Fly Ash Mineral Admixture Research

Fly ash is produced by coa l-fire d power stations for coal originally a kind of industrial waste,With the progr ess of fly as h and concrete r esearch 。Dosage of fl y ash in conc rete raw material has become the most i mpor tant and large st mineral admi xtures 。Fly ash from industrial was te into the important raw materials of concrete,because of i ts relative spe cial performance.The main chemi cal composit ion of fly as h is the active SiO2 and Al2O3,belonging to the pozzolanic ac tivi ty of material 。 Fly ash particles are s pheric al,most particle size less than 45 microns 。 Used as mineral a dmixtures in conc rete,activity of fl y ash not only has a certain effect,but also improve the conc rete mixture workability,i ncrease the compactness of c oncret e。Early volcanic activity of fly a sh is l ow,After a lot of fly ash replac ing c ement wil l reduce the early strength of ceme nt concrete,limiting i ts as mineral admixtures in conc rete with large a mount of a pplic ation 。 Activity of fly ash excitation methods at home and abroa d made a more in-depth a wide range of research,puts for war d the way of physi cal chemis try and composite act ivat ion。In this paper,t he pr operties of fly a sh and activation me thods,different dosage of fly ash concrete durabili ty of mec hanical properties and microstructure,environmental and economi c effect of fly ash concrete has made a survey and experimental research,the conclusion i s as follows:(1)The additi on of fl y a sh can obviously improve t he perfor mance of concre te mixing because of i ts char acteristic physical properties.The amount of fly a sh has a clear effect on the time of the concrete,and the concrete col lapse of the non-powdere d coa l ash is the biggest,the amount of fly ash is increas ed.Dosage of fly ash in the s ett ing time of concrete has si gnificant delay effect,The setting time of conc rete with the extension of the increase of dosage of fly ash;(2)The early act ivity of fly ash is low,and when the ce ment is replaced in equal amount,it can significantly r educe the heat of cement hydration,especiall y the early wate r heat.(3)The mi xing of fly ash will reduce the early strength of concrete i n different degrees,but it wil l not decrease or even slightly increase.The experimental r esults show that 7 d content 20% ~ 60% of fly ash concret e are lower than the benchmark concrete compre ssive strength,After more than 40% dosage of fly as h,t he 28 d strength is s light ly lowe r than the benchmark concrete,But mixi ng fly ash concrete 60 d basic close to or even higher than t he reference concrete,compressive strength and the late s trength also has a larger increase i n space;(4)The mixing of fly ash will reduce the a nti-carbonization performance of conc rete.The experiment al results show that the addition of the concrete to t he concrete is relatively poor i n the concrete resistance to carbonization,and the act ual anti-carbonization index will decrease with the increase of the amount ofadmi xture,more than 50%,the downward trend obviously,Bet ween 20% ~ 60%,t he dos age of fly ash concrete carbonation resistance ability can ke ep t he steel from corrosion;(5)M ixed with fly ash can r educe the por osity of c oncret e,mixed with 20% ~60% of fly ash can significantly improve permeability resist ance of concrete,and conc rete permeabi lity resistance inc rease with the increase of dosage of fly ash;(6)In the ant i-free ze study of concrete,the two hypot hesis of frozen concrete destruc tion i s learned,and the expe r iment shows that the relative loss modulus of fly ash concrete and decreased wit h t he increase of freeze-thaw cycle s,Concrete with hi gh volume of fly-ash in the process of freezing and thawing cycle,the formed surface pee ling off around 1 mm,mass l oss increase s with the increa se of freeze-thaw cycles,Fr eeze-thaw c ycle of 100 t imes,mixe d with 20% ~ 60% of fly ash concrete frost resistance meets the r equirements;(7)The mixing of fl y ash has positive effect on the anti-sulphate corrosion of conc rete.Along with the increase of the dosage of fly ash concrete corrosion r esis tance coe fficient i s on the rise,namely can big improvement with high volume of fly-ash conc rete sulfate a tta ck resistance.(8)Using s canning electron microsc opy,the i nfluenc e of fly ash on the structure of concrete hardeni ng structure was studied.From fly ash concrete i n different age a nd diffe rent dosage of fly a sh of SEM figure can be seen that the mixed fly ash concre te ca n effectively impr ove the micros tructure,reduce the porosity,with the increasing dos age of fly ash,a lkal i cont ent of c oncrete wi ll decrea se gradually.(9)The use of fly ash mi neral admi xture not only has t he funct ion of energy s aving and emi ssion re ducti on(CO2 emis sion reduction),but also re duces the production cost of concrete and creates grea ter economic benefits for enterpr ises.Through study on characte ris tics of fly ash and concrete with high volume of fly-a sh is te st.Mixe d with 40% ~ 60% of fly a sh can be drawn from various performance can meet the standard requirements of high performance concrete,fly ash of the high performance concrete in a dosage can be appli ed.