CONCRETE RECYCLING SYSTEM

Description

Field of the invention

[0001] The invention relates to a concrete recycling system comprising a concrete-slip classifier with a concrete slip inlet, a bulk material outlet and a fluid phase outlet, wherein the concrete-slip classifier is configured to separate at least a portion of aggregates comprised in concrete slip from the concrete slip to thereby obtain a first fraction of aggregates and a fluid phase. The concrete recycling system further comprises a fluid-phase reservoir with a fluid phase inlet, a fluid-phase outlet and an agitator. A first conduit connects the fluid-phase outlet of the concrete-slip classifier with the fluid-phase inlet of the fluid-phase reservoir.Description of the related art

[0002] Manufacture of concrete involves preparing an aqueous dispersion of aggregates and cementitious materials. This dispersion can be cast into an intended shape and then cures at least i.a. due to hydration of the cementitious materials. The dispersion is herein as well referred to as concrete slip or concrete slurry. Often, the terms fresh concrete, green concrete or wet concrete are used as well.

[0003] Concrete slip is prepared in so called ready-mix plants: In these ready-mix plants the constituents of the concrete slip (hereinafter "slip") are dosed in predefined quantities to prepare a concrete of a given grade. The dosed constituents are mixed to thereby obtain the slip that is then transported to a building side. In some applications, mixing takes place at least in part during the transport by so called concrete mixing trucks, which have mixing drums for storing and mixing the concrete slip during the transport. In other applications, mixing of the concrete is finalized in a mixer of the concrete plant and from there filled into the "concrete mixing trucks". During the transport, the fresh concrete, i.e. the concrete slip, is agitated to avoid sedimentation of the dispersion during the transport.

[0004] After delivery of a batch of concrete slip to a construction site, concrete mixing trucks return to the ready-mix plant to pick up a further batch of concrete slip for delivery. Before a further batch of concrete slip (or its constituents) can be dosed into to the mixing drum, the remaining concrete slip of the prior batch is discharged to a concrete slip recycling system. In addition, the concrete drum is often rinsed with water, prior to loading another batch of concrete slip to the concrete mixing trucks.

[0005] Rinsing the mixing drum provides as diluted concrete slip, which may hence, like the discharged remaining concrete of the prior batch, as well be provided the concrete slip recycling system.

[0006] The concrete slip recycling system separates a first fraction of the particles in the concrete slip or mortar from a fluid phase. The first fraction of the particles corresponds at lear essentially to the aggregates that had been mixed into the batch being recycled. The fluid phase essentially comprises water and a second fraction of the particles being dispersed in water. This second fraction typically has a diameter below 0.25mm. The fluid phase may as well be referred to as waste-water and may be considered as a solid-liquid suspension. Soluble ingredients or liquid portions of concrete slip batches may as well be dissolved in or mixed with the waste-water.

[0007] The aggregates and the fluid phase can be reused in the ready-mix plant. The aggregates can be classified, e.g. by size, and reused when preparing another batch of concrete slip. The waste-water is stored in a waste-waste reservoir and can be used as batching water and for rinsing mixing drums, conduits, chutes, tools or and the like that require cleaning from mortar or concrete slip.

[0008] US 2002 / 108537 A1 relates to a concrete recovery system.Summary of the invention

[0009] The problem to be solved by the invention is to reduce the fresh water consumption of a ready-mix plant and as well to reduce the power consumption of the concrete slip recycling system.

[0010] A solution to the problem is defined in the independent claim.

[0011] Advantageous embodiments are subjects of the dependent claims.

[0012] The invention is based on a number of observations: In prior art ready-mix plants and precast concrete plants, the concrete slip recycling system has a fluid-phase reservoir, from which amounts of the fluid-phase are withdrawn as required, e.g. for rinsing mixing drums or as batching water being dosed into a mixing vessel when preparing a batch of concrete slip. To this end it is important that the fines being dispersed in the fluid-phase are evenly distributed in the fluid-phase reservoir. It is common practice to agitate the fluid-phase in the fluid-phase reservoir to avoid sedimentation of the fines. In prior art installations, a fluid-phase agitator (agitator for short) is controlled by a timer configured to operate the agitator for a given duration in predefined intervals. Typically, the agitator operates intermittently between 7h to 10h per day. Second, if the fluid-phase has a high cement / water ratio and / or a high aggregate / water ratio, e.g. if a high amount of (often at least partially hydrated) cementitious material is dispersed in the fluid phase, use of the fluid phase as batching water for mixing reduces the grade of the concrete slip and is hence not acceptable. Similar considerations apply to batching water with a high aggregate / water ratio. To ensure a predefined grade of the concrete slip, the density of the waste-water in the waste-water reservoir is determined manually, typically daily at a point in time when it is expected to peak. This manual density measurement provides an assumed maximum density. If the assumed maximum density is above a predefined density value (see DIN EN 1008), then fresh water is used instead of the waste-water to ensure a given grade of concrete slip is produced or fresh water is used to dilute the waste water to thereby obtain an acceptable aggregate / water ratio and / or an hydrated cement / water ratio. In any case, waste water usage is limited to concrete grades not higher than C50 / 60 or LC50 / 55.

[0013] The concrete slip recycling system comprises a concrete-slip classifier with a concrete slip inlet, a bulk material outlet and a fluid phase outlet. The concrete-slip classifier is hereinafter briefly as well referred to as "classifier" and is configured to separate at least a portion of aggregates comprised in concrete slip from the concrete slip. The classifier thus provides a first fraction of aggregates and a fluid phase. The aggregates may be provided to the bulk material outlet and the fluid phase to the fluid phase outlet.

