Structural panel with shoulders, and method of production

Abstract

A structural panel (10) and method (300) are provided. The structural panel (10) comprises a structural body (100) formed from cementitious material, and an insulation body (138) formed from thermal i

Description

5 Embodiments of the present invention relate to a structural panel with shoulders and a method of production. In particular, but not exclusively, they relate to a precast concrete structural panel with shoulders and insulation, and a method of its production. 10 BACKGROUND TO THE INVENTION In construction, precast concrete structural panels are desirable because they are manufactured off-site and provide a high degree of strength. Thermal insulation is also desirable for energy efficiency. Traditionally, thermal insulation is added by contractors on-site. BRIEF DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION According to various, but not necessarily all, embodiments of the invention 20 there is provided a structural panel comprising a structural body formed from cementitious material, and an insulation body formed from thermal insulation material, wherein the structural body has a cross-section shape defining a laterally-extending front member and rearwardly-extending webs connected to a rear of the front member, wherein a rear face of the front member and inner 25 side faces of the webs define a rear cavity of the structural panel in which the insulation body is located to thermally insulate the structural panel, wherein each web comprises a laterally-protruding shoulder at the end of the inner side face, wherein the shoulders face each other, wherein a lateral separation between the shoulders defines a gap behind the rear cavity, wherein at least 30 part of the gap is narrower than a corresponding lateral width of the insulation body, and wherein the gap is an air gap or is filled with a further, second insulation body. The shoulders provide the advantage of forming undercuts to clamp the insulation body in the rear cavity, to prevent the insulation body from peeling out of the rear of the structural panel. Further, during manufacture, a backing 5 pad can be placed in the gap between the shoulders to seal in the insulation body. The backing pad is then removed after the cementitious material has set and before site delivery. A further advantage of the shoulders is an improved second moment of area of 10 the structural body since the shoulders are formed from the cementitious material. This enables material to be moved from the webs to the shoulders at the design phase, with additional material efficiency. A further advantage of the shoulders is the provision of a larger rear area on 15 which to mount a window frame if required. A further advantage of the shoulders is that the shoulders provide a large surface area to pour the cementitious material. 20 Optionally, one or each of the shoulders has a tapered width in cross-section such that a lateral separation between the shoulders increases rearwardly. Optionally, one or each of the shoulders comprises a chamfered face defining the taper. Optionally, the chamfered faces face each other across the gap. Optionally, the above-mentioned backing pad seats against the chamfered 25 faces. An advantage of the chamfered faces is making the backing pad easier to pull out. Optionally, an angle of the taper is selected from the range 2 to 85 degrees. Optionally, the angle is selected from the sub-range 5 to 45 degrees. Optionally, 30 the angle is approximately 15 degrees. An advantage of this angle or range of angles is that the backing pad can be removed easily and without destroying mould components, increasing the longevity of the mould components, and providing an efficient use of material for achieving a large clamping surface to clamp in the insulation body. Optionally, a minimum width of the gap is defined between front edges of the 5 shoulders, wherein the minimum width is less than the lateral width of the insulation body. Optionally, a maximum width of the gap is defined between rear edges of the shoulders. Optionally, the maximum width of the gap is equal to or less than the lateral width of the insulation body. 10 Optionally, the rear face of the front member, the inner side faces of the webs, and lip faces of the shoulders define boundaries of the rear cavity. Optionally, the boundaries are rectilinear. The lip faces of the shoulders refer to the undercut faces of the shoulders that trap the insulation body in the rear cavity. 