Contour Crafting Seminar 1

SEMINAR REPORT 2017

CONTOUR CRAFTING

1. INTRODUCTION 3D printing technology is not a brand new discovery. It was created in the 1980s, but due to some main challenges, it has not revolutionized the way we live yet. It has shown endless possibilities of application. Areas, such as medicine, engineering, architecture, medicine and even cookery will be truly impacted by this technology. The world population has now exceeded the 7 billion mark, and if the prognosis of the United Nations comes true, there will be 9.2 billion people in 2050. As the case is today, most of the people will want to live in the megacities because they promise a better life and wealth. Due to this, the population density in the cities would increase like never before. This would lead to redevelopment and slum rehabilitation projects to be undertaken on large scale. Imagine a situation wherein a huge bunch of people will need an urgent space to live in. Thus, a situation will arise when the cities will have to grow rapidly but also sustainably, keeping in mind the environmental effects and also the economy. Contour Crafting is an emerging technology that uses robotics to construct free form structures by repeatedly laying down layers of material such as concrete. This has a great potential in automated construction of whole structures as well as sub-components. Using this process, a single house or a colony of houses, each with possibly a different design, may be automatically constructed in a single run. Tool path planning and optimization benefits the technology by increasing the efficiency of construction of complicated structures. CC can automatically construct custom-designed structures by repeatedly laying down construction material. CC has the capability to fabricate with thick layers using various materials and without compromising surface quality unlike other automation methods.

1 DEPARTMENT OF CIVIL ENGINEERING

SEMINAR REPORT 2017

CONTOUR CRAFTING

2. CONVENTIONAL METHOD AND AND AUTOMATED AUTOMATED CONSTRUCTION Presently, the construction industry is facing various problems including high project costs, low labor efficiency, high at-site accident rates, vanishing skilled workforce, and poor control of construction projects. Automation has resolved several similar problems in the manufacturing industry. The construction industry, however, largely remains manual and manpower intensive. The few attempts made towards automating certain aspects of construction have aimed only at mechanizing the same manual approach without introducing any new paradigm. Development of new automation paradigms for whole structure construction may mitigate many of the problems that the industry is facing. In fact, new automation paradigms seem imperative for several applications, including construction of emergency homes and low income housing projects. Furthermore, the development of construction automation technologies is necessary if colonization of other planets is to become a reality in the coming century. Conventional methods of manufacturing automation do not lend themselves to construction of large structures with internal features. This explains why the evolution of construction automation has been slow. By the beginning of the twentieth century automation has grown and prevailed in almost all production domains other than in infrastructure. Implementation of automation in the construction domain has been slow due to:Conventional design approaches that are not suitable for automation. 1. Unsuitability of the available fabrication technologies for large scale products. 2. Smaller ratio of production quantity of final products. 3. Limitations in the materials that could be used by an automated system. 4. Due to expensive automated equipments. 5. Managerial issues. 6. Lack of technical efficiency. On the other hand, the following are the serious problems that the construction industry is facing today:1. Accident rate at construction site is very high. 2. Labor efficiency is quite low. 3. Work quality is low. 4. Control of the construction site is difficult, and skilled workforce is less.


SEMINAR REPORT 2017

CONTOUR CRAFTING

In the last two centuries, automation of various products has evolved considerably but very few of them are successful. Still construction of whole structures remains largely as a manual practice. This is because the various conventional methods of manufacturing automation do not fit in the construction of large structures. Layered fabrication is a promising new approach generally known as Solid Free Form Fabrication (SFF). Although several methods of SFF have been developed in the last 2 two decades and successful applications of these methods have been reported in various industries including industrial tooling, medical, toy making, etc., most of the current “layered fabrication” methods cannot deliver the wide variety of materials applicable to

construction industry. Currently Contour Crafting (CC) seems to be the only layer fabrication technology that is uniquely applicable to construction of large structures such as buildings.

3. RAPID PROTOTYPING During the last 18 years, construction automation and robotics have been implemented at various extents to address problems facing the construction industry such as productivity, quality, safety, high costs and skilled labor shortages in the United State and Japan. The Japanese construction industry, in particular, is very active in automated construction research, seeking a solution to the skilled labor shortage. Many large Japanese construction companies have their own research centers with sophisticated equipment and large staffs researching new construction technologies. Kajima Corporation, for example, spends more than $900M / year on construction research; a significant portion is invested in construction automation. Approximately 89 single task construction robots have been prototyped and deployed in construction sites in Japan .These single task robots replace simple human tasks thereby reducing labor costs and construction time. Automated construction systems such as AMURA, SMART and FACES are capable of fabricating high raised structures. These systems typically use precision fabricated components such as pillars, beams, ceilings, floor slabs and others during operation. Also, fully automated construction systems do not allow much flexibility in the design of structures. The cross section of a structural member, for example, cannot be readily changed. A system capable of generating a variable cross section structure would be rather expensive. Furthermore, current


SEMINAR REPORT 2017

CONTOUR CRAFTING

automated systems require many prefabricated parts. This translates into extra costs for inventory, transportation, and additional machinery. In recent years rapid prototyping (RP) processes have been implemented in a variety of applications and disciplines such as architecture, automobile design, aerospace and medical industries. RP processes are capable of fabricating complex structures, as shown in Fig. 1. However, RP systems today are not suitable for fabrication of larger scale parts. A special RP technology developed at the University of Southern California (USC) is Contour Crafting, which was introduced at the 19th International Symposium on Automation and Robotics in Construction (ISARC) in 2002. CC technology adapts RP capabilities and extends them to the field of large scale construction. As in other RP methods, in Contour Crafting (CC) material is added layer by layer according to a computer control sequence.

