APPLICATION OF COMPOSITE CEMENT MIXTURES

Technical Field

[0001] The present invention relates to mixing, transport, acceleration and application of a cement mixture. The comprehensive system is designed for 3D printed composite cement mixtures. Especially for the additive method of 3D printed cement mixtures.

Background Art

[0002] The prior art puts together various mechanical systems which combine diverse application techniques already used in the construction industry. This system is directly designed especially for the requirements of additive 3D printing of composite cement mixtures. Many application techniques are created by combining systems which have been designed for a wide use. For this reason, however, they are limited by their parameters to a certain segment of activities. The aim of the robotic fabrication is to limit the necessity of physical work of human workers. Ideally, purely autonomous systems would be concerned. The comprehensiveness of this invention lies in the possibility to respond to the changes in external conditions very precisely and quickly, especially for the in situ printing version, where sudden changes of not only weather conditions are very common. This system is also suitable for experimental testing of newly created mixtures.

Disclosure of the Invention

[0003] The above stated shortages are eliminated by an apparatus for application of composite cement mixtures according to this invention comprising a linear mixer. The linear mixer is continuously followed by a transport section connected with an application head, wherein the linear mixer is provided by a linear mixing system with a screw feeder to which an inclined first screw dispenser of binder components and fine fractions of a bulk material, an inclined second screw dispenser of cement mixture aggregate and a mixing water dispenser are connected. The linear mixing system is followed by a transport section comprising a storage bin with a paddle mixer feeder, a spindle pump and a hose system, which is used for connecting the application head comprising a screw feeder, a liquid accelerator injector, a closable mixer of the cement mixture with the liquid accelerator and a temporarily closable nozzle, wherein the mixing system, the storage bin and the spindle pump are driven by one common shaft.

[0004] Another aspect of the invention is an apparatus for application of composite cement mixtures using the application head provided with a fibre feeder into the mixture coming out of the nozzle.

[0005] Another aspect of the invention is an apparatus for application of composite cement mixtures with a mixing water dispenser and an injector with a peristaltic pump.

[0006] The invention combines three main systems into one continuous system.

[0007] The first part is formed by the linear mixer. The mixer enables mixing of the composite cement mixture. The innovativeness of this solution lies in the possibility of a three-stage mixture mixing. The reason is the possibility of a fast and precise regulation of the ratio of the three components of the mixture according to currently required properties of the mixed mixture. Each of individual motors is digitally controlled to enable synchronization of respective processes. The first dosed component is represented by binder components and other fine fractions of the prepared mixture. These are dosed by a digitally controlled inclined screw dispenser with a bulk material storage bin. The other stage is represented by mixing water injection (water with plasticizer). This component is injected using a peristaltic pump into a poured bulk binding mixture. This enables gradual moistening of the poured bulk mixture in small doses, contrary to mixing in drum mixers, enabling to change the mixture liquidity swiftly and precisely. These two components are mixed and simultaneously pushed by a screw feeder; subsequently, the binder part is liquefied to the desired viscosity. The third stage is mixture thickening by mixing in a required amount of aggregate which is dosed by the same screw feeder as the binder.

[0008] Contrary to other mixing applications, this system is less energy-intensive, since the liquefaction of the mixture is performed only at mixing of reacting components, i.e. the plasticizer and the cement component of the mixture. The aggregate component is not required for the liquefaction of the mixture. Another advantage is a uniform saturation of the binder parts of the mixture.

[0009] Another part is the transport section of the system. This consists of three consecutive parts. The first part is formed by a storage bin with a paddle mixer feeder. The feeder shaft is driven by a digitally controlled motor. The shaft further drives a spindle pump which pushes the cement mixture under pressure into a hose system. The hose system guides the mixture to the third part which is an application head containing a temporarily closable mixer of the cement mixture with a liquid accelerator. [0010] The application head consists of four parts. The first part is a screw feeder which partially regulates the mixture flow and also homogenizes the compressed mixture in the hoses. The second part is injection and mixing of the cement mixture with the liquid accelerator. The third part is regulation and temporary stoppage of the mixture flow using a screw at the shaft end. The uniqueness of this part of the invention is in the combination of three functions which are controlled by a rotary movement of one motor-driven shaft. The fourth part is a feeding system for laying a continuous reinforcing fibre into the printed mixture using the rotating shaft of the printhead.

[0011] The printhead together with the mixer are located at the end of a CNC machine. The printhead is the last section where the mixture can be accelerated. Since the mixer is located at the end of the whole system, it is possible to add the accelerator into the mixture without the risk of mixture solidification in the hose system when the flow stops. This variant makes it possible to accelerate the mixture in a matter of minutes. Such accelerated mixture can be printed even in arched forms, which the unaccelerated or accelerated but slowly solidifying mixture could not form. The liquid accelerator is a solution of aluminium sulphate which is injected into the mixture under the pressure of at least two bars. This is mechanical mixing using a paddle system with an upstream screw feeder with a slow rise. By the slow rise of the screw feeder it is achieved that the automatically driven shaft rotates at a higher speed, "which results in even mixing of the mixture in the paddle mixer area. The third part of the whole system is a lockable system having a screw shape and, at the end, a closure with a conical shape which corresponds to the angle of the nozzle narrowing to the required diameter, which defines the diameter of the printed track. The sequence and the shape of the paddles in the area of mixing with the accelerator are formed in such a way that there is no accumulation of the accelerated mixture. The paddle shape is adjusted also for mixing the mixture containing fibres.

