Study On The Performance Evolution Of Hydraulicconcrete Under Contact Corrosion

Corrosion of concrete is also called soft water erosion.For hydraulic structures in service,it is unavoidable to contact with environmental water and gets different degrees of corrosion.Therefore,corrosion is one of the common and major diseases of hydraulic concrete.Among them,the corrosion of the concrete slabs of concrete faced rockfill dams,concrete impervious walls which protect the safety of dams and thin concrete structures deserve special attention.Concrete corrosion is divided into osmotic corrosion and contact erosion.Contact erosion is caused by the direct contact of the environmental water with the concrete surface and is extremely common in practical projects.Therefore,it is very necessary to carry out research on the performance evolution of hydraulic concrete under contact erosion.It is of great theoretical and practical significance to evaluate the long-term safety of concrete structures in the service environment,improve the future hydraulic concrete materials and prolong the life of the hydraulic structures.In view of the shortcomings of previous studies,this paper carries out experimental research from the following aspects:(1)The corrosion of concrete in practical engineering is relatively slow.In order to obtain more complete corrosion characteristics in a short time,the chemical reagent accelerated dissolution method was introduced,and the accelerated medium was 6mol/L ammonium chloride solution.(2)By using chemical reagents to accelerate the dissolution method,macro and microscopic research methods were combined to systematically study the performance changes of hydraulic concrete under contact corrosion.The corrosion mechanism of hydraulic concrete under contact corrosion was obtained,and the corrosion resistance of mortar and concrete specimens was compared and analyzed.The results show that the various macroscopic properties before and after the dissolution of concrete and mortar specimens have different degrees of change,and the general rules of change are consistent.As dissolution progresses,the dissolution of calcium ions in the specimen causes increase of the p H value of the etching solution,loss of specimen quality,increase of surface porosity,and decrease of compressive strength and surface impermeability.Microscopic observations are briefly described below.Firstly,as the dissolution progresses,the crystals of hydration products on the surface of the concrete and mortar specimens gradually become smaller.Secondly,the pores between the crystals increase relatively and the pore size increases.Thirdly,the structure is relatively loose,and the density is reduced.Next,the crystals formed by the hydration of the transitional zone are coarser than those away from the transition zone,and the amount is relatively small.Then,the pores between the crystals are relatively more and have larger pore diameters and the structure is more loose.Finally,under the same corrosion,the appearance damage,mass loss rate,calcium ion dissolution quantity,porosity increase,and strength loss rate of the mortar specimens were greater than those of the concrete specimens.That is,from the macroscopic point of view,the corrosion resistance of the concrete was stronger than that of the mortar specimens.(3)The ultrasonic method was used for nondestructive detection.The relationship model of the macroscopic properties of the specimen,the dissolution rate of calcium ion and the parameters of the ultrasonic wave velocity was established,which provides a reference for the evaluation of the degree of dissolution in the actual engineering.(4)Based on deionized water soaking,the accelerating rate of accelerated dissolution of chemical reagents was explored,and the rationality of the accelerated method was evaluated.The results are briefly shown below.Firstly,compared with the deionized water soaking environment,by using the sample’s mass loss rate,calcium ion dissolution,and soaking solution p H value as indicators,the accelerated dissolution method using 6mol/L ammonium chloride solution is reasonable and efficient.Secondly,The accelerated corrosion rate of accelerated reagents on concrete specimens was approximately 274 times,and that of mortar specimens was approximately 312 times.Accelerated corrosion results were significantly consistent with the results of several scholars.