[0014] The fluid phase may comprise a second fraction of the aggregates, water and cementitious matter, wherein the cementitious matter may be fully hydrated or partially hydrated. The particles in the fluid phase preferably have a diameter d equal to or below 0.5mm, preferably, below 0.3mm, 0.25mm, 0.2mm, 0.15mm or 0.1mm, (in short: d ≤ α, wherein α / mm ∈ {0.5, 0.4, 0.3, 0.25, 0.2, 0.15, 0.1}), wherein smaller values are preferred over larger values. The diameter is not crucial for the invention, lower diameters simply result in a lower density of the fluid phase and hence in an enhanced usability of the fluid phase.

[0015] The concrete slip recycling system further comprises a fluid-phase reservoir.

[0016] The fluid-phase reservoir enables decoupling (in the time domain) of the production of the fluid phase by the classifier from use of the fluid phase, e.g., as batching water for mixing concrete slip or for rinsing mixing drums, chutes or other equipment that may have been soiled with concrete slurry. Accordingly, the fluid-phase reservoir may hence be a basin, a tank or any other vessel configured to receive the fluid phase from a fluid-phase outlet of the classifier. The fluid-phase reservoir may have a fluid-phase inlet being connected to the fluid-phase outlet of the classifier. In other words, a first conduit may connect the fluid-phase outlet of the concrete-slip classifier with the fluid-phase inlet of the fluid-phase reservoir.

[0017] An agitator is located in fluid-phase reservoir. The agitator may be configured to homogenize the fluid phase stored in the fluid-phase reservoir, i.e. of the solid-liquid suspension in the fluid-phase reservoir. Corresponding agitators are known in the art and are generally motor driven. The agitator (= agitation device) may be or resemble a blade impeller, but other impellers may be used as well. The agitator is preferably configured for (re)dispersing (sedimented) particles, i.e. particles of the second fraction of aggregates and cementitious matter that may settled on the bottom of the fluid-phase reservoir. The objective of (re)dispersing (sedimented) particles is to obtain or maintain, respectively, a homogenized fluid phase. A perfectly homogenized fluid phase has the same density over the entire depth of the fluid phase.

[0018] Optionally, the concrete slip recycling system may comprise a fluid-phase feeding pump with a pump inlet being connected to a fluid-phase outlet of the fluid-phase reservoir and with a pump outlet being configured to be connected with an inlet of a concrete slip mixing chamber (hereinafter briefly "concrete mixing chamber" or "mixing chamber"), e.g. via an optional flow meter configured to determine the amount of waste water being pumped into the mixing chamber. The optional flow meter may as well be installed in between the fluid-phase outlet of the fluid-phase reservoir and the pump inlet.

[0019] After installation of the concrete slip recycling system, the pump outlet may of course be connected with the inlet of the concrete slip mixing chamber. Alternatively of in addition, the pump outlet may be connected to an outlet of a mixing drum filling station, wherein the mixing drum filling station may be configured to provide a flow of the fluid phase into a mixing drum of a concrete mixing truck.

[0020] The fluid-phase feeding pump may hence provide a fluid flow from the fluid-phase reservoir via the respective connection to a concrete slip mixing chamber, wherein the concrete slip mixing chamber is not necessarily a part of the concrete slip recycling system or of a ready-mix plant, but it may be.

[0021] The fluid-phase reservoir comprises an observable meter. The observable being metered by the observable meter is indicative of the density of the fluid phase stored in the fluid-phase reservoir and / or of a change of the density of the fluid-phase stored in the fluid-phase reservoir as function of time. The observable meter thus enables an indirect measurement of the density of the fluid phase. An example observable meter would by an optical measurement system configured to determine the half thickness of the intensity of light propagating through the fluid phase. Alternatively or in addition, the optical measurement system is configured to determine an amount of light being scattered by particles being suspended in the fluid phase.

[0022] Different from mechanical density meters, such indirect measurement system are less prone to damage by the fluid phase. Such optical observable meters may be used, as changes in the density of the fluid phase are essentially due to the number of particles being dispersed in the fluid phase. Light scatter and / or the half thickness of the intensity of light by these particles hence provides a good estimate of the mount of particles dispersed in the fluid phase and thus is indicative for the density of the fluid phase. As already apparent, herein the temperature is not the observable being metered by the observable meter, as a purely temperature induced density change does not change the ability of a given fluid-phase to be used as batching water for a given concrete grade. Hence, to be more precise, the observable meter is preferably configured to meter an observable being indicative of the density of the fluid phase stored in the fluid-phase reservoir for a given temperature and at a known (i.e. given) distance above the bottom of the fluid-phase reservoir. Hence, the observable being metered is preferably at least almost temperature independent. For example, the observable being metered may be (and / or be a function) of the number and / or size of particles being dispersed in the fluid phase. The observable being metered may be mapped from the observable space to fluid-phase density space and thereby enable not only an estimate of the particle volume in a given fluid phase volume, but as well to manufacture concrete slip by obeying the rules for such preparation, which are defined as maximum density values for the batching water.

[0023] The concrete slip recycling system further comprises a controller. The controller has an observable input port being connected with an output port of the observable meter and is configured to obtain an observable value from the observable meter via the connection. The connection may be provided via a signal line as a voltage signal and / or current signal. The connection may as well be provided via any data link between the observable meter and the controller. Typical data link standards include CAN, RS485, ethernet, RS232, .... It is not important how a value being indicative of the metered observable (i.e. an observable value) is provided from the observable meter to the controller, as long as the controller is able to receive observable values via the connection from the observable meter. The observable meter may be configured to provide observable values to the controller in given intervals, (almost) continuously and / or in response to transmit requests being sent from the controller to the observable meter.

[0024] As apparent, the concrete slip recycling system enables to (preferably at least almost continuously) monitor at least an observable being indicative of the density of the fluid phase in the fluid-phase reservoir. Based on this measurement, the motor driving the agitator (i.e. the agitator drive) can be controlled. A change in the metered observable value is indicative for a degree of sedimentation of the second fraction, at least if no additional fluid-phase volumes have been stored in the reservoir during the time interval in which the change has been observed.

