Experimental Study on Preparation and Application of Sulphoaluminate-Phosphate Cementitious Composite Material Using Industrial Solid Waste
Author:Ren Chang Zai
Supervisor:wang wen long
In China,industrial solid waste has huge dumped volume,wide geographical distribution and far-reaching environmental harm.The preparation of construction materials from industrial solid waste,is one of the feasible large-scale utilization methods for the current technology.The main obstacles to the application of the preparation of construction materials from industrial solid waste on a massive scale were low added value of products,secondary pollution,low effective utilization rate of industrial solid waste and limited capacity of product market.This study aimed to prepare the high value-added green cementitious materials by 100%industrial solid waste with low environmental impact,taking desulfurized magnesium slag,aluminum ash,coal gangue,carbide slag as a main raw materials and developing a novel technology to prepare sulphoaluminate-magnesium potassium phosphate cementitious composite material(SAC-MKPC)entirely with solid waste.The feasibility and the reaction mechanism of preparation of SAC-MKPC clinker form industrial solid wastes was studied by combing experimental,microscopic analysis and thermodynamic theory simulation method.The mechanism of magnesium-phosphorus ratio(M/P),ingredients and hydration method on the microstructure,mechanical properties and water resistance of SAC-MKPC was studied.Experimental study on the application of SAC-MKPC in 3D printing construction,and an environmental impact assessment was also obtained for SAC-MKPC clinker preparation from industrial solid wastes,The main work as follows.(1)The theoretical feasibility of SAC-MKPC clinker preparation from typical industrial solid waste was researched.The formation path of ye’elimite in the SAC-MKPC clinker system was investigated,and obtained the complete thermodynamic data of ye’elimite for different formation paths.Based on the complete thermodynamic data of ye’elimite,the influence of raw material ratio and calcination temperature on the formation of SAC-MKPC clinker phase was analyzed.There are four kinds formation paths,Al2O3,CaO,and CaSO4 can form 3CaO·3Al2O3·CaSO4 in the temperature range of 850-1000 0C,CaO·Al2O3,3CaO·Al2O3,12Ca0·7Al2O3 were also produced at the same time.For the system temperature of 1000～1200℃,CaO Al2O3,3CaO·Al2O3 and 12Ca0·7Al2O3 combined with Al2O3,CaO,and CaSO4 to form 3CaO·3Al2O3 CaSO4,respectively.The optimal formation region for main phases are MgO,Ca2SiO4,3Ca0·3AlO3 CaSO4,was from 1200 ℃ to 1300℃,and the theoretical MgO content is above 60%,the minor phase MgAl2O4,Ca3MgSi2O8 and CaSO4 accompanied in the clinker system.Hence,the theoretical of SAC-MKPC clinker preparation from typical industrial solid waste is feasible.(2)A method of preparing SAC-MKPC clinker with typical industrial solid waste(such as desulfurization magnesium slag,coal gangue,aluminum ash and calcium carbide slag)was proposed.The effects of calcination temperature and raw materials composition on the phase and content of SAC-MKPC clinker were studied,and the mechanism of influence of calcination temperature and MgO content on mechanical properties,mineral composition and microstructure of hydration products of SAC-MKPC was explored.When the calcination temperature is between 1250℃and 1300℃,the theoretical MgO content is above 60%,the main mineral phases are MgO,Ca2SiO4,3CaO·3Al2O3·CaSO4 in the SAC-MKPC clinker.When the calcination temperature is 1350℃,ye’elimite decomposed partially,and the relative content of 3Ca0.3Al2O3·CaSO4 decreased.The minor phase MgAl2O4,Ca3MgSi2O8 and CaSO4 was in each clinker system.The MgKPO4·6H2O and AFt mineral phases were shown in the electron micrographs of SAC-MKPC hydration products prepared by 1300℃ and the content of MgO was 70%.It was feasible to prepare SAC-MKPC clinker from typical industrial solid waste.(3)The effects of the M/P and ingredients on the hydration characteristics of SAC-MKPC were investigated,and the application of SAC-MKPC in 3D printing construction was validated.The effect of ingredients and M/P on the fluid characteristics,compressive strength development,and pH variation of SAC-MKPC paste were investigated.In addition,the shaping performance of SAC-MKPC-based 3D printing concrete was established,and then,the effect of the W/C and composite components on the shaping performance of the 3D printing concrete was analyzed.When the M/P and theoretical MgO content was 7 and 70%,respectively,the hydration pastes of the SAC-MKPC has dense micro-structure,stable property and high strength in the early,deepest reaction degree,meanwhile,it has the strongest water resistance,no retrogression of strength within curing time.After improving their properties,the SAC-MKPC-based 3D printing concrete exhibit advantages of a controlled setting time of between 40 and 50 min,a rapid hardening and an early stable strength,the hydrated-specimen compressive strength reached 15-20 MPa after 2 h of curing,best print results.SAC-MKPC has strong water resistance,and it can be used for 3D printing after modifying.(4)An environmental impact assessment was obtained for SAC-MKPC clinker preparation from typical industrial solid wastes.A quantitative analysis and prediction of the environmental burden that results from natural resources consumption,and CO2,SO2 emissions in SAC-MKPC clinker preparations using typical industrial solid wastes and in SAC,MKPC clinker preparations using natural resources as raw materials was provided.The functional unit for the three techniques was established as 1 tonne SAC-MKPC,SAC,MKPC clinker production,it is more eco-friendly that preparation of SAC-MKPC clinker from industrial solid waste,the SAC-MKPC clinker production with comprehensive waste utilization can reduce the total environmental burden by 16.2%,39.84%compared with the SAC clinker,MKPC clinker conventional process respectively.The preparation of SAC-MKPC with solid waste belongs to a low energy consumption and low emission process of high-performance green building materials production,and it was found that comprehensive waste utilization to produce SAC-MKPC clinker reduces resource consumption and CO2 emissions by 90.15%,60.75%and 37.96%,38.61%,respectively,compared with the conventional preparation of SAC and MKPC clinker.It was also found that the comprehensive waste utilization to produce SAC-MKPC clinker reduces SO2 emissions by 32.87%,compared with the conventional preparation of MKPC clinker,however,it was increase SO2 emissions by 21.79%compared with the conventional preparation of SAC clinker.It has a more obvious effect on reducing environmental pollution for preparation of SAC-MKPC clinker from industrial solid wastes,but there is still much room for improvement in SO2 emissions.