Device and method for producing concrete, especially concrete with high early strength

Abstract

The invention relates to a device (1) for producing concrete, comprising a cement premixer (3) for mixing a cement suspension, wherein the cement premixer (3) has at least one ultrasonic generator, in particular an ultrasonic probe (6), for preparing the cement suspension; at least one first crystallization tank (4 or 5), in particular a crystallization tank device having a first crystallization tank (4 or 5), for increasing the early strength of concrete, and a concrete mixer (201) for producing a concrete mixture from the premixed cement suspension, in particular with the addition of aggregates (206-208), and also to a method for producing concrete.

Description

Technical Field

[0001] The invention relates to a device for producing concrete, in particular concrete with high early strength, and a method for producing corresponding concrete. Background Art

[0002] US 2018 / 318778A1 and RU 2496748C1 are cited as relevant prior art.

[0003] An important characteristic parameter of concrete components is their early strength. Possible solutions for increasing the early strength of concrete are established processes, such as heat treatment, the use of accelerated concrete admixtures, or concrete technology measures, such as increasing the cement content to a level above that required by the design or reducing the w / c value (ratio of water to cement). However, these variants are usually a compromise, in which the time factor is exchanged at the expense of significantly increased production costs. In addition, although the early strength is increased due to the change in composition, it also leads to undesirable changes in the material properties as a whole (such as shrinkage cracks).

[0004] DE 37 16 438 A1 discloses a device having a cement premixer, a concrete mixer and a tank arranged between them. In this case, cement and water are mixed to form a cement paste. This cement paste is temporarily stored and then mixed with aggregates as usual to produce concrete.

[0005] The difficulty that arises when mixing cement pastes is that only at (very) high w / c values ​​is there enough free water available to mix cement and water correctly. Since a large part of the water often enters the concrete mixer with the rock moisture, the available water content of the premix is ​​reduced. For medium and low w / c values ​​(<0.50), cement pastes can only be produced using high-performance plasticizers.

[0006] Furthermore, high mixing speeds are necessary for complete dissolution of cement and water. This is taken into account in E01 DE 37 16 438 A1 by dependent claims 3 and 4. Due to the high abrasiveness of cement, these high-speed mixing tools wear quickly and can easily become clogged (especially at low water contents).

[0007] The greatest challenge in this process is to provide a uniform suspension quality over the entire production day. The above-mentioned documents do not provide any answers here. However, it must be assumed here that the suspension is stored in a tank ("storage hopper"). The tank is emptied for concrete mixing and refilled again, during which the pre-storage time must be waited again. Therefore, economical operation of the mixing plant is not possible. If a large tank is filled and gradually emptied at this time, the suspension contained therein will age over time, thereby significantly changing the properties of the produced concrete. Ultimately, the cement suspension may solidify in the tank and cannot be processed further.

[0008] Furthermore, two-stage mixing methods are known, by means of which the early strength is increased. The use of two-stage mixing methods is also described in particular in DE 15 84 305 A or DE 10 2016 003 644 B4. Here, the workability and early strength of the concrete are to be improved by means of a two-stage mixing process, namely by 1.) intensive premixing of the cementitious material components with and without sand and 2.) final mixing in a concrete mixer.

[0009] It is also known to use ultrasound for premixing, as has been described in more detail in DE 10 2007 027 080 A1 and in particular in DE 10 2019 120 939 A1.

[0010] All two-stage concrete mixing processes have the disadvantage that a certain amount of (mixing) water is required for the production of the suspension. The water content of the concrete depends on the water requirement of the aggregates (Gk), the w / c value and the cement content. However, since the added aggregates, and especially the sand, never dry completely (for example, during the filling of underground silos, the aggregates are watered to keep dust formation to a minimum), the moisture adhering to the aggregates must be removed from the mixing water. This is done either by weighing or transport or by moisture measurement in the concrete mixer. If there is a moderate to high moisture content of the aggregates (3-8 m.-% (mass percentage)), this moisture must be removed from the mixing water accordingly. The calculation example below is based on a precast concrete with a w / c value of 0.46 in ongoing production at a precast concrete plant.

[0011] Table 1: Concrete recipe w / c-value 0.46

[0012]

[0013] After deducting the moisture in the aggregate, the water available for making the suspension is 106 kg / m 3, i.e. about 2 / 3 of the initial amount. In this case, a w / c value of 0.30 must be selected for the production of the suspension. In order to mix such a low w / c value correctly, a higher water reducer dosage is required, which may increase the spread of the concrete to a level higher than necessary and also delay the hardening reaction of the cement.

[0014] Example 2 is used for illustration: if the w / c value is 0.35 in the production process of prestressed concrete components, the following calculation results are obtained:

[0015] Table 2: Concrete recipe w / c-value 0.35

[0016]

[0017] The amount of water available for the preparation of the suspension during the premixing process is still 67 kg / m 3 , whereby a suspension with a w / c value of 0.19 is thus obtained, which can no longer be premixed and metered without error based on currently available technology.

[0018] Known methods attempt to solve this problem, for example by pre-treating the fine fraction of the aggregate with the highest moisture content (usually sand) in a pre-mixer (DE 15 84 305 A or DE 10 2016 003 644 B4). This is self-evident, however, because more water is then available for the suspension mixing process. In this method, however, the increased wear on the mixer mechanism due to the ground sand and the known problem of "overmixing" must be taken into account. In the case of overmixing, small parts of the sand particles are knocked off by the rapidly rotating mixing tools, i.e. the sand is broken up, thereby increasing the water requirement and impairing the processability.

[0019] The problems with the two-stage mixing process can thus be summarized as follows: low w / c values ​​ensure high early compressive strength, short mixing times ensure fast concrete placing, especially for large elements poured in multiple steps. High inherent humidity in some parts reduces the water available for the suspension mixing process.

