U.S. patent application number 12/086062 was filed with the patent office on 2009-12-10 for concrete floor device.
Invention is credited to Jorgen Falk, Thomas Johansson, Markus Peterson, Peter Svenmar.
Application Number | 20090301009 12/086062 |
Document ID | / |
Family ID | 38091665 |
Filed Date | 2009-12-10 |
United States Patent
Application |
20090301009 |
Kind Code |
A1 |
Falk; Jorgen ; et
al. |
December 10, 2009 |
Concrete Floor Device
Abstract
A concrete floor assembly is disclosed including a subfloor
element with a floor side and a ground/ceiling side, and a top
casting layer. In at least one embodiment, the subfloor element
includes a concrete portion on the floor side, which concrete
portion has a bottom casting surface with a surface roughness. The
top casting layer includes a casting composition, which includes a
self-compacting concrete and a shrinkage reducing admixture. The
top casting layer is cast on the floor side of the subfloor element
so that at least a portion of the bottom casting surface is covered
by the top casting layer, the bottom casting surface having such
surface roughness that the top casting layer adheres to the bottom
casting surface. A method of providing such a concrete floor
assembly is also disclosed, as well as a floor assembly.
Inventors: |
Falk; Jorgen; (Malmo,
SE) ; Johansson; Thomas; (Solna, SE) ;
Peterson; Markus; (Solna, SE) ; Svenmar; Peter;
(Lund, SE) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 8910
RESTON
VA
20195
US
|
Family ID: |
38091665 |
Appl. No.: |
12/086062 |
Filed: |
December 5, 2006 |
PCT Filed: |
December 5, 2006 |
PCT NO: |
PCT/SE2006/001385 |
371 Date: |
September 4, 2008 |
Current U.S.
Class: |
52/220.1 ;
52/250; 52/742.14; 52/745.05 |
Current CPC
Class: |
E04B 5/043 20130101;
C04B 2111/00612 20130101; C04B 28/02 20130101; C04B 2111/60
20130101; C04B 2111/00103 20130101; C04B 40/04 20130101; C04B 40/04
20130101; C04B 41/5323 20130101; C04B 14/22 20130101; C04B 41/5323
20130101; C04B 2111/62 20130101; E04B 5/38 20130101; C04B 28/02
20130101; C04B 14/28 20130101; C04B 28/02 20130101; E04F 15/12
20130101; E04B 5/17 20130101 |
Class at
Publication: |
52/220.1 ;
52/250; 52/745.05; 52/742.14 |
International
Class: |
E04B 5/48 20060101
E04B005/48; E04B 5/32 20060101 E04B005/32 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 6, 2005 |
SE |
0502666-1 |
Claims
1. A concrete floor assembly, comprising: a subfloor element with a
floor side and a ground/ceiling side; and a top casting layer,
wherein the subfloor element includes a concrete portion on the
floor side, the concrete portion including a bottom casting surface
with a surface roughness, the top casting layer including a casting
composition which comprises a self-compacting concrete and a
shrinkage reducing admixture, and wherein the top casting layer is
cast on the floor side of the subfloor element so that at least a
portion of the bottom casting surface is covered by the top casting
layer, and wherein the bottom casting surface has such surface
roughness that the top casting layer adheres to the bottom casting
surface.
2. A concrete floor assembly as claimed in claim 1, wherein the
surface roughness of the bottom casting surface, when measured
according to the Swedish Standard for determination of surface
roughness SIS812005, is S>1.5.
3. A concrete floor assembly as claimed in claim 1, wherein the
bottom casting surface is seeded with granular material.
4. A concrete floor assembly as claimed in claim 1, wherein the
bottom casting surface is treated by a surface roughening
method.
5. A concrete floor assembly as claimed in claim 4, wherein the
bottom casting surface is brushed and/or combed.
6. A concrete floor assembly as claimed in claim 4, wherein the
bottom casting surface is embossed.
7. A concrete floor assembly as claimed in claim 4, wherein the
bottom casting surface has exposed aggregate.
8. A concrete floor assembly as claimed in claim 7, wherein coarse
aggregate grains in the exposed aggregate surface of the subfloor
element are exposed at a depth of >1/3 of the maximum size of
the surface aggregate.
9. A concrete floor assembly as claimed in claim 7, wherein coarse
aggregate grains in the exposed aggregate surface of the subfloor
element are exposed at a depth of <1/2 of the maximum size of
the surface aggregate.
10. A concrete floor assembly as claimed in claim 1, wherein at
least one of conduits and electrical installations are embedded in
the top casting layer.
11. A concrete floor assembly as claimed in claim 1, wherein the
bottom casting surface covers substantially the entire floor side
of the subfloor element.
12. A concrete floor assembly as claimed in claim 1, wherein the
top casting layer is cast on substantially the entire floor side of
the subfloor element.
