A colemite comprising ultra-high performance concrete

Abstract

The present invention relates to a durable and economical ultra-high performance concrete comprising at least one aggregate, at least one binder, at least one reinforcing element, and colemanite, and to a method for producing the same concrete. The present invention provides the ultra-high performance concrete with a decreased number of shrinkage cracks, an increased setting time, as well as an increased compressive strength and an increased flexural strength in both in the medium term and the long term.

Description

[0001] TECHNICAL FIELD The present invention relates to an ultra-high performance concrete comprising at least one aggregate, at least one binder, at least one reinforcing element, and colemanite. BACKGROUND OF THE INVENTION As one of the most critical ores in the world, boron is becoming more popular day by day and is currently used as the main raw material in many industries. Such industries include glass fiber (hardened plastics, automotive parts, aircraft industry, sports equipment), optical glass fiber (electronics industry), borosilicate glass (automotive glass, washing machines), ceramic industry (hardener and tile pavement), cleaning and bleaching industry (as germicide and bleach in soaps and detergents), agriculture (to increase or prevent vegetation growth), metallurgy (as melting accelerator, or for formation of protective slag), nuclear applications, and many other sectors and sub-sectors. Ultra-high performance concretes (UHPC) are currently used in many applications, including cladding, roofing components, repair of structures, offshore structures, industrial floors, pavements, prefabricated structures, bridge elements, especially those with a longer span, and the like, and are regarded as a material of the future with the potential to improve the sustainability of buildings and infrastructure components by enabling innovative designs. UHPCs are different from conventional concretes in that new generation super plasticizers, aggregates, nano materials and / or fibers are used in UHPC mixes, and thus, as long as a good mix design is provided, it is possible to obtain a sustainable concrete that is improved in terms of both mechanical properties and durability. However, due to the high number of ingredients in ultra-high performance concrete mixes, it is quite difficult to obtain a concrete with desired mechanical values in an economical and cost effective manner. In terms of durability and strength of concrete, it is essential to select the proper materials for use therein. In the production of UHPC, high cement usage and low water / cement ratio result in problems such as high hydration heat, thermal expansion, early setting, and shrinkage cracks, especially during fresh concrete phase. At the level of the state of the art, there is still a need in the art for ultra-high performance concretes which can be obtained in an economical way while retaining durability and strength thereof at a desired level, or even having a high workability and an improved level of strength and durability compared to that in the state of the art. DESCRIPTION OF FIGURES Figure 1 – comparison of spread diameters of reference and colemanite-added UHP fresh concretes. Figure 2 – comparison of air contents of the reference and colemanite-added UHP fresh concretes. Figure 3 – comparison of densities of the reference and colemanite-added UHP fresh concretes. Figure 4 – comparison of temperature and shrinkage values of the UHPC specimens in Examples 1-4. Figure 5 – SEM images of the 28-day-old reference and colemanite-added cements in Examples 1-4 (a: R, b: C25, c: C50, d: C100). Figure 6 – density values measured at different days of age for the reference and colemanite-added specimens in Examples 1-4. Figure 7 – compressive strength values measured at different days of age the for reference and colemanite-added specimens in Examples 1-4. Figure 8 – flexural strength values measured at different days of age for the reference and colemanite-added specimens in Examples 1-4. Figure 9 – Schmidt hammer rebound values measured at different days of age for the reference and colemanite-added specimens in Examples 1-4. Figure 10 – ultrasonic pulse velocities measured at different days of age for the reference and colemanite-added specimens in Examples 1-4. Figure 11 – impact strength values of the 56-day-old reference and colemanite-added specimens in Examples 1-4. Figure 12 – electrical resistivity