Advanced Construction Technology Project

Advanced Construction Technology
Course: DT117/4
Lecturer: Mr. Ruairi Hayden

ADVANCED CONSTRUCTION TECHNOLOGY
Continuous Assessment
Scenario 3 (The Contractor)

Student Name: Gemma Rice
Student No: D05107441 Page 1 of 18

Course: DT117/4

Contents:

Introduction ……………………………………………………………………....... Page 3

What are modern methods of construction? ……………………………………..... Page 4

Benefits of MMC ………………………………………………………………...... Page 6

Proposed MMC for South Cumberland Street Development…………................... Page 9

Precast Wall Panels ………………………………………………………….......... Page 10

Precast Floor Slabs, Stairs & Internal Finishes …………………………………….Page 13

Reduction in Programme………………………………………………….............. Page 15

Conclusion …………………………………………………………………............ Page 16

References………………………………………………………………................. Page 17

Appendices…………………………………………………………………............ Page 18


Course: DT117/4
Introduction:

The purpose of this paper is to put forward a proposal on the most appropriate way to
reduce the overall construction programme on the South Cumberland Street development
adopting modern methods of construction (MMC) to achieve same.

In this report, I will define MMC and outline the advantages of using this type of
construction. I will also discuss and analyse the proposed MMC’s which I believe, as the
contractor, should be adopted to best achieve a reduction in the overall programme
duration, while still achieving the specification and high level of quality required by the
client.


Course: DT117/4

What are modern methods of construction (MMC)?

In a report published by the National Audit Office, MMC is defined as follows:
“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” (National Audit Office, 2005, p.4)

In a similar report published by NHBC Foundation entitled ‘A guide to modern methods
of construction’, MMC is defined as a collective term which is used to describe a number
of construction methods including industrialised construction, off-site assembly, off-site
construction, modular construction, system building etc. (NHBC Foundation, 2006, p. 3)

Different types of MMC’s include:

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.
Panellised 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.
Hybrid construction Volumetric construction integrated with panelised
construction e.g. kitchen pod as volumetric unit with the
rest of the dwelling constructed using panels.
Sub-assemblies and Larger components that can be incorporated into either
components conventionally built MMC structures e.g. pre-fabricated
foundations, floor cassette systems, pre-assembled roof
structures, pre-fabricated chimney stacks etc.


Course: DT117/4

Most modern methods of construction are based off site but there are also site based
methods including tunnelform construction, insulated permanent formwork and aerated
concrete products used to form major elements of a structure.


Course: DT117/4
Benefits of MMC:

There are many beneficial factors associated with MMC’s, not only for the benefit of the
client but also for main contractors, sub-contractors, local communities etc. Some of the
main advantages to using modern methods of construction include the following:

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) 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.

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.


Course: DT117/4
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.

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.

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 workforces 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.


Course: DT117/4

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.

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.


Course: DT117/4

Proposed MMC for South Cumberland Street Development:

As the contractor, I believe that the best way to achieve a reduction in the programme
would be in the concrete frame and the internal finishes and I will discuss and analyse
this through-out the report.

The proposed modern methods of construction for this development include the use of
precast wall and floor panels, precast stairs and also the use of Alltek spray on plastering
to the internal walls. I believe that this will give a signification reduction on the overall
programme while also adding additional benefits which will also be discussed in detail
later in the report.

It is proposed that the insitu basement walls be substituted with 300mm double precast
retaining walls with factory applied Volclay waterproofing and the insitu walls from
ground to fourth floor will be substituted with 200mm thick solid precast walls.

It is also proposed to use 100mm wideslab flooring with a 150mm screed finish as well as
precast stairs at all levels. All of the precast products are manufactured in a factory
controlled environment and delivered to site ready to be lifted into place easily via a
mobile or tower crane.

