| In the coastal area,buildings are eroded by the complex and harsh environment such as offshore,tidal and saline-alkali land all year round,and the cracking phenomenon of concrete components is particularly serious.In recent years,the use of permanent removable formwork can improve the cracking resistance,enhance its durability and extend the service life of components,but the removable formwork is generally prone to cracking at the joint.Most of them are due to the insufficient bonding performance of joint materials,large self-shrinkage and other reasons,which indirectly lead to the functional failure of free template.But excellent interface repair materials can solve the above problems.Therefore,it is very important to study a kind of interfacial repair material with low cost,high toughness,low shrinkage and excellent bonding property.Compound material is the frontier of building material development.Polymer cement based material is a typical organic-inorganic composite material.In this paper,polymer cellulose ether(HPMC),polymer redispersible emulsion powder(VAE)and wollastonite are adopted to modify sulfoaluminate cement repair materials,and the bonding properties of sulfoaluminate cement repair materials under the action of mixed polymers are studied.The mix ratio of polymer modified sulfoaluminate cement repair material was obtained.The cement repair material with controllable setting time,stable mechanical properties and microexpansibility was prepared.The polymer cement repair material was further improved by mixing ordinary silicate cement(PO)-sulfoaluminate cement(SAC)system.Finally,polypropylene(PP)fiber toughened polymer repair materials are added to design polymer cement repair materials that meet the requirements.The main conclusions of this paper are as follows:(1)Through orthogonal test analysis,HPMC content has more significant effects on fluidity,consistency and water retention than other factors,and silica fume content has more significant effects on setting time.HPMC content is the most important factor affecting compressive strength and flexural strength.HPMC and VAE content have more significant influence on the interface bond performance.The bond strength of 1d interface is significantly higher than that of unmixed polymer.According to the SEM results,the porous structure of Ca(OH)2 induced by VAE and the polymer film formed by HPMC covering the hydration products are observed.The two polymers work together to improve the interfacial bond strength of cement mortar significantly.The optimal mix ratio of the two interfacial bonding methods is the same,so the optimal mix ratio of the three factors is obtained: 0.2% cellulose ether,0.6% redispersible emulsion powder,and10% silica fume.The measured fluidity was 200 mm,the initial and final setting times were 22 min and 33 min,respectively,and the interfacial bond strength of 1d was 4.5MPa.(2)With the increase of PO content,the coagulation time and fluidity of PO-SAC composite cementitious system will show a trend of first decreasing and then increasing.When PO content is 60%,70% and 1,mortar shrinkage is large,and the mixing content shows the effect of micro-expansion under other proportions.The composite cementing system will reduce the compressive strength,flexural strength and interfacial bond strength of polymer repair materials at each age.With the increase of PO content,compressive strength,flexural strength and interfacial bonding strength will first decrease and then increase.PO accounts for 90% of the composite system,which can obtain excellent repair performance.According to the SEM results,it is observed that the microstructure of AFt crystal of hydration product presents a short rod-like shape with uniform distribution.Under the age of 1d,the content of AFt crystal of hydration product of mortar gradually decreases with the increase of PO content.In the composite system where PO accounts for 50% and 70%,AFt crystal content is rare.And the microstructure of polymer repair materials is not as dense as that of pure components.Finally,adding0.5% defoamer into the repair material can effectively reduce the bubbles in the paste,making the paste more dense,so as to meet the strength of the test block.(3)PP fiber toughened polymer repair material.The fluidity of the mortar decreases with the increase of fiber volume.The fibers are beneficial for improving the strength of polymer repair materials.With the addition of fiber,the compressive and flexural strength of polymer repair materials at each age increased first and then decreased.When the content of PP fiber is 1.5%,the compressive and flexural strength of polymer repair material at each age reaches the maximum.Moreover,it can be found that the toughness of polymer repair material is obviously improved after the addition of fiber through the trend of mortar folding ratio.It is found through the bonding property test and uniaxial tensile test of mortar.When the content of PP fiber is 2%,the bond property of 28 d mortar can reach 5.3MPa,which is 32.5% higher than that of blank group.The ultimate tensile strength reaches the maximum of 3.96 MPa and the ultimate tensile strain reaches 1.16%.Through SEM analysis,it was found that fiber played the role of skeleton bridge in polymer repair materials,effectively preventing the development of microcracks.PP fiber was tightly wrapped by cement slurry,which enhanced the mechanical bite force between the cement paste and fiber after hardening.Figure:[37]table:[20]reference:[87]... |
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