[0025] Based on the metered observable values (and / or a chance thereof) the agitator drive can be controlled: For example it may be switched on and off if corresponding threshold values are reached.. This reduces the duration of agitator operation per day and hence the energy consumption of the concrete slip recycling system. In other words, the controller is preferably configured to control operation of the agitator drive as a function of observable values obtained from the observable meter. Preferably, activation and / or shut down of the agitator is controlled by the controller in response to an observable value being received from the observable meter. Particularly preferred, the rotational speed of the agitator is controlled by the controller as function of the metered observable values. This allows as well to reduce the energy consumption of the agitator drive.

[0026] In addition or alternatively, the agitator drive may be controlled (at least i.a.) based on the filling level of the fluid-phase reservoir (140). For example, a lower filling level of the fluid-phase reservoir may be agitated using a lower power setting of the agitator drive and vice versa. The method may hence comprise the step of determining a power setting of the agitator drive based on i.a. the filling level of the fluid-phase reservoir and / or the observable value.

[0027] Further, measuring the observable enables to replace the daily assumed maximum density by a more accurate estimate which can be obtained by mapping at least some of the measured observable values into density space. This measure reduces the fresh-water consumption as higher amounts of the stored fluid-phase can be used as batching water. In addition, the (preferably automated) measurement of the observable enables to determine an amount of fresh water being required to ensure that batching water being obtained by mixing a first amount of fluid-phase being drawn from the fluid-phase reservoir and a second amount of said fresh water have a density being below a predefined value. The predefined value may depend on the concrete recipe being prepared, which typically depends on the intended usage of the corresponding batch of concrete slip.

[0028] For example, the controller may be configured to obtain an initial observable value from the observable meter. In a preferred example, the initial observable value, may be measured after or during agitation of the fluid phase as an initial value and / or during a flow of fluid phase from the classifier into the fluid-phase reservoir has been detected. The point in time when the initial observable is connected hence preferably allows to assume that the fluid phase is homogenized to given level of homogenization.

[0029] Further, it may be assumed that the agitator is or remains switched off after the initial value has been obtained by the controller. In this case any change of the observable value indicates a change of the density. For example, in case the observable meter is located in the vicinity of the bottom of the reservoir sedimentation of the fines in fluid phase will cause a rise of the density being observable indirectly using the observable meter. A change in a measured observable value associated with an increase of the density may in the example configuration indicate a certain degree of sedimentation. The controller may hence compare the initial value and a subsequently measured value and activate the agitator if the absolute value of a change of the metered observable is above a threshold and thus indicates a predefined magnitude of sedimentation. In another alternative, the observable meter may be positioned in an upper portion of the fluid reservoir, e.g. in the upper half of the reservoir. A change in a measured observable value associated with a decrease of the density may in this example configuration indicate a certain degree of sedimentation, because if the fluid phase is not agitated, the fines sink down and accumulate in the lower portion of the fluid-phase reservoir. The particle density in the upper portion hence reduces during sedimentation. Accordingly, the controller may again compare an initial value and a subsequently measured value and activate the agitator if an absolute value of the change of the metered observable is above a threshold value. From these examples, it can be seen that the location of the observable meter in the fluid-phase reservoir does not change the general method. However, it is preferred, if the observable meter is located in the vicinity of fluid-phase outlet, as in this case a metered observable value is indicative of the density of fluid-phase being drawn from the fluid-phase reservoir. In this context the "in the vicinity of fluid-phase outlet" means approximately at the same distance from the bottom of the reservoir as the fluid-phase outlet. "Approximately at the same distance" is within ±15% of the distance of the fluid-phase level at the maximum design filling level of the fluid-phase reservoir, preferably with 10% even more preferred within 5% of the distance of the fluid-phase level at the maximum design filling level of the fluid-phase reservoir.

[0030] The controller is configured to receive, via a human-machine interface (hereinafter briefly "HMI"), a density value of the fluid phase in the fluid-phase reservoir. Further, the controller is configured to obtain an observable value via the observable input port that corresponds to the received density value. Such correspondence can be assumed if the two measurements at least essentially coincide. This enables the controller to calibrate the observable input value based on the density value that has been received by the HMI. It as well enables determining parameters of a mapping function for mapping an observable value from observable space to density space (i.e. to obtain a density value as a function of the observable value) and / or the inverse mapping function mapping density space into observable space. In a preferred example, the corresponding step of providing the controller with a density value being associated with a metered observable value may be repeated in intervals, e.g. once per day, week or month and / or after given events, e.g. a change of the density or size of the aggregates that have been used in the ready-mix plant and / or after given volume or number of batches of batching water that has / have been withdrawn from the fluid-phase reservoir. This step avoids that the approximation being involved by metering the observable instead of the density remained sufficiently precise.

[0031] The mapping functions (i.e. for mapping from observable space to density space and / or for the inverse mapping from density space to observable space) may include a temperature correction. It has been found that optical observables of the fluid phase show a different temperature dependence than the density of the fluid phase. In a preferred example, a temperature probe is located in the reservoir and configured to provide a temperature value via a connection to a temperature input port of the controller. Further, the controller is preferably configured to apply a temperature corrected mapping function and / or a temperature corrected inverse mapping function to the observable values and / or the density, respectively, to thereby obtain a temperature corrected density and / or observable value, respectively, wherein the temperature correction is based on a temperature value being obtained from the temperature probe. In other words, the controller may have a temperature inlet port configured to receive a temperature value being indicative of the measured fluid phase temperature in the reservoir and / or a change of the fluid-phase temperature in the reservoir. This temperature value may be used to determine a temperature correction.

