| As the main material for modern infrastructure construction,cement-based materials have a very large amount of usage,and modern civil buildings as well as water conservation projects cannot dispense with the use of cement-based materials.However,the cement-based materials themselves also have some flaws,such as poor tensile strength,poor acid strength,susceptibility to cracking,and uncontrolled width of the crack after the crack has formed.This often occurs during use,especially in wet environments where the performance of cement based materials drops more significantly.Given the shortcomings of cement-based materials noted above,some steps need to be taken to improve the overall performance of cement-based materials.To prevent the failure process of cement based materials,the most effective solution is to add different lengths and fiber types within them to cope with the failure process at various levels and stages.The purpose of this paper is to investigate the relevant properties of cement-based composite materials with hybrid basalt and polypropylene fibers,and improves the interfacial performance between the hybrid fibres and the mortar with mineral admixtures(silica fume,diatomaceous earth,and mineral powder).In this study,the effects of fibre type,volume fraction and length on the mechanical properties,toughness and durability of cement-based composite materials were investigated under the condition of a constant cement-based material ratio.The purpose of this comparative study was to investigate the effects of single fibers and mixed fibers,as well as mineral admixtures,on the flowability,flexural strength,compressive strength,flexural compression ratio,shear bond strength and water uptake of composite materials based on cement.Optimal fiber length and dosing,and optimal dosing of mineral admixtures were obtained.(1)Basalt fibres can significantly enhance the mechanical properties of cement based materials,with an optimal fiber content of 0.2%-0.3% and an optimal fiber length of 12 mm.With a fibre content of 0.3% and a fibre length of 12 mm,for the mortar reinforced with basalt fibre alone,the flexural strength at 7 days and 28 days is8.7Mpa and 12.4Mpa respectively,which is 58.2% and 61% higher than the control group;At 7d and 28 d,the compressive strength was 30.4MPa and 41.7MPa,respectively,resulting in an increase of 29.4% and 32% relative to the control group;At 7d and 28 d,the compression ratio was 0.29 and 0.3,respectively,resulting in an increase of 26.1% and 25% relative to the control group;At 7d and 28 d,the shear bond strength was 6MPa and 7.9MPa,respectively,resulting in an increase of 36.4%and 29.5% compared to the control group.The water uptake of cement-based materials shows a tendency to first increase,then decrease,and then increase with increasing volume fraction.The performance of mixed basalt fiber modified cement-based materials is superior to that of single basalt fiber modified cement-based materials.When basalt fibres of different lengths are mixed together,the overall performance of the mortar is best when all four fibre lengths,6mm,9mm,12 mm and 18 mm,are also mixed together.For example,the 7-day flexural strength of mortar blended with four equal fiber lengths increased by a maximum of 32%compared to the experimental group of basalt fiber mortar with only one length,and flexion strength increased maximally by 23.5% at 28 days;The compressive strength of the 7d and 28 d mortar increased by 17.7% and 11.8%,respectively,compared to that of the single-fiber basalt mortar;For the basalt fibre mortar alone,the 7-day flexural compression ratio increased by a maximum of 23.1%,and the 28 day flexural compression ratio increased by a maximum of 11.1% compared to the basalt fibre mortar alone;The shear bond strength of the 7d and 28 d mortar increased by 25% and24.6%,respectively,compared to that of the single-fiber basalt mortar;Compared to the control group,the rate of water uptake in the 7d and 28 d groups decreased by4.7% and 8.6%,respectively.