values measured at different days of age for the reference and colemanite-added specimens in Examples 1-4. Figure 13 – capillary water absorption coefficients of the reference and colemanite- added specimens in Examples 1-4. DETAILED DESCRIPTION OF THE INVENTION This invention relates to an ultra-high performance concrete comprising at least one aggregate, at least one binder, at least one reinforcing element, and colemanite. As used in this application the term "ultra-high performance concrete" means a cement-based composite with 120-200 MPa Compressive Strength, 8-15 MPa Splitting Tensile Strength, 30-50 MPa Flexural Tensile Strength, and superior durability properties. (P. Richard and M. Cheyrezy, “Composition of reactive powder concretes”, Cem. Concr. Res., volume 25, issue 7, page 1501–1511, 1995.). In one embodiment of the invention, the amount of colemanite in the ultra-high performance concrete is in the range of 0.1% to 2%, preferably in the range of 0.15% to 1.5%, and more preferably in the range of 0.2% to 1%, relative to the amount of binder. The inventors observed that the ultra-high performance concrete comprising colemanite in said range exhibits a decreased number of shrinkage cracks, an increased setting time, as well as an increased concrete compressive strength and a increased flexural strength in both the medium term and the long term. In particular, concretes with the best spread values are obtained with a colemanite content ranging preferably from 0.2% to 0.5% relative to the amount of binder. The inventors noted that the correct adjustment of the amount of colemanite has a great influence on the consistency of concrete. In case of addition of colemanite at a higher rate than said range, a decreased concrete density was observed due to an increase in an air content in the concrete. The air content of concrete is measured by methods known in the art. According to the present invention, the binder is selected from the group consisting of fly ash, slag, cement, silica fume, and mixtures thereof, and is preferably a mixture of cement and silica fume. In a preferred embodiment of the invention, the ultra-high performance concrete comprises the mixture of cement and silica fume as the binder, wherein the silica fume is in the range of 10% to 40%, and preferably in the range of 15% to 30%, by weight relative to the cement. The cement used in the present invention is preferably a white cement. For the white cement, a CEM I 52.5 / R white cement produced in accordance with the TS EN 197- 1 standard can be used. The physical properties of said cement increase the compressive strength of the ultra-high performance concrete according to the present invention. In the present invention, the silica fume is preferably a white silica fume. Said silica fume provided improved properties to the ultra-high performance concrete and the specific mortar formulation, and allowed the concrete to be mixed with desired color pigments to produce a colored concrete. Thus, the amount of colemanite in the ultra-high performance concrete is in the range of 0.1% to 1%, preferably in the range of 0.15% to 0.75%, and more preferably in the range of 0.2% to 0.5%, relative to the total amount of cement and silica fume. According to the present invention, the colemanite in the ultra-high performance concrete is micronized, with a particle size ranging from 0.1 µm to 100 µm, preferably from 1 µm to 60 µm, and even more preferably from 2 µm to 50 µm. The particle size of colemanite is measured by laser diffraction particle size analysis. Said measurement is carried out with a Mastersizer 3000 particle size analyzer. According to the invention, the ultra-high performance concrete comprises at least one aggregate, wherein said aggregate is selected from the group consisting of silica sand, quartz sand, basalt, and a mixture thereof, and is preferably a mixture of silica sand and quartz sand. According to the invention, the ultra-high performance concrete comprises at least one reinforcing element, wherein said reinforcing element is in the range of 0.1% to 5%, and preferably in the range of 1% to 5%, by volume relative to the concrete. The reinforcing element is preferably a stainless microfiber, and is selected from the group consisting of a steel fiber, an alkali resistant glass fiber, a PVA fiber, a nylon fiber, a polypropylene (PP) fiber, a carbon fiber, a plastic fiber, a cellulose fiber, a cotton fiber, an acrylic fiber, a basalt fiber, and a mixture thereof, and