[0020] In extreme cases, such as during wet weather, there is not enough water available for the suspension mixing process. Currently, this can only be compensated by increasing the water reducing agent concentration, which may increase the fluidity of the concrete beyond the necessary level, delay hardening and increase the cost of the concrete. Summary of the invention

[0021] Based on this preliminary consideration, the object of the present invention is to provide a device and a method for producing concrete with high early strength while avoiding the above-mentioned problems.

[0022] The invention achieves this object by a device having the features of claim 1 and a method for producing concrete having the features of claim 17 .

[0023] The device for producing concrete according to the present invention comprises

[0024] i Cement premixer for mixing cement suspension;

[0025] ii at least one first crystallization tank to increase the early strength of the concrete, and

[0026] iii Concrete mixers, used to make concrete mixes from premixed cement suspensions, especially with the addition of aggregates.

[0027] Device according to the present invention especially has one or more crystallizers, and described crystallizer has realized that single component included in cement is crystallized before they are added in concrete.Within the framework of the present invention, a plurality of crystallizers can form a crystallizer device.Here, crystallizer is preferably arranged on top of each other in the crystallizer device, so that cement suspension can be transferred from the upper crystallizer to the crystallizer arranged thereunder under gravity.

[0028] The device is based on the knowledge that for the reactive activation of cement and water premixes, especially when using ultrasound, there is a favorable water to cement ratio (w / c value). The w / c value depends on the cement type and is preferably in the range of 0.50-2.0. Due to the higher solids content, lower w / c values ​​lead to stronger particle interactions, which can promote strong heating of the suspension and in some cases have negative effects.

[0029] By pre-treating the cement suspension, in particular by means of ultrasound, metastable crystal nuclei are produced which, due to storage in the crystallization tank, gain additional time for growth and are (subsequently) metered into the concrete mixer as stable crystal nuclei.

[0030] The crystallization tank preferably comprises a mixer with an agitator which keeps the cement suspension in motion at a slow speed during the crystallization cycle.

[0031] Here, preferred stirring speeds are less than 50 rpm (revolutions per minute), preferably 2-25 rpm, particularly preferably 5-20 rpm.

[0032] Due to the onset of crystallization of the cement components, the concrete subsequently produced therefrom achieves a significantly higher early strength of the concrete than would be achieved without a crystallization tank.

[0033] In this case, not all cement used in the concrete has to be pretreated in this way, but it is sufficient to activate a portion of the cement, which additionally promotes the crystallization of the remaining cement directly introduced into the concrete mixer. Accordingly, the dimensioning and energy budget for operating cement premixers and crystallizers can be advantageously optimized.

[0034] According to the invention, for preparing the cement suspension, the cement premixer has at least one ultrasonic generator, in particular an ultrasonic probe.

[0035] In contrast to DE 37 16 438 A1, in the present invention the pulping is not carried out by means of high-speed mixing tools, but by using ultrasound.

[0036] At the same time, since only a small portion of cement (e.g. 20%) with a high water content (w / c>>1.0) is premixed, the ultrasound is also less attenuated and the concrete is heated to a lesser extent due to its smaller proportion of the entire concrete suspension.

[0037] A higher water content also facilitates metering and cleaning of the device, in particular also after the method of installing the device and the subsequent cleaning method.

[0038] Further advantageous embodiments of the device according to the invention are the subject matter of the dependent claims.

[0039] An ideal ultrasound-assisted cement premixer is known from DE 10 2019 120 939 A1, to which reference is made in its entirety with regard to the preferred structural design of the cement premixer within the scope of the present invention.

[0040] By this cement premixer, not only pure mixing of cement and water is achieved, but also activation of cement components and cement suspension is achieved, thereby also promoting crystallization. The cement premixer also has an agitator, which preferably moves the cement suspension at a higher stirring speed than the agitator in the first crystallizer.

[0041] Since premixing with the above parameters and / or stirring speeds usually leads to the formation of bubbles in the cement suspension, this has a negative impact on the final strength of the concrete. During the period when the cement suspension stays in the crystallizer, these bubbles are expelled. Therefore, the combination of the crystallizer specifically with an ultrasonic cement premixer is particularly preferred.

[0042] Another preferred aspect of using crystallizer is that ultrasonic cement premixer can only provide a small amount of cement suspension for use within a certain time interval due to its type of construction, because ultrasonic wave only has limited penetration depth under the situation of a large amount of cement suspension.At this, crystallizer also can be used for storing cement suspension.

[0043] For low energy consumption and trouble-free operation, the cement premixer, the crystallizer and the concrete mixer are preferably arranged relative to the earth's gravitational field in such a way that the cement suspension can flow from the cement premixer into the crystallizer and from there into the concrete mixer under the effect of gravity. Where this is not possible, a pump can be used to convey the suspension into the concrete mixer.

[0044] The connection between the individual tanks and the mixer can accordingly be a flange connection with a closing device, such as a gate valve.

[0045] The first and each further crystallization tank has stirring means and can in particular have a drive for moving the stirring means.

[0046] The first and each other crystallization tank can have a side wall and a preferably curved bottom surface. The side wall can extend parallel to the longitudinal axis of the crystallization tank. The mixer can have a rotatable stirring attachment as a stirrer. These structures can preferably be spiral structures. The structure can be designed so that it can be guided at a distance of less than 10 cm, preferably less than 5 cm, especially at a spacing between 0.5-4 cm above at least 50% of the bottom surface. As a result, a large amount of cement suspension, including settled components, can be moved and preferably suspended again.

[0047] The construction, in particular a spiral construction in the design, can have an edge scraper towards the bottom. The construction can preferably be made of metal, while the edge scraper is preferably designed to be formed from a softer material than the construction. The edge scraper can preferably be designed in the form of a rubber lip and / or a PTFE lip.