15 Optionally, the structural body comprises two of the webs, the first web connected to a first end of the front member, the second web connected to a second end of the front member opposite the first end, and the rear cavity and insulation body extending continuously between the first and second webs. 20 Alternatively, optionally, the structural body comprises three or more of the webs, the first web connected to a first end of the front member, the second web connected to a second end of the front member opposite the first end, and the third web connected to the front member between the first and second webs, wherein the three webs define two insulation cavities therebetween, each 25 comprising one insulation body. An advantage is further improvement of the second moment of area against demoulding loads, and in-service wind loads. Optionally, the third web is located between the first and second webs. 30 Optionally, the third web comprises a pair of the shoulders, one facing the shoulder of the first web, and the other facing the shoulder of the second web. The gap between the shoulders can be optionally filled with a further, second insulation body. The rear cavity may be a primary cavity comprising the larger (first) insulation body, and the gap between the shoulders may be a smaller secondary cavity comprising the smaller second insulation body. An advantage is that thermal performance is improved because the gap between the shoulders after removal of the backing pad is filled with further insulation. Optionally, the second insulation body is secured to the insulation body. Optionally, the second insulation body is secured to the insulation body by one or more insulation pins or pigtail screws. Optionally, this is performed on-site 10 15 30 Alternatively, the gap between the shoulders may comprise an air gap layer. The air gap layer may be a closed air cavity. Optionally, a second insulation body is mounted to a rear surface of the structural body, behind the shoulders, the air gap layer being defined between the rear face of the front member and the second insulation body. This advantageously assists with acoustic insulation when a closed air gap is provided between two layers. Optionally, rear surfaces of the structural body and of the second insulation body are flush with each other. Optionally, the structural body is formed from fibre reinforced concrete. Optionally, the fibre reinforced concrete is metal fibre or glass fibre or organic (e.g., plastic) fibre reinforced concrete. Optionally, the metal fibres are steel fibres. Optionally, the fibres define a maximum aggregate size of the concrete, in other words the mixture is free from gravel or similar aggregates. Optionally, the fibres are the primary or only tensile reinforcement within the concrete. Optionally, the fibre reinforced concrete is ultra-high performance fibre reinforced concrete. Optionally, the insulation body is formed from mineral wool, or expanded material. Optionally, the structural panel is a precast concrete structural panel. Optionally, the minimum lateral separation between the shoulders is at least 40% or at least 70% or at least 90% of the lateral width of the insulation body. 5 In other words, this defines the minimum width of the gap between the shoulders, the gap being very large in comparison with the span of the shoulders. Optionally, the minimum lateral separation between the shoulders is less than 99% of the lateral width of the insulation body. An advantage is that the shoulders are long enough to trap the insulation body in the rear cavity, but 10 not long enough to substantially affect the weight of the structural panel. Optionally, the shoulders each define a flange thickness less than 120mm or less than or equal to 70mm. Optionally, the structural body is formed from fibre reinforced concrete and the shoulders formed from the fibre reinforced concrete 15 have a thickness less than or equal to 55mm or less than or equal to 50mm. This is thinner than what would be achievable without UHPFRC. Optionally, the shoulders formed from the fibre reinforced concrete have a thickness greater than 25mm or greater than 45mm. 20 Optionally, a thickness ‘a’ of the structural body relative to the centre-to-centre lateral separation ‘b’ of neighbouring webs defines a ratio a:b selected from the range 1:1.5 to 1:5. Optionally, the structural body comprises a U-shaped cross-section profile, 25 defined by the front member and webs. Optionally, each web is thicker than the front member and shoulders. An advantage is an improved second moment of area against demoulding loads, and in-service wind loads. Alternatively, the webs may be thinner than the front 30 member and shoulders. Optionally, the structural body comprises a hanging point to enable the structural panel to be hung from at least part of a structural frame. Optionally, the structural body comprises a window opening. 5 According to various, but not necessarily all, embodiments of the invention there is provided a method of forming the structural panel, the method comprising: pouring the cementitious material into a formwork to form the structural 10 body, wherein the insulation body is part of the formwork to form the rear cavity; and separating from the formwork the structural panel including the structural body and the insulation body, once the cementitious material has set. 15 Note that the cementitious material may not be entirely set and may continue to gain strength after this point. Optionally, the formwork comprises an outer formwork, and an inner formwork positioned to a rear face of the front member, and wherein the inner formwork comprises the insulation body. An advantage is that the insulation body provides a permanent formwork for the moulding, that does not need to be demoulded from a coffer. 