Study On The Building And Preparing Of Phospho-Sulphoaluminium New Cementitious System

Sulphoaluminate cement(SAC)has been widely used in rapid repairing,component prefabrication and anti-seawater corrosion engineering due to its unique performance such as high early strength,short setting time and excellent corrosion resistance.But under the condition of long time practice using,SAC’s shortcoming are gradually appearing such as low bound strength and slow long-term strength growth.The main research of this thesis is improving SAC’s shortages by synthesizing calcium phosphoaluminate(C8A6P),the characteristic mineral of phosphoaluminate cement(PAC),into SAC system.In this research,XRD,IR,DSC,TAM,SEM,strength test etc.were used to characterize effects of C4A6$ in Calcium sulphoaluminate(C4A3$)and SAC system respectively.A new concept of Calcium phospho-sulphoaluminate(CPSA)and a new cementitious materials system named phosphor-sulphoaluminate cement(P-SAC)was built.The conclusions were as follows.C4A3$ and C8A6P were combined and burned in one system under iron rich condition which fixed with 10%C4AF.C8A6P has a homologous crystal structure with C4A3$,so it was hard to distinguish these two phase on XRD pattern due to many overlapping peaks.The results of Rietveld-XRD indicated that[PO4]could substitute the[SO4]in some C4A3$ crystals,which distort C4A3$ crystal lattice,decrease unit cell volume and improve the transformation of cube-calcium sulphoaluminate(c-CSA)to orthorhombic-calcium sulphoaluminate(o-CSA).The results of FT-IR and XPS declared that such substitution reaction did not impact on C4A3$ crystal lattice directly but lead a formation of C8A6P.This mineral dissolve in C4A3$ to form a new mineral named calcium phosphor-sulphoaluminate(CPSA),which’s molecular formula could be indicated as C4A3$xP0.5-x.In addition,CPSA had better pyrolysis resistance than C4A3$ under the long time burning.Further research showed that the binary system performed variety hydration properties under different C8A6P contents.3%content of C8A6P had little effect on strength or hydration flow.6～9%C8A6P content could extent induction period of hydration.Especially under 9%C8A6P content,the system had the smoothed hydrated exothermic curve and it’s induction period was extended by 10 hours compared to the control group.The 3d and 7d compressive strength of paste samples had a significant increase in this range of C8A6P content,but 14 and 28d strength decreased seriously.When C8A6P content reached 12～24%,the hydration induction period of the system as well as 1,3d paste compressive strength decreased with the C8A6P content increasing,and the exothermic heat gradually concentrated.In addition,the compressive strength of paste samples at each age could also increase steadily at this range of C8A6P content.Among all groups,15%content of C8A6P was considered the optimal content The early crystalline hydration product of this system was Ms10.5,which would be converted to Ms 12 as the hydration reaction proceeded.The results of SEM shown that the P element was mainly distributed in gel phase in hydration product,so the possible hydration products of the system are AFm,aluminum(iron)gel and C-A-P-H gelThen the effect of C8A6P on SAC clinker system was studied.The best level combination among C8A6P content,C2S content and calcination temperature was determined as the mineral composition of 65%CPSA(15.2%C8A6P and 49.8%C4A3＄),25%C2S and 10%C2F and the calcination temperature of 1360℃ through orthogonal test.From the analysis of the mean value and range,it could be seen that the existence of C8A6P mainly affected the 7d and 14d compressive strength of paste samples.The higher the content,the greater the average 7d and 14d strength.The samples with best mineral composition were calcined at 1300,1330,1360,and 1390℃,respectively.The compressive strength showed that P-SAC performed greater at each temperature and age than rapid harding SAC.With the increase of calcination temperature,the strength of 14d and 28d showed an upward trend.Taking into account the strength of all ages,the best calcination temperature was 1390℃.XRD Rietveld refinement results showed that the mineral composition of cement is approximately:56%CPSA,23%6C2S-C3P,8%C4AF and 13%C2AS.In addition,it could be seen from the SEM micro-morphology that as the calcination temperature increases,the firing condition of P-SAC was improvedThe extra content of Fe2O3 or P2O5 had no impact on the mineral composition of P-SAC clinker but impose a significant influence on mineral content and strength growth.The increase of Fe2O3 extra content was not only contribute to the increase of C4AF,but also lead a decline in 6C2S-C3P content and a growing in C2AS content,Especially when its extra content reached 150%.Under 50%extra dosage of Fe2O3,P-SAC had a prominent increase in later period after 14d with a tiny decrease in early hydration stage,but compressive strength of P-SAC at all ages would decline when extra dosage of Fe2O3 was at a overlarge number.In addition,extra dosage of P2O5 could cause a decrease in calcium sulphoaluminate content and an increase in C2AS content.3d and 7d compressive strength of P-SAC would have a significant increase under the 30～40%extra content of P2O5.When P2O5 extra content reach 50%,P-SAC’s 14d and 28d compressive strength increased significantly but its 3d and 7d compressive strength had a slight decline though performed greater than reference group.At last,in the research of the effect of P2O5 on the sintering of C4A3$,as calcination temperature raising,the total content of C4A3$ at all P2O5 addition would decrease while aluminates would increase.At different calcination temperature,C12A7 would gradually transform into CA with the addition of P2O5,and C12A7 would disapper when P2O5 content reached 4%.