US20180134620A1

US20180134620A1 - Concrete mix designs using a plurality of reinforcement fibers systems

Info

Publication number: US20180134620A1
Application number: US15/573,391
Authority: US
Inventors: Jeremy ESSER; Davide Zampini; Alexandre GUERINI; Giovanni VOLPATTI
Original assignee: Cemex Research Group AG
Current assignee: Cemex Research Group AG
Priority date: 2015-06-11
Filing date: 2016-06-10
Publication date: 2018-05-17
Also published as: MX2017015570A; CR20170561A; BR112017025418A2; US20180111876A1; EP3307692A1; CO2017012578A2; IL255597A; EP3307691A1; WO2016198108A1; US10259747B2; IL255598B; MX2017015680A; CO2017012589A2; US20180141867A1; WO2016198603A1; MA43201A; EP3307692B1; CR20170560A; EP3307690A1; ES2764135T3

Abstract

A concrete mix having sand, fine aggregates, binder, fibers, and various admixtures is provided. The mix has a consistency from S2 to SF3, a compressive strength in the range of 30-80 MPa and a ductility represented by fc, ffl, fR1 and fR3 values, wherein the concrete mix contains at least 390 Kg of binder, the concrete mix has a paste volume of 300-600 liters, the concrete mix contains at least two systems of fibers and a general admixture system that is composed of at least 2 sub-admixture systems.

Description

FIELD OF THE INVENTION

The present invention relates to concrete formulations for high mechanical performances in structural designs, fiber reinforcement special mix designs to limit or avoid steel rebars or pre-stressing. More specifically, the invention discloses concrete mix designs with high volumetric content of fibers and that the concrete contains different types of fibers to form a so-called hybrid fiber system.

BACKGROUND OF THE INVENTION

Conventional fiber reinforced concrete technology is known, it has been described in various National and International Norms e.g. RILEM 162 TDF International), Model Code 2010 (International), CNR DT 204 (Italy SS 812310 (Sweden), TR63 (UK) ACI 318 (USA) ACI 360 (USA), DBV (Germany), DAFSTB (Austria). Fiber reinforced concrete mix designs containing different types of fibers have been for examples disclosed for example in WO 2011/053103 and more recently in CN102976697 and KR100940550. Such concrete are mainly used for pavement or deck repairs or to minimize the shrinkage of the concrete during hardening.
In WO 2011/053103, the main objective is to provide with a concrete to build large slabs, therefore, one property to be achieved is shrinkage resistance in order to avoid cracks formation. Therefore, shrinkage reducing agents, namely ethylene glycol, free lime or calcium sulfoaluminate, is used in combination with polymer fibers (synthetic fibers) whose role is mainly to reduce cracking due to shrinkage.
According to WO 2011/053103, the workability of the concretes is located in the classes F5 to F6, yet no data are disclosed concerning the workability retention (opening time) of the final concrete produced. Furthermore, no data and results are disclosed concerning the compressive and flexural strength of the concretes according to the invention.
Amongst others, one important disadvantage of the patent application WO 2011/053103 is the requirement to prepare a separate slurry containing water, cement and all shrinkage reducers and plasticizers (or water reducers admixture—namely powdered melamine or phosphonates), or fillers as well as fillers. The slurry is then added to the concrete prepared separately and the fibers are added.
A further important drawback of the invention according to WO 2011/053103 is the fact that the final placed concrete has to be cured using water after placing.
An additional drawback of the invention according to WO 2011/053103 is that the volume of paste is very low to ensure limited shrinkage and avoid cracking, thus reducing the scope of application and placement properties and well as the level of mechanical resistances that can be achieved, both in terms of compressive strength and in terms of flexural strength or ductility. Finally the document does not disclose water/total binder content (kg/kg) others than 0.42 and 0.46, which limits drastically the type of properties that can be achieved.

DESCRIPTION OF THE INVENTION

Relevant information related to Norms and normative tests mentioned in this patent application is described in Tables 1 and 2.

TABLE 1

Consistency of concrete (slump) with respect to EN (European)
and FR (French) Norms and normative tests.

EN 12350-2

NF P 18-305

Consistency	slump [mm]	Consistency	slump [mm]

S1	10 to 40	Stiff	0 to 40
S2	40 to 90	Plastic	50 to 90
S3	100 to 150	highly plastic	100 to 150
S4	160 to 210	fluid	>160
S5	>220

TABLE 2

Consistency of concrete (flow) with respect
to EN 12350-8 (European) Norms
EN 206-1

	category	Flow [mm]

