WO2019089968A2

WO2019089968A2 - Hydrophilic fiber reinforced concrete

Info

Publication number: WO2019089968A2
Application number: PCT/US2018/058766
Authority: WO
Inventors: Isaac Iverson; Varunesh Sharma
Original assignee: Invista Textiles UK Ltd; Invista North America LLC
Current assignee: Invista Textiles UK Ltd; Invista North America LLC
Priority date: 2017-11-06
Filing date: 2018-11-01
Publication date: 2019-05-09
Anticipated expiration: 2020-05-06
Also published as: WO2019089968A3

Abstract

Disclosed is concrete comprising Portland cement, water, aggregate and bifunctional thermoplastic reinforcing fibers having hydrating functionality and mechanical reinforcing functionality. The thermoplastic reinforcing fibers can be present in concentration sufficient to improve the workability time of the concrete before hardening, and can also suppress cracking during curing compared to an unfilled concrete.

Description

HYDROPHILIC FIBER REINFORCED CONCRETE

Field

The present disclosure relates to concretes with improved mechanical properties arising from the inclusion of bifunctional reinforcing thermoplastic fibers with both hydrating functionality and mechanical reinforcing functionality.

Background

Concrete is one of the most widely used materials in the world. Problems with concrete persist, including cracking upon curing, moisture management during the curing process and balancing working time and cured strength.

Despite significant progress in such materials development; internal curing to address the crack formation was not common until the early 1990s.

Concrete cures via several hydration reactions. As water is used up in the process by the hydration and drying process; it causes concrete to shrink, which leads to cracking. To overcome this problem, industry has been using water absorptive materials like SAP and pulp so that these can continue to provide water during the curing phase via desorption, reducing early shrinkage of concrete.

To solve the problem of cracking upon curing, it would be desirable to provide controlled release of water into the bulk of the concrete. While wood pulp can serve this function, it would be desirable to provide a reinforcing filler material that improves the mechanical properties of the concrete as well as providing the controlled water release.

For installing concrete, it would be desirable to provide a conveniently manageable working time, so that the concrete can be transported, poured into forms and finished before curing makes it stiff and unworkable. The usual way to extend working time is to add more water to the mixture. Unfortunately, adding water can compromise the as-cured final properties, so it would be desirable to find a way to manage the curing time while also achieving good mechanical properties in the final cured product. Further, it would be desirable to improve the fire-resistance of concrete, as well as the impact resistance and toughness via blending staple fibers. Examples include polyethylene fibers, polyvinyl alcohol [PVA] fibers, carbon fibers, cellulose pulp, polypropylene fibers, steel fibers, glass fibers and asbestos fibers. The higher the energy absorption capability in fibers; the higher the performance in concrete application. Most fibers currently in use are either steel or polypropylene fibers.

One approach to improving the mechanical properties of concrete has been to incorporate fibers, including steel, polyolefin (such as polyethylene and polypropylene), polyesters and nylons. Higher mechanical performance, crack resistance, reduced plastic shrinkage and higher residual strength are the key value add properties that fibers enable in fire resistant fiber reinforced concrete. Steel fibers provide higher modulus of elasticity, thus higher performance concrete. Concrete containing bicomponent fibers is disclosed in U.S. Patent 6,844,065 to Reddy et al., and concretes containing various other synthetic fibers are disclosed in U.S. Published Applications 2003/0219580 to Tagge et al. and 2009/0075073 to Biddle et al.

Another approach to improving the mechanical properties of concrete is to incorporate reinforcing bars or wire mesh. It would be desirable to provide a component that improves the mechanical properties of the concrete structural element while resisting the alkaline environment of the as-formed concrete structural element. Both structural steels and stainless steels can be susceptible to general corrosion, pitting and cracking in such environments.

Cellulose pulp and SAP (super-absorbent polymers such as polyacrylates, often added as spheres) can provide moisture management properties but can not be suitable to improve mechanical properties of FRC over the long term. Polypropylene [PP] fibers can suitably be added to improve mechanical properties but lack the desired moisture management properties. Nylons, and specifically nylon-6,6, would have better energy absorption vs. PP to enhance toughness and impact resistance of FRC.

