Method of making concrete

Abstract

The present invention relates to a method for making concrete from cement, and more particularly to a method for making usable standard concrete from aged or otherwise substandard cement.

Description

Technical Field

[0001] The present specification relates generally to a method of making concrete, and more particularly to a method of making concrete from off-spec cement. Background Art

[0002] The following includes information that may be useful in understanding the present disclosure. It is not an admission that any of the information provided herein is prior art, is not material for the presently described or claimed invention, nor is it an admission that any publication or document explicitly or implicitly referenced is prior art.

[0003] It is generally known in the industry that exposure of cement to the surrounding atmosphere results in the absorption of moisture from the air and an irreversible chemical interaction of the cement with water - hydration. As a result, cement loses its activity over time with increasing duration of exposure to air. Portland cement is designed to react chemically with water, and any exposure to ambient moisture will cause it to set and harden. It is generally believed that this inevitable deterioration of cement during transportation and storage explains its limited guaranteed shelf life, which is usually limited to six months, and in some cases, the cement remains useful to the end user for a period of only three months or less. The negative impact of this pre-hydration on cement activity and concrete strength has long been recognized.

[0004] Therefore, attempts have been made to solve this problem by chemical modification of cement. A historical example is found in U.S. Pat. No. 2,996,394 (Stoll), which discloses a hydrophobic, non-caking cement product suitable for extended storage in high humidity areas consisting of Portland cement, 0.1 to 0.4% oleic acid and 0.04 to 0.20% tri-n-butyl phosphate (degassing agent).

[0005] Another example is found in U.S. Pat. No. 10,590,040 (Ozersky et al.), which discloses a large cement and related methods for preparing pastes, mortars, concretes and other cement-based materials with high workability, high density and high strength. A method for producing a large cement is disclosed, the large cement comprising cement, a supplementary cementitious material (SCM) including siliceous submicron-sized particles and nano-sized particles, and a polymer in the form of a liquid or dry chemical admixture for concrete. The cement mixture can be used to make ultra-high performance concrete (UHPC). The large cement can be produced in the form of particles, pellets, lumps or tablets by mechanical activation during coating and / or loading of the cementitious material to extend the shelf life.

[0006] The above patent describes "macro-cement", which refers to a mixture of dry cement produced from the combination of the above ingredients and the ingredients themselves. Macro-cement can exist in various forms, such as granulated, pelletized, agglomerated, tableted, engineered dust-free macro-cement forms with extended shelf life and high workability, which can be used to prepare pastes, mortars, concretes and other cement-based materials with high density and strength, increased early and final strength and accelerated reaction rate in cementitious mixtures.

[0007] Another example is found in International Patent Application Publication No. WO2020 / 073119A1 (Ozersky et al.), which discloses a method for producing self-protecting cement by combining a cement precursor and a wax, wherein the wax comprises an alkyl ketene dimer wax and / or an alkenyl ketene dimer wax; and grinding the cement precursor and the wax to produce cement particles coated with the wax, thereby extending the shelf life of the cement.

[0008] The above-mentioned publication describes "self-protected cements", which refers to cements which, prior to the preparation of the cementitious composition, are protected to a significant extent against deterioration by contact with atmospheric moisture and accidental short-term contact with water, or in other words, are substantially hydrophobic.

[0009] However, shelf life remains an issue with cement. In addition, there remains the problem of trying to use or otherwise recycle damaged cement to form useful concrete.

[0010] Therefore, there is still a need for improvement in this area. Summary of the invention

[0011] In one aspect of the present invention, there is provided a method for making concrete from substandard cement, the method comprising: adding a superplasticizer to the substandard cement during the wet mixing stage of the concrete, wherein the superplasticizer comprises at least 125% of the normally recommended amount for use with standard cement; adding a deaerator during the wet mixing stage of the concrete, wherein the deaerator comprises at least 140% of the normally recommended amount for use with standard cement; producing a cementitious material from the aforementioned steps; and degassing the cementitious material during discharge of the cementitious material from a mixer via a vibrating thin layer reactor, wherein the thin layer reactor forms a thin continuous layer of plastic cementitious material and temporarily reduces the viscosity of the plastic cementitious material in the reactor.

