The Effect Of Limestone On Sulfate Attack Of Cement Concrete At Low Temperature

Limestone powder is usually blended during cement concrete being mixed to reduce costs and improve the performance of cement concrete.Its unfavorable factors on concrete structure have also attracted more and more attention.Among them,the influence of limestone powder on sulfate corrosion is very prominent,and there is a big controversy about the effect of limestone powder on sulfate corrosion with the large applying of limestone powder in cement concrete.There is considerable controversy about the effect of limestone powder on sulfate attack.Therefore,this experiment used appearance observation,intensity test,XRD and FTIR to study the limestone powder with different fineness and different content and the different proportion with fly ash under the action of accelerated sulfate erosion and fineness compounding on the impact of cement concrete sulfate attack at low temperature.Research indicates:(1)When mixing limestone powder alone,the higher the amount,the lower the compressive strength.In the case where the dosage is not too high,the finer the fineness,the higher the compressive strength in the early and middle stages,and the later stage is susceptible to erosite type erosion,resulting in a sharp drop in strength.When mixed with limestone powder and fly ash,the 1:2 ratio of limestone powder to fly ash has the highest compressive strength at the same age,and delays the time of strength decline,and the finer the limestone powder,the higher the strength.(2)Within 150 days of low-temperature sulfate attack,all test pieces had obvious gypsum and ettringite sulfate attack.Among the specimens mixed with limestone powder at 150 d,400 mesh 10%,20%,30% and 800 mesh 10% blended specimens did not produce thaumasite.After mixing with fly ash,2000 mesh limestone powder and fly ash were mixed according to the proportion of 20% and 10% of cementitious materials,and 800 mesh 10% limestone powder and 20% fly ash were mixed produced the thaumasite.(3)The formation of hydrated calcium aluminate and carbelite is different to the activity of limestone powder,and the former should be more sensitive.Carbelite can only be produced in a mixed system with a fineness of 800 mesh.And the higher the activity of limestone powder,it is not easy to produce carbasite in the compounding system.(4)During the entire erosion process,gypsum-type and ettringite-type erosion are mutually transformed.However,this may be affected by the instability and easy decomposition of ettringite under the action of an electric field.In summary: the effect of limestone powder on the low-temperature sulfate corrosion of cement concrete depends on the quality of the limestone powder used,whether other mineral admixtures containing active aluminate are added,and the amount of both.When mixing limestone powder alone,limestone powder with low mesh number and low activity should be used,and the dosage can be appropriately large;the higher the fineness of limestone powder,the higher the dosage.When mixing limestone powder and fly ash,it is advisable to use high-mesh and high-activity limestone powder and mix at a ratio of1:2,because high-activity limestone powder and sufficient active aluminate can react to form hydration.calcium carboaluminate,so it can inhibit the production of thaumasite to a certain extent.