13. A concrete floor assembly as claimed in claim 1, wherein the
maximum thickness of the top casting layer is <100 mm.
14. A concrete floor assembly as claimed in claim 1, wherein the
minimum thickness of the top casting layer is >40 mm.
15. A concrete floor assembly as claimed in claim 1, wherein the
casting composition further comprises a lime filler.
16. A concrete floor assembly as claimed in claim 1, wherein the
subfloor element is a prefabricated element.
17. A concrete floor assembly as claimed in claim 16, wherein the
subfloor element is a hollow core slab.
18. A concrete floor assembly as claimed in claim 1, wherein the
self-compacting concrete has a slump-flow of >520 mm.
19. A floor structure for construction works comprising a concrete
floor assembly as claimed in claim 1.
20. A method of making a concrete floor assembly comprising:
providing a subfloor element having a floor side and a
ground/ceiling side, the subfloor element including a concrete
portion on the floor side, the concrete portion including a bottom
casting surface with a surface roughness; providing a casting
composition which comprises a self-compacting concrete and a
shrinkage reducing admixture; and casting the casting composition
on the floor side of the subfloor element so that a top casting
layer forms which covers at least a portion of the bottom casting
surface, the bottom casting surface having such surface roughness
that the top casting layer adheres to the bottom casting
surface.
21. A method as claimed in claim 20, further comprising applying a
membrane curing compound to the top casting layer.
22. A method as claimed in claim 20, further comprising
pre-moistening the subfloor element before the step of casting the
casting composition.
23. A method as claimed in claim 20, further comprising bull
floating the top casting layer.
24. A method as claimed in claim 20, wherein the providing of a
subfloor element comprises seeding the bottom casting surface with
granular material.
25. A method as claimed in claim 20, wherein the providing of a
subfloor element comprises treating the bottom casting surface by a
surface roughening method.
26. A method as claimed in claim 25, wherein the treating of the
bottom casting surface by a surface roughening method comprises at
least one of brushing and combing the bottom casting surface.
27. A method as claimed in claim 25, wherein the treating of the
bottom casting surface by a surface roughening method comprises
embossing the bottom casting surface.
28. A method as claimed in claim 25, wherein the treating of the
bottom casting surface by a surface roughening method comprises
exposing the aggregate of the bottom casting surface.
29. A method as claimed in claim 28, wherein the providing of a
subfloor element comprises casting the subfloor element in
concrete, applying a retarding admixture to a surface of the floor
side before curing of the subfloor element, and cleaning the
surface of mortar after curing of the subfloor element, thus
exposing the aggregate of the surface.
30. A method as claimed in claim 20, further comprising arranging
conduits or electrical installations on the subfloor element before
the casting of the casting composition, and wherein the casting of
the casting composition comprises embedding of conduits or
electrical installations in the top casting layer.
31. A method as claimed in claim 20, wherein the casting
composition is cast with a thickness of <100 mm at its thickest
point.
32. A method as claimed in claim 20, wherein the casting
composition is cast with a thickness of >40 mm at its thinnest
point.
33. A method as claimed in claim 20, wherein the self-compacting
concrete has a slump-flow of >520 mm.
34. A method of making a floor assembly for a floor structure in
construction works comprising: providing subfloor elements which
have a floor side and a ground/ceiling side and comprise a concrete
portion on the floor side, the concrete portion including a bottom
casting surface with a surface roughness; providing a casting
composition comprising a self-compacting concrete and a shrinkage
reducing admixture; joining the subfloor elements to form a
subfloor unit; casting the casting composition on the subfloor unit
by covering at least portions of the bottom casting surfaces, the
bottom casting surfaces having such surface roughness that the top
casting layer adheres to the bottom casting surface, thereby
forming a top casting layer with a flat upper side which has a
desired inclination.
35. A method as claimed in claim 34, wherein the providing of a
subfloor element comprises exposing the aggregate of the bottom
casting surface.
36. A method as claimed in claim 34, further comprising arranging
conduits or electrical installations on the subfloor unit before
the casting of the casting composition, and wherein the casting of
the casting composition comprises embedding of conduits or
electrical installations in the top casting layer.
37. A method as claimed in claim 34, wherein the casting
composition is cast over substantially the entire subfloor
unit.
38. A method as claimed in claim 34, wherein the casting of the
casting composition comprises pumping out the casting composition
over the subfloor unit.
39. A method as claimed in claim 34, wherein the casting of the
casting composition comprises levelling of the top casting
layer.
40. A concrete floor assembly as claimed in claim 1, wherein the
bottom casting surface is seeded with granular material.
41. A concrete floor assembly as claimed in claim 1, wherein the
bottom casting surface is treated by a surface roughening
method.
42. A method as claimed in claim 21, further comprising
pre-moistening the subfloor element before the step of casting the
casting composition.
43. A method as claimed in claim 21, further comprising bull
floating the top casting layer.