[0012] In an embodiment, the method further comprises dry processing the off-spec cement with fine aggregate in a high shear mixer prior to the concrete wet mixing stage.

[0013] In an embodiment, dry processing further comprises adding a supplemental gelling material in a high shear mixer.

[0014] In an embodiment, dry processing in a high shear mixer provides compression and shear forces capable of breaking up cement agglomerates without breaking up individual particles.

[0015] In an embodiment, the dry processing further comprises adding water such that the ratio of water to cement is between 0.07 and 0.15.

[0016] In embodiments, the superplasticizer comprises 125% to 400% of the normal recommended amount.

[0017] In an embodiment, the superplasticizer is selected from one of a conventional water-reducing admixture, a medium-effective water-reducing admixture and a high-efficiency water-reducing admixture.

[0018] In an embodiment, the superplasticizer is a polycarboxylate-based high-efficiency water reducer.

[0019] In an embodiment, the getter comprises 140% to 500% of the normal recommended amount.

[0020] In an embodiment, the getter is selected from one of the following: tributyl phosphate, dibutyl phosphate, dibutyl phthalate, polydimethylsiloxane, dodecyl (lauryl) alcohol, octanol, polypropylene glycol, water-soluble esters of carbonic acid and boric acid, and lower sulfonate oils.

[0021] In an embodiment, the thickness of the plastic cementitious material layer is in the range of 2 times the diameter to 10 times the diameter of the largest aggregate size in the plastic cementitious material.

[0022] In an embodiment, the plastic gelled material resides on the thin layer reactor for a duration between 4 seconds and 40 seconds.

[0023] In an embodiment, the thin layer reactor has an inclination angle of 0 to 20 degrees relative to the horizontal plane.

[0024] In an embodiment, the thin layer reactor has a plate oscillation amplitude of 0.5 mm to 15 mm and a vibration frequency of 7 Hz to 50 Hz.

[0025] In an embodiment, the oscillation of the thin layer is one of the following: a circular oscillation and a linear oscillation.

[0026] In an embodiment, the thin layer reactor consists of an inclined vibrating plate.

[0027] In an embodiment, the vibration frequency of the vibration plate is between 7 Hz and 0 Hz.

[0028] In an embodiment, the vibration amplitude of the vibration plate is between 0.5 mm and 0 mm.

[0029] In an embodiment, the inclination angle of the vibration plate relative to the horizontal plane is between 10 degrees and 40 degrees.

[0030] In order to summarize the present invention, some aspects, advantages and novel features of the present invention are described herein. It should be understood that according to any one specific embodiment of the present invention, it is not necessary to realize all of these advantages. Therefore, the present invention can be implemented or performed in a manner that realizes or optimizes an advantage or a group of advantages taught herein without realizing other advantages taught or suggested herein. Features of the present invention that are considered to be novel are particularly pointed out and clearly claimed in the concluding portion of the specification. These and other features, aspects and advantages of the present invention will be better understood with reference to the following drawings and detailed description.

[0031] Other aspects and features according to the present application will become apparent to those of ordinary skill in the art after reading the following description of the embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Reference will now be made to the accompanying drawings which show, by way of example only, embodiments of the invention and how they may be implemented, and in which:

[0033] Figure 1A is an optical microscope image of a polished cross section of concrete made with fresh (0-day aged) cementitious dry mix and ordinary Portland cement;

[0034] Figure 1B is an optical microscope image of a polished cross section of concrete made from ordinary Portland cement and aged (90-day accelerated weathering) cementitious dry mix;

[0035] Figure 2A is a graph showing the relationship between the compressive strength of concrete after 28 days and the duration of accelerated aging;

[0036] Figure 2B is a graph of the air content in concrete versus the duration of accelerated aging;

[0037] Figure 2C is a graph of the compressive strength of concrete after 28 days versus the amount of air in the concrete; and

[0038] Figure 3 is a flow chart of a method for making standard concrete from substandard cement.

[0039] The same reference numerals in the drawings denote the same or corresponding elements. DETAILED DESCRIPTION

[0040] The present invention relates to a method for making concrete from cement, and more particularly to a method for making usable concrete from aged or otherwise substandard cement.

