CHAPTER 1
INTRODUCTION
Modern methods of construction are about better products and processes. They aim to improve business efficiency, quality, customer satisfaction, environmental performance, sustainability and the predictability of delivery timescales. Modern methods of construction are, therefore, more broadly based than a particular focus on product.
They engage people and process to seek improvement in the delivery and performance of construction, modern methods of construction are about better products and processes. They aim to improve business efficiency, quality, customer satisfaction, environmental performance, sustainability and the predictability of delivery timescales. Modern methods of construction are, therefore, more broadly based than a particular focus on product. They engage people and process to seek improvement in the delivery and performance of construction
With developments in technology, general construction knowledge and manufacturing processes, Modern construction technology have evolved from the more conventional methods to a large extent. Modern construction technology can be defined as those that provide greater efficiency in the construction process, resulting in increased production, better quality, in less time and with less waste, so reducing the environmental impact. MMC is a process to produce more, better quality homes in less time.
Modern construction technology is a collective term used to describe a number of construction methods. The methods being introduced into the world house building differ significantly from so-called conventional construction methods such as brick and block.
In this report, we use the term MMC. This is because this term is increasingly being used and because it also includes several important new types of construction methods that involve some element of fabrication on site.
Advanced technologies in housing construction are not used as frequently as the more standard construction technologies, which involve the use of masonry, timber, and concrete. However, as with other innovations, it is expected that over time these newer technologies will gain wider acceptance. For purposes of the World Housing Encyclopedia, advanced technologies include seismic isolation and passive-energy dissipation devices.
MMC are about better products and processes. They aim to improve business efficiency, quality, customer satisfaction, environmental performance, sustainability and the predictability of delivery timescales. Modern methods of construction are, therefore, more broadly based than a particular focus on product. They engage people and process to seek improvement in the delivery and performance of construction.
CHAPTER 2
ADVANTAGES
2.1. Quicker on site build time/shorter programmes/reduced preliminaries:
With MMC, much of the work is removed from the site and it is therefore possible to execute various activities of the project concurrently or even before the project has commenced on site. This reduces the projects construction time as the building or elements of the building can be manufactured off site while the ground and site works are taking place. MMC leads to a reduction in trades on site and a shorter construction programme which in turn leads to reduced preliminaries, overheads and a quicker return on investment for the client.
2.2. Reduced waste and better waste management:
As production is often executed in a factory controlled environment, the waste stream can be easier to manage. Exact quantities of materials can be purchased, materials can be used more efficiently and because materials are properly stored, breakages and damage are less likely to occur. Furthermore any un-used materials can be easily collected, re-used or recycled contributing to less waste. Constant monitoring also takes place within a production plant allowing new waste management strategies to be implemented without difficulty, if necessary. Waste reduction is a very significant advantage as waste from construction is one of the principle waste streams to landfills and it has been proven that a high percentage of materials delivered to site are never even used and go straight into the waste cycle.
2.3. Reduction in defects and increased quality control:
As you can imagine, a building site in Ireland, fully exposed to our rainy and windy climate is not exactly the perfect working environment for high quality workmanship.
Construction work exposed to the elements of wind and rain proves more difficult to monitor with regard to quality control. Human error is also another significant factor which deters the achievement of high quality construction as it can prove difficult to work in extreme weather conditions.
Factory based constructions forms, engage better and safer working conditions with no interference by the Irish climate and therefore a very high standard of quality control can be achieved which includes testing, trials, checks and re-checks. For more reasons than one, factory based construction provides better working conditions than a building site and in turn produces better quality too.
2.4. Increased Health & Safety:
Construction work carried out in a factory controlled environment is without doubt a safer working environment for all trades. Safety controls are implemented and monitored and safe working conditions are easier to meet and maintain. With off-site construction there is a significant reduction in the number of trades working on site and this proves more manageable from a health and safety perspective. Construction work on site can incorporate some very dangerous activities and in turn lead to a large number of causalities and/or fatal injuries. Construction is among the largest number of fatal injuries between all the main industries in Ireland. Statistics from 2002 to 2009 (as seen in Appendix A) show that the construction sector has been either the first or second largest contributor to fatal injuries in the past 8 years.
2.5. Social benefits and reduced local impacts:
MMC’s and in particular off-site construction, allow local communities to benefit from the process of manufacturing away from site. The main advantage to communities is that there is much less traffic and smaller on site work forces adding to traffic congestion in the area. Furthermore due to speedier on-site programmes, noise and pollution levels will decrease and the locality surrounding the site will be disrupted for a far shorter period of time.