(2)Polypropylene fibres can significantly enhance the mechanical properties of cement based materials.The optimal volume fraction of polypropylene fibers is 1.0%-1.5%,and the optimal fiber length is 12 mm.With a fibre content of 0.3% and a fibre length of 12 mm,at 7d and 28 d,the flexural strength of the mortar reinforced with basalt fibre alone is increased by 60% and 42.3%,respectively,compared to that of the control group;Compared to the control group,the compressive strength of the 7d group and the 28 d group increased by 55.3% and 29%,respectively;The compression ratio of the 7d and 28 d groups increased by 24% compared to the control group;Compared to the control group,the shear bond strength of the 7d group and the 28 d group increased by 24.4% and 17.7%,respectively;There is a tendency for water uptake of cement-based materials to first increase,then decrease,and then increase with increasing volume content.When different lengths of polypropylene fibers are mixed,the mechanical properties of cement-based composite materials are improved when the four lengths of polypropylene fibers,6mm,9mm,12 mm,and 19 mm,are equally mixed,and the performance is better than that of single polypropylene fiber mortar.The flexural strength of the mortar mixed with four lengths of polypropylene fiber in equal amounts at 7 days and 28 days increased by 34.8% and 20.7%,respectively,compared to the mortar mixed with polypropylene fiber alone;The compressive strength of the 7d and 28 d mortar increased by 27.9% and 12.2%,respectively,compared to that of the single-fiber polypropylene mortar;Compared to the single polypropylene fiber mortar,the compressive bending ratio of the 7d and28 d mortar was increased by 20.8% and 11.5%,respectively;Compared to the single polypropylene fiber mortar,the shear bond strength of the 7d mortar and the 28 d mortar increased by 19.7% and 14.9%,respectively;Compared to the control group,the rate of water uptake in the 7d and 28 d groups decreased by 11% and 15.4%,respectively.(3)On the basis of the optimal comprehensive performance of the mortar when four lengths of basalt fibers,6mm,9mm,12 mm,and 18 mm,and four lengths of polypropylene fibers,6mm,9mm,12 mm,and 19 mm,were mixed in equal quantities.To further investigate the impact of simultaneously mixed basalt and polypropylene fibres on the performance of cement-based composite materials,four mixing methods of equal length were chosen.Compared to mortar mixed with a single fibre,the mechanical properties,toughness and durability of cement based composite materials mixed with basalt fibre and polypropylene fibre have been improved to some extent.The optimum mixing ratio when mixed with equal amounts of fibres of different lengths is for the volume content of the basalt fibre and polypropylene fibre to be0.3% and 1.0%,respectively.At this stage,the flexural strength of the cement-based composites at 7d and 28 d increased by 21.3% and 30.6%,respectively,compared to that of the mixed-fiber mortar;Compared to the mixed fiber mortar,the compressive strength of the 7d mortar and the 28 d mortar increased by 6.7% and 1.4%,respectively;Compared to the mixed fibre mortar,the 7d and 28 d flexural compression ratio increased by 3.1% and 10% respectively;Compared to the mixed fiber mortar,the shear bond strength of the 7d mortar and the 28 d mortar increased by35.3% and 20.5%,respectively;Compared to the simple addition of basalt fibre and polypropylene fibre,the water absorption of 7d and 28 d was increased by 12.1% and10.9%,respectively.Microscopic analysis of SEM morphology shows that both basaltic and polypropylene fibres can effectively suppress the formation and expansion of small cracks in the cement matrix,resulting in significant improvements in the various properties of cement-based materials.(4)By using equal amounts of fibres of different lengths and by mixing 0.3%basalt fibres and 1.0% polypropylene fibres simultaneously,as the mineral admixtures(silica fume,diatomaceous earth,mineral powder)are increased,the flexural strength,compressive strength,and shear bond strength of the fiber mortar exhibit a tendency to first increase and then to decrease,but the bending compression ratio enhancement effect is not significant.The optimum silica fume dosage is 8%,the optimum diatomaceous earth dosage is 6%,and the optimum mineral powder dosage is 10%.By applying the volcanic ash effect and the micro aggregate fill effect,effectively improving the performance of the interface between the fibres and the mortar,leading to a tighter packing of the fibres and mortar,thus improving the fibre-to-mortar bonding strength and overall mortar performance. |
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