Specialised Machines forming the element perimeter using magnetic steel moulds


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In addition to the benefits of MMC mentioned above, precast construction offers many
other benefits over insitu as follows:

1) No scaffolding required – this can save time on site and leads to further cost
savings.
2) Less co-ordination needed on site – there is no need to co-ordinate the shuttering
carpenters, the concrete deliveries and pump, deliver & positioning of re-
enforcement etc and therefore problems and delays on site are eliminated before
the arise.
3) Fair faced finish on wall panels – the precast wall panels offer a fair faced finish
on one side which is ready to be painted without the need for a skim coat plaster
finish. The external walls will take a cladded or external insulation finish
therefore will not require any finishes as the rough side of the panel will face the
external or cavity of the building. On the other hand the internal walls will require
further finishing on the rough trowel side of the wall and this will be carried out
using a spray on plaster finish of just a few millimetre thickness. In this case
finishing works will be kept to a minimum while also eliminating the need for
drying out of wet trades.
4) Electrical conduits and sockets can be cast into the precast wall panels during
manufacture thus saving further time on site for chasing of walls and installation
of services by mechanical and electrical contractors.
5) Connections for external cladding such as dywidag sleeves etc can also be cast
into the walls speeding up the external completions process.

Dywidag Sleeve – is cast into
wall allowing for connection of
cladding panels to wall
afterwards i.e. bolt can be
screwed in to this sleeve

Precast Wall Panels:


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It is proposed that a 300mm precast double wall panel will be used on the
perimeter at basement level with 200mm solid walls being used internally.
The double wall will act as a retaining wall and also as a shear wall to take
the load from above. Further details on double walls can be found in
Appendix D.

The double wall will be waterproofed using the Volclay Voltex waterproofing system
which can be factory applied. Full factory application details including step-by-step
photographs can be found in Appendix C.

It is also recommended that 200mm thick, 60N solid precast wall panels be used from the
ground to fourth floor. These panels will be manufactured on an automatic production
system therefore resulting in overall lengths and opes to within mm accuracy. The walls
will carry the vertical load and act as shear walls within the structure.

The Erection Process:

The precast crew will work off a finished ground floor with starter bars already in place.
Starter bars are vertical bars cast into the floor slab and set out, as per the positioning
details for the wall panels. A 20mm shim and grout bedding is then applied at this level.
The wall panels are lifted in place via a mobile or tower crane. Lifting brackets located at
the top of the panels are slung with chains and the walls are set down on these starter bars
which connect the building to the ground floor slab. (See Fig 1.3 in Appendix E) If the
starter bars are not in position or in an incorrect position, the following method should be
applied:
1) Drill a hole 400mm deep, with the diameter of the hole being 12mm greater than
the diameter of the bar.
2) Clean out the hole and remove all dust. Place the resin in accordance with the
manufacturer’s instructions.


Course: DT117/4
3) Place the bar into the hole displacing the resin to the top and hold the bar in
position until the resin has set.
4) Wait at least 24 hours before placing walls over bars.

The panels themselves are connected to each other on the vertical side using Philips loops
and threaded bar. The Philips loops are connectors at the sides of each of the solid panels
and provide a fully grouted rigid connection. The threaded bar is pushed down through
these loops interlocking the panels. (See Fig 1.0 in Appendix E) There is usually up to a
20mm gap between panels here and it may be necessary to shutter these joints prior to
filling with grout else the joints could be sealed and left to set and then the filled in from
above with grout. This 20mm gap can also be advantageous when the building is to be
plumbed and lined as it may offer some leeway. The wall panels are connected on the
horizontal with threaded bar which sits down a dowel tube in one panel and up the tube in
the other. These tubes are then also filled with grout. The result of all these connections is
that all elements are connected together and the building is also connected to the ground
thus providing maximum stability.

Electrical socket outlets and conduits can be cast in to both faces of these wall panels and
the service tube allows for easy wiring of the sockets and eliminates chasing of walls by
electricians at a later stage. Steel sections or additional reinforcement can also be cast
into the walls at the production stage if necessary. Opening for doors, windows or
services can be provided within the wall panel but extra reinforcement must be used
around these opes to prevent cracking or breakage.