[0032] Further, the controller is preferably configured to determine a temperature correction of the observable value and configured to control operation of the agitator as a function of the temperature corrected observable value. This further reduces the cost of operation of the fluid-phase reservoir.

[0033] In a preferred example, the controller may be configured to determine an estimate of the density of the fluid phase in the fluid-phase reservoir based on an observable value that has been received via the observable input port. Further, the controller may be configured to activate the agitator (e.g. by powering the actuator drive), if the estimate of the density value is above an upper density threshold and / or below a lower density threshold. For example, if the observable meter is located in the vicinity of the bottom of the reservoir, an increase of the density value being obtained by mapping the observable value to density space is indicative for a degree of sedimentation of the dispersed particles. If however the observable meter is located in an upper region, a decrease of the density value indicates a sedimentation.

[0034] Alternatively or in addition, the controller is preferably configured to determine an upper observable threshold and / or a lower observable threshold, wherein the two thresholds are associated to an upper density threshold and / or a lower density threshold. Further, the controller may be configured to activate the agitator if an observable value received from the observable meter is above the upper observable threshold and / or below the lower observable threshold. The technical effect is the same as explained above, but in this case the comparison is performed directly in the observable space. The latter provides the technical advantage that the computational effort is lower as the mapping of the observable value to density space is not necessary and the mapping of the density threshold to observable space to thereby obtain a corresponding threshold in observable space has to be performed only once.

[0035] In preferred example, the controller is configured to meter the observable value at two different heights above the bottom of the fluid-phase reservoir. The additional information enables to obtain an estimate of the mean density (or a corresponding observable value) if the fluid phase would be perfectly homogenized. Further, it allows to determine if the fluid phase is at least homogenized to a given degree, e.g. if the two metered observable values (and / or the corresponding density values) are at least essentially identical. In this context at least essentially identical means that the difference of the two observable values (and / or density values) indicates a degree of inhomogeneity of the dispersed particles being irrelevant for the purpose of using the fluid phase as batching water. If one maps the difference of the observable valuesΔO to the density ρ (f: ΔO → ρ), a density change of 0.005 − 0.01 kg m 3 is in most cases neglectable for concrete mixing, provided the density requirements as defined in DIN EN1008 are met.

[0036] If a predefined degree of homogeneity is obtained, the agitator drive may be shut off again, hence agitation time is further reduced. Determining if a predefined degree of homogeneity is obtained may be based on the difference of at least two observable values being measured at least essentially synchronous at two different heights above the bottom of the fluid-phase reservoir. In another example determining if a predefined degree of homogeneity is obtained may be based on determining the change of the observable values as a function of time during agitation. If the change of the observable values as a function of time falls below a change threshold, a corresponding degree of homogeneity is obtained and the agitator may be switched of. Both examples enable to further reduce the energy costs for operating the agitator.

[0037] Only to avoid any misunderstandings, it is clarified that the estimate of the density may be based on a relation between the density value and the associated observable value, i.e. on said mapping of an observable value to density space.

[0038] The lower observable threshold and / or the upper observable threshold may be based on the relation between the density value and the associated observable value. These may be obtained starting from corresponding density thresholds by said inverse mapping of the corresponding density thresholds to observable space.

[0039] The observable meter preferably includes a light source configured to direct light into the fluid phase and a light detector configured to determine an observable of light scattered by particles dispersed in the fluid phase. The intensity of the scattered light may be considered as a measure of the particle volume in a given fluid volume and is thus indicative of the density of the fluid phase, assuming that the mean density of the dispersed particles is known or at least essentially constant, what can be assumed for most ready-mix plants.

[0040] Further, in ready-mix plants, it is known from which batch of concrete a batch of fluid phase has been separated by the classifier. Thus, a change of the mean density of the dispersed particles is known and can be considered in the mapping and inverse mapping functions. In other words, the information on the aggregates and the cementitious material in the batch of concrete being recycled is generally known upfront and may be used to determine a density value based on a measurement value provided by the light detector.

[0041] The controller is preferably configured to control a fluid flow from the fluid-phase reservoir to the concrete slip mixing chamber and as well to control a fresh-water flow from a fresh-water port of the ready-mix plant to the mixing chamber. Further, the controller is preferably configured to determine, for a given batch of concrete slip to be mixed in the concrete mixing chamber using a given amount of batching water an amount of the fluid-phase to be drawn from the fluid-phase reservoir, and an amount of fresh water to be drawn from the fresh-water port. These two amounts of batching water can be determined based on the conditions that the sum of the two amounts corresponds to the given amount of batching water. Further, a calculated density of the batching water may be below a predefined density value. The predefined density value may depend on the recipe of the given batch of concrete. As already explained, the predefined density value can be defined lower for higher grade concretes and higher for lower grade concretes. The invention hence enables to reduce the amount of fresh water being required to produce a given batch of concrete slurry, resulting in a reduction of the cost of operation of the ready-mix plant and as well in a reduction of the environmental impact of the ready-mix plant. The controller may preferably further be configured to display and / or dose the amount of the fluid-phase and the amount of fresh water into the concrete mixing chamber.

[0042] In addition to the above-described operation of the agitator, the controller may include a timer and be configured to control operation of the agitator as a function of the time. This allows to further reduce the energy consumption of the concrete slip recycling system. The density-controlled operation of the agitator as described above reduces the power consumption of the concrete slip recycling system during normal operation, as agitation needs only be effected, if an inhomogeneity of the fluid-phase prevents use of the fluid phase as batching water. Further, if no batching water is used, the density-controlled agitation can be paused. In practice, this may occur during the night hours, when concrete production is mostly paused. Such pausing of agitation for a prolonged amount of time results in sedimentation and often in curing of cementitious material at the bottom of the fluid-phase reservoir. This curing at the bottom can be avoided by agitation of the fluid phase in given intervals. These intervals, however, can be longer than those required to ensure a given grade of the fluid phase being drawn from the fluid reservoir is ensured.