[0041] In many practical applications, cement may show deterioration and / or deactivation properties, for example during storage due to the formation of a crust of hydration products on the surface of the cement particles. It is helpful to restore the activity of the old cement by regrinding it and thereby exposing the non-hydrated interior of the cement particles [Yelisieieva Μ.O., "Experience and prospects of application of mechanical activations in the technology of concretes production", Young Scientist, Vol. 6 (21), Part 1, June 23-26, 2015].

[0042] WO2009 / 120115A1 (Olkhovsky) suggests using high-speed impact mills and pulverizers for cement regrinding, which uses a method of cement grinding and mechanical activation in a vortex. Rotation speeds of 100,000 to 300,000 revolutions per minute, impact effects caused by collisions of particles that have derailed, and particle crushing caused by centrifugal forces. However, the cement regrinding method has not been widely used due to its inherent disadvantages.

[0043] It is generally accepted that cement degrades (hydrates) over time by absorbing ambient moisture from the surrounding atmosphere. This approach is described by Dubina et al. [Dubina et al., Impact of environmental moisture on C3A polymorphs in the absence and presence of CaSO4·0.5H2O, Adv. Cem. Res. 26 (2014), 29-40], who argue that "during inappropriate storage of actual cement, capillary condensation may occur between cement particles, initiating partial surface hydration and leading to products identical to those formed under normal hydration conditions" and that "prehydration of cement results in a significant delay in hydration" [Dubina et al., Interaction of water vapour with anhydrous cement minerals, Adv. Appl. Ceram. 109 (2013), 260-268].

[0044] However, if it is assumed that this explanation only partially describes the phenomenon of concrete strength reduction with prolonged cement storage time, other factors may be considered issues to be addressed when making concrete from cement.

[0045] Another factor, which may be even more important, is the air content in concrete made from aged cement, a factor that determines the reduction in strength in concrete based on the extended shelf life of the cement and which had not previously been considered. Experimental data and subsequent statistical analysis indicated the existence of a previously unknown phenomenon, namely that the air content in concrete increases with the storage time of the cement used to make the concrete. The recognition of this phenomenon laid the foundation for the development of methods for making standard concrete from old substandard cement.

[0046] The usual bulk density of cement is less than 1.5g / cm 3 , and its specific gravity is higher than 3g / cm 3 , which indicates that air occupies more than half of the volume of bulk cement, or in other words, the cement particles are clearly spaced apart. It was found that the hydration products on the surface of cement particles exhibit long and thick crystals and produce "bridges" between adjacent cement particles. As cement ages, the number of "bridging" particles gradually increases, and these bridging particles form agglomerates with air locked between the particles. The number of agglomerates, their size and their strength increase with the storage time (aging) of cement. During the concrete mixing process, these agglomerates are partially broken into smaller pieces, releasing the air trapped therein. Most of the air remains in the plastic concrete mix and then in the final hardened concrete in the form of air voids. It can be observed that concrete made from aged cementitious compositions ( Figure 1B ) is greater in number and size than concrete made from fresh cementitious compositions ( Figure 1A ) The number and size of air voids and hardened agglomerates in the

[0047] Based on this data, a method of improving the quality of hardened concrete produced from aged cement requires a method of reducing the air content (air voids) in hardened concrete. The method of reducing air in concrete is performed in two stages: first, breaking up the agglomerates to release the air trapped within the agglomerates, and second, removing this released air from the newly mixed cement paste (mortar or concrete).

[0048] Figure 3 A method of making concrete according to an embodiment of the present invention is shown. In instances where aged cement exhibits an unacceptable amount of caking, it is preferred that an initial stage be performed in the method. However, it should be understood that an initial stage may not be required, for example, where caking is acceptable or where alternative methods of mitigating caking are used.

[0049] In a preferred embodiment, method 300 comprises, at frame 302, a preliminary stage of breaking cement agglomerates by dry processing a mixture of old cement with fine aggregate and, in some cases, supplementary cementitious materials (SCM) in a high shear mixer. The SCM may include micron-sized siliceous, submicron-sized particles and / or nano-sized particles to coat cement particles with a monolayer of micron-, submicron- and / or nano-particles containing SiO2. Dry processing is performed under conditions that expose the processed mixture to compression and shear forces that can break cement agglomerates without crushing individual particles. Cement agglomerates are broken up by strong compression and shear forces, and under the influence of strong friction between the mixture particles, the outer shell of the hydration products on the cement particle surfaces is peeled off from the cement particle surfaces.

