| In recent years,with the continuous development of science and technology,people put forward higher requirements for the performance of cement-based materials to meet the more demanding use environment and more complex application scenarios,such as hydraulic engineering,marine engineering and road and bridge repair engineering.Moreover,cementbased material is a kind of hydrophilic,heterogeneous and porous brittle material.How to improve toughness and durability,corrosion resistance and cracking resistance,is the current research hotspot.Emulsified asphalt powder(EAP)is a redispersible asphalt powder made from modified emulsified asphalt and spray dried.As a modifier of cement-based materials,it has potential application in the field of waterproofing and repair engineering.However,the research and application of EAP in the modification of cement-based materials are few,and the mechanism is still unclear.Therefore,the effects of EAP on the mechanical properties,durability and microstructure of cement-based materials and the related mechanism were studied in this paper,in order to lay a technical and theoretical foundation for the further research and wide application of such materials.The results show that:The additon of EAP reduced the rigidity of cement mortar,improved the toughness of cement mortar and concrete,and improved the anti-cracking ability of materials.When the EAP content was 15wt%,the elastic modulus and the compressive strength/flexural strength ratio of the modified cement mortar were reduced by 24.6% and 35.2% respectively,and the impact toughness of the concrete was significantly improved.When the EAP content was in the range of 4-6wt%,the tensile strength was about 40% higher than that of ordinary cement mortar.At the same time,it should be pointed out that EAP had a certain adverse effect on the compressive strength and strength development of cement mortar during 7d to 28 d.EAP significantly improved the surface properties of cement mortar.When the EAP content was 15wt%,the surface water absorption of the modified cement mortar was reduced to half of that of the ordinary cement mortar and the internal contact angle reached 84.8 °.In addition,the improvement of surface barrier property was also conducive to improving the carbonation resistance of cement mortar.On the other hand,EAP can effectively reduce the water transport property in cement mortar.Within the content of 15wt%,EAP can reduce the drying mass loss and capillary water absorption of cement mortar,which was also helpful to improve the chloride penetration resistance of cement mortar.When EAP content was less than 6wt%,the microstructure of hardened cement paste hardly changed,and the hydration process was slightly delayed.However,when the dosage was up to 15wt%,the asphalt membrane interacted with the hydrated product and partly encapsulated some hydration products,thus reducing the production of C-S-H gel and hindering the hydration process of cement.The experimental results of pore structure showed that the critical pore size of cement mortar decreased gradually with the increase of EAP content.The indexes of transport property of cement mortar in different capillary water absorption stage had a good linear relationship with the critical pore diameter.The decrease of the critical pore diameter weakened the water transport process in the cement mortar,which was conducive to improving the durability of the cement mortar.The setting time,consistency,consistency loss rate and water retention rate of the fresh EAP-modified cement mortar met the requirements of relevant specifications.The effect of EAP on the initial consistency and consistency loss rate of fresh cement mortar was better than that of the same amount of styrene acrylic emulsion and VAE emulsion.Meanwhile,5wt% EAP can slightly improve the water retention of fresh cement mortar. |
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