4Chapter Construction

Introduction

Construction Technology Programme

Development and Implementation of Key Programmes

Future Direction of Construction Technology

Authors:

Er. Lau Joo Ming

Er. Teh Poh Suan

Technology

1. Introduction

The HDB’s mechanisation programme evolved out of the need to meet its accelerated building programme in

the 1970s and early 1980s. The development of construction technology since 1960s will provide a good backdrop.

In the 1960s, HDB’s contractors were mainly small operators with low paid-up capitals. The professionalism in site management as well as the level of technology used tend to be low. The construction industry then employed the traditional labour-intensive methods of cast-in-situ construction using timber forms, resulting in the need for a large pool of skilled carpenters. The building was constructed with reinforced concrete structural frame and solid blocks as infill wall. Plastering work using cement mortar

for the finished surfaces was common. For steel reinforcement work, bending and fabrication of steel rebars were all done manually and the only tools used were the cutters and bar-bending table. For concreting, the one bag mixers were used and transportation of concrete was carried out by buckets.

At that time, the HDB’s building construction rate was still low at about 10,000 units annually. Moreover, labour and materials were also readily available. Therefore, the contractors were able to produce the buildings with acceptable standards and costs, despite their relative backwardness in their construction technology then.

In the 1970s, the increase in building programme had doubled that of the 1960s. This gave rise to the high demand for skilled workers which were a limited resource then. At that time, the private sector also experienced a construction

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The construction technology programme could then be seen as a major effort by HDB to increase the capacity of the

industry through the use of more mechanised methods of construction. This was necessary if HDB was to satisfy the long list of applicants for the flats. Besides this, the other objectives of the programme were:

i. To increase workers’ productivity;

ii. To reduce the dependence on foreignworkers in line with government policy;

2. Construction Technology Programme

building boom. Many Malaysian workers returned to Malaysia due to economic expansion there. All these resulted in a severe shortage of workers and the direct impact was delay encountered in many of the HDB projects.

In order to overcome these problems to meet the target of building programme, one of the approach was to upgrade construction technology through mechanisation programme.

iii. To improve the image of the construction industry in order to attract more workers; and

iv. To improve construction quality.

The approach then was based on three basic concepts:

i. Transfer work off site;

ii. Mechanisation and standardisation; and

iii. Work in phases.

To achieve the set objectives, key programmes were derived based on the three basic concepts. The key programmes were:

i. Use of Mechanised formwork systems;

ii. Upgrading of concreting / material handling machinery;

iii. Upgrading of steelbending trade;

iv. Adopt buildable design;

v. Use of small equipment / handy tools and improved work processes; and

vi. Use of precast components.

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3.1 Use of mechanised formwork system

Metal formwork was introduced in the construction of public housing structures since 1974. This was part of the drive to upgrade construction technology and to reduce the demand on skilled carpenters and plasterers.

This method of construction uses the simple concept of assembling small panels of metal moulds of various dimensions to form the require shapes and sizes of the structural elements in the building. The sizes and weights of these metal moulds are carefully designed to facilitate easy handling and transfer from one place to another manually. No special skill, except for the initial period of familiarisation, is required to join and dismantle the metal moulds. Metalforms thus enabled the industry to replace skilled carpenters who were then in short supply with

By the late 1970s, the use of metalforms had clearly shown a construction speed faster by one month in completion time when compared to timberform contracts. Gradually, HDB increased the use of metalforms in more HDB projects. Steps were taken to ensure that contractors’ supervisors and workers were quickly trained in the various aspects of metalform construction. Training were conducted and site construction manuals were produced to educate them on the assembling and dismantling of formwork, site organisation, storage, transportation and maintenance of formwork. Such measures helped to achieve a rapid and smooth switch from

Figure 1: Standard modular metal-forms were used in the construction of public housing projects.

3. Development and Implementation of Key Programmes

unskilled workers. At the same time, there was reduced need for skilled plasterers who were also then in short supply. This was because the metal form formwork system produces structurally straight alignments with flat, smooth finishes that require little or no plastering.

During that time, most of the contractors had very low capital reserves. They were reluctant to buy their own metalform sets as the capital cost for the purchase of metalforms was very high. With due consideration on the high capital cost that contractors need to incur upfront, HDB decided to set up a formwork hiring operation system to rent out these metalforms to contractors.