[0048] The device can have a second, third, fourth, fifth and further crystallizers between the first crystallizer and the concrete mixer, preferably with a separate mixer. This allows an increase in the volume of cement suspension that can be stored for crystallization. In particular, a second tank is advantageous when large volumes are required, since the second tank can be used to meter the activated (premixer) and pre-stored (crystallizer 1) suspension into the concrete mixer. This ensures that no suspension leaves the crystallizer without sufficient pre-storage time.

[0049] The device can also be advantageously designed as a system operating without pressure. An open or pressure-free system means that in each container, i.e. the mixer and / or the crystallizer or crystallizers, the pressure characteristics are identical or, in the event of pressure differences during the transfer of the cement suspension, pressure equalization is achieved via open valves.

[0050] At least along the connection between the first and / or second crystallization tank and the concrete mixer, a regulating mechanism for emptying and / or partially emptying the corresponding crystallization tank into the concrete mixer is arranged. The regulating mechanism can preferably be designed as a valve, in particular a pinch valve.

[0051] Similarly, corresponding regulating mechanisms, such as valves, in particular pinch valves, can also be arranged between the cement premixer and the first crystallization tank and / or between the crystallization tanks.

[0052] In addition, the device can have a facility for detecting a measured variable for controlling the emergency emptying of the first and / or each other crystallizer. Such a facility can be, for example, a sensor for detecting the torque of a rotatable agitator and / or a sensor for detecting the torque of a rotatable drum of a crystallizer in a rotating crystallizer. Such measurement allows indirect determination of the hardened state of cement suspension.

[0053] Other measured variables, such as the viscosity, density, the change in the speed of sound of the reflected ultrasonic signal and / or the temperature of the cement suspension related thereto, can also be used to monitor the emergency draining.

[0054] The device can also have an addition device, in particular a metering device, for adding a water reducing agent, in particular based on the detected measured variable. This allows the composition of the cement suspension to be reset when a setpoint value is exceeded.

[0055] The device, in particular at least one of the crystallizers, also has a sensor for determining the temperature of the cement suspension according to the invention. Ideally, the temperature should be between 25 and 45° C. The corresponding target value for the residence time of the cement suspension during automatic emptying and / or partial emptying of the crystallizer can be adapted according to the determined temperature.

[0056] Preferably, the first and / or second or each other crystallizer can be designed for at least 2 cubic meters, preferably 0.5 to 4 cubic meters of cement suspension. Such an amount is not typical for cement premixers, especially ultrasonic cement premixers, because under larger volumes, especially under strong ultrasonic conditions, ultrasonic introduction cannot be carried out uniformly enough on the volume of the mixer.

[0057] Strong ultrasonic treatment can achieve the activation of cement components. Unlike ultrasonic-induced vibration mixing by ultrasound, vibration or other methods, in a preferred variant of the method, the ultrasonic treatment has the following characteristic data, which, individually or in combination with each other, characterize the type of ultrasonic treatment in more detail:

[0058] The ultrasonic probe is designed in particular as an ultrasonic generator and, within the scope of the method, is preferably operated in the following range (values ​​relate to T=25° C. and normal pressure):

[0059] The intensity of the ultrasonic wave emitted by the ultrasonic probe: 25-250W / cm 2

[0060] When ultrasound waves are introduced into a medium, the particles and the medium vibrate. This vibration transfers the kinetic energy of the ultrasound waves. Intensity (I) here corresponds to the power transmitted per unit area, for example Watts. The unit is the power per unit area (for example W / cm 2 )

[0061] Amplitude of ultrasonic waves emitted by the ultrasonic probe: 15-500 μm, preferably 15-120 μm.

[0062] The amplitude (u) describes the deflection of the ultrasound wave (e.g. in μm). If the frequency remains constant, a higher amplitude leads to an increase in intensity. The greater the amplitude, the greater the pressure difference between the high-pressure period and the low-pressure period.

[0063] The frequency of the ultrasonic wave emitted by the ultrasonic probe: preferably 10-30kHz

[0064] The frequency (f) describes the rate of vibration at the tip of the ultrasonic probe. Since bubble formation, growth and implosion is a time-dependent process, higher frequencies result in smaller cavitation bubbles.

[0065] ·Specific energy introduction (into the medium - water): preferably 25-250Ws / ml

[0066] The aforementioned values ​​can be determined electroacoustically in water, for example, by means of hydrophones.

[0067] In order to meter cement into the premixer, a flow guide can be installed after the cement scale, so that cement can be metered both into the concrete mixer and into the premixer. However, it is also possible to lead a separate metering screw conveyor to the premixer.

[0068] It has proven to be advantageous in terms of energy and / or technology to mix and precrystallize only a portion of the cement required for producing the concrete as a cement suspension and to mix the other portion directly in the concrete mixer, for example with aggregates. This is particularly advantageous in the case of the method according to the invention compared to the prior art.

[0069] To achieve an improvement in early strength, the entire cement quantity does not need to be pre-treated, which provides additional water for the premixing process (the w / c value of the suspension can be chosen higher), saving energy and advantageously reducing the size of the required machine.

[0070] According to the invention, there is also provided a method for producing concrete, in particular using the device according to the invention, wherein the method comprises the following steps:

[0071] i) Preparation of cement suspension in cement premixer

[0072] ii) stirring the cement suspension in the crystallization tank during a predetermined residence time period, and

[0073] iii) After a predetermined residence period, the cement suspension is transferred to a concrete mixer.

[0074] A crucial measure for the development of early strength is the residence time. This corresponds to the residence time of the premixed suspension in the crystallization tank or the crystallization time.

[0075] The residence time depends on the concrete production process (mixing time, concrete volume per hour, concrete composition) and the desired strength increase.

