Effect Of Particle Size Distribution On Properties Of Cement Incorparating Supplementary Cementitious Materials

A large number of metallurgical wastes with coal combustion fly ashes can be used supplementary cementitious materials to produce blended cement due to potential hydraulic activity.Traditional cement industry produces blended cement by grinding clinker and supplementary cementitious materials together.But these blended cement shows some problems such as low early strength,long setting time and low dosage and so on due to variation grindability of clinker and supplementary cementitious materials leading to irrational particle size distribution of blended cement.Therefore.there is a great significance to investigate the effect of particle size distribution on performance of cement-based materials incorporating supplementary cementitious materials,which can give full play to pozzlanic activity of supplementary cementitious materials and improve properties of cement.This paper selects two supplementary cementitious materials:low calcium fly ash and Si-Mn slag.They are precisely classified into 3 fractions of fine,middle and coarse(D50=5.06?m,15.63?m,35.01?m and D50?6.87?m,17.85?m,56.4?m)by an air classifier respectively.The effect of different size and additions on mechanical properties and anti-chemical corrosion properties of cement mortar incorporating fly ash and Si-Mn slag were investigated,and the effects of particle size distribution on hydraulic productions,hydration heat,microstructure and hydraulic products of the chemical erosion incorporating fly ash and Si-Mn slag were also discussed.Afterwards.the following conclusions can be drawn:(1)Fine fly ash fraction had more amounts of CaO,SO3,alkali and loss on ignition.There were no obvious differences in phase compositions of fly ashes with difference particle size fractions.As the particle size of fly ash became coarser,the spherical particles with smooth surface decreased.And as the particle size of Si-Mn slag became coarser,the amounts of SiO2,Al2O3 and SO3 decreased but the amounts of CaO,MnO,BaO and TiO2 conversely.The intensity of quartz and calcium aluminate increased with the decrease of particle size of Si-Mn slag.The coarse Si-Mn slag mainly consists of angular particles with densified surface.(2)The compressive strength of blended cement mortar decreased with an increase in the replacement of fly ash at every age.But the compressive strength of fine/middle Si-Mn slag cement mortar increased with an increase in the replacement of slag at later age.As the particle size of fly ash and Si-Mn slag became finer,strength of cement mortar increased at every age.(3)The pore size distribution of hardened cement paste were significantly affected by particle size of fly ash and Si-Mn slag.The most probable pore size of hardened cement decrease with the decrease of size of fly ash and Si-Mn slag.(4)The rate of heat evolution and cumulative heat of hydration of cement pastes with fly ash were lower than Portland cement,and the peak of rate of heat evolution of cement appeared at about 12 hours.The peak of rate of heat evolution of cement with fine fly ash was much higher than cement with middle and coarse fly ash.The cumulative heat of hydration of cement increased with the decrease of size of fly ash at 120 hours.Si-Mn slag promoted the rate of heat evolution of cement at cement initial hydration and stabilization periods.The peak of rate of heat evolution of cement with fine Si-Mn slag was higher than other samples.In 24 hours,the cumulative heat of hydration of Portland cement was higher than cement with Si-Mn slag.The curve of cumulative heat of hydration was in accordance with cement with Si-Mn slag of different size fractions.After 24 hours,the rate of cumulative heat of hydration of the Si-Mn slag cement pastes was significantly improved and as the particle size of Si-Mn slag became finer,cumulative heat of hydration of cement increased.(5)At 3 days,the intensity of Ca(OH)2 in the cement with different sizes of fly ash and Si-Mn slag were almost similar to that of Portland cement.And at 60 days,as the particle size of fly ash and Si-Mn slag became finer,the intensity of Ca(OH)2 in the blended cement decreased.Fine and middle sizes fly ash and Si-Mn slag could decrease the intensity of Ca(OH)2 in cement effectively.Hardened blended cement paste containing finer fly ash and Si-Mn slag produced a denser structure and more hydraulic products than containing coarser fly ash and Si-Mn slag.The surface of fly ash and Si-Mn slag produced C-S(Al)-H gel with Ca/Si=0.74 and C-S(Al,Mg)-H with Ca/Si=1.54 molar during pozzolanic reaction respectively.(6)Resistant index of fly ash and Si-Mn slag cement mortar reached a maximum value at 28 days and 60 days exposed to Na2SO4 solution,subsequently resistant index began to decline.As the particle size of fly ash and Si-Mn slag became finer,the resistant index increased at every age.Fine and middle fly ash and Si-Mn slag were more effective for improving the resistance property of sulfate attacks.Resistant index of fly ash cement mortar increased with curing time increasing exposed to artificial sea water solution but Si-Mn slag cement mortar reached a maximum value at 28 days.As the particle size of fly ash and Si-Mn slag became finer,the resistant index of cement mortar increased at every age.(7)At 28 days,the intensity of gypsum and ettringite in cement pastes were not obvious exposed to Na2SO4 solution.As the particle size of fly ash and Si-Mn slag became finer,the intensity of ettringite and gypsum decreased at 150 days.Ca4Al2O6Cl2·10H2O(Friedel's salt)was a kind of major erosion of hydration products in cement exposed to artificial sea water.At 28 days,the intensity of Friedel's salt in cement pastes with different sizes of fly ash and Si-Mn slag were almost similar to each other exposed to artificial sea water.But at 150 days,as the particle size of fly ash and Si-Mn slag became finer,the intensity of Friedel's salt in cement pastes decreased,respectively.