[0050] The mixing energy density should be sufficient to deagglomerate, uniformly and completely disperse the cement particles and at the same time homogenize the cement by high shear without component segregation and separation. As non-limiting examples, various equipment can be used as a high shear mixer; for example, the TM Hybridizer TM , from Hosokawa Micron TM Mechanofusion TM and Cyclomix TM System, from Aveka TM The Magnetic Assisted Impact Coater (MAICTM), and other devices that provide high internal friction in the mixture.

[0051] In some cases, the internal friction in the mix can be increased by adding small amounts of water to the mix having a water to cement ratio in the range of 0.07 to 0.15. The processing of old cement with fine aggregate and in some cases with supplementary cementitious materials can be done immediately prior to wet mixing of the concrete and the processed material can then be fed directly from the high shear mixer into the wet concrete mixer.

[0052] Mixing with fine aggregate allows the shaped element or structure to be subsequently cast and hardened. The fine aggregate used herein may be any conventional mineral aggregate, such as sand or a mixture of sand with gravel, crushed stone or equivalent material. Crushed stone may be limestone, basalt, granite, bauxite, etc.

[0053] The method of making concrete 300 includes breaking up agglomerates during wet grinding of the agglomerates during the concrete mixing process; in a preferred embodiment, the agglomerates remain after dry processing as described herein. The grinding process can be enhanced by the use of surfactants, which enhance the Rebinder wedging effect, increase the wettability of the solids, and promote water penetration into smaller cracks in the cement block, thereby facilitating a more complete and accelerated breaking of the agglomerates.

[0054] Water reducing admixtures can be used to reduce the water demand of concrete admixtures including the addition of surfactants. In particular, high range water reducing admixtures (HRWRA) such as ether based polycarboxylate (PCE) superplasticizers are often suitable surfactants for use.

[0055] Therefore, at box 304 of the method 300 for making standard concrete from off-spec cement, an excess amount of superplasticizer, such as PCE superplasticizer, is added during the concrete wet mixing stage in an order of magnitude of 125% to 400% of the normal recommended amount of superplasticizer used in a concrete mix with fresh standard cement (depending on cement age and mixing conditions). For example, if the dosage rate of a particular HRWRA is typically in the range of 200 mL to 400 mL / 100 kg of cementitious material with fresh standard cement, the recommended dosage of the same HRWRA would be in the range of 250 mL to 1,600 mL / 100 kg of cementitious material with off-spec cement.

[0056] However, it is known in the art that polycarboxylates having relatively high surface energy at the liquid-air interface exhibit a significant air entrainment effect, i.e. they introduce some foam when mixed into concrete, and the use of defoamers or deaerators is generally recommended when using PCEs.

[0057] Therefore, at box 306 of the method of making standard concrete from substandard cement, an excess amount of deaerator is added during the concrete wet mixing stage, the excess amount of deaerator being about 140% to 500% of the normal recommended amount of deaerator for concrete mixes with fresh standard cement (depending on cement age and mixing conditions). For example, if the dosage rate of a certain deaerator is in the range of 0.1% to 0.7% by weight of fresh standard cement, the recommended dosage rate of the same deaerator will be in the range of 0.14% to 3.5% by weight of substandard cement.

[0058] Suitable getter admixtures may include, but are not limited to, tributyl phosphate, dibutyl phosphate, dibutyl phthalate, polydimethylsiloxane, dodecyl (lauryl) alcohol, octanol, polypropylene glycol, water-soluble esters of carbonic acid and boric acid, and lower sulfonate oils.

[0059] However, the control of the degassing process in concrete mixers is generally poor, since effective degassing agents (also called deaerators and / or defoamers) exhibit insolubility in the medium to be treated, i.e. the deaerator mixture should be insoluble in water (hydrophobic) to be effective. This insolubility results in poor mixing of the degassing agent in low-strength concrete mixers or separation of oily defoamers from the aqueous concrete mix and formation of a top layer in higher-strength concrete mixers.