[0043] In a preferred example, the controller is configured to control operation of the fluid-phase feeding pump. Further, the controller may be configured to execute the following steps upon a request to provide an amount of batching water to the concrete mixing chamber: Determine a measure of the density and / or of the homogeneity of the density in the fluid-phase reservoir and if said measure is indicative of a density value above density threshold and / or a of a vertical density gradient being above a density gradient threshold, then operate the agitator for a given amount of time or until at least one of the above conditions is no longer met. Subsequently activate the fluid-phase feeding pump. This method further reduces the energy consumption of the concrete slurry recycling system.

[0044] For the present invention, it is not relevant if the constituents of the concrete slip are mixed in the ready-mix plant or only during the transportation by cement mixer trucks.

[0045] A concrete slip recycling system may be comprised by a ready-mix plant. The pump outlet of the fluid phase feeding pump may at least in this case be connected with an inlet of a concrete slip mixing chamber. The connection may include a switch valve enabling to provide fluid phase as well to other parts of the ready-mix plant, e.g. with the purpose to rinse these.

[0046] The ready-mix plant may further comprise a fresh water inlet port being connected to the inlet of the concrete slip mixing chamber. This allows to use fresh water as batching water and as well to blend a volume of fluid-phase drawn from the fluid-phase reservoir with fresh water.

[0047] A method for providing batching water, e.g. to a ready-mix plant may comprise at least one of the following steps: Determining an observable value being indicative of the density of a fluid phase being stored in a fluid phase reservoir, e.g. in a fluid-phase reservoir of a concrete slip recycling system according to one of the herein described examples. Preferably, the observable is an optical observable being indicative of the number and / or size of particles dispersed in the fluid phase. The method may further comprise a flow the fluid phase based on the observable value thereby meeting a constraint on the density of the batching water.

[0048] The method may further comprise, based on the determined observable value, starting and / or interrupting agitation of the fluid phase. For example, if the observable value is indicative for a degree of sedimentation that is above a threshold value, agitation may be started. If the observable value is indicative for a degree of sedimentation that is below a threshold value, agitation may be stopped. Agitation can be obtained by controlling an agitation drive being configured to drive an agitator in the fluid-phase reservoir. Starting and / or stopping the agitation based on the observable value vastly reduces the energy consumption of the corresponding agitator.

[0049] In addition or alternatively, the method may comprise: Based on the observable value determining an estimate value of the density of the fluid phase in the fluid-phase reservoir. The method may further comprise, using this estimate to determine a first amount of fluid-phase to be dosed into a mixing chamber and a second amount of water (as a pars pro toto for or an aqueous fluid) having a lower particle density than the fluid phase such that the density of an assumed a mixture of the two amounts would be at or below an upper density limit. For example, if ρ mix = m mix / V mix is the density of the assumed mixture, wherein M mix and V mix are the mass and the volume, respectively of the assumed mixture and ρ 1 = m 1 v 1 , ρ 2 = m 2 v 2 are the densities, masse and volumes of the first and the second amounts, respectively, the first amount can be determined as V 1 = V mix ρ − ρ 2 ρ 1 − ρ 2 , wherein V mix = V 1 + V 2 is the volume of the mixture of the fluid phase and the aqueous fluid with the lower density, hence V 2 = V mix - V 1 . The method thus enables to reduce usage of fresh water when preparing a batch of concrete slip.

[0050] The method may as well Ide the step of dosing the first amount to be dosed into the mixing chamber wherein the amounts of fluid phase and the amount of fresh water sum up to the amount of water to be added to the batch being mixed in the mixing chamber.

[0051] Any one of the above method steps can be executed by a controller being configured to control a corresponding device and / or to obtain the respective data, like e.g. the observable value form a corresponding observable meter. In a preferred example is the controller the controller of the concrete slurry recycling system and / or the ready-mix plant being disclosed herein.

[0052] In the cement industry and in the context of this application, the term cementitious materials includes of course Portland cement and other Alite and / or Belite based cements, but as well tempered pozzolana. Still as usual, aggregate means particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates (see https: / / en.wikipe-dia.org / wiki / Construction aggregate retrieved on Jan. 15, 2024).

[0053] Again, as usual in field of process engineering, the term batching water means water being mixed with the other concrete constituents, commonly used synonyms are mixing water and gauging water. Still as usual in the field, herein, an observable a physical property or physical quantity that can be measured (see https: / / en.wikipedia.org / wiki / Observable as retrieved on Jan. 15, 2024).

[0054] The term fluid phase herein denotes the liquid obtained by separating aggregates from the concrete slip in the concrete slip classifier. This liquid still comprises a particulate matter, so called "fines" is hence still a dispersion and may in some contexts be referred to as waste-water.

[0055] As usual in the art, the terms "a connection" and "to connect" indicate a functional connection of two devices, parts or the like. A connection may but does not necessarily imply a tangible connection of these two devices. For example, if a fluid outlet of a first device is connected with a fluid inlet of a second device, the connection can be any provided by any conduit or the like, thereby enabling via the connection a fluid flow from first device's outlet to the second device's inlet (i.e. there is tangible connection). Similarly, if a data port of a measurement device is connected to another data port of, e.g., a controller, then the connection is provided by a data link. Such data links may be provided by an optical fiber connection or an electrical conductor (both being examples tangible connections). Alternatively, a wireless connection (a non-tangible connection) can be used. Hence the terms "a connection" and "to connect" are different from the terms "a contact" and "to contact" implying a physical contact (touch) between the respective devices or parts. Both are again different from the terms "an attachment" and "to attach" implying that two parts, pieces, devices or the like are mechanically connected to each, e.g. in a force transmitting manner. Such force transmitting mechanical connection (i.e. attachment) may be obtained by a clamp, a glue, a bolt, a weld, a rivet, etc.....

