Effect Of Admixture On GRC Durability Under Different Aging Conditions

Glass Fiber Reinforced Cement(GRC)is a high-performance cement-based composite material.It is based on cement mortar or paste and incorporates high modulus of elasticity glass fiber.As a new type of composite material,because of its many excellent properties,it has been widely concerned and developed by the material industry since its advent.At present,it has been widely used in civil,municipal,water conservancy,horticulture,fisheries,agriculture,military and other fields.However,due to the poor long-term performance of GRC in actual engineering,it can not be used in load-bearing components,which greatly limits the promotion and development of GRC materials.For many years,scholars at home and abroad have been working on the mechanism of long-term performance degradation of GRC and its durability improvement measures.Although technical measures such as the use of low alkalinity cement,the improvement of the alkali resistance of glass fiber,and the incorporation of admixture to inhibit the corrosion of glass fiber are summarized,these methods are not particularly perfect,and there are still some minor problems.In this paper,the effects of admixtures in different aging environments on the durability of GRC were further studied.The main research contents of this paper are as follows:(1)The effect of admixtures such as fly ash,slag,silica fume and metakaolin on the durability of GRC under natural curing conditions.The GRC specimens mixed with four admixtures were placed in a natural environment for curing 28 d,180d and 360 d,and their strength properties and microscopic morphology of the glass fibers were tested;(2)The SIC accelerated aging method was used to simulate the long-term durability of GRC specimens,and the inhibitory effect of fly ash,slag,silica fume and metakaolin on the corrosion of glass fibers in this environment was studied.The test was carried out by accelerated aging under hot water at 80 °C.The performance changes of different GRC curing time,the effect of different admixture types on the durability of GRC and the effect of different content of admixture on the durability of GRC were studied.In addition,in order to study the corrosion condition of glass fiber in chemical medium,an experiment of soaking glass fiber in alkaline solution was also carried out;(3)Study the effect of autoclaved curing on GRC performance.Each group of GRC specimens was autoclaved and cured at a curing temperature of 190 ° C and a pressure of 1.30 MPa in the autoclave.The effects of fly ash,slag,silica fume,metakaolin and their complex addition on the mechanical properties of GRC under autoclaved curing conditions and the changes of glass fiber morphology under autoclaved curing were studied.Natural maintenance test results show that the change in GRC strength is a combination of cement matrix strength change and glass fiber corrosion.Within 360 days,the flexural strength of each group of GRC increased with the increase of curing time,and higher than that of the same age-free glass fiber cement mortar test piece.The strength of the glass fiber is reduced by the corrosion of the internal glass fiber,but the strength of the GRC remains strong as the strength increase due to cement hydration dominates during this period of time.The 80 ? hot water accelerated aging test results show that the use of fly ash,slag,silica fume,metakaolin and other admixtures is effective for improving the durability of GRC based on ordinary Portland cement.Among them,the test group of fly ash and slag GRC showed good effect of inhibiting glass fiber corrosion in both natural curing and 80 ?hot water accelerated curing environment.In the 80 ?hot water accelerated test,the flexural strength of the standard GRC(CF1)without admixture decreased significantly after 6d,the strength decreased by 1.50 MPa,the decrease was 15.34%,and the blended with 40% fly ash The intensity of GRC(CF2)increased significantly from 0 to 2d,and the intensity increased by 1.20 MPa,which was 16.44%.After 4d,the growth tends to be stable,but the strength is still growing.The 40% slag GRC(CF3)also maintained growth during the curing period,and there was no decrease in strength.Combined with the microscopic topography of glass fibers of various ages,the corrosion degree of the reference GRC without admixture is obviously more serious than that of fly ash GRC and slag GRC when accelerated by aging at 80 ? for 6 days.The sorghum glass fiber and the ordinary soda lime silicate glass fiber have different corrosion damage forms,and the corrosion damage form of the sorghum glass fiber is characterized by corrosion peeling from the outside to the inner layer,and the alkali glass of the ordinary soda lime silicate.The form of corrosion damage of the fiber is characterized by tiny corrosion holes in the surface layer.As the corrosion deepens,the hole gradually expands and becomes deeper,forming a larger corrosion pit.The results of autoclaved curing test showed that under autoclaving conditions,The admixture under autoclaved conditions has been unable to inhibit the corrosion of glass fibers in the GRC.Through SEM microscopic observation,the glass fiber is very corroded regardless of whether or not the admixture is incorporated.In combination with the analysis of the bending stress-deflection curve,the glass fiber has completely lost the toughening effect.