| In this paper,a new type of cement-based fiber reinforced composite plates was prepared by using medium alkali glass fiber as reinforcing material and basic magnesium sulfate cement as matrix material.The effects of the molar ratio of cement matrix,the position of glass fiber,the glass fiber layers and mineral admixtures on the physical properties,mechanical properties and durability of basic magnesium sulfate cement-based composite plates were studied.At the same time,the erosion of glass fibers,the bond between cement matrix and glass fibers and the micro-morphology of hydration products were studied by means of SEM.The results show that the location and number of layers of fibers have a greater impact on the toughness and bending strength of the composite plates,but have a smaller impact on the bulk density and moisture content of the composite plates.With the increase of cement paste molar ratio,the toughness of composite plates does not change,but the volume density and bending strength will gradually increase.The bending strength of composite plates decreases with the addition of mineral admixtures,and the strength loss increases with the increase of mineral admixtures.With the increase of slag and fly ash content,the volume density and toughness of composite plates will gradually increase.At the same dosage,the effect of fly ash and slag on the volume density of composite plates is similar,but the effect of fly ash on the water content and water absorption of composite plates is stronger than that of slag,and the decline speed of bending strength is faster.When silica fume is added,the toughness of composite plates decreases with the increase of silica fume content.Through the frost resistance test,it is found that increasing the molar ratio and layers of glass fibers can effectively improve the frost resistance of composite plates.When the molar ratio of specimens is low and the number of layers is small,the damage is serious and the strength loss is large after the freeze-thaw cycle.Compared with the pure slurry specimens,the frost resistance of composite plates is improved obviously by adding mineral admixtures,and the strength loss after freeze-thaw cycles decreases correspondingly with the increase of the content ofmineral admixtures.However,the strength loss rate of specimens with 15% silica fume is higher than that of specimens with 10% silica fume,which shows that this rule is effective only in a certain range of silica fume content.It is found that the frost resistance of the specimens with fly ash is stronger than that of the specimens with slag.Through acid corrosion test,it is found that increasing molar ratio can improve the acid corrosion resistance of composite plates to a certain extent.In the early stage of the test,citric acid solution had a certain enhancement effect on the sample.After adding mineral admixtures,the acid corrosion resistance of composite plates was improved obviously.The strength loss of specimens with 5% silica fume was the lowest after 14 days of foaming acid,which was only 1.54%.Through hydrothermal test,it is found that the strength of the specimens with fibers laid on the bottom decreases greatly even in hydrothermal environment,but it is still larger than that of the specimens with fibers laid on the middle of the same age.The addition of slag or fly ash can effectively improve the hydrothermal resistance of composite plates.It is found that the strength of slag-doped specimens decreases rapidly in hydrothermal environment,while that of silica fume-doped specimens in the same period has better stability and strength.It was found by SEM that after freeze-thaw cycle,acidic environment and hydrothermal environment,the glass fibers in the specimens showed no signs of erosion.Mineral admixtures can effectively improve the bonding between cement matrix and glass fibre after composite plates experiences various environments,and also help to restrain the decomposition of 517 phase. |
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