	SF1	550-650
	SF2	660-750
	SF3	760-850

The present invention provides a concrete mix comprising sand, fine aggregates, binder, fibers, and various admixtures, having a consistency from S2 to SF3, a compressive strength in the range of 30-80 MPa and a ductility represented by the following values:
30<fc<80 MPa
3<ffl<12 MPa
3<fR1<12 MPa
2.5<fR3<15 MPa
wherein the concrete mix contains at least 390 Kg of binder, the concrete mix comprises a paste volume of 300-600 liters, the concrete mix contains at least two systems of metallic fibers A1 and A2, the fibers system A1 consists of metallic fibers with a dosage of 25-100 kg/m3 with respect to the concrete mix and have an ultimate resistance of at least 1200 MPa, the fibers system A2 consists of low carbon steel fibers with a wavy shape having carbon content of 0.02-0.15% weight and having yield strength of 350-850 MPa and have a dosage of 10 kg-40 kg by m³of the concrete mix, the concrete mix contains a general admixture system that is composed of at least 2 sub-admixture systems I and II, wherein the first Admixture system I comprises at least 2 polycarboxylic acid co-polymers (PCE), a strong water reducer PCE and a workability retention PCE, wherein the second Admixture system II is a stabilizer obtained from a compound selected from the group consisting of modified cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, natural starch, modified starch, branched modified starch, naturals gums, Xanthan gum, fine silica, colloidal silica, silica fume and any combination thereof, herewith concrete mix of the invention.
The meaning of fc, ffl, fR1 and fR3 is the following (see FIG. 1).
fc is compressive strength, ffl is flexural strength, fR1 is strength for crack mouth opening 0.5 mm, fR2 is strength at CMOD 1.5 mm and fR3 is Strength at CMOD 2.5 mm.
The concrete mix of the invention is for slabs, floors or structural constructions with high ductility and workability retention.
Another embodiment is the concrete mix of the invention, wherein the shape of the wavy fibers of fibers system A2 have an amplitude of 0.5-7 mm and a frequency of 0.5 cm⁻¹-6 cm⁻¹.
Another embodiment is the concrete mix of the invention, wherein the wavy fibers have a length of 25-50 mm.
Another embodiment is the concrete mix of the invention, further comprising fibers system B.
Another embodiment is the concrete mix of the invention, wherein fibers system B have a dosage of 0.03 to 0.2% in volume by m3 of the concrete mix.
The present invention proposes a solution to overcome the various drawbacks of WO 2011/053103. The concrete mix designs according to the present invention are not limited to shrinkage resistance enhancement using shrinkage reducers and synthetic fibers for this unique goal and true structural properties to be used in structural engineering for decks, bridges, pillars, etc. Also, the fiber reinforced fresh concrete mix designs according to the invention are engineered to comply with industrial production requirements, they are produced in conventional concrete mixing plants, can be transported over large distance since they have a high workability retention and do not need special curing techniques once placed.
Also, the present invention enables to provide a concrete presenting a real ductility behavior in fracture, from the matrix cracking point, exhibiting smooth post peak reinforcement without abrupt reduction in mechanical resistance.
Another embodiment is the concrete mix of the invention, further comprising coarse aggregates.
Another embodiment is the concrete mix of the invention, wherein the dosing of the Admixture system I is of 0.5-5% weight percent with respect to the binder content and the dosing of the admixture system II is of 0.1-2% weight percent with respect to the binder. This concrete mix is for high ductile thin slabs or floors with a consistency of S5-SF3.
Another embodiment is the concrete mix of the invention, wherein the dosing of the Admixture system I is of 0.1-1% weight percent with respect to the binder content and the dosing of the admixture system II is of 0.1-0.5% weight percent with respect to the binder. This concrete mix is for high ductile this slabs or floors with a consistency of S2-S4.
Another embodiment is the concrete mix of the invention, wherein the concrete mix comprises an admixture system III, wherein the third Admixture system III is obtained from a compound selected from the group consisting of cellulose microfibers, synthetic waxes, natural waxes, superabsorbing polymers, starch crosslinked polymers, acrylate crosslinked polymers, hexylene glycol (2-Methyl-2,4-pentanediol) and any combination thereof and the dosage of the admixture system Ill is of 0.3-6 weight percent with respect to the binder.
Another embodiment is the concrete mix of the invention, wherein fibers system C, comprising synthetic fibers, is added to the concrete mix.
Another embodiment is the concrete mix of the invention, wherein the dosage of fibers system C is of 0.02% to 2% volume with respect to the concrete.
Another embodiment is the concrete mix of the invention, wherein a part of the sand or the fine aggregates or the coarse aggregates are substituted by lightweight aggregates selected from the group consisting of expanded glass, expanded clay, pumice and expanded shale.
Another embodiment is the concrete mix of the invention, wherein the substitution rate for all aggregates (sand or/and fine or/and coarse aggregates) is at least 30% in volume.
The invention concerns special concrete mix designs to achieve any desired classes of compressive strength, while providing a high ductility and the fresh and hardened stages.
The ductility at hardened stages (28 days) is measured using flexural stress-strain measurement according to Norm EN 14651 (load increase needed to further opening the mouth size of the notch using a CMOD (Crack Mouth Opening Device)).
FIG. 1 shows typical such Load versus Crack Mouth Openings behaviors a fiber reinforced concrete according to the invention.
Table 3 indicates the resistances and ductility values expressed by the strength at various CMOD with respect to norm EN 14 651.

TABLE 3

Various requirements for the mechanical
resistances in fiber reinforced concrete.

Strength requirements

Application for fiber	fc	ffl	fR1	fR3
reinforced concrete	[MPa]	[MPa]	[MPa]	[MPa]

Industrial slab-on-grade	30-60	3-8	2-10	2-10
ICF	40-100	4-10	5-13	3-25
Structural rehabilitation/	80-200	8-15	10-30	15-60
seismic design for
ancient buildings/strengthening
of old structures
Precast industry - bridge segments	60-200	5-15	7-35	15-50
Precast industry - tunnel	30-100	3-8	2-12	2-20
lining segments
Precast industry - new jersey	30-50	3-5	2-8	2-8
Precast industry - pipes	40-80	3-7	4-10	4-10
Precast industry - refractory	40-100	4-9	8-30	5-15
concrete
Columns	30-200	3-10	3-10	5-40

The concrete mix designs according to the invention contain at least 2 Fibers Systems A1 and Fibers System A2 that in combination provides the targeted mechanical properties. The Fibers System A contains only metallic fibers as described in Table 4:

TABLE 4

Characteristics of the Fibers System A1
and A2(high resistance, structural)

	Fibers of Fiber	Fibers of Fiber
	system A1	system A2
	Hooked flattened end	Deformed slit
Geometry	or straight wire,	sheet

