Further, prefabricated columns may be in the form of a double or single-storey height. However, the method of connecting the lower column to the one above and foundation varies from one manufacturer to another (Collins n.d.). For example, the column-to-foundation connection can be through reinforcing the bars which protrude from the column ends and passing into sleeves that are then gout-filled. Alternatively, the columns can be connected to the foundation through a base plate linked to the column. Besides these two options, columns may set into preformed holes in the foundation blocks. Afterwards, the component is then grouted into position.
On the other hand, column-to-column connections can be achieved by joining threaded rods using appropriate connectors (Collins n.d.). During the process, the cement mixture is consequently cast round to the column’s cross-sectional dimension resulting in thin stitches between the columns. Examples of Prefabricated Components ready for Prefab column-to-column Connection is shown in the following figures.
Figure 3.1 (a): Prefabricated Components for Colum-Column Connection (Behera 2013).
In most manufacturing designs, columns are provided with sufficient supports for the end of the cast beams. In addition to the support, some form of connections is also provided for column-beam continuity and moment connections (Collins n.d.). For interior columns, the connection may be through holes for the passage of the reinforcement bars from one beam to another (Collins n.d.). However, for edge columns, some form of sockets or brackets are necessary.
Figure 3.1 (b): Precast Columns and Beams (Collins n.d.).
Figure 3.1 (c): Concrete Columns and Beams (Collins n.d.).
The use of prefabricated columns provides various benefits. For example, in nearly all types of building, from multi-storey to single-storey, precast columns reduce the construction time by increases the building speed. These advantages are mainly realized because ready columns are delivered to the site for erection (Suryakanta 2017). With prefabricated columns, the building process is often easy since the construction sections are ready and complete with cast-in components for fast connection to building elements, beams, and footings. Besides, using these components lowers the associated construction costs (Collins n.d.). Moreover, hollow-core concrete columns provide high strength because they are lighter compared to the solid types. Since prefabricated columns are made under a controlled manufacturing, the process offers more economical columns with strong reinforced concrete.
Although using precast columns offer various benefits in construction, there are different limitations associated with the application of these elements in the building. According to Suryakanta (2017), some of the shortcomings of using prefabricated columns include:
- Columns demand great care in handling to avoid damages which may results from mishandling.
- Producing satisfactory connections between the prefabricated columns may be a challenge.
- In some cases, handling precast columns may require the use of special machines for moving and lifting the prefabricated units.
- There is often the risk of loss involved when ready columns break during transportation.
In concrete construction, Formwork is applied as moulds for structures whereby concrete is poured for subsequent hardening. A Formwork is a critical temporary structure elements in building (Mishra 2012). They provide the required support up the time the concrete member attains the desired strength necessary for supporting its weight and that of the load. Mainly, Formworks shutters can be made from different materials including aluminium, steel, and wood.
Figure 3.3 (a): Formwork/Shuttering (Mishra 2012).
Depending on the material used in making the formwork, different Formworks can be identified for shuttering in construction. However, for many manufacturers, wood is the preferred material for the manufacture of formwork shutters. Nevertheless, in making formworks from wood, it is necessary for the designer to consider factors such as the element size, beam and column stabilities, load duration, and moisture component. Additionally, the architect should focus on producing Formwork which is strong enough to withstand all types of live and dead loads (Mishra 2012). Besides, a proper Formwork should allow for the removal of different parts based on the desired sequence without damaging the concrete.
Figure 3.3 (b): Wooden Formwork (Mishra 2012).
Plywood Formwork, the most commonly applied formwork type for shuttering, uses timber frames attached to Resin bonded plywood sheets to form up-panels of the required sizes. The application of panels of large sizes allows for the cost of labour required from fixing to removal the formwork to be significantly reduced. At the same time, with plywood shutters, the material reuse is considerably incorporated, and for this reason, the cost of Formwork is lower. However, despite the fact that timber and plywood are the most commonly preferred for making formwork shutters for construction, these materials disadvantageous for various reasons.
For instance, with plywood as the primary material for making Formwork, the resulting component will often swell, shrink, and warp when subjected to water (Mishra 2012). However, the defect is mitigated by making the material surface impermeable to water.