[0056] As usual, a meter is a measuring device providing a value being indicative of an observable being metered (=measured). For example, a thermometer provides a temperature value, Voltmeter a voltage, a flow-rate meter a flow rate, a reflectance meter provides a reflectance coefficient, a half-value thickness meter provides the thickness after which the intensity of a given radiation (e.g. of light of a given spectrum) has been reduced to half the initial intensity, etc... The set of all possible values of an observable defines an observable space. These observable spaces may be mappable to each other. For example, an (e.g. optical) observable value being indicative for volume being occupied by particles being dispersed in test volume of a fluid may be mapped e.g. by a functional relationship or a lookup table into density space, i.e. to a density value being associated to the observable value given a set of boundary conditions (e.g. a given temperature, the density of the particles, etc.).

[0057] Herein, a controller is an electronic device configured to control devices based on input data received. Controllers may comprise I-O ports, network connections, a CPU, a memory, etc.

[0058] The verbum "to dose" describes the provision of a predefined amount of a liquid or a bulk material to a vessel, e.g. to a mixing chamber. Dosing may involve conveying the dosed matter into the vessel and as well monitoring the conveyed amount. There are numerous dosing systems available enabling to dose given amounts of liquids and bulk material. Some comprise a balance configured to determine changes of the mass being provided to and / or removed from the vessel into which the matter is dosed and / or a balance to determine changes of the mass being provided and / or removed from storage of said matter to be dosed.

[0059] Liquid dosing systems often comprise flow meters configured to determine a liquid flow rate into the vessel. In addition or alternatively, dosing of matter can be obtained by feeding wheels, screw conveyers or other conveying devices enabling to control a flow rate of the matter to be dosed.

[0060] The term "amount" identifies a quantity, it can be measured as a volume, as a mass or as well as a percentage.Description of Drawings

[0061] In the following the invention will be described by way of example, without limitation of the general inventive concept, on examples of embodiment with reference to the drawings. Figure 1presents a view of a ready-mix plant with a concrete slip recycling system. Figure 2shows a simplified cross section of a fluid-phase reservoir. Figure 2presents a sequence of method steps that may preferably be executed by a controller.

[0062] As shown in FIG. 1, a ready-mix plant 1 may comprise bulk material storages 10 (e.g. aggregate silos, cement silos, pozzolana silos, etc.) and conveying means 15 configured for conveying a given amount of a bulk material into a concrete mixing chamber 30. The operation conveying means may be controlled by a controller 40.

[0063] The concrete mixing chamber 30 may be mixing drum of a concrete mixing truck, but it may as well be stationary mixer. The ready-mix plant 1 may further comprise a fresh-water inlet port 20 being connected with a fresh water outlet, wherein the fresh water outlet is configured to provide fresh water to the concrete mixing chamber 30. The fresh-water flow may be controlled by the controller 40 as indicated by a dashed line connecting a corresponding valve-drive with the controller 40. In other words, the controller may further be configured to dose fresh water into the mixing chamber 30.

[0064] The controller may as well be configured for controlling the conveying means to thereby dose bulk material according to concrete recipe into the mixing chamber 30. Only to declutter the figure, the corresponding dashed lines have been omitted.

[0065] The ready-mix plant 1 may further comprise a concrete-slip recycling system 100. The concrete-slip recycling system 100 may comprises a concrete-slip classifier 120 with a concrete slip inlet 121, at least one bulk material outlet 122 and at least one fluid phase outlet 123. The concrete-slip classifier 120 is configured to separate concrete slip that has been provided to the concrete slip inlet 121 into a fraction of coarser bulk material and a fluid phase. This coarser bulk material is herein as well referred to as a first fraction of aggregates and is provided to the bulk material outlet 122. The first fraction may be further classified (see bulk material classifier 60) e.g. by size and may be provided the corresponding storages, from where it may be dosed into another batch of concrete slip or used for other purposes. A finer fraction of particles remains in the fluid phase being provided to the fluid-phase outlet 123. Finer and coarser relate to the respective other, i.e. the median of the diameter of the particles in the coarser fraction is generally greater than median of the particles of the finer fraction that remain suspended in the fluid phase. The fluid phase is essentially water and the finer fraction. It may further comprise additives that may have been dosed to batches of concrete slip that have been (partially) provided to the concrete slip recycling system 100. The concrete-slip classifier 120 may classify the particles by size. Typical market available concrete-slip classifiers for use in the concrete industry enable to separate particles as small as 0.25mm from the fluid phase. More expensive solutions enable to separate even smaller particles.

[0066] The concrete slip recycling system 100 may further comprise a fluid-phase reservoir 140 having a fluid phase inlet 141, a fluid-phase outlet143 and an agitator 148. A first conduit 130 may connect the fluid-phase outlet 123 of the concrete-slip classifier 120 with the fluid-phase inlet 141 of the fluid-phase reservoir 140.

[0067] An optional fluid phase feeding pump 135 may have a pump inlet being connected to the fluid-phase outlet 143 of the fluid-phase reservoir 140. A pump outlet of the fluid phase feeding pump 135 may be configured to be connected with an inlet of the concrete slip mixing chamber 30 and / or a rinsing water outlet port 138. Hence, by controlling the fluid phase feeding pump 135 (and the optional valves), an amount of fluid phase stored in the fluid-phase reservoir 140 may be dosed into the concrete slip mixing chamber 30 and / or may be used as rinsing water. The fluid phase-feeding pump 135 may be controlled by a controller of the concrete slip recycling system 100. Only for conceptual simplicity, the controller of the concrete slip recycling system 100 is shown to be unitary with the controller 40 of the ready-mix plant 1, however it should be noted that this is only an advantageous integration of the concrete slip recycling system into a ready-mix plant and there may be two different controllers that may preferably be connected by a data link.