E modulus [Gpa]	150-250	150-250
Yielding strength YS	1000-4000	350-850
[MPa]
Ultimate strength US	1200-5000	400-1000
[MPa]
length [mm]	35-100	25-50
Equivalent diameter	na	0.5-3
[mm]
Thickness [mm]		0.5-3
Width [mm]		1-5
Wavy shape	No	Yes
Wave Amplitude A		0.5-7
[mm]
Wave frequency F	no	0.5-6
[cm−1]
length/diameter [—]	30-120	na
Length/equivalent	30-120	10-100
diameter [—] d eq.
coating	no coating	no coating
	or zinc	or zinc
density [kg/m3]	6800-8000	6800-8000

The Fibers system A1 can be prepared with different types of metallic fibers corresponding to the characteristics indicated in Table 4.
The fibers system A2 consists of low carbon (typically 0.02-0.15 weight %) and low silicon (below 0.15 weight %) steel fibers with low mechanical resistance (ultimate strength between 400 and 1000 MPa and yield strength between 350 and 850 MPa) compared to the fibers in fibers system A1, that have been processed to exhibit a wavy geometry as shown in FIG. 2. The parameter A describes the amplitude of the wave and the parameter F describes the frequency of the wave along the fiber length.
The Fibers System B contains high strength fibers that are shorter than the Fibers of Fibers System A1 and is described in table 5.

TABLE 5

Characteristics of the Fiber System B single or
multi-filaments (high resistance, structural)

	Glass	Aram id	Carbon	Basalt	Steel

E modulus [Gpa]	40-100	40-200	100-400	50-500	150-220
Ultimate strength	700-2800	2000-6000	1000-7000	2000-6000	1300-5000
(US) [MPa]
length [mm]	5-60	5-60	0.1-30	5-100	5-35
length/diameter	10-300	30-150	10-1000	10-10000	30-120
coating	no coating	no coating	no coating	no coating	no coating
					or zinc
density [kg/m3]	2000-4000	1200-1600	800-2500	1500-4000	6800-8000

The Fibers System B can be made out of steels fibers, glass fibers, polyaramid, carbon fibers and/or basalt fibers or any combination thereof.
The geometry of the none metallic fiber are normally straight whereas the metallic fibers in system B can be hooked end wire, straight, straight slit sheet or wire, deformed slit sheet or wire, flattened-end slit sheet or wire, machined chip, melt extract, etc. The metallic fibers in fibers system B can be made of amorphous metal.
The fibers in fibers system A2 aim at dispersing energy by plastic deformation of the wavy fibers under deformation and pull out, bridging the micro cracks are providing the strength hardening just after the fracture of the concrete matrix.
The fibers in System A1 are used to bridge macro-cracks and provide ductility by pull-out whereas the fibers in fibers system B have mainly the function to bridge micro cracks to enhance the effect of the fibers in fibers system A2, and delay the micro-cracks propagation with energy dispersion on pull out and further micro-cracking.
Preferably, the fibers in the fibers system A1 are hooked, with an ultimate resistance above 1100 MPa, preferably above 1300 MPa and even more preferably above 1500 MPa.
The ratio length divided by diameter (mm/mm) for fibers in fibers system A1 is typically located between 40 and 100, preferably between 45 and 95.
The fibers in fibers system A2 have a minimum length of 25 mm and a maximum length of 50 mm, the system A2 may contain fibers of different length between 25 mm and 50 mm. The wavy shape of the fibers in fibers system A2 have a frequency located between 0.5 and 6 cm-1, and amplitude located between 0.5 mm and 7 mm.
The selection of the values for amplitude A and frequency F are justified by the expected effect of combined friction and local compression in the concrete related to the convex/concave geometry of the fibers when it is pulled out.
Also, the selected geometry (amplitude, frequency) is industrially simple to realize without complex prot processing that would affect the costs of the fibers.
Preferably, the steel fibers in system B are hooked or straight with an ultimate resistance above 1100 MPa, preferably above 1500 MPa and even more preferably above 2000 MPa.
The ratio length divided by diameter (mm/mm) for fibers system B is typically located between 50 and 95 preferably between 55 and 90.
Preferably the fibers system B may contain non-metallic fibers like glass fibers, with a minimum strength of 900 MPa, more preferably over 1000 MPa and a minimum length of 12 mm. the fiber system B may also contain basalt fibers, preferably with a minimum strength of 2500 MPa and a minimum length of 12 mm. Both glass and basalt fibers used are straight. In another preferred embodiment, the fiber system B contains only none metallic fibers, and preferably only glass fibers with a minimum length of 5 mm and a maximum length 50 mm.
Alternatively, the fibers system B contains both metallic and none metallic fibers, whereas the volume ratio between none metallic to metallic fibers is located between 1 and 5.
Alternatively a third synthetic fibers System C can be added to the concrete mix according to the invention, for instance acrylic fibers, polyethylene fibers, polypropylene fibers, polyester fibers to enhance properties like fire resistance or intrinsic shrinkage. Alternatively, cellulose fibers may be used in fibers system C.

TABLE 6

Characteristics of the Fibers system C

	Acrylic	Nylon	Polyester	Polyethylene	Polypropylene

E modulus [Gpa]	5-30	1-10	5-40	1-15	1-15
Ultimate strength	150-1400	100-2000	500-1500	100-600	100-1100
(US) [MPa]
length [mm]	1-100	1-100	1-100	1-100	1-100
length/diameter	30-150	30-150	30-150	30-150	30-150
bundling	loose	loose	loose	loose	loose
coating	no coating	no coating	no coating	no coating	no coating
density [kg/m3]	1000-1400	1000-1400	1200-1500	800-1200	800-1200

The concrete is designed to allow achieving the targeted performances in terms of strength, ductility, elasticity Modulus, placement and rheological properties, workability retention, etc.
The targeted properties are not only achieved by selecting the appropriate fibers mix design. The concrete formulation also plays an important role and is an integral part of the invention. The required ductility and mechanical properties are thus obtained by a combined effect of the concrete matrix and the special design of the hybrid fiber mix design.
Typically, the concrete according to the invention contains the following ingredients per cubic meter of produced concrete (Table 7).