During shuttering, the fresh concrete is placed inside the formwork which, as already mentioned, could be made from plastic, wood, steel, aluminium, or other materials. In these applications, the formwork is used as a temporary structure for supporting the concrete by confining it within the formwork material (Suryakanta 2017). Therefore, the shuttering is left in position until the concrete has enough strength to support itself. However, to serve its purpose successfully, the formwork must meet certain quality standards. These requirements largely depend on the material used for shuttering as well as how the structure is made. However, in general, the three top objectives considered for the appropriate design of formwork include quality, safety, and economy (Allen and Iano 2011). Based on these factors as the primary modelling guidelines, the following are some of the necessary quality requirements for a proper shuttering/formwork.
- The structure should be strong to withstand the weight or the pressure of any superimposed load and the concrete (Suryakanta 2017). In this way, the formwork must be designed with care since under loads may cause failure. Usually, the consideration of the overloads will have influences on the economy.
- It is necessary for the designers to ensure that the structure is sufficiently rigid. The rigidity will allow the shuttering to retain the intended shape without causing unnecessary deformation (Mishra 2012). Accordingly, the formwork needs to be designed in such a way that in normal cases, the deflections do not exceed 1/900th of the span.
- It must be tightly constructed so that the structure does not allow concrete to break through the joints.
- The enclosed inside the formwork should be consistent with the design size (Suryakanta 2017). Therefore, to meet this requirement, the shuttering should not warp, bulge, sink, or bend.
- For the resulting concrete surface to possess good appearance, the inside of the formwork should be made smooth (Mishra 2012). In most construction processes, this quality specification is achieved through the application of crude oil on the internal surface of the formwork. An alternative to oil for the same use is soap solution which gives equally a smooth surface. Besides providing smoothening, applying soap solution or crude oil on the inside surface often facilitates the removal of the formwork.
- The complete formwork must be made in a manner that will not cause injuries to the edge or surface of the concrete during disassembly. In short, the design should support easy removal.
- Most importantly, it should be noted that the formwork will not be contributing to the finished structure (Mishra 2012). In this regard, formwork should be economical through cost reduction by proper use of materials, appropriate design, and construction.
There are different types of formwork depending on the classification criteria used. Nevertheless, the discussion considers three most common types. These include:
- Conventional Formwork:
This class of Formwork/Shuttering is constructed on site out of moist-resistant particle-board, plywood, or timber. The traditional formwork is usually easy to produce. However, the plywood used mostly has a short lifespan and the structure is time-consuming. Despite these limitations, the conventional Formwork continues to be used where the cost of labour is relatively lower compared to the cost of purchasing reusable formwork (Forming America, LTD, 2016). Additionally, this formwork is the most flexible type, and therefore complicated sections may still use it even where other systems are in use.
- Modern-Day Formwork
These are mainly modular formworks produced for efficiency and speed. In some applications, modern formworks are built for waste reduction and accuracy enhancement (Suryakanta 2017). Additionally, it is always common to find these types designed with safety features. The main classes in use are:
- The system column formwork
- The table form (also called the flying form)
- Horizontal panel
- Tunnel form
- Slip form
- Prefabricated or Engineered Formworks
These are Formworks which are constructed out of prefabricated modules. They are built with a metal frame (often aluminium or steel) and covered with the concrete or application side using a material with the required surface (aluminium, timber, or steel) (Forming America, LTD 2016). Indeed, many constructors prefer prefabricated forms to the other two types because of their different advantages as discussed in the next section.
Now, depending on the material used, formworks are majorly of two categories. The first is the steel formwork which is made of either Tee Iron, Steel sheets, or Angle Iron (Forming America, LTD 2016). The second primary classification based on the material is the wooden formwork which includes Formworks made from Props, Ledgers, Planks battens, or Sheeting.
Figure 3.3.2 Formwork by Materials (Forming America, LTD 2016).
The prefabricated formworks are advantageous over the traditional timber types for various reasons. First, they speed up the construction process in addition to the fact that very little on-site skilled labour is required because they are constructed off-site (Forming America, LTD 2016). Secondly, the prefabricated formwork lowers the life-cycle costs and can bear major forces due to the indestructible nature of the frames (Forming America, LTD 2016). Moreover, like all prefabricated systems, prefab formworks are designed for heavy and light constructions and constructors can bid for any work; curved, straight, cut-up, or battered.
