Autoclaved Silicate Material Prepared By Calcium Carbide Slag Mixed With Waste Concrete And Brick

At present,the main components of construction waste in China are waste concrete,waste brick and mortar wrapped on the surface.From the perspective of reducing the cost of raw material treatment and improving the utilization rate of construction waste,it is necessary to develop the recycling technology of waste concrete and waste brick mixture.Waste concrete is rich in calcium and silicon resources,which can be used as raw materials for autoclaved silicate materials / products.However,the calcium in the waste concrete is mainly provided by the coarse aggregate limestone,which exists in the form of Ca CO₃ and cannot directly participate in the hydrothermal reaction.At present,most of the relevant researches only use the waste concrete as the silicon raw material,while the coarse aggregate is either separated for other use or only used as the aggregate in the material / product,resulting in the waste of calcium resources.In this paper,the autoclaved silicate materials were prepared by calcination hydrothermal synthesis process with the waste concrete and brick mixture as the main raw materials and the industrial solid waste calcium carbide slag as the supplementary calcium raw materials.Among them,the purpose of calcination is to decompose Ca CO₃ in waste concrete into Ca O which can participate in hydrothermal reaction.The research of this paper will provide new ideas for the transformation and reuse of effective mineral resources in waste concrete and waste brick,as well as the collaborative disposal of multi-source solid waste.Firstly,the paper studies and determines the activation system of raw materials:according to the actual composition of construction waste at present stage in China,mix the waste concrete and brick?corresponding to a,B and C mixture respectively?according to the proportion of 80%,50% and 20% of waste concrete,calcine the mixture,research the thermal decomposition of Ca CO₃ in the mixture,calcination temperature on the Ca O content and reaction activity in the calcined products Influence,determine the suitable calcination temperature of three sets of mixtures,take calcination and digestion activation method for carbide slag,research the influence of calcination on mineral composition and microstructure of carbide slag,influence of calcination temperature and digestion system on the activity of Ca?OH?2 emulsion,and determine the appropriate calcination digestion activation system of carbide slag.Furthermore,autoclaved silicate materials were prepared by hydrothermal synthesis of raw materials after activation.The effects of water-solid ratio,molding method,calcium silicon ratio and autoclave system on compressive strength and micro composition of materials were studied.The water resistance,pore solution alkalinity and frost resistance of autoclaved silicate materials under different calcium silicon ratio and autoclave system were studied.The main research of this paper is as follows:?1?Under the experimental conditions of this paper,the best activation system of carbide slag is: calcining 30 min at 800 degrees,adding 80 degree deionized water and stirring 30 min to remove the Ca?OH?2 emulsions?m?H2O?/m?Ca O?=12?,and emulsion without aging treatment,and directly drying the powder.Considering the content and activity of effective calcium in the calcination products,the optimal calcination activation temperatures of A,B and C groups of waste concrete and brick mixtures are 890°C,920°C and 810°C respectively.?2?The compressive strength of autoclaved silicate materials is significantly affected by the water-solid ratio and molding method.Under the experimental conditions of this paper,the best water-solid ratio is 18%,and the best forming method of the specimen is pressing forming and forming pressure is 30 MPa.?3?The hydrothermal products of autoclaved silicate materials are mainly CSH?B?,tobey mullite and anorthite.Under hydrothermal condition,hydrated calcium silicate gel produced by hydration of cement paste in dehydrated concrete and hydration of unhydrated cement particles provide extra strength for materials.The influence of Ca/Si ratio and autoclave system on the quantity,type,crystallinity and structural transformation of hydrated calcium silicate is different,and the macroscopic effect is different on the material properties.?4?The Ca/Si ratio has no significant effect on the compressive strength of autoclaved silicate materials.For the determined raw materials and autoclave system,there is an optimal value of Ca/Si ratio.The compressive strength of the specimen can be improved by reasonable matching of the autoclave pressure and the holding time,and the effect of the holding time on the strength is more significant than that of the autoclave pressure.With the increase of autoclave pressure,holding time and time pressure Q?autoclave pressure ×holding time?,the compressive strength of the whole specimen shows an increasing trend..Under the same condition of Ca/Si ratio and autoclave system,the compressive strength of the specimen is high when the content of waste concrete in the raw material is high.After calcination and activation of waste concrete and brick mixture,the compressive strength of the test piece is significantly higher than that of the non calcined group.?5?In this paper,the softening coefficient of autoclaved specimens is in the range of 0.67 0.92,the p H value is in the range of 11.02 ? 12.37,and the strength loss rate after 15freeze-thaw cycles is in the range of 6.26%⁹.67%.The Ca/Si ratio has no significant effect on the water resistance,pore solution alkalinity and frost resistance of autoclaved silicate materials.With the increase of time product and vapor pressure,the softening coefficient of the specimen increases,and the holding time is short and the increase is large;Q = 18MPa·h?2MPa,9h?is the critical point for the reduction of water resistance of the test piece;there is no single relationship between water resistance and strength.The influence direction of autoclave pressure and holding time on the alkalinity of pore solution of autoclaved silicate materials is different;With the increase of the time-dependent product,the p H value of the sample decreases,and the maximum value of the time-dependent product needs to becontrolled.With the increase of time compression and the prolongation of holding time,the strength loss rate of the specimen decreases generally.The strength loss rate is the smallest and the frost resistance is the best when the holding time is kept for 9h.