TABLE 7

Ingredients of the concrete matrix without admixture Systems

	Unit	Value

Total binder	kg/m3	280-1000
Cement (any type)	% mass of total binder	40-100
Fly ash	% mass of total binder	0-50
Silica fume	% mass of total binder	0-40
GGBS	% mass of total binder	0-40
Other pozzolanic	% mass of total binder	0-40
materials
Fillers (limestone, . . .)	% mass of total binder	0-40
By pass dust	% mass of total binder	0-40
Total aggregates + sand	kg/m3	1000-2000
Sand - 0/4 mm	% volume of total	20-100
	aggregates
Aggregates - 4/8 mm or	% volume of total	0-80
equivalent	aggregates
Aggregates > 7-8 mm,	% volume of total	0-50
less than 20 mm	aggregates
Water/total binder in	kg/Kg	0.1-0.8
weight
Air	% volume of concrete	0.1-20
Volume of paste	liters	min 250
Volume of fibers System	% volume of concrete	0.03 to 4
A1
Volume of fibers System	% volume of concrete	0.12-0.6
A2
Volume of fibers System	% volume of concrete	0.03 to 3
B
Volume of fibers System	% volume of concrete	0 to 2
C
PCE Admixtures systems	dry solid content weight %	0.1 to 5
	of the total binder
Internal Curing admixture	dry solid content weight %	0 to 3
system	of the total binder

The cement is typically CEM I, II and III, the fly ash is a conventional fly ash the sand is round or crushed sand, typically 0-4 mm and the fine or coarse aggregates are either round or crushed.
All ingredients of the final concrete are mixed using conventional industrial concrete mixers. The mixing time is conventional for about 30 seconds to some minutes.
Samples of dimensions 700 mm×150 mm×150 mm were prepared, de-molded at 24 hours and were cured for 28 days at constant temperature 22° C. air humidity (relative humidity 95%) before mechanical testing. Test Machine was an Universal Testing Machine (UTM) a Zwick Roell Z250.
According to the invention, the concrete mix has the following values of mechanical properties with respect to FIG. 1

30<fc<80 MPa
3<ffl<12 MPa
3<fR1<12 MPa
2.5<fR3<15 MPa with consistencies from S2 to SF3, the concrete mix of the invention preferably contains a total binder weight that is located between 370 and 800 Kg per m³of concrete, a water to total binder located between 0.2 and 0.6, more preferably between 0.3 and 0.55, a total volume of paste that is located between 300 and 600 liters, a total weight content of sand+fine aggregates+coarse aggregates of 1000-1900 Kg per m³of concrete, the quantity of sand represents 30-60% of the total mass of the sand+fine+coarse aggregates.

Preferably, the concrete mix of the invention contains:

- Fibers System A1 from 25 Kg to 100 Kg of concrete
- Fibers System A2 from 10 Kg to 40 Kg of concrete

A third optional fibers system B can be optionally used whereas the fibers volume in Fibers system C ranges from 0.03 to 0.2 volume % of concrete.
A fourth optional third Fibers system C can be optionally used, whereas the fibers volume in Fibers system C ranges from 0.01 to 1.2 volume % of concrete.
More preferably, the concrete mix of the invention has the following characteristics:

35<fc<80 MPa
3.5<ffl<10.5 MPa
3.5<fR1<10.5 MPa
3<fR3<12 MPa
- Fibers System A1 from 25 Kg to 80 Kg per cubic meter of concrete
- Fibers System A2 from 10 Kg to 30 Kg per cubic meter of concrete

The concrete mix of the invention optionally comprises:

- Fibers system B from 0.03 to 0.15% in volume of concrete
- Fibers System C from 0.02 to 0.06% in volume of concrete

Fibers in System B contains either 100% volume metallic fibers or 100% none metallic fibers, or a mix of metallic and none metallic structural fibers. Preferably the non-metallic fibers are glass fibers or basalt fibers or any mix thereof.
According to other embodiment of the invention, the concrete mix of the invention contains a steel fibers system A1, a fibers system A2 that is consisting of low carbon steel (0.01-0.05% weight %) having a wavy shape as described in the FIG. 2, a fibers system B that contains any mix or combination of high strength fibers metallic, organic, glass based, carbon based or basalt based and a fibers system C containing synthetic fibers.
The 3 admixture systems I, II and III used according to the invention are characterized below:

Admixture System I: Superplasticizing

This admixture system is a combination of at least two polycarboxylate ethers, with homo- or co-polymeric backbone, based on acrylic, methacrylic, maleic or allilic constitutional repeating units:
A strong water reducer PCE of molecular weight ranging from 20000 to 100000 g/mol, with grafting density ranging from 10 to 35%, ethereal side chains ranging from 750 to 5000 g/mol, optionally cross-linked with ethereal and alkylic bridges of length up to 14 EO (Ethylene Oxide Unit), PO (Propylene Oxide Units), Carbon unit, optionally containing etheroatomic functions, such as Sulphonate or Phosphonate organic derivatives.
As workability retention PCE, of molecular weight ranging from 20000 to 100000 g/mol, with grafting density ranging from 10 to 60%, ethereal side chains ranging from 750 to 5000 g/mol, optionally cross-linked with ethereal and alkylic bridges of length up to 14 EO, PO, Carbon unit, optionally containing etheroatomic functions, such as Sulphonate or Phosphonate organic derivatives, optionally bearing protective groups on acrylic residues, based on linear and branched alcohols, alkyl methoxy, ethoxy, propoxy end-capped linear groups or ethereal chains up to 5000 g/mol.
The dosage of the Admixture System I typically ranges from 0.05-5% solid content based on weight of total binder (total cement+total fly ash or slag+total silica fume) depending on the concrete placement properties targeted.
The ratio in weight (dry solid content) of the strong water reducer PCE and the workability retention PCE is typically located between 20:80 and 60:40 depending of the targeted application.