Figure 1: A complex geometry (Hagia Sophia in Istanbul) fabricated by a RP process

4. CONTOUR CRAFTING TECHNOLOGY Contour Crafting (CC) is an advanced building printing technology being researched by Behrokh Khoshnevis of the University of Southern California’s in the Viterbi School of

engineering that uses a computer-controlled crane to build homes rapidly and efficiently with substantially less manual labor. It was originally designed as a method to construct molds for industrial parts. Khoshnevis decided to adapt the technology for rapid home construction as a way to rebuild homes after natural disasters, like the devastating earthquakes. Using a quick setting, concrete-like material, contour crafting forms the walls of houses layer by layer until floors and ceilings are set in place by the crane. This great concept calls for the insertion of structural components, air conditioning, plumbing, wiring, utilities, and even consumer devices like audiovisual systems as the layers are 4 DEPARTMENT OF CIVIL ENGINEERING

SEMINAR REPORT 2017

CONTOUR CRAFTING

built. It is based on printing the building layer by layer using special material ejection. This method promises an automated construction process that is safe, fast and reliable. 3d printing helps us make one step further towards lean principles by minimizing waste in construction duration and increasing error proofing through activity automation. Furthermore, it guarantees an evolution in building textures that increases the quality of life for its residents without having a negative impact on public safety and welfare.6 This has a great potential in automated construction of whole structures as well as components. Using this process, a single house or a colony of houses, each with possibly a different design, may be automatically constructed in a single run. Tool path planning and optimization benefits the technology by increasing the efficiency of construction of complicated structures. CC can automatically construct custom-designed structures by repeatedly laying down construction material. CC has the capability to fabricate with thick layers using various materials and without compromising surface quality unlike other automation methods.

Material feed barrel

Side trowel control mechanism

Nozzle

Top trowel

Figure 2: Simple Historical Construction Tools

Side trowel

Figure 3: Contour crafting process

In CC, computer control is used to take advantage of the superior surface forming capability of troweling to create smooth and accurate, planar and free-form surfaces. The layering approach enables the creation of various surface shapes using fewer different troweling tools than in traditional plaster handwork and sculpting. It is a hybrid method that combines an extrusion process for forming the object surfaces and a filling process (pouring or injection) to build the object core. As shown in Figure 3, the extrusion nozzle has a top and a side trowel. As the material is extruded, the e traversal of the trowels 5 DEPARTMENT OF CIVIL ENGINEERING

SEMINAR REPORT 2017

CONTOUR CRAFTING

creates smooth outer and top surfaces on the layer. The side trowel can be deflected to create non-orthogonal surfaces. The extrusion process builds s only the outside edges (rims) of each layer of the object. After complete extrusion of each closed section of a given layer, if needed filler material such as concrete can be poured to fill the area defined by the extruded rims. Some internal walls can be extruded within each layer to create square hatches or other types of hatches(see Figure). The hatching process may be required for large objects, since setting or curing can start before the filler material gets a chance to spread over the entire surface of the layer. However, when hatching is used, each of the small hatches is filled separately, which because of their small size allows more control over the spreading and curing of the filler material. Hatching can also accelerate the forming process because it provides for concurrent extrusion and filling (i.e., as the extrusion nozzle creates new hatches, previously made hatches can be filled).

5. CC MACHINE The machine consists of a trowel rotation system, and a vertical extrusion head capable of linear motion along three coordinate axes. The trowel rotation mechanism consists of a bevel gear, and a connector.The connection mechanism allows the raw material to flow continuously from the cylinder to nozzle, and can rotate the extrusion system without disturbing the material flow while fabricating complex curves.The extrusion system consists of a top and side trowel, a cylinder that contains the raw material, and a piston and a threaded feed rod that extrudes the raw material through a nozzle. The process utilizes a Programmable Multi-Axis Controller (PMAC), a high-performance servo motion controller, capable of controlling up to eight axes of motion (Delta Tau Data Systems, 1996 a, b). The eight axes can be all synchronized for completely coordinated motion; each axis can be put into its own coordinate system for eight completely independent operations; any intermediate arrangement of axes into coordinate systems is also possible. Limit switches are used to restrict motion to specified limits.


SEMINAR REPORT 2017

CONTOUR CRAFTING

Figure 4: Creation of internal wall

Figure 5: Close view of a nozzle

5.1 Single Nozzle

The extrusion process forms the smooth object surface by constraining the extruded flow in the vertical and horizontal directions by the use of trowels. A schematic view of extrusion using a single nozzle is shown on the left side of Figure 6. The orientation of the side-trowel is dynamically cha nged for better surface fit for each decomposed layer. The side-trowel allows thicker material deposition while maintaining high surface finish. Thicker material deposition cuts down fabrication time, which is essential for building large-scale parts by using the additive process . 5.2 Multi Nozzle On a compound nozzle assembly concurrent extrusion of two wall sides and filling of the previously built layer may be performed. As the extrusion nozzle moves according to the predefined material deposition path of each layer, the rims (smooth outer and top surface of outside edges) are first created. The troweled outer surface of each layer determines the surface finish quality of the object. The smooth top surface of each layer is also important for building a strong bond with the next layer above. Once the boundaries of each layer are created, the filling process begins and material is poured or injected to fill the internal volume.