is preferably a steel fiber. Such fibers range in length from 5 to 15 mm, and in diameter from 0.1 to 0.2 mm. According to the present invention, the ultra-high performance concrete further comprises at least one super plasticizer. In an embodiment of the invention, the ultra-high performance concrete according to the invention is obtained by a method comprising the following steps: a) mixing colemanite with at least one binder and at least one aggregate to obtain a dry mix, b) adding a portion of water to the dry mix, and stirring, c) adding the rest of the water along with at least one super plasticizer, and stirring, d) adding at least one reinforcing element to the mix, and stirring, e) transferring the resulting mix into molds. In the method according to the present invention, the stirring operation in each step of the production method takes 5 to 15 minutes, and preferably 7 to 12 minutes. In the method according to the present invention, the amount of water added in step b) ranges from 50% to 80%, and preferably from 60% to 75%, of the total amount of water in the formulation. In the method according to the present invention, an additional stirring operation may be carried out between steps c) and d). According to the present invention, the stirring operation in step a) is carried out at a speed from 20 rpm to 35 rpm; the stirring operations in steps b) or c) are carried out at a speed from 35 rpm to 50 rpm; and / or wherein the stirring operation in step d) is carried out both at a speed from 35 rpm to 50 rpm and at a speed from 50 rpm to 70 rpm. In a preferred embodiment of the invention, the ultra-high performance concrete according to the invention is obtained by a method comprising the following steps: a) mixing colemanite with at least one binder and at least one aggregate to obtain a dry mix, b) adding an amount of water in the range of 60% and 75% of the total water to the dry mix, and stirring for 1 to 5 minutes, c) adding the rest of the total amount of water along with at least one superplasticizer, and stirring for 1 to 5 minutes, d) stirring the resulting mix for another 1 to 5 minutes, e) adding at least one reinforcing element to the mix, and stirring for 1 to 5 minutes, f) transferring the resulting mix into molds. In another preferred embodiment of the invention, the ultra-high performance concrete according to the invention is obtained by a method comprising the following steps: a) mixing colemanite with cement, silica fume, silica sand, and quartz to obtain a dry mix, b) adding an amount of water in the range of 60% and 75% of the total water to the dry mix, and stirring for 1 to 5 minutes, c) adding the rest of the total amount of water along with at least one superplasticizer, and stirring for 1 to 5 minutes, d) stirring the resulting mix for another 1 to 5 minutes, e) adding a steel fiber to the mix, and stirring for 1 to 5 minutes, f) transferring the resulting mix into molds. In another preferred embodiment, the ultra-high performance concrete according to the invention is obtained by a method comprising the following steps: a) mixing colemanite with at least one binder and at least one aggregate at 20 to 35 rpm for 1 to 5 minutes, and obtaining a dry mix, b) adding water to the dry mix at a rate of 50 to 80% relative to the total amount of water in the formulation, and stirring at 35 to 50 rpm for 1 to 5 minutes, c) adding the rest of the water along with at least one superplasticizer, and stirring at 35 to 50 rpm for 1 to 5 minutes, d) adding at least one reinforcing element to the mix, and stirring first at 35 to 50 rpm for 1 to 5 minutes and then at 50 to 70 rpm for 1 to 5 minutes, e) transferring the resulting mix into molds. EXAMPLES Example 1 - UHPC without colemanite Production Method for Example 1: A Hira Pump mixer with a stirring capacity of 56 liters and an operational speed of 70 rpm was used in each of the production methods in the examples. The binder, the sand, and if available the colemanite were mixed dry for 3 minutes, after which 70% of the available water was added to the resulting dry mix and stirred for 2 minutes, followed by addition of the rest of, i.e.30% of, the available water along with the super plasticizer to the mix, and a 1-minute stirring operation, and then a 3-minute stirring operation was carried out, which was followed by addition of the steel fiber and a 3-minute stirring operation, and finally, the resulting mix was transferred into molds without vibration. The molds were covered