| The 2018 the State Council of the PRC government work report pointed out that China’surbanization rate has increased from 52.6% to 58.5% in the past five years,and more than 80 million agricultural migrants have become new urban residents.With the deepening of the process of industrialization and urbanization in China,there is a huge amount of construction waste brought by the demolition of old buildings in the city.At the same time,new construction also generates a lot of construction waste.,And the increment and stock size are amazing.Construction waste has become China’s largest urban waste source,and it is a major problem that plagues urban green and sustainable development.Many components in construction waste can be recycled,but the domestic and foreign recycling methods of construction waste still remain at the stage of primary recycling products such as backfill materials,foundation cushions,and recycled aggregates.A series of problems such as complex technology,low added value of recycled products,unstable performance,lack of unified technical specifications,and difficulty in product sales.As the main components of construction waste,waste concrete and clay bricks are mainly composed of oxides of calcium and silicon,which can be used as calcareous and siliceous raw materials to produce silicate materials.At present,in the related research on the preparation of silicate material products from construction waste,waste concrete is mainly used as siliceous raw material,while concrete aggregate and clay brick are only used as the aggregate of silicate material products.it is necessary to add quicklime,hydrated lime and so on as calcareous raw materials.And in the demolition of construction waste,waste concrete and clay bricks are usually bonded together and difficult to break and separate.This paper studies the hydrothermal synthesis of silicate material products using waste concrete and clay brick as the main raw materials,which can realize the whole group differentiation and reuse of waste concrete and clay brick.alleviate the consumption of natural resources such as sand,limestone and clay in the production process of silicate materials,and reduce the recycling process of construction waste,which has good economic benefits and broad research prospects.There are two main problems to be solved in this paper: one is to explore the suitable calcination temperature for different proportions of waste concrete and clay brick samples.On the basis of reducing energy consumption,the best proportion of samples is determined on the basis of Ca O content and activity index of the main calcined products.The second is to find suitable water-solid ratio,ingredient ratio,type and amount of admixture and autoclave reaction system to prepare silicate products with good properties.In this paper,unseparated all-component waste concrete and waste clay brick are used as the main raw materials,and after crushing and grinding,several groups of samples arecalcined at low temperature according to different mass proportions.Through thermogravimetric analysis and chemical test analysis,the Ca O content and Ca O activity in the calcined products at different calcination temperatures are studied,and the calcination system of the best proportion of samples is determined.Then change the ratio of water to solid,the ratio of calcium to silicon,the type of admixture(sodium hydroxide,sodium carbonate,potassium hydroxide,water glass,manganese acetate,calcium chloride,sodium sulfate,zirconium oxychloride,strontium chloride hexahydrate and strontium nitrate)and the content,autoclave temperature,holding time,The properties of hydrothermal synthetic products were studied by means of compressive strength test,pore solution alkalinity test,water resistance test,mercury injection analysis,XRD analysis,thermogravimetric analysis and durability test,and the suitable proportioning ratio,type and content of admixture and autoclave system were determined.The main conclusions of this paper are as follows:(1)thermogravimetric analysis shows that the decomposition temperature of Ca CO3 in 100% waste concrete is about 840 ℃,and the burning loss of waste clay bricks with28.24% burning loss is only 0.75%,and there is almost no thermal decomposition and crystal transformation.Compared with the decomposition temperature of other proportion samples,it is found that the decomposition temperature of Ca CO3 in 60% waste concrete and 40% waste clay brick is about 830 ℃.Taking the Ca O content and Ca O activity in the calcined products as the evaluation index,the Ca O content of 60% waste concrete and 40% waste clay brick is12.20%,and the activity index is 20 s.Considering all the evaluation indexes,the samples of60% waste concrete and 40% waste clay brick group calcined at low temperature are selected as the follow-up production raw materials.(2)The waste concrete-waste brick calcined products are used as the main siliceous and calcareous raw materials of the recycled silicate materials.After being pressed by the Ca O group,the specimen appears obvious cracking phenomenon,while the specimen after autoclaved is loose and cannot be formed.The surface of the pressed specimen mixed with Ca(OH)2 is relatively flat with few cracking,while the specimen after autoclaved is angular and flat with no cracking basically.The color of the specimen was obviously lighter than that of the Ca O group,showing the gray-white of hydration products.(3)Three proportions of C/S are 0.7,0.9 and 1.1,and four water-solid ratios of 0.10,0.15,0.20 and 0.25 are selected.The recycled silicate materials with high strength can be obtained under the autoclerotic pressure system of 1.5mpa,203℃ and 4h.The experimental results show that the compressive strength of autoclaving specimens increases first and then decreases with the increase of the water-solid ratio,and the optimal water-solid ratio for the three samples with different ca-Siratios is 0.20.(4)The ratio of calcium to silicon has little influence on the compressive strength of specimens under the low autoclavate strength system,and the range of strength variation is small.It has a great influence on the compressive strength of the specimens under the high autoclaving strength system.The effect of autoclaving system on various calcium and silicon specific parts is different.(6)Na OH and KOH have remarkable excitation effect on the calcined products of waste concrete-waste clay brick.However,there is an optimal amount of alkaline admixture,too high will have a negative impact on the strength of the product,so that the strength of autoclaving specimen shrinks.Na OH solution excites autoclaving specimens better than KOH solution.Other admixtures have poor excitation effect on autoclaving specimens.(7)XRD pattern can be used to characterize the influence of water-solid ratio,calcium-silicon ratio,autoclavate system,admixture and other factors on the mineral composition of the regenerated silicate materials.(8)Under the experimental conditions of this paper,the autoclaving system and the ratio of calcium and silicon to the p H value of autoclaving specimens have a certain influence;The softening coefficient of each sample ranged from 71.83% to 85.06%.The durability test of autoclaving specimen shows that the test result of lime burst is good.In the acid corrosion resistance test,the strength ratio of each group is lower than 1,indicating that acid solution will accelerate the erosion of autoclaved specimens.In the test of sulfate resistance,the strength ratio of most specimens is greater than 1.It shows that sulfate has little erosive effect on autoclaved specimens.Specimens meet the strength and mass loss rate standards after 15 and 25 freeze-thaw cycles in AUTOclaved Fly ash Brick(JC/T239-2014).The autoclaved specimen has certain high temperature resistance. |
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