The Research For The Multilayer Type Of Controlling Permeable Formwork Liner Based On PP Needle Felt

In this paper, polypropylene needle felt laminated with spun-bond and melt-blownnonwovens respectively, obtained certain permeability of permeable formwork cloth bycontrolling the hot-pressing temperature、time and pressure of the plate vulcanizing machine.Using the hot-pressing surface as the filter layer, bearing surface as the permeable layer,discussed the influence of various hot-pressing factors on the permeability, and madecorresponding analysis and comparison on the change of the thickness, tensile, air permeabilityand so on.Getting certain performance of nonwovens by setting hot-pressing time, temperature andpressure according to orthogonal test table with hydraulic conductivity as a test index. Throughrange analysis and variance analysis, we can infer that three hot-pressing factors have significanteffect on the formwork cloth, water diversion can achieve the best when the hot-pressingconditions of needling, spun-bonded/needling and melt-blown/needling permeable formworkliner was made under170℃/6s/1.5MPa,171℃/4s/1.5MPa and171℃/6s/1.5MParespectively.The best hot pressing time and pressure which were obtained through orthogonal test wereused as hot-pressing conditions in the single factor experiment. The effect on the formwork linerwas observed by changing hot-pressing temperature. Thickness of the formwork cloth decreasedwith the increase of hot-pressing temperature. The vertical and horizontal strength and strippingstrength increased, but the aperture became smaller, water retention and permeability becameworse; Hydraulic conductivity increased, but when the needled felt was adhered by surface layeror melt itself, the conductivity performance became poor. It may also produce certain effect onthe formwork cloth with the change of the weight of spun-bonded/needling andmelt-blown/needling, under the same hot-pressing condition, drainage capacity decreased withthe rise of the weight of spun-bonded/needling and melt-blown/needling, but water retentionperformance enhanced. Integrated three kinds of controlled permeable formwork liner, althoughmelt-blown/needling type permeable formwork liner has the best performance of drainage and water retention, and it has good filtering quality because of the small aperture, its poorpermeability is not suitable for the application of permeable formwork liner; Drainage and waterretention performance of spun-bonded/needling type was similar to needling type formworkliner, but the aperture was less than needling permeable formwork liner greatly, and30g/㎡，50g/㎡，70g/㎡spun-bonded/needling type permeable formwork liner also has good permeabilitywhen the hot-pressing temperature was under180℃, thus spun-bonded/needling type permeableformwork liner will play an important role to our country in the development of controllingpermeable formwork liner.Results showed that spun-bonded/needle type permeable formwork liner achieved the bestperformance when the weight of the spun-bonded layer was50g/㎡, hot-pressing temperature,time and pressure was175℃,4s and1.5MPa respectively, it could reduce the permeableformwork liner aperture greatly, reducing the loss of mineral fine admixture effectively duringthe casting process, which can make up the existing defects of traditional controlling formworkliner, bring the dawn for the development of high performance concrete. Because of the smallaperture and poor permeability, melt-blown/needling type controlling permeable formwork lineris not suitable to the gas-solid separation fields.