FR2837819A1 - Fibrous concrete composition for making non-flat elements includes additives for modifying tensile strength and elasticity during setting - Google Patents

Abstract

Fibrous concrete composition for making non-flat elements includes additives for: (A) ensuring that the tensile strength of the concrete increases more rapidly than the tensile stress during setting; (B) reducing the modulus of elasticity of the concrete during setting; and optionally (C) creating microbubbles of air in the concrete. Fibrous concrete composition for making non-flat elements, comprising cement, optionally another binder, sand, optionally quartz, organic fibers, silica or metakaolin or equivalent, additives, and water in an amount such that the ratio of water to cement and optional other binder is 0.2-0.3, includes additives for: (A) ensuring that the tensile strength of the concrete increases more rapidly than the tensile stress during setting; (B) reducing the modulus of elasticity of the concrete during setting; and optionally (C) creating microbubbles of air in the concrete. Independent claims are also included for: (1) production of non-flat concrete elements by pouring the above composition into a mold or form and placing the concrete under compression during setting; (2) concrete elements produced by molding or casting the above composition.

Description

claims 1 to 6.

  The invention relates to the improvement of the qualities of concrete of so-called very high performance organic fibers (resistance to compression, traction and bending), which have superior performance to that of conventional fiber-reinforced concrete due to the presence in very large quantities. fine reagents (cement and pozzolanic additions) coupled with a very low water content, for example a ratio "quantity of water to quantity of equivalent binder"

in the range of 0.2-0.3.

  This particularity of ultra high performance fiber concretes can lead to cracking of these concretes in the hours following pouring, following different types of shrinkage: for flat parts poured horizontally, this shrinkage is not a problem because it can be done freely, the flat panel being able to retract freely without the development of tensile stresses arising from a withdrawal, but this is no longer the case for non-planar elements, such as panels with single or double bridging, or elements of complex shape such as shower stalls, tubs, etc. There is the appearance of micro-cracks very unpleasant from an aesthetic point of view on elements subjected either to rain or to the humidity of a bathroom. Indeed, by a phenomenon of capillarity, the cracks pump surface water and, during the drying of the element, the pumped water which evaporates more slowly, makes

  appear, by color difference, the ghost of micro-

  cracks. The observed withdrawal comes from two phenomena which combine:

  - so-called endogenous withdrawal which is a self-withdrawal

  desiccation increasing sharply when the "quantity of water / quantity of binder" ratio decreases, which is the case with these fiber concretes, and the quantity of fines increases. This shrinkage is due to the contraction of the paste: the volume of hydrates formed is smaller than the initial volumes of non-hydrated cement and water. The significant contraction, which can reach 18%, generates gas voids in the cement paste, with the creation of menisci and internal capillary traction, as in the classic phenomenon of desiccation by leaving water outwards. During the taking, this phenomenon can trigger important withdrawals which can exceed the

  0.5% or 5mm for a length of 1 meter.

  - so-called shrinkage shrinkage for vertically cast elements, this is a compaction for elements of the solid phase due to a discontinuous granular distribution between the solid elements; in fact, the aggregates usually used for these concretes have a granular spindle varying: - from 1/100 to 1/10 m for very reactive additions which are silica fumes or metakaolins, - from 2 to 40 m for cements deflocculated due to the use of very powerful superplasticizers, - from 80 µm to a few millimeters for sands. Therefore, a settlement of the finest particles occurs between the largest particles, i.e. settlements which can reach 2 to 3 cm for a height

2m.

  The object of the invention is in particular to reduce these

settlement phenomena.

  To this end, according to the invention, a curable composition is used, which essentially comprises cement, possibly another binder, sand, possibly quartz, organic fibers, fumes of silica or metakaolin or equivalent of the point of view of the fineness, of the adjuvants, and of the water so that the ratio of quantity of water to quantity of cement and other binder is of the order of 0.2-0.3, characterized in that the adjuvants comprise : components (A) chosen so that the tensile strength of the concrete increases faster than the tensile stresses during setting, - components (B) chosen to reduce the elastic modulus of the concrete during setting, as necessary to restore a more continuous grain size without bearing, components (C) chosen to create concrete microbubbles of air in the concrete.

varied and stable diameter.

  Optionally, the components (B) act as components (C) or supplement the components (C) to

  provide the desired continuous particle size.

  Typically, a composition according to the invention is a conventional formulation of fiber concrete, characterized in that it comprises, for lm 3 of hardened concrete, 20 to 60 kg of components (A), 5 to 20 kg of components (B) and O to 2 kg of

components (C).

  The rapid development of the tensile strength of concrete during hardening is done by coupling (A) a superplasticizer, not setting retarder, to a

efficient setting accelerator.

  Preferably, the superplasticizer is chosen from those originating from the new chemical generation based on modified polycarboxylic ether allowing very strong reduction of water without causing a setting retarding effect. The tap accelerator can be chosen in the

  range of particularly effective chlorine accelerators.