44. The method of claim 34, wherein the desired inclination is
horizontal.
45. A method as claimed in claim 35, further comprising arranging
conduits or electrical installations on the subfloor unit before
the casting of the casting composition, and wherein the casting of
the casting composition comprises embedding of conduits or
electrical installations in the top casting layer.
46. A method as claimed in claim 35, wherein the casting
composition is cast over substantially the entire subfloor
unit.
47. A method as claimed in claim 35, wherein the casting of the
casting composition comprises pumping out the casting composition
over the subfloor unit.
48. A method as claimed in claim 35, wherein the casting of the
casting composition comprises leveling of the top casting layer.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to a concrete floor device or
assembly and to a method of providing such a concrete floor element
as well as a method of providing a floor assembly.
TECHNICAL BACKGROUND OF THE INVENTION
[0002] A floor structure is a substantially horizontal, structural
element which separates different storeys of a building, or the
ground floor of the house and the ground. In addition to a
structural element, the so-called structural floor, a floor
structure also includes floor and ceiling. The structural floor is
part of the structural framework of a building and its main
function is to carry the load of the storey, such as the floor, the
ceiling, interior walls and fittings, and to transfer the weight of
this load to structural walls and columns.
[0003] A floor structure must satisfy a number of requirements. It
must have the capacity to carry the load of the storey and have
sufficient stiffness, so that the deflections (the resilience) are
minimised and do not damage, for instance, the interior walls and
fittings. A floor structure should furthermore satisfy specific
requirements regarding fire resistance and acoustic and thermal
insulation. Sometimes it should also have the capacity to include
conduits or electrical installations.
[0004] A prior-art floor structure comprises prefabricated
structural concrete elements with longitudinal holes, so-called
hollow core slabs. Several hollow core slabs can be joined to form
a hollow core floor. These hollow core slabs have increased
stiffness and strength by being provided with pretensioned
reinforcement which gives the hollow core slabs a curved shape. Due
to this curvature, it is usually not possible to lay a floor
directly on top of them.
[0005] There are several systems on the market for providing a flat
floor on top of a curved hollow core floor. According to one
system, a plurality of pins are first attached at equal distance
over the hollow core floor. Then carefully levelled joists are
attached to the pins, so that the joists form a horizontal base for
a parquet floor or a subfloor in the form of, for instance,
chipboard. The mounting height of the joists can be selected so as
to leave enough room for electric or water conduits under the
floor. One disadvantage of this system is that it requires much
work and is time-consuming. In addition, it is difficult to achieve
high precision, which may result in a resilient or inclined
floor.
[0006] Another system for providing a flat base for floor laying is
application of so-called screed to the hollow core floor. One
disadvantage of the use of screed is that it is expensive. Thus, it
is not desirable to apply screed in layers that are thick enough
for the embedment of electric or water conduits. In addition, it is
difficult to predict how well the screed will dry out and how long
it will take for the screed to dry when applied in such thick
layers. If the base is not dry enough when the floor is laid (for
instance a parquet or a plastic carpet), the floor can be damaged
by the moisture or mildew problems can arise.
[0007] Experimental studies have also been carried out using
ordinary concrete instead of screed. They have shown that if
ordinary concrete is cast on a prefabricated hollow core slab in
layers thinner than 100 mm, problems arise in the adhering of the
concrete to the base both centrally and along the edges due to loss
of bond and edge lifting, respectively. This is above all due to
the fact that thin layers have a high moisture gradient, which
causes the surface layer to bend. In most cases, it is not possible
to use concrete layers with sufficient thickness to avoid these
problems, since this requires such large volumes that also the use
of ordinary concrete would be too expensive. It is also a problem
that thick concrete layers need a long time to dry out, which
delays the construction process, thus also making it more
expensive.
SUMMARY OF THE INVENTION
[0008] Therefore object of the present invention is to provide a
concrete floor assembly, which makes it possible to lay a flat
floor in a cost-effective manner and at a desired vertical level,
and to provide a method of making such a concrete floor assembly
and a method of making a floor assembly.
[0009] According to the invention, these objects are achieved by a
concrete floor assembly and methods according to claims 1, 20 and
34.
[0010] The concrete floor assembly according to the invention
comprises a subfloor element with a floor side and a ground/ceiling
side, and a top casting layer. The subfloor element comprises a
concrete portion on the floor side and the concrete portion has a
bottom casting surface with a surface roughness. The top casting
layer comprises a casting composition, which comprises a
self-compacting concrete and a shrinkage reducing admixture. The
top casting layer is cast on the floor side of the subfloor element
so that at least a portion of the bottom casting surface is covered
by the top casting layer, the bottom casting surface having such
surface roughness that the top casting layer adheres to the bottom
casting surface.
[0011] Owing to a sufficient surface roughness of the bottom
casting surface of the subfloor element, good adhesion is obtained.
