TECHNICAL FIELD

The invention relates to an optimization method for the performance of concrete produced with concrete printed by a three-dimensional printer (3DCP) in solving the sheltering problems experienced by the victims after major disasters such as earthquakes, in as a qualified manner as possible.

PRIOR ART

The vast majority of Turkey's lands have the risk of various disaster, earthquakes being in the lead. In earthquakes, which are known as the most effective disasters in Turkey, as a result of the insufficient strength of a significant part of the existing building stock due to various reasons, heavy damage and destruction in the buildings at the epicentre of the earthquake and loss of life occur after moderate and severe earthquakes. The fact that especially big cities are very close to active fault system causes the majority of residential buildings to be located in the earthquake zone, and this causes the buildings that survive even in a moderate earthquake but suffer significant damage to become unusable for a short or long time.

One of the most important social and economic problems by earthquakes create is that the shelter needs of earthquake survivors, whose houses have collapsed or are not convenient to live in until they are strengthened, and the necessary controls are performed, cannot be fully met in short and long periods. In the earthquake prone region, where the most important need is shelter after the destruction caused by the earthquake disaster, the production of qualified permanent housing can last for at least a few years in today's conditions, depending on various reasons. Structures such as tents and light prefabricated shelters, which provide the opportunity to meet shelter and basic needs of earthquake victims during this period of time for the construction of permanent houses after mid and large-scale earthquakes, are called "temporary housing".

Tents and light prefabricated shelters, which meet the shelter needs maybe in a very short time as a temporary solution, are highly affected by environmental conditions and cause life difficulties for earthquake victims if reside in these during the period until the permanent residences are built. It is not possible to use tents for a long time, especially after the earthquakes in the winter season. There also are some difficulties in using light prefabricated shelters, which are more durable than tents but can take a few weeks (usually 2-4 weeks) to be produced, for a relatively longer time (at least a few years) until permanent residences are built, depending on seasonal conditions. Since mass production is carried out in the form of type projects without considering the number of people to be sheltered while temporary residences are being built, problems such as heating, cooling, sound insulation and security may arise in the accommodation of large families. In cases where the construction of permanent residences is prolonged, temporary residences taking the form of shanty areas, and additions and removals made in accordance with the needs of temporary residences can also disrupt the city silhouette and cause aesthetically bad results.

Post-disaster sheltering action is examined under sub-headings as emergency aid, rehabilitation (emergency shelter and temporary housing solution) and sheltering in reconstruction stages (permanent housing). In the study conducted by Gregory et al. (2016), temporary and permanent housing processes after the earthquake were assessed and the potential of the structures that can be obtained by layered production was evaluated. Examining the times required to meet the housing types within this study, it is seen that the permanent houses were completed long after the earthquake. The need for sufficient temporary housing in the period until the construction of permanent housing stands out as the most important basic need to be solved after the disaster.

BRIEF DESCRIPTION OF THE INVENTION

The invention relates to an optimization method for the performance of concrete produced with concrete printed by a three-dimensional printer (3DCP) in solving the sheltering problems experienced by the victims after major disasters such as earthquakes, in as a qualified manner as possible. 3DCP is a new research area in structural engineering with the increase in technological opportunities today. In Turkey, on the other hand, comprehensive studies on this subject have not been carried out yet.

The invention aims to optimize, depending on the production and environment parameters, the concrete that is produced with 3DCP, that can be manufactured in a few days in the areas determined in the disaster area after the earthquake and can be used for at least 1-2 years (perhaps until the end of their economic life), has sufficient rheological and mechanical properties (resistant to environmental conditions as much as possible) and will be used in the construction of temporary housing after the disaster. It is estimated that temporary housing structures built with 3DCP will be a good alternative solution in near future, in addition to other traditional methods, in solving the wide-ranging housing problems that occur after disasters such as earthquakes that turn into catastrophes in residential areas. It is thought that the living spaces, the construction of which is completed quickly after the earthquake using the 3DCP technique, serving until the completion of the permanent residences and after that, if desired, may be more economical than other methods in a long-term perspective.

