| Cement-based materials are the largest man-made building materials used by humans.The application of repairing materials can repair damaged cement-based materials to a certain extent,guarantee the safety of their structural facilities,and extend their service years.This has great value for the national economy,and it also fits the idea of sustainable development strategy and the concept of building energy conservation.This research refers to the latest published building materials industry standards,with Alkali-activated Slag Cement(AASC)as cement material,trying to prepare AASC rapid repairing mortar to meet the standard requirements.The effect of different factors on the performance of AASC repairing mortar preparation and the effect of different admixtures on the bonding performance of AASC repairing mortar were studied.The interface properties of AASC repairing material bonding interface transition zone were studied and analyzed.The results shows:AASC repairing mortar stimulated by water glass is more suitable for the preparation of rapid repairing mortar,but the early strength(6 h)of AASC repairing mortar used for water glass stimulating is slower than that of sodium hydroxide.The effect of Ca(OH)2 on the early strength increase of the water glass-activated mortar is obvious,and the shrinkage of the repairing mortar can be reduced.The addition of fibers in the AASC repairing mortar can improve the drying shrinkage of the repairing mortar to some extent,but it cannot fundamentally solve the problem of large shrinkage of the AASC repairing mortar.In the basic preparation parameters,the water-binder ratio had the greatest effect on the early bond performance of the AASC repairing mortar,followed by the alkali equivalent,the type of activator,the water glass modulus,and the sand-binder ratio.The development of the early strength of the alkali slag repair mortar and the development of the interfacial flexural-tensile strength are positively correlated to a certain extent.Under test conditions,using water glass to excite AASC rapid repairing mortar with the best mix as follows: alkali equivalent 6%,water glass module 1.2,water-binder ratio 0.4,sand-adhesive ratio 2.5,Ca(OH)2 dosage 3%,compounded with 0.1% polypropylene fiber and 0.1% basalt fiber.The initial setting time is 24 min,the final setting time is 41 min,the mortar fluidity is 178 mm,the compressive strength of 6h,1d and 28 d are 15.87 MPa,38.83 MPa and 63.78MPa;the interfacial flexural-tensile strength at 28 d is 6.14 MPa.In addition to shrinkage control,the rest of the test results basically meet the standard performance indicators.In general,the addition of mineral admixtures in AASC in place of ore fines will reduce the bond strength of the repairing mortar.The weakening effect was most obvious when the fly ash was incorporated,followed by cement,silica fume and Nano-silica.When the other conditions are the same,the early bond strength of the bonded specimens stimulated with sodium hydroxide is higher than the water glass activated.At the later stage,the activator has little effect on the bond properties.When 10% silica fume or 1% Nano-silica was doped,the bond ability of the repairing mortar was enhanced to some extent,but the incorporation of silica fume and Nano-silica increased the poor calcium phenomenon of the AASC system.AASC materials have good chemical compatibility with cement-based materials.The bond interface transition zone is mainly composed of the reaction-reinforced layer on the cement-based material side and the weak boundary layer on the side of the AASC,and it forms a gradual interface transition zone under the combined action of adsorption,diffusion,and reaction.The alkali equivalent affects the thickness of the reaction layer on the cement substrate side.AASC repair cement-based material of bonding mechanism is mainly mechanical bite,but the bonding interface there is also a strong chemical bonding and intermolecular forces. |
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