Admixture System II: Stabilizing

The stabilizer is a solid, a water solution, emulsion or dispersion of compounds such as:

- Modified cellulose, such as carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose.
- Natural and modified starch, preferably branched.
- Naturals gums such as Xanthan gum.
- Fine silica, such as colloidal silica,
  or any combination thereof.

The dosage of the admixture system B is typically located between 0.05-2.5% solid content based on weight of binder (total cement+total fly ash or slag+total silica fume), depending on the segregation risk related to the fibers and the workability retention targeted.

Admixture System III: Internal Curing

The internal curing agent: a solid, paste, a water solution, emulsion or dispersion of compounds such as:

- Cellulose microfibers
- Synthetic or natural waxes
- Superabsorbing polymers, such as modified starch or acrylate crosslinked polymers.
- Hexylene glycol (2-Methyl-2,4-pentanediol)

The total dosage of the admixture system I and system II cannot exceed however the value of 5 weight % of the total binder.
The typical dosage of Admixture system III ranges from 0.05 to 6% solid content based on weight of binder depending on the conditions (size, temperature, relative humidity of the air, etc.).
The concrete mix of the invention may contain strength development accelerators, to reach 4-6 MPa resistance after a couple of hours. This is important for post treatment of slabs (helicopter finishing for instance) that can be done a couple of hours after the casting of the slab, thus saving time and improving efficiency.
The concrete mix of the invention may also include a retarding agent for instance and sugar modified structures, vinasses, molasses, or chelating agents, etc.
The concrete mix of the invention may use an air entrainer (like surfactants, soaps or hydrophobic compounds) to ensure a trapped volume of air from 2% to 15% in volume of the final concrete for freeze-thaw resistance or fire resistance depending on the application.
The general admixture System, consisting of the 3 Admixture Systems I, II and III not only enables to obtain a controlled workability over various classes (S1 to SF3), it also enables to perfectly disperse the high amount of fibers in the Fibers Systems A and B (and optionally in fibers System C) providing a very good stability of the fibers in the concrete matrix, avoiding segregation of the fibers or bleeding of the none metallic fibers thanks to optimized mixing conditions. This explains why the concrete mix of the invention can be produced using conventional concrete mixing techniques.
There are many advantages associated with the concretes according to the invention as will be seen from the examples below.
The first advantage is that the combination of the concrete mix designs, the fiber mix designs (fibers systems A, B and optionally C) and admixtures systems (I, II and III) enables to overcome all the problems from the prior art and provide a wide range of consistencies, that can by managed and controlled by the 3 admixture systems I, II and II.
Furthermore, the invention provides concrete mixes having high volume of paste that can achieve very high shrinkage reducing and enables to cast very large slabs up to 3000 m²without the appearance of cracks due to elevated ductility and resistances without having to use synthetic fibers that are weakening the resistance of the matrix and limits the applications. The combined usage of the high strength fibers system B and the admixture systems provides an optimum combination of shrinkage reduction and mechanical performances (compressive strength, flexural strength and ductility—see FIG. 1).
The concrete mix of the invention doesn't require special time consuming and costs ineffective curing actions, due to the presence when needed of the admixture system III, enabling self curing.
The concrete mix of the invention applies to wide range of construction elements, like slabs up to 3000 m2 without joints and without shrinkage cracks, floors, seismic applications, Insulated Concrete Frame for vertical walls, bridge segments, precast industry—tunnel lining segments, structural rehabilitation, etc.
The controlled rheology of the concrete mix of the invention enables building flat slabs or slabs with a designed slope.
The concrete mix of the invention has applications in large seamless thin slabs, floors and levels, bridges elements, concrete beams, concrete for impact resistance, seismic applications, etc. The concrete mix of the invention do not require any particular mixing processes or sequences and can be obtained in any dry of wet concrete batching plant.
One further characteristic of the concrete mix of the invention is that it provides consistency up to the SF3 self placing and self leveling consistency classes in a controlled manner through a sophisticated overall system of admixtures, and do not require any specific curing protection (water spraying, surface covering, etc.).
The concrete mix of the invention has high opening times or workability retention (period of time from the initial mixing of the ingredients during which the workability expressed by the consistency classes of the concrete S1-S5 and SF1-SF3 for self placing concretes) of the concrete does change, and remains in the same consistency class. The combination of the concrete mix design, the fibers mix design and the admixture system together enables to achieve the targeted improvements and properties.