3DCP is a very innovative method of obtaining light, durable and economical complex structures by using Additive manufacturing, (AM), also known as three- dimensional (3D) printed concrete in industrial production. This method allows to obtain the design created in digital environment as a concrete object by using computer aided design program (CAD) software. In the method, which is a technology of transition from analogue to digital production, the 3D concrete object is obtained by separating the design created in the digital environment into two- dimensional (2D) layers of certain thickness and connecting the successive layers to the previous layer. Due to the advantages of layered 3D production such as freedom of geometry, fast, mould-free printing, low waste generation, environmental friendliness, being economical, etc., the applications of it are encountered in the fields of military, aerospace and aviation, as well as in the automobile, biomedicine, architecture and construction sectors.

In general, the advantages of 3DCP are as follows;

• Since there is no mould work for the element to be produced with a concrete printer, there is freedom of element geometry with its ability to produce complex geometries more easily.

• There is no need for placement by vibration in the structure created by layered production.

• With 3DCP, it is possible to make mass production in a short time since there is no manpower-based mould, iron, etc. work in production. • Since CAD-based computer software is used in the production of complex and non-geometric elements, it provides architectural freedom in designs by means of its ability to embody every design created in the digital environment.

• Due to the structure and production features of 3DCP, different elements can be produced at the same time without affecting the production cost and production time.

LIST OF FIGURES

Figure 1 . Flow chart of the method that is the subject of the invention

Figure 2A. 3DCP concrete modelling with ABAQUS finite elements software Figure 2B. 3DCP concrete modelling with ABAQUS finite elements software

DETAILED DESCRIPTION OF THE INVENTION

As with conventional concrete, the fresh and hardened performance of the concrete produced with 3DCP is extremely important. In the process until the solidification (initial setting) stage that starts with the effect of the chemical reactions taking place in the structure of the layer whose writing process has been completed, there is the fresh mixture situation. The performance required for production means that the concrete mix to be used is processable, pumpable (extrudable) and have the properties that can build layered structure (buildability) and of the workability time. As distinct from the traditional concrete, 3DCP, which is manufactured without moulds and generally does not require the use of steel bars, etc., must carry its own weight, i.e. , be constructable. Therefore, it seems that the primary performance of 3DCP is buildability.

To provide the required performance in the layered production process of the concrete mix, the lower layers must have the appropriate viscosity to enable pumpable and buildability behaviour with enough shear strength to support the upper layers. After the mixture prepared with 3DCP in the production technique is conveyed to the pump by pipes taking certain proportions of the materials into account, it is pumped to the nozzle (printer head) through a pipe with a certain pressure. The first layer is completed by printing (extruding the mixture from the nozzle) after the mixture, which is pumped through the pipes with its viscosity feature, moves at a certain speed and is transferred to the nozzle according to the model information obtained from the CAD computer design, and 3DCP repeats the same process to form the next layers on top of one another. The viscosity and shear strength of the mixture are important in the fresh mixture created for 3DCP having the feature of creating a layered structure after it is pumped through pipes and transferred to the nozzle and determining the height of the structure that can be obtained with the layered structure. It has been emphasized in several studies in the literature that in order to meet these criteria, the ideal value of the mixture components should be obtained.

One of the biggest problems in temporary residences to be produced after earthquakes is climatic conditions. When the climatic conditions of Turkey are examined, different climate types are seen especially in the region of North Anatolian Fault line. For instance, the fact that earthquakes also happen in Erzincan-Erzurum region, where the air temperature is generally in the range of -10/-15 °C in the winter season, and in Adapazan-Gdlcuk region, where the air temperature is in the range of 30-/35 °C in the summer season, may cause a significant change in the structural performance of standard 3DCP concrete production. The use of additives has different effects on the abovementioned fresh concrete and hardened concrete performances of 3DCP. There is no study in the literature conducted on 3DCP produced at different ambient temperatures. In this respect, these parameters should also be considered in the production of temporary houses that will be built with 3DCP after the disaster.

It is not possible to obtain multi-stage performance outputs of the concrete produced with 3DCP such as a) sufficient open time, b) easy pumpability c) stability d) buildability e) as low drying-shrinkage as possible and f) sufficient mechanical strength, etc. with just a single concrete mixture recipe. Considering that these outputs may change depending also on the ambient temperature, it will be understood that the subject of the invention solves a complex optimization problem that depends on many parameters.