25 Optionally, the inner formwork comprises the insulation body and a backing pad. Optionally, the insulation body is located to form the rear cavity, and wherein at least a front of the backing pad is narrower than the insulation body and is 30 located to form the shape of a facing pair of the shoulders and fills the gap between the facing pair of shoulders. Optionally, the method comprises: pouring a first portion of the cementitious material into an outer formwork to form the front member; positioning the inner formwork to the rear face of the front member 5 before the front member has set; and pouring a second portion of the cementitious material into a space between the outer form work and inner form work, before the front member has set, to form the webs including the shoulders. 10 Alternatively, the inner formwork may be added before the first portion is poured. Alternatively, a single portion of the cementitious material, poured in a single pour, forms the front member, webs, and shoulders. 15 Optionally, the backing pad comprises one or more tapered edge faces to define the tapering of the shoulder or shoulders. Optionally, the method comprises removing the backing pad from the insulation body after the second portion of cementitious material has been poured. Optionally, the backing pad is formed from a timber product. Optionally, the insulation body is secured to the backing pad. Optionally, the insulation body is secured to the backing pad by pigtail screws, insulation pins, or clamped pads. Optionally, separating the structural panel from the formwork comprises removing the pigtail screws, insulation pins, or clamped pads and then removing the backing pad from the insulation body. 30 Optionally, the method further comprises adding a second insulation body to the gap between the shoulders, where the backing pad was previously located. This may be done in the factory or on-site. Alternatively, the backing pad is in the form of an insulation body, and is left in place after the second insulation body has set. According to various, but not necessarily all, embodiments of the invention 5 there is provided a structural panel comprising a structural body formed from cementitious material, and an insulation body formed from thermal insulation material, wherein the structural body has a cross-section shape defining a laterally-extending front member and a rearwardly-extending web connected to a rear of the front member, wherein a rear face of the front member and a side 10 face of the web define at least part of a rear cavity of the structural panel in which the insulation body is located to thermally insulate the structural panel, wherein the web comprises a laterally-protruding shoulder at the end of the side face to retain an edge of the insulation body, and wherein the shoulder has a tapered width in cross-section. 15 BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of various examples of embodiments of the present invention reference will now be made by way of example only to the 20 accompanying drawings in which: FIG. 1 illustrates a cross-section view of a first example structural panel; FIG. 2 illustrates a cross-section view of a second example structural panel; FIG. 3 illustrates an example method of manufacture; FIG. 4 illustrates a rear elevation of a structural panel with hanging points; 25 FIG. 5 illustrates a front elevation of a structural panel with window openings; FIG. 6 illustrates a cross-section view of an example window frame secured to a structural panel; and FIG. 7 illustrates a cross-section view of a third example structural panel. 30 DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION FIG. 1 illustrates a cross-section view of a first example of a precast concrete structural panel 10. The lateral axis (width) extends from left to right on the page, the front-rear axis extends up and down on the page, and height extends in and out of the page. The structural panel 10 comprises a U-shaped structural body 100 formed from cementitious material, which is in this case ultra-high performance fibre reinforced concrete (UHPFRC). UHPFRC has a compressive strength exceeding 150 megapascals tested under BS EN 12390-3 conditions. The fibre 10 reinforcement can comprise steel fibres or glass fibres, for example. The cementitious material may be free from stone-based aggregates and steel reinforcing bar, due to the high compressive and tensile strength achieved by the mix design and particle packing. 15 The structural body 100 comprises a laterally-extending front member 102, and a pair of rearwardly-extending webs 104 integrally connected to the rear of the front member 102 to define a U-shaped profile. The front member 102 has a laterally extending front face 106, a parallel 20 laterally extending rear face 108, and opposite first and second lateral ends 126, 128 wherein the webs 104 are located at the ends 126, 128. The webs 104 are each connected to the opposite ends of the rear face 108 of the front member 102. 