Definitions

Hydraulic binder Material with cementing properties that sets and hardens due to hydration even under water. Hydraulic binders produce calcium silicate hydrates also known as CSH.
Cement Binder that sets and hardens and bring materials together. The most common cement is the ordinary Portland cement (OPC) and a series of Portland cements blended with other cementitious materials.
Ordinary Portland cement Hydraulic cement made from grinding clinker with gypsum. Portland cement contains calcium silicate, calcium aluminate and calcium ferroaluminate phases. These mineral phases react with water to produce strength.
Mineral Addition Mineral admixture (including the following powders: silica fume, fly ash, slags) added to concrete to enhance fresh properties, compressive strength development and improve durability.
Silica fume Source of amorphous silicon obtained as a byproduct of the silicon and ferrosilicon alloy production. Also known as microsilica.
Total binder Is the sum of all cementitious components (cement, flay ash, slag, silica fume, etc.)
Volume of paste Is the total volume of the cement, +fly ash+slag+silica fume+water+entrained air
Fibers Material used to increase concrete's structural performance. Fibers include: steel fibers, glass fibers, synthetic fibers and natural fibers.
Alumino silicate-by-product (Fly Ash-bottom ash) Alkali reactive binder components that together with the activator form the cementitious paste. These are minerals rich in alumina and silica in both, amorphous and crystalline structure.
Natural Pozzolan Aluminosilicate material of volcanic origin that reacts with calcium hydroxide to produce calcium silicate hydrates or CSH as known in Portland cement hydration.
Inert Filler A material that does alter physical properties of concrete but does not take place in hydration reaction.
Admixture raw material Chemical component in an admixture formulation system of one main chemical polymer.
Admixture Chemical admixtures used to modify or improve concrete's properties in fresh and hardened state. These could be air entrainers, water reducers, set retarders, accelerators, stabilizers, superplasticizers and others.
Air entrained Total volume of air entrained in the concrete by the air entrainer.
PCE PCE are Polycarboxylic Acid Co-Polymers used as a class of cement and concrete admixtures, and are comb type polymers that are based on: a polymer backbone made of acrylic, methacrylic, maleic acid, and related monomers, which is grafted with polyoxyalkylene side-chain such as EO and/or PO. The grafting could be, but is not limited to, ester, ether, amide or imide.
Initial dispersant Initial dispersant is a chemical admixtures used in hydraulic cement compositions such as Portland cement concrete, part of the plasticizer and superplasticizer familiy, which allow a good dispersion of cement particles during the initial hydration stage.
Superplasticizers Superplasticizer relates to a class of chemical admixture used in hydraulic cement compositions such as Portland cement concrete having the ability to highly reduce the water demand while maintaining a good dispersion of cement particles. In particular, superplasticizers avoid particle aggregation and improve the rheological properties and workability of cement and concrete at the different stage of the hydration reaction.
Concrete Concrete is primarily a combination of hydraulic binder, sand, fine and/or coarse aggregates, water. Admixture can also be added to provide specific properties such as flow, lower water content, acceleration . . . .
Pourable construction A material is consider as pourable as soon as its fluidity (with our without vibration) allow to full fill a formwork or to be collocate in a definite materials surface.
Construction materials Any materials that can be use to build construction element or structure. It includes concrete, masonries (bricks-blocks), stone, ICF . . . .
Structural applications A construction material is consider as structural as soon as the compressive strength of the material is greater than 25 MPa
Workability The workability of a material is measure with a slump test (table 1: slump)
Workability retention Is the capability of a mix to maintain its workability during the time. The total time required depends on the application and the transportation.
Internal Curing Admixture Strength development—setting/hardening Admixture agent that retains water and release the eater internally in a delayed matter to compensated form water depletion due to drying The setting time start when the construction material change from plastic to rigid. In the rigid stage the material cannot be poured or moved anymore. After this phase the strength development corresponding to the hardening of the material
Coarse Aggregates Manufactured, natural or recycled minerals with a particle size greater than 6 mm and a maximum size lower than 32 mm
Fines Aggregates Manufactured, natural or recycled minerals with a particle size typically greater than 3 mm and a maximum size lower than 10 mm
Sand aggregates Manufactured, natural or recycled minerals with a particle size lower than 3 or 4 mm
Ductility Is the capacity of the concrete to deform in a none elastic way, keeping resistances expressed by residual strength a certain displacement (CMOD) according to norm EN 14651
Flexural strength Is the strength measured on 3 points bending tests (notched prismatic samples 500 mm×150 mm×150 mm) according to norm EN 14651
Yield strength (YS) Is the strength measured in traction or tension from which the constitutive law between elongation and applied stress in no longer linear
Ultimate strength (US) Ultimate strength of the fibers before rupture in traction
w/b Total free water (w) mass in Kg divided by the total binder mass in Kg

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1. Flexural test results showing Crack Mouth Opening (CMOD) versus Strength according to EN 14651. This figure shows the values ffl, fR1 and fR3.

FIG. 2, Schematic drawing of the wavy fibers in fibers system A2 showing the amplitude A and frequency F of the wavy shape.

EXAMPLES OF THE INVENTION

Various examples of mix designs and corresponding results are presented here according to the invention
It is clear that the invention is not limited to the provided examples and that the selection of the various ingredients depend on the final application, placing and mechanical targeted properties and cost of the mix design.

Example 1


Material	Unit	Quantity

Total binder content	kg/m3	410
CEM I 52.5 N	kg/m3	410
w/b eff	—	0.43
Admix System I	% total binder	1.40%
	content
Admix System II	% total binder	0.50%
	content
Sand 0/4 round	kg/m3	707
Gravel 4/8 crushed	kg/m3	443
Gravel 8/11 crushed	kg/m3	621
Fiber type A1 - l/d = 80-l = 60 mm, YS =	% volume	0.50%
2400, US = 2890 MPa, hooked
Fiber type A2 - l/d eq. = 50-l = 38 mm,	% volume	0.25%
YS = 800 MPa, US = 870 MPa, Wavy
shape, A = 3 mm, F = 2 cm−1
Entrained air	l/m3	15
Paste volume	l/m3	321.46
Slump class	—	SF1
Slump	mm	670
Workability retention	min	90
fc	MPa	40
ffl	MPa	5.1
fr1	MPa	4.7
fr3	MPa	5.2
E modulus	Gpa	31.8

Example 1 shows a concrete mix design with medium compressive strength and low paste volume according to the invention, with fibers systems A1 and A2, as well as admixture systems I and II.