In the studies in literature conducted on the mixture components used in 3DCP production, it has been seen that the researchers carried out this research by trial and error method according to their experimental experience and knowledge (Le et al. 2012; Jayathilakage et al. 2020; Jo et al., 2020). Even if suitable mixing ratios are obtained by trial-and-error method, it is not guaranteed to obtain the optimum result among all combinations of selected mixture components, and the fact that these trials are time-consuming and have high research costs is another issue that should be considered. In an experimental study, which is normally done by considering the water/cement ratio, aggregate/cement ratio, fine aggregate particle size, superplasticizer additive amount and viscosity modifier additive amount (5 different design parameters), and for example, four different values for these components, the number of all mix combinations corresponds to 4 ⁵ =1024 mixes. In order to obtain the optimum shear resistance and viscosity value among all combinations, 1024 trials must be done, and the appropriate mixture must be selected.

The invention includes experimental and statistical analysis and numerical modelling steps. In this context, the ideal ratios of cement, water, fine aggregate, superplasticizer, and pozzolans (supplementary cementitious materials) and fibre additives that will be used to increase production performance in 3DCP are optimized. This optimization is carried out by the Taguchi method and the mixture designs are produced. The purpose of using the Taguchi method is to accelerate the working program and reach the result with high accuracy by doing much less experimental studies for this engineering problem with a large number of parameters and variation ranges. 3DCP productions are made according to 16 different mixing ratios for four different mixture types targeted by the Taguchi method. Different mixing ratios selected in four different concrete categories multi-stage performance outputs of the concrete to be produced such as sufficient working time, easy pumpability, stability, buildability, extrudability, low drying-shrinkage as much as possible and sufficient mechanical strength are evaluated experimentally. Furthermore, in the method, the effect ratios of the selected design parameters on each performance criterion are obtained by statistical analysis. Apart from this comprehensive experimental set-up, the effect of the ambient temperature change on the expected performance of the concrete is also tested in the method. Especially in cases where the climatic data is very diverse (for example, Turkey), the effect of the production status under different temperatures of the disaster houses, which will be produced in the open area after the earthquake, on the target performance of the concrete is also determined with the extreme temperature values of -20 °C and + 40 °C. For this, the 3DCP setting is heat-insulated, the ambient temperature is adjusted during production, and four different types of 3DCP are obtained according to the changes in the ambient temperatures. Mechanical properties of concrete are determined experimentally for each experimental group. The disaster house, which will be built in the earthquake region by using the obtained mechanical properties, is modelled with the advanced finite element software ABAQLIS. In the modelling, the global behaviour of the building is also evaluated in designing a temporary house to be produced with 3DCP and can be used for a long time after a real disaster by looking at the stress-deformation data that occurs under the current loads in these houses.

Generalization of the process steps to be applied within the method that is the subject of the invention is as follows:

- Determination of component values and levels for different mixture types,

- Implementation of Taguchi design,

- Carrying out the 3DCP production process and experimental studies,

- Statistical analysis and determination of optimum mixture values,

- Examining the effect of different temperature values on 3DCP,

- Numerical analysis of the temporary housing design to be produced with 3DCP

1. Determination of Component Values and Levels for Different Mixture Types:

At this stage, within the scope of its effects on buildability, extrudability and pumpability in 3DCP production, the quantity ranges of cement, fine aggregate, superplasticizer (SP) additive, viscosity modifier additive (VMA), pozzolans (fly ash, ground granulated blast furnace slag), polyvinyl alcohol fibre and the superplasticizer required to increase the rheological fluidity of the mixture with increased mechanical strength and to release the trapped water in the voids in the concrete mix to be produced using a three-dimensional printer are decided.

2. Implementation of Taguchi design:

The Taguchi method is a method that minimizes the effect of uncontrollable factors as well by conducting a small number of experiments or studies using orthogonal arrays. Using this method, it is possible to determine the effect of parameters affecting the result and quality. With this feature, the Taguchi method has efficient applications in experimental designs, which are the basis of scientific research, as it reduces the number of experiments and experimental errors. It minimizes the effect of uncontrollable factors as well by conducting a small number of experiments using orthogonal arrays. The general representation of orthogonal arrays created by Taguchi, which allows simultaneous changing of parameter levels with a small number of tests, is Ld(a) ^k or Ld. Here, d, is the total number of experiments, a, is the number of levels of the parameters, k, is the number of parameters and L, is the orthogonal array. One of the L4, L8, L9, L18, L16 and L25 orthogonal array tables is selected according to the number and level of parameters to be considered in the statistical experiment design (Table 1 ).