Thereby, the invention allows the use of a casting composition
based on a self-compacting concrete provided it contains a
shrinkage reducing admixture. Such a casting composition is much
more economical than prior-art screed. Due to the good adhesion to
the subfloor element and the shrinkage reducing admixture, it is
possible, according to the invention, to cast a layer that is
sufficiently thick to satisfy the acoustic insulation requirements
and the requirements regarding embedment of conduits, but not so
thick that unnecessary amounts of material are consumed.
Furthermore, the casting composition, which according to the
invention is based on a self-compacting concrete, advantageously
requires little labour input since it does not, as ordinary
concrete, have to be vibrated, but spreads itself substantially
horizontally. According to the invention, a flat upper surface is
thus provided, also without the use of screed. Owing to a
cost-effective casting composition and a rational application
method, the concrete floor assembly according to the invention is
thus much more cost-effective than conventional alternatives.
[0012] The concrete floor assembly according to the invention is
intended to be part of a floor structure for construction works,
for instance buildings, such as dwelling houses, office or
industrial premises, or structures such as sports centres,
underground cavities or silo buildings.
[0013] The concrete floor assembly according to the invention can
be part of or constitute the entire structural floor of the floor
structure. It can also be a non-structural part of the floor
structure.
[0014] According to the invention, a concrete floor assembly is
thus a portion of a floor structure, which portion forms a base
which is suitable for floor laying or which itself can function as
a floor.
[0015] The term subfloor element here means an element cast on the
spot or a prefabricated element. The subfloor element can extend
over the entire floor of a room or over the entire floor of a
storey, but it can also be a slab with limited extension. The
subfloor element has a floor side and a ground/ceiling side. The
floor side is the side which in normal use is part of the base of a
floor. The ground/ceiling side is the side which in normal use is
facing the ceiling of a lower storey or the ground if the subfloor
element belongs to the ground floor.
[0016] According to an embodiment of the invention, the subfloor
element is a structural prefabricated hollow core slab. Several
such hollow core slabs can be joined together so as to extend over
an entire storey.
[0017] According to an embodiment of the invention, the subfloor
element is a hollow core slab with pretensioned reinforcement. Due
to the prestress, such hollow core slabs are usually curved, that
is they have an arched longitudinal section. By casting the top
casting layer according to the invention on the arched floor side
of the hollow core slab, the concrete floor assembly can be given a
flat floor side that is suitable as a base for floor laying.
[0018] If the subfloor element has a curvature, or in other words
an arched cross-section, and the top casting layer is such that the
concrete floor assembly has a flat floor side, the thickness of the
top casting layer will vary over the cross-section. Its smallest
thickness is where the curve of the arch is at its maximum.
Usually, such a subfloor element has its smallest thickness
approximately at the centre and its greatest thickness at two
opposite edge sides.
[0019] The subfloor element according to the invention can be made
of concrete or reinforced concrete, but it can also comprise other
materials. According to the invention, at least a portion of the
floor side of the subfloor element has a concrete surface of which
at least a portion constitutes a bottom casting surface. The bottom
casting surface is intended to interact with the casting
composition.
[0020] According to the invention, the bottom casting surface has
such surface roughness that the top casting layer adheres to the
bottom casting surface. This means that the casting composition
forms a top casting layer with desired thickness over at least part
of the bottom casting surface of the subfloor element, the top
casting layer adhering to the bottom casting surface so that the
requirements of the building sector are met, for instance, those
referring to loss of bond and edge lifting and those referring to
the strength of the adhesion area between the subfloor element and
the top casting layer.
[0021] According to an embodiment of the invention, the bottom
casting surface has a surface roughness which, when measured
according to the Swedish Standard for determination of surface
roughness SIS812005, is preferably S>1.5. Reference is made to
this Standard, for instance, in the Swedish concrete code
(BBK04).
[0022] According to the invention, this surface roughness can be
obtained by any suitable method. One example is to seed the bottom
casting surface with granular material, such as crushed stone
material. Examples of particle sizes are 2-4 mm or 4-8 mm.
[0023] Another example of providing a bottom casting surface with a
rough surface structure is, according to the invention, to treat
the bottom casting surface by a surface roughing method. By this is
meant any optional method that removes, transfers and/or compacts
material unevenly over the surface so as to make the surface rugged
or, in other words, rough.
[0024] According to an embodiment of the invention, the bottom
casting surface is brushed or combed. This can suitably be
performed in connection with the manufacturing of the subfloor
elements, by a brush or comb being attached to a casting machine.
In such a method, it may sometimes be desirable to remove possible
loose material originating from the brushing/combing from the
bottom casting surface before the casting of the top casting layer.
By this means, the adhesion properties are further improved.
[0025] According to an embodiment of the invention, the bottom
casting surface is embossed. This can, for instance, be achieved by
a rotating cylinder or several rotating wheels which are attached
to a casting machine in connection with the manufacturing of the
subfloor elements.