Example 2


Material	Unit	Quantity

Total binder content	kg/m3	750
CEM II/A-LL 52.5 N	kg/m3	500
Fly ash	kg/m3	200
Silica fume	kg/m3	50
w/b eff	—	0.32
Admix System I	% total binder	2.70%
	content
Admix System II	% total binder	0.30%
	content
Admix System III	% total binder	6.20%
	content
Sand 0/4 crushed	kg/m3	646
Gravel 4/8 round	kg/m3	453
Gravel 8/10 round	kg/m3	194
Fiber type A1 - l/d = 80-l = 60 mm, YS =	% volume	0.75%
2400, US = 2890 MPa, hooked
Fiber type A2 - l/d eq. == 50, l = 38 mm,	% volume	0.30%
YS = 800 MPa, US = 870 MPa, Wavy
shape, A = 2.5 mm, F = 4.5 cm−1
Entrained air	l/m3	26
Paste volume	l/m3	530.79
Slump class	—	SF2
Slump	mm	740
Workability retention	min	120
fc	MPa	74
ffl	MPa	8.5
fr1	MPa	11.8
fr3	MPa	14.7
E modulus	Gpa	41.9

Example 2 shows a concrete mix design according to the invention with high compressive strength and high paste volume, with fibers systems A1 and A2, as well as admixture systems I and II and III.

Example 3


Material	Unit	Quantity

Total binder content	kg/m3	630
CEM III/B 52.5R	kg/m3	400
Fly ash	kg/m3	80
Silica fume	kg/m3	50
w/b eff	—	0.35
Admix System I	% total binder	1.80%
	content
Admix System II	% total binder	0.45%
	content
Sand 0/4 round	kg/m3	721
Gravel 4/8 Crushed	kg/m3	289
Gravel 8/11 crushed	kg/m3	434
Fiber type A1 - l/d = 40-l =	% volume	0.75%
100 mm, YS = 1850
MPa, US = 1920 MPa, straight
Entrained air	l/m3	38
Paste volume	l/m3	441.54
Slump class	—	S5
Slump	mm	240
Workability retention	min	105
fc	MPa	65
ffl	MPa	6.7
fr1	MPa	2.1
fr3	MPa	2.5
E modulus	Gpa	37.5

Example 3 shows a concrete mix design with high compressive strength medium to high paste and high binder content, using fibers system A1 only (without fiber system A2 or fiber system B). The concrete mix design of example 3 is not according to the invention since it does not contain fibers system B and does meet the requirements related to the ductility values to be achieved.

Example 4


Material	Unit	Quantity

Total binder content	kg/m3	630
CEM III/B 52.5R	kg/m3	400
Fly ash	kg/m3	80
Silica fume	kg/m3	50
w/b eff	—	0.35
Admix System I	% total binder	1.80%
	content
Admix System II	% total binder	0.45%
	content
Sand 0/4 round	kg/m3	721
Gravel 4/8 Crushed	kg/m3	289
Gravel 8/11 crushed	kg/m3	434
Fiber type A2 - l/d eq. ==	% volume	0.75%
60-l = 35 mm, YS = 650
MPa, US = 870 MPa,
Wavy shape, A = 4 mm,
F = 0.3 cm−1
Entrained air	l/m3	38
Paste volume	l/m3	441.54
Slump class	—	SF1
Slump	mm	610
Workability retention	min	95
fc	MPa	61
ffl	MPa	6.5
fr1	MPa	7.4
fr3	MPa	1.2
E modulus	Gpa	64.3

Example 4 shows a concrete mix design similar to examples 3 yet having only fibers system A2. The concrete mix design of example 4 is not according to the invention since it does not contain fibers system A and does meet the requirements related to the ductility values to be achieved.

Example 5


Material	Unit	Quantity

Total binder content	kg/m3	530
CEM I 42.5 N	kg/m3	300
Fly ash	kg/m3	180
Silica fume	kg/m3	50
w/b eff	—	0.45
Admix System I	% total binder	1.70%
	content
Admix System II	% total binder	0.50%
	content
Sand 0/3 Round	kg/m3	693
Gravel 3/8 round	kg/m3	362
Gravel 8/11 round	kg/m3	454
Fiber type A1 - l/d = 75-l =	% volume	0.35%
55 mm, YS = 3100 MPa,
US = 3280 MPa, straight
Fiber type A2 - l/d eq. ==	% volume	0.15%
50-l = 38 mm, YS = 800 MPa,
US = 870 MPa, Wavy shape,
A = 0-6 mm, F = 5 cm−1
Fiber type B - Glass - l/d =	% volume	0.05%
80-l = 12 mm, US = 2750
MPa, straight
Fiber type B - Steel - l/d =	% volume	0.25%
80-l = 30 mm, YS = 2570
MPa, US = 3020 MPa, hooked
Entrained air	l/m3	31
Paste volume	l/m3	462.47
Slump class	—	SF3
Slump	mm	810
Workability retention	min	90
fc	MPa	72
ffl	MPa	6.9
fr1	MPa	7.2
fr3	MPa	9.1
E modulus	Gpa	40.1

Example 5 shows a concrete mix design according to the invention with high compressive strength medium to high paste and high binder content, using fibers system A1 and A2 with optional fiber system B (mix of glass and steel fibers) as well as admixture systems I and II.