The wall panels will be erected using a crane. (See Fig 1.1 in Appendix E) Lifting
brackets located at the top of the panels will be slung with chains and erected into
position. M16 sockets can be pre-cast into the panel face to take diagonal push pull props
on site, thus increasing erection speed and reducing damage to the panel on site. (See Fig
1.2 in Appendix E) Once the wall panels are erected all joints between walls will be
insitu filled with a cement and fine aggregate grout and this will provide a smooth even
surface on the panels.


Course: DT117/4
Precast Floor Slabs:

For this project it is proposed to use pre-stressed wideslab as wideslab 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 5.5m
simply supported but this type of slab is not as widely used in the industry. Hollowcore
flooring is another alternative but this is only really necessary for spans greater that 8m
and up to 16.5m 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. (See Fig 1.5 in
Appendix E)

For this structure, the proposed wideslab will have a 100mm slab depth and a width of
2400mm 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 70mm 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 125mm screed over the 100mm wideslab will be sufficient and can incorporate
services into the floor if necessary. It may be possible to cast upstands 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 35-40N structural screed will be poured over this. The
perimeter of the floor, opes, 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 powerfloat 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. (See Fig 1.4 in
Appendix E) Handrail will also be necessary around the perimeter and large opes. There
will be a plastic leg on the handrail posts that can be left in the screed afterwards. The


Course: DT117/4
perimeter handrail will be moved up floor by floor as screeding progresses but handrail
around opes must remain until it is safe to remove.

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.

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 200-300m2 of two coat Alltek
application can be achieved per day. Further details of Alltek products can be seen in
Appendix B.


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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
programme 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
programme 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.
Basement 1st Floor 2nd Floor 3rd Floor 4th Floor
Double Walls 144 m²
Solid Walls 95 m² 241 m² 254 m² 228 m² 162 m²
Wideslab 168 m² 168 m² 168 m² 168 m²

Further reductions in programme durations can be achieved through erection on site of
the precast elements. Further figures from Alcrete show that 325m2 of double walls and
450m2 of solid walls can be erected per week by a 5 man crew. In addition, 280m2 of
wideslab 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 dependant than insitu
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.


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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 Alltek plaster finish will also provide a high quality finish with all Alltek materials
undergoing extensive testing before being released onto the market. Furthermore surfaces
can be emulsion painted after only 24-48 hours with only a mist-coat and finish coat
being required. Further details of Alltek standards can be seen on Appendix B, page 2.

In addition, there are other MMC’s which could be adopted on this project to further
reduce the programme if necessary. Such methods include the use of bathroom and/or hot
press PODs in the apartments and/or office units.

References:


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Alcrete Ltd.
www.alcrete.ie

Allco Waterproofing Solutions
http://www.allco.co.nz/Precast+Panel+Presentation.html

Construction & Property News; Volume 34; Number 07; February 2008

Construction & Property News; Volume 33; Number 11; May 2007

Elliott, K. & Tovey, A (1992). Precast Concrete Frame Buildings: Design Guide. U.K.:
British cement Association

Future Build Ltd. Alltek Spray Plaster. Retrieved April 19, 2010 from
http://www.futurebuild.ie/alltek_spray_plaster.html

Health & Safety Authority. Statistics. Retrieved April 18, 2010 from
http://www.hsa.ie/eng/Statistics/Fatal_Injury/

International Coating Products
http://www.icp-alltek.com/en/standards.php

National Audit Office. (2005). Using Modern Methods of Construction to build homes
more quickly and efficiently. London: National Audit Office

NHBC Foundation. (2006). A Guide to Modern Methods of Construction. IHS BRE Press

Previous Projects Gemma Rice - Off-site Construction DT134/4
- Work Placement Project DT134/4
Appendices:


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Appendix A HAS Statistics (1 Page)

Appendix B Alltek Data Sheets (2 Page)

Appendix C Volclay Voltex Waterproofing (4 Pages)

Appendix D Double/Twin Walls System (1 Page)

Appendix E Precast Details (1 Page)


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