It would be desirable to provide a single component/additive that decreases cracking upon curing while also improving the mechanical properties of the as-cured concrete. Summary

An intensive study of the problems of cracking and moisture management led to the present discovery of concrete formulations containing reinforcing fibers with two

functionalities. These fibers are referred to herein as "bifunctional reinforcing fibers."

Disclosed are concrete formulations containing bifunctional reinforcing fibers. The bifunctional reinforcing fibers provide hydration for the early curing phase and mechanical property enhancement for later stage performance in place.

Figures

Figures 1 and 2 compare weight loss as a function of time for various reinforcing fibers in accordance with the disclosure.

Description

Concrete formulations including the disclosed bifunctional reinforcing fibers can surprisingly exhibit other improved properties including more flexible working times and enhanced fire resistance.

The bifunctional reinforcing fibers can comprise polyamides. Condensation reaction products of diacids and diamines are especially useful. With such polyamides, either the diamine or the diacid can be modified (in accordance with the invention) with the addition of hydrophilic monomers. Two suitable polymer families for making the bifunctional reinforcing fibers of the disclosed invention are taught in INVISTA patent families: INVISTA Matter PI3400 (WO2014/057363 - published 17 Apr 2014) and poly(olefin) glycol diacids as disclosed in INVISTA Matter PI4220 (PCT/US17/43608 - filed 25 Jul 2017)..

The concrete formulations disclosed here can contain from > 0.001 vol.% to < 10 vol.%, for example, > 0.001 vol.% to < 2 vol.% of bifunctional reinforcing fibers. The vol.%, as used herein, is defined as the volume of bifunctional reinforcing fibers per total volume of the concrete formulation. For example, 1 vol.% means the concrete formulation contains unit volume of bifunctional reinforcing fibers per 99 units making the rest.

The concrete formulations disclosed here can contain from > 0.002 vol.% to < 10 vol.%, for example, > 0.002 vol.% to < 9 vol.%, > 0.002 vol.% to < 8 vol.%, > 0.002 vol.% to < 7 vol.%, > 0.002 vol.% to < 6 vol.%, > 0.002 vol.% to < 5 vol.%, > 0.002 vol.% to < 4 vol.%, > 0.002 vol.% to < 3 vol.%, > 0.002 vol.% to < 2 vol.%, > 0.002 vol.% to < 1 vol.% of bifunctional reinforcing fibers. Other vol.% values of bifunctional reinforcing fibers in these ranges are inclusive.

The addition of bifunctional reinforcing fibers in accordance with the disclosed process can exhibit several different beneficial technical effects, including improvements in: (i) crack resistance; (ii) toughness; and (iii) controlled strain-hardening. Thus the addition of bifunctional reinforcing fibers can be adjusted within the disclosed ranges (with reasonable trial and error by one of ordinary skill in the art) to emphasize one or more of the desired technical effects. For example, within the disclosed range, from > 0.5 vol.% to < 1 vol.% can be suitable to enhance crack resistance. Similarly, > 1 vol.% to < 2 vol.% can be suitable to enhance mechanical properties like toughness. For strain-hardening, > 0.5 vol.% to < 1 vol.% can be suitable. (Ref: P. Jongvisuttisun, 2014, Dissertation: Utilization of Eucalyptus pulp in

cementitious materials, Georgia Institute of Technology, Atlanta, GA) The bifunctional reinforcing fibers can comprise bifunctional thermoplastic reinforcing fibers.