Example 6


Material	Unit	Quantity

Total binder content	kg/m3	515
CEM I 32.5 R	kg/m3	150
CEM II I/A 52.5 R	kg/m3	160
Fly ash	kg/m3	180
Silica fume	kg/m3	25
w/b eff	—	0.5
Admix System I	% total binder	1.25%
	content
Admix System II	% total binder	0.70%
	content
Sand 0/2 round	kg/m3	684
Sand 2/4 round	kg/m3	358
Gravel 4/8 round	kg/m3	448
Fiber type A1 - l/d = 60-l =	% volume	0.35%
40 mm, YS = 2850,
US = 3120 MPa, hooked
Fiber type A2 - l/d eq. ==	% volume	0.65%
85-l = 55 mm, YS = 800 MPa,
US = 825 MPa, Wavy shape,
A = 4 mm, F = 1.65 cm−1
Fiber type B - Glass - l/d =	% volume	0.15%
57-l = 27 mm, US = 3150
MPa, straight
Entrained air	l/m3	24
Paste volume	l/m3	466.28
Slump class	—	S5
Slump	mm	250
Workability retention	min	150
fc	MPa	58
ffl	MPa	4.7
fr1	MPa	6.7
fr3	MPa	9.8
E modulus	Gpa	34.5

Example 6 shows a concrete mix design according to the invention with medium compressive strength, medium paste and medium binder content, using fibers system A1 and A2 with optional fibers system B (100% glass fibers) as well as admixture systems I and II.

Example 7


Material	Unit	Quantity

Total binder content	kg/m3	580
CEM I 52.5 R	kg/m3	250
Fly ash	kg/m3	250
Silica fume	kg/m3	80
w/b eff	—	0.35
Admix System I	% total binder	3.00%
	content
Admix System II	% total binder	1.74%
	content
Sand 0/4 round	kg/m3	928
Gravel 4/8 round	kg/m3	620
Fiber type A1 - l/d = 85-l =	% volume	0.45%
75 mm, YS = 1880
MPa, US = 2350 MPa, hooked
Fiber type A2 - l/d eq. ==	% volume	0.30%
75-l = 51 mm, YS = 650
MPa , US = 725 MPa, Wavy shape,
A = 6 mm, F = 0.5 cm−1
Fiber type B - Glass - l/d = 88-l = 16 mm,	% volume	0.06%
US = 3450 MPa, straight
Fiber type B - Steel - l/d = 80-l = 25 mm,	% volume	0.10%
YS = 2740 MPa, US = 3020 MPa, hooked
Fiber type C - Polypropylene - l/d =	% volume	0.25%
75-l = 50 mm, YS = 550
MPa, US = 680 MPa, straight
Entrained air	l/m3	14
Paste volume	l/m3	436.90
Slump class	—	SF3
Slump	mm	780
Workability retention	min	120
fc	MPa	79
ffl	MPa	11.5
frl	MPa	11.8
fr3	MPa	14.7
E modulus	Gpa	42.3

Example 7 shows a concrete mix design according to the invention with medium compressive strength, medium paste and medium binder content, using fibers system A1 and A2 with optional fibers system B (mix of glass and steel fibers) and with optional system C, as well as admixture systems I and II.

Claims

1. A concrete mix comprising sand, fine aggregates,

binder, fibers, and various admixtures, having a consistency from S2 to SF3, a compressive strength in the range of 30-80 MPa and a ductility represented by the following values:

30<fc<80 MPa

3<ffl<12 MPa

3<fR1<12 MPa

2.5<fR3<15 MPa

wherein the concrete mix contains at least 390 Kg of binder, the concrete mix comprises a paste volume of 300-600 liters, the concrete mix contains at least two systems of metallic fibers A1 and A2, the fibers system A1 consists of metallic fibers with a dosage of 25-100 kg/m3 with respect to the concrete mix and have an ultimate resistance of at least 1200 MPa, the fibers system A2 consists of low carbon steel fibers with a wavy shape having carbon content of 0.02-0.15% weight and having yield strength of 350-850 MPa and have a dosage of 10 kg-40 kg by m³of the concrete mix, the concrete mix contains a general admixture system that is composed of at least 2 sub-admixture systems I and II, wherein the first Admixture system I comprises at least 2 polycarboxylic acid co-polymers (PCE), a strong water reducer PCE and a workability retention PCE, wherein the second Admixture system II is a stabilizer obtained from a compound selected from the group consisting of modified cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, natural starch, modified starch, branched modified starch, naturals gums, Xanthan gum, fine silica, colloidal silica, silica fume and any combination thereof.

2. Concrete mix according to claim 1, wherein the shape of the wavy fibers of fibers system A2 have an amplitude of 0.5-7 mm and a frequency of 0.5 cm⁻¹-6 cm⁻¹.

3. Concrete mix according to claim 1, wherein the wavy fibers have a length of 25-50 mm.

4. Concrete mix according to claim 1, wherein the concrete mix further comprises fibers system B.

5. Concrete mix according to claim 5, wherein fibers system B have a dosage of 0.03 to 0.2% in volume by m3 of the concrete mix.

6. Concrete mix according to claim 1, further comprising coarse aggregates.

7. Concrete mix according to claim 1, wherein the dosing of the Admixture system I is of 0.5-5% weight percent with respect to the binder content and the dosing of the admixture system II is of 0.1-2% weight percent with respect to the binder.

8. Concrete mix according to claim 1, wherein the dosing of the Admixture system I is of 0.1-1% weight percent with respect to the binder content and the dosing of the admixture system II is of 0.1-0.5% weight percent with respect to the binder.

9. Concrete mix according to claim 1, wherein the concrete mix comprises an admixture system III, wherein the third Admixture system III is obtained from a compound selected from the group consisting of cellulose microfibers, synthetic waxes, natural waxes, superabsorbing polymers, starch crosslinked polymers, acrylate crosslinked polymers, hexylene glycol (2-Methyl-2,4-pentanediol) and any combination thereof and the dosage of the admixture system III is of 0.3-6 weight percent with respect to the binder.

10. Concrete mix according to claim 1, wherein fibers system C, comprising synthetic fibers, is added to the concrete mix.

11. Concrete mix according to claim 10, wherein the dosage of fibers system C is of 0.02% to 2% volume with respect to the concrete.