materials in traditional foamed concrete process are lime,cement,etc.,which is a process with high energy consumption and high carbon emission,threatening the environment.In this paper,fly ash,carbide slag and curing agent are used instead of lime and cement as the main raw materials to produce autoclaved foamed concrete blocks by physical foaming,aiming at solving the problems of high cost and high energy consumption of traditional foamed concrete,and low strength and poor foaming performance with carbide slag instead of lime in aerated concrete process.Firstly,the properties of different kinds of foaming agents were tested,and the suitable foaming agent was selected.The effects of the content of carbide slag,granulated slag,activator and steaming system on the properties of autoclaved foamed concrete were investigated by single factor experiment,to obtain the appropriate range of each factor.On this basis,three factors were selected for orthogonal experiment:carbide slag content,granulated slag content and activator content.The optimal ratio of basic material proportioning of autoclaved foamed concrete block is obtained:fly ash 53.5%,carbide slag 30%,slag 5%,cement 10%,desulfurization gypsum1.5%,activator 0.5%,foaming agent 0.1%.It is proved that the performance of the foamed concrete meets the requirements of JC/T 1062-2007.Secondly,the proportioning of the autoclaved foamed concrete block is further optimized to improve product performance.Fly ash was replaced by polysilicon waste residue and waste block respectively,achieving the resource utilization of solid wastes.Two kinds of metallurgical slag based cementing materials were used to replace cement,further reducing costs and the emissions of carbon dioxide.The results show that steel slag based cementing material can replace 50%cement,and granulated blast-furnace slag based cementing material can replace 100%cement.The optimized autoclaved foamed concrete has excellent drying shrinkage performance,freeze-thaw resistance and heat preservation performance.Then,the hydration products and hydration mechanism of autoclaved foamed concrete block were analyzed by XRD.The results show that the hydration products of the block in the pre-curing stage mainly include hydrated calcium silicate(C-S-H)and ettringite.The incorporation of granulated blast-furnace slag improves the initial strength of the test block.The hydration products of the foamed concrete block after autoclaving are mainly CSH(I),tobermorite and water garnet.The incorporation of granulated blast-furnace slag based cementing material enhances hydration process and increases the strength of the test block.Proper proportioning of the adjustment agents produces synergistic effect and optimizes the hydration products.Finally,the economic analysis and environmental impact assessment of autoclaved foamed concrete were carried out for a process of annual capacity of 500,000 m~3.Compared with traditional autoclaved aerated concrete,the production cost of autoclaved foamed concrete produced by this process is reduced by 11%,with the consumption of solid waste of 298,500 tons,carbon dioxide emission reduction 140,000 tons and energy consumption is decreased by 5.08×10~100 kJ.The use of fly ash,carbide slag instead of lime,metallurgical slag based cementing material instead of cement for the production of autoclaved foamed concrete blocks,not only reduces the pollution caused by solid waste,but also solves the problems of low strength and poor foaming performance with carbide slag instead of lime in aerated concrete process.It possesses good economic and environmental benefits.