25 Each web 104 has a rearwardly extending outer side face 123, a parallel rearwardly extending inner side face 122, connected to a laterally extending rear surface 132 of the structural body 100. The rear surface 132 connects the outer and inner side faces 123, 122. 30 The outer side face 123 of each web 104 connects the front face 106 of the front member 102 to a rear surface 132 of the structural body 100. The inner side face 122 of each web 104 connects the rear surface 108 of the front member 102 to a shoulder 112 that protrudes laterally from the rear end of the web 104 to provide a small undercut connected to the inner side face 122 of the web 104. Optionally, facing building members (not shown), such as bricks, tiles or shaped stones, can be secured to or partially embedded in the front face 106 of the front member 102 to provide an architectural fagade. 10 Further, the facing building members could extend around the front corners of the front face 106 and along the outer side faces 123 of the webs 104. The structural body 100 may therefore be concealed when viewed from an exterior side. 15 A shoulder 112 is provided at the rear end of each web 104, and is located to the inner side of the web 104. The shoulders 112 on the opposite webs 104 face each other and extend towards each other, but do not connect to each other, leaving a gap 114 therebetween. Each shoulder 112 has a short span, so that the width of the gap 114 is multiple times longer than the combined 20 spans of the shoulders 112 in the lateral direction. Each shoulder 112 extends in a direction generally parallel to the front member 102. The detail view of FIG. 1 shows that the shoulder 112 is connected to the inner side face 122 of the web 104. The shoulder 112 has a short laterally extending 25 lip face 124 which forms an undercut. The lip face 124 extends generally parallel to the faces of the front member 102. The lip face 124 of the shoulder 112 is connected at a front edge 118 of the shoulder 112 to a rearwardly-extending chamfered face 116 of the shoulder 30 112, that extends diagonally. The chamfered face 116 of the shoulder 112 is connected at a rear edge 120 of the shoulder 112 to a rear surface of the structural body 100. The rear edge 120 of the shoulder 112 connects the chamfered face 116 of the shoulder 112 to a rear surface 132 of the structural body 100 (FIG. 1). The shoulder 112 is at least partially flange-shaped. If the shoulder 112 has a longer span, as shown in FIG. 2, a portion of the rear 5 surface 132 is cantilevered laterally beyond the plane of the inner side face 122 of the web 104, towards an opposite web 104, to define a rear surface of a shoulder 112. Therefore, the cantilevered portion of the rear surface 132 together with the lip face 124 of the shoulder 112 define a flange-shaped shoulder 112. 10 Although FIGS. 1-2 show the shoulders 112 being connected to the rear surfaces 132 at the webs 104 of the structural body 100, in another embodiment the webs 104 continue past the shoulders 112 and extend rearwardly beyond the rear edges 120 of the shoulders 112. 15 A rear cavity 110 of the structural panel 10 is defined by the rear face 108 of the front member 102, the inner side face 122 of each web 104, and the lip face 124 of each shoulder 112. These faces are the boundaries of the rear cavity 110. 20 In FIG. 1, the rear cavity 110 extends continuously from the web 104 at the first lateral end 126 of the front member 102 to the web 104 at the second lateral end 128 of the front member 102. 25 The rear cavity 110 is filled with an insulation body 138. The insulation body 138 is formed from mineral wool, or an expanded material such as expanded polystyrene, or another suitable thermal insulation material. If the insulation body 138 is of sheet form, it would be appreciated that the insulation body 138 can be formed from either a single sheet or multiple layered sheets of insulation. 30 The insulation body 138 is trapped within the rear cavity 110 by the lip faces 124 of the shoulders 112, to resist translation of the insulation body 138 in a rearward direction. While it may be possible to forcibly pull out some types of insulation due to their compressibility, the shoulders 112 ensure that the insulation body 138 does not gradually peel out of the opening defined between the webs 104, during storage or transportation. The Figures illustrate that the rear cavity 110 may be rectilinear in shape, and the insulation body 138 may comprise a rectangular shape in contact with the rectilinear faces 108, 122, 124 defining the rear cavity 110. 10 The external perimeter of the illustrated structural body 100 is defined by at least the front face 106 of the front member 102, the outer side face 123 of each web 104, and the rear surfaces 132 of the structural body 100 at each web 104. The envelope defined by the external perimeter may be rectilinear, such as rectangular. 15 When multiple structural panels 10 are installed side-by-side, the outer side face 123 of each web 104 may face the outer side face 123 of a corresponding web 104 of an adjacent structural panel 10. 