with glass plates, kept at room temperature for 24 hours, and stored in a curing cabinet until the test days. In detail, the steps of the method can be described in order as follows: - mixing cement, silica fume, silica sand, quartz (100) and quartz (5) as a dry mix at a low speed (20-35 rpm) for 3 minutes, - adding 70% of water to the dry mix, and stirring at a medium speed (35-50 rpm) for 2 minutes, - adding 30% of water, along with the super plasticizer, to the dry mix, and stirring at the medium speed (35-50 rpm) for 1 minute, - stirring the mix for another 3 minutes at the medium speed (35-50 rpm), - adding the steel fiber to the mix, and stirring for 3 minutes, wherein 1 minute of the stirring operation is carried out at the medium speed while the other 2 minutes of the same is carried out at a high speed (50-70 rpm), and - transferring the final mix into molds. Example 2 – UHPC comprising colemanite at a rate of C25 (0.25% by weight of binder (silica fume + cement)) 5Example 3 – UHPC comprising colemanite at a rate of C50 (0.50% by weight of binder (silica fume + cement)) Example 4 – UHPC comprising colemanite at a rate of C100 (1% by weight of binder (silica fume + cement)) Production Method for Examples 2, 3 and 4: - mixing cement, silica fume, silica sand, quartz (100), quartz (5) and colemanite as a dry mix at a low speed (20-35 rpm) for 3 minutes, - adding 70% of water to the dry mix, and stirring at a medium speed (35-50 rpm) for 2 minutes, - adding 30% of water, along with the super plasticizer, to the dry mix, and stirring at the medium speed (35-50 rpm) for 1 minute, - stirring the mix for another 3 minutes at the medium speed (35-50 rpm), - adding the steel fiber to the mix, and stirring for 3 minutes, wherein 1 minute of the stirring operation is carried out at the medium speed while the other 2 minutes of the same is carried out at a high speed (50-70 rpm), and - transferring the final mix into molds. Results: Microstructural Analysis (SEM): SEM microstructures of the reference and 0,25%, 0,50%, 1% colemanite-added cement pastes on the 28th day of hydration are given in Figure 5, respectively. According to the respective SEM images, the reference and colemanite-added cement pastes were found to comprise C-S-H and crystalline CH on the matrix surfaces. Clinker particles are surrounded by a radial fibrous structure of C-S-H. This fibrous structure is rich in lime, and more porous than a C-S-H structure in pozzolans. Portlandite (CH) crystals were observed as a dense layered structure, while AFt (Ettringite) crystals were located in the voids. As a result of 28 days of hydration, it comprises a web-shaped morphology and this web-like structure forms bridges between particles. In the colemanite-added pastes, most of the voids across the matrix were filled with the C-S-H formation and a denser structure was formed compared to the reference paste. This means that colemanite reduces the porosity, resulting in a more compact microstructure. The results of the microstructural analysis of the colemanite-added pastes show that the porous structure is reduced, the mechanical properties are improved with a more impermeable structure, and colemanite promotes an increase in the pozzolanic activity of silica fume by day 28. Fresh Concrete Properties and Shrinkage Tests: Spread diameter, air content, density, and shrinkage properties of the fresh concrete specimens in Examples 1-4 were measured, and the results are shown in Figures 1 to 4. According to the results obtained, the addition of colemanite to UHPC mixes had a positive effect on the consistency. However, as a higher amount of colemanite means a higher air content, a slight decrease in density of fresh concrete has observed with each increase in colemanite amount. According to the results of the shrinkage tests, the addition of colemanite, and an increase in the amount of colemanite added have resulted in a decrease in hydration temperature. In addition, the shrinkage reducing effect of colemanite on UHPC was also confirmed. The spread diameter was determined in accordance with the ASTM C1611 / C1611M- 21 standard. In order to measure the self-spreading property of the UHPC mixes, spread diameter measurements were made through the concrete's own weight. On a flat surface, a spreading table of 100x100 cm was placed, on top of which a truncated cone with an upper diameter of 10 cm, a lower diameter of 20 cm and a height of 30 cm was centered and filled with approximately 6 liters of a concrete