Patent Abstract:
This invention relates to a composite panel for a rooftop surface having a core material board having a top surface and a bottom surface with a plurality of openings through said core material board extending from said top surface to said bottom surface; a rigid outer shell of solid material that encapsulates said core material board; a plurality of supports of said solid material wherein each of said plurality of supports extends through one of said plurality of openings in said core material board; and a plurality of legs on a portion of said rigid outer shell covering said bottom surface of core board material.

Full Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to composite cement panel for use in a roof deck or similar structure, and a fabricating method of the cement panel. 
       BACKGROUND ART 
       [0002]      FIG. 1  illustrates a typical construction  100  of a cladding construction system of a concrete roof deck  102 . A cement sand base  104  is formed over the roof deck  102 , the base  104  being screed to form a slope or slope-to-fall gradient to create a drainage fall into a drain  106  and downpipe  108 . A waterproof membrane  110  is laid over the cement sand base  104 , interrupted only by downpipe  108 , and extending a height  112  of 300 mm up the inside surface of walls  114 . Where the deck  102  meets some walls  114 , the transition of the waterproof membrane from the horizontal surface to the vertical surface may be effected by use of waterproof filler such as poly foam  116 . A thermal insulating layer  118  is constructed on top of the membrane  110 , the layer  118  comprising extruded polystyrene insulation board of 50 mm thickness. A separation fleece layer  120  overlies the thermal insulating layer  118 . Finally an overlying protective screed concrete layer  122  of 75 mm thickness is provided, comprising 4.5 m by 4.5 m panels separated by joints filled with bituminous compound. Plastering  124  is applied to walls  114 . 
         [0003]    The thermal insulating material  118  reduces heat transfer through the concrete roof deck  102  into the building below. The protective cement screed  122  protects the thermal insulating material  118  and the waterproofing membrane  110 , and bears the human traffic on the roof deck. Such a construction  100  is constructed in-situ on site, with an expansion joint provided at regular intervals. 
         [0004]    Construction  100  suffers from a range of problems. The expansion joints in concrete screed layer  122  are a weak point in the construction and a source of leaks. Residual water becomes lodged between the thermal insulating material  118  and the waterproofing membrane  110  after rain. When exposed to heat from the sun, the water expands and evaporates, exerting pressure on the thermal insulating material  118  which in turn exerts pressure onto the protective screed concrete  122 . Both the protective screed concrete  122  and thermal insulating material  118  will generally crack due to such stress, leading to leakage and/or “sickness” in the construction  100 . 
         [0005]    A further problem is that on site cladding construction makes quality control difficult, can cause damage to the waterproofing system, and is subject to the vagaries of inclement weather during construction leading to time delay. In addition, mixing, handling and/or applying concrete slurry on site can be messy and laborious. 
         [0006]    Still further, in the event that maintenance is required to the underlying roof deck  102 , waterproofing membrane  110  and/or components of the built-up waterproofing system  104 ,  118 ,  120 ,  122 , the protective screed  122  and some or all underlying layers need to be destructively removed such as by being cut away, effectively destroying the construction  100 . The entire process of building up the waterproofing system must then be repeated to re-establish a waterproof cladding. 
         [0007]    Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application. 
         [0008]    Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  illustrates a typical roof cladding construction; 
           [0010]      FIG. 2  is a perspective view of a formwork for cement casting for a composite cement panel according to one embodiment of the present invention; 
           [0011]      FIG. 3  is a perspective view of a foam board placed in the formwork of  FIG. 2  for fabricating a composite cement panel according to one embodiment of the present invention. 
           [0012]      FIG. 4  is a flowchart showing a process for fabricating a cement panel using the formwork of  FIG. 2 . 
           [0013]      FIG. 5A  is a top view of a composite cement panel according to one embodiment of the present invention. 
           [0014]      FIG. 5B  is a bottom view of  FIG. 5A . 
           [0015]      FIG. 6A  is a front view of  FIG. 5A . 
           [0016]      FIG. 6B  is a cross sectional side view of  FIG. 5A . 
           [0017]      FIG. 6C  is a partially enlarges view of  FIG. 6B . 
           [0018]      FIG. 7A  is a perspective bottom view of  FIG. 5A . 
           [0019]      FIG. 7B  is a partially cross sectional perspective view of  FIG. 5A . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]      FIG. 2  shows a formwork  2 , made of metal for example, for casting a composite cement panel  800  shown in  FIG. 7A . Formwork  2  has an array of recesses  3  formed on the base surface  4 . Recesses  3  are positioned spaced apart from each other across the base surface  4  of the formwork  2 . Guide abutments  6  are provided on two adjacent inner surfaces  214 ,  215  of the metal formwork  2 . Formwork  2  further includes pins  8  positioned on the bottom surface  4 . Pins  8  extend upwardly from the base surface  4  of formwork  2 . Formwork  2  ends with an upturn skirting  7  along the peripheral edge, allowing ease of handling the formwork  2  during casting or transportation of the cement panel  800 . 