20 The geometry of the shoulders 112 is now described in more detail. The chamfered face 116 of the shoulder 112 is chamfered so that part of the formwork in contact with the chamfered face 116 is easy to remove after concrete pouring. This process is described later in relation to FIG. 3. The 25 illustrated taper angle of the chamfered face 116 is 15 degrees. In other examples, the angle is selected from the range 2 to 85 degrees or 5 to 45 degrees. The illustrated chamfered face 116 of the shoulder 112 is a straight edge. 30 As described earlier, each shoulder 112 comprises a front edge 118 where the lip face 124 of the shoulder 112 meets the chamfered face 116 of the shoulder 112, and a rear edge 120 where the chamfered face 116 of the shoulder 112 meets the rear surface 132. Due to the tapering effect of the chamfer, the lateral separation between the 5 front edges 118 of the opposite shoulders 112 is less than the lateral separation between the rear edges 120 of the shoulders 112. The lateral separation between the front edges 118 of the shoulders 112 defines the minimum width of the gap 114 between the shoulders 112, and the 10 lateral separation between the rear edges 120 of the shoulders 112 defines the maximum width of the gap 114. The width of the insulation body 138 in the lateral direction is less than the lateral separation between the front edges 118 of the shoulders 112. If the 15 shoulders 112 have a short span as shown in FIG. 1, the lateral separation between the rear edges 120 of the shoulders 112 is equal to or perhaps greater than the width of the insulation body 138. However, if the shoulders 112 have a long span as shown in FIG. 2, the lateral separation between the rear edges 120 of the shoulders 112 is also less than the width of the insulation body 138. 20 Therefore, for the longer shoulders 112 of FIG. 2, the thickness of structural body 100 from the outer side face 123 to the rear edge 120 of the shoulder 112 is greater than the thickness of the structural body 100 from the outer side face 123 to the inner side face 122. 25 Since the insulation body 138 fills the rear cavity 110, the same can be said about the width of the rear cavity 110. The minimum width of the gap 114, that is, illustrated separation between the front edges 118 of the shoulders 112 in FIG. 1 is approximately 97% of the 30 width of the insulation body 138 / rear cavity 110. For the longer shoulders 112 of FIG. 2, the separation is approximately 86%. Therefore, a range of 80% to 99% is defined, or 70% to 99%, or even 40% to 99%. The maximum width of the gap 114 is greater than the minimum width and in FIG. 2 is less than 100% of the width of the insulation body 138 / rear cavity 110. FIG. 1 shows that the maximum width of the gap 114 may in some instances be equal to or greater than 100% of the width of the insulation body 138 / rear cavity 110. Regarding the thicknesses of each member, the high strength and lack of cover requirements of the UHPFRC material allows thin members to be formed. 10 15 To give an example, the thickness of at least some of the members formed from UHPFRC can be less than less than or equal to 55mm or less than or equal to 50mm, which would not be possible with steel reinforced concrete or stone aggregate based concrete. For example, the front member 102 and / or the shoulders 112 may have this limited thickness. It is of course possible to specify a higher thickness for higher load applications. Assuming that the structural panel 10 is a fagade panel for a building and is subject to wind loads at the front face 106 of the front member 102, the thickness of each web 104 between its inner and outer side surfaces may be greater than the thickness of the front member 102 and shoulders 112. The thick webs 104 provide a high second moment of area against wind loading, as well as other loads that may be encountered. The aspect ratio of the depth (front-rear axis) of the structural panel 10 (between faces 106 and 132) relative to width (lateral axis) of the structural panel 10 between web-centres can be from the range 1:1.5 to 1:5. In FIG. 1 it is about 1:2.2. 30 The illustrated structural panel 10 is symmetric in cross-section, but this may vary with implementation. FIG. 2 illustrates a second example of the structural panel 10, in which a third, intermediate web 104A has been added at a central location between the aforementioned webs 104. The intermediate web 104A may be added because the width of the structural panel 10 in the lateral direction is greater, requiring 5 central stiffening, or because the loads are greater or the materials are thinner or weaker. The intermediate web 104A in FIG. 2 divides the rear space of the structural body 100 so that two rear cavities 110 are provided. Therefore, a separate 10 insulation body 138 is located within each rear cavity 110. The intermediate web 104A has two inner side faces 122 rather than separate inner and outer side faces 122,123. One inner side face 122 of the intermediate web 104A is an inner face of one of the rear cavities 110, and the other inner 15 side face 122 of the intermediate web 104A is an inner face of the other of the rear cavities 110. The intermediate web 104A comprises a pair of the shoulders 112, one facing the shoulder 112 of the first web 104, and the other facing the shoulder 112 of 20 the second web 104. By contrast, the first and second webs 104 are end webs and therefore have only one shoulder 112 each. FIG. 3 illustrates stages of completion of a structural panel 10, demonstrating a manufacturing method 300. 