Despite its many advantages, prefabricated formwork has various limitations as well. For example, in certain cases, the wood covering of prefabricated formwork may need regular replacement after some dozens of uses. Manufacturers, though, mitigate this limitation by using aluminium or steel for the covering (Forming America, LTD 2016). In this way, the prefabricated or engineered formworks can achieve almost two thousand uses depending on the applications and care during use.
Another disadvantage of prefabricated formwork is that they deflect quite often during placement. This problem is mostly the result of the placing rate, which is usually too fast (Forming America, LTD 2016). So, for avoidance purpose, close supervision needs to be maintained, and the placing rate must be determined. Secondly, the prefabricated formwork systems tend to leave poor finishes at the joints where there is a framing member. This problem is a major challenge because the inside surface of a formwork needs to leave smooth surfaces at all points.
Precast concretes are essential building materials made by casting concrete in form or reusable moulds. After casting, the materials are then subjected to a curing process in a controlled environment. From curing, concrete precast panels are then placed into large tracks which transport them to the construction site. Once delivered to the building location, the components are lifted into place (Allen and Iano 2011). Primarily, the concrete precast is distinct from the Standard Concrete. The latter is poured into forms which are unique to the site where they are then cured. Additionally, precast concretes are distinguished from precast stones through the use of a fine aggregate in the mixture. This procedure makes the final product to trace a naturally occurring stone or rock regarding its appearance.
The precast concrete products are often made in different shapes and sizes to fit a variety of applications and are employed within ranges of interior and exterior walls. The panels are compressed in stone and concrete resulting in a solid face or wall which is easy to manoeuvre (Allen and Iano 2011). Mainly, producing the engineered concrete in a precast plan or a controlled environment provides the opportunity for proper curing and close monitoring by plant workers.
Figure 4.1 Precast Concrete for Different Applications (a) Piping (b) Floor
During the planning of a construction project where Precast Panels are to be used, various factors need be taken into account. For instance, suppose the weather is windy, the crane should be unable to lift the heavy object and place them safely. Therefore, many days will be lost because of such this type of the weather condition (Birkeland and Birkeland 1996). Additionally, since the installation of Precast Panels is entirely dependent on the use of a crane, the machine will need to be sufficiently large enough to lift panels up to eleven tonnes at a certain radius (Allen and Iano 2011). Moreover, the precast will require using the crane the whole day. As such, the material handling for the other activities such as scaffolds and formworks will be delayed for them to complete their work.
However, there are many benefits in using the precast panels. The wall is already finished at the warehouse, where the concrete is patched and sanded to achieve a finished level. Therefore the only thing left to do on these walls to finish them is to paint them. The primary use of these panels is for balcony walls as these are the only structural walls that are not covered in gyprock or tile. Through the use of precast panels, the building process is shortened as well as the finishing process.
Figure 4.1 (b): Walls under Construction Using Precast Concrete Panels (Cpci.ca, 2017).
In regards to construction using precast panels, a joint is essentially an intentional gap between an element and a portion or between adjoining members, mostly cladding (NPCAA 2013). Whether vertical or horizontal, joints are used between precast components to physically separate the units (in the case of isolation joints). By isolating the adjacent the members, joints ensure that one element can move independently of the other (CCAA 2014). Apart from separation function, joints prevent the ingress of air and water into the building and also provide continuity of the structural action between the joining elements (NPCAA 2013). Therefore, a well detailed and constructed joints are significant for the maintenance of the integrity of the external envelope of the structure by ensuring that requirements such as waterproofing, acoustic performance, and fire resistance are met at the outer shell.
Joints are required for various reasons and purposes in building using concrete precast panels. However, according to the National Precast Concrete Association Australia (NPCAA 2013), there are four fundamental reasons why joints are required. Primarily, joints are needed because:
- The structure or member cannot be built as a monolithic unit within one concrete placement.
- The element or structure on either side of the joint needs to move relative to the other. For instance, joints will accommodate the local wall movements typically caused by changes in structural dimensions or wall panels due to deflection from applied load design, temperature variations, or effects of the moisture contents.
- It is necessary for the member to be of limited sizes to enable for easy handling by cranes.
- Joints are required at particular points of the structure for the simplicity of the analysis based on the design assumptions of the building or structure.