[0076] The crystallization tank (or holding tank / retention tank / storage tank) is a container in which the suspension is stored for a predefined period of time (0.5-6 hours) under continuously stirred / circulated conditions. After the residence time, the suspension is metered into the concrete mixer.

[0077] The residence time or residence time corresponds to the time during which the activated suspension remains in the crystallization tank under continuous stirring or circulation conditions.

[0078] Advantageously, the first crystallizer has an outlet which leads to the inlet of a concrete mixer or to a second (or third, fourth ...) crystallizer. The device also has a regulating mechanism arranged in the outlet of the first crystallizer and / or the inlet of the concrete mixer. The device can also have a first evaluation unit and / or a control unit which is configured to operate the regulating mechanism for partially or completely emptying the first crystallizer after a residence time period of 0.5 to 6 hours of cement suspension in the first crystallizer.

[0079] The cement premixer can also advantageously have a treatment container with a treatment space, wherein the at least one ultrasonic probe at least partially extends into the treatment space and wherein the ultrasonic probe emits ultrasound, wherein the emitted ultrasound or ultrasound signal is set, for example, by an evaluation and / or control unit such that it has a power of 25-250 W / cm 2 Intensity and amplitude of 15-500μm.

[0080] When producing concrete, it is also possible to add a first partial amount of cement to a cement premixer and a second partial amount of cement to a concrete mixer, which is particularly advantageous in terms of energy.

[0081] The share of cement pretreated in this way preferably accounts for 5-95% of the total cement share, particularly preferably 10-25%. For the preferred residence time period of the cement suspension in the crystallizer, the control or setting of the setpoint value can advantageously be carried out based on a predetermined time at a predetermined temperature. Since crystallization depends on temperature, this control provides a better control of the quality of the cement suspension.

[0082] For better and more comprehensive transportation, the cement suspension can be transferred to the concrete mixer in batches.

[0083] The stirring speed in the first and each other crystallizer and / or the inflow and / or outflow of the cement suspension in the first or each other crystallizer can be controlled by sensors and / or sensor devices. For this reason, preferably one or more temperature sensors, ultrasonic sensors for determining the ultrasonic wave propagation time and / or sensors for torque detection can be used to monitor the quality of the cement suspension, and in particular its intensity.

[0084] By means of temperature regulation, the temperature of the cement suspension in the first or each further crystallization tank can be adjusted to a temperature between 10 and 45° C. The adjustability to below 20° C., in particular to 10-20° C., enables better storage.

[0085] The crystallization time or residence time and the time of the emergency draining can be set as a function of the temperature and / or the above-described detected measurement variables.

[0086] The cement suspension may preferably not be added to the concrete mixer until after a residence time of between 1 and 8 hours has elapsed. The cement suspension is transferred to the concrete mixer according to a pre-established production plan.

[0087] The water / cement (w / c) value of the cement suspension can advantageously be between 0.5 and 2. The choice of residence time depends on the reaction speed of the cement. The times given are optimal for the above-mentioned provisions for the residence time.

[0088] The pre-storage time of the cement suspension before being transferred into the concrete mixer may advantageously be between 1 and 8 hours.

[0089] Particularly preferably, however, the above-mentioned w / c values ​​can also be combined with a settling phase of the above-mentioned ultrasonic treatment of the cement suspension.

[0090] The proportion of ultrasonically pretreated cement in the concrete may advantageously be between 5 and 95% by weight, ideally between 10 and 25% by weight.

[0091] The stirring speed in the first and / or second crystallizer and / or the inflow and / or outflow of the cement suspension in the first and / or second crystallizer can be controlled by sensor and / or sensor device. For this reason, preferably one or more temperature sensors, ultrasonic sensors for determining the ultrasonic wave propagation time and / or sensors for torque detection can be used to monitor the quality of the cement suspension, and especially its intensity.

[0092] Furthermore, it is advantageous within the scope of the method to provide an intelligent control method and / or a control device for maintaining a defined suspension quality. The properties of the suspension (especially temperature, viscosity, density, conductivity, ultrasonic transmission time) are continuously checked by a series of sensors in the tank, evaluated, and measures are taken based on the sensor measurement data, such as adding new suspension and draining old suspension.

[0093] The temperature in the tank is a particularly important factor that influences the suspension quality (=reactivity). This can advantageously remain within the desired range through cooling means and heating means, therefore for example through forming a double-walled container wall as a part for the first and / or second crystallizer, or through a heat exchanger on or in the crystallizer.

[0094] In particular, material-dependent physical measured variables of the cement suspension located in the first and / or second crystallization tank can be sensed.

[0095] A control of the inflow and / or outflow, the stirring speed and / or the temperature can then preferably be carried out as a function of the measured values ​​determined by the sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0096] The device for producing concrete according to the invention is explained in more detail below based on an embodiment with the aid of the drawings. The drawings contain a number of features which, when viewed individually, can be combined in an obvious manner with other embodiments not shown. The entirety of the embodiment should not be understood as limiting the scope of protection of the invention. The drawings show:

[0097] Figure 1 A side view of an embodiment of a cement premixer and a first and a second crystallization tank comprising the device according to the invention is shown;

[0098] Figure 2 Shows Figure 1 A perspective view of an embodiment of the present invention;

[0099] Figure 3 A cross-sectional view along the longitudinal axis of the crystallization tank is shown;

[0100] Figure 4 shows a schematic diagram of manufacturing concrete according to a conventional method;

[0101] Figure 5 A schematic diagram showing the manufacturing of concrete according to an embodiment of the present invention;

[0102] Figure 6 A graph showing the heat release rate;

[0103] Figure 7 The composition of a first concrete mixture is shown;

[0104] Figure 8 The composition of the second concrete mixture is shown;

[0105] Fig. 9 The mixing ratio of cement suspension and water is shown;

[0106] Fig.10 A graph showing the relationship between the start of curing and the pre-storage time;

[0107] Fig.11 A graph showing the pre-storage time of ultrasonically treated cement mortar with respect to slump and spread; and

[0108] Fig.12 A graph of compressive strength versus age of concrete is shown. DETAILED DESCRIPTION

[0109] Figure 1 An apparatus 1 according to the invention is shown, comprising a cement premixer 3 and two crystallization tanks 4 and 5 .

