Preparation And Properties Of Soybean Oil-Based Polyurethane/Epoxy Resin Grouting Material

Compared to the compressive strength,the tensile strength of concrete is relatively low,resulting in its susceptibility to cracking under the combined action of external environmental factors such as erosion,external forces,temperature changes,and internal factors including self-cracking and shrinkage.The development of cracks will damage the appearance and reduce the durability and overall stiffness of the concrete,resulting in a decrease in their load-bearing capacity and service duration.Therefore,effective maintenance and repair are necessary to ensure the safety and durability of concrete structures.Polymer grouting materials are currently one of the most commonly used repairing materials for concrete structures.In particular,epoxy resin has the advantages of high strength,strong adhesion to concrete matrix,good chemical stability,and being curable rapidly at room temperature.However,the epoxy resins also have the disadvantages of brittleness and toughness after curing,and are high-cost compared with other polymer-based grouting materials.In this study,a bio-based polyurethane was synthesized using acrylated epoxidized soybean oil（AESO）as a polyol feedstock,and then used to toughen epoxy resin for preparing a polyurethane/epoxy interpenetrating polymer network（IPN）grouting material.Firstly,AESO and isophorone diisocyanate（IPDI）were used to synthesize polyurethane（PU）precursor.The PU precursor obtained was further blended with epoxy resin with different proportions to form interpenetrating crosslinked network structures,and finally a novel grouting material was obtained as waterproofing,plugging,and reinforcing for concrete structures.The AESO molecule has a long chain structure of fatty acids,and this endows the polyurethane prepared from AESO with flexible chain segments,being beneficial to improve the toughness of the polyurethane.In addition,AESO contains three active hydroxyl groups and one epoxy group,which are easy to react with isocyanate groups to form polyurethane precursor.Their epoxy groups can also participate in the crosslinking of epoxy resin and polyurethane precursor,and thus improve the degree of crosslinking and the performance of the cured grouting materials.The chemical structure,curing mechanism,mechanical properties,thermal properties,rheological properties,and interfacial adhesion properties of the prepared grouting materials were investigated comprehensively.The main research contents and conclusions are drawn as follows.（1）PU precursors were successfully synthesized from AESO and IPDI,and then reacted with epoxy resin to form an interpenetrating polymer network.The results of Fourier transform infrared spectroscopy（FTIR）and nuclear magnetic resonance（NMR）analyses confirmed the reactions among the AESO,IPDI,and epoxy resin.（2）PU/epoxy IPNs were synthesized using polyurethane precursor and epoxy resin as raw materials.A polyurethane/epoxy resin grouting material was prepared by mixing them,along with a curing agent,i.e.,diethylenetriamine,and glycerol.The effect of PU content on the mechanical properties,thermal properties,and rheological properties of the grouting materials were investigated.The results showed that the mechanical properties of PU/epoxy grouting material increased with the increasing PU content when it is less than 20%,and then decreased with a content of more than 20%.With a polyurethane content of 20%,the static mechanical properties,thermal mechanical energy,and thermal stability of polyurethane/epoxy resin grouting material had a highest tensile strength of 35.9 MPa,a flexural strength of 47.5 MPa,a flexural modulus of 1238 MPa,a crosslinking density of 2287 mol/m³,and a glass transition temperature（T_g）of 66.8℃.And the grouting material had a storage modulus（E′）of 1873 MPa at room temperature and a maximum thermal decomposition temperature(T_max)of 395℃.（3）The Brazilian disc concrete specimens and convex column concrete specimens were adopted for evaluating the interfacial adhesion between the grouting materials and concrete matrix.The interfacial bonding performance of PU/epoxy grouting material to concrete were evaluated through the splitting tensile tests and the pushout shear tests.The effects of the grouting material strength,the concrete matrices strength,and the thickness of grouting adhesive layer on the interfacial bonding strength were investigated.The results showed that polyurethane/epoxy resin grouting materials can effectively bond with concrete matrix.The interfacial bonding strength increased with increasing the PU contents with a PU content less than 20%,and then decreased with a PU content of more than 20%.With a polyurethane content of 20%,the grouting material has the highest interfacial tensile bonding strength of 4.56 MPa and a maximum interfacial shear bonding strength of 21.73 MPa.The strength of concrete matrix influenced the strength of the grouting materials;compared with the matrix of C40,the interfacial tensile bond strength of the grouting material increases by 40%with a concrete matrix of C120,and its interfacial shear bond strength increases by 21%.The interfacial tensile bonding strength decreases with the increase of the thickness of the grouting material adhesive layer,and the interfacial tensile bonding strength of the adhesive layer with a thickness of 1mm reduced by 11%,compared to the adhesive layer with a thickness of 0.5mm.The prepared grouting materials had both the advantages of high strength and toughness,being cured rapidly at room temperature,and high bonding strength with concrete matrix.In addition,it was prepared using biobased feedstocks,and could be applied widely as a low carbon-emissions material in the maintenance and repairing for buildings and structures.