Method of producing Nanoconcrete with High-Energy Mixing
1. A method of producing nanoconcrete according to the bottom-up approach of nano technology with the High-Energy Mixing of composition of cement and water, the mixing is performed with a mixture flow characterized by dimensionless Reynolds number and Power number in the range of 20-800 and 0.1-4.0 respectively with installation a disk horizontally into mixing assembly on the top layer of activated mixture coaxially with vertical axis of assembly and with the axis of impeller rotation on the adjustable level, to avoid destroying created gel as a result of interruptions of High-Energy mixing, to increase laminarity of the mixture flow, energy absorption by the mixture, and shear stress for creation additional quantity of the nanostructured Calcium Silicate Hydrate (C—
H) gel necessary for making nanoconcrete.
In a method of producing nanoconcrete according the bottom-up approach of nano technology with the High-Energy Mixing of composition including cement, water, sand, additives and superplasticizers, the mixing is performed with flow of mixture characterized by Reynolds number and Power number in the range of 20-800 and 0.1-4.0 respectively with installation a disk horizontally into mixing assembly on the top layer of activated mixture coaxially with vertical axis of assembly and with the axis of impeller rotation on the adjustable level to avoid destroying created gel as a result of interruptions of process, to increase laminarity of the mixture flow, energy absorption by the mixture, and shear stress for creation additional quantity of the nanostructured Calcium Silicate Hydrate (C—S—H) gel necessary for making nanoconcrete.
- 1. A method of producing nanoconcrete according to the bottom-up approach of nano technology with the High-Energy Mixing of composition of cement and water, the mixing is performed with a mixture flow characterized by dimensionless Reynolds number and Power number in the range of 20-800 and 0.1-4.0 respectively with installation a disk horizontally into mixing assembly on the top layer of activated mixture coaxially with vertical axis of assembly and with the axis of impeller rotation on the adjustable level, to avoid destroying created gel as a result of interruptions of High-Energy mixing, to increase laminarity of the mixture flow, energy absorption by the mixture, and shear stress for creation additional quantity of the nanostructured Calcium Silicate Hydrate (C—
H) gel necessary for making nanoconcrete.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
The present invention relates to methods of producing nanoconcrete by means of the bottom-up approach in Nano technology. It may correspond to International Classification: C04B 28/00, C04B 40/00, C04B 14/06 and U.S. Classification: 106/709, 106/654, 106/705.
Most of modern methods for creation nano structured cement based materials use the top-down approach of nano technology where nano-sized material is introduced in traditional material for its nano modification (Florence Sanchez, Konstantin Sobolev “Nano technology in concrete—A review” Construction and Building Materials 24 p.p. 2060-2071, 2061 ). Perumalsamy Balaguru, Ken Chong “Nano technology and concrete: research opportunity” National Science Foundation, USA, November 2006, paragraphs 4.1-4.8 , considered nano-sized cement particles, carbon nano-tubes as well as nano-scaled silica fumes and others nano-materials as perspective for nano technology of concrete using the top-down approach of Nano technology. Uniform dispersion of nano-scaled additives is attainable using various types of mechanical methods, including ultrasonication, ball milling etc. (Samuel Chuah, Zhu Pan et al. “Nano reinforced cement and concrete composites and new perspective from graphene oxide” Construction and Building Materials 73, 2014, p.p. 113-124, see p. 116 paragraph 3.1 and p. 122 left column, paragraph 3 ). These processes require increased energy spending (p. 116). For instance effective dispersion of fibers made of carbon nano tubes requires 2800 Kj/l of energy. Agglomeration of nano materials is a common problem due to the strong Van der Waal'"'"'s attractive forces at the nano-scale (p. 122). This requires a combination of sonication for mechanical separation and special surfactants to avoid re-agglomeration of nano particles in the cement matrix.