[0110] An inlet opening 7 is provided above the cement premixer 3 .

[0111] The cement premixer 3 and the two crystallization tanks 4 and 5 are connected to each other through the frame 2.

[0112] The cement premixer 3 has an ultrasonic probe 6 which extends through the wall of the cement premixer into the inner space.

[0113] A delivery pipeline is provided between the cement premixer 3 and the two tanks 4 and 5. The delivery pipeline may have a regulating mechanism, such as a valve device. The tank 5 has an outlet 10.

[0114] Each crystallization tank 4, 5 and cement premixer 3 has a mixer 7-9.

[0115] Figure 2 Shows Figure 1 A perspective view of the device of FIG. 1. Support planes A, B and C can be seen, along which the various containers are supported.

[0116] Figure 3More details are disclosed in . Therefore, the crystallization tank 4 has a stirrer 8, which has a rod 15 and a spirally wound stirring blade 13. The crystallization tank has a cylindrical housing section 11 and a bottom area 12 designed as an arch.

[0117] A sensor element 17 is arranged in the upper region of the crystallizer 4. This can be, for example, a temperature sensor. The crystallizer 4 has an outlet 18 which merges into a conveying line 20. In addition, the crystallizer 4 has an emergency discharge line 16, via which the tank 4 can be emptied urgently, for example in the case of an overlying mud suspension.

[0118] The crystallization tank 5 is constructed similarly. The sensor element 27 and the mixer 9 can be seen. In the bottom area 22 there are two discharge pipe connections 26 and 28, each having a flange end 24. One of the two discharge pipe connections is again used for emergency emptying, while the other is used to enable transfer to the concrete mixer.

[0119] Figure 4 A conventional method 100 for making concrete is shown, wherein water 103, cement 104 and 105, admixture 102, and, if necessary, cementitious materials and admixtures are mixed with stone 106, 107 or sand 108 in a concrete mixer 101.

[0120] Those skilled in the art of concrete know that cementitious materials are inorganic or organic substances which can be processed in a plastic state and harden after a certain period of time and at the same time firmly connect other materials, such as aggregates, to one another. The cementitious materials used in the concrete industry are of mineral origin and, with a few exceptions, are obtained from certain rocks by combustion and ground into a fine powder. Mixing with water first produces a cementitious material glue. By chemical reactions and partly also by physical surface forces, the cementitious material glue can be cured into a stone-like state, in which any fillers can be bonded to one another.

[0121] Furthermore, the term admixture or concrete admixture is known to those skilled in the art of concrete. This refers to materials that are added to concrete in finely divided form, for example in liquid, powdered form or also as granules or as a paste, in small quantities in order to influence specific properties of fresh or hardened concrete by chemical or physical action. Typical admixtures are concrete plasticizers, water reducers, air entraining agents, sealants, retarders, accelerators, grouting aids and / or stabilizers.

[0122] Furthermore, the term admixture or concrete admixture is known to those skilled in the art of concrete. This refers to finely divided materials that are used in concrete in order to improve or achieve specific properties. Such materials are present in the concrete composition as a volume component in a much larger amount than admixtures. They are therefore also referred to as fillers. According to DIN EN 206-1 and DIN 1045-2, two types of inorganic admixtures are distinguished. Class I admixtures are virtually inactive admixtures, such as rock powder, aggregates or colorants. Class II admixtures are pozzolanic or potentially hydraulic admixtures, such as pozzolanic ash, fly ash or silicate dust.

[0123] Finally, concrete mixtures contain a large proportion of aggregates, such as stone and sand, whose particle size and proportion can vary depending on the particle size depending on the type of concrete. These aggregates are sometimes also classified together with other materials under the general term aggregate.

[0124] The core of the present invention is here to provide a method that solves these technical obstacles and still ensures high early strength of concrete with, for example, an ultrasonic premix stage.

[0125] Here, cement 209, water 210 and admixture 211 are mixed and activated by ultrasound in a cement premixer 212. The cement suspension is then transferred to a crystallization tank 213 and from there to a concrete mixer 201. Within the framework of the method 200 according to the invention, further admixtures 202, water 203, cement 204 and 205 as well as stone 206, 207 and sand 208 can be added to the concrete mixer 201.

[0126] The invention is based on the fact that there is a favorable w / c value or a favorable w / c range for the production of cement suspensions, in which the suspension can be well homogenized and activated (for example with the aid of ultrasound). This favorable w / c value depends on the type of cement and the admixtures used and is between 0.5 and 2. The invention is also based on the fact that it is not necessary to premix and activate all the parts of cement and water in order to achieve a significant increase in early strength.

[0127] In a preferred variant of the present invention, the cement suspension provided in the cement premixer is made of cement, water and, if necessary, an admixture as an optional component. In contrast, no aggregate is provided in the cement suspension.

[0128] This means that part of the cement is metered into the premixer for activation and part of the cement is metered into the concrete mixer. This can be done either via a separate metering device (hopper + screw conveyor) on the premixer or on an existing concrete mixing plant via a distributor on the cement scale and a screw conveyor from the cement scale to the premixer.

[0129] Furthermore, according to one part of the method according to the invention, the premixed and activated cement suspension is not metered into the concrete mixer immediately after mixing, but is conveyed to a settling tank or crystallization tank downstream of the suspension mixer. The crystallization tank has a volume of approximately the amount of suspension required for one hour of concrete production.

