The invention relates to a method for manufacturing a concrete construction element which is provided with a fire- resistant cover layer.

Constructions of reinforced concrete in house building, utility construction or in road and hydraulic engineering are subject to increasingly strict requirements in the field of fire safety.

These requirements are for instance satisfied by manufacturing concrete partition walls in buildings, or walls and ceilings in tunnels, from a concrete mixture to which synthetic fibres or limestone parts have been added in order to make the concrete fire-resistant. The thus obtained fire- resistant concrete has the drawback that the fibres or limestone parts incorporated therein melt or degrade in the case of prolonged exposure to very high temperatures, wherein channels or cavities are formed in the concrete which make the concrete accessible to water and salts dissolved therein, as a result of which the remaining lifespan of the concrete can decrease to an unacceptable extent.

Known from WO 2006/074913 Al is a reinforced concrete floor deck which is provided on an outer side with at least one rail to which for instance a fire-retardant or heat or sound-resistant layer can be attached.

Such a concrete construction element, which is provided according to the prior art with a fire-resistant cover layer, has the inherent drawback of the additional costs involved in mounting this cover layer.

It is an object of the invention to provide a method for a construction element provided with a fire-resistant cover layer, wherein arranging of the cover layer does not result in additional costs.

This objective is achieved, and other advantages gained, with a method of the type specified in the preamble, comprising the steps of (i) providing a formwork for the construction element to be manufactured, (ii) casting the concrete reguired for the construction element in the formwork, and (iii) allowing the concrete cast in accordance with step (ii) to cure in order to obtain the construction element, for instance a fire-resistant wall element, ceiling element or floor element, wherein according to the invention the formwork is at least partially formed by a fire-resistant panel, which panel is adapted for coupling to the

construction element to be obtained by curing of the concrete in accordance with step (iii) .

It is noted that step (i) can also comprise of providing a reinforcement which is enclosed by the formwork.

In the method according to the invention the fire- resistant panel forming part of the formwork is coupled during the casting and curing of the concrete to the obtained construction element so as to form an integrated part thereof .

In an embodiment of the method according to the

invention the panel is fire-resistant in that it is

manufactured from a fire-resistant material.

In a subsequent embodiment, wherein the panel is manufactured from concrete, the panel is fire-resistant in that it is provided on a side to be directed toward the interior of the formwork with a layer of a fire-resistant material .

In a practically advantageous embodiment the panel is provided with coupling means for coupling the panel to the construction element.

The invention also relates to a concrete construction element manufactured according to the above described method, comprising a concrete first panel which is coupled on at least one side to a fire-resistant second panel, wherein the concrete first panel comprises at least one of the components cement, limestone meal, quartz-containing material, synthetic fibres, in particular polypropylene fibres, blast-furnace slag and steel fibres. The invention further relates to a concrete construction element provided with a fire-resistant cover layer and manufactured according to the above described method, comprising a concrete first panel which is coupled on at least one side to a concrete second panel, wherein the concrete second panel comprises at least one of the

components cement, limestone meal, quartz-containing

material, synthetic fibres, in particular polypropylene fibres, blast-furnace slag and steel fibres.

In an embodiment of such a concrete construction element the concrete second panel is obtained from a mixture

comprising 6-10% by weight CE I, 10-14% by weight limestone meal, 5-10% by weight blast-furnace slag, 7-9% by weight water, 60-65% by weight aggregate and 1% by weight additives and fibre material. The aggregate comprises for instance river gravel, granite or limestone. The additives comprise for instance a plasticizer, the fibre material comprises for instance synthetic fibres or steel fibres.

It has been found that in a concrete second panel of such a composite mixture a new phase, made up of the

components calcium oxide (CaO) , aluminium oxide (AI2O3) and silicon oxide (SXO2) , results at a temperature of about

1000°C, this phase having a vitreous structure and being highly fire-resistant.

In an advantageous embodiment the concrete second panel is obtained from a mixture comprising 6% by weight CEM I, 14% by weight limestone meal, 8% by weight blast-furnace slag, 7% by weight water, 64% by weight aggregate and 1% by weight additives and fibre material.

In a subsequent advantageous embodiment the concrete second panel is obtained from a mixture comprising 10% by weight CEM I, 11% by weight limestone meal, 11% by weight blast-furnace slag, 7% by weight water, 60% by weight aggregate and 1% by weight additives and fibre material.

It is noted that a concrete second panel according to the above described exemplary embodiments is also suitable per se as fire-resistant cover layer which according to the A prior art can be attached to a separately manufactured concrete first panel.

The invention further relates to a concrete construction element provided with a fire-resistant cover layer

manufactured according to the above described method and comprising a concrete first panel which is coupled on at least one side to a fire-resistant second panel, wherein the second panel is provided on its side facing toward the first panel with a layer of a non-combustible material, this layer for instance comprising a silica aerogel.

In an advantageous embodiment of a construction element according to the invention, wherein the second panel is manufactured from concrete, the first panel is coupled to the second panel by means of at least one anchor bolt.

Coupling the first panel to the second panel by means of anchor bolts during manufacture of a construction element is per se simple and is relatively inexpensive. In addition, a coupling by means of anchor bolts has the advantage that after exposure to fire, wherein the second panel has become unusable but the first panel and the anchor bolts have not, the second panel can be replaced by a fire-resistant panel which can be attached to the first panel by means of the still usable anchor bolts.

The anchor bolt is for instance manufactured from steel with a thermal conductivity coefficient λ amounting to about 50 /m.K.

The first panel is for instance manufactured from a concrete with a thermal conductivity coefficient λ amounting to about 1 W/m.K.

The second panel is for instance manufactured from a concrete with a thermal conductivity coefficient λ amounting to about 1 W/m.K.

The layer of a fire-resistant material has for instance a thermal conductivity coefficient λ amounting to about 0.01 W/m.K.

The method and a concrete construction element obtained according to this method are widely applicable in house building, utility construction and in road and hydraulic engineering .

The advantages of the invention become particularly manifest in a tunnel which is characterized by at least one concrete construction element manufactured according to the above described method. In the construction of a tunnel which must satisfy strict fire safety requirements a great

reduction in cost and construction time, compared to the case of a tunnel constructed according to a prior art method, can be realized by applying the method according to the

invention .

The invention will be elucidated hereinbelow on the basis of an exemplary embodiment and with reference to the drawing .

In the drawings fig. 1 shows a cross-section of an embodiment of a concrete construction element according to the invention.

Fig. 1 shows a cross-section 5 through a reinforced concrete construction element 1 (reinforcement not shown) which is provided with a concrete cover panel 2 coupled thereto by anchor bolts 4, as seen along a line through anchor bolts 4. A mat 3 of a fire-resistant material on the basis of a silica aerogel is clamped between cover panel 2 and concrete construction element 1.

Construction element 1 is manufactured by casting concrete into a formwork (not shown) of which the concrete cover panel 2 formed part. Prior to being placed in the formwork, concrete cover panel 2 is provided with mat 3 of a fire-resistant material, and is already provided with anchor bolts 4 at an earlier stage during the manufacture of cover panel 2.