Concrete itself as a cement based material is an example of real nano-material because the cement hydration is a typical nano-process. The main and unique result of this process is formation of so called Calcium Silicate Hydrate colloidal material or C—S—H gel. C—S—H gel consists of globules about 5 nm in diameter which are held together mainly by Van der Waals'"'"' forces creating nano-structured layers of semi-crystalline material (Laila Raki at al. “Cement and Concrete Nano-science and Nano technology”, Review, J. Materials 2010, 3, p.p. 919-942, see p. 921 ). However, even after three years of hardening, 30-40% (and up to 50% in conditions of low humidity) of the volume of cement grains remains unhydrated, as a result of the formation of watertight hydrated shells around the cement grains (O. A. Gershberg “The Technology of concrete and reinforced concrete items” Moscow GSI 1971, p. 27, translation is enclosed ). In High strength concrete made with low w/c value a significant fraction of cement must remain unhydrated due to a lack of space for hydration products formation (J. Thomas, H. Jennings “The Science of Concrete”, Report of Department of Civil and Environmental Engineering Northwestern University, Evanston Ill., Chapter 5.6, page 60, paragraph 2 ). In the inventive method this unhydrated part of cement is considered as a potential reserve for creation of new portions of nano particles of Calcium Silicate Hydrate. The proposed process allows using this reserve at the stage of concrete mixture preparation to significantly increase the volume of the nano-structured gel and to obtain a material that can be called Nanoconcrete.
In the present invention, the principle of intensive mixing with increased energy absorption by the mixture consisting of at least cement and water was chosen as general one. M. Young and H. Jennings (influences of Mixing Methods on the Microstructure and Rheological Behavior of Cement Paste”, Elsevier Science Inc, 1995, page 71, paragraph 2, page 77, paragraph 2 ) suggested the processes of intensive mixing, in which the shear deformations between the layers of liquid depend on shear rate developing with the increase of the angular velocity of impeller. After increasing shear rate more than 1000 s−1 they could achieve dispersive forces 9×10−6 N to break agglomerates of 0.3 mm (page 77 column 2, paragraph 2). Such a dispersive force is not enough to break cement agglomerates smaller than 0.3 mm especially to create nano sized particles. A further increase in shear rate requires to significantly accelerating rotation of the impeller. This leads to a sharp increase in the Reynolds number, i.e. creates greater turbulence and therefore reduces energy absorption by the activated mixture. Thus this way is not acceptable.
In the inventive method the Portland Cement concrete is considered as a natural sours of nano-material for creation nanoconcrete in accordance with the bottom-up approach of Nano technology.
The application Ser. No. 13/476,003 published Nov. 21, 2013, as invention No: 2013/0395963A1  suggests the Method of producing activated construction mixture including cement, and water with or without sand as well as traditional additives and superplasticiser. Activation is performed with dimensionless criteria Reynolds and Power numbers within the limits 20-800 and 0.1-4.0 respectively for increasing water adsorption with Calcium Silicate Hydrate colloid formation and acceleration cement hydration. The research of this process was continued by testing the mixtures with and without sand and shows that the development of Calcium Silicate Hydrate colloid formation in some cases accompanied by increase of the mixture viscosity. As a result of this phenomenon starting from some point the circulation of the mixture breaks off, and interruptions of the mixture flow happen causing strokes and partial gel destruction. This phenomenon is more typical for mixtures containing sand. Some of mixtures require increasing impeller velocity in order to shorten process of activation. This increases of turbulence and reduces energy absorption worsening effectiveness of High-Energy Mixing process. All of these negative phenomena should be reduced or eliminated to make process more effective.
Two representative mixtures with relation cement, sand and water 1:0.00:0.37 (1) and 1:0.64:0.37 (2) were considered as a binders for making nanoconcrete when using two stage mixing concrete. According to this technology the binders mechanically activated in the High-Energy mixer (first stage) then are mixed with aggregates in conventional mixer (second stage). As a result of this inventive method these binders will possess increased quantity of nanostructured C—S—H gel that is necessary for creation of Nanoconcrete in accordance with the bottom-up approach of nano technology.