[0026] According to an embodiment of the invention, at least a
portion of the floor side of the subfloor element has a concrete
surface with a bottom casting surface which has exposed
aggregate.
[0027] In this application, "exposed aggregate" means that surface
skin, surface silt and fine aggregate particles have been removed
from the concrete surface so that coarse aggregate protrudes.
[0028] Such exposed aggregate surfaces are known to provide
aesthetical effects. However, according to the embodiment of the
invention, the exposed aggregate is used to increase the surface
roughness of the surface of the subfloor element. Increased
roughness of the surface of the subfloor element results in
improved adhesion between the subfloor element and the top casting
layer, which reduces the risk of loss of bond and edge lifting.
Another positive effect is that the upper surface is also
strengthened since loose mortar is removed. Thus, the exposure of
aggregate according to this embodiment provides two properties
which are beneficial for the adhesion of the top casting layer to
the subfloor element, that is increased surface roughness and
strong concrete in the joint.
[0029] According to the invention, substantially the entire floor
side of the subfloor element can have exposed aggregate or only a
portion thereof. The top casting layer can cover substantially the
entire floor side of the subfloor element or a portion thereof, in
which case at least a portion of the exposed aggregate surface,
i.e. the bottom casting surface, is covered. In some embodiments,
the adhesion of the top casting layer can be sufficient even if the
surface of the subfloor element covered by the top casting layer
does not in its entirety have an exposed aggregate finish.
[0030] According to an embodiment of the invention, the concrete
portion of the subfloor element has a surface with a deep exposure
of aggregate, i.e. aggregate in the concrete surface is exposed to
such depth that the coarse aggregate grains appear clearly. The
depth can be greater than 1/3 of the maximum size of the surface
aggregate.
[0031] According to an embodiment of the invention, a membrane
curing compound is applied to the top casting layer so that the
after-curing proceeds under the effect of the membrane curing
compound. Membrane curing compounds or (liquid membrane curing
compounds) are compounds that delay the drying out of the concrete
during curing. The membrane curing compound forms a thin film over
the newly cast surface so that usually it does not have to be
moistened. Membrane curing compounds with different chemical
compositions, such as wax dispersions, acrylate polymers or latex
emulsions, are commercially available. Preferred membrane curing
compounds comply with the specifications laid down in ASTM C 309,
Liquid Membrane-Forming Compounds for Curing Concrete, for instance
the specifications in this document concerning maximum loss of
moisture. Thanks to the application of the membrane curing compound
to the top casting layer, the top casting layer does not dry out
too quickly during the first hours after casting, whereby plastic
shrinkage cracking in the surface layer is advantageously
avoided.
[0032] According to an embodiment of the invention, the subfloor
element is pre-moistened before the casting of the casting
composition on the subfloor element. This advantageously prevents
water from the casting composition from being absorbed into the
subfloor element, which would reduce the strength of the layer of
the top casting layer that is closest to the subfloor element.
[0033] According to an embodiment of the invention, a plurality of
subfloor elements are joined together to form a subfloor unit with
or without the aid of interconnecting means. The subfloor elements
can, for instance, be joined by grouting but the subfloor elements
can also be loosely placed next to each other or be attached to
each other or to a base. Subsequently, the casting composition is
cast so that a top casting layer forms which extends over several
subfloor elements, whereby a floor assembly according to the
invention is provided. According to an embodiment, substantially
the entire floor side of the subfloor elements has exposed
aggregate and the top casting layer extends over substantially the
entire subfloor unit. Owing to the self-levelling properties of the
casting composition, it is thus possible to provide a flat base for
floor laying by one single casting of a layer. In addition,
electric and/or water conduits can be embedded in the top casting
layer.
[0034] In some construction projects, use is made of prefabricated
wall elements in which windows are already mounted. Furthermore,
the construction process is sometimes such that also the ceiling is
applied before a method of providing a flat base is initiated. In
such constructions, it is possible, according to an embodiment of
the invention, to seal door openings and bushings, if any, in the
wall elements, for instance, by means of plastics so that a
relatively airtight room is obtained. Only thereafter, the top
casting layer is applied. Hereby, the moisture evaporated from the
top casting layer can be maintained in the sealed room, which
delays the drying out of the top casting layer. Owing to the slower
drying-out process, plastic shrinkage cracking in the top casting
layer can be avoided. It is often sufficient to keep the room
airtight for about 24 hours.
[0035] The inventive casting composition comprises a
self-compacting concrete and a shrinkage reducer. Self-compacting
concrete is compacted homogenously under its own weight and fills
formwork without using the vibratory unit required for ordinary
concrete. This makes it possible to obtain a rational casting
process without vibrating, which is less time-consuming and
requires less manpower. The concrete will also be self-levelling,
which means that it does not have to be coated with screed before
the floor is laid, which is a great saving in costs.