In general, the successful performance of the external parts of the structure is often defined by the ability of this outer part to prevent rain from entering. Although water will not always penetrate through precast concrete, the panels are relatively permeable to moisture (Allen and Iano 2011). Therefore, it is necessary to ensure that panel-to-panel joints or element-to-panel joints are well considered to prevent the penetration of air and water through the building envelope. For this reason, the design and implementation of joints in construction using precast concrete are vital and therefore, has to be completed in a manner which is economical and rational (Schlaich et al. 1987). Additionally, joint treatment is another aspect with substantial impact on the overall appearance of the project. For the sealant and joint to give the required performance, proper joint design, right product selection, and appropriate preparation of the surface and application techniques must be maintained. Mostly, two aspects of joint selection should be highlighted. These include
- The position of the joint in regards to the structure and the windows can impact on the construction serviceability and maintenance (Birkeland and Birkeland 1996). In particular, weak joint location often leads to complications which cannot be solved through joint detailing.
- Ensuring the integrity of the cladding system through careful control of the construction tolerance.
Designing for joints can be challenging especially when requirements are not well understood. Therefore, to achieve appropriate design, designers need to have a clear understanding of specific requirements for particular project (CCAA, 2014). Having a clear understanding of the requirements of a joint is essential for developing a joint which will be easy to maintain and repair. Although the requirements for joints vary depending on the type of joints, certain aspects are common to all joints. Some of these are discussed as follows.
- “Buildability” and minimum size
Before finalizing the details for the joint, it is critical for the designer to ensure that the chosen specifications are easy to construct or fabricate and will permit safe and simplicity in construction. The proven specifications should be reused as appropriate to avoid reinvention (CCAA, 2014). Additionally, it is necessary for the joints to be made sufficiently wide to ensure the joints accommodate fabrication, construction, and erection tolerance. Usually, 20mm for width is ideal.
- Maintenance and Repair
In most constructions, joints are the main points of wear. Therefore, at the design stage, the deterioration aspects of maintenance need to be considered (CCAA, 2014). First, it is important to choose relevant sealant. Although most modern sealants are long-lasting, any sealant will eventually need to be repaired or replaced for some reasons. Therefore, considerations for repair and replacement should form a critical part of the design stage (CCAA, 2014). In this regard, good designs provide for inspection and maintenance for face sealants. Secondly, the designers should choose appropriate cross-section for the joint.
- Number of Joints
Primarily, the architectural design must try to minimize the number of joints. Achieving this requirement reduces the overall cost of the joints which consequently lowers the maintenance costs as well. Additionally, reducing the number of joints increases economy by employing large panels. According to Schlaich et al. (1987), it is not recommended to limit the panel sizes to minimize movements in the joints. Instead, selecting large concrete panels to provide for anticipated shifts is highly economical. Therefore, it is better to determine the optimal precast panel sizes by considering factors such as:
- Limitations on the panel sizes and weights by local transportation
- Erection conditions
- Availability of handling equipment
In case additional joints are necessary as demanded by the desired appearance, then false joints can be applied for achieving more balanced architectural appearance. However, there is always the challenge of matching the appearance when false joints are used. This problem is best mitigated through simulating the finish of the false joints with the sealants used for the actual joints (Schlaich et al. 1987). Mostly, it should be noted that caulking false joint is often associated with adding unnecessary expenses.
- Location of Joints
With maximum panel thicknesses, the design and execution of concrete precast panels is a simple process. However, if the panel edges have ribbed projections, then these are the location on which joints should be placed. Primarily, ribs at the edges enhance the structural behaviour the units. Additionally, with joints between the ribs, the panel variation is much less traceable compared to the case in which the joints are located in horizontal positions. Nevertheless, it is not recommended to design the panels with complete ribs at their peripheries (Schlaich et al. 1987). This argument true because ribs at the panel edges may cause the runoff of localized water leading to unsightly staining. Therefore, the best locations for the ribs is at the vertical edges of the panels. However, the full ribs can be placed in one panel only if the ribs are narrow and hence unable to accommodate joints.
Further, for horizontal joints, they should be positioned near, but above, floor lines while the vertical one should be located on the grid lines. Additionally, as illustrated in Figure 4.2.2 (a) below, joints should be wide enough and recessed to minimize the possible effects of unexpected weathering (Schlaich et al. 1987). Mostly, recessed joints are ideal for sealing the joints from rain by reducing pressure in the face of the sealant through providing a dead-air space. Moreover, the joint profiles the rain runoff which is essential for keeping the building façade free from unattractive runoff patterns.
