Fluidity And Adhesion Of Self-Compacting Alkali-Activated Slag Repair Mortar

Due to many reasons such as structure design,material quality,construction technology,foundation settlement and natural disasters,a large number of cracks appeared during the service of concrete structure.It is very necessary to repair the existing cracks formed in the concrete structures.The alkali-activated slag material has many advantages,such as high early strength and high strength,and it is especially suitable for preparing green and economic repairing material.A kind of self-compacting alkali-activated slag repair mortar?SCAASRM?was prepared and its fluidity,adhesive strength,mechanical properties,expansion properties and setting time are studied.Through the experiment,the following conclusions are obtained:?1?When the alkali equivalent increased from 4%to 6%,the fluidity of SCAASRM decreased,the setting time shortened,and the interfacial flexural tensile strength continued to increase.When the alkali equivalent is 5%,the interfacial tensile strength is larger,and when the alkali equivalent is between 4%and 5%,the compressive strength and flexural strength are better.?2?When the Na₂SO₄ content is 1.5%,SCAASRM fluidity,flexural strength and compressive strength are better;when the Na₂SO₄ content is between 0?2%,the SCAASRM interfacial tensile strength,1d flexural and compressive strength are improved and the setting time is shortened.The effect on the interfacial flexural tensile strength is not obvious.?3?The maximum particle size(D_max)of sand increases from 0.5mm to 4.75mm,the fluidity of SCAASRM increases,and the interfacial tensile strength of the SCAASRM decreases,but the D_max of sand has little effect on the flexural strength and compressive strength of SCAASRM.When the sand D_max is 4.75mm,the interfacial flexural tensile strength is large.When the sand D_max is 2.36mm,the setting time is longer.?4?The content of active component MgO is reduced from 3%to 0,the fluidity of SCAASRM is increased,and the interfacial tensile strength is decreased.When the dosage is 1%to 2%,the interfacial flexural tensile strength is better.Active MgO has little effect on the flexural strength and compressive strength of SCAASRM.When the content of active MgO is between 1%and 3%,SCAASRM exhibits the microexpansion within 48 hours after preparation,and higher active MgO content results in an earlier begin of expansion and a higher expansion.It is found that active MgO can improve the crystallinity of hydration products.?5?Through the scanning electron microscope,the different shapes hydrotalcite and C-S-H are found in the hydration products and a kind of nepheline is also observed.Finally,considering the comprehensive properties of SCAASRM,the superior mix design is alkali equivalent of water glasse 4%?5%,4%?5%NaCl,1.5%Na₂SO₄,2%active MgO and 2%PCS.D_max of sand is 2.36mm.Water-binder ratio and binder-sand of SCAASRM is 0.40 and 1:1,respectively.At this point,the initial fluidity and 30min fluidity of alkali slag mortar are between 250mm and 290mm.The compressive strength of 1d,3d,and 28d are up to 31MPa,43MPa and 74MPa.The flexural strength of 1d,3d,and 28d are up to 3.6MPa,6.4MPa and 6.6MPa,respectively.The interface tensile strength of 3 days and 7 days are 1.67MPa and 1.92MPa,respectively.The interface flexural tensile strength of 3 days and 28 days are 3.53MPa and 5.34MPa respectively.Vertical expansion is 0.05%.The setting time is 75min.