Self-compacting concrete and various types thereof are described in
The European Guidelines for Self-Compacting
Concrete--Specification, Production and Use, May 2005, issued by
the Self-Compacting Concrete European Project Group, with
representatives from BIBM, CEMBUREAU, ERMCO, EFCA and EFNARC.
[0036] Concrete mainly consists of mineral particles (aggregate) of
different grain sizes which are bonded by cement paste consisting
of cement and water. A common mixing ratio based on parts by volume
is one part water, one part cement, two parts sand and three parts
coarse aggregate. Admixtures modifying the properties of the
concrete in various ways can also be included. In general, in the
case of self-compacting concrete, the ratio of fine aggregate (e.g.
sand and gravel) is greater, and the ratio of coarse aggregate
(e.g. stone material) is smaller, than in traditional concrete. It
is also common to use fine-particle material in self-compacting
concrete, such as lime or glass filler. A common admixture in
self-compacting concrete is commercially available water reducing
agents, so-called superplasticisers, which can make the
self-compacting concrete plastic and workable.
[0037] According to an embodiment of the invention, the
self-compacting concrete has a slump-flow of >520 mm, preferably
>650 mm. The measurement of slump-flow is a test to assess the
flowability of self-compacting concrete in the absence of
obstructions. It is based on the slump test described in EN
12350-2. The result is an indication of the filling ability of the
self-compacting concrete. Slump-flow is thus the mean diameter of
the spread of fresh concrete using a conventional slump cone. The
measuring of slump-flow is defined in Annex B.1 of The European
Guidelines for Self-Compacting Concrete--Specification, Production
and Use and is summarised below. [0038] Prepare the cone and
baseplate as described in EN 12350-2. [0039] Place the cone
coincident with the 200 mm circle on the baseplate and hold in
position by standing on the foot pieces (or use the weighted
collar), ensuring that no concrete can leak from under the cone.
[0040] Fill the cone without any agitation or rodding, and strike
off surplus from top of the cone. Allow the filled cone to stand
for not more than 30 s. During this time remove any spilled
concrete from the baseplate. Ensure the baseplate is damp all over
but without any surplus water. [0041] Lift the cone vertically in
one movement without interfering with the flow of concrete. Without
disturbing the baseplate or the concrete, measure the largest
diameter of the concrete flow and measure the diameter of the flow
spread at right angles to the largest diameter. [0042] The
slump-flow is the mean of the two measured diameters.
[0043] Self-compacting concrete can have a very high tendency to
shrink due to a small amount of coarse aggregate and a large amount
of fine material and/or lime filler, which can be used to make the
concrete self-compacting. To reduce shrinkage and thus the risk of
loss of bond and edge lifting, shrinkage reducing admixtures are
used. Such shrinkage reducing admixtures comprise, for instance,
various types of alcohols. They are supposed to primarily reduce
the surface tension of the pore water, whereby the shrinkage
tensions in the concrete are reduced. Shrinkage reducing admixtures
are commercially available and a person skilled in the art can
choose a suitable agent based on the composition of the concrete
and its shrinkage tendency, etc. A suitable shrinkage reducing
admixture can comprise a polyalcohol, preferably
2,2-dimethylpropane-1,3-diol.
[0044] Lime fillers contribute to the self-compacting properties of
the concrete. Lime fillers have also been found to accelerate the
drying-out process due to their effect on the structure of the pore
system. The accelerated drying-out allows concrete comprising lime
filler to comply with the relative humidity (RH) requirements on
concrete before carpeting. Lime fillers are commercially available
in a number of qualities. For the inventive use, it has been found
that a lime filler, for instance a crystalline limestone filler,
with a mean particle size of <0.05 mm, preferably 0.025-0.05 mm,
provides the desired combination of contributions to the
self-compacting properties of the concrete and to the accelerated
drying-out.
[0045] The high amount of fine material in self-compacting concrete
increases the water requirement, which further increases the
shrinkage tendency. Self-compacting concrete for use according to
the invention has a water-cement ratio of >0.5, preferably
>0.55.
[0046] By exploiting the positive effect of lime fillers on the
drying-out process, quick drying-out can be achieved according to
the invention without reducing the water-cement ratio, which could
have increased the risk of loss of bond and edge lifting. Owing to
the quick drying-out of the casting composition, the floor laying
is not delayed and a quick and efficient construction process can
be maintained.
[0047] Thus, an embodiment of a concrete floor assembly according
to the invention comprises a subfloor element with a floor side and
a ground/ceiling side, and a top casting layer. The subfloor
element comprises a concrete portion on the floor side and the
concrete portion has an exposed aggregate surface, and the top
casting layer comprises a casting composition which comprises a
self-compacting concrete and a shrinkage reducing admixture. The
top casting layer is cast on the floor side of the subfloor element
so that at least a portion of the exposed aggregate surface is
covered by the top casting layer.
