Research on High Performance Cementitious Repair Materials and Interfacial Properties
|Keywords||sulphoaluminate cement redispersible polymer powders repair mortar interfacial agent durability|
It is important to research on high performance cement-based repair material in concrete repair engineering. Repair mortars was produced by mostly adopting rapid hardening sulphoaluminate cement, and modified by using redispersible polymer powders. The effect of redispersible polymer powders on mechanical properties （fluidity, flexural and compressive strength, bond flexural strength and shrinkage property） and durability （impermeability, frost resistance and carbonization resistance） of sulphoaluminate cement mortars were researched. The effect of redispersible polymer powders on bond strength （tensile bond strength and shear bond strength） and durability （frost resistance, heat resistance and erosion resistance） of interfacial agent were also researched. With the help of SEM and mercury intrusion apparatus, modified mechanism of redispersible polymer powders in sulphoaluminate cement mortar was analyzed. Test results show that:The fluidity of freshly mixed mortar was increased by mixing redispersible polymer powders. The flexural strength, compressive strength and bond flexural strength were also be raised significantly. When the mass fraction of T was 1.5%, flexural and compressive strength of repair mortar were highest. When the mass fraction of T was 0.9%, bond flexural strength can reach 4.7MPa and 7.05MPa respectively at 7d and 28d ages. Flexural strength and compressive strength couldn’t be raised with the incorporation of super fine slag and silica fume. The hardened paste of repair mortars present a little shrinkage with the incorporation of redispersible polymer powders T.When the redispersible polymer powders T was added, impermeability and frost resistance of modified sulphoaluminate cement mortars was improved significantly. Carbonization resistance of the sulphoaluminate cement mortars was best when the mass fraction of T was 1.5%. When super fine slag and silica fume were added, impermeability and carbonization resistance couldn’t be improved.When the redispersible polymer powders F was added, water requirement of normal consistency became larger and setting time became longer. Redispersible polymer powders M and T made water requirement of normal consistency become smaller. With the increase of powders M, water requirement of normal consistency became lower and setting time became shorter. With the incorporation of powders T, water requirement of normal consistency was changed at the P/C of 4%.Powders M、F and T in sulphoaluminate cement interfacial agent all could modify the tensile bond strength, but powders M couldn’t modify the shear bond strength. Based on comprehensive consideration of tensile bond strength and shear bond strength, powders T is appropriate to modify sulphoaluminate cement interfacial agent.With powders T incorporation of interfacial agent, frost resistance of bonding specimen could be improved significantly, but heat resistance couldn’t be improved. Tensile bond strength of all groups of bonding specimen could be decreased after erosion of MgSO4 and MgCl2, but increased after erosion of KCl, NaCl, K2SO4 and Na2SO4.With the help of SEM-EDS and mercury intrusion apparatus, the morphology of the hydrates and the pore structure of the cement mortars were observed. The results show that polymer film was formed in hydration paste which modified by redispersible polymer powders. The effect of gap-filling and film-forming function can reduce microcrack, lower total porosity, improve cohesive strength of mortars and promote compact hardened paste formed.