Table 1. Orthogonal array tables For example, if five design parameters with four levels each are to be considered for mixture types, the L16 orthogonal array should be used. In other words, a total of 16 mixture types are evaluated. Mixture values are arranged for the optimum components to be investigated statistically. Experimental design sufficient to use the orthogonal array suggested by Taguchi is also created on the basis of parameters and levels. An example experimental set-up is given in Table 2.

Table 2. Example L16 orthogonal array table and organized example experiment design table

Here, Pi (i=1 , ... ,a) is given as the design parameter and a corresponds to the design parameter number. With the experimental design table recommended to be used for Mixture 1 , 16 different test mixtures are prepared, each with different component values. In the next step for each prepared mixture, 3DCP concrete is produced and shear stress and viscosity values are obtained for 16 different mixtures. For Mixture 1 , the optimum design parameters that give the optimum mixture are obtained by the method detailed in the fourth chapter and are used as references for the mixture components of Mixture 2, Mixture 3 and Mixture 4. Thus, for Mix 2, Mix 3 and Mix 4, design tables for mixture designs to be used in 3DCP concrete production are developed as well.

3. Carrying out the 3DCP Production process and Experimental Studies

Ideal water/cement ratio, ideal aggregate/cement ratio, ideal cement amount, ideal aggregate particle diameter, ideal superplasticizer ratio and viscosity modifier additive ratio are determined with the help of the mixing parameters specified in the previous step. First, concrete is produced using the mixtures specified in the previous step and a three-dimensional printer, and shear stress, flow diameter, compressive strength and flexural strengths are determined for all concretes produced. Taking all the properties into account, the most ideal mixture is determined within the buildability, extrudability and pumpability of the concrete. The experiments to be performed in this step are listed below.

3.1. Shear stress determination: The shear stress of the concretes to be produced with 3DCP is obtained with the help of Vane shear test device. With this test, the shear stresses of the samples to be produced with 3DCP according to the mixtures given in the second step are obtained to determine the ideal water/cement ratio, ideal aggregate/cement ratio, ideal cement amount, ideal aggregate particle diameter, ideal SP ratio and viscosity modifier additive ratio. In this experiment, a four-bladed Vane shear test device with blades 12 mm in diameter and 24 mm in height is used. Within the scope of the test, the material is subjected to a constant stress rate. The maximum torque value is recorded and using the following Formula- 1 suggested by Dzuy and Boger (1983), converted to shear stress. (1 )

Here, T is the maximum torque measured and Ty is the shear stress. H and D are blade height and diameter. To perform the test, the concrete to be produced using a 3D printer is immediately transferred to a cylindrical container (5 cm in diameter and 7.5 cm in height) after mixing. The blades of the vane shear test device are immersed in the cylindrical container. The same conditions are applied to all samples produced using a three-dimensional printer with the mixing parameters given in the second step. It is necessary to obtain an appropriate shear stress of 0.5-2 kPa, which will enable the production of concrete with 3DCP. In this range of shear stresses, the buildability, extrudability and pumpability of the concrete produced with a three- dimensional printer are ensured.

3.2. Consistency Test: The flow diameters of the concretes to be produced with 3DCP are determined using the EN 1015-3 (2000) standard. With this test, the experiment on the flow diameter of the samples to be produced using a three- dimensional printer according to the mixtures given in the previous step (application of Taguchi design) to determine the ideal water/cement ratio, ideal aggregate/cement ratio, ideal cement amount, ideal aggregate particle diameter, ideal superplasticizer ratio and viscosity modifier additive ratio. The samples produced in this test are filled into the conical mould of the test device by shaking 25 times in two layers and placed on the flow table. Then, the conical mould is removed slowly and again 25 vibrations are applied within 15 seconds. After the shaking process, the flow diameters of the samples are measured in both directions and the average is taken. The obtained flow diameter values give information about the viscosity of the samples produced with different parameters.