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5••timberforms to metalforms. By 1984, dwelling units constructed using metalforms accounted for 30% of all dwelling units completed for that year.

With more metalforms stock under its management, warehouses were set up in various parts of Singapore to store the array of formworks not in use. In 1982, a main warehouse and workshop costing $3 million was set up in the HDB Industrial Estate at Defu for the cleaning and maintenance of used metalforms after each contract. The latter ensured that the quality of finishing of the buildings achieved by the formwork was maintained.

By 1993, all building contracts were constructed using metal formwork. The introduction of prefabrication technology however changed the relevance of site metal formwork. With precast technology, the usage of metal formwork was reduced to joints of precast elements like walls. Offering benefits of higher construction productivity, the precast technology has resulted in a decreasing reliance on metal formwork over the years. With this, HDB’s metalform warehouse ceased operation on 30 December 2000. The contribution of metal formwork to the industry will certainly leave a mark in the construction history of HDB.

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In the 1960s, the concreting trade used the one-bag mixer for mixing of concrete and bucket for transportation of concrete. The whole process was laborious and required a big group of concretors. The 1970s saw a building rate requirement which was more than double the rate of the sixties and a scarcity of skilled workers. To cope with this problem, simple machineries were introduced to the worksites. For the concreting trade, two-bag mixers were introduced to replace one-bag mixers and wheelbarrows were used

3.2 Upgrading of concreting / material handling machinery

The first set of heavy machinery introduced were batching plants, truck mixers and concrete pumps to replace the old concrete mixer, dumper and wheelbarrows in the concreting trade. For each category of machinery or equipment introduced, the machinery manufacturers/suppliers were required to provide the necessary training for supervisors and operators on the use of the technology and to provide the technical backup service.

Figure 2 : Simple machineries such as bag concrete mixer, bucket and dumper were used in 1960/70s.

to replace bucket for the transportation of concrete.

The replacement of manual labour with mechanised methods was done gradually to ensure that the following 3 main criteria for introduction of mechanised methods were set:

i. It must be affordable by contractors;

ii. It must be able to create a big impact in improving the contractors’ work and in reducing labour requirements; and

iii. It must be machinery that site workers can adapt to.

The initial efforts to mechanise the concreting trade were not enthusiastically taken up by the local contractors. They were reluctant to buy recommended machinery due to the initial heavy capital investment and the uncertainty of earning the required rates of return on their investment. To overcome this reluctance, the HDB introduced two major incentive schemes to assist the contractors to mechanise.

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The first scheme was the “Interest-free Financial Scheme” started in 1981. The HDB contractors were offered interest-free financing loans to purchase selected and approved machinery and equipment. Loans of up to $1 million were given for every $12 million worth of contract. Repayment of the loans was spread over the entire contract period of about seventeen months so as to reduce the financial burden of the contractor. The scheme improved the cash flow positions of the contractors and received very favourable response. The second scheme was the “Core-contractor Scheme” introduced in 1982. It assured contractors with good performance records of a certain amount of work for a three-year period, this period being the average write-off period for most construction machinery and equipment.

Figure 3: Heavy machineries such as concrete mixer truck, concrete pump and automatic concrete batching plant were introduced since 1980s.

The two incentive schemes saw a fair measure of success in attracting contractors to purchase the initial concreting machinery recommended. In turn, these machinery succeeded in speeding up the concreting operations and increasing the productivity of the concretors. In most cases, concretors were able to carry out 50% more work with these machinery within the same period as before. This success paved the way for the introduction of the next series of machinery for trans-portation and materials handling. These were rough terrain forklift, the passenger and material steel hoist and the crane.

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The rough terrain forklift and the material steel hoist enabled more efficient handling of construction materials. The introduction of bigger and higher capacity cranes in a way facilitated the introduction of precast components, prefabricated reinforcement and mechanised formwork system.

As part of its continuous effort in upgrading the construction technology in the industry, HDB pioneered the use of Automated Building Construction System (ABCS) in the construction of HDB Hub and the first 40-storeys HDB residential project located at Toa Payoh. The objectives of such initiative were three folds. They are:

a. To adopt the latest state-of-the-art ABCS in improving the site labour productivity,

Figure 4: Automated Building Construction System known as “The New Smart System” was used in the construction of the HDB Hub at Toa Payoh.

reducing the labour content and achieving high quality public housing;

b. To have technology transfer that is beneficial to HDB and the local industry players; and

c. To take lead in introducing automation to construction industry.