mix, and the cone was lifted for 5 seconds to allow the concrete to flow onto the table. Upon completion of the spreading of concrete, the diameter in two perpendicular directions was measured and averaged and the test results were recorded. Fresh concrete air content was determined in accordance with the TS EN 12350-7 standard. A chamber in an aerometer was filled with three layers of a fresh concrete mix without leaving any air voids in the chamber, and a lid was clamped to the chamber of the aerometer by avoiding any pressure leakage. A main air valve was closed, two water valves were opened, and the device was filled with water until water came out of the other valve. An inner surface of the lid was lightly tapped with a mallet to remove air bubbles. An air discharge valve connected to the closed air cell was closed, and air was pumped into the closed air cell until the pressure gauge reached the initial pressure line. The two water valves were closed, the main air valve was opened, and the value indicated by the pressure gauge was read and recorded as air percentage. Fresh concrete density was determined in accordance with the TS EN 12350-6 standard. Fresh concrete was placed in a rigid and sealed container of known volume and mass, and the weight was measured. The fresh concrete density D for the specimens is calculated through the following equation: wherein: D: density (kg / m3) of fresh concrete, M1: mass (kg) of container, M2: mass (kg) of container plus concrete specimen, V: volume (m3) of container. Temperature and Shrinkage Relationship: Shrinkage is defined as a decrease in the volume of concrete over time after the concrete has hardened. This decrease is due to moisture and physicochemical changes in the concrete. Expansion refers to a volumetric increase in hardened concrete which is induced by moisture gain. Shrinkage can be conveniently expressed as a dimensionless strain (in. / in. or m / m) under constant relative humidity and temperature conditions, and includes drying shrinkage, autogenous shrinkage and carbonation shrinkage. Drying shrinkage is due to moisture loss in the concrete, autogenous shrinkage is caused by the hydration of cement, and carbonization shrinkage results from the presence of CO during cement hydration (ACI 209R, 1997). Shrinkage and temperature values of ultra-high performance fresh concrete specimens were determined with a Schleibinger Tester in accordance with the ASTM C1698 standard. A 25x25x290 mm steel mold system capable of measuring early- age shrinkage was used. Using tips secured with steel pins and equipped with movable stops, the system was closed with a steel plate on the free-end side, and temperature, shrinkage and time data were recorded simultaneously by means of a probe by a computer for up to 24 hours prior to hardening. In order to minimize friction and prevent ambient moisture loss during autogenous strain measurements, fresh concrete was covered with a cling film when placed in the mold. Hardened Concrete Tests: Density: On days 2, 7, 28 and 56, all specimens were removed from the curing cabinet, and their densities were calculated by measuring their weights and dimensions. Density values calculated on days 2, 7, 28 and 56 for UHPC specimens are given in Figure 6. When said values were analyzed, it was found that the highest density value was in the reference specimen and the lowest density value was in the C100 specimen on all days. Compressive Strength: Compressive strength was determined in accordance with the French Standard / NF P 18-470 standard. Cylindrical specimens with 70 mm diameter and 140 mm height were prepared and kept in the curing cabinet until the test days, and compressive strength tests were performed on days 2, 7, 28 and 56. In a hydraulic concrete press machine with a capacity of 300.000 kN, said specimens were subjected to a compressive load at a selected constant loading rate ranging from 0,4 Mpa / s to 0,8 Mpa / s until failure, whereby the maximum loads the same specimens could withstand were determined to calculate compressive strength values of the same.3 specimens were prepared for each group, and the compressive strength was calculated by taking the arithmetic average of these 3 specimens. The compressive strength was calculated according to the following formula. The compressive strength is calculated through the following equation: ^ = ^ ^ wherein: ^: compressive strength (N / mm2), P: maximum load (N) at failure, A: cross-sectional area (mm2) (for