Figure 6: Single nozzle

Figure 7: Multi nozzle


SEMINAR REPORT 2017

CONTOUR CRAFTING

6. TROWEL PATH PLANNING AND NOZZLE CONTROL The analysis deals about the ability to physically realize the task by specifying the trowel path, trowel/nozzle orientation, and nozzle flow control. At this level the constraints include collision avoidance of trowel/nozzle assembly with previously built portion of the structure, and minimization of layering imperfections (such as bulges, gaps and cracks). Again, we can potentially reduce these constraints to geometric reasoning problems by breaking each layering into smaller segments and then analyzing each segment. To extrude layers of more thickness, the volume of material extruded by the nozzle should be proportional to the speed at which the nozzle is displaced. Also, as the nozzle moves and extrudes, the trowel orientation must be tangent to the layering path at all times in order to form smooth surfaces. For straight or smoothly curved segments trowel orientation adjustments should be readily achievable.

Figure 8: Motion System Of The CC Machine

6.1 Reasoning About Corners

When the trowel reaches a corner it must change its orientation to be tangent to the opposite side of that corner. At such times the nozzle stops extruding as the trowel rotates and pushes the extruded material from the opposite edge. However, the push-in technique tends to create bulges around sharp acute corners because of excess material. The nozzle has to reduce its flow rate as it approaches the corner and the exact amount of material reduction can be computed based on the angle of the corner and geometry of the nozzle.


SEMINAR REPORT 2017

CONTOUR CRAFTING

7. CONCRETE PROPERTIES 7.1 Workability

The ease of placing,consolidating and finishing freshly mixed concrete and the degree to which it resists segregation is called workability.The workability on 3D printed concrete is a crictical factor on CC.The layers first poured have to support the layers that will be poured sequentially but also cannot cure very fast causing bond problems between the layers. 7.2 Extrudability

Extrudability refers to the ability to transport the fresh concrete through a hopper and pumping system to a nozzle where it must be extruded as a continous filament.The concrete mixture in this process need to have a good extrudability rate,otherwise it is going to create concrete clog points inside the 3D printing machine,causing delays and maintainance necessity.It is known for every proffessional on construction that once you start pouring concrete you should stop when the labour is done. 7.3 Curing

Curing is the process in which the concrete is protected from loss of moisture and kept within a reasonable temperature range. This process results in concrete with increased strength and decreased permeability. Curing is also a key player in mitigating cracks, wh ich can severely affect durability.Due to the fact that CC construction has accelerated rhythm, its curing must be speeded up as well. However, this high velocity should not be too fast to the point of harming the bond between the layers. To reach this precise curing speed, many techniques may be used, for example thermal and chemical ones. 7.4 Mixture

Concrete is a mixture of several components in certain proportions which goes by the name of concrete mix design on construction language .The mix ranges depends on the application necessities.The mixture designs for 3D printed concrete are not cheap or easy to come up with. Many researches going on in the CC area are committed to study and improve the mix designs. Therefore, the perspective is to decrease the cost of the materials. For example, usually, the size of the aggregates should not be over 2 mm, and most part of the times, additives like superplasticizer, retarder, accelerator, and polypropylene fibers are needed, and they are very expensive. Through several trial and error experiments, a mixture characteristic found to be suitable for the new CC machine is as follows;(1lb =4.309kg)


SEMINAR REPORT 2017

CONTOUR CRAFTING

•

Type II hydraulic Plastic Portland cement: 9.5 lb

•

Sand: 10.5 lb

•

Plasticizer: 0.8 lb

•

Water: 4.8 lb

7.5 Strength

•

Compressive strength may be defined as the measured maximum resistance of a concrete specimen to axial loading. It is generally expressed in megapascals (mpa) or pounds per square inch (psi) at an age of 28 days(1 mpa=145.038psi). As all the other kinds of concrete, the printed concrete must be able to hold the weight of the structure. In this point, the printed concrete has shown an excellent strength average rate. It is due the small size of the aggregates, causing a reduction of voids in the concrete. Lesser the number of voids, higher the compressive strength rate.

8. COST ESTIMATION Once the machine parameters have been defined, cost of deposition for each wall segment can be calculated according to its geometrical information. Cost of traveling between the edges is related to the cost of moving between the vertices and the cost of rotation along the edges. This cost can be estimated according to the relevant position of edges. The total construction can be evaluated once a tool path has been defined. Each edge has two end points; therefore, there are a total of four possible traveling costs from one edge to another edge. Since the nozzle of the Contour Crafting machine has to orient itself to be perpendicular to the tangent of the wall segment, the nozzle may need to be re-oriented when traveling between edges. For example, in order to construct a corner, the nozzle must rotate 90° between the constructions of two wall segments.

9. SUSTAINABILITY POTENTIAL OF CONTOUR CRAFTING With growing concerns,regarding what are considered environment friendly methods and materials,any new method of construction must take environmental concerns under consideration. Simply saving on construction cost is not enough to justify the new use of system. Contour crafting must have the potential of being employed as a sustainable alternative to traditional methods of construction with regards to carbon emission, embodied energy, life cycle costs and the use of recycled materials. While a specific integrated approach is required for any building to be less hazardous to environment as


SEMINAR REPORT 2017

CONTOUR CRAFTING

compared to other approaches, the method of construction chosen has a great impact on sustainability of any project. While no construction method can be considered as inherently sustainable, there are practices considered more sustainable than others. In order to further understand the sustainability potential in contour crafting in application to single family housing it was reviewed using the USGBC, LEED (United States Green Building council,Leadership in Energy and Environment Design)for homes point system published in 2008 as a guideline. LEED was selected as a baseline since the guidelines set by LEED have become the current accepted international standard for defining sustainable building practices. Contour crafting reduces the amount of time spent on site thereby reducing the negative environmental impact of prolonged construction. Concerns such as silt and runoff due to disturbed topsoil are reduced notably through diminished exposure to weather before being permanently reset into the landscape.Since workers are needed on the site for less time and they must travel to the site less and more efficient the construction process becomes. The amount of waste generated on site also reduces as CC process only mixes the cement and polymer right before the application. However due to the nature of contour crafting and requirements necessary for the construction process to be effective, other areas of LEED for homes became affected through the use of CC.