The HDB Hub development project was designed and built by the contracting team of Shimizu Corporation, RSP Architects Planners & Engineers (Pte) Ltd and Squire Mech Pte Ltd. The project cost was $450 million with a main contract period of 42 months starting from 1 June 1998 to 30 November 2001. High level of precast was used and made it ideal for ABCS implementation. The ABCS used in HDB Hub project was known as New SMART System. It has an all weather protection roof that allowed workers to continue working during wet weather. The roof was about three storeys higher than the working level and is able to climb automatically through synchronised climbing hydraulic jack system. This mechanised construction method enabled the contractor to achieve 8 days per floor work cycle.

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The Toa Payoh Redevelopment Contract 30 (TPRC30) comprised of 4 blocks of 40-storey tower block and 1 multi-storey carpark, providing 926 dwelling units. Two stage tender was called and the successful tenderer was Penta-Ocean Construction. The project was awarded in October 2001 with a contract value of $71.6 million. The construction period was 35 months for block 145 with ABCS and 40 months for the other three blocks with no ABCS. This was a tangible benefit of deploying technology on an industry whereby it is manpower intensive and where costs, especially those related to productivity and wastage are difficult to control. About 90% of the building elements were precast components. These include the newly introduced full size precast wall panel integrated with precast beam to eliminate crack lines on finished wall surfaces. Other precast components were columns, beams, slabs, household shelters and bathroom units. The project achieved a buildability score of 89, 8 points higher than a typical HDB project in 2001.

Figure 5: The Automated Building System provides an all weather protection and safe environment for the workers.

The ABCS system proposed by Penta Ocean was a simplified version of “Faces”. “Faces” was developed by Penta Ocean for use in the construction of fully prefabricated steel structure. It was used in Japan for the construction of high rise building by providing an all weather shelter through its temporary roof and sidings. Material conveyor equipment was installed inside similar to that of factory production line. As the construction of each floor is completed, the system will be lifted up to the next floor by an automatic control system. The system incorporated fully automated conveying and original self lifting technology.

The ABCS system used in TPRC30 comprised of a temporary roof supported by four masts. The mechanized materials lifting system was made up of two computerized cranes which had automatic delivery capability where the material will be transported by the shortest way that is calculated by computer program to the installation point.

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3.3 Upgrading of steelbending trade

The introduction of high capacity cranes to the sites for material handling also resulted in several benefits for the steel bending trade. Until the 1970s, the means of hoisting steel bars was by mechanised winches. The drawback with winches is their low capacity per lift. Also, they are fixed in only one position of a building. With the introduction of high capacity cranes, steel bars and meshes could be transported vertically in large volume at faster rates and placed exactly where they are being used.

Before prefabrication was introduced, steel reinforcement was individually designed, detailed and then taylor-made on site as there was very little standardisation of detailing and therefore, resulted in time consuming and laborious work. Since early 1970s, welded fabric meshes were used extensively in HDB projects to increase the labour productivity of steel bender in the laying of reinforcing bars for concrete floor slabs.

The implementation of the computerized material management system consistently controls building components, beginning with the delivery through installation on site.

The overall effect of using the ABCS system translated to more efficient use of manpower, a heightened comfort level in working conditions and shorter construction periods. High and consistent quality standard had been assured by precast components and improvements of work environment. The safe working environment created with less physically demanding work exerted on the workers.

The development of ABCS system was timely for the industry and augered well for the future of construction with the efficient use of resources as enhanced by cutting edge advantage conferred by the ABCS technology. As a result construction of future HDB estates will be different and technology driven. A new revelation has been tried out in the construction arena by HDB with the use of Automated Building Construction System in the construction arena.

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Figure 6: In the 1980s, the use of welded meshes and pre-fabricated cages helped to improve the site productivity.

In the 1980s, the use of welded meshes was extended to reinforced concrete wall, parapet and other smaller components such as stiffener, coping, kerb and etc. The prefabrication concepts were further extended to the beam and column reinforcement.

In the late 1980s, prefabricated beam and column cages were developed and implemented for HDB projects. A “Traffic Light” system tags the beam with different colours – green, yellow and red. The beam reinforcement cages were then installed according to the traffic light sequence – green first, yellow and then red.