[0130] Compared to the variant in which the whole amount of cement and water (and sand if necessary) is used for pretreatment, this has the advantage of reducing the volume required for the premixer. The production and activation of the suspension and the subsequent storage in the crystallization tank also have the advantage that after a sufficient crystallization time, the suspension can be removed or metered as quickly as desired, and thus a further shortened mixing time can also be selected. The resting or crystallization time leads to a significant increase in early strength, even compared to the variant in which the total amount of cement and water calculated for use is premixed and activated. This potential cannot be realized without a rest phase. If ultrasound is used for activation in the premixing phase, the early strength is significantly increased again. Ideally, this rest phase should last 1-8 hours, depending on the type of cement and the composition of the suspension.

[0131] During production, the mixing time of the suspension mixing process should be very short in order to achieve a short total mixing time. In particular, in the activation of the cement suspension, for example by ultrasound, this cannot always be guaranteed. When producing large concrete components (such as bridge trusses), a relatively large amount of concrete must be produced in a short time in order to quickly produce the concrete components. This also places special demands on the premixing of the cement suspension in the ultrasonic premixer, because the mixing chamber is limited to a certain structural size for effective ultrasonic application. By producing a "storage" suspension, these components can also be manufactured without a corresponding increase in the concrete mixing time.

[0132] Compared to the prior art, the method presented here is characterized by the following novel measures:

[0133] Premix and activate only the cement suspension required for optimum strength development, ideally between 10-25% of the cement content.

[0134] The premixed and activated cement suspension is transferred to a settling tank or crystallization tank for storage, where it remains for a certain period of time, ideally 1-8 hours, and is continuously mixed at a low shear rate or circulated by a pump.

[0135] After the pre-storage time, the removal from the crystallization tank takes place continuously, without prolonging the concrete mixing time.

[0136] Therefore, the problem of high moisture in aggregate can be effectively solved.

[0137] Do not extend the mixing time of the concrete mixing process.

[0138] With the same concrete composition, the early strength is significantly increased.

[0139] When supplementing the crystallization tank with other tanks of the same size, even very large concrete volumes can be produced without error with activated cement suspensions (e.g. ready-mix concrete production)

[0140] The following describes the optimal pre-storage time in the crystallization tank:

[0141] Figure 6 The time curve of the heat exchange rate in J / gh is shown. This involves thermal conductivity calorimetric measurements of Portland cement, which is designated CEM I 52.5R in the figure, with and without ultrasonic treatment, which is designated PUS in the figure.

[0142] It was identified that the onset of the acceleration phase was significantly earlier and the heat development reached a maximum after approximately 4-5 hours.

[0143] The reaction of cement with water follows a specific kinetic path. For a typical water-cement value of 0.5, the heat release rate curve is as follows Figure 6 shown.

[0144] Patent application DE 10 2020 132 015.9 proposes the use of a pre-storage of an activated cement suspension, which does not interfere with the concrete manufacturing process but increases the early compressive strength.

[0145] Intensive studies have now shown that a significant increase in the water content of the suspension and / or the prestorage time provides process technology advantages in certain cases.

[0146] In concrete terms, this means that the time of addition of the suspension is linked to the rate of heat release and that the suspension is metered in only when the curve has passed through a rest phase of between 1 and 3 hours and shows a renewed increase in heat release (=chemical reaction).

[0147] This point in time varies greatly with the materials used (type of cement and type of water reducing agent and water content) and should be determined in advance.

[0148] Here, the preferred parameters of the cement suspension are:

[0149] - Water / cement (w / c) value = 0.5-2

[0150] - Pre-storage time = 1-8 hours

[0151] - Share of pre-treated cement 5-95%, ideally 10-25%

[0152] The w / c value must be chosen so that the rise of the curve (the so-called "acceleration phase") does not last too long (lower w / c values), but also so that no curing of the material occurs during the pre-storage period (higher w / c values). Very suitable w / c values ​​for this are around 1.0 ± 0.25, depending on the type of cement and the type and amount of water reducer.

[0153] The pre-storage time depends on the selected w / c value and the reactivity of the cement. In order to keep the process technology expenditure associated with pre-storage low, a maximum pre-storage time of 4 hours is targeted.

[0154] In this way, the early strength can again be significantly increased and the portion of cement that has to be premixed and activated can be reduced.

[0155] In an exemplary process flow, a portion of the cement is premixed with water, subjected to ultrasound treatment, and subsequently stored for a longer period of time. After storage, the cement suspension is metered into a concrete mixer. As already described above, ultrasound activation is performed by ultrasound treatment. This is done at an ultrasound power of 25-250 W / cm 2 The intensity and amplitude were 15-500 μm.

[0156] Hydrate nuclei are formed in the suspension, which have a significant influence on the early strength of the concrete. This can also be demonstrated by microscopic images.

[0157] Since the water calculated for the premixing process is often insufficient, the portion of cement to be premixed is reduced.

[0158] In concrete with dry aggregate, e.g. Figure 7 As shown, there are three main components.

[0159] In this case, the water content is low but sufficient for the premixing process, since a flowable suspension can still be produced and metered out when using a water reducer.

[0160] If the aggregate is moist, the share of aggregate in the material space calculation is increased and the share of water is reduced by the share of moisture bound to the aggregate. Figure 8 . Figure 7 and 8 The dosage of the corresponding components is shown respectively. Figure 8 In the case of aggregate Figure 7The column "H2O" in the figures only indicates the amount of water to be metered in addition to the aggregate. "H" and "H2O" are to be understood as synonyms in the figures.

[0161] Currently only very small amounts of water are still available for mixing processes and premixing processes are very difficult to apply, if at all. In the case of ultrasonic treatment, high solids concentrations often lead to undesirable side effects, such as negative interactions of the water reducer with the cement, intense heating and problems with metering / emptying the premix container.