10. APPLICATIONS OF CC Contour Crafting technology is relatively straight forward and simple. The significant benefits of Contour Crafting are short construction times, no human workers, cheaper cost and flexible of materials. These characteristics gave researches several brilliant applications. 

Application in constructions



Commercial applications



Low income housing



Space colonies



Emergency housing

10.1 Applications In Construction

A single house or a colony of houses, each with possibly a different design can be automatically constructed in a single run using Contour Crating technology. Conventional structures can be built by integrating the CC machine with a support beam


SEMINAR REPORT 2017

CONTOUR CRAFTING

picking and positioning arm and adobe structures. It may be built without external support elements using shape features. 

Design Flexibility: The process allows architects to design structures with functional and exotic architect geometries that are difficult to realize using the current manual construction practice.



Multiple Materials: Various materials for outside surfaces and as fillers between surfaces may be used in CC. The quantity of each material may be controlled by computer and correlated to various regions of the geometry of the structure being built.



Paint Ready Surfaces: The quality of surface finish in Contour Crafting is independent of the size of the nozzle orifice. Sand, gravel, reinforcement fiber and other applicable materials available locally are mixed and extruded through the CC nozzle. The surface quality in CC is such that no further surface preparation would be needed for painting surfaces..

10.1.1 Automated Reinforcement

Robotic modular embedding of steel mesh reinforcement into each layer may be devised. The three simple modular components may be delivered by an automated feeding system that deposits and assembles them between the two rims of each layer of walls built by Contour Crafting. A 3D mesh can be built for columns. The mesh will follow the geometry of the structure. It is possible to feed glass or carbon fiber tows through the CC nozzle to form continuous reinforcement consolidated with the matrix materials to be deposited.

Figure 9: Automated reinforcement


SEMINAR REPORT 2017

CONTOUR CRAFTING

10.1.2 Automated Tiling Of Floors And Walls:Automated tiling can be integrated by

robotically delivering and spreading the material for adhesion of tiles to floor or walls. Another arm can then pick the tiles from a sack and place it over the area treated with the adhesive material.

Figure 10 : Automated tiling

10.1.3 Automated Plumbing

Contour Crafting based construction system has the potential to build utility conduits within the wall. For plumbing after fabrication of several wall layers,a segment of any material pipe is attached through the constructed conduits into the lower segment already installed. The robotic system delivers the new pipe segment and in case of copper pipes having heater element in the form of ring. The inside or outside rim of each pipe segment is pretreated with a layer of solder. The heater ring heats the connection area, melts the solder and once the alignment is made bonds the two pipe segments. The needed components may be pre-arranged in a tray or magazine for easy pick up by the robotic assembly system. Using this components various plumbing networks may be automatically imbedded in the structure.

Figure 11: Automated plumbing


SEMINAR REPORT 2017

CONTOUR CRAFTING

10.1.4 Automated Electrical And Communication Line Wiring

A modular approach similar to industrial bus-bars may be used for automating electrical and communication line wiring used in Contour Crafting. The modules have conductive segments of power and communication lines imbedded in electrically non-conductive materials. All modules are capable of being robotically fed and connected. The automated construction system could properly position the outside access modules behind the corresponding openings on the wall.

Figure 12: Automated wiring

10.1.5 Automated Painting

During layer wise construction of wall a spray painting robotic manipulator attached to the CC main structure will paint each wall according to the specification. The painting mechanism may be a spray nozzle or inject printer head. 10.2 Commercial Application

The cost of construction includes huge amounts of material waste, labour problems and uneconomical building design. Conventional construction is not eco-friendly, it produce air, water and noise pollution. Hundreds of thousands of people injured or killed annually at construction field. Contour Crafting make robots do the risky work preventing any kind of human injuries. It has lessen the harmful impacts. Since materials will be precisely measured prior to construction, there will be no material waste. It will produce less pollution than the conventional method. In the end when the people use CC, the commercial industry will not be restricted by inefficient costs and human labor. 10.3 Low-Income Housing

The population is growing faster than ever. Population in developing countries re growing five times faster than those of developed countries. They do not have residence or money to afford such population boom. Slums form because the country’s rate of 14 DEPARTMENT OF CIVIL ENGINEERING

SEMINAR REPORT 2017

CONTOUR CRAFTING

urbanization is too slow to accommodate all poor citizens. The cheap and rapid characteristics of CC provides a solution since a fully functional house can be made in less than one day. By using this technology developing countries will be able to solve housing problems of the current and future population. 10.4 Emergency Housing

The people are prone to some kind of emergency due to war, natural disasters or economic crisis.So many peoples are suffering from these problems.So the best option for them is a home.The house should be cost effective, good quality with proper facilities. The CC creates a fully functional house including pumping and heating within a day. 10.5 Space Colonies

Contour Crafting is the best solution for any extraterrestrial construction that NASA approved. Scientists are already using tremendous amounts of money on shipping research machines from earth to another planet.They need to minimize the cost on the actual construction. Astronauts do not have much labor power and time to construct building by themselves. Sending construction materials from earth is too expensive and inefficient to carryout. By using lunar Contour Crafting, there is no need for human labor .

