Preparation And Performance Of Water Permeable Concrete With The Binder Of Modified Epoxy And Cement

Permeable concrete is one of the new multifunctional paving materials that can effectively reduce water accumulation on road and is beneficial for water infiltration into soil.However,the application of cement-based permeable concrete in road engineering is still limited by its low strength which results in defects such as poor durability,threshing and scaling-off of pavement.Permeable concrete with epoxy resin and cement as binder is widely used currently due to its advantages including high strength,toughness and fatigue strength as well as chemical corrosion resistance.However,epoxy resins are expensive and have high brittleness and poor crack propagation resistance.In this paper,woodtar,a byproduct of wood pyrolysis,is used to react with formaldehyde and trimethylenetetramine for modifying epoxy resin.Then the modified epoxy was mixed with cement to form binder together with coarse aggregates for preparing permeable concretes.The physical and mechanical properties and durability of concretes for pavement were measured.The reaction mechanism of woodtar-formaldehyde modified epoxy resin was revealed by Fourier infrared spectroscopy(FTIR),nuclear magnetic resonance(NMR)and scanning electron microscope(SEM)analyses.The effects of resin modification on the macro-performances of permeable concretes were evaluated.The main conclusions are drawn as follows.(1)By using trimethylenetetramine,woodtar and formaldehyde as raw materials,phenolic amine was synthesized via Mannich route.The chemical structure of the reaction products was analyzed by FTIR and NMR.The resulting phenolic amine can be used as epoxy resin modifier,and then the modified epoxy resin was further mixed with cement as a high performance binder for permeable concrete preparation.(2)Taking the modified epoxy resins with addition of 30 wt%woodtar as an example,the resulting permeable concrete with modified epoxy cementing material which accounts for 4 wt%of the total coarse aggregates weight has a 28d compressive strength of 16.2 MPa,which is significantly higher than that of unmodified epoxy resins with a compressive strength of 13.7 MPa;while the permeable concretes with 6and 8 wt%cementing materials have compressive strengths of 22.2 and 27.5 MPa,respectively,being slightly higher than those of pure epoxy binders which are 21.7and 25.8 MPa,respectively.The flexural strengths of the permeable concretes with modified epoxy cementing materials have similar trends in the compressive strengths.The concretes with modified epoxy binders of 4,6 and 8 wt%fractions have flexural strengths of 4.5,6.0 and 6.8 MPa,respectively,while those of pure epoxy resins are4.1,5.8 and 6.6 MPa,respectively.(3)Taking the permeable concrete with 6 wt%cementing materials of the coarse aggregates as an example,the concrete with modified epoxy resin has a 28d abrasion loss of 10.7 kg/m~2,and a 52.5%less than that of the pure epoxy resin.Both kinds of concretes have a freeze-thaw recycle of 16;and their porosities do not have significant difference.The modified epoxy concrete had a 94.5%retention rate of compressive strength and 88.1%retention rate of flexural strength,indicating a good resistance of aging.Results showed that the mechanical performance and durability of the concrete with modified epoxy resins were significantly improved.(4)The SEM images of the concretes fracture surface after flexural tests indicated that the interfacial layer between the aggregates and the binder was densified and strengthened,resulting in the improved compressive and flexural strengths of the concretes.The addition of cement into the epoxy resins is helpful for decreasing the porosity of the concretes and the sizes of internal pores as well as the proportion of large pores in the total pores.The internal structures of the concretes were more reasonable for improving the mechanical strengths and permeability.In conclusion,the reaction products of woodtar and formaldehyde can be used for modifying epoxy resins and applied in cementing materials for preparation of water permeable concretes.The modification of epoxy with woodtar-formaldehyde not only improves the mechanical properties and durability of the resulting concretes,but also makes full use of wood industries by-products and greatly reduces preparation cost of water permeable concrete,which is of prominent economical and ecological benefits.