In forward sloping surfaces, joints are difficult to weatherproof especially when ice or snow is involved. As such, as much as possible, the design should avoid this joint as much as possible (Schlaich et al. 1987). However, if it becomes necessary to include forward sloping joints, then special precautions must be taken against water penetration.
Finally, throughout their lengths, all joints need to be aligned and not staggered (Figure 4.2.2 (b)). The preference to aligned joints is because disadvantages associated with non-aligned joints. For instance, if non-aligned, joints subject the sealant to elongation, compression, or shear forces and also force the panel take literal movement relative each. In this way, non-aligned joint cause high tensile forces.
(c) Location of Joints (NPCAA 2013)
Figure 4.2.2: Typical Architectural Joints ((a) and (b) Schlaich et al. 1987))
- Width and Depth of Joints
The most important factors take note in determining the width for the joints are of the need to (1) provide erection tolerance for the panel and (2) accommodate variation in the dimensions of the panel. Besides, the width should in achieving sufficient sealing and good virtual lines (Schlaich et al. 1987). Furthermore, width for the joints should be related to adjacent surfaces, panel sizes, joint sealant material, and building tolerance. Mostly, the choice of joint width is dictated by various factors including
- The approximations for temperature extremes at the project location.
- The initial temperature at which the sealant is applied
- The panel size
- The capacity of movement of the sealant to be used
- Panel installation method
- The precast concrete units’ fabricated tolerance
Besides precast concrete walls or cladding, there are mainly three types of joints. These include (1) Open-drained joints (2) face-sealed joints and (3) compression-sealed joints. The three categories are discussed as follows.
- Open-drained joints
This type of joint is made up of a rain-barrier which is an expansion chamber fitted with an air-seal at the interior face of the panel and a loose fitting between the baffle. The baffle prevents rainwater from direct entry while the air-seal acts as the demarcation barrier between the internal and external air pressures. The design (Figure 4.2.4 (a)) ensures that no water enters the joint and any droplets which enter through the baffle are drained downwards (NPCAA 2013). These open-drained are majorly recommended for high-rise and medium-rise constructions due to their ability to withstand large movements.
Figure 4.2.4 (a): Typical Open-drain joint (NPCAA 2013).
Figure 4.2.4 (b): Open-drained joints, Design, and Construction (NPCAA 2013).
- Face-sealed Joints
The face-sealed types are mostly recommended for low-rise construction applications. These joints are more economical and straightforward than other types. They are sealed by applying sealant close to the external surface of the joint.
- Compression Joints
The compression joint uses a compressible impregnated polyethylene foam strip. After the panels are erected, the strip is subjected to pre-compression then inserted into the joint (NPCAA 2013). These joints are best suited for low-rise building such as warehouses and factories in which the wind pressure is low.
Figure 4.2.4 (c): (i) Face-Sealed Joint (ii) Compression Joint (NPCAA 2013).
|Table 4.2.5 Strengths and Weaknesses of Joints Types|
|Open-drained||-Can tolerate large movements
Rear sealant is protected from weather and UV light.
-Best for high-and-medium-rise building applications (NPCAA 2013).
|-Requires careful supervision during installation.
-Unable to tolerate joint gaps larger than 5mm
-Unsuitable for tall vertical panels
|Face-sealed||-Applicable with complex concrete panel shapes
-No grooves are required which enables panel edges to have simple profile
Suitable for low-rise building
|Sealant is exposed to weather and UV light
Requires more inspection
Needs to be applied from external scaffolding
|Compression||Panel edges can take different shapes –simple or plain
Easy and quick to install
Economical (NPCAA 2013).
|Joint width is critical
Cannot be fully waterproof
Limited to low-rise construction
Maintenance is difficult
In choosing the most appropriate sealant for use, for instance, between wall panels, the designer should consult different sealant manufacturers to ensure that selected sealant meets the specific project needs. Additionally, in specifying a sealant, it is necessary to study the product content to avoid uncalculated risks (Schlaich et al. 1987). In this regard, the designer may need to obtain a warranty from the manufacturer.