Construction sites are only temporary employment locations and offer little or no amenities for the local communities whereas manufacturing facilities very often provide long term social services and economic benefits for the surrounding community. Manufacturing facilities are also more likely to invest in education and training for their workforce and develop a highly trained local workforce within their facility.
2.6. Greater efficiency in the use of resources and transport
Over the years it has been noted that the use of labour, plant and materials on building sites is extremely inefficient as is not the case with factory based activities which are kept under extreme scrutiny, monitored and controlled. Re-cycling and re-using of materials is also more difficult to enforce on a building site but is easily implemented in a factory based environment. On another note, monitoring of transport patterns and schedules can be very difficult on construction sites especially if the site is condensed and compact. With off-site MMC the number of deliveries direct to the building site is reduced and deliveries to factories can be planned and controlled so that full loads can be used and transport costs are kept to a minimum. On the other hand, transport of prefabricated or modular buildings to site must be carefully planned and heavy plant and equipment necessary for off-loading and erection requires careful site management and consideration.
CHAPTER 3
DIFFERENT TYPES OF MMC
3.1. Volumetric Construction
Three dimensional units produced in a factory fully fitted out and dropped onto foundations to form a structure e.g. bathroom or kitchen PODS.
Fig 3.1 Volumetric Construction
3.2. Panelised construction
Units produced in a factory and assembled into a three-dimensional structure on site e.g. concrete wall panels, structural insulated panels (SIPS), curtain walling etc.
Fig 3.2 Panellised construction
3.3. Hybrid construction
Volumetric construction integrated with panelised construction e.g. kitchen pod as volumetric unit with the rest of the dwelling constructed using panels.
Fig 3.3 Hybrid construction
CHAPTER 4
STRUCTURAL COMPONENTS
4.1. Precast Floor Slabs:
For this project it is proposed to use pre-stressed wide slab as will span up to 8m simply supported. This is sufficient for the development as the maximum floor span is around five and a half meters. Other options are Filigree slabs which can span 5.5 m simply supported but this type of slab is not as widely used in the industry. Hollow core flooring is another alternative but this is only really necessary for spans greater that 8 m and up to 16.5 m and the building is in excess of seven or eight floors and a lighter weight option is required. It will be necessary to prop the floor at 600 centres using acro type props with timber girders running horizontally from prop to prop.
For this structure, the proposed wide slab will have a 100 mm slab depth and a width of 2400 mm as standard will be used where possible. This shallow floor will give maximum floor-to-floor height resulting in no loss of space. It will also provide a smooth soffit finish, which can be used as a finished surface in areas where suspended ceilings are not specified i.e. the apartments. The floor slab will sit approx 70 mm into the wall panel and the slabs will also be lifted in by crane via projecting lifting hooks on the surface of the slab. A 125 mm screed over the 100 mm wide slab will be sufficient and can incorporate services into the floor if necessary. It may be possible to cast up stands on the precast walls instead of shuttering the perimeter for screeding. A393 mesh along with tie steel will be placed on the slab and a 35-40 N structural screed will be poured over this. The perimeter of the floor, opens, stairwells etc will have to be shuttered to house the screed and prevent spillages. The concrete will be pumped in using a concrete pump and all floors will receive a power float finish.
The floors will be connected to the wall panels via U bars which are wrapped around the treaded bar projecting from the panel to connect the wall directly above. Handrail will also be necessary around the perimeter and large opens. There will be a plastic leg on the handrail posts that can be left in the screed afterwards. The perimeter handrail will be moved up floor by floor as screeding progresses but handrail around opens must remain until it is safe to remove.
Fig 4.1 Precast Floor Slabs
4.2 Precast Stairs:
It is proposed to use precast stairs from basement to fourth floor. The stairs are prefabricated off site and are cast in a steel mould for manufacture. The use of precast stairs means that while they can be erected by crane with the wall and floor panels, they also allow access up the building for the precast crew as the building progresses.
