UHPC-XPS Insulation Composite Board Reinforced By Glass Fiber Mesh: Design,Preparation,and Properties

To significantly reduce heat loss of buildings,sandwich thermal insulation composite board(TICB)has been widely used in building enclosure structures,due to relatively higher strength and low thermal conductivity.For inorganic thermal insulation materials,such as foamed concrete and aerated concrete,have high strength and desirable fire resistance,but also present disadvantages,such as high thermal conductivity and high density.The thermal insulation properties can be improved by increasing the thickness of the thermal insulation material,which leads significant increase in the total thickness,weight and cost of the TICB.In contrast,organic thermal insulation materials,such as extruded foamed polystyrene(XPS),have higher thermal resistance and superior thermal insulation.Advantages of low strength,poor weather resistance and flammability of organic thermal insulation materials can be solved through structure design of sandwich and multi-layer composite,which is regarded as the future development of TICB.Due to poor wettability of XPS and the volume shrinkage of cement-based materials,the interfacial bonding between XPS(core layer)and cement-based materials(protection layer)is relatively low,and consequently results in cracking,hollow and fall off of TICB.At present,the interfacial bonding was usually improved by increasing interfacial roughness,setting connectors and adding steel wire mesh,which results in local stress concentration and thermal bridge and then higher thermal conductivity and density.Additionally,the temperature and stress distributions of TICB during heat transmission and loading have not been clarified yet.In this study,XPS and ultra-high performance concrete(UHPC)were used as the thermal insulation layer and the bearing layer,respectively.Interfacial agents were used to improve the surface wettability of XPS,and polymer modified adhesive mortar was designed to improve the interfacial bonding between XPS and UHPC.Moreover,the glass fiber mesh was also introduced to unify the stress distribution.Finally,a lightweight TICB with ultra-high strength,lower thermal conductivity and strong interfacial bonding was prepared.The dynamic temperature and stress distributions of TICB were expounded based on the finite element simulation,which laid a theoretical and technical support for further structure design and properties optimization.The research significant are described in details as following:The effects of polymer modified adhesive mortar and interfacial modification of XPS on the interfacial bonding of XPS-adhesive mortar were studied.The tensile adhesive strength of XPS-adhesive mortar increased with the addition of redispersible latex powder(EVA).Such as,the tensile adhesive strength increased by 35.0%when the addition of EVA was 5%,no significant improve was observed when the content of EVA was higher than 5%.The reason may lies in that the water contact angle of XPS surface modified by styrene-acrylic emulsion(SA)reduced from 118.3°to 66.2°(from hydrophobic to hydrophilic),then the tensile adhesive strength of XPS-adhesive mortar was higher than the tensile strength of XPS,indicating the fractures can only occurred in XPS layer.Thermal insulation contribution efficiency(α)and thermal insulation proportion(ω)of XPS were conceptionized,to quantify the effectiveness of XPS during steady-state heat transmission.Then relationships between thickness,αandωof XPS and heat transfer coefficient(K)of TICB were established.With the increase of XPS thickness from 1mm to40mm,The K value decreased by 90.5%and theωincreased by 79.1%,however theαdecreased from 6.1°C/mm to 0.8°C/mm.There is no significant change in theα,ωand K with further increase of thickness of XPS,indicating the thermal insulation contribution decreased dramatically with the increase of XPS thickness.As the bearing load can be dispersed by glass fiber mesh,The load bearing area of XPS-mortar board with glass fiber mesh was 2.8 times as that of XPS-mortar board,which leading to 100%increase in maximum bearing stress and 400%increase in bending strength.After adding PVA or stell fiber into UHPC,The TICB changed from brittle material to strain hardening material.Meanwhile,the bending strength increased by 68.1%to 160.2%,the bending toughness index increased by 13.0 to 39.0 times,and the area of impact pit was also significantly reduced.Multilayer lamination on the heat transmission,bending resistance and impact resistance of the TICBs were investigated.The heat transfer coefficient of the TICB depended on the total thickness of XPS,presenting that XPS layers played the role of thermal insulation in series.Secondary strain hardening of TICB with multilayer lamination were observed,which can be contributed to the multi-directional cracking of UHPC layers at mid-span zone.As a result,the bending toughness index increased by 2.3～2.4 times,and the bending residual toughness index increased by 1.50～1.65 N·mm."absorption energy of elastic deformation(E_a)"and"energy absorption of crack propagation(k)"were proposed to quantify the impact resistance of TICBs before and after cracking respectively.The E_a increased by 7.9 times and the k decreased by24.5%when two UHPC layers divided into 4 layers for the same total thickness.The TICBs with strong interfacial bonding,low thermal conductivity,high bending resistance and impact resistance were prepared using XPS and UHPC in this study,which also present simplified preparation procedure,materials efficiency and rapid easy installment.Therefore,the present research lays a theoretical foundation and technical support for building industrialization,prefabricated buildings,and building energy saving.