Accordingly, it is an object of the present invention to provide a Method of producing nanoconcrete using traditional materials—cement and water with or without sand by means of creating conditions for increasing quantity of nano-structured C—S—H gel in the process of High-Energy Mixing (HEM). This method is a development of the “Method of producing activated construction mixture” (The application Ser. No. 13/476,003 published Nov. 21, 2013, as invention No: 2013/0395963A1 ). In keeping with this object and with others which will become apparent hereinafter the main feature of the present invention resides in a method of producing nanoconcrete according to the bottom-up approach of nano technology with the High—Energy Mixing (HEM) of a composition consisting of at least cement and water, mixing is performed with a mixture flow characterized by dimensionless criteria Reynolds number and Power number in the range of 20-800 and 0.1-4.0 respectively with installation a disk horizontally into mixing assembly on the top layer of activated mixture coaxially with vertical axis of assembly and with the axis of impeller rotation (
The novel features which are considered as characteristic for the present invention are set force in particular in the appended claims. The invention itself however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings and table.
According to the present invention, a method for producing nanoconcrete in compliance with the bottom-up approach of nano technology, based on a High-Energy Mixing of a composition consisting at least of cement and water, mixing is performed with a mixture flow characterized by dimensionless criteria Reynolds number and Power number in the range of 20-800 and 0.1-4.0 respectively is proposed.
These criteria are taken as generalizing parameters that characterize the optimal flow of the mixture achieved in a working laboratory prototype of facility for the reproduction of the same flow on the production scale assembly.
The inventive method includes installation a disk horizontally into mixing assembly at the top layer of activated mixture coaxially with vertical axis of assembly and with the axis of impeller rotation on the adjustable level, to avoid destroying created gel as a result of interruptions of High-Energy Mixing, to increase laminarity of the mixture flow, energy absorption by the mixture, and shear stress for creation additional quantity of the nanostructured Calcium Silicate Hydrate (C—S—H) gel necessary for making Nanoconcrete.
The movable disk having the central hole located horizontally at the top layer of activated mixture (
The inventive method comprise forming the activating assembly as a small scale working prototype of a production scale activating assembly, monitoring a temperature of the activated mixture, power consumption and impeller rotation parameters with and without mixture by a sensor and measuring devices, and inputting running values of said parameters as variables and geometrical parameters of the activating assembly namely L and Ds—height and diameter of cylindrical surface formed when the impeller rotates, Dc—diameter of container (
In activation with High-Energy Mixing according the present invention the main part of the activated mixture is located under a disk. The volume of circulating mixture increases in comparing with original one when impeller doesn'"'"'t rotate and excess of it is moving up around flexible disk (
In the device of a disk suspension the opportunity of its displacement on vertical direction is provided. The viscosity of mixture changes during the process of HEM activation as a result of C—S—H gel formation. In some cases especially if the mixture contains sand the interruptions of the mixture circulation occurs and the power consumption fells down. The shift of the disk down allows to avoid interruptions of the process and restores the power consumption.
In the inventive method vertical adjustment of disk location is provided through hangers (
The results of tests presented in graphs
The special method based on determination the development of penetration resistance of mixtures at the temperature −15° C. created to get an approximate quantitative index of C—S—H gel increase to compare different variants of HEM activated mixtures with the control mixtures prepared without activation (see therein below, paragraph ). The effectiveness of different methods of HEM activation was estimated with the coefficient of increase quantity of C—S—H gel in comparing with the control conventionally mixed variants. Coefficient Kc-s-h was created and defined as the ratio of areas of the graphs “Penetration Resistance in psi—aging time at −15° C. in hours” getting for activated and control mixtures (see
Development of penetration resistance at the temperature −15° C. of the Cement—Water mixture (W/C=0.37) after High-Energy Mixing with movable disk made of flexible material is 2 times more intensive in comparing with variant without disk (
Analogous results are shown on
Test 3 and test 4 are accomplished with the mixtures containing Cement, Sand and Water in proportions 1:0.64:0.37 respectively. This kind of mixture may be used also as HEM activated binder for Nanoconcrete.