11. COMPARISON

BETWEEN

CC

AND

CONVENTIONAL

METHOD 11.1 Cost

Conventional Construction: In the traditional method, there is a high cost of production because of the quantity of materials, labour and time. In addition, sometimes it becomes even higher due to the complexity of projects. For example, during extreme weather conditions, the construction process has to slow down significantly because of the employee’s incapacity to work in these conditions, which would not affect a CC machine. Delays on project’s execution raise costs.

CC Method: Contour Crafting is an alternative that can decrease about four times of the construction cost because of its simplicity, materials’ saving and short time productivity

(10 houses in one day, for example). In addition, it can give more liberty to design projects that might be easily done without much difference (in terms of cost and feasibility) from simple projects. 11.2 Labour


SEMINAR REPORT 2017

CONTOUR CRAFTING

Conventional Method: Besides being one of the most hazardous industry, construction nowadays has become overpast because it still depends mainly on the man force. One of the challenges of Civil Construction industry today is to find well-qualified workers because most of them still need to be trained, causing additional costs and schedule delays. In addition, its labor is very expensive because of the big number of workers that it brings to the construction site. CC Method: The great advantage of this technology is the use of few workers at the construction site. Only specialized people (computer and management skills) would be required to operate the machine. Due to this fact, not only men would be able to work in construction, but women and elderly people as well. In conclusion, CC machine does not get tired, does not give excuses of failures, and does not need to be trained. In contrast, it might work 24 hours a day, thus it speeds up the job schedule. 11.3 Safety

Conventional Method: Construction industry is the most hazardous of major industries. One of five worker deaths in 2013 were in construction, according to the United States Department of Labor. The causes of deaths were falls, followed by struck by object, electrocution, and caught in between. Every time that a mega construction is being built, the human loss is very high. For example, the construction of Hoover dam (in the Colorado River) took life of more than a hundred of workers. CC Method: With Contour Crafting, work injuries and fatalitiy rate are reduced to zero because of the very safe method of construction. As it has a low number of workers and a computer executes almost everything, it does not bring any danger to the construction site. 11.4 Sustainability

Conventional Method: This method is very harmful to the environment. First, it pollutes the environment. Second, it also emits many harmful toxic materials, which are dangerous for the whole environment (soil, air, people and animals), such as dust. Finally, the number of waste materials is very high. Usually, the quantity of materials used to make a building could easily be enough to build one more building, but the wastage does not make it possible. CC Method: Due to its accuracy, Contour Crafting technology provides construction without waste, being considered as environmental friendly and a sustainable process, consequently. In addition, it does not make any noise, besides of being a fast process. It


SEMINAR REPORT 2017

CONTOUR CRAFTING

uses less material, less energy for all construction activities and less transportation of material, equipment, and people. 11.5 Productivity

Conventional Method: Construction today can last months, and even years. It is liable to schedule delays and work failures. For example, when the concrete is poured, it cannot be stopped until the job is finished, forcing workers to spend a long time at the construction site, which causes loss of productivity because human beings get tired. In addition, the use of formwork is a big factor that causes delay in job’s flow because it requires a lot of labor to work with forms. CC Method: With Contour Crafting, 10 houses can be built in a single day, or even more. This method does not use formwork, which is a shortcut in the construction time. Computers execute everything in the construction, so it might be as much as 50 times faster than conventional method. In addition, this method is very accurate to execute its assigned commands, so it is able to make its jobs faster.

PROJECT

SAVINGS

HOW

PARAMETER

Financing

20-25%

Short project Length& Control Over Marketing Time

Materials

25-30%

Negligible wastage,No Requirement of Formwork

Labour

50-75%

Automation of Construction

TABLE I Cost Savings In Contour Crafting Compared To Conventional Construction


SEMINAR REPORT 2017

CONTOUR CRAFTING

Chart no: 1 Number and Rate of Fatal Occupational Injuries, by Industry Sector, 2010

Chart no.2 Comparison chart showing cost efficiency and speed o construction

Chart no.3 comparison chart showing CO2 emission and embodied energy for concrete masonry and contour crafting


SEMINAR REPORT 2017

CONTOUR CRAFTING

12. FABRICATION OF CONCRETE WALL USING CC 12.1 Experiment

To fabricate a concrete wall of specified dimensions 0.75 inch 6 inch 2 feet concrete Concrete form

Figure 13: Schematic view of target concrete wall

Figure 14: CC nozzle

12.2 CC Nozzle

To fabricate the target geometry a new CC nozzle system was designed and integrated with a new CC machine. Unlike previous designs, the new CC nozzle is equipped with dual trowels to control both the internal and external surface finish of the extruded rims. The nozzle assembly is offset 70mm (2.75”) from the flow center of the extrusion system

To fabricate the rounded ends, extrusion in the X-direction is stopped and the assembly is rotated 180 degrees. With this configuration the Y axis is not used, hence reducing the 5feet

machine complexity at the cost of being limited to fabrication of straight wall sections 12.3 Mortar Strength

Cylinders

Compressive strength (PSI)

Specimen 1

2,786

Specimen 2

2,830

Specimen 3

2,606

Mean

2,741

Table 2. Results of testing compressive strength


SEMINAR REPORT 2017

CONTOUR CRAFTING

To verify its early compressive strength, three cylindrical test specimens, 5 cm X 10 cm (2” X 4”) were made and cured for 7 days in room temperature. Tests were conducted at USC’s Civil Engineering structural testing laboratory w ith the results shown in Table 2.