Welded steel reinforcement cages are fabricated by machines in the factory and transported to site before being hoisted by cranes to the top of the building. This eliminates site fabrication of mild steel cages and speeds up the laying of the reinforcements. As a result of these changes in materials and operations, the number of steel benders needed has been reduced by about 30%. ••11

Figure 7(a): The cut and bend operation at site resulted in high wastage of reinforcement. HDB initiative of introducing pre-cut and pre-bend from factory had helped to improve trade production and reduce wastage.

Presently, there are three main welded mesh companies supplying the prefabricated reinforcement to all HDB sites. Over the years, they have developed a close partnership with HDB and rendered invaluable technical assistance and support, especially in the development of prefabricated cage reinforcement and automatic CAD detailing of mesh. To facilitate drafting and mechanisation, the series of standardised cages were given a code. These are stored in the CAD system’s database, when the code is keyed into the system, the cage details will automatically appear. This automatic CAD detailing of mesh has improved the operation efficiency of the factory through sharing of drawings electronically. This allows the suppliers’ staff to perform the scheduling without any manual recording. It resulted in 50% saving in time and manpower. This system

revolutionalizes the industry’s practice by making use of IT to improve the factories’ productivity and efficiency.

To promote the use of prefabricated reinforcement technology, a Prefabricated Reinforcement Task Force (PRTF) was set up involving the HDB representatives and the main suppliers of welded meshes. The PRTF actively carried out research studies on potential areas for prefabrication, reviewed the detailing and standardisation to facilitate production and installation of prefabricated reinforcement at site and provided design guide on the use of prefabricated reinforcement. The recent developments in prefabricated reinforcement were the flat slab F-series meshes and pilecap meshes. Today, we have achieved 90% implementation of prefabricated steel reinforcement in our work sites.••12

Figure 7(b): The cut and bend operation at site resulted in high wastage of reinforcement. HDB initiative of introducing pre-cut and pre-bend from factory had helped to improve trade production and reduce wastage.

All reinforcement supplied to HDB sites had either been cut and bend at site or pre-cut and pre-bend in a factory, however since April 1998, it has been formalised only to the latter. This move by HDB is mainly to increase the productivity and to reduce reinforcement wastage of this trade. At the same time, to free the site space previously used for cutting and bending of steel for other purposes e.g. precast components storage. The size of space required for steel cutting and bending is typically 300 square metres.

To ensure good quality of pre-cut and pre-bend reinforcement, HDB established a set of pre-qualification criteria to qualify any cut and bend steel operators who are interested in providing their service to HDB contractors. The approved operators will subsequently be incorporated in HDB’s List of Approved Materials and Suppliers.

Through surveys conducted on HDB sites and in the factory, it was found that the shift of cut and bend steel on-site to the factory increased the productivity from 0.06 ton/man-hour to 0.375 ton/man-hour. This worked out to a 525% gain and it was basically due to the higher level of mechanisation in the factory. As for wastage level, it reduced from an average of 10% at site to less than 2.5% at factory. This was mainly due to the more quality-controlled environment in the factory.

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3.4 Adopt buildable design

Buildable design is about ease of construction and is characterised by simplicity, standardisation and single integrated elements. HDB had been promoting buildable design long before “buildability” became an industry buzzword. HDB’s initiatives to promote buildability design began with the use of modular coordination and standardisation of elements, more recently through the greater use of prefabrication. There will be more elaboration on modular coordination in the following paragraphs while the use of prefabrication technology will be dealt with in separate chapter.

Modular Coordination and Dimensional Coordination are often used interchangeably in the building industry and there seems to be confusion among building professionals in the use of the terms. However, there is a subtle but Important difference in the definition of the two terms.

Dimensional Coordination is the use of a range of interrelated dimensions for component sizing. It does not make use of any modulus but attempts to provide an adaptable range of components which will combine to give any required dimension. For example, dimensional coordination is always used in prefabrication

Tabulated above is a cost comparison between reinforcement cut and bend on site and at the factory.

construction in a particular project to ensure all components fit together. Those components however, may not be suitable for another design. Hence, dimensional coordination in general terms has difficulty in achieving industry wide benefits.