[0060] In addition, the low efficiency of known degassing agents used according to the prior art for degassing in the wet mixing stage is a result of the relatively high viscosity of the plastic cement paste (mortar, concrete), and the considerable distance that the bubbles need to travel to the surface of the mixture, where they are unstable and therefore burst. Considering the low rising velocity of the bubbles, which follows Stokes' Law (proportional to the square of the radius of the bubble), this velocity is significantly reduced for micron-sized bubbles and is also inversely proportional to the viscosity of the cement paste (mortar, concrete), which is known to be relatively high. Therefore, given the large distance that the bubbles must travel to the surface of the mixture effectively, even extended mixing times are not long enough to completely remove the air.

[0061] Thus, at box 308 of the method for making standard concrete from substandard cement, the cementitious material is degassed during discharge of the material from the mixer in a specially designed thin layer reactor to form a thin continuous layer of plastic cementitious material and temporarily reduce the viscosity of the material in the reactor. By reducing the viscosity of the plastic cementitious material, the rising speed of the gas bubbles within the material increases proportionally according to Stokes' law as described above; the creation of a thin continuous layer reduces the distance that the gas bubbles must travel to reach the surface of the cementitious material, which generally increases the speed and thoroughness of the degassing of the cementitious material.

[0062] The active element of the thin-layer reactor is an inclined vibrating plate on which the gelled material is removed from the mixer. Considering the thixotropic nature of plastic gelled materials and the fact that their viscosity decreases with increasing shear rate, the vibration of the plate significantly reduces the viscosity of the material.

[0063] The thickness of the plastic cement layer on the vibrating plate, in order to provide effective degassing of the material without causing separation (demixing) of the material, should be in the range of 2 diameters of the largest aggregate size in the mix to 10 diameters of the largest aggregate size in the mix. The residence time of the material on the vibrating plate should be in the range of 4 to 40 seconds, depending on the design of the mix. The inclination angle of the plate relative to the horizontal plane is in the range of 0 degrees (i.e., completely horizontal) to 20 degrees; the amplitude of the plate oscillation is in the range of 0.5 to 15 mm; the vibration frequency is 7 to 50 Hz, and the vibration direction can be linear or circular.

[0064] Although degassing of the cementitious material increases on the fixed plate when vibrating, in cases where the installation of the vibrating plate is not easily possible, a fixed inclined plate can be used on which the cementitious material moves during discharge of the cementitious material from the concrete mixer. In this case, the inclination angle of the fixed plate relative to the horizontal plane ranges between 10 degrees and 40 degrees.

[0065] Examples

[0066] The following examples are illustrative in nature and should not be construed as representing all uses of the present method, nor as any commitment to effectiveness for any use.

[0067] This example illustrates the compressive strength of concrete samples prepared using cement and the air content in these concrete samples after various storage periods of the cement under artificial accelerated conditions, again reflecting the atmosphere. The concrete mixes used are detailed in Table 1.

[0068]

[0069] Table 1

[0070] In order to confirm that, as described above, when the shelf life of cement increases, the amount of air in concrete made from the cement increases, and that the increase in air content is an important factor determining the reduction in strength in the final concrete, according to experiments conducted during accelerated aging (at a temperature of about 40° C. and a relative humidity (RH) close to 100%) of cement samples for a certain period of time (0, 15, 30, 75 and 90 days), concrete was prepared from the compositions having these cement samples, and the compressive strength (after 28 days) of the concrete samples and the air content in the samples were measured, and the results are shown in Table 2.

[0071]

[0072] Table 2

[0073] As shown in Figure 2, regression analysis was performed in the R statistical computing environment to process the strength data and air content of concrete made with fresh cement and cement exposed to accelerated aging. Figure 2A It is shown that the strength decreases with aging time. Figure 2B It is shown that the air content increases with aging time. Figure 2C The negative relationship established between intensity and air content is shown.

[0074] Thus, where a negative relationship is established between air content and strength, the method of producing concrete with reduced air content by a combination of chemical and mechanical processes as disclosed herein can be applied to substandard (e.g., aged) cement to produce standard (usable) concrete.