The results indicated that the compressive strength of thee test specimens were both consistent and adequate for their use as a permanent structural component of the finished concrete wall. 12.4 Fabrication

The mortar mixture was prepared using power drill driven mixing paddles and was loaded into the material carrying tank, shown in Figure 15. The velocity of the extrusion system in the horizontal direction was set to 20 mm/sec with stabilized continuous extrusion flow from the CC nozzle assembly. Initial extrusion flow is discarded until the flow is stabilized and the system starts its fabrication. Once an entire batch of the mortar mixture loaded inside the material carrying tank is used up, the CC system pauses until another batch of mortar is loaded and the extrusion continues to form the remaining concrete form. A batch of mortar is consumed in approximately 10 minutes and yields a concrete form approximately 64 mm (2.5”) high. To complete the target geom etry shown in

Figure13, nine batches were needed. The final concrete form fabricated by the CC system exceeded a height of 60 cm (2 feet)

Figure 15: CC machine used for fabricating the concrete wall 12.5 Lateral Pressure On Concrete Form

The function of the concrete form is to contain freshly poured concrete in a contained mold until the placed concrete sets. Lateral pressure against the concrete form is a function of the height and mass of the poured concrete; the pressure is not affected by the 20 DEPARTMENT OF CIVIL ENGINEERING

SEMINAR REPORT 2017

CONTOUR CRAFTING

wall thickness. The following is a standard formula widely used as a design guide for vertical formwork based on ACI standard 347: P=W*H Where: P = Lateral pressure W = Unit weight of fresh concrete H= Depth of fresh concrete These are design guides for wall concrete for work. The actual pressures may vary. Note that reliable data is difficult to obtain in published references when the pour rate is less than 1 ft / hr. 

For CC applications, pour rates less than 13 cm/hour (5”/hour) will allow erection of a 3m (10 feet) tall concrete wall without using special high strength form materials.



Once concrete inside the form hardens, pressure is no longer generated below the level of fresh concrete.



Wait until the concrete hardens completely since even partially cured concrete generates minimal lateral pressure on the form.

Figure 16: Placing of concrete

Figure 17: Pouring of concrete layer by layer



Figure 16 illustrates the concrete pouring process.



The bottom cross -hatched section represents concrete which has been cured for one hour.



The cured concrete produces minimal lateral pressure on the form but the exact value was difficult to quantify in our experiments. Data was not available in the available literature; therefore, a simple test was devised to validate the strength capability of the form. Figure 17 shows the test bed.


SEMINAR REPORT 2017



CONTOUR CRAFTING

A batch of concrete was poured to a height of 13 cm (5”). The second batch was poured

on top of the first batch after one hour without problems. 

The test procedure, if repeated 24 times, will result in the erection of a 10 feet high “conventional” concrete wall in 24 hours. Ten feet is a standard height for concrete

walls in residential housing construction. 12.6 Results 

Concrete was manually poured into the extruded form in 13 cm incremental depths (one hour intervals) to a final height of 60 cm (2ft).



Figure 18 shows the finished wall.

The compressive strength of this wall will vary depending on the type of concrete chosen. Concrete pouring in this demonstration, however, has been independent of the extrusion forming process. With more experimentation, the filling process can be synchronized with the extrusion process. The coupling of these two processes will depend on many factors including extrusion rate, pour rate, and cure time and strength requirements. In the next generation CC system, the mechanical assembly for continuous concrete pouring will be integrated into the CC extrusion nozzle assembly.

Figure 18: concrete wall made by cc machine

13.ROBOTICS APPROACH IN CC The original robotics approach proposed for Contour Crafting is depicted in Figure 19. This approach uses a gantry robot that has to be large enough to build an entire house within its operating envelope and lays one continuous bead for each layer. Such an


SEMINAR REPORT 2017

CONTOUR CRAFTING

approach is not without its attractions, but it requires a large amount of site preparation and a large robot structure.

Figure 19: CC using a gantry robotics approach

Figure 20: CC using coordinated mobile robots for construction and other auxiliary activities

An alternative robotics approach for CCC is the use of an inverted Stuart Platform system, such as the one developed at the US National Institute of Standards and Technology and named RoboCrane (see Figure 19). Application of RoboCrane in CCC is currently under study by researchers at NIST. In this project a concrete delivery system is devised and used in conjunction with a CC nozzle installed on the RoboCrane platform. Ease of transport and installation are the major advantages of this approach.

Figure 21: CC using mobile robots

A third alternative robotics approach involves the coordinated action of multiple mobile robots. The mobile robotics approach depicted in Figure 21, has several advantages including ease of transportation. and setup, the possibility of concurrent construction where multiple robots work on various sections of the structure to be constructed, the possibility of scalable deployment (in number) of equipment, and the possibility of


SEMINAR REPORT 2017

CONTOUR CRAFTING

construction of structures with unlimited foot print. In this arrangement various mobile robots performing various activities such as fabrication, plumbing, electrical work, etc. work in coordination. A CC Mobile Robot may use a conventional joint structure, as shown in Figure 21, and be equipped with material tanks as well as material delivery pump and pipes. The end effectors of the robot could carry a CC nozzle that can reach from ground level all the way to the top of a wall. If the mobile robot arm could be made of a rigid structure, position sensing at the end effecter may not be necessary. Instead, a position sensor (e.g., a laser tracker) may be mounted at a fixed location, and the related retro reflectors may be installed on each mobile robot base. In this configuration, the robot does not engage in fabrication while moving. Once it reaches a pre defined post (called mobile platform post), it anchors itself by extending some solid rods from its bottom. Then it starts the fabrication from the last point fabricated while at the previous post. This arrangement is routinely practiced in some industrial applications such as robotic welding of large parts, such as in ship building. 13.1 Roof Construction

