Construction boards bonded by organic and/or inorganic cementing means
BACKGROUND OF THE INVENTION 
     The invention concerns components provided with reinforcing means such as fibers, preferably construction boards, in particular wood-cement boards, which are bonded together by organic and/or inorganic cementing means such as cement or plastics. 
     Components and construction boards of this kind incur the drawback that it is difficult to achieve with them a non-combustibility per German Industrial Standard DIN 4102, in particular that of Combustion Class A2 of this regulation. 
     It is already known in this respect to provide additives of borates, phosphates, carbonates, chlorides etc. in wood-cement boards. When additives of this kind are used, either the non-combustibility is achieved at the cost of an often substantial decrease in strength of the construction boards, or the required reduction in toxicity of the combustion smoke is not achieved. 
     SUMMARY OF THE INVENTION 
     It is therefore the object of the invention to create components or construction boards of the initially cited kind of which the strength shall not be degraded, or not substantially, in spite of additives being present, and wherein furthermore the toxicity of the combustion gases is reduced while the prescribed non-combustibility is observed. 
     This problem is solved by the invention in that the components or construction boards include a proportion of 20 to 70% of manganese dioxide (MnO 2 ). 
     By means of this manganese dioxide ingredient, a component or construction board is created which surprisingly achieves very easily the non-combustibility of the above DIN (German Industrial Standard) regulation, combustion class A2, without thereby significantly degrading the strength. Furthermore the toxicity of the combustion gases in the component of the invention is substantially reduced compared to that of a component without that ingredient, namely to about 1/10. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     When using the composition of the invention for a wood-cement board, the following ranges in proportions are applicable: 
     EXAMPLE 1 
     Wood fibers: about 8 to 20% 
     cement: about 10 to 70% 
     manganese dioxide: about 20 to 70%. 
     The following mixture ratio was found especially advantageous: 
     EXAMPLE 2 
     wood fibers: about 12% 
     cement: about 48% 
     manganese dioxide: about 40%. 
     The following examples clarify the further applicability of the composition of the invention. 
     EXAMPLE 3 
     A wood-chip board bonded together by synethetic resin 
     wood chips: about 60% 
     urea resin+hardener: about 10% 
     manganese dioxide: about 30%. 
     EXAMPLE 4 
     Chip-board bonded together by water-glass 
     wood chips: about 35% 
     sodium-silicate glass+hardener: about 35% 
     manganese dioxide: about 30% 
     EXAMPLE 5 
     mica-board bonded together by synthetic resin 
     mica, muscovite: about 65% 
     phenolic resin+hardener: about 5% 
     manganese dioxide: about 30% 
     EXAMPLE 6 
     cement-bonded cellulose board 
     Cellulose suspension in water: about 7% 
     Portland cement: about 57% 
     manganese dioxide: about 37% 
     In addition to the manganese-dioxide ingredient further additives may be provided, in particular additives to increase the strenght of the components, for instance formic acid (HCOOH). An addition of about 5% of formic acid was found advantageous. 
     Also additions of aluminum sulfate [Al 2  (SO 4 ) 3 .XH 2  O] and water glass are useful.