The HEM activation of the Cement, Sand and Water mixture without movable disk show about 10 interruptions of process where Re number increases from 500 to 2500 (
In the present invention the average value of Reynolds number significantly reduced by using disc made of an elastic material or a metal lattice, i.e. turbulence decreases and laminar flow of the mixture increases during the process of High-Energy mixing. This corresponds to an increase in the absorption of energy by a mixture consisting only of cement and water, and also containing sand. As a result the shear stress between the particles of the mixture significantly increases (see Table 1). This indicates an improvement in activation efficiency because of greater localization of the circulating mixture in comparing with activation without disk where the mixture is scattered throughout the full volume of the mixer (
In the inventive method it is possible to provide changing a volume of activated mixture by proportionally changing geometric parameters of the activating assembly while maintaining constant average values of net specific power and Reynolds and Power numbers for each particular task and mixture.
In the inventive method it is possible also to provide occurring at production small changes in the volume of the mixture activated with HEM by moving up and down the disk made of flexible material or the metal lattice inside the same cylindrical container designed for required maximal volume.
State of water in the volume of C—S—H gel increased as a result of High-Energy Mixing according the inventive method can be present within the interlayer structure as H2O or OH′. The capillary pores 10-50 nanometers in diameter and larger than 3-5 micrometers outside and between C—S—H clusters can contain free water, solution so called bulk water. According R. A. Olson at al. (“Interpretation of the impedance spectroscopy of cement paste via computer modeling, Part III Microstructural analysis of frozen cement paste”, Journal of materials science 30, 1995, p. 5081 ) the calorimetric results of hardened cement paste show three well-defined peaks at approximately −8, −23, and −40° C. The peak at −8° C. is due to freezing bulk water in macro pores. The peak at −23° C. corresponds to the freezing of the smaller capillary pores of C—S—H gel, while the rather broad peak at −40° C. represents the low temperature transition of supersaturated solution in gel pores. Very little additional freezing occurs below this last peak.
Taking into account the results of the Mr. Olson research shown here above in order to evaluate the main result obtained from the application of the present invention, in the inventive process an approximate quantitative method of comparing mixtures with different amounts of C—S—H gel was created and used (see therein above). The method is based on the determination of Penetration Resistance development of the cement containing mixtures hardening at temperature −15° C. during several days. At these conditions the liquid phase in nano-sized pores of C—S—H gel doesn'"'"'t freeze and able to interact with cement increasing the Penetration Resistance. The index of penetration resistance is determined every day after thawing of samples when the mixture temperature increases from −15° C. to +5° C. This non standardized method was broadly used in this invention for approximate estimation of the quantity of C—S—H gel increase after the inventive method of High-Energy Mixing in comparison with already known method (“Method of producing activated construction mixture”, the application Ser. No. 13/476,003 published Nov. 21, 2013, as invention No: 2013/0395963A1 ) and conventionally mixed control variant. For this purpose the coefficient (Kc-s-h) was created and used. Kc-s-h is defined as the ratio of the areas of the graphs “Penetration Resistance in psi—aging time at −15° C. in hours” (see
Water in nano pores of C—S—H gel has a greater density i.e. smaller specific volume than ordinary water, filling micro and macro pores and capillaries in hardening cement paste. This can cause chemical shrinkage, which in ordinary concrete is small and does not create large internal stresses (J. Thomas, H. Jennings “The Science of Concrete” 2108, § 18.104.22.168., p. 50 [6A]). In the case of nanoconcrete, where the volume of gel can be increased several times the risk of chemical shrinkage increases, which may cause the necessity of adding shrinkage compensating additives. This is provided by current invention.