cylindrical specimens, πr2). Compressive strength results of UHPC specimens at days 2, 7, 28 and 56 are given in Figure 7. When the compressive strength values of UHPC specimens were analyzed, it was found that 2- and 7-day-old colemanite-added specimens had lower values compared to the reference, while 28- and 56-day-old specimens had higher values compared to the reference. At days 28 and 56, the highest compressive strength value was recorded in the C100 specimens. Non-pozzolanic colemanite does not have a direct effect on the pozzolanic activity. However, it increases the pozzolanic activity of silica fume in the mixes on days 28 and 56. In the literature, it is suggested that this is due to the concentration of B2O3in the structure of colemanite. Flexural Strength: Flexural strength was determined in accordance with the French Standard / NF P 18- 470 standard. Beam specimens with dimensions of 70x70x280 mm were prepared, kept in the curing cabinet until the test days, and tested on days 2, 7, 28 and 56. By means of a device with a capacity of 30.000 kN and a loading rate of 0,04 MPa / s, the prism specimens were subjected to a load until failure to determine the maximum load they can withstand.3 specimens were prepared for each group, and the flexural strength was calculated by taking the arithmetic average of these 3 specimens. The four-point flexural strength is calculated through the following equation: wherein: Rf: flexural strength (N / mm2), Ff: force (N) applied to the center of the prism at failure, b: side length (mm) of square section of the prism, L: distance (mm) between the support cylinders. Flexural strength results of UHPC specimens at days 2, 7, 28 and 56 are given in Figure 8. When the flexural strength values of UHPC specimens were analyzed, it was found that the non-reference specimens had lower values compared to the reference on all of the test days. According to a comparison between the colemanite- added specimens, the best flexural strength value among said specimens was in the C25 specimen. In other words, the addition of colemanite had a positive effect on compressive strength, but not on flexural strength. Considering how important the adherence between aggregate and binder paste is for flexural strength, it is believed that the low amount of colemanite added does not provide a sufficient adherence between binder paste and aggregate, resulting in an adverse effect on flexural strength. Schmidt Surface Hardness: Schmidt surface hardness was determined in accordance with the ASTM C805 standard. Cylindrical specimens with 70 mm diameter and 140 mm height were prepared and kept in the curing cabinet until the test days, and Schmidt surface hardness tests were performed on days 2, 7, 28 and 56 (Figure 9). Due to the importance of the angle of impact, the test hammer was placed and applied perpendicular to the surface of the specimen. Mean values were obtained for each group at the end of 12 tests. Schmidt hammer rebound test results of UHPC specimens at days 2, 7, 28 and 56 are given in Figure 9. When the Schmidt hammer rebound values of UHPC specimens were analyzed, it was found that the colemanite-added specimens had higher values than the reference on all days. Owing to the hard mineral structure of colemanite, an increase in surface hardness values was observed with the increase in the addition rate. Ultrasonic Pulse Velocity: Ultrasonic Pulse Velocity (UPV) was determined in accordance with the ASTM C597 standard. Cylindrical specimens with 70 mm diameter and 140 mm height were prepared and kept in the curing cabinet until the test days, and ultrasonic pulse velocity tests were performed on days 2, 7, 28 and 56.3 specimens were prepared for each group, and the intended calculation was made by taking the arithmetic average of data obtained from these 3 specimens. Ultrasonic pulse velocity test results of UHPC specimens at days 2, 7, 28 and 56 are given in Figure 10. When the ultrasonic pulse velocity values of UHPC specimens were analyzed, it was found that the colemanite-added specimens had higher values than the reference on all days. Higher values of ultrasonic pulse velocity were observed with the higher addition rates of colemanite. Therefore, both the addition of colemanite and an increase in the amount of colemanite added provide a decrease in porosity, thereby resulting in a more impermeable concrete. Impact Strength: Impact strength was determined in accordance with the TS EN ISO 179-1 (Type 3 specimen) standard. Beam specimens with dimensions of 25x25x125 mm were prepared, and impact strength tests were carried out at day 56. Loading with a force of 50J was used in these impact tests. 