25 As shown in step 302, the method 300 comprises pouring a first portion of the UHPFRC into an outer formwork 144 to form the front member 102. The outer formwork 144 is a U-shaped trench of shuttering, that defines the front face 106 of the front member 102 and later the outer side faces 123 of the webs 104. 30 Then, as shown in step 304, an inner formwork 146 is positioned over the front member 102 before the first portion of UHPFRC has set. The inner formwork 146 is created by the insulation body 138 and a backing pad 142 formed from timber (e.g., layered plywood sheets). The insulation body 138 is fastened to the backing pad 142 by spiral screws (pigtail screws), to hold the foam or sheet wool material against the more rigid backing pad 142. As a result, the insulation body 138 is layered between the backing pad 142 and the front member 102. The illustrated rectangular insulation body 138 occupies what will become the 10 rear cavity 110. The insulation body 138 defines the formwork for the inner side faces 122 of the webs 104 and the lip faces 124 of the shoulders 112. The illustrated backing pad 142 occupies what will become the gap 114 between the shoulders 112. 15 The illustrated backing pad 142 is trapezoidal in cross-section, because its left and right edge faces 148 have been pre-cut into the tapered / chamfered shapes. The tapered edge faces 148 of the backing pad 142 define the formwork for the chamfered faces 116 of the shoulders 112. 20 The empty space between the inner formwork 146, the outer formwork 144 and the already-poured front member 102 forms the negative of the webs 104 and shoulders 112, so at step 306 a second portion of UHPFRC is poured into the space. This is performed while the UHPFRC of the front member 102 is still 25 fresh and has not yet set, so that the webs 104 will bond to the front member 102. At step 308, the backing pad 142 and outer formwork 144 are removed, leaving behind completed structural panel 10. The shoulders 112 have the chamfered 30 faces 116 as shown. Removal of the backing pad 142 comprises removing whatever fastenings were used, such as the pigtail screws insulation pins. At optional step 310, a second insulation body 140 is added to fill the gap 114 between the shoulders 112. The second insulation body 140 may be cut into a cross-section shape, e.g., trapezoidal shape, such that its left and right edge faces parallelly abut the chamfered faces 116 of the shoulders 112. Adding the second insulation body 140 may be performed on-site in some examples, but could be performed at the factory. Assuming that the thickness of the backing pad 142 was selected to conform 10 to a standard insulation sheet thickness, or a multiple thereof, it is possible to make the rear face of the second insulation body 140 lie flush with the rear surfaces 132 of the structural body 100 without any subsequent cutting or finishing operations. For example, the thickness of the gap 114 (thickness of the shoulders 112) may be 48-50mm which conforms to a standard insulation 15 sheet thickness. Optionally, a thickness of the second insulation body 140 is approximately equal to this gap 114. An advantage is allowing a standardthickness second insulation body 140 to be inserted into the gap 114. The above method 300 allows the rapid and accurate assembly of a strong 20 precast concrete structural body 100 with integral insulation. This minimises the period of time that the formwork is in use, and the amount of time before the structural body 100 can be stood up vertically for space-efficient storage. In another embodiment, the inner formwork 146 is positioned before step 302. 25 In a further alternative embodiment, the structural body 100 is formed by a single pour rather than the separate pours of steps 302 and 306. FIG. 4 illustrates a rear elevation of a structural panel 10 incorporating the 30 invention. FIG. 4 further schematically illustrates a pair of hanging points 134 formed in the rear side of the structural panel 10, to enable the structural panel 10 to be hung from part of a structural frame. Alternatively, one hanging point 134 may be provided, or more than two hanging points 134. As shown, the pair of hanging points 134 are located proximal to opposite left and right corners of the structural panel 10. As shown, the hanging points 134 may be located at or proximal to the top edge 10 of the structural panel 10. The hanging points 134 may comprise sockets or plugs, for example. The hanging points 134 may comprise embedded brackets, for example. LD CM 15 A top face of the structural panel 10 may comprise lifting points (not shown) ¢2¾ such as in-moulded hooks or sockets, to enable the structural panel 10 to be hung from a crane in an upright orientation. FIG. 4 also separately shows some other features that a structural panel 10 20 may have. Firstly, FIG. 4 shows that a rear cavity 110 may have a height less than the height of the structural panel 10. Specifically, FIG. 4 shows the structural body 100 further comprising an upper cross member 148 and / or a lower cross 25 member 150, defining top and bottom end boundaries of the rear cavity 110 or cavities 110. The upper and lower cross members 148, 150 of the structural body 100 may be connected to, for example integrally formed with the front member 102 and 30 the ends of the webs 104, 104A. The upper and lower cross members 148, 150 and end webs 104 of the webs 104 together define a perimeter frame of the structural body 100, framing the rear cavity 110 or cavities 110. 