[0068] The fluid-phase reservoir 140 comprises an observable meter 145. The observable meter 145 is a measurement device configured to determine an observable value. The observable being metered by the observable meter 145 is indicative of the density of the fluid phase stored in the fluid-phase reservoir 140 and / or of a change of the density of the fluid-phase stored in the fluid-phase reservoir 140 as function of time. As shown, the observable meter is preferably located in the fluid-phase reservoir 140, i.e. configured to be immersed into the fluid phase. Corresponding measurements can be executed by an optical measurement system configured to determine an amount of scattered light and / or the half-value thickness of the light intensity. Both observables provide an estimate for the portion of a cross section of an optical path that is blocked by particles being dispersed in the fluid phase. These particles increase the density of the fluid phase, hence if the blocked portion of the cross section of the optical path increases the density of the fluid phase increases and vice versa.

[0069] The controller 40 has an observable input port being connected with an output port of the observable meter 145 as indicted by a dashed line. Hence the controller 40 is configured to receive and / or read information about an observable value being measured by the observable meter 145 or can at least retrieve it from the observable meter 145. Based on this information, the controller 40 can determine an estimation of the density of the fluid phase at the level of the observable meter. Such estimate can be obtained using a look-up table being stored in the controller's memory and / or by applying a function mapping observable values into density space on the metered observable value.

[0070] A temperature probe 144 may be connected to a temperature inlet port of the controller 40, enabling the controller to correct the observable values to compensate for temperature changes.

[0071] The fluid-phase reservoir 140 may further comprise an agitator 148 being driven by an agitator drive 149. The agitator drive 149 and hence operation of the agitator is preferably controlled by the controller 40 (again as indicated by a dashed line). The controller 40 may control the agitator drive 149 using an observable value being representative of the density and / or the density as obtained based on the observable value to control operation of the agitator 148. Further, the filling level of the fluid-phase reservoir may be used as an input parameter by the controller 40 for controlling the rotational speed of the agitator drive 149. Preferably, the controller 40 has a Human Machine Interface (HMI) 48, e.g. computer screen and / or a keyboard and / or a mouse or the like. Via the HMI 48 the controller 40 receives a density value of the fluid phase in the fluid-phase reservoir 140. The controller 40 may associate an observable value that has been measured by the observable meter 145 with the density value. The controller 40 may be configured to determine at least one parameter of a mapping function for mapping an observable value to density space based on the density value and the associated observable value. Similarly, the controller 40 may be configured to determine at least one parameter of a corresponding inverse mapping function mapping density space to observable space.

[0072] As already apparent data links and other control enabling connections are indicated in FIG. 1 as dashed lines. Each of these is optional but preferred.

[0073] FIG. 2 shows a cross section of a fluid-phase reservoir 140 that may be used as a fluid-phase reservoir 140 of the concrete slip recycling system shown in FIG. 1. As can be seen, the fluid-phase reservoir 140 has multiple fluid phase outlets 143 being located at different distances above the bottom 147 of the fluid-phase reservoir 140. As shown at least one of these may point upwards or sidewards. If the outlet opening 143 points upwards of sidewards, it can be avoided that fluid phase from lower levels of the fluid-phase reservoir 140 is sucked into the outlet opening. Hence an estimate for a density at the level of the outlet can be considered as a maximum value of the density of the fluid phase which is delivered to e.g. the mixing chamber 30 when drawing the fluid phase through the corresponding fluid phase outlet 143. The controller 40 may be configured to determine based on an observable value (or multiple observable values) a degree of sedimentation and / or an estimation for the fluid phase density at a given distance above the bottom of the fluid-phase reservoir 140, e.g. at the heights of the fluid phase outlets. This enables to draw an amount of fluid phase from the fluid-phase reservoir 140 with a 'required' density. For lower concrete grades and / or as rinsing fluid, fluid phase from lower outlets 123 can be used, whereas for higher concrete grades the batching water can be drawn from upper fluid phase outlets. Arrows of connections indicate connections to the entities being indicated by their refence number.

[0074] Fig. 3 shows a method 200 for providing batching water, e.g. for the ready-mix plant shown in FIG. 1. The method 200 has a sequence of optional method steps. These can be altered and steps may be omitted, but the shown sequence is preferred. Step 210 may include determining an observable value being indicative of the density of a fluid phase being stored in a fluid phase reservoir, e.g. in a fluid-phase reservoir of a concrete slip recycling system according to one of the herein described examples. Preferably, the observable is an optical observable being indicative of the number and / or size of particles dispersed in the fluid phase. The observable value can be obtained from an observable meter being located in the fluid-phase reservoir.

[0075] The method may include the step 220 of starting and / or interrupting agitation of the fluid phase based on the determined observable value. For example, if the observable value is indicative for a degree of sedimentation that is above a threshold value, agitation may be started. If the observable value is indicative for a degree of sedimentation that is below a threshold value, agitation may be stopped. Agitation can be obtained by controlling an agitation drive being configured to drive an agitator in the fluid-phase reservoir. Starting and / or stopping the agitation based on the observable value vastly reduces the energy consumption of the corresponding agitator.

[0076] In addition or alternatively, the method may comprise the step 230 of determining an estimate value of the density of the fluid phase in the fluid-phase reservoir based on the observable value. Such determining may be based on a lookup table and / or a functional relationship mapping values from observable space into fluid phase density space. The method may further comprise (step 240), using this estimate to determine a first amount of fluid-phase to be dosed into a mixing chamber and a second amount of water (as a pars pro toto for or an aqueous fluid) having a lower particle density than the fluid phase such that the density of an assumed a mixture of the two amounts would be at or below an upper density limit.