Roof construction may or may not need support beams. Supportless structures such as domes and vaults may be built by all of the above robotics approaches. For planar roofs, beams may be used. Under each beam a thin panel may be attached to sustain the roof construction material delivered by the CC nozzle. In the mobile robotics approach the beams may be picked and positioned on the structure by two robots working collaboratively, each being positioned on the opposite sides outside of the structure. Delivery of roof material becomes challenging with mobile robots and may be done by a robot inside the structure. This robot may progressively deliver the material over the beam panels as each beam is placed on the roof. For the last few beams this robot could exit the structure and perform the material delivery from outside. An alternative approach for beam positioning and roof material delivery, which may be used in conjunction with the mobile robotics approach, is the use of the NIST RoboCrane system. RoboCrane may be installed on a conventional crane as shown in the lower part of Figure 22(the top part of this figure shows the RoboCrane moving an actual steel beam.)


SEMINAR REPORT 2017

CONTOUR CRAFTING

Figure 22: Robocrane for roof construction

14. CASE STUDY 14.1 Extra Terrestrial Construction Using Contour Crafting By NASA

As interest in space exploration increases, human beings are to return to Moon and land on Mars in the future. To carry out experiments and live a longer time on extraterrestrial planets, permanent habitats are needed to shield heat, cold, cosmic rays and meteorite impact. Due to negligible lunar atmosphere or scarce Martian atmosphere, spaceship landing and launching off will cause frozen ice crystal from the fuel and gravels flying at a fast speed far away. from radiation and micrometeorites and roads are needed to transfer the landers between the landing pads and the hangars. Most proposals for construction on Moon and Mars are based on transporting structural elements from Earth and assembling them at the destination. Such approach is expensive and infeasible for large-scale implementation. This approach is based on the use of in-situ material and digital fabrication techniques to construct the infrastructure elements. Intense research has been carried out in In-Situ Resource Utilization (ISRU) and specifically lunar regolith characteristics have been extensively studied. In our research we are exploring the possibilities of using sulfur based concrete and molten regolith as construction materials to be processed by Contour Crafting.


SEMINAR REPORT 2017

CONTOUR CRAFTING

Figure 23: A Contour Crafting robot is shown here printing a road in front of a parabolic hangar structure housing a lunar Lander. In the background can be seen a plant intended for processing regolith that will be used in the construction process

Figure 24: A Contour Crafting robot, housed on an 'ATHLETE' rover, is shown here printing a parabolic vault structure out of processed regolith. The structure is intended to house a lunarlander or other equipment, and is unpressurized. The parabolic form has been adopted, because it is structurally efficient and lends itself to the Contour Crafting mode of construction. In the background can be seen an array of solar panels intended to supply power to the robot.

14.1.1 Site Selection:

Site selection for lunar Lander sortie operations is of the utmost importance. A strategic Location will provide several advantages. They include: • Safety 26 DEPARTMENT OF CIVIL ENGINEERING

SEMINAR REPORT 2017

CONTOUR CRAFTING

• Least fuel expenditure (depending on landing site altitude) • Terrain character – plains vs. highlands, bedrock vs. loose regolith • Steady surface/terrain temperature 14.1.2 Infrastructure Elements

The following are the originally proposed structures that were being considered for building using a CC system and employing ISRU materials at the D-RATS field test and simulation site. 14.1.2.1 A Lunar Landing Pad And Blast Apron: The landing pad surface could potentially be patterned to diffuse the high thrust loads of about 40MT and severe heat imparted on it by the descent engines. A blast apron to curtail eject is also needed to keep hazardous projectiles from striking/damaging high value assets in the vicinity (3-5km) of the landing zone. 14.1.2.2 A Dust-Free Stabilized Road From The Landing Pad To Habitat Zone: It is well known that lunar dust will hamper buildup as well as routine activities around the settlement. Therefore all dust prevention measures are being evaluated. Again, lunar CC application may provide an option to pattern a dust-free platform that traps, repels and thus ameliorates dust transport to the habitat zone and contamination of lunar settlement interiors. 14.1.2.3 Thermal Shade Walls And Protective Micrometeorite (Mm) Shields: Once the habitat components are assembled, in order to operate it at optimum safety and energy efficiency, the complex must be covered with a suitable mm shield that will also regulate thermal control. Patterns, louvers and other openings will be built into the surface of this protective enclosure to facilitate thermal regulation during lunar solar diurnal cycle. 14.1.2.4 A Communication And Observation Tower: Since the high ground provides a better view, especially in the lunar case where the horizon is just 3km away, an observation tower for a suite of cameras and communications equipment has been suggested in earlier studies. A tower may also be located high enough to be able to directly observe lunar Lander operations. 14.1.3 Infrastructure

Initial requirements for infrastructure will be landing pads, landing aprons and blast walls for protection of equipment or resources close to the landing sites. Unless fortuitous naturally protected sites are located from data being scoured currently, research stations or settlements will need to be further away from the landing path to avoid damage from 27 DEPARTMENT OF CIVIL ENGINEERING