         [0021]      FIG. 3  illustrates a light-weight core material board, such as a foam board  200 , placed in formwork  2  before the process of cement casting of the composite cement panel  800 . Foam board  200  has through holes  202  formed thereon by, for example, drilling, stamping, cutting, punching or pre-made integratedly during a molding process forming the foam board. Through holes  202  are configured such that, when foam board  200  is placed in formwork  2 , each through hole faces one recess of formwork  2 . When placed in formwork  2 , foam board  200  sits on pins  8 , leaving a gap between foam board  2  and bottom surface  4  of formwork  2 . 
         [0022]      FIG. 4  is a flowchart of a process  300  for fabricating a cement panel using the formwork  2  shown in  FIG. 2 . At step  302 , foam board  200  having through holes  2  formed there on, is placed in the formwork  2 , with two adjacent sides of the form board acting against a respective guide abutment  6 . This way, there is remained a side gap between the periphery of foam board and inner surfaces  214  and  215  of formwork  2 . 
         [0023]    At step  312  a pre-mixed self-levelling high strength cement grout, with or without concrete hardener or chemical additive, is prepared. At step  306 , the cement grout is poured onto foam board  200  and into formwork  2 . During this step, cement grout will fill up the round recesses  3  in the formwork  2 , the gap between the foam board and the bottom surface  4  of formwork  2 , the gap between the periphery of foam board  200  and inner surfaces  214 ,  215 ,  216  and  217  of formwork  2 , and the holes  202  of the foam board  200 . At step  308 , the cement grout fills formwork fully, and is trowelled and finished. At step  310  the cement grout is left to dry and harden, hence to form a cement casing  502  encapsulating foam board  200 , and form the composite cement panel. At step  314  the formed cement panel is removed from the formwork  2 . 
         [0024]    Depending the building roof conditions and the finishing requirements, the composite cement panel may be fabricated with a suitable finishing layer on its top surface. For example, at an optional pre-dry finishing step  318 , pebbles may be pours onto the top surface of the wet composite cement panel. The pebbles are then attached onto the top surface of the panel, and dried together with the panel. Alternatively, color cement powders may be supplied onto the top surface of the wet composite cement panel and dried together, so as to form a colored finishing layer. Imprints with predetermined patterns may also be formed, by molding or pressing the patterns on the top surface of the composite cement panel. In a further optional after-dry step  320 , as an alternative of step  318 , the dried composite cement panel may be covered by tiles, wood panels or natural/artificial stones and/or a layer of heat-insulating or waterproof coating. 
         [0025]      FIGS. 5A ,  5 B,  6 A,  6 B,  6 C,  7 A and  7 B illustrate a composite cement panel  800  produced after step  314  of process  300  (shown in  FIG. 4 ). With reference to  FIG. 6A  and  FIG. 6B , it can be seen that the foam board  200  is encapsulated in the cement casing  502 . Also, it can be seen from  FIG. 6C  that the top portion  204  and bottom portion  206  of the cement casing is bound by portions of cement  520   a  surrounding the foam board  200  as well as the portions filling the holes  202  of the foam board  200 . Portions of cement casing  502  fills in the holes  202  of foam board  200 , forming columns  570 . These columns  570  increase the strength and rigidity of the cement panel  800 , and serve to distribute applied weight, such as foot traffic, to reduce the likelihood of foam board  200  being crushed. Portions of the cement casing filling in the round recess  3  of formwork  2  form legs  220  at the bottom side  250  of the composite cement panel  800 . Additionally, the foam board  200  is chemically bonded to the cement casing  502  by additives in the cement grout. 
         [0026]    With reference to  FIGS. 7A and 7B , legs  220  extend downwardly from the bottom surface  250  of the cement panel  800 . When leveled on top the roof top surface of a building, legs  220  rests on the roof top surface, providing a network of multi-directional free-flow paths between the spaces of the legs  220  for draining water along the underside of the cement panel  800 . Provision of legs  220  of cylinder shape and multi-directional flow paths reduces trapping of residual water in the cement panel  800 , and at the same time allows the water to flow in multiple-directions on the roof top surface level. Thus, better drainage of water can be achieved even in heavy rainfall. By encapsulating the foam board in the cement casing, water or moisture is prevented from penetrating into the panel and wet the foam board, hence the likelihood of the foam board deformation or damage caused by water or moisture content is avoided. 
         [0027]    The size and thicknesses of foam boards  200  are kept in appropriate ratio to the size and thickness of the finished cement panel  800  to achieve a satisfactory effect of thermal insulating. In one embodiment, the dimensions of foam board  200  are 18 mm thick by 480 mm width by 480 mm length. Specifications of the one exemplary polystyrene foam board  200  are listed in Table 1 below. 
         [0000]    
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Specification of foam board 
               