[0012] The flow closure system is based on the shape and the function of the screw which closes and opens the nozzle purely due to its shape and rotation direction. The whole shaft is connected to the motor. The connection of the shaft and the motor is designed so that the shaft can move on the axis up and down, and thus enables the printing nozzle to be closed and opened. The last component of the ’whole system is a nozzle for laying a continuous reinforcement into the printed matter. The reinforcement fibre is supplied by a digitally controlled motor unwinding the spool with the fibre. The fibre goes through a hollow rotating shaft of the printhead.

[0013] The mixing of the cement mixture with the accelerator in the last system part enables to use the accelerators with the setup time within 2-20 minutes.

[0014] This is a system specifically defined for 3D printing of cement mixtures with the minimum amount of water. This way, higher strengths of the final products can be achieved.

[0015] The advantage of this arrangement is the option to change the mixture parameters during the mixing process. This is an advantage also in the event of a sudden change in environmental conditions (temperature, humidity...) but also in the event of experimental testing of new material compositions of the mixture.

[0016] In the first stage, the plasticizer is injected into a bulk cement mixture, with witch it reacts and thus the mixture is quickly liquefied. This reduces the energy intensity of mixing, which is higher in the event of mixing the mixture also with the aggregate part, which is not necessary for liquefaction.

[0017] The advantage is the process mechanization when there is no need to manually clean the mixing system during the processes as is the case with common drum mixers, where mixing is performed in batches between which the mechanism needs to be continuously cleaned.

[0018] The connection of the mixture mixer with the accelerator and the system of a temporary flow stoppage and the option to lay the continuous reinforcement into one comprehensive system.

[0019] The system includes a feeder of continuous reinforcement, which is longitudinally laid into the print material. This increases the tensile strength of the final products.

Brief Description of Drawings

[0020] The invention will be described in more details by examples of a specific embodiment with reference to the accompanying drawing. Fig. 1 is a schematic drawing of the system for continuous mixing, transport, acceleration and application of composite cement mixtures.

Examples of the Invention Embodiments

[0021] An exemplary equipment for application of composite cement mixtures comprises a linear mixer A which is continuously followed by a transport section B connected with an application head C, wherein the linear mixer A is provided by a linear mixing system _4 with a screw feeder to which an inclined first screw dispenser _1 of binder components and fine fractions of a bulk material, an inclined second screw dispenser 2 of cement mixture aggregate and a mixing water dispenser 3 are connected. The linear mixing system 4 is followed by a transport section B comprising a storage bin 5. with a paddle mixer feeder, a spindle pump 6 and a hose system 7 connecting the application head C. The application head C comprises a screw feeder 8, a liquid accelerator injector 9, a closable mixer 10 of the cement mixture with a liquid accelerator and a temporarily closable nozzle 11. The mixing system 4, the storage bin 5 and the spindle pump _6 are driven by one common shaft.

[0022] The preferred embodiment comprises an equipment for application of composite cement mixtures using the application head C provided with a fibre feeder 12 into the mixture coming out of the nozzle 11.

[0023] Another preferred embodiment comprises an equipment for application of composite cement mixtures with a mixing water dispenser 3 and an injector 9 with a peristaltic pump.

[0024] The mechanism is designed so that most of its paddle and screw parts can be made by FDM (Fused Filament Fabrication) printing. This enables to quickly respond to defects caused by wear. The basic material is ASA (acrylonitrile-styrene-acrylate) or ABS (acrylonitrile- butadiene-styrene) thermoplastics which resist to abrasive environment due to their properties. The cylindrical envelope may be made using transparent PVC (polyvinylchloride) to enable flow monitoring. Another option is to use standardized steel pipes, e.g. stainless steel or aluminium. For the shaft, steel is suitable.

[0025] The mixed and pumped mixtures are high and ultra-high performance concrete mixtures (HPC and UHPC), which contain a minimum amount of water, thus require a special mixing process. The mixture liquefaction is based especially on the reaction of the liquid plasticizing additive with the cement parts of the mixture. The components of the mixtures are Portland cement, fine aggregate, silica fume, silica flour, water reducing additive, accelerator, plastic fibres and continuous reinforcement.

Industrial Applicability

[0026] The equipment for continuous mixing, transport, acceleration and application of composite cement mixtures according to this invention finds its use especially in the field of construction industry, mainly within its robotization. The system can be used for application of both industrially prepared mixtures directly in the construction site with changeable conditions and it is also suitable for experimental purposes in laboratories for testing of new cement mixtures. The system is designed for high and ultra-high performance concrete mixtures (HPC and UHPC).

Reference Signs List

A- Linear mixer

B- Transport section

C- Application head

1- First screw dispenser of binder components of the cement mixture

2- Second screw dispenser of binder components of the cement mixture

3- Mixing water dispenser

4- Linear mixing system

5- Storage bin

6- Spindle pump

7- Hose system

8- Screw feeder

9- Liguid accelerator injector by peristaltic pump

10-Cement mixer with accelerator

11-Temporarily closable nozzle

12-Fiber feeder for continuous reinforcement