[0048] Due to the exposed aggregate surface of the subfloor
element, which allows good adhesion, it has been found possible,
according to this embodiment of the invention, to use a casting
composition based on a self-compacting concrete if it contains an
admixture of a shrinkage reducer. Such a casting composition is
considerably more economical than prior-art screed. According to
the invention, the good adhesion to the subfloor element and the
shrinkage reducing admixture make it possible to cast a layer that
is sufficiently thick to comply with the requirements on acoustic
insulation and the requirements on the embedment of conduits, but
not so thick that an unnecessary amount of material is consumed.
Advantageously, the casting composition, which according to the
invention is based on a self-compacting concrete, requires little
labour input since it does not, as ordinary concrete, have to be
vibrated but spreads itself substantially horizontally. Thus,
according to the invention, a flat upper surface is provided, also
without the use of screed. Thanks to an economical casting
composition and a rational application method, the concrete floor
assembly according to the invention is thus considerably more
cost-effective than the conventional alternatives.
[0049] Furthermore, an embodiment of a method of making a concrete
floor assembly according to the invention comprises the steps of
providing a subfloor element having a floor side and a
ground/ceiling side, the subfloor element comprising a concrete
portion on the floor side, which concrete portion has an exposed
aggregate surface, providing a casting composition which comprises
a self-compacting concrete and a shrinkage reducing admixture,
casting the casting composition on the floor side of the subfloor
element so that a top casting layer forms which covers at least a
portion of the exposed aggregate surface.
[0050] Finally, an embodiment of a method of making a floor
assembly for a floor structure in construction works comprises
according to the invention the steps of providing subfloor elements
which have a floor side and a ground/ceiling side and comprise a
concrete portion on the floor side, which concrete portion has an
exposed aggregate surface, providing a casting composition
comprising a self-compacting concrete and a shrinkage reducing
admixture, joining the subfloor elements to form a subfloor unit,
casting the casting composition on the subfloor unit by covering at
least portions of the exposed aggregate surfaces, thereby forming a
top casting layer with a flat upper side which has a desired
inclination, preferably substantially horizontal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0051] The invention will now be described in more detail by way of
examples and with reference to the accompanying drawings.
[0052] FIG. 1 is a schematic longitudinal section view of a
concrete floor assembly according to the invention.
[0053] FIG. 2 is a schematic cross-section view of a concrete floor
assembly according to the invention.
[0054] FIG. 3 is a schematic top plan view of a subfloor element
according to the invention.
[0055] FIG. 4 is a schematic top plan view of a floor assembly
according to the invention, in which part of the Figure shows
joined subfloor elements under the top casting layer.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0056] With reference to FIGS. 1 and 2, a concrete floor assembly
according to the invention is schematically shown. The concrete
floor assembly comprises a subfloor element in the form of a
prefabricated hollow core slab 1. The hollow core slab 1 comprises
longitudinal reinforcement wires 2 that prestress the hollow core
slab 1, whereby it obtains a curved longitudinal section. The
prestress and the curved shape advantageously provide a good
ability to absorb tensions and thus also a good load-carrying
ability. The hollow core slab 1 is furthermore formed with
weight-reducing recesses in the form of longitudinal holes 3. The
hollow core slab 1 according to the example is 10 m.times.1.20
m.times.0.265 m.
[0057] The hollow core slab 1 has a floor side 9 which in use is an
upper side and a ground/ceiling side 10 which in use is an
underside. The hollow core slab 1 has an arched shape, the
curvature being directed upwards in use. If the hollow core slab 1
is placed on a flat base, the difference in height of the upper
side 9 of the hollow core slab 1 above the base measured at half
the length of the hollow core slab 1 and at its short ends is 15
mm.
[0058] The hollow core slab 1 is made of a prior-art concrete mix
also comprising coarse aggregate grains 5 with a diameter of about
12 mm. The hollow core slab 1 has a concrete surface that covers
the entire floor side 9, and in the shown example the entire
concrete surface of the floor side 9 forms a bottom casting surface
which has been provided with a desired roughness by aggregate
exposure, cf. FIG. 3. The concrete surface has deep aggregate
exposure, down to a depth corresponding to about half the diameter
of the coarse aggregate. In this example, the depth of aggregate
exposure is 6 mm.
[0059] A top casting layer 6 is cast on the arched floor side 9 and
covers the floor side 9 over its entire exposed aggregate surface
4. The top casting layer 6 has a substantially flat upper side 7
facing away from the exposed aggregate surface. When using the
hollow core slab 1 according to the shown example in a floor
structure, the upper side 7 of the top casting layer 6 is
horizontal. Furthermore, conduits 8 for electric cables are
embedded in the top casting layer 6. In the shown example, the top
casting layer 6 has a thickness of 55 mm at the smallest
cross-section where the curve formed by the hollow core slab 1 has
its maximum and a thickness of 70 mm at the short ends of the
hollow core slab 1.