ITEMS ON-SITE ($/TON) AT FACTORY ($/TON)

Materials 509 509

Labour 50 35

Wastage 40 10

Transport - 15

General O/H - 25

TOTAL 599 (minimum) 594

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Modular Coordination is dimensional coordination in which buildings and components are sized in terms of a basic unit or module. This module therefore, must be small enough to provide the necessary flexibility in the design of various buildings for various purposes, as well as large enough to promote simplification of the number of sizes for various components. In addition, in order to ensure dimensional coordination on both national and international levels, the

basic module must be internationally accepted. The 100mm module or 1M seems to meet the two principal requirements and therefore has been adopted by most countries as the basic module. From this basic module, multi-modules are derived, say 3M, 6M etc and building dimension could be based on multiples again of the multi-module. Building components, depending on their size ranges, could make use of multi-modules, the basic module, or even sub-modules i.e. a fraction of the basic module e.g. 0.5M. It is thus potentially possible to derive components which can be used on all building projects.

Multi-modules have been introduced for use in the planning of the main dimensions in a building. They have been prescribed for both the horizontal and vertical dimensions. Most countries working with modular coordination have agreed on using a multi-module of 3M for horizontal planning. Vertical multi-modules of 3M and 2M are used.

The basic aim of modular coordination is to improve productivity in the building industry, particularly for multi-storey repetitive structures. Modular coordination aims to guide the sizing of components so as to reduce as much as possible the need to further trim and shape these to fit together in construction. Convenient and speedy mass production of building components in factories and assembly at the construction sites are therefore possible. The principal objective of modular coordination is to assist the building industry and its associated industries, through standardisation, to improve workmanship and reduce wastage of labour and materials.

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Figure 8: Modular system is adopted for both horizontal and vertical dimension. This is illustrated through the

floor plan, elevation and section shown.

The aims of modular coordination are thus as follows:

i. To facilitate cooperation between building designers, manufacturers, contractors and authorities;

ii. To enable buildings to be so dimensioned that they can be erected with standard components without undue restriction on freedom of design;

iii. To permit a flexible type of standardisation, which encourages the use of a limited number of standardised building components for the construction of different types of building;

iv. To optimise the number of standard sizes of building components;

v. To encourage the interchangeability of components; and

vi. To simplify site operations by rationalising the setting out, positioning and assembly of building components.

HDB has adopted Modular coordination since 1973. The modular system adopted by HDB is based on it’s building structure which is basically a frame system. The basic module is 100mm or 1M. A multi-module of 3M is use for horizontal planning and 2M for vertical dimensions. 2M modules for vertical dimension is favoured as it permits more gradual adjustments to floor heights, sill heights, door and window heights. This is illustrated through a sample floor plan, elevation and section as shown.

FLOOR PLAN OF TYPICAL UNIT

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Figure 9: Standard door sizes used in HDB projects.

With this modular dimension, it is clear how the various components of an apartment unit join together. The wall panels of 9X3M width can be filled in with a 6X3M window and 3X3M brick horizontally. In the vertical plane, the floor to floor module of 14X2M can accommodate a 11X2M door height and a 2X3M deep beam or a 5X2M window sill with a 6X2M window height and a 2X3M deep beam.

The next stage after defining a modular coordinated dimension is the process of standardisation of the various components. This is a logical progression as room sizes as determined by their length and width are limited by the minimum requirements for usage and maximum for economy. This is translated into a few wall panel sizes.

HDB has achieved this and the sizes of bricks, doors, windows, beams and columns are standardised. Table 1 tabulates a sample of the sizes in use and this is illustrated in the following.

The corresponding modulation for the building components are as follows:

i. 9M to 21 M in 3M increments for door widths and 2M for height;

ii. 6M to 30M in increments of 3M for window widths and 2M for height;

iii. 3M and 2M for brick length and 1M for height;

iv. 3M for beam and column with an alternative of 2M; and

v. 1M with a sub-module of 0.25M and 0.5M for floor slab thickness.

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Modular coordination is the way to improve the building industry. HDB has implemented this concept progressively since 1973 and have reaped the benefits that it afforded. This is reflected in HDB achieving it’s objective of completing 700,000 apartment units within schedule and budget.

a) The premixed mortar system is a pneumatic conveying system that delivers the mortar powder in a dry state to the point of application at height ( maximum 100 metres or approximately 35 storey ). This system replaced the traditional method of site preparation of wet mortar which was labour intensive, messy and often resulted in inconsistent quality. The new system redefined the process of conveying and mixing mortar for plastering, brick laying and tiling works. The benefits of such system include improved productivity, reduced wastage, improved site

3.5 Use of small equipment /handy tools and improved work processes

Besides the big machinery, HDB also promoted the use of small equipment and handy tools to further improve construction productivity to meet the demands of public housing. HDB had explored and adopted various handy tools such as mini hacker for concrete, power drill, grinding tool, power cutter, welding equipment and etc. Generally these tools have helped to facilitate the works and shorten the construction time. Other significant initiatives that HDB has successfully introduced include but not limited to the followings:

Table 1. Typical standard size of building components.