In overall, in making the final selection for a sealant, the following are some guidelines which can help in making an appropriate choice.
|Table 4.3.1 Types of Sealants and Properties which Determine the Choice of Sealant|
|Types of Sealants||Properties which Determine the Choice|
- Sealants do not have high strength but convey many properties which make them useful for sealing top structures to the substrate in construction. Sealants are, therefore, effective for waterproofing. Sealants keep moisture in (or out of) the component on which they are applied.
- Sealants used on the joints of precast panels provide acoustical and thermal insulation. As such, they can serve as fire barriers.
- Some types of sealants have electrical properties as well. They can also be useful for simple filling or smoothing
- A corking sealant performs multiple functions. It is used to fill the gap between substrates by forming a barrier through adhesion and sealant’s physical properties. Secondly, a corking sealant can maintain the sealing properties for the expected service condition, lifetime, and environment.
- Sealants are applied on vertical and horizontal masonry-to-masonry and metal-to-metal expansion and control joints
- Joints between precast concrete façade panels
- Dissimilar material joints such as concrete to wood or metal to masonry
- Exposed exterior masonry control joints
- Perimeter of fixed doors and window frames
- Control or expansion joints in curtain walls
- Repair of larger cracks
- Concealed masonry to floor structure joints
- Joints in exterior walls
In order to ensure that the sealant and the joint provide a satisfactory performance, some of the points to be noted include:
- Correct joint geometry
- Proper joint preparation
- Reliable sealant-backing systems
- Sufficient curing time
Using precast concrete panels offers many advantages. The following are some benefits of using these prefabricated components
- Aesthetic Variety
Precast panels provide many of styles (Birkeland and Birkeland 1966). This is especially evident due to the ability to produce panels according to the desired texture, colours, and finishes. In this way, precast concrete panels offer a broad range of aesthetic options.
- High Quality
Mostly, concrete precast panels are manufactured according to the design requirements based on the construction policies and standard laid by the government or quality control agencies (Behera 2013). These guidelines ensure that manufacturers supply standard precast panels. So, consumers get components produced with uniform consistency.
- Low maintenance
Structures constructed using precast concrete panels often demand less maintenance than those that are built from other materials. Further, the level of support can be reduced by controlling the panel sizes (Birkeland and Birkeland 1966). For example, incorporating large-sized panels into the structure reduces the number of joints which in turn minimizes the resulting maintenance requirements.
Precast construction using precast concrete panels helps in maintaining a clean site, enhances worker safety, and improves logistics. Usually, there is no site storage required because cranes place the precast components directly to the necessary building position (Behera 2013). The safety and cleanliness offered by prefabricated construction are critical in enabling other businesses near the site to operate without interruptions.
- Effecting pricing
The production process of precast concrete is shorter and tightly controlled. Consequently, the approximation of costs is more accurate and this is critical particularly at the start of the project. So, the project budget can always remain stable when precast concrete panels are used.
- Interior Design Flexibility
Through the use of long-span precast concrete systems, the structure owner can easily modify the building to fit any future client needs. Double tees and hollow core slabs can span between 14 meters and 16 meters to minimize the need for interior columns and also to match a typical composite steel framing (Behera 2013). Precast is capable of spanning up to 21 meters to offer required flexibility for challenging interior designs.
Figure 4.3.5: Design Flexibility through Precast
- Early Input
Mostly, manufacturers of precast components provide support to designers and constructors during the initial stages of construction. The assistance facilitates the benefits of using precast concrete by ensuring that the building takes the full advantage of the prefabrication technology. Additionally, the timely input allows the project to remain efficient and cost-effective.
- Design efficiency
Many manufacturers of concrete precast panels offer early and precise design support to assist in the selection of the most appropriate component shapes and sizes. This support is useful for optimizing the structural efficiency (Behera 2013). The information provided by the supplier allows for early planning of tasks such as transportation and erection of the components. Moreover, member repetition aids design speed and reduces form costs while maintaining the flexibility of conception.
- Green Design
Environmental friendliness is another benefit of using precast concrete. For example, the reusability of precast concrete helps in reducing wastes and keeps the environment clean by avoiding excessive disposal of components and their parts. The use of waste materials such as slag and fly ash in precast construction is key to meeting acceptable environmental standards which are also critical to clients.
- Construction Speed
The application of precast concrete is increasingly becoming important for meeting tight deadlines. With precast concrete construction, the design, fabrication, and erection are done with speed. Moreover, prefabricated panels do not need much work to be done because the construction begins ones the foundation is prepared.