[0060] According to the invention, the top casting layer comprises
a casting composition based on a self-compacting concrete. The
casting composition can, for instance, comprise the following
materials:
TABLE-US-00001 Materials Amount (kg/m.sup.3) Building cement
250-500 Lime filler 50-200 Sand 0-2 mm 400-700 Gravel 0-8 mm
500-1000 Stone material 8-11 mm 400-700 Water reducing agent 0.1-10
Shrinkage reducing admixture 0.1-10 Water 100-500
[0061] A preferred casting composition has the following
composition:
TABLE-US-00002 Amount Manufacturer/ Materials (kg/m.sup.3) supplier
Building cement 385 Cementa Lime filler "Limus 40" 135 Nordkalk
Sand 0-2 mm (Ro) 586 Skanska Gravel 0-8 mm (Enkoping) 747 Skanska
Stone material 8-11 mm (Vallsta) 598 Skanska Water reducing agent
"Evo 26" 2.7 Sika Shrinkage reducing admixture 5.8 Sika "Control
40" Water 207
[0062] The invention also relates to a floor structure comprising
at least one concrete floor assembly according to the invention.
With reference to FIG. 4, such a floor structure can, according to
the invention, comprise a floor assembly according to the
invention, which can be obtained in the following manner.
[0063] First, a subfloor element is manufactured in the form of a
hollow core slab 1 with an exposed aggregate surface 4. The hollow
core slab 1 is cast in prior-art concrete and comprises a
prestressed reinforcement 2. To obtain the exposed aggregate
surface 4 of the hollow core slab 1, a retarding admixture (in
liquid form) is applied before curing of the hollow core slab. This
means that curing is delayed down to a depth of 6 mm, which has
been selected in consideration of the fact that the aggregate
grains have a maximum diameter of 12 mm. The hollow core slabs are
then high-pressure washed, which means that the surface layer is
"cleaned" of cement paste, i.e. the aggregate is exposed and a
rough and clean surface 4 appears. In this example, the entire
floor side 9 of the hollow core slab 1 has exposed aggregate.
[0064] A plurality of such hollow core slabs are subsequently
transported to the desired building site.
[0065] The hollow core slabs 1 are joined together on site to form
a subfloor unit, which in this example extends over a storey and in
which all the floor sides 1 of the hollow core slabs are upwardly
directed. The hollow core slabs 1 are joined by grouting. In other
embodiments of the invention, it may be sufficient to place the
hollow core slabs adjacent to each other or to attach them to each
other or to a base in some other convenient manner. The curved,
arched longitudinal section of the joined hollow core slabs 1 gives
the upper side of the subfloor unit a waveform. Furthermore, owing
to the exposed aggregate floor side 9 of the hollow core slabs, the
entire floor side of the subfloor unit has exposed aggregate.
[0066] Subsequently, conduits 8 are placed over the subfloor unit
in a desired pattern.
[0067] Furthermore, a casting composition according to the above
formula is mixed and supplied to the building site.
[0068] The ready-mixed casting composition is pumped out over the
subfloor unit so that the conduits 8 are covered and the desired
thickness, for instance with regard to acoustic insulation class,
is obtained. Before that, the subfloor unit has been slightly
pre-moistened. The casting composition forms a top casting layer 6
which covers the entire upper side of the subfloor unit and the
conduits 8. The casting composition is self-levelling, which means
that it compacts under its own weight, which makes vibration
unnecessary. Moreover, the casting composition spreads so that the
top casting layer obtains a substantially horizontal surface.
[0069] When spreading, use is made of a laser, to obtain the
desired vertical level, and by bull floating, to obtain plane and
smooth surfaces. Bull floating means that the concrete surface is
treated by a so-called bull float. Usually, a bull float consists
of a board or a plastic tube provided with a handle. The surface is
easy to work manually so that a plane and smooth surface is
obtained. The top casting layer finally has a thickness of 55 mm at
its thinnest point and a thickness of 70 mm at the short ends of
the hollow core slab 1.
[0070] In other embodiments, it is, of course, possible to perform
levelling and smoothing by other suitable methods.
[0071] Before the top casting layer has cured, a membrane curing
compound is injected over the surface of the top casting layer.
This is done immediately after the free water has disappeared from
the concrete surface, usually within an hour after casting. Owing
to this, the after-curing of the top casting layer proceeds under
the action of the membrane curing compound, whereby plastic
shrinkage cracking in the surface layer is advantageously
avoided.
[0072] Due to the lime fillers of the casting composition, it is
possible, according to the invention, to obtain quick drying out
and the relative humidity (RH) requirements on concrete before
carpeting can be complied with and long waiting times in the
construction process are avoided.
[0073] According to the invention, a separate concrete floor
assembly can also be provided by the above-described method.
* * * * *