  Pouring "superplasticizer / setting accelerator" causes the hardening of the fresh concrete quickly, thus limiting the phenomenon of shrinkage in the first phase, then, as a result of the acceleration of the hardening phenomenon of the concrete, very rapidly increasing the mechanical strength by concrete traction so that it is greater than the traction generated by the phenomenon of annoyed shrinkage. The reduction in the modulus of elasticity making it possible to reduce the stresses of traction which develop following withdrawals, is done by adding to the fresh concrete of particular products (B) in the liquid state, such as: acrylic resins , vinyl or based on strydene-butadiene, in emulsion with globules of a few microns in diameter, resins which have the effect of reducing fissurability by reducing the elastic modulus due to the coating of the grains of cement at the start of mixing by the micelles of the emulated resin. These products can cause, during the mixing of fresh concrete,

  micro air bubbles as the air entrainers do

  after. - salts of fatty acids, such as stearates or oleates; these products have the advantage, in addition to reducing the modulus of elasticity, of entraining occluded air in the form of micro-bubbles in the concrete, thus reducing the compaction of the fresh concrete; they also make it possible to reduce the absorption of surface water which has an aesthetic advantage with water beading on the skin of the concrete, which results in less soiling

in time.

  If the components (B) are not sufficient to restore the desired particle size continuity between the different fines composing the concrete, an air entraining adjuvant (C) is added which, due to very good compatibility "formulation of the concrete / air entrainer "will multiply micro-air bubbles in the concrete: indeed it is known that the more the concrete has a" quantity

  of water on a weak quantity of binder and more the micro-

  bubbles are small in diameter, which is what we are looking for; thus due to the synergy between the air entrainers and the concrete formulation, stable micro-bubbles are obtained in the concrete which complete the particle size of the aggregates and fines. In addition, these micro-bubbles improve the implementation of the concrete by increasing the

fluidity of it.

  Components (C) are for example surfactants based on alkaline abietates, soaps

  alkaline fatty acids or equivalent salts.

  In addition, according to another optional feature of the invention but which preferably combines with the foregoing characteristics, the fresh concrete is compressed during setting, which contributes to reducing

  strongly packing cracking.

  I! Compression can be done using springs or cylinders, when the element has just been poured, by means of profiles placed at the interface of fresh concrete, compressing elements and formwork side panels .

EXAMPLE

  The composition indicated below, in accordance with

  the invention is given for lm3 of hardened concrete.

  - CEM I to CEM V cement: 500 to 900 kg depending on resistance

sought.

  - Silica or metakaolin smoke or equivalent

particle size: 50 to 200 kg.

  - Fine sand and quartz with a particle size of 40-5000 microns:

1700 to 950 kg.

  - PVA (polyvinylacrylic) organic fibers or mixture of

  PVA fibers and polypropylene fibers: 10 to 45 kg.

  - Superplasticizer based on polycarboxylic ether: 10 to kg.

  - Setting accelerator: 10 to 30 kg.

  - Stearates or equivalent or butadiene styrene or

equivalent: 5 to 20 kg.

  - Air entrainment (surfactant based on alkaline abietates, alkaline soaps of fatty acids or salts

equivalent): O to 2 kg.

  - Addition water: 150 to 190 kg (so that the ratio of quantity of water to quantity of cement is of the order of

0.2-0.3).

  The invention is not limited to this exemplary embodiment and applies to any concrete of organic fibers. The invention also relates to any element manufactured by molding or casting a composition according to the invention, optionally with compression of the concrete during the

outlet.

Claims (6)

  1. Curable composition for manufacturing non-planar fiber concrete elements, which essentially comprises cement, possibly another binder, sand, possibly quartz, organic fibers, fumes of silica or metakaolin or equivalent, adjuvants, and water so that the ratio of quantity of water to quantity of cement and any other binder is of the order of 0.2 0.3, characterized in that the adjuvants comprise: - components (A) chosen for that the tensile strength of the concrete increases faster than the tensile stresses during setting, of the components (B) chosen to reduce the elastic modulus of the concrete during setting, - as necessary to restore a more continuous particle size components (C) chosen without bearing to create micro-bubbles in the concrete   air of varied and stable diameter.   2. Composition according to claim 1 and which comprises for lm3 of hardened concrete, 20 to 60 kg of components (A), 5 to   kg of components (B) and 0-2kg of components (C).   3. Composition according to claim 1 or 2, in which the components (A) comprise a non-retardant superplasticizer associated with a setting accelerator. 4. Composition according to claim 3, in which a superplasticizer based on polycarboxylic ether is used. 5. Composition according to claim 3 or 4, in which _ an optionally chlorinated setting accelerator is used.   6. Composition according to one of claims 1 to 5,   in which the components (B) comprise acrylic, vinyl or styrydene-butadiene-based resins, in   emulation with globules a few microns in diameter.   7. Composition according to one of claims 1 to 6,   in which the components (B) comprise salts   fatty acids such as stearates or oleates.   _ Composition according to one of claims 1 to 7,   in which the adjuvants (C) comprise surfactants based on alkaline abietates, soaps   alkalis of fatty acids or equivalent salts.   _ Composition according to one of claims 1 to 8 and   which includes, for lm3 of hardened concrete: - cement: 500 to 900 kg - silica fumes, metakaolin or particle size equivalent: 50 to 200 kg - fine sand and quartz: 1700 to 950 kg organic fibers: 10 to 45 kg - additives (A ): 20-60 kg additives (B): 5-20 kg additives (C): 0-2 kg - addition water: 150 190 kg 10. Process for the production of non-planar concrete elements, into which we pour in a mold or formwork, a   composition according to one of claims 1 to 9, and in   which we compress the fresh concrete during outlet.   11. Concrete elements produced by molding or   casting of a composition according to one of claims 1   to 9 and / or by the implementation of a process according to the claim 10.