The necessity to control the flow of the mixture developing in the mixer and effectiveness of energy usage requires considering additional parameters to calculate Reynolds and Power numbers. This also allows transferring the technological process fulfilled on the small scale activator to big production scale machine keeping the same levels of these criteria. It requires to consider some groups of parameters: geometrical parameters such as diameter of impeller rotation—Ds (m), height of blade—L (m), diameter of container—Dc (m) and height of mixture in container before mixing-activation—H (m), see
Physical parameters values of the turned on empty activator labeled here as X0, the current values of them taken in the process of activation are labeled as Xt. The present invention is based on experiments with variations of these parameters during the activation of construction mixtures shown therein above prepared with variety of impellers and their rotational speed.
Formulas for above mentioned dimensionless criteria to control their flow during the activation are the formulas for stirred vessel (P. K. Biswas, K. M. Godiwalla, D. Sanyal, S. C. Dev “A simple technique for measurement of apparent viscosity of slurries: sand-water system”, Materials & Design, India Elsevier Science Ltd. Vol. 23, 2002, p. 511-519, see p. 512, right column, ):
where ρ is a density of the mixture in kg per cu. m, Nt is a speed of impeller in Rps (revolutions per second), Ds—diameter of impeller in m, η—apparent dynamic viscosity in Pas (Pascal-second), ΔP—net power in watt.
In the present invention the mixer-activator considered as a kind of rotational viscometer. It creates a possibility to use equations (1), (2) and (5) from (E. Freire et al. “Process ability of PVDF/PMMA blends studied by torque rheometry,” Materials Science and Engineering C 29, pp. 657-661, Elsevier 2009 ), to calculate the apparent dynamic viscosity (η) values in Pas through shear stress and shear rate determined with formulas (see p.p. 658,659) transformed for conditions of High-Energy mixing:
Where τ is shear stress in N/m2, γ is shear rate in sec−1.
Thus all these values may be calculated having the geometrical parameters of activator (Rc, Rs and L) mentioned above (see
The equation for dynamic viscosity is valid for rotational viscometers with the rotated cylinder or blades immersed into liquid. In the present invention the main apparatus consists of the cylindrical container and impeller with straight or skewed blades (
In the inventive method further comprising forming the activating assembly as a small scale working prototype and/or a production scale activating assembly, monitoring a temperature of the activated mixture, power consumption and impeller rotation parameters with and without a mixture by a sensor and measuring devices; and inputting running values of said parameters as variables and geometrical parameters of the activating assembly and density of mixture as constants and outputting running and average values of measured and calculated parameters including gross and net power consumption, shear stress, apparent dynamic viscosity, and the dimensionless criteria Reynolds and Power numbers as well as interruptions of process and temperature of the mixture are fulfilled by a computer device.
The expected rotational velocity of the production scale mixer loaded with mixture, N (Rps) calculated as average from the conditions:
1-st, Resmall scale mixer=Reproduction scale mixer;
2-nd, Nsmall scale mixer=Nproduction scale mixer.
The expected velocity of impeller for the empty production scale mixer should be increased by multiplying this calculated value on the ratio Nempty/Nloaded known for the small scale mixer.
In the inventive method calculation of production scale High-Energy mixer comprising proportionally changing a volume of small scale working prototype and other geometric parameters named here above while maintaining equals for small and production scale of mixing assembly maximal and average values of gross and net specific power and average values of Reynolds and Power numbers in order to correctly choose drive and geometry of the production scale mixer for each particular task and mixture. See the example of the results of calculation of the production scale the High-Energy mixer in “Method of producing activated construction mixture”, U.S. Patent application Ser. No. 13/476,003 publication No US 2013/0305963, 2013, Table 3, page 6 .
It will be clear that changes in the details, materials, steps and arrangement of parts which have been described and illustrated to explain the nature of the present invention as well as eliminating some of claimed parameters of invented process may be made by those skilled in the art upon reading of this disclosure with attaining considerable increase of C—S—H gel and other shown above changes of properties of the High-Energy Mixed mixture and in spite of it continue to stay within the principles and scope of present invention.
It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of method differing from the type described above.
While the invention has been illustrated and described as embodied in a method for producing nanoconcrete with the High-Energy Mixing, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.
Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the stand point of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.