Study On Influence Factors Of MgO Solid Solution In Recycled Cement Clinker

Recycled cement utilizing all components of the waste concrete without separation treatment as raw materials,provides an effective method for the high value-added resource recovery of waste concrete with alleviating the increasing shortage of natural mineral resources in cement industry.However,the content of MgO in waste concrete varies in a large range,especially the concrete with dolomite limestone or low-grade high-magnesium limestone as coarse aggregate resulting in the high content of MgO in recycled cement raw meal.In fact,due to the increasing consumption of high-quality limestone resource,cement industry has also focused how to use low-grade high-magnesium limestone and industrial waste to produce qualified cementand how to diminish the negative impact of high-magnesium raw materials on cement production and performance.This paper aims to explore the effective measures to change the tendency of MgO solid solution and control the content of f-MgO in the clinker of high magnesium raw material.This paper provides the oretical foundation for recycled cement in quality control of raw materials and expansion of raw materials selection,and it also provides the oretical reference in performance optimization for other high-magnesium cement.In this paper,the effect of CaF₂ and MgO,compound doping?fluoride-sulfur,fluoride-sulfur-zinc,fluoride-sulfur-titanium,fluoride-sulfur-manganese?and SM on MgO solid solution and cell parameters of Alite of recycled cement clinker were studied by means of burnability test,chemical analysis and Rietveld quantitative analysis.The main conclusions of the paper are as follows:?1?As CaF₂ dosage was 0.82%,the contents of f-CaO in the clinkers with different MgO dosages were all less than 0.20% and with insignificant change.The contents of f-CaO in the clinkers with compound doping?fluoride-sulfur,fluoride-sulfur-zinc,fluoride-sulfur-titanium,fluoride-sulfur-manganese?were in accordance with GB requirements.When the content of MgO in clinker was 3% or 5%,the content of f-CaO was low and decreased with the increase of SM.?2?As CaF₂ dosage was 0.82%,solid-solution rate of MgO,content of MgO solid solution and content of f-MgO in clinker ascended with the increasing dosage of MgO.The formation of C₃S could be promoted when MgO content was adding.In the case of MgO dosage under 5%,the contents of C₂ S and silicate minerals decreased with the increasing content of MgO.?3?The changing amplitude of C₃S cell parameters in clinker slightly decreased first and then increased with the increase of CaF₂ content.When the CaF₂ content exceeded 1.64%,the changing amplitude of each parameter except ?? tended to be stable.When MgO content increased to 1%,the changing amplitude of C₃S cell parameters diminished significantly.The changing amplitude of parameters excepting ?? developed reversely at the inflection point of 4% MgO.Meanwhile,the parameters excepting ?? were the closest to the standard cell parameters.In addition,all parameters were negative except for ?b.?4?Fluorine-sulfur compound dopingcould promote the solid solution of MgO in recycled cement clinker.For fluoride-sulfur-zinc compound doping,the effect of various SO₃ content on the solid solution of MgO in clinker was different.In this paper,the content of TiO₂ over 0.5%was not conducive to the solution of MgO in the clinker,and the adverse effect was more obvious when the SO₃ content was higher.Fluoride-sulfur-manganese compound doping was beneficial to promote the solid solution of MgO,and the content of f-MgO was the least when the content of SO₃ was 5%.?5?The formation of C₃S in recycled cement clinker could be inhibited by fluoride-sulfur,fluoride-sulfur-titanium or fluoride-sulfur-manganese compound doping.Fluorine-sulfur-zinc compound doping had a certain promoting effect on the formation of silicate minerals,but the promoting effect weakened with the increasing content of SO₃ when the content of SO₃ was no more than 2%.ZnO and TiO₂ could promote the solid solution of MgO in silicate minerals.?6?The C₃S cell size grew with the increase of SO₃ content in the recycled cement clinkers with fluoride-sulfur-zinc orfluoride-sulfur-titanium compound doping.The C₃S cell was more close to the standard cell in the clinker with fluorine-sulfur-manganese compound doping.?7?For fluorine-sulfur compound doping,the content of f-MgO increased with SM rising,when the content of MgO was at 3% or 5%.In case of 3% MgO,the solid solution of MgO was mainly affected by the silicate phase and MgO was more likely to be dissolved in the liquid phase.In case of 5%MgO,the solid solution of MgO in clinker was mainly affected by the mesophase,and MgO was also more likely to be dissolved in the liquid phase when the content of MgO was 5%.As SM rising,the C₃S cell parameters were larger than the standard cell parameters.