- All-weather Construction
Construction using precast concrete can be continued amidst poor weather condition. As such, it is possible to create a schedule which is accommodative different weather conditions (Schlaich e al. 1987). Therefore, the building can be carried out all the year round because since precast components can be produced and erected at any time.
- Easy Handling
Prefabricated components are transported to the site ready for placement into positions. So, Site construction proceeds smoothly because special techniques or equipment are not necessary for lifting or carrying a combination of architectural or structural components. Instead, these tasks, if emerge may call for an additional review of the structure.
Although concrete precast panels offer many advantages when used in construction, the prefabricated components have certain disadvantages as well. For example, some of the significant limitations associated with using concrete precast panels are (1) high capital cost, (2) sophisticated connection works, (3) transport-related issues, (4) handling challenges, and (5) structural modification difficulties.
- High capital cost
Construction using precast concrete products require a lot of resources to be invested. The large initial investment cost is particularly incurred in starting a by the precast plant. For example, the machines required for transportation, handling/lifting, and for performing other tasks, are sophisticated, expensive, and therefore, the entrepreneur has to invest heavily (Schlaich e al. 1987). At the same time, the scale of construction where precast concrete is to be used must be sufficiently large for cost-effectiveness by having adequate profits that offset the capital cost. For this reason, precast concrete is mainly applicable in high-rise construction of building and flats which are at least five stories tall. Besides, precast concretes are used in constructing large stadiums, warehouses, factories, halls, hangers, or airports (Schlaich e al. 1987). It is also ideal for building housing estates where the design is uniform.
- Sophisticated Connection works
Mostly, the performance of the concrete structure depends on the behaviour of the links. Therefore, precast components must be closely and carefully supervised during the assembling of precast concrete structures to ensure the achievement of the desired behaviour of the connections. Additionally, if the connection and insulation are not properly done, the structure may end up with water leakage problems. For this reason, high building quality with precast concrete panel construction is only possible in the presence of well-trained and skilled labour to ensure the connections are proper. As such, the cost of labour can be substantially high.
- Transportation, handling, and modification challenges
Constructions in which precast concrete are used requires site labourers to be extremely careful while handling the components. Workers must be trained on how to manage the precast concrete to avoid mishandling which can cause damage to the components (Schlaich e al. 1987). Furthermore, prefabricated components are made in factories. Since the plants are not located at the construction site, the components must be transported, using trailers, to the area where the building will take place. However, the elements are often vast and massive. As such, it becomes difficult to transport the precast products to the site safely. Additionally, there are often costs associated with the transportation result which results in an additional cost of the overall project. Moreover, the possibility of components damage during transportation to the site is a further limitation of using precast concrete (Behera 2013). Also, because of the transport issues, the sizes of precast products are restricted for ease of carrying.
At the construction area, tower-cranes or portable cranes are required for lifting the components into place to be erected. And to increase the building speed, several cranes may be needed. At the same time, many cranes mean space must be large enough for operational efficiency in addition to the fact that the site must be properly managed, and the construction must be well-planned.
Moreover, in many cases, structures which are built using precast concrete are inflexible considering future modifications requirements. For instance, it is not possible to demolish walls of a flat which is constructed using load bearings for purposes of renovation because attempting to do so will compromise the stability of the entire structure (Behera 2013). For this reason, modifying and renovating precast concrete structures becomes a challenge. Finally, prefabricated components are expensive when used in non-modular buildings beside the fact that joining pieces are mostly involving.
Finished pods are bathroom pods used in the high rise construction industry. They are enclosed bathrooms which are prefabricated off site and kept in a warehouse until required to be installed on site (Modular Building Institute 2011). There have been a variety of ways in which the pod is manufactured and installed on site, and even to this day, the pod system is constantly being re-designed and re-innovated to suit a better process and smoother installation. Most of these pods have failed in the past and once installed, the walls have failed, and tiles cracked. Although there have been recent successes in the way the pod is designed and these new models have been very successful, although there are still many issues that need to be rectified.
