Macroscopic And Microscopic Study On Bonding Performance Of GFRP Bar Exposed To Alkaline Environment

Under the joint action of stress damage and alkaline solution corrosion,the degradation of the bond strength between glass fiber composite material(GFRP)and concrete is related to the normal use and safety performance of GFRP reinforced structure,which is the key to the design calculation and engineering application of GFRP bar structure.The change rules of bond properties of GFRP bars were analyzed by studying the single factor action of alkaline solution and the interaction of alkaline solution and loading.By applying the damage and corrosion to GFRP bars with a diameter of 20 mm,the effects of corrosion period,damage degree and corrosion state on the bond durability of GFRP bars were studied.The damage of the internal structure of the specimens was observed by scanning electron microscopy.The bond performance degradation law of the GFRP bars was carried out by macroscopic and mesoscopic analysis.The main conclusions are as follows:(1)The corrosion time has the greatest influence on the bond strength,the influence of the corrosion state is the smallest,and the stress damage is between the two.After 150 d corrosion under alkaline solution,the ultimate bond strength of GFRP bars decreased by half;after stress damage,the bond properties degradation of the specimens increased significantly.The bond strength of 25% stress-damaged specimens and non-stress-damaged specimens differs by about 10%,but after 150 days,the difference is about 20%;while the influence of static and dry-wet cycling corrosion is only about2%.(2)The bond strength decreased obviously during the period of 90~150d alkaline solution,and the strength decayed fastest during the period of 90~150d.This is because the interface between the bar and the concrete began to damage and the ions penetrated quickly.The fiber and the resin matrix of GFRP bar were seriously damaged,the compactness of fiber arrangement was worse,the resin-fiber bond condition was deteriorated,many holes appeared on the surface of the bar,the micro-cracks and holesof concrete were gradually enlarged,the ion exchange rate was accelerated,and bond performance degradation was accelerated.(3)With the increase of corrosion time,the stiffness of ascending and descending stages tends to decrease,and with the increase of stress damage,the stiffness decreases.The stiffness of static state decreases more than that of dry-wet cycle,which is the same as that of macro and micro analysis.