Owing to the shortage of space for land reclamation in Hong Kong, it is difficult to dispose of tons of masonry waste generated daily from construction activities. Adoption of recycled aggregate from concrete waste thus becomes a burning issue. The Hong Kong SAR Government has set up a recycling plant in Tuen Mun Area 38 aiming at turning concrete waste into recycled aggregate with a practice note and specifications issued for controlling the quality of recycled aggregate. However, the use of recycled aggregate concrete to high grade applications is rarely reported because of its poorer compressive strength and high variability in mechanical behavior. This paper proposes a new approach in mixing concrete, namely "two-stage mixing approach (TSMA)", intended to improve the compressive strength for recycled aggregate concrete and hence lower its strength variability. Based upon experimental works, improvements in strength to recycled aggregate concrete were achieved. The effect can be attributable to the porous nature of the recycled aggregate and hence the pre-mix process can fill up some pores and cracks, resulting in a denser concrete, an improved interfacial zone around recycled aggregate and thus a higher strength when compared with the traditional mixing approach.

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With a rising tide of adoption of recycled aggregate (RA) for construction, investigation on ways to improve the quality of RA has been overwhelming. The adoption of RA brings benefits including savings in the limited landfill spaces and the use of natural resources. However, the poorer quality of RA often limits its utilization to low grade applications such as sub-grade activities, filling materials and low grade concrete. The major reason that affects the quality of RA is the large amount of cement mortar remains on the surface of the aggregate, resulting in higher porosity, water absorption rates and thus a weaker interfacial zone between new cement mortar and aggregates, which weakens the strength and mechanical performance of concrete made from RA. This paper attempts to study three pre-soaking treatment approaches; namely ReMortar HCl , ReMortar H2SO4 and ReMortar H3PO4 in reducing the mortar attached to RA. The results show that the behaviour of RA has improved with reduction in water absorption, without simultaneous exceeding the limits of chloride and sulphate compositions after the treatment. This work has also compared the compressive strength, flexural strength and modulus of elasticity of concrete made from the approaches, which shows marked improvements in quality when compared with those using traditional approaches.

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Environmental problems have been considered as a serious situation in the construction.Waste management is pressing harder with the alarming signal warning the industry.Reuse, recycling and reduce the wastes consider as the only methods to recover those waste generated; however, the implementations still have much room for improvement. This paper reviews the technology on construction waste recycling and their viability. Ten material recycling practices are studied, including: i) asphalt; ii) brick; iii) concrete; iv) ferrous metal; v) glass; vi) masonry; vii) non-ferrous metal; viii) paper and cardboard; ix) plastic; and x) timber. The viable technology of the construction material recycling should be provided an easy reference for future applications.

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The increasing awareness of waste management concerns from construction and demolition waste has led to the development of waste management as an important function of construction project management. The Hong Kong government started employing the implementation of a waste-management-plan (WMP) method for all construction projects in 2003. During the trial period, the government received different version of feedback from the industry. It also came out that detailed descriptions of waste management procedures in the WMP method largely affect the productivity of companies. This paper investigates the effectiveness of the existing implementation of the WMP method in the Hong Kong construction industry. A questionnaire survey and structured interviews were conducted. The result showed that "Propose methods for on-site reuse of materials" and "Propose methods for reducing waste" are the main benefits gained from the implementation of the WMP method. However, "Low financial incentive" and "Increase in overhead cost" are considered as the major difficulties in the implementation. From that, "Use of prefabricated building components" is considered as the major effective measure to encourage the implementation of the WMP method.

The increasing awareness of environmental impacts from construction wastes has led to the development of waste management as an important function of construction project management. Various approaches for managing construction wastes have been developed in the existing research works and practices, and these works can be grouped largely into three areas: waste classification, waste management strategies (avoiding waste, reducing waste, reusing waste and recycling waste), and waste disposal technologies. Nevertheless these approaches give less attention to the management of waste handling process during construction. Form their generation to final disposal, construction wastes will pass through a number of processes where various measures will be used to handle with wastes. It is considered that proper flow of these handling processes can improve overall waste management effectiveness. This paper extends the existing research studies to examining the process of waste management during construction on site by using mapping presentations. This examination is undertaken through analyzing six cases selected in Hong Kong construction.The examination leads to developing a waste management flow model (WMFM), which is designated to incorporate the good operations embodied in the existing practice and function as a standard model of waste management procedures. The model has been tested in two projects. 2 The model can provide an alternative tool assisting in planning waste management procedures on site. It also serves as a vehicle to compare the waste management practices between construction sites, thus both good practices and weak areas in managing wastes can be found.