[0162] In order to ensure the advantages of the premixing process using ultrasound, a premixing and storage concept was developed. The key point here is to use only a part of the cement available, see Fig. 9 .

[0163] Since the solids content of the suspension produced in this way is very low, the production process is simplified compared to variants in which all cement is premixed.

[0164] However, the number of hydrate nuclei that can be formed is limited by the amount of cement. This leads to the concept of storing or crystallizing the suspension for such a long time that a sufficient number of hydrate nuclei have formed to accelerate hydration. The amount of hydrate phase increases with the pre-storage time. The start of curing is then measured, i.e. the point in time at which the hardening process has progressed to the point at which the concrete can no longer be processed further.

[0165] Fig.10 The beginning of curing of cement mortar with the following parameters can be seen:

[0166] -Mortar w / c value = 0.50

[0167] - w / c value of the pre-stored suspension = 1.0

[0168] - Share of pre-treated cement = 25%

[0169] - Ultrasonicate the suspension at 20 kHz and 60 sec / L

[0170] exist Fig.10 As can be seen in the graph, the onset of solidification (Y axis) decreases with increasing pre-storage duration (X axis). This behavior is particularly evident in the suspension treated with ultrasound (cross-hatching). In the case of no ultrasound treatment, the reduction in solidification time is not so pronounced (hatched).

[0171] Usually, pre-storage also influences workability. This is determined at the cement level by means of slump and spread. Fig.11 The cement suspensions pre-stored for different lengths of time are shown in FIG. Fig.10 Slump and spread of cement mortar explained. Here the distance the mortar flows on the tabletop without shaking (slump) and after 15 impacts (spread) is measured. It can be seen here that both the slump and the spread decrease with increasing pre-storage time. This means that the workability of the mortar decreases. However, within the first 240 minutes, the reduction is very small, which means that the concrete has not changed significantly. A larger decrease occurs after 240 minutes.

[0172] From these results it can be concluded that the ideal storage time for the observed mortars is about 240 minutes, at which the workability changes only slightly while the early strength increases significantly.

[0173] For concrete rulers, the following data can be used to illustrate the effect:

[0174] Concrete was made using Portland cement (CEM I 52.5R) with a w / c value of 0.47. The concrete was mixed with a water reducing agent (type: polycarboxylic acid) and a suspension (w / c = 1.0) pre-stored for 240 minutes and treated with ultrasound and in a volume of 0.3 m 3 Stir while stirring.

[0175] Fig.12 The compressive strength development of the concrete produced according to the method according to the invention in comparison with conventionally produced concrete within the first 24 hours can be seen in FIG. Here it can be clearly seen that the concrete samples with the pre-stored suspension according to the method according to the invention have a significantly higher compressive strength at all measured time points.

[0176] Reference numerals list

[0177] 1 Device

[0178] 2 racks

[0179] 3 Cement premixer

[0180] 4 Crystallization tank

[0181] 5 Crystallization Tank

[0182] 6 Ultrasonic probe

[0183] 7. Blender

[0184] 8. Blender

[0185] 9. Blender

[0186] 10 Exit

[0187] 11 Shell section

[0188] 12 Bottom area

[0189] 13 Mixing blade

[0190] 14 -

[0191] 15 shots

[0192] 16 Emergency discharge line

[0193] 17 Sensor element

[0194] 18 Exit

[0195] 19 -

[0196] 20 pipeline

[0197] twenty one -

[0198] 22 Bottom area

[0199] twenty three -

[0200] 24 Flange end

[0201] 25 -

[0202] 26 Discharge pipe connector

[0203] 27 Sensor element

[0204] 28 Discharge pipe connector

[0205] 100 Methods

[0206] 101 Concrete mixer

[0207] 102 Admixture

[0208] 103 Water

[0209] 104 Cement

[0210] 105 Cement

[0211] 106 Stone

[0212] 107 Stone

[0213] 108 sand

[0214] 201 Concrete mixer

[0215] 202 Admixture

[0216] 203 Water

[0217] 204 Cement

[0218] 205 Cement

[0219] 206 Stone

[0220] 207 Stone

[0221] 208 sand

[0222] 209 Cement

[0223] 210 Water

[0224] 211 Admixture

[0225] 212 Cement premixer

[0226] 213 Crystallization Tank

Claims

1. A device (1) for producing concrete, comprising: a cement premixer for mixing a cement suspension, wherein the cement premixer has at least one ultrasonic generator for preparing the cement suspension, ii. at least one first crystallization tank (4), or a crystallization tank device with a first crystallization tank (4), for increasing the early strength of the concrete, and iii. a concrete mixer (201) for producing a concrete mixture from a premixed cement suspension, The cement premixer, the crystallization tank and the concrete mixer (201) are arranged relative to the earth's gravity field so that the cement suspension can flow from the cement premixer into the crystallization tank under the action of gravity, and from there into the concrete mixer (201).

2. The device according to claim 1, characterized in that The ultrasonic generator is an ultrasonic probe (6).

3. The device according to claim 1, characterized in that The concrete mixer (201) is provided for producing a concrete mixture from a premixed cement suspension with the addition of aggregates.

4. The device according to claim 1, characterized in that The first crystallization tank (4) has a stirrer (8).

5. The device according to claim 4, characterized in that The first crystallization tank (4) has a side wall and a bottom surface, wherein the stirrer (8) of the first crystallization tank (4) has a rotatable stirring attachment, and the stirring attachment has a structure, and the structure is designed so that the structure can be guided at a distance of less than 10 cm above at least 50% of the bottom surface.

6. The device according to claim 5, characterized in that The first crystallization tank (4) has a curved bottom surface.

7. The device according to claim 5, characterized in that The stirring attachment has a spiral configuration.

8. The device according to claim 5, characterized in that The formation can be guided over at least 50% of the bottom surface at a distance of less than 5 cm.

