The Polycondensation And Sintering Mechanism Of Lightweight Ceramsite And Its Application In Concrete

With the development of prefabricated buildings,ceramsite concrete has the characteristics of light weight and thermal insulation,so the high-performance ceramsite concrete has great application prospects and development potential.In this paper,the low-silicon aluminum-iron ore tailings peculiar to southern Shaanxi are used as the main material,and a small amount of coal gasification slag is added to prepare ceramsite that meets the national standard requirements.The activity of raw materials of iron tailings and coal gasification slag is studied and the shaping of ceramsite raw ball is carried out in the form of alkali excitation,which improved the performance of ceramsite.Through XRD and micro analysis,the polycondensation and sintering mechanism of ceramsite are studied,and industrial tests are carried out to prepare LC35 ceramsite concrete,and its mechanical properties are experimentally studied.Main contents and results are shown as follows:（1）Through the analysis of the chemical composition and phase composition of iron tailings and coal gasification slag,it is found that both raw materials contain active substances such as Si O₂,Al₂O₃ and partially amorphous aluminosilicates,which verifies the possibility that iron tailings can form a geopolymeric structure.Therefore,the raw material activity was first stimulated with Na OH to prepare the raw ceramsite ball,and then sintered.（2）Through a large number of experiments,the optimal ratio and preparation conditions of the iron tailings raw ceramsite ball are as follows:the ratio of iron tailings and coal gasification slag is 8/2,the Na OH concentration is 12mol/L,and the curing temperature is120°C,and the curing time is 4 hours.Under the above conditions,the compressive strength of the prepared ceramsite raw ball is 12.34 MPa.Through microscopic analysis,we found that a three-dimensional network structure of geopolymers was formed inside the ceramsite raw material ball,the network-like structure of the mullite precursor was filled into the pores of the matrix,closely related to the geopolymer gel phase,and together formed the strength of the ceramsite raw material ball.（3）Through laboratory experiments,the optimal firing process is determined as follows:the preheating temperature is 400°C,the preheating time is 20min,the roasting temperature is1050°C,the roasting time is 20 min,and natural cooling.The basic properties of the sintered ceramsite are as follows:the cylinder pressure strength is 25.49 MPa,the bulk density is 934.28kg/m³,and the water absorption is 7.86%.Each property index can meet the requirements of the national standard for 1000-grade ceramsite and belongs to high-strength ceramsite.Through infrared spectrum and X-ray diffraction,it was found that the geopolymer structure inside the ceramsite raw ball was enhanced at 650-850°C,but the increase was not obvious;when the temperature reached 1050°C,the mullite precursor inside the ceramsite transformed and crystallized into mullite crystals,and the source of ceramsite strength has changed,and during the high temperature process,the Fe³⁺ions can partially replace the octahedral or tetrahedral Al³⁺ions of mullite to supplement the shortcomings of insufficient Al³⁺content.（4）In order to combine with actual production,the industrial rotary kiln firing test was performed on the iron tailings ceramsite.In the industrial test,the roasting temperature of the ceramsite is 1060°C,and the properties of the sintered ceramsite are as follows:the packing density of 811kg/m³,the apparent density of 1756kg/m³,the water absorption rate of 5.94%,the cylinder pressure strength of 5.43MPa.Although the cylinder pressure strength is lower than the results of laboratory preparation,the bulk density and water absorption rate are further lower,and they can all meet National standard requirements.（5）Using iron tailing ceramsite prepared by industrial tests as coarse aggregate,the mix proportion design and mechanical properties of ceramsite concrete with LC35 strength grade were studied.It was found that ceramsite with cylinder pressure strength of 5.43MPa can be configured with LC35 Grade ceramsite concrete,and the apparent density of the concrete is below 1950kg/m³.The test of basic working performance and mechanical properties of iron tailing ceramsite coagulation provided a basis for practical application in engineering.