The bifunctional reinforcing fibers can similarly be sized to emphasize one or more desired technical effects. If control of plastic shrinkage is a principally desired technical effect, then microdenier fibers (for example, >3 to <10 denier) can be used. It can be desirable to use microdenier staple, for example, staple having length of >½ inch to <2 inches. For shrinkage and/or cracking control, suitable dosages include > ½ to < 2 pounds per cublic yard of concrete mix (as described below in Example 1). The dosage can be adjusted with reasonable trial and error using ASTM 1579 to test shrinkage of the finished concrete. On the other hand, if strength is a principally desired technical effect, macrodenier fibers (for example > 100 to < 10,000 denier, for example, 1000 denier) can be used, and can similarly be used as staple at lengths including > ¼ inch to < 3 inches, for example, 2 inches). Higher volumetric dosages can be desired for strength with macrodenier fibers, including > 3 to < 11 pounds per cubic yard of concrete mix (as described below in Example 1). The macrodenier bifunctional reinforcing fibers can at least partially fibrillate (split lengthwise) into thinner fibers during mixing, and a portion of the thinner fibers can be microdenier fibers. The bifunctional reinforcing fiber loading in the concrete formulation can be from about 0.05 to about 40 lb/cubic yard, for example, from about 0.25 to about 40 lb/cubic yard, from about 0.5 to about 38 lb/cubic yard, from about 0.5 to about 36 lb/cubic yard.

The bifunctional reinforcing fiber loading in the concrete formulation can be from about 0.01 to about 30 kg/m³, for example, from about 0.1 to about 28 kg/m³, from about 0.2 to about 27 kg/m³, from about 0.3 to about 25 kg/m³.

The disclosed bifunctional reinforcing fibers can exhibit moisture absorption and desorption rates needed to enable free as well as constrained shrinkage reduction in FRC. Additionally, the disclosed bifunctional reinforcing fibers can be formulated for resistance to an alkaline environment and can be produced in a variety of staple fiber lengths or continuous filament form to yield the optimum mechanical properties in various types of FRC products.

The disclosed bifunctional reinforcing fibers can be formulated to exhibit energy absorption comparable or higher to polypropylene fibers and glass fibers.

The disclosed concrete formulations can find particular utility in high performance concrete end-uses where water to cement ratio is relatively low. Additionally, the disclosed concrete formulations find utility in stucco, plaster and thin overlays where cracking can be a significant problem.

The disclosed concrete formulations can be useful as precast tunnel linings

(http://tunnelingonline.com/innovations-precast-concrete-segmental-linings-case-studies/) and ICF (Insulating Concrete Forms) construction. The bifunctional reinforcing fibers can be incorporated into concrete formulations in accordance with American Concrete Institute standards ACI 301, 316 and 318 (showing recommended ingredient blends for FRC).

The disclosed concrete formulations can contain a blend of steel fiber of > 0.5 vol.% to < 2 vol.% along with the ranges of concentrations of bifunctional reinforcing fibers as disclosed above.

The disclosed concrete includes:

a. Portland cement;

b. Water;

c. Aggregate; and d. Bifunctional reinforcing thermoplastic fibers having hydrating functionality and mechanical reinforcing functionality.

The concrete can contain bifunctional thermoplastic reinforcing fibers in concentration sufficient to improve the workability time of the concrete before hardening. The bifunctional thermoplastic reinforcing fibers can be present in concentration sufficient to suppress cracking during curing compared to an unfilled concrete. The bifunctional thermoplastic reinforcing fibers can be in the form of staple. The concrete can optionally include other reinforcing components including metal fibers, for example, steel fibers. The bifunctional thermoplastic reinforcing fibers are present in concentration to enhance mechanical performance of FRC while minimizing flaws like voids. The bifunctional thermoplastic reinforcing fibers can comprise at least one of polyolefin, polyester and polyamide. The bifunctional thermoplastic reinforcing fibers can comprise polyamide. Suitable polyamides comprise at least one added monomer to improve the water uptake of the polyamide compared to the same composition without the added monomer. For example, the added monomer can be selected from the group consisting of polyetheramines (as disclosed in INVISTA Matter PI3400 (WO2014/057363 - published 17 Apr 2014) and poly(olefin) glycol diacids as disclosed in INVISTA Matter PI4220 (PCT/US17/43608 - filed 25 Jul 2017).