3 specimens were prepared for each group, and the intended calculation was made by taking the arithmetic average of data obtained from these 3 specimens. The impact strength is calculated through the following equation: wherein: acU: impact strength (kJ / m2), h: thickness (0,025 m), b: width (0,025 m), Ec: corrected energy (J) absorbed upon failure of the test specimen. Impact strength results of UHPC specimens at day 56 are given in Figure 11. When the impact strength values of UHPC specimens were analyzed, it was found that the colemanite-added specimens had higher values than the reference. Higher values of impact strength were observed with the higher addition rates of colemanite. Electrical Conductivity: Cylindrical specimens with 70 mm diameter and 140 mm height were prepared and kept in the curing cabinet until the test days, and the respective tests were performed on days 2, 7, 28 and 56. In the literature, various resistivity measurement methods have been proposed (Dehghanpour and Yilmaz, 2020; Dehghanpour et al., 2019; Dehghanpour and Yilmaz, 2020:119948). In this study, the resistivity value of each specimen was obtained according to Ohm's law by applying a current flow and using the two-point uniaxial measurement method. Current was measured at 40 volts. 3 specimens were prepared for each group, and the intended calculation was made by taking the arithmetic average of data obtained from these 3 specimens. Electrical resistivity is calculated through the following equation: wherein: ρ: electrical resistivity (Ω.cm), R: electrical resistance (Ω), V: voltage (40 volts) applied to the specimens, I: measured current (A), A: cross-sectional area (cm2) of specimen, L: length (cm) of specimen, σ: electrical conductivity; it is inversely proportional to the resistivity. Electrical resistivity values measured under wet conditions at days 2, 7, 28 and 56 for UHPC specimens are given in Figure 12. As can be appreciated from the electrical resistivity values of UHPC specimens, the number of hydration products increases as the specimens age, as confirmed by the SEM images, and the electrical resistivity values also increase with this increase. However, the colemanite-added specimens were found to have lower values compared to the reference, and the electrical resistivity values decreased with the increase in addition rate of colemanite. Capillary Water Absorption: Capillary water absorption was determined in accordance with the ASTM C1585 standard. Cubic specimens with dimensions of 70x70x70 mm were prepared, and capillary water absorption tests were performed after 56 days of curing. After being kept under normal water curing conditions for 56 days, the specimens were taken out of the curing environment, and placed in an oven at 105 C° for 24 hours to make them oven dry, and then their masses were weighed. In order to ensure water transfer from the bottom, a mattress was laid on the floor and the experimental setup was installed. The specimens were then immersed in water so that only 5 mm of the specimen base was submerged. At the end of 15, 30, 60, 120, 180, 240, 300, 360, 720, 1440 minute-long (24 hours in total) time intervals, the specimens were weighed in order to determine how much water they absorbed, whereby capillary water absorption values were calculated. The capillary water absorption coefficient S is calculated as the slope of the best-fit line between the mass increase and the square root of time. 3 specimens were prepared for each group, and the intended calculation was made by taking the arithmetic average of data obtained from these 3 specimens. The capillary water absorption is calculated through the following equation: wherein: S: capillary water absorption coefficient (mm / s0.5), I: absorption (mm), mt: weight change (g) of specimen at time t (sec), d: water density (0,001 g / mm3), a: surface area (mm2) of specimen in contact with water. When the test results were analyzed (Figure 13), it was found that the lowest water absorption value was in the C100 sample and the highest water absorption value was in the reference sample. In addition, it was shown that the water absorption values decreased with the increase in the addition rate of colemanite, resulting in a more impermeable structure due to a more compact microstructure, as confirmed by the SEM images.