Figure 5.1 (a): Example of Finished Pod
Concrete finished bathroom pods are manufactured offsite in different sizes. Currently, many manufacturers attempt to modify the product sizes during by making light-weight finished pods to facilitate the ease transportation (Modular Building Institute 2011). The structures incorporate slim floor profile and have small wall-thickness. Mostly, finished pods are made with excellent acoustic insulation and fire resistance performance. They are internally finished according to the requirements of the customers. Additionally, the units of prefabricated bathroom pods are completed with a range of shower and bath fittings, sanitary ware, laminate panels, and wall tiles.
Figure 5.1 (b): Units of Bathroom Pods
Moreover, during the manufacture, emphases are made to ensure significant compliance with electrical and mechanical requirements based on building and construction policies. The products are usually of high quality especially due to the incorporation of technology in the design as well as the entire process of producing finished bathroom pods. For instance, in many companies today, employ varieties of computer applications such as 3D software to assist and guide clients in selecting and developing the most beneficial solutions for projects through precast panel option.
Like most prefabricated components, finished pods are delivered to the site after manufacturing at the factory. Ones in position, the pods, readily accept a broad range of wall finishes. Indeed, among the most critical benefits of prefabricated bathroom pods is that the products are manufactured through a rigorous quality process and testing procedures (Interpod 2016). For this reason, finished pods reach the site ready for the final connection. Mostly, producers often ensure that the products are complete with all electrical and mechanical installations such that before delivery to the location, the structures are tested and certified. Further, suppliers pay close attention to local area infrastructure and environmental impacts during the manufacturing of finished pods (Interpod 2016).
The aim is to ensure that all the materials, procedures, and technological influences adopted during the production of prefabricated bathroom pods are well established to reduce the possible negative impacts of the manufacturing process on the environment.
The idea of prefabricated bathrooms was initiated by an American author, system theorist, architect, inventor, and designer, Buckminster Fuller. In 1940, Fuller received a patent for prefabricated bathroom following his assertion to have invented an object which would be helpful for lowering the cost of constructing bathrooms into a dwelling (Richard and Phelps Dodge Corp 1940). In his claim, the inventor argued that the traditional Bathrooms were bulky and expensive in regards to their construction, shipping, and installation for use. Therefore, according to the architect, his invention would offer a bathroom with the following features to offset the limitations of the traditional types
- Weight: The prefabricated bathroom would be a light and easy to install either in a dwelling which is already in use or one that is still under construction (Richard and Phelps Dodge Corp 1940).
- Portability: Fuller’s structure would adopt a compact construction with five separable sections that can be hand-carried with ease through the doorway and along the staircase of an average building.
- The new prefabricated bathroom would be designed from a few units implemented using sheet materials to provide a primary structure with the required rigidity and strength after assembling (Richard and Phelps Dodge Corp 1940).
In response to Fuller’s claim of the invention, he received patent 2220482 for a prefabricated bathroom. Nevertheless, the first practical application of bathroom pods appeared in 1960’s in a volume format. For example, during the Tokyo Olympic Sports of 1964, bathroom pods were used in the Athletes Village Accommodation (Richard and Phelps Dodge Corp 1940). Afterwards, Toyota, Hitachi, and Mitsubishi dedicated to making bathroom pods throughout 1970’s and 1980’s.
Bathroom pods have evolved through decades with increasing focus on lean construction. Years ago, most manufacturers employed the same procedure of on-site bathrooms in the manufacture of prefabricated bathroom pods. The only difference was that the prefabricated types were constructed in small firms, but the general architecture was almost the same.
However, over the time, the manufacturing process has refined and streamlined to provide better, lightweight, and high-quality pod models which are easily carried and dropped directly into the building structure. Indeed, with the emerging technology in robotics, some companies currently produce pod pieces using robots (David, 2014). According to the David, the application of robot technology has been instrumental in driving the change towards a more cost friendly production process.
Additionally, the use of specialized computer programs for pod design helps in achieving fast and accurate pod design which further facilitates the products’ quality especially for manufacturers who have not started using robots. For example, 3D pod design using specialized software such as Navisworks improves design flexibility. It is notable that major bathroom pod manufacturing companies such as SurePods are speedily adopting computer-based pod design procedures in pod construction.
On the other hand, the products used in manufacturing bathroom pods have evolved and improved as well. For example, most companies are currently focusing on incorporating materials mixes which can offer complete crack and waterproof ceiling assembly. The main aim is to get pod products with a longer service life (David, 2014).