Suitable thermoplastics for the bifunctional reinforcing fibers include polyamides comprising a nylon and a polyetherdiamine, for example, a polyetherdiamine having a molecular weight of at least 1500 and an Amine Hydrogen Equivalent Weight (AHEW) of less than 10 percent higher than the idealized AHEW for the polyetherdiamine.

The disclosed concrete can, for example, contain a polyamide having a moisture regain ranging from about 405% to about 3£35%. The disclosed concrete can contain a polyamide having a moisture regain ranging from about 7% to about 30%, for example, from about 9% to about 28%.

The moisture regain property of the polyamide fibers can allow for a lower fiber concentration in FRC while still enabling crack resistance, compared to a polyamide fiber of otherwise similar mechanical properties but having lower moisture regain. The nylon can be a functionalized nylon-6,6 or nylon-6. SAP (Super Absorbent Polymer) additives can also be used to if additional moisture levels are needed in FRC for specific applications. As used herein, the moisture regain basis is by wt.%.

The polyamide for the bifunctional thermoplastic reinforcing fibers can contain a polyetherdiamine having an AHEW of less than 8 percent higher than the idealized AHEW for the polyetherdiamine.

The concrete can contain bifunctional thermoplastic reinforcing fibers comprising the reaction product of:

a. an aliphatic diamine; and

b. a diacid, wherein at least a portion of the diacid is poly(ether glycol) dicarboxylic acid.

The poly(ether glycol) dicarboxylic acid can have a number-average molecular weight (Mn) > 250 Daltons and < 2000 Daltons. The poly(ether glycol) dicarboxylic acid can be an aliphatic dicarboxylic acid. The polyamide containing the poly(ether glycol) can be

characterized by moisture regain of from > 5% to < 35%. The polyamide can contain an aliphatic diamine such as hexamethylenediamine. The polyamide can optionally contain an aromatic moiety at concentrations selected from the group consisting of:

a. < 10 wt.% of repeating units; and

b. < 5 wt.% of repeating units.

The disclosed concrete can contain bifunctional thermoplastic reinforcing fibers comprising polyamide having a moisture uptake of from > 5 wt.% to < 40 wt.%, for example > 6 wt.% to < 35 wt.%, for example > 6 wt.% to < 35 wt.%, for example, > 8 wt.% to < 35 wt.%, for example, > 10 wt.%, to < 35 wt.%, for example > 12 wt.% to < 35 wt.% .

Test Equipment

A twin-screw extruder [Coperion ZSK 18 MEGAlab] includes two conveying screws, 18- mm diameter with a 56L/D [i.e., L/D ratio of 56] co-rotating turning at the speed of 300 RPM that provide the high-shear, forward momentum to the heated mass inside the barrel. The processing section of the Coperion twin screw compounder ZSK 18 MEGAlab is set up to suit various process needs and to allow a wide variety of processes, for example, reaction polymerization and compounding processes. Polymer and additives are continuously fed into the first barrel section of the twin screw using a metering feeder. The products conveyed along the screw get melted and mixed by kneading elements in the plastification section of the barrel. The polymer then travels along to an injection port where liquids can be added and then onto degassing zones and from there to a pressure build zone where it then exits the die via a 3-mm hole as a lace. The cast lace is fed into a water bath to cool and to enable it to be cut into chips via a pelletizer.

The twin-screw extruder [TSE] includes several sequential zones; namely, a throat area for feeding the material, conveying and mixing the material, forward mass movement, poly- condensation zone for polymer build, followed by transport out of the extruder screens and quenching of the polymer lace ad cutting into the pellets. An axial temperature profile across the extruder barrel is maintained in the range where the polycondensation reaction is most effective.

A liquid injection [LI] system is integrated into the extruder for feeding liquid additives. The LI system connection point to the extruder barrel is about in the middle section of its length. The LI system is enclosed within a cabinet inside which the temperature is controlled to keep the additives in flowable state and prevent line plugging due to solidification. The LI system is calibrated to deliver the desired feed flowrate corresponding to the target additive concentration in the polymer make.