Fig 4.2 Precast Stairs
4.3 Internal Finishes:
It is also proposed that a thin coat spray on plaster system will be used on the rough side of the precast walls and also on the ceilings. The material recommended for this is a thin spray on plaster known as Alltek which is supplied by International Coating Products (ICP) and who many suppliers and applicators across Ireland, the United Kingdom and Europe. The Alltek product is packaged in standard 25kg bags and comes in the form of a white powder which comes from fine graded marble. Alltek is applied in two coats and is suitable to be sprayed onto fair faced concrete surfaces, gypsum boards, smooth plastered surfaces etc. The Alltek Red Label can also be sprayed over the Alltek Blue Course plaster which is used on rough surfaces.
Alltek also supply dry fillers used to fill joints in panels, the filler is just mixed with water on site and applied to the joint. Once the joints are dried and sanded down, the walls are then ready to receive the plaster spray coat. The Alltek red label is poured into the spray machine and the applicator then commences spraying the Alltek onto the prefilled surface. The second coat of spray can only be applied once the first has fully dried out. Alltek can be applied in a flat or textured finish and in several pastel shade thus reducing painting and decorating costs. Between 200-300 m2 of two coat Alltek application can be achieved per day.
CHAPTER 5
REDUCTION IN PROGRAMME
It is my belief as the contractor that by adopting the above mentioned modern methods of construction on the South Cumberland Development we can significantly reduce the program duration for this project. Based on figures from one precast manufacturer, Alcrete Ltd, 1450m2 of precast walls can be produced in their factory in just one week. As can be seen from the below chart, this is more walls that needed for the entire development. Hence production of precast walls off-site will automatically reduce the program and even taking into account the lead in time required by the manufacturer, signification time savings can be achieved here. It must also be noted that lead in times for precast manufacturers has reduced significantly due to lack of workload in this economic downturn.
Further reductions in program duration can be achieved through erection on site of the precast elements. Further figures from Alcrete show that 325 m2 of double walls and 450 m2 of solid walls can be erected per week by a 5 man crew. In addition, 280 m2 of wide slab can be erected per day by a 4 man crew thus showing how the frame can be erected in just a number of weeks.
Furthermore with no scaffolding, drying out time, erection or dismantling of shutters/pans etc needed, the precast frame is less weather dependent than in-situ construction forms and is therefore less likely to experience delays or set backs on site. Once erection of the frame has been completed additional time savings can also be achieved in the finishes such as plastering works, mechanical and electrical works, installation of cladding etc.
CHAPTER 6
CASE STUDY
6.1 Concrete walls and floors
Concrete walls is an eclectic category with options for everything: seat walls; decorative interior or exterior finishes; sound walls that abut a freeway; retaining walls to hold back the earth; to the very walls that comprise the exterior of a home. Concrete has become the new flooring material of choice for designers and homeowners across the United States. Concrete floors are popping up in retail stores, trendy restaurants, offices, and homes everywhere. Whether it's acid-stained, painted, overlays, micro toppings, radiant floors, or a unique personal floor, concrete floors offer a range unlike any other material. Concrete flooring, sometimes referred to as cement flooring, no longer has to be gray and boring. Now coloring concrete or applying textures, patterns, saw cuts, etc., can bring new life to this traditional substrate.
One of the major benefits of concrete floors is their affordability compared to other flooring options. Installing a decorative concrete floor can be quite cost-effective, particularly if you already have a concrete slab that’s ready for staining, polishing or application of a coating or overlay. A basic concrete floor will carry a comparable price tag to linoleum, vinyl, ceramic tile or carpet. While a more complex concrete floor design will run you about the same or slightly less than marble, granite, slate, or high-end wood. Furthermore, the lifetime cost of a concrete floor is very low because they require little upkeep and last for years.
A second thing that attracts business and homeowners to concrete flooring is its ease of maintenance. When properly sealed, concrete floors can be cleaned with a quick pass of a dust mop. For an occasional deep clean a neutral cleaner and water can be used. The frequency of maintenance is dependent on the amount of traffic the floor receives. Restaurants and businesses with considerable foot traffic may want to use a sacrificial floor wax in addition to a sealer to further protect from abrasion.
Here are some additional benefits of concrete floors according to Barbara Sargent of Kemiko Concrete Floor Stains:
• They enhance the integrity of architect's designs.
• They are easy to change, especially if you sell your home; the next owner can place carpet or wood on top of the concrete slab.
• They are great in regions with a lot of sand or snow.
• They are a good alternative to carpet if you have allergies.
Fig 6.1 Concrete wall
6.2 Precast Cladding Panels
Precast concrete panels are reinforced concrete units available in a wide range of mixes, colours and finishes. Finishes can include acid-etched, smooth or coarse ground, grit or sand-blasted, rubbed or polished. Mixes designed to resemble natural stone can also be produced. Highly articulated designs can be accommodated by the mouldable concrete mix.
