Study On The Anti-erosion And Abrasion Resistance Ability Of Iron-rich Phosphoaluminate Cement

Iron-rich phosphoaluminate cement?iron-rich PAC?is a new type of special cement,which is developed by phosphoaluminate cement.The Fe₂O₃ content in the cement clinker system is improved,which has the advantages of low calcination temperature and early strength.In this paper,the properties of chloride binding and abrasion resistance of iron-rich PAC are studied,the transmission of chloride ions in wet-dry cycling condition,the effects of supplementary cementitious materials such as fly ash and silica fume,on the sulphate erosion resistance,anti-penetration of chlorine ion and frost resistance were investigated deeply.The microstructures and morphology of the hardened paste were analyzed by means of XRD,SEM and MIP,and the reason for the improvement of performance of the cement were analyzed.The main conclusions are as follows:The chloride binding rate of OPC,SAC and iron-rich PAC was 21.92%,19.85%and26.32%,respectively after hydration of 28d,and the iron-rich PAC had better chloride curing properties.Iron-rich PAC system contains CA,calcium phosphoaluminate,C₄AF and C₃P mineral phase,they all can be chemically bonded forms to binding of chloride ion,and form Friedel salt?3CaO·Al₂O₃·CaCl₂·10H₂O?and chlorine apatite?Ca₅?PO₄?₃Cl?,the chloride ion content in the chemical method was 22.69%,far higher than the 6.18%of SAC and 12.85%of OPC,and chloride ion binding of cement paste was more stable.The curing ability of iron-rich PAC to chloride ion increased with the increase of chloride ion concentration,when the content of chloride ion content was 1.0%,the chloride ion binding rate was the highest and the binding rate was 27.94%.Sample in different hydration ages of chloride ion curing ability is different,the mixed mass fraction of chloride ion is smaller,the difference caused by different degree of hydration is larger with the increase with the increase of the degree of hydration,iron-rich PAC can be used in a large amount of highly effective chemical curing Cl^-,effectively shielding Cl^-from direct erosion of the steel bar.The chloride transfer rate of cement concrete in the wet-dry cycling condition is much higher than that in the whole immersion state.Due to the low porosity of iron-rich PAC,the resistance to Cl^-transmission is greater than that of SAC and OPC.The diffusion of Cl^-in concrete has universal regularity and follows the second Fick's law.Under the wet-dry cycling condition,the effective diffusion coefficients of OPC,SAC and iron-rich PAC are 3.08×10^-6,2.33×10^-6 and 1.82×10^-6mm²/s,respectively,according to the law of diffusion,the diffusion rate of Cl^-in iron-rich PAC is slow;By reference mathematical model to predict the service life of the structure,OPC and SAC in reinforced cement concrete structure surface reaches a critical concentration of Cl^-content time is 21.5 and 27.9 years,iron-rich PAC as the raw materials of reinforced concrete structures in the service life of the complex ocean environment is higher,at 36.7 years.The silica fume is higher than the surface,which can absorb a lot of free water and increase the water demand.When the fly ash content is fixed at 9%,the more the silica fume content,the less the iron-rich PAC clinker,the hydration degree of the cementing material system decreases,and the setting time of cement increases.When the content of silica fume in2%,4%and 6%,the iron-rich PAC hardened slurry of chloride ion electric flux in turn,315,264 and 315 C,sulfate attack resistance coefficient were 1.23 and 1.00,compressive strength after 150 times of freeze-thaw cycle were 41.18,45.12 and 39.70 MPa;When silica fume quantity is higher than 6%,the resistance to chloride ion permeability of the specimens,the sulfate attack resistance and freeze resistance began to drop sharply,when the dosage reached12%,electric flux increased to 572 C,the resistance to sulfate erosion coefficient decreased to0.362,after 100 times of freeze-thaw cycle compressive strength decreased to 31.54 MPa;Silicon ash grain fineness is lesser,can fill the system and improve the pore structure of hardened cement paste,improve the ability to resist Cl^-penetration and sulfate attack resistance,reduce the hydrostatic pressure in the process of freeze-thaw cycle,makes the frost resistance increased;At the same time,silica fume will react with cement hydration products to generate calcium silicate aluminate,thus improving the strength of cement paste.When the amount of silica fume is too high,the hydration degree of the system will decrease,and the low alkali cement system is difficult to stimulate the activity of the silica fume and fly ash,results in the decrease of hardened cement paste density;The optimum content range of silica fume is 2%⁶%and the durability of the hardened paste is better.Iron-rich PAC,OPC and SAC during hydration ages to 28d impact ductility index is 2.5,1.95 and 2.13,in addition,the strength of the shock resistance of 90d is 44.76 h/?g/cm²?,36.17h/?g/cm²?and 38.35h/?g/cm²?,compared with the OPC and SAC,iron-rich PAC has better anti-wear performance;The dense structure of rich-iron PAC can hinder the continuous development of the crack,the system can resist wear and tear,and can withstand some friction loads,so as to improve abrasion resistance ability of the cement paste.The wear rate of rich-iron PAC increases with the increase of wear content,and is basically linear;A proper amount of silica fume can be used to improve abrasion resistance ability of the hardened paste containing fly ash,amorphous silica can react with the cement hydration products generates tabular C₂ASH₈,improving the surface structure of slurry and cement mechanical stress distribution,and silica fume can increase the structure compactness,when the fly ash content was 9%and the silica fume content was 4%,the ductility index and anti-abrasion strength were the highest,respectively 2.9259 and 50.63h/?g/cm²?.