Claims

CLAIMS 1. An ultra-high performance concrete, comprising at least one aggregate, at least one binder, and at least one reinforcing element, characterized in that said ultra-high performance concrete further comprises colemanite.

2. An ultra-high performance concrete according to claim 1, wherein the amount of colemanite is in the range of 0.1% to 2% by weight relative to the amount of binder.

3. An ultra-high performance concrete according to claim 2, wherein the amount of colemanite is in the range of 0.15% to 1.5% by weight relative to the amount of binder.

4. An ultra-high performance concrete according to claim 3, wherein the amount of colemanite is in the range of 0.2% to 1% by weight relative to the amount of binder.

5. An ultra-high performance concrete according to any one of the preceding claims, wherein the binder is a hydraulic binder.

6. An ultra-high performance concrete according to any one of the preceding claims, wherein the binder is selected from the group consisting of fly ash, slag, cement, silica fume, and mixtures thereof.

7. An ultra-high performance concrete according to claim 6, wherein the binder is a mixture of cement (hydraulic binder) and silica fume.

8. An ultra-high performance concrete according to claim 7, wherein the amount of silica fume is in the range of 10% to 40% by weight relative to the amount of cement.

9. An ultra-high performance concrete according to claim 8, wherein the amount of silica fume is in the range of 15% to 30% by weight relative to the amount of cement.

10. An ultra-high performance concrete according to any one of the preceding claims, wherein the particle size of colemanite ranges from 0.1 µm to 100 µm.

11. An ultra-high performance concrete according to claim 10, wherein the particle size of colemanite ranges from 1 µm to 60 µm.

12. An ultra-high performance concrete according to claim 11, wherein the particle size of colemanite ranges from 2 µm to 50 µm.

13. An ultra-high performance concrete according to any one of the preceding claims, wherein the aggregate is a mixture of silica sand and quartz sand.

14. An ultra-high performance concrete according to any one of the preceding claims, wherein the reinforcing element is in the range of 0.1% to 5% by volume relative to the concrete.

15. An ultra-high performance concrete according to any one of the preceding claims, wherein the reinforcing element is selected from the group consisting of a steel fiber, a glass fiber, a PVA fiber, a nylon fiber, a polypropylene (PP) fiber, a carbon fiber, a basalt fiber, and / or a mixture thereof.

16. An ultra-high performance concrete according to any one of the preceding claims, wherein the concrete further comprises at least one super plasticizer.

17. A method for obtaining an ultra-high performance concrete, comprising the following steps: a) mixing colemanite with at least one binder and at least one aggregate to obtain a dry mix, b) adding a portion of water to the dry mix, and stirring, c) adding the rest of the water along with at least one super plasticizer, and stirring, d) adding at least one reinforcing element to the mix, and stirring, e) transferring the resulting mix into molds.

18. A method according to claim 17, wherein the stirring operations take 5 to 15 minutes.

19. A method according to claim 18, wherein the stirring operations take 7 to 12 minutes.

20. A method according to any one of claims 17 to 19, wherein the stirring operation in step a) is carried out at a speed from 20 rpm to 35 rpm.

21. A method according to any one of claims 17 to 20, wherein the stirring operations in steps b) or c) are carried out at a speed from 35 rpm to 50 rpm.

22. A method according to any one of claims 17 to 21, wherein the stirring operation in step d) is carried out both at a speed from 35 rpm to 50 rpm and at a speed from 50 rpm to 70 rpm.

23. A method according to any one of claims 17 to 22, wherein the amount of water added in step b) is in the range of %50 to %80 of the total amount of water in the formulation.

24. A method according to any one of claims 17 to 23, comprising the following steps: a) mixing colemanite with at least one binder and at least one aggregate at 20 to 35 rpm for 1 to 5 minutes, and obtaining a dry mix, b) adding water to the dry mix at a rate of 50 to 80% relative to the total amount of water in the formulation, and stirring at 35 to 50 rpm for 1 to 5 minutes, c) adding the rest of the water along with at least one superplasticizer, and stirring at 35 to 50 rpm for 1 to 5 minutes, d) adding at least one reinforcing element to the mix, and stirring first at 35 to 50 rpm for 1 to 5 minutes and then at 50 to 70 rpm for 1 to 5 minutes, e) transferring the resulting mix into molds.

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