Benefits
• Faster programme times - not affected by weather or labour shortages.
• Improves buildability.
• Early enclosure of dry envelope enables follow-on trades to start sooner.
• Produces a high standard of workmanship in factory conditions - reduces potential for accidents, addresses on-site skill shortage.
• Has a high quality finish that can be left exposed - concrete's thermal properties can
• be exploited in low-energy buildings
Fig 6.2 ACP Cladding
6.3 Precast Flat Panel System
Floor and wall units are produced off-site in a factory and erected on-site to form robust structures, ideal for all repetitive cellular projects. Panels can include services, windows, doors and finishes. Building envelope panels with factory fitted insulation and decorative cladding can also be used as load-bearing elements. This offers factory quality and accuracy, together with speed of erection on-site
Fig 6.3 Panel system
6.4 Volumetric modules
3D Volumetric construction (also known as modular construction) involves the production of three-dimensional units in controlled factory conditions prior to transportation to site.
Modules can be brought to site in a variety of forms, ranging from a basic structure to one with all internal and external finishes and services installed, all ready for assembly. The casting of modules uses the benefits of factory conditions to create service-intensive units where a high degree of repetition and a need for rapid assembly on-site make its use highly desirable.
Fig 6.4 Volumetric Module
6.5 Twin Wall Technology
Twin wall technology is a walling system that combines the speed of erection and quality of precast concrete with the structural integrity of in-situ concrete to provide a hybrid solution. The prefabricated panels comprise two slabs separated and connected by cast-in lattice girders. The units are placed, temporarily propped, then joined by reinforcing and concreting the cavity on site. Twin wall is usually employed in association with precast flooring systems.
The panels are manufactured to exacting tolerances, have a high quality finish, and can incorporate cast-in cable ducts, electrical boxes and service ports. Installation rates are of up to 100m2 per hour. Twin wall has excellent inherent fire resistance and acoustic performance.
Fig 6.5 Twin Wall Technology
6.6 Flat Slabs
Flat slabs are highly versatile elements widely used in construction, providing minimum depth, fast construction and allowing flexible column grids. Because this is one of the most common forms of construction, all construct members and many other concrete frame contractors can undertake this work. Flat slabs are particularly appropriate for areas where tops of partitions need to be sealed to the slab soffit for acoustic or fire reasons. Flat slabs are considered to be faster and more economic than other forms of construction, as partition heads do not need to be cut around down stand beams or ribs.
Flat slabs can be designed with a good surface finish to the soffit, allowing exposed soffits to be used. This allows exploitation of the building’s thermal mass in the design of heating, ventilation and cooling requirements, increasing energy efficiency. Flat slabs provide the most flexible arrangements for services distribution as services do not have to divert around structural elements.
Fig 6.6 Flat Slab
6.7 Thin Joint Masonry
In masonry, mortar joints are the spaces between bricks, concrete blocks, or glass blocks that are filled with mortar or grout. Mortar joints can be made in a series of different fashions, but the most common ones are raked, grapevine, extruded, concave, V, struck, flush, weathered and beaded.
In order to produce a mortar joint, the mason must use one of several types of jointers (slickers), rakes, or beaders. These tools are run through the grout in between the building material before the grout is solid and create the desired outcome the mason seeks
Thin joint block work (thin joint masonry) is a fast, clean, accurate system for construction using autoclaved aerated concrete blocks of close dimensional tolerance with 2mm-3mm mortar joints. Thin layer mortar is a pre-mixed cement-based product that only requires the addition of water to make an easily-applied mortar. The benefits offered by thin layer mortars are provided by a system with many of the characteristics of traditional block work construction.
Fig 6.7 Thin Joint Masonry
6.8 Concrete Formwork
Formwork is a structure, usually temporary, used to contain poured concrete and to mould it to the required dimensions and support until it is able to support itself. It consists primarily of the face contact material and the bearers that directly support the face contact material. Formwork systems used for concrete frame construction have continued to develop significantly since the early 1990s. The major innovations have focused on on-site efficiency of production, health and safety, and environmental issues, driving the concrete construction industry towards ever-increasing efficiency. Different formwork systems provide a wide range of concrete construction solutions that can be chosen to suit the needs of a particular development.
