Designing out waste in high-rise residential buildings: Analysis of precasting methods and traditional construction
Introduction
The construction industry has always been a major producer of material waste. In Hong Kong, like most developed countries, construction waste has posed an important environmental issue. The construction industry in Hong Kong generates a huge quantity of Construction and Demolition (C&D) waste. In 2000 this amounted to 37,690 tonnes of waste per day, of which 80% was transported to public filling areas for reclamation and the remaining 20% was disposed at landfills. Hong Kong will soon be running out of both landfill spaces and public filling areas [1], and to help reduce construction waste the Hong Kong SAR government has recently introduced waste disposal charges.
There is currently a call for the construction industry to look for new ways of avoiding, minimizing, reusing, recycling and handling C&D waste [2], [3]. The Construction for Excellence Report of the Construction Industry Review Committee [4] recommended that construction waste should be minimized at source. This recognizes that if we are to significantly reduce the level of construction waste designers should consider waste reduction early in the design stage and throughout the design of a construction project.
Whilst construction waste is produced from a range of construction activities not all activities produce the same amount of construction waste. The majority of waste found on traditional construction projects is generated from the concreting process and the associated wet trade, which constitutes over 80% of the construction waste produced [5]. Concrete waste is generated mainly from both the direct work, steel from the cutting of reinforcement bars, surplus or spilled concrete, etc. and the temporary works needed for construction, timber boards from formwork and false work, bamboo from scaffolding, etc. Rework, the need to replace, remove or extend work previously considered completed also results in construction waste. One way of reducing construction waste is by precasting.
Precast construction in buildings includes precast concrete frames, precast flooring units and other components such as walls, floors, stairs and lift towers. More recent developments have focused on volumetric components, e.g. bathroom and kitchen modules which, used non-structurally, can be laden onto the floor slab as the structure is erected.
Precasting is considered to be an effective means to reduce the construction waste produced at site and is frequently recommended to replace cast-in-situ concrete wherever possible. This paper studies the potential of applying precast technique to minimize the level of construction waste produced at site and describes research carried out to investigate how techniques such as the modelling of information requirements, the Design Structure Matrix (DSM) technique, and other related methods may be used to evaluate the outcomes of design decisions. We conclude that the use of generic information models and the DSM technique can benefit the management of the design process for precast design in high-rise residential buildings and that these techniques can be used to evaluate design decisions and their impact on the level of construction waste produced.
Section snippets
Types of construction waste
Construction waste may be considered as the difference between the materials ordered and those placed or fixed on building projects [6]. It is important to distinguish between physical losses and monetary losses; under certain circumstances it may be cheaper to waste material than to attempt to prevent it. More importantly to examine the physical loss alone considerably understates the problem. Skoyles ER and Skoyles JR [6] classify material construction waste as natural waste (unavoidable
Precasting techniques
Precasting moves the construction process from on-site to factory production off-site and can reduce the construction waste produced on site [8]. Precasting techniques are highly applicable in high-rise buildings of standard and repetitive design, which is common in all metropolitan cities like Hong Kong. The Hong Kong Housing Authority of the Hong Kong SAR has been actively promoting the use of precast elements such as external facades, staircases, bathrooms, etc. in recent years. This
Advantages of precast technique
As the construction process is carried out off-site, precasting has several advantages over conventional cast-in-situ methods. Removal of the concreting process from site reduces labour intensive activities on site and provides a safer working environment. In-situ construction of areas with extensive amounts of architectural shape and profile are minimized. Less construction waste will be produced. Finishes e.g. tiles can be affixed in factories providing a cleaner, safer setting for tiling
Design process in high-rise residential buildings
The research reported in this paper compares the design process of a high-rise residential building using precast design with that used for conventional cast-in-situ construction methods. A detailed study on the design process of high-rise residential buildings has already been reported in a previous paper “Modelling Designers' Information Requirements to Reduce Waste in Repetitive High rise Building Construction, 2005” by Baldwin et al. [14]. The paper describes the design process for the New
Modelling the design process by using the Design Structure Matrix (DSM)
The authors have modeled the design process using IDEF diagrams and information modelling methods. A methodology known as the analytical design planning technique (ADePT) has been used to review the design process of a high-rise residential development of the New Harmony type. This technique which is based on a Generic Process Model for the detailed design process and a technique known as the Design Structure matrix (DSM) [16], [17], [18], [19], [20] was used. First the Generic Design Process
Modification to the Generic Building Design Model (summary) for precast technique
Based on the analysis on precast technique in Section 3 above, the Generic Building Design Model (summary) for cast-in-situ method was modified to analyse the differences in the detailed design process when precasting techniques are adopted.
Consultation with designers confirmed that the following additional information is required: (this analysis when completed formed the new model NHB (5))
- a)
A.0 External information requirements: feasibility report from precaster
- b)
A.0 External information
Analysis and discussion on the new design process for precast concrete
The NHB (5) model in Diagram 3 shows the design process of a high-rise residential building that has adopted precast technique. The 8 tasks of the greatest number of outputs identified are:
- a)
A.0 External inputs to design
- b)
A 1.2 Site layout plan
- c)
A.1.3.1.2 Ground floor setting out plan
- d)
A.1.3.1.3 Upper floor setting out plan
- e)
A.1.3.2.3 Upper floor spatial coordination G.A.
- f)
A.3.3.3.2 Precast floor slab design
- g)
A.3.3.3.4 Precast staircase design
- h)
A.3.3.3.6 Assembling details of precast elements
A.0 External
Conclusion
Prefabricating building elements off-site in precast design can effectively reduce generating construction waste on site. Standardization in design is a pre-requisite criterion for precast design and is most suitable for the design of high-rise residential buildings. Techniques that adopt information modelling such as ADePT have been proven to enable designers to visualize the complicated building design process and to increase efficiency by optimization. Feedback from designers at the start of
Acknowledgement
This research was undertaken at The Hong Kong Polytechnic University under the direction of the lead author. The paper was first published as part of the Proceedings from The International Conference on Asia-European Sustainable Urban Development, Chongqing, China, 4–6 April, 2006. Funding for this research has been supplied through the Research Grant Council of Hong Kong through allocation from the Central Earmarked Research Grant for 2004–2005 under Grant Number: PolyU 5157-04E. The authors
References (20)
- et al.
Analytical design planning technique: a model of the detailed building design process
Design Studies
(April 1999) - et al.
Reducing building waste on construction sites in Hong Kong
Construction Management and Economics
(June 2004) - et al.
Demonstrating waste minimization benefits
(2001) ‘Construction for excellence’ the report of the Construction Review Committee
(2001)Reduction of construction waste, final reports
(March 1993)- et al.
Waste prevention on sites
(1987) - Lemaire S, Chevalier J, Gvarrasino G. Decision and tool to choose building products introducing their environmental and...
- et al.
A guide for managing and minimizing building and demolition waste
(2001) - Chiang YH, Lok KL. Clients driving innovation: the case of public housing construction in Hong Kong. Proceedings of the...