The color measurement is performed using CIE Lab technique. The color is measured with a Konica Minolta Chroma Meter CR-410 instrument. D65 illuminant is used with a CIE 1931 0° standard observer. The results are reported using the CIELAB color scale, wherein L* is a measure of brightness (L* of 100 = white; L* of 0.0 = black), a* is a measure of redness (+) or greenness (-) and b* is a measure of yellowness (+) or blueness (-). The term "Yl" is the

Yellowness Index color value that is measured by ASTM E313 method. Definitions

Aggregate is used as is commonly understood and includes sand, gravel and rock of the same or different sizes, selected by those skilled in the art for the desired strength, workability, finishability and durability of a given concrete.

FRC is an acronym meaning Fiber Reinforced Concrete.

Portland cement is used as is commonly understood in the art and defined by Hawley's Condensed Chemical Dictionary 12Supth /SupEd., R. Lewis, Van Nostrand Co., NY, p 239, 1993.

The term "poly(ether glycol) dicarboxylic acid", as used herein, refers to a class of poly(ethylene glycol)bis(carboxymethyl) ether having a general chemical structure of

, wherein n is a numerical value.

As used herein, all molecular weights (Mw) of polymers are weight-average molecular weights, unless otherwise specified.

The term "N66", as used herein, refers to a polymer synthesized by polycondensation of hexamethylenediamine (HMD) and adipic acid. The polymer is also known as Polyamide 66 (or PA66), Nylon 66, nylon 6-6, nylon 6/6 or nylon 6,6.

ELASTAMINE^® RE-2000 amine, as used herein, is a commercial product of Huntsman International LLC. It is a water-soluble aliphatic polyetherdiamine with an approximate molecular weight of 2000.

The term "dpf", as used herein, means denier per filament which is a unit measure of mass density of fiber. One dpf equals one-gram weight of fiber per 9000 m of linear fiber length.

The term "pcy" or "PCY", as used herein, means lbs per cubic yard.

The conversion units used in the present application:

1 gram/cm³ (or g/cc) = 1685.56 lb/cubic yard

1 Ib/cu.yard = 0.593 kg/m³ Test Methods

ASTM C39 Compressive strength measurement

ASTM C78 Flexural strength measurement

ASTM C157 Free shrinkage measurement

ASTM C496 Splitting tensile strength measurement

ASTM C1399 Residual strength measurement of FRC

ASTM C1579-13 Test Method for Evaluating Plastic Shrinkage Crack

Restrained Fiber Reinforced Concrete

ASTM C1581 at Cracking under Restrained Shrinkag

Examples

Example A - Prepo ration of N66 incorporated with polyetheramine

A N66 polymer, having an RV of 34.8 and AEG of 56, is fed to the twin-screw extruder described above. A screw speed is maintained at 300 RPM. Upon establishing a stable temperature profile and operation of the extruder, a transparent lace of molten N66 is discharged from the extruder. Continuing under these conditions, molten Elastamine^® RE-2000 polyetheramine (55-67°C hot cabinet) is introduced in the extruder barrel through the LI connection port. The LI system is calibrated such that the delivered feed rate would yield about 8 wt% polyetheramine (Elastamine^® RE-2000) incorporated into the polymer, based on the total composition.

The extruded polymer is visually opaque in appearance. The polymer is extruded at the die head of the extruder as a lace and quenched into a water bath to solidify before being fed into a cutter to produce fine pellets of about 3.0mm x 1.6mm dimension. Significant foaming is not observed either at the vent port of the extruder of the die head of the extruder. The polymer has an RV 25.1, AEG of 73.9 mpmg. Example B - Prepo ration of short staple fibers

The extruded polymer pellets, prepared in the above Example A, were dried for 15 hours at 180 °C under the nitrogen environment. The dried polymer pellets were fed to a single-screw melt extruder. The extrusion conditions were: polymer temperature of 290°C and a total draw ratio of 4.0. The melt-extruded, continuous polymer fibers were approximately 4 dpf (denier per filament) with a round cross-section.