             
          
           
               
                 Property 
                 Test Method 
                 Unit(s) 
                 Typical Value(s) 
               
               
                   
               
               
                 Density 
                   
                 kg/m 3   
                 40~50 
               
               
                 Thermal 
                 ASTM C518: 
                 W/m ° K 
                 0.02207 
               
               
                 Conductivity 
                 1991 
                 kcal/mm ° K 
                 0.01897 
               
               
                 10% Compressive 
                 ASTM D 1621: 
                 N/mm 2   
                 0.30 
               
               
                 Strength (Average) 
                 2000 
               
               
                 Flammability 
                 ASTM C635: 91 
                 cm/min 
                 10.0 
               
               
                 Classification 
               
               
                 (Average burning 
               
               
                 rate) 
               
               
                 Water Absorption 
                 ASTM C272: 
                 % 
                 0.01 
               
               
                 (Average) 
                 2001 
               
               
                 Temperature of Hot 
                   
                 ° C. 
                 40.77 
               
               
                 Surface 
               
               
                 Temperature of 
                   
                 ° C. 
                 19.95 
               
               
                 Cold Surface 
               
               
                 Mean Temperature 
                   
                 ° C. 
                 30.36 
               
               
                   
               
             
          
         
       
     
         [0028]    The composition of an exemplary pre-mixed, self-leveling, high strength cement grout is listed in Table 2 below. 
         [0000]                                      TABLE 2                   Composition of cement grout                Name   CAS   Proportion                       Portland Cement   65997-15-1   10-60%           Sand (Crystalline Quartz)   14808-60-7   10-60%           Flow Aid, Plasticiser       0-1%           Concrete Strengthener Additive       250 ml                        
The specification of an exemplary concrete strengthener is listed in Table 3 below.
 
         [0000]    
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 specification of the concrete strengthener 
               
             
          
           
               
                   
                 Property 
                 Unit 
                 Typical Value 
               
               
                   
                   
               
               
                   
                 Solid Content 
                 % 
                 &gt;40 
               
               
                   
                 Density 
                 kg/m 3   
                 1.16 ± 0.04 
               
               
                   
                 Crack Filing 
                 mm 
                 0.1-2   
               
               
                   
                 Depth of Absorption (for 
                 mm 
                 1-8 
               
               
                   
                 Grade 20 Concrete) 
               
               
                   
                 Flash Point Waterborne 
                   
                 Not flammable 
               
               
                   
                 Drying Time 
                 hours 
                 1-3 
               
               
                   
                 Weather Condition 
                 ° C. 
                 10-50 
               
               
                   
                 UV Resistance 
                   
                 Stable 
               
               
                   
                   
               
             
          
         
       
     
         [0029]    It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Technology Classification (CPC): 4