Traditional formwork for concrete construction normally consisted of bespoke solutions requiring skilled craftsmen. This type of formwork often had poor safety features and gave slow rates of construction on-site and huge levels of waste.
The main types of formwork systems in use now are:
• Table form/flying form
• System column formwork
• Horizontal panel
• Slip form
• Tunnel form
The modern formwork systems listed above are mostly modular, which are designed for speed and efficiency. They are designed to provide increased accuracy and minimize waste in construction and most have enhanced health and safety features built-in.
Fig 6.8 Concrete Formwork
6.9 Precast Foundation
Precast concrete foundation and wall panels can take many forms. Some consist of steel-reinforced concrete ribs that run vertically and horizontally in the panels. Others are solid precast concrete panels. Panels are precast and cured in a controlled factory environment so weather delays can be avoided. A typical panelized foundation can be erected in four to five hours, without the need to place concrete on site for the foundation. The result is a foundation that can be installed in any climate zone in one sixth of the time needed for a formed concrete wall.
Some manufacturers cast the concrete against foam insulation that provides the form during manufacture and added R-value in the wall. Panels range in size from 2'-12' in width by 8' - 12' in height and are typically installed with a crane on top of 4" to 6" of compacted stone. The stone facilitates sub-slab drainage and adequately carries and transfers the load from the foundation wall. Panel connections consist of bolts and sealant. The foundation can be backfilled as soon as it is braced per manufacturer's specifications.
The controlled temperature of the processing plant allows the manufacturer to work with concrete admixtures that focus on ultimate strength rather than cure time and temperature. Manufacturers are able to produce mixes that harden to 5,000 psi, which is stronger than concrete block or concrete walls formed and cast in the field. Better control of the concrete mixture and curing environment allows the use of low water/cement ratios that results in a dense material that prevents water penetration.
Fig 6.9 Precast Foundation
CHAPTER 7
CONCLUSION
As can be seen through-out the above report, the use of a precast frame and a thin coat spray on plaster finish on this development can produce significant reductions on the overall construction programme while also not only maintaining, but excelling the standards set out in the original specification.
The precast frame exceeds specification as it will be 60N concrete and manufactured to a very high specification in a factory controlled environment. Tight factory production control ensures that the re-enforcement is located accurately and the panels are made to tight dimensional tolerances. Structural connections are also accurate which assists in the accurate installation of cladding, windows and other elements thereafter. Furthermore precast concrete improves structural efficiency as longer spans and shallower construction depths can be obtained using prestressed floors and/or beams. Most importantly, there will be no additional work created for the design team as the precast manufacturer produces their own in-house precast drawings for approval by the architect thus design costs do not change or increase.
The limitations of the topic “Modern Construction Technology” is very enormous and massive. Therefore, it not possible to covers all the topic and chapters in this report. Therefore , this report has limited topics related to “Modern Construction Technology” which are as follows:-
1. Concrete Walls and Floors.
2. Precast Cladding Panels.
3. Precast Flat Panel System.
4. Volumetric Modules.
5. Twin Wall Technology.
6. Flat slabs.
7. Thin Joint Masonry.
8. Concrete Formwork.
9. Precast Foundation.
The benefits of modern methods of construction are too positive to be ignored.. Modern methods of construction can provide large numbers of sustainable, well-designed homes in a short period of time. Modern methods of construction also afford an opportunity to overcome the skills shortage in the construction industry through factory production.. Modern methods of construction will be a key tool in addressing this challenge and should be viewed as an opportunity for the house building sector to increase capacity and choice in the housing market.Modern construction technology have evolved from the more conventional methods to a large extent. Modern construction technology is those that provide greater efficiency in the construction process, resulting in increased production, better quality, in less time and with less waste, so reducing the environmental impact. Modern construction technology is a process to produce more, better quality homes in less time.
REFERENCES
1. Modern methods of constructions and their components (Lenka Kyjaková , Tomáš Mandičák & Peter Mesároš)
2. Modern methods of construction: a solution for an industry characterized by uncertainty (Ylva Sardén1 And Susanne Engström)
3. Study on modern methods of constructions used in Srilanka H.M.M.Uthpala1, T.Ramachandra.
4. Modern methods for cost management in construction enterprises Peter Mesároš, Tomáš Mandičák, Jozef Selín
5. Acceptance theories of innovation and modern methods in construction industry Daniela Ma˘Ckov´ A, Tom´A˘S Mandi˘C´Ak
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