It is to be noted that, while round cross-section fibers were prepared and used in the Examples, other non-limiting fiber cross-section shapes can include trilobal, 4-hole square, triangular, oval, and other possible shapes that are known and used in the fiber industry.

Table 1 is a summary of the measured physical properties of the melt-extruded, continuous polymer fibers prepared herein.

TABLE 1

The above melt-spun continuous filaments were subsequently cut into short staple fibers in the ¼ " to 2.0 " linear length range, for example, ¼ " or ½ " or ¾ " or 1 " and such. It is to be understood that other linear lengths and combinations of multiple linear lengths of these short staple fibers can be used as well. The short staple fibers prepared herein were used in the examples below. Examples 1-3 - Concrete for Testing & Control

The concrete used in the following Examples is prepared using the following

formulations and procedure. Slow water addition and high shear mixing is used along with vibration mechanism to achieve well dispersed and homogeneous FRC samples for testing the performance. The concrete mix is sampled to assure random (uniform) distribution of fibers. It is observed that random (uniform) distribution of fibers improves the performance of the resulting concrete for cracking resistance during curing and in use.

TABLE 2

The composition of the bifunctional reinforcing fibers are published. A polyetheramine- containing polyamide fiber is disclosed at Example 1 at page 40 of Published PCT Application WO2014/057363 (Attorney Docket PI3400), and a PEG-dicacid-containing polyamide fiber is disclosed at Example 6, Table 7 at page 83 of Published PCT Application WO2018/031229 (Attorney Docket PI4220).

Example 5 - Compressive Strength Testing

Examples 1-4 and control are tested for compressive strength. The concretes are cast into cylinders (1500 X 300 mm) to evaluate compressive strength in accordance with ASTM C39 and splitting tensile strength (ASTM C496). Specimens according to Examples 1-4 formulations exhibit improved performance vs. control. Example 6 - Flexural Strength Testing

Examples 1-4 are repeated and cast into beams having dimensions 100 X 100 X 350 mm. The beams are tested for flexural strength (ASTM C78). Specimens according to Examples 1-4 formulations exhibit improved performance vs. control.

Example 7 - Residual strength of FRC

Examples 1-4 are repeated and the control samples are tested via ASTM C1399.

Specimens according to Examples 1-4 formulations improved performance vs. control.

Example 8 - Free shrinkage

Examples 1-4 and control are repeated to be tested via ASTM C157. Specimens according to Examples 1-4 formulations improved performance vs. control.

Example 9 - Age at Cracking under Restrained Shrinkage

Examples 1-4 and control are repeated to be tested via ASTM C1581. Specimens according to Examples 1-4 formulations improved performance vs. control.

Example 10 - Plastic Shrinkage Cracking

Beams are also cast for ASTM C1579 - 13, Test Method for Evaluating Plastic Shrinkage Cracking of Restrained Fiber Reinforced Concrete. Specimens according to Examples 1-4 formulations improved performance vs. control.

Example 11 - Comparison of Reinforcing Fibers with Hvdrophilic Coating (as disclosed in U.S. 4,073,993) vs. Bifunctional Reinforcing Fibers

Example 10 is repeated with hydrophilic coating (in accordance with U.S. patent 4,073,993) on the bifunctional reinforcing fibers of Example 1. Plastic shrinkage cracking of all fiber containing samples improved vs. the control. Examples 12-14 - Short Staple Fiber Testing [ASTM C39 and C157 Methods!

The below three short staple fiber test specimens were prepared and tested in these examples. Testing was performed at an external contracting facility, which specializes in concrete testing.