5 A steel reinforcing bar arrangement (not shown) may be installed proximal to the hanging points 134 and / or lifting points, to reduce reliance on fibre alignment near the connections. In some examples, the steel reinforcing bar arrangement may extend along four 10 sides of the perimeter frame of the structural body. The illustrated hanging points 134 are formed in the upper cross member 148. FIG. 4 also shows that a wide structural panel 10, for example wider than its 15 height, may comprise a four or more of the webs 104 and / or 104A each extending parallel to each other. Seven are shown. FIG. 4 (rear elevation), FIG. 5 (front elevation), and FIG. 6 (cross-section) further illustrate window openings 136 cast in the structural body 100, to receive 20 a window frame 152. As shown in FIG. 5, the window openings 136 are through-holes. The structural body 100 may comprise one or more of the window openings 136. The left and right boundaries of each window opening 136 may be defined by 25 left and right webs 104 each of the type illustrated in FIG. 1. The shoulder 112 of each web 104 points away from the window opening 136. FIG. 6 shows that a window fixing system 154 for the glazing assembly 152 may be fastened, e.g., embedded, into a rear surface 132 of the structural body 30 100, either into the web 104 or into the shoulders 112. The shoulders 112 advantageously provide additional volume and depth to receive the window fixing system 154, while the rest of the web 104 between the faces 122, 123 is thinner. The longer shoulders 112 shown in FIG. 2 particularly provide greater lateral tolerance for positioning the fixings 154. FIG. 4 also shows that a rear cavity 110 may be located between a pair of 5 adjacent window openings 136. FIG. 4 also shows that a rear cavity 110 may be located between a window opening 136 and an end web 104 of the structural panel 100. The top and bottom boundary of the or each window opening 136 may be 10 defined by upper and lower cross-members 148, 150, respectively. 15 Although FIG. 4 shows no further rear cavities 110 above or below each window opening 136, in other examples a further rear cavity 110 may be provided above a window opening 136 and / or a further rear cavity 110 may be provided below a window opening 136. FIG. 4 shows that the top boundary of each window opening 136 may optionally be aligned with and parallel to the top boundary of each rear cavity 110, and / or the bottom boundary of each window opening 136 may optionally be aligned with and parallel to the bottom boundary of each rear cavity 110. FIG. 7 further illustrates an example implementation of the structural panel 10 in which three or more layers of insulation bodies 138, 156, 160 are located to 25 the rear of the structural body 100. A pair of front insulation bodies 138 are as shown in FIG. 2, separated by the illustrated intermediate web 104A. 30 An intermediate insulation body 156 is mounted to the rear surface 132 of the structural body 102, extending over the web 104. A rear insulation body 160 is mounted to the structural panel 10, extending behind the intermedia insulation body 156. The rear insulation body 160 might be battened off from the intermediate insulation body 156. 5 The layers of insulation bodies 138, 156, 160 are separated by respective air gap layers 155, 158. A closed air gap between the layers provides a sealed air cavity to trap in sound, acting as acoustic insulation. The shoulders 112 of the structural body 100 extend within and along the air 10 gap layer 155, between the insulation bodies 138, 156. The air gap layer 158 is located between the intermediate insulation body 156 and the rear insulation body 160. 15 The arrangement in FIG. 7 advantageously provides continuous insulation, rather than insulation that is interrupted by webs 104 or intermediate webs 104A. In another example, the insulation body 160 is omitted so the insulation body 156 is rearmost. 20 Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed. For example, not all the webs 104 may have shoulders 112 connected thereto. In a further alternative 25 example, only one web 104 of the structural panel 10 has a shoulder 112 or shoulders 112 connected thereto. Features described in the preceding description may be used in combinations other than the combinations explicitly described. 30 Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not. 5 Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and / or shown in the 10 drawings whether or not particular emphasis has been placed thereon.