SEMINAR REPORT 2017

CONTOUR CRAFTING

rocket ejects and secondary hyper-energetic regolith projectiles. This will require construction of roads, dust-free platforms, shade walls, equipment storage hangars and radiation and meteorite protection shelters. All of the above infrastructure can be built from regolith and other ISRU materials utilizing several methods of robotic fabrication investigated in this proposed study. Maximizing ISRU using robotic construction technology as an enabler is the prime driver for this architecture. Several construction tasks will be necessary to achieve safe and productive conditions for extended human presence at extraterrestrial sites. 14.1.4 Materials And Processes For Construction

CC Technology Using Sulfur Concrete Creation of sulfur-based concrete is fairly straightforward once sulfur is extracted from regolith. As shown in the top portion of Figure 25, sulfur concrete is made of about 80% regolith and 20% sulfur. Contour Crafting structures using sulfur concrete requires mixing the two components and then extruding the dry mix through a CC nozzle barrel that is heated to 130 C, the melting temperature of sulfur. Sulfur concrete structures can have a compressive strength of 3000 psi which is higher than the strength of most ordinary hydraulic concrete structures, such as those built with concrete blocks.

Figure 25: Sulfur, sand, sulfur/sand mix Figure 26: Experimental machine for ielding sulfur concrete extrusion testing of sulfur concrete


SEMINAR REPORT 2017

CONTOUR CRAFTING

On Earth, sulfur concrete is a relatively new construction material compared with hydraulic concrete. To use sulfur concrete, aggregates is mixed with sulfur powder and then is heated up to around 1300C then is cooled down to ambient temperature. The cooled down mix has a compressive strength as high as 17.24 MPa (2500 psi). Sulfur concrete cures faster than hydraulic concrete, and achieves 90% of its final strength within 6 hours. Sulfur concrete is more resistant to acidic and salt and hence it has been made into sewage pipes especially in food processing industries. Sulfur concrete also has better properties under large temperature cycles. The aggregate in our experiments is washed dry sand1 with a grain size below 1 mm, similar size distribution to that of JSC1A. Loosely compressed sand has a specific gravity of 1.64g/cm3, and that for regolith simulant is 1.73g/cm3, and for sulfur and sand mixture is 1.68g/cm3. Both sand and regolith simulant grains are irregular, and the chemical composition does not affect the binding strength. 14.2 Winsun Constructions, China

In China, a company named Win Sun Decoration Design Engineering has built ten 3D printed houses entirely out of recycled materials in less than 24 hours. The printer used for this purpose was assembled by importing its parts from overseas. It measures 32 meters long by 10 meters wide and is 6.6 meters in height. The printer is capable of printing houses having a plan area of about 200sq.m. The materials used for construction included a mixture of industrial wastes and other inexpensive materials. The construction task was fully automated and there was no requirement of labour at all. The approximate cost for construction of each unit was under 5000 USD, which is quite an achievement for a relatively new construction process

Figure 27: Houses built by winsun constructions


SEMINAR REPORT 2017

CONTOUR CRAFTING

15. LIMITATIONS OF CC 1. Due to its size and weight, the machine has to be attached to another machine that would be able to move it. 2. The difficulties of the environment. How these machines would surpass the issues of the environment, such as unleveled ground, weather impacts, etc. There are some researches with great ideas to improve this issue, such as a machine suspended by cables oriented by a Cartesian system 3. The cost is still an obstacle to develop this technology because of its recent discovery. The maintenance fees for these machines are also very expensive. If CC development had more support from sponsors, maybe it could be developed faster. 4. The great challenge of the construction industry will be adapting to the transition between conventional construction and CC method. One of the CC technology limitations are the fact that it is not compatible with conventional design.

16. INDIAN SCENARIO AND FUTURE PERSPECTIVE Our planet is running out of raw material, due to its irresponsible use by people. Contour Crafting is an environment’s friend because it wastes no material at all. In addition, it

does not bring noise, dust or make harmful emissions to the environment. All the major industries of the world work mostly with automated systems, except construction industry. However, it has inevitably changed, and Contour Crafting is a potential agent of this transition. India is one of the fast developing nations of the world which is facing an acute shortage of space due to major population migrating towards the big cities in search for jobs and better living. As a result of this various redevelopment projects are being undertaken in the mega cities. But with the use of conventional techniques the rate of construction is very slow to match the demand for space and moreover the harm to the environment due to these construction practices is very alarming. Also the rate of construction is bound by the economy as the cost involved in the redevelopment and city expansion projects is huge. But with the advent of contour crafting technology, all of these shortcomings can be mitigated if given a broad platform in our country. This paves the way for complete mechanization in the industry and what better example than this technology would be needed to provide the onset for it.


SEMINAR REPORT 2017

CONTOUR CRAFTING

17. CONCLUSION The world has walked more and more in destination to automated systems. In the future, computers will make all the processes of major industries. It also includes construction industry. There will be a time when all the steps of buildings will be performed by machines. For example, design, plumbing, reinforcement, and electrical systems would be made by CC technology Another point of Contour Crafting is that it has a great productivity, building houses in a matter of hours, without wasting any material. In addition, its cost can be much lower than the conventional method cost because CC uses less workers and materials. This new technology is an environmental friend, which does not pollute or cause any evil effect to our environment. However, even with all its benefits, Contour Crafting has some challenges to overcome. First, CC developers should study how this technology would be managed at a construction site. Second, it is necessary to see how people would react to this transition between conventional method of construction (many workers, wasting and fatalities) and the automated construction method (less workers, wasting and more safety). Finally, the great challenge is to overcome the current cost barrier of this technology. The authors believe that the more this technology is developed, the cheaper it will become to be applied in the reality.


Contour Crafting Seminar 1

Recommend Documents