Simultaneous and contiguous integration of mineral-bonded carbon reinforcement into additive manufacturing with concrete
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| Anzahl der Teile | 12 | |
| Autor | 0000-0002-8256-1455 (ORCID) | |
| Lizenz | CC-Namensnennung 3.0 Deutschland: Sie dürfen das Werk bzw. den Inhalt zu jedem legalen Zweck nutzen, verändern und in unveränderter oder veränderter Form vervielfältigen, verbreiten und öffentlich zugänglich machen, sofern Sie den Namen des Autors/Rechteinhabers in der von ihm festgelegten Weise nennen. | |
| Identifikatoren | 10.5446/56113 (DOI) | |
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00:00
MinarettBauausführungTransportbetonVorlesung/Konferenz
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16:32
Beton
Transkript: Englisch(automatisch erzeugt)
00:00
Hi, my name is Tobias Neff. I am research assistant from the Institute of Construction Material. I am dealing with additive manufacturing or better known as concrete 3D printing and today I want to show some aspects about simultaneously and contiguous integration
00:26
of mineral bound carbon reinforcement into additive manufacturing with concrete. And I want to start with the special reinforcement we are using. The next part we are dealing
00:52
with the integration of the reinforcement in the printing process and the obtained mechanical
01:19
results. Finally I will give you an expression how this technology can be downsized for fine
01:29
filament printing with a high reinforcement grade. Typical concrete structures are reinforced
01:43
with steel rebars. In the last decades nonmetallic reinforcements are in common. One advantage is that the nonmetallic reinforcement requires only a very thin concrete cover for the
02:03
bond. They are not prone to corrosion like standard reinforcement. A thin cover leads to material saving and so is the more environmentally friendly construction. For the full activation of the yarn coating is required which is normally polymer based.
02:27
This solution leads a lot of temperature sensitive mechanical load bearing and adhesive behavior. This problem are avoided with mineral impregnation significantly higher
02:45
temperature resistance than polymeric impregnation materials can be reached. One advantage is that the easy formability of the freshly impregnated yarn in the first four hours
03:07
you can see in the video. The yarn can be deposed in any geometry without strain so the full potential of the geometric freedom of 3D printing can be used. For the most
03:24
the fresh and fresh technology generates an intensive bond between the reinforcement and the concrete. The mineral impregnation we use is based on cement and to do the
03:43
crane size distribution of ordinary cement and the diameter of the fiber of the carbon fiber filament it was found that they does not fit together. Both have nearly the same
04:06
dimension so the distance between the carbon filament is too high. To prevent this we use two ultrafine cements and a micro silica suspension. The impregnation slurry has
04:23
a water binder ratio of 0.8 and the flowability is adapted by a super plasticizer. In the figure low right you can see the grading curves of the constituents of the suspension
04:43
in comparison to a typical ordinary cement and in the picture of the scanning electronic microscope you can see that the solution works. Before we start with the fiber
05:04
integration I'd like to introduce you the concrete printing process developed at the Theodristen. In this video we can see the printing process of wall corner with a wide
05:30
of 50 cm and a layer high of 5 cm but processes like these are not comparable to ordinary
05:41
reinforcement forced concrete. They compete to the missing reinforcement. To overcome this disadvantage the integration of reinforcement is necessary. Today reinforcement technology
06:01
is parallel to printed concrete filament are in focus of the presentation. The easiest way is to lay down the carbon yarn on top of the concrete filament and based on that step-by-step production it's classified as a continuous process. The extrusion of
06:27
the concrete filament is followed by the deposition of the carbon rovings onto it and subsequently covering the reinforcement yarn by extrusion a new concrete filament.
06:47
The advantage of this method is that the placement of the concrete and the reinforcement are decoupled in time. This video shows us the ugly prototype status.
07:06
The number of deposition reinforcement between the concrete filaments can be varied according to the expected local loading. This reduces the cost of the reinforcement
07:24
and promotes environmentally friendly and resource-saving construction. One disadvantage is that the placement of the reinforcement in the joint between two concrete filaments is the weakening of the porous region. So transfer tensile stress
07:48
resulting from the bond between yarn and concrete can lead to splitting along the bonded joint.
08:02
The second possibility is the reinforcement integration through a simultaneous process. The carbon reinforcement is embedded in the concrete filament and deposed with it. The advantage of this method
08:22
are completed encasement of the yarn without weakening the joint in an efficient and time-saving manner. This disadvantage is lack of intersection and overlaps of
08:44
reinforcement layers. This can make the transfer of tensile force into compression zones difficult. Note that for a simultaneous process the degree of reinforcement in the concrete filament
09:02
can be adapted by using special nozzle geometries. Our actual printing nozzle can take up to six row rings which are integrated simultaneously. In the next steps
09:24
the mechanical parameters of both production processes can be compared. The graph on the right hand shows both techniques achieve nearly the same load bending but the stiffness
09:46
is even lower in the contiguous process. To do the difference of the static high the results are not really comparable. The more significant difference is the
10:09
failure mode. In case of the continuous process the specimen failures is as expected in the
10:21
center of the first printed layer and then the crack went horizontal and horizontal direction and delimitation occurs. For the other production technologies the simultaneous process
10:45
shows the typical failure mode of a bending specimen. Besides the bending test only actual tensile tests were performed. Additionally to the LVDTS
11:08
a photogramical measurement system was used to become ideas on the crack development. The experimental results shows a fine and well-distributed crack pattern
11:24
with narrow crack openings. The mechanical properties shows meaningful results but there is still some potential for future optimization.
11:44
One methodology is to generate better insights is the CT scan. In one collaboration a specimen with three embedded yarns was scanned.
12:05
Following these insights we found four different optimization potentials. In the picture on the left we see the ligament is not perfect
12:21
and moreover some air inclusions become visible and additionally the bond between the yarn and the cementus matrix can be improved.
12:47
The next challenge we are working on is downsizing the filament. The step will increase the reinforcement ratio and lowers the material needed.
13:03
This leads to a more environmental friendly material and reduce the carbon footprint. With this development step we are facing new challenges like pumpability,
13:21
small cross sections with high demand on the surface quality and continuous concrete deposition, utter consistency of the concrete and the robotic control. In the first step we learned how
13:43
to control the robot with different geometries and additionally what happens when we like to produce more than one specimen with regarding the collision or other issues. In the next step we focus on the buildability of the chosen concrete material.
14:06
To do the lab scale we had a fast over build which gives a relatively high stress in the layer below. Without any chemical helps we are able to reach a high of 25 to 30 centimeter.
14:25
To overcome this border we use an accelerator which is sprayed on the surface and you can see the results here. In the next step we like to automate this spraying process.
14:48
To improve the pumpability, particle optimization of the concrete matrix was conducted and additionally the mixing energy was observed.
15:06
This gives some hints regarding of the efficiency of the optimization process. After this optimization steps we performed rear scale tests to see the pumpability,
15:25
extrudeability and buildability. With this we focus on reproducibility and processing time, placing multiple elements, printing with a second batch or integrate short fibers to prevent
15:49
shrinkage cracks. This experimental work shows stable results so that the next development step is to integration of the mineral coated yarns in the concrete filament.
16:07
And with this final slide I like to show you the ideas how the integration can be performed. For a stable flow of the concrete an external integration of the
16:27
mineral bonded carbon yarn is planned. So thank you for your attention and on the right side you can see our printed specimens.