[0077] The method may as well include the step 250 of dosing the first amount to be dosed into the mixing chamber wherein the amounts of fluid phase and the amount of fresh water sum up to the amount of water to be added to the batch being mixed in the mixing chamber.List of reference numerals

[0078] 1ready-mix plant 10bulk material storages (e.g. silos) 15bulk material conveying means 20fresh water inlet port 25fresh water valve 30mixing chamber, e.g. mixing drum of a concrete mixing truck 40controller 45Human Machine Interface 100concrete slip recycling system 120concrete slip classifier, classifier for short 121concrete slip inlet 130first conduit 135fluid phase feeding pump 138rinsing water outlet port 140fluid phase reservoir, reservoir for short 145observable meter, e.g. scattered light detector, light intensity half-value thickness meter 147bottom of fluid phase reservoir 148agitator 149agitator drive 200method 210method step 220method step 230method step 240method step 250method step

Claims

1. A concrete slip recycling system (100), comprising: - a concrete-slip classifier (121) with a concrete slip inlet (121), a bulk material outlet (122) and a fluid phase outlet (123), wherein the concrete-slip classifier (120) is configured to separate at least a portion of aggregates comprised in concrete slip from the concrete slip to thereby obtain a first fraction of aggregates and a fluid phase, - a fluid-phase reservoir (140) having a fluid phase inlet, a fluid-phase outlet and an agitator, - a first conduit (130) connecting the fluid-phase outlet (143) of the concrete-slip classifier (120) with the fluid-phase inlet of the fluid-phase reservoir (140), wherein (i) the fluid-phase reservoir (140) comprises an observable meter (145), wherein the observable being metered by the observable meter (145) is indicative of the density of the fluid phase stored in the fluid-phase reservoir (140) and / or of a change of the density of the fluid-phase stored in the fluid-phase reservoir (140), (ii) the concrete slip recycling system (100) further comprises a controller (40), (iii) the controller (40) has an observable input port (45) being connected with an output port of the observable meter (145) and is configured to obtain an observable value from the observable meter (145) via the connection, characterized in that the controller (40) is configured to receive via a human-machine interface (48) a density value of the fluid phase in the fluid-phase reservoir (140), to obtain an observable value via the observable input port (45) that corresponds to the received density value, and to use the density value as calibration value for mapping an observable space into density space and / or for mapping the density space into the observable space.

2. The concrete slip recycling system (100) of claim 1, characterized in that the controller (40) is configured to control operation of the agitator as a function of the observable value obtained from the observable meter (145).

3. The concrete slip recycling system (100) one of the previous claims, characterized in that said mapping includes a temperature correction.

4. The concrete slip recycling system (100) of one of the previous claims, characterized in that the controller (40) is configured to determine: (i) an estimate of the density of the fluid phase in the fluid-phase reservoir (140) based on an observable value that has been received via the observable input port and in that the controller (40) is configured to activate the agitator, if the estimate of the density value is above an upper density threshold and / or below a lower density threshold, and / or in that (ii) an upper observable threshold and / or a lower observable threshold, wherein the two thresholds are associated to an upper density threshold and / or a lower density threshold and in that the controller (40) is configured to activate the agitator (148) if an observable value received from the observable meter (145) is above the upper observable threshold and / or below the lower observable threshold.

5. The concrete slip recycling system (100) of at least claim 4, characterized in that the controller (40) is configured to determine - the estimate of the density based on a relation between the density value and the associated observable value and / or - the lower observable threshold and / or the upper observable threshold based on the relation between the density value and the associated observable value.

6. The concrete slip recycling system (100) of one of the previous claims, characterized in that the observable meter (145) includes a light source configured to direct light into the fluid phase and a light detector configured to determine an observable of light scattered by particles dispersed in the fluid phase.

7. The concrete slip recycling system (100) of one of the previous claims, characterized in that the controller (40) has a temperature inlet port configured to receive a temperature value being indicative of the measured fluid phase temperature in the reservoir and / or a change of the fluid-phase temperature in the reservoir.

8. The concrete slip recycling system (100) of one of the previous claims, characterized in that the controller (40) is configured to determine a temperature correction of the observable value and configured to control operation of the agitator as a function of the temperature corrected observable value.

9. The concrete slip recycling system (100) of one of the previous claims, characterized in that the controller (40) includes a timer and controls operation of the agitator as a function of the time.

10. The concrete slip recycling system (100) of one of the previous claims, characterized in that the controller (40) activates the agitator in response to an activation of a fluid phase feeding pump.

11. A ready-mix plant (1) comprising the concrete slip recycling system (100) of one of the previous claims, wherein a pump outlet of the fluid phase feeding pump (135) is connected with an inlet of a concrete slip mixing chamber (30).

12. The ready-mix plant (1) of the previous claim, characterized in that - it comprises a fresh water inlet port (20) being connected to the inlet of the concrete slip mixing chamber (30) - a controller (40) configured to control a fluid flow from the fluid-phase reservoir (140) to the concrete slip mixing chamber (40) and to control a fresh-water flow from the fresh-water port (20) of the ready-mix plant (1) to the mixing chamber (30), - the controller (40) is configured to determine, for a given batch of concrete slip to be mixed in the concrete mixing chamber (30) using a given amount of batching water: ∘ an amount of the fluid-phase to be drawn from the fluid-phase reservoir (140), and ∘ an amount of fresh water to be drawn from the fresh-water port. - the amount of batching water is the sum of the amount of the fluid-phase and the amount of fresh water, - a calculated density of the batching water as a function of the amount of the fluid-phase and amount of fresh water is below a predefined density value, - the controller (40) is configured to display and / or dose the amount of the fluid-phase and the amount of fresh water into the concrete mixing chamber.