3.3. Compressive and Flexural Strength: The compressive and flexural strengths of the concretes to be produced with 3DCP are obtained according to EN 196-1 (2016). For flexural strength, the samples produced with three 40x40x160 mm prismatic 3DCPs are loaded with a speed of 50 N/s in accordance with EN 196-1 and flexural strengths of 7, 28 and 90 days are found, and flexural strength averages of the three samples are used. 7, 28 and 90-day compressive strength tests are carried out with a test setup on six samples with 40x40 mm sections that will be formed at the end of the flexural strength. The compressive strength device is set at a loading speed of 2400 N/s. Half prisms to be obtained after the flexural test are centrally placed between the plates of the device so that they do not protrude more than ±5 mm, and the device is loaded at 2400 N/s until the prism breaks. The mean values of the results of the compressive strength tests are taken.

3.4. Determination of Stress-Strain Data: By using ABAQLIS software, which is a finite element-based stress analysis and simulation program, the stress and strain changes of the samples produced with 3DCP as a result of additive production can be simulated. ABAQLIS is a software that can provide information about the behaviour of the model under loads in real life by performing model and simulation analysis in engineering. With this behaviour obtained, it helps modelling with minimum material and maximum efficiency by making optimization in the models. Stress-strain graphs, elasticity module, tensile and compressive strengths of the material are required for the numerical study at the stage of disaster house modelling to be made with ABAQLIS. For this purpose, <£>15x30 cm concrete cylindrical samples are produced from each mixture to determine the stress-strain curves of the concretes to be produced with 3DCP. For these samples, stress-strain curves are obtained with the help of concrete pressure testing machine and displacement gauges.

4. Statistical Analysis and Determination of Optimum Mixture Values

The shear stress and viscosity (flow diameters) obtained as a result of the experiments specified in the third step for the mixtures are used in this step for each mixture in the statistical estimation of the components of the optimum mixtures. Statistica statistical analysis software is used to perform signal/noise, variance, and Taguchi optimization analysis. Statistica is an advanced analysis software package that provides data analysis, data management, statistics, data mining, machine learning, text analysis and data visualization procedures. In addition, by the analyses of variance (ANOVA) conducted by using the test results for each mixture type, the effects of the mixture components on the shear stress and viscosity values (design parameter) are determined in percentages. “Signal/Noise (S/N)” ratios recommended by Taguchi are used in the processes of obtaining the optimum mixture and determining the parameter effect ratios.

The “Signal/Noise Ratio (S/N)” defined by Taguchi is a ratio used in experimental design to minimize the effect of design parameters on the result and called the analysis variable or performance criterion. The S/N ratio, which is expressed as a set of statistics, is divided into three according to the target situation to be achieved by the study (Taguchi et al., 1989 and 2005); “Smallest-Best”, “Biggest-Best” and “Target Value-Best”. In the experimental studies conducted by Kate (2021 ) and Zaimoglu (2015), the "Biggest-Best" situation given by Formula-2 was taken into account within the scope of the invention, since it was seen that the calculation of S/N in large value gave better results in evaluating the factor levels of the optimum mixture.

Here, n corresponds to the number of experiments and Yj corresponds to the target value. In this study, the target value was taken as the shear stress and viscosity value of the concrete produced with 3DCP.

Within the scope of the invention, analysis of variance (ANOVA) was carried out to investigate the effect of design parameters on shear strength and viscosity values for all mixture types.

5. Examining the Effect of Different Temperature Values on 3DCP

For the three-dimensional disaster house design, which is thought to be produced immediately for the immediate shelter need after the earthquake, its buildability, extrudability and pumpability should be examined by casting it at -20 °C and +40 °C extreme temperature range values in different earthquake zones and considering different temperature values. Calcium nitrate based antifreeze additive is used in the mixtures to produce concrete with 3DCP at -20 °C. In this step, optimum mixtures that will give ideal results for the concrete to be produced with 3DCP are examined. Thus, ideal designs that can be produced after earthquakes at different temperatures are determined.

6. Numerical Analysis of the Temporary Housing Design to be Produced with 3DCP

Using the mechanical properties obtained, different disaster houses are modelled with the advanced ABAQUS finite element software and looking at the stress-deformations that occur under the current loads in these houses, the global performance of the structure is evaluated in the case of a temporary house that can be used for a long time after a real disaster. An example of the stress to be obtained after modelling is given in Figure 2A and Figure 2B.