S/N BUILDING COMPONENT STANDARD SIZE (NOMINAL)(mm)

1 Brick 300X100X100, 200X100X100

2 Window1200X1200, 1500X1200, 1800X1200. 2100X1200

3 Door 900X2200, 1200X2200

4 Beam 300X600, 200X600

5 Column 300X900, 300X1200, 300X1500

Figure 10: Premixed mortar system redefines the process of conveying and mixing mortar.

housekeeping and consistent good quality mortar. From the trial at four HDB sites, it was found that the operating cost of this premixed mortar system was 25% lower than the existing practice.

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b) The chemical spray curing system uses chem-ical compound rather than water to cure the fresh concrete. After the concreting of floor slab, there is a need to go through a process called “curing” to allow the fresh concrete to set. Conventionally, gunnysacks were placed on top of the slabs and water was sprayed on them frequently to keep them moist.

With the introduction of chemical spray curing, the contractor only need to spray the slab once

Figure 11: Chemical curing compound is used to cure fresh concrete in all HDB projects.

to achieve the same effect. The benefits included a productivity gain of 13 times and manpower cost saving of about 10%.

c) The mechanised spray painting system was introduced for internal painting in May 92. It replaced the conventional labour intensive painting process. Mechanised spray painting helps to achieve a productivity gain of 700% and a manpower cost saving of 26%.

Figure 12: Mechanical spray system helps to improve the trade productivity.

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d) Construction of ground beams without propping. It has been the industry practice to provide props to support formworks during the casting of ground beam. Through our comprehensive R&D works in concrete technology and metal formwork, it was found that the assembled metal formwork is strong enough to sustain the self weight of ground beam and formwork as well as allowable construction load.

Therefore, the ground beams could be constructed using metal formwork without props during casting. This has resulted in substantial savings in manpower and material besides a higher productivity achieved.

Figure 13: Continual research and development and testing works enabled HDB to explore a faster and cheaper way in constructing ground beams without propping.

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e) Removal of re-propping to beams/slabs for typical floor. With the use of grade 40 concrete, the early concrete strength developed is able to sustain the construction loads without causing much deflection during construction stage. Therefore, the requirement on re-propping of the typical floor beams and slabs was removed. This had resulted in potential saving of $2.2 million per annum.

Figure 14: The use of higher strength concrete enables the removal of propping requirements. The left photo show the propping in place and the right photo show the new practice with no propping.

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f) The ideal roof which sees an innovative f) The ideal roof which sees an innovative f) The ideal roofuse of precast ferrocement roof slab that serves to insulate intense heat from the sunlight and to drain the rain water away from the main roof of the building. The new system totally removes the need for additional waterproofing membrane on the roof. With this, the problem of stains on building facades associated with the use of waterproof membrane is also solved. The new system has simplified the overall roof construction work process and resulted in 50% increase in site labour productivity for the roof construction. Most importantly, it avoided the recurring cost for maintaining the waterproof membrane periodically.

The HDB’s contruction technology programme has achieved its objectives. Today, HDB is playing the leading role in

the area of buildability design and construction technology. With the integration of buildability and prefabricated components in its building design coupled with productive and innovative methods of construction, significant increase in construction productivity was achieved. The overall site labour productivity for public housing stood at 1.0 m2 per manday, more than 3 times that of the private sector.

More can be done to achieve even higher productivity level and shorter construction time. Dry construction methods and automated construction system are methods to further reduce labour usage, shorten construction cycle time and achieve higher quality. HDB will continue to be at the fore front of construction technology, constantly promoting the use of advance construction methods and machineries.

Figure 15: The ideal roof is dual purpose. It provides the heat insulation and drains away rain water. It is relatively maintenance free.

4. Future Direction of Construction Technology

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BluePrints for Successful Public Housing Development

BluePrints for Successful Public Housing Development