[0075] It should also be noted that the steps described in this method can be performed in many different orders depending on user preferences. In the claims herein, the use of "steps of" should not be interpreted as "steps for" and is not intended to invoke the provisions of 35 U.S.C. §112(f). It should also be noted that other methods are taught herein, where appropriate, taking into account issues such as design preferences, user preferences, marketing preferences, costs, structural requirements, available materials, technological advances, etc.

[0076] The embodiments of the invention described herein are exemplary, and many modifications, variations, and rearrangements are readily conceivable to achieve substantially equivalent results, all of which are intended to be included within the spirit and scope of the invention. In addition, the purpose of the above summary is to enable the U.S. Patent and Trademark Office and the public, especially scientists, engineers, and practitioners in the field who are not familiar with patent or legal terms or phraseology, to quickly ascertain the nature and essence of the technical disclosure of the present application from a cursory inspection.

[0077] Without departing from the spirit or essential features of the present invention, the present invention may be implemented in other specific forms. Some changes and modifications of the present invention will be apparent to those skilled in the art. Therefore, the embodiments discussed herein are considered to be illustrative rather than restrictive, the scope of the present invention is indicated by the appended claims rather than the preceding description, and all changes within the meaning and scope of the equivalents of the claims are therefore intended to be included therein.

Claims

1. A method for producing concrete from substandard cement, comprising: a) adding a superplasticizer to the substandard cement during the concrete wet mixing stage, wherein the superplasticizer comprises at least 125% of the normal recommended amount for use with standard cement; b) adding an air depressant at the wet mixing stage of said concrete, said air depressant comprising at least 140% of the normal recommended amount for use with standard cement; c) producing a cementitious material from steps a) and b); and d) degassing the gelled material during its discharge from the mixer via a vibrating thin layer reactor which forms a continuous thin layer of plastic gelled material and temporarily reduces the viscosity of the plastic gelled material in the reactor.

2. The method of claim 1 further comprising dry processing the off-spec cement with fine aggregate in a high shear mixer prior to the concrete wet mixing stage.

3. The method of claim 2, wherein the dry processing further comprises adding a supplementary gelling material to the high shear mixer.

4. The method of claim 2, wherein the dry processing in the high shear mixer provides compression and shear forces capable of breaking up cement agglomerates without breaking up individual particles.

5. The method of claim 1, wherein the superplasticizer comprises 125% to 400% of the normally recommended amount.

6. The method according to claim 1, wherein the superplasticizer is selected from one of a conventional, medium-effective and high-efficiency water-reducing admixture.

7. The method of claim 6, wherein the superplasticizer is a polycarboxylate-based high-efficiency water reducer.

8. The method of claim 1, wherein the getter comprises 140% to 500% of the normally recommended amount.

9. The method according to claim 1, wherein the getter is selected from one of the following: tributyl phosphate, dibutyl phosphate, dibutyl phthalate, polydimethylsiloxane, dodecyl (lauryl) alcohol, octanol, polypropylene glycol, water-soluble esters of carbonic acid and boric acid, and low-grade sulfonate oils.

10. The method of claim 1, wherein the thickness of the layer of plastic cementitious material is in the range of 2 to 10 diameters of the largest aggregate size in the plastic cementitious material.

11. The method of claim 1, wherein the plastic gelled material resides on the thin layer reactor for a duration between 4 seconds and 40 seconds.

12. The method according to claim 1, wherein the thin layer reactor has an inclination angle of 0 to 20 degrees relative to a horizontal plane.

13. The method according to claim 1, wherein the thin layer reactor has a plate oscillation amplitude of 0.5 mm to 15 mm and a vibration frequency of 7 Hz to 50 Hz.

14. The method according to claim 1, wherein the oscillation of the thin layer is one of the following: circular oscillation and linear oscillation.

15. The method according to claim 1, wherein the thin layer reactor comprises an inclined vibrating plate. The method according to claim 15 , wherein the vibration frequency of the vibration plate is between 7 Hz and 0 Hz. The method according to claim 15 , wherein the vibration amplitude of the vibration plate is between 0.5 mm and 0 mm.

18. The method according to claim 15, wherein the inclination angle of the vibration plate relative to a horizontal plane is between 10 degrees and 40 degrees.

Images