9. The device according to claim 5, characterized in that The construction has an edge scraper towards the bottom.

10. The device according to claim 9, characterized in that The construction has a design of a spiral construction.

11. The device according to claim 9, characterized in that The edge scraper is configured in the form of a rubber lip and / or a PTFE lip.

12. The device according to any one of the preceding claims 1 to 11, characterized in that The device (1) comprises a second crystallization tank (5) between the first crystallization tank (4) and the concrete mixer (201).

13. The device according to claim 12, characterized in that The second crystallization tank (5) has a separate stirrer (9).

14. The device according to claim 12, characterized in that The device (1) is designed as a system that operates without pressure.

15. The device according to claim 12, characterized in that In the delivery pipeline (20) between the crystallization tanks, the regulating mechanism is designed as a valve.

16. The device according to claim 15, characterized in that The regulating mechanism is designed as a pinch valve.

17. The device according to claim 12, characterized in that The device (1) has means for detecting a measured variable.

18. The device according to claim 12, characterized in that At least one crystallization tank has facilities for detecting a measured variable.

19. The device according to claim 17 or 18, characterized in that The measured parameter is used to control the emergency emptying of the first crystallization tank (4) and / or the second crystallization tank (5).

20. The device according to claim 17 or 18, characterized in that The device has an adding device for adding a water reducing agent.

21. The device according to claim 20, characterized in that The adding device is designed as a metering device.

22. The device according to claim 20, characterized in that The adding device of the device is used for adding a water reducing agent based on the detected measured variable.

23. The device according to claim 22, characterized in that The adding device is designed as a metering device.

24. The device according to claim 12, characterized in that The device (1) has a sensor for determining the temperature of the cement suspension.

25. The device according to claim 12, characterized in that The first crystallization tank (4) and / or the second crystallization tank (5) are designed for an amount of at least 2 cubic meters of cement suspension.

26. The device according to claim 25, characterized in that The first crystallization tank (4) and / or the second crystallization tank (5) are designed for an amount of cement suspension of 1.5-4 cubic meters.

27. The device according to claim 12, characterized in that The first crystallization tank (4) and / or the second crystallization tank (5) has a heat exchanger device for controlling the temperature of the cement suspension along the wall of the crystallization tank.

28. The device according to claim 27, characterized in that The first crystallization tank (4) and / or the second crystallization tank (5) has a double-wall section for controlling the temperature of the cement suspension along the wall of the crystallization tank.

29. The device according to claim 12, characterized in that The device (1) has a cement storage hopper having a first partial cement feed line to the cement premixer and a second partial cement feed line to the concrete mixer (201).

30. The device according to claim 12, characterized in that The device has a cement scale for metering a first partial amount of cement into the cement premixer and a second partial amount of cement into the concrete mixer (201).

31. The device according to claim 12, characterized in that The first crystallization tank (4) and / or the second crystallization tank (5) comprises a sensor element for determining the mass of the cement suspension in the crystallization tank.

32. The device according to claim 31, characterized in that The sensor elements include temperature sensors, torque sensors for measuring viscosity, conductivity sensors for determining thermal or electrical conductivity, sensors for determining ultrasonic propagation time and ultrasonic velocity and / or density sensors.

33. The device according to claim 31 or 32, characterized in that The device (1) has a control and / or evaluation unit for controlling an actuator, an inlet valve and / or an outlet valve based on the measured values ​​determined by the sensor element.

34. The device according to claim 33, characterized in that The actuator is a temperature control device.

35. A method for manufacturing concrete using a device according to any one of the preceding claims 1 to 34, characterized by the following steps: i) producing a cement suspension in a cement premixer using ultrasound; ii) stirring the cement suspension in the crystallization tank during a predetermined residence time period, and iii) transferring the cement suspension to a concrete mixer (201) after a predetermined residence time period.

36. The method according to claim 35, characterized in that The cement premixer has a process chamber, wherein the at least one ultrasonic probe (6) at least partially extends into the process chamber, and The ultrasonic probe (6) emits ultrasonic waves, wherein the emitted ultrasonic waves have a power of 25-250 W / cm 2 The intensity and amplitude of the oscillations were 15-500 μm.

37. The method according to claim 35, characterized in that The control of the residence time period is performed based on a predetermined time at a predetermined temperature.

38. A method according to any one of the preceding claims 35 to 37, characterised in that The emergency emptying of the first crystallization tank (4) and / or the second crystallization tank (5) is controlled based on a predetermined time at a predetermined temperature and / or based on determined measured values.

39. The method according to claim 38, characterized in that The emergency emptying of the first crystallization tank (4) and / or the second crystallization tank (5) is controlled according to the determined torque.

40. The method according to any one of the preceding claims 35 to 37, characterized in that The residence time period of the suspension is based on a previously determined heat release.

41. The method according to any one of the preceding claims 35 to 37, characterized in that The water / cement (w / c) value in the cement suspension is between 0.5 and 2.

42. The method according to any one of the preceding claims 35 to 37, characterized in that The pre-storage time of the cement suspension before being transferred to the concrete mixer (201) is 1 to 8 hours.

43. The method according to any one of the preceding claims 35 to 37, characterized in that The proportion of pretreated cement in the concrete is 5-95% by weight.

44. The method according to claim 43, characterized in that The proportion of pretreated cement in the concrete is 10-25% by weight.

45. The method according to any one of the preceding claims 35 to 37, characterized in that Physical material-dependent measured variables of the cement suspension in the first crystallization tank (4) and / or the second crystallization tank (5) are detected by sensor.

46. ​​The method according to claim 45, characterized in that The inflow and / or outflow, the stirring speed and / or the temperature are controlled based on the measured values ​​determined by the sensor detection.

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