TABLE 3

The purpose of the testing was to evaluate the short staple fiber loading of 13.5 lb/cubic yard [pcy], which corresponds to about 8 kg/m³, in a typical slab concrete mix with a compressive strength of 4,000 - 5,000 psi at an age of 7 days. The concrete was batched and mixed in accordance with ASTM C192-16a - Standard Practice for Making and Curing Concrete Test Specimens in the Laboratory. The fibers were added at the beginning of the batch sequence and mixed with the rock and sand for 1 minute prior to the addition of the cementitious material. The concrete was then mixed for 3 minutes, allowed to rest for 3 minutes, and mixed for 2 additional minutes. Plastic properties were then determined and recorded in accordance with the applicable standards. Three 3" x 3" x 11.25" beams were cast from each mix for testing in accordance with ASTM C157. Fifteen 4" x 8" cylinders were also cast for compressive and weight determination.

Mix proportions, plastic, and hardened properties are reported in Table 4 below. In Table 4, the term "Synthetic Fiber" means Fiber A or Fiber B or Fiber C, as described in Table 3.

TABLE 4 - Concrete Mix Design, Properties and Compressive Strength

ASTM C39 - Compressive Strength Testing

Fifteen 4.00" cylinders were air cured for 3, 7, 28 and 56 days prior to testing.

Specimens were loaded at a rate of 35 ± 7 psi/sec until failure. The peak loads and failure types were recorded and subsequent stress values calculated based on the average diameter of the specimens. Test results are reported in Table 5-8. Weights of the cylinders were also taken to determine moisture loss vs. time. Test results are illustrated in FIG. 1. TABLE 5 - Summary Test Results

TABLE 6 - ASTM C157 Test Results - Air Cured

TABLE 7 - ASTM C39 Results - Compressive Strength - Control

TABLE 8 - ASTM C39 Results - Compressive Strength - Fiber A

TABLE 9 - ASTM C39 Results - Compressive Strength - Fiber B

TABLE 10 - ASTM C39 Results - Compressive Strength - Fiber C

ASTM C157 - Length Change (Air Cured)

Three length change specimens (3" x 3" x 11.25") were cast from each mix with initial readings taken at 24 hrs. All length change specimens were air cured in a drying room with a relative humidity of 50 ±4% and temperature of 73 ±3°F for 28 days. The specimens were also weighed each time they were tested. Test results are reported in Table 6. Weight loss results, in terms of Shrinkage Beam Weight versus Time, are illustrated in FIGURE 2.

Claims

Concrete comprising:

a. Portland cement;

b. Water;

c. Aggregate; and

d. Bifunctional thermoplastic reinforcing fibers having hydrating functionality and mechanical reinforcing functionality.

The concrete of claim 1 wherein the bifunctional thermoplastic reinforcing fibers are present in concentration sufficient to improve the workability time of the concrete before hardening.

The concrete of claim 2 wherein the bifunctional thermoplastic reinforcing fibers are present in concentration sufficient to suppress cracking during curing compared to an unfilled concrete.

The concrete of claim 1 wherein the bifunctional thermoplastic reinforcing fibers are present in concentration of like dimensions under like mechanical conditions.

The concrete of any of claims 1 to 4 wherein the bifunctional thermoplastic reinforcing fibers comprise at least one of polyolefin, polyester and polyamide.

The concrete of claim 5 wherein the bifunctional thermoplastic reinforcing fibers comprise polyamide.

The concrete of claim 6 wherein the polyamide comprises at least one added monomer that improves the water uptake of the polyamide compared to the same composition without the added monomer.

The concrete of claim 7 wherein the added monomer is at least one selected from the group consisting of polyetheramines and poly(olefin) glycol diacids.

The concrete of any one of claims 1 to 8 wherein the bifunctional reinforcing fibers are in the form of staple.

The concrete of any one of claims 1 to 8 further comprising metal fibers.

The concrete of claim 10 wherein the metal is steel.

12. The concrete of claim 8 wherein the polyamide comprises a nylon and a

polyetherdiamine, the polyetherdiamine having a molecular weight of at least 1500 and an Amine Hydrogen Equivalent Weight (AHEW) of less than 10 percent higher than the idealized AHEW for the polyetherdiamine.

