Effect Of Cationic Asphalt Emulsion On Microstructure、Mechanical Properties And Durability Of Cement Paste

Cement-based material is a kind of brittle material,which is easy to crack in use.Cationic asphalt emulsion is an organic material with a certain degree of flexibility.Cement-asphalt mortar(CA mortar for short)formed by modifying cement mortar with cationic asphalt emulsion has the advantages of high mechanical properties of cement-based materials and good flexibility of asphalt.In recent years,CA mortar has been widely used in the fields of high-speed railways and road transportation.Mechanical property is one of the main properties of CA mortar.However,during its long service life,CA mortar will be attacked by water and salt solutions in the air.These are the main reasons for the deterioration and failure of CA mortar.Therefore,it is of great significance to study the transport behavior of water and salt solution in CA mortar to prepare CA mortar with good durability.CA mortar is a composite material composed of cement,asphalt emulsion,sand,water and additives.The mechanical properties and durability of CA mortar are closely related to its microstructure.This paper mainly studies the influence of the addition of cationic asphalt emulsion on the mechanical properties,durability and microstructure of cement paste,and explores the internal relationship between microstructure and its mechanical properties and durability.The main research results of this paper are as follows:(1)The effects of cationic asphalt emulsion on the flexural strength,compressive strength and failure characteristics of cement mortar are investigated.The mortar strength test results show that flexural and compressive strength of CA mortar in 3d,7d,28d,90d and 180d gradually decrease with the increase of A/C(A/C is the mass ratio of cationic asphalt emulsion to cement).The compression ratios of CA mortars of different ages increase with the increase of A/C,indicating that the incorporation of cationic asphalt ermulsion improves the flexibility of cement mortar;The ultrasonic test results of CA mortar show that the ultrasonic wave velocity of CA mortar decreases continuously with the increase of A/C,indicating that the compactness of CA mortar gradually decreases.(2)The effect of cationic asphalt emulsion on the water transmission behavior,sulfate resistance and frost resistance of cement mortar is investigated.The water absorption test and anti-permeability test of CA mortar show that the water absorption,water absorption coefficient and water penetration height of CA mortar gradually decrease with the increase of A/C,and the incorporation of cationic asphalt emulsion hinders the transmission of water in cement mortar;The sulfate resistance test of CA mortar shows that:after immersed in 5%sodium sulfate solution for 90 days,the influence of sulfate solution on the relative dynamic elastic modulus and compressive strength of CA mortar is gradually reduced with the increase of A/C,indicating that the addition of cationic asphalt emulsion improves the sulfate resistance performance of cement mortar;The freeze-thaw resistance cycle test of CA mortar shows that with the increase of A/C,the mass loss rate,compressive strength loss rate and relative dynamic elastic modulus loss rate of CA mortar gradually increase under the 150 freeze-thaw cycles,indicating that the incorporation of cationic asphalt emulsion reduces the freeze-resistance ability of cement mortar.(3)The effect of cationic asphalt emulsion on the microstructure of cement paste is explored.Through TG,chemically bound water and infrared experiments,it is found that with the increase of A/C,the generation of Ca(OH)2 is gradually inhibited,the polymerization degree of H2SiO42-is gradually reduced,and the hydration degree of cement is gradually reduced;Through SEM test,it is found that the cationic asphalt emulsion adsorbs on the surface of ettringite,C-S-H and other hydration products,and forms an organic-inorganic whole with them.Cationic asphalt emulsion adsorbs on the pore wall to block the communication pores inside the CA paste;Through the low-field nuclear magnetic test,it is found that the porosity of the CA paste increases and the pore size becomes larger with the increase of A/C.The results show that the incorporation of cationic asphalt emulsion delays the formation of cement paste microstructure.(4)The internal relationship between the microstructure of CA paste and its mechanical properties and durability is investigated.The study finds that:cationic asphalt emulsion inhibits the formation of cement hydration products,increases the porosity and pore size of CA mortar,and gradually reduces the compressive strength,flexural strength and compactness of cement mortar.Cationic asphalt emulsion adsorbs on the surface of cement and hydration products,forms an organic waterproof membrane on the surface,and adsorbs on the pore wall,blocking the connecting pores,making it difficult for water and salt solution to enter the interior of the mortar.The hydrophobicity of cationic asphalt emulsion was greater than the change of mortar pore structure,which hinders the transmission of water in cement mortar and improves the sulfate resistance performance of cement mortar.However,during the freeze-thaw cycle,due to the small binding force between cationic asphalt emulsion and hydration products,the pore size of CA mortar gradually increased with the increase of A/C.Under the combined action of larger expansion pressure,osmotic pressure and temperature difference stress,CA mortar is easier to be broken down,thereby cationic asphalt emulsion reduces the frost resistance of cement mortar.