Claims

1. A structural panel comprising a structural body formed from cementitiousmaterial, and an insulation body formed from thermal insulation material, 5 wherein the structural body has a cross-section shape defining a laterally-extending front member and rearwardly-extending webs connected to a rear of the front member, wherein a rear face of the front member and inner side faces of the webs define a rear cavity of the structural panel in which the insulation body is located to thermally insulate the structural panel, wherein each web 10 comprises a laterally-protruding shoulder at the end of the inner side face, wherein the shoulders face each other, wherein a lateral separation between the shoulders defines a gap behind the rear cavity, wherein at least part of the gap is narrower than a corresponding lateral width of the insulation body, and wherein the gap is an air gap or is filled with a further, second insulation body.

152. The structural panel of claim 1, wherein one or each of the shoulders has a tapered width in cross-section such that a lateral separation between the shoulders increases rearwardly.20 3. The structural panel of claim 2, wherein each of the shoulders comprisesa chamfered face defining the taper, and wherein the chamfered faces face each other across the gap.

4. The structural panel of claim 2 or 3, wherein a minimum width of the gap 25 is defined between front edges of the shoulders, wherein the minimum width is less than the lateral width of the insulation body.

5. The structural panel of any preceding claim, wherein the rear face of the front member, the inner side faces of the webs, and lip faces of the shoulders 30 define boundaries of the rear cavity.

6. The structural panel of claim 5, wherein the boundaries are rectilinear.

7. The structural panel of any preceding claim, wherein the structural body comprises two of the webs, the first web connected to a first end of the front member, the second web connected to a second end of the front member 5 opposite the first end, and wherein the rear cavity and insulation body extend continuously between the first and second webs.

8. The structural panel of any one of claims 1 to 6, wherein the structural body comprises three or more of the webs, the first web connected to a first end 10 of the front member, the second web connected to a second end of the front member opposite the first end, and the third web connected to the front member between the first and second webs, wherein the three webs define two insulation cavities therebetween, each comprising one insulation body.15 9. The structural panel of claim 8, wherein the third web comprises a pairof the shoulders, one facing the shoulder of the first web, and the other facing the shoulder of the second web.

10. The structural panel of any preceding claim, wherein rear surfaces of the 20 structural body and of the second insulation body are flush with each other.

11. The structural panel of any preceding claim, wherein the structural body is formed from fibre reinforced concrete, optionally ultra-high performance fibre-reinforced concrete defined by a compressive strength greater than 150 25 megapascals.

12. The structural panel of claim 11, wherein the shoulders and / or the webs formed from the fibre reinforced concrete have a thickness less than or equal to 55mm or less than or equal to 50mm.3013. The structural panel of any preceding claim, wherein each web is thicker than the front member and shoulders.

14. The structural panel of any preceding claim, wherein the insulation body is formed from mineral wool, or expanded material.5 15. The structural panel of any preceding claim, wherein a minimum lateralseparation between the shoulders is at least 70% of the lateral width of the insulation body.

16. The structural panel of any preceding claim, wherein the structural body10 comprises a hanging point to enable the structural panel to be hung from a crane and / or from part of a structural frame.

17. The structural panel of any preceding claim, wherein the structural body comprises a window opening.1518. A method of forming the structural panel as claimed in any one or more of the preceding claims, the method comprising:pouring the cementitious material into a formwork to form the structural body, wherein the insulation body is part of the formwork to form the rear cavity; andseparating from the formwork the structural panel including the structural body and the insulation body, once the cementitious material has set.

19. The method of claim 18, wherein the formwork comprises an outer 25 formwork, and an inner formwork positioned to a rear face of the front member, and wherein the inner formwork comprises the insulation body.

20. The method of claim 19, wherein the inner formwork comprises the insulation body and a backing pad.3021. The method of claim 20, wherein the backing pad comprises one or moretapered edge faces to define a tapering of the shoulder or shoulders.

22. The method of claim 20 or 21, wherein the insulation body is located to form the rear cavity, and wherein at least a front of the backing pad is narrower than the insulation body and is located to form the shape of a facing pair of the 5 shoulders and fills the gap between the facing pair of shoulders.

23. The method of any one of claims 19 to 22, wherein:the pouring step comprises pouring a first portion of the cementitious material into the outer formwork to form the front member;10 wherein the method further comprises positioning the inner formwork tothe rear face of the front member before the front member has set; andwherein the pouring step further comprises pouring a second portion of the cementitious material into a space between the outer formwork and inner formwork, before the front member has set, to form the webs including the 15 shoulders.

24. The method of claims 23, as dependent through claim 20, comprising removing the backing pad from the insulation body after the second portion of cementitious material has been poured.2025. The method of claim 24, further comprising adding a second insulation body to the gap between the shoulders, where the backing pad was previously located, or behind a rear surface of the structural body.

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