13. The concrete of claim 12 wherein the polyamide has a moisture regain ranging from about 5% to about 40%.

14. The concrete of claim 12 or 13, wherein the nylon is nylon 6,6.

15. The concrete of claim 12 or 13, wherein the nylon is nylon 6.

16. The concrete of claim 12 wherein the polyetherdiamine has an AHEW of less than 8 percent higher than the idealized AHEW for the polyetherdiamine.

17. The concrete of claim 8 wherein the polyamide comprises the reaction product of:

a. an aliphatic diamine; and

18. The concrete of claim 17 wherein the poly(ether glycol) dicarboxylic acid has a number- average molecular weight (Mn) > 250 Daltons and < 2000 Daltons.

19. The concrete of claim 8 wherein the poly(ether glycol) dicarboxylic acid is an aliphatic dicarboxylic acid.

20. The concrete of any one preceding claim wherein the polyamide is characterized by moisture regain of from at least one range selected from the ranges:

a. > 5% to < 40%;

a. > 6% to < 35%;

a. > 8% to < 35%;

b. > 10% to < 35%; and

a. > 12% to < 35%.

21. The concrete of any one of claims 17-20 wherein the aliphatic diamine is

hexamethylenediamine.

22. The polyamide of claim 17 wherein the number of repeating units containing an

aromatic moiety is selected from the group consisting of: a. < 10 wt.% of repeating units; and

b. < 5 wt.% of repeating units.

23. Concrete comprising reinforcing fiber, wherein the reinforcing fiber comprises polymer containing poly(glycol) segments.

24. The concrete of claim 27 wherein at least a portion of the poly(glycol) segments are poly(olefin glycol) segments.

25. The concrete of claim 28 wherein at least a portion of the poly(olefin glycol) segments are polyethyleneglycol segments.

26. The concrete of at least one of claims 27-29, wherein the polymer is a thermoplastic.

27. The concrete of claim 30 wherein the thermoplastic is a polyamide.

28. The concrete of claim 1 containing bifunctional thermoplastic reinforcing fibers at

concentration of at least one range selected from:

a. > 0.5 vol.% to≤10 vol.%; and

b. > 0.5 vol.% to≤2 vol.%.

29. The concrete of claim 1 containing an amount of bifunctional reinforcing fibers to

improve at least one of: (i) crack resistance; (ii) toughness; and (iii) controlled strain- hardening.

30. The concrete of claim 29 containing bifunctional reinforcing fibers at concentration of at least one range selected from:

a. > 0.5 vol.% to≤l vol.%; and

b. > l vol.% to≤2 vol.%;

to enhanced at least one property selected from crack resistance and strain-hardening.

31. The concrete of claim 30 wherein the bifunctional reinforcing fibers are microdenier fibers.

32. The concrete of claim 31 wherein the microdenier fibers comprise fibers of >3 to <10 denier.

33. The concrete of claim 32 wherein the microdenier fibers comprise staple.

34. The concrete of claim 33 wherein the microdenier staple includes stable having length of > ¼ inch to <2 inches.

35. The concrete of claim 34 containing > ½ to < 2 pounds of bifunctional reinforcing fiber per cubic yard of concrete mix.

36. The concrete of claim 34 wherein the bifunctional reinforcing fibers comprise

macrodenier fibers.

37. The concrete of claim 36 wherein the macrodenier fibers comprise fibers of > 100 to < 10,000 denier.

38. The concrete of claim 37 wherein the macrodenier fibers include fibers of 1000 denier.

39. The concrete of claim 37 wherein the macrodenier fibers comprise staple.

40. The concrete of claim 39 wherein the staple includes fibers of length > ¼ inch to < 3 inches.

41. The concrete of claim 40 containing > 3 to < 11 pounds per cubic yard of concrete mix.

42. The concrete of claim 41 wherein the macrodenier bifunctional reinforcing fibers are at least partially fibri Mated into thinner fibers.

43. The concrete of claim 42 wherein at least a portion of the thinner fibers are microdenier fibers.