Housing Authority Research Fund
Project Title : Developing Innovative Precast Systems, including Application of Structural Lightweight Aggregate and Rapid Hardening PFA Concrete, for Economic Production (ref: CB20030026)
Summary of Report
Research Provider : City University of Hong Kong
Project Coordinator : Dr. Tommy Y. Lo Department of Building and Construction City University of Hong Kong
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2006
Paper: HARF Project by City University of Hong Kong
Project: Developing Innovative Precast Systems, including Application of Structural Lightweight Aggregate and Rapid Hardening PFA Concrete, for Economic Production
1. Executive Summary
In June 2003, the Housing Authority Research Fund commissioned the City University of Hong Kong to undertake a research study on the feasibility of using structural lightweight concrete (LWAC) in precast systems for high-rise housing block construction. The study commenced on 23 June 2003 for a period of two years.
As structural lightweight concrete is typically 25% to 35% lighter than ordinary concrete yet exhibits a compressive strength for the same order. LWAC can offer design and construction flexibility and savings in the overall project cost. Compared with the NWC, LWAC has better thermal and sound insulation, resistance to fire, impact and cyclic loading, and reduced micro-cracking at cement/aggregate interface. However, structural LWAC has not been widely used in Hong Kong.
This study has examined the properties of LWAC, mix design, design standards, relevant codes of practice and the current use of precast concrete construction for high-rise structures in both Hong Kong and overseas. The study has also reviewed the precast techniques being used in the Hong Kong Housing Department’s high-rise domestic housing blocks. Prototype design and test methods were proposed and laboratory testing and full scale trial were carried out for design verification and modification.
In this study, the lightweight expanded clay aggregate (Leca) was used to produce the lightweight aggregate concrete. 60 trial mixes including PFA were made and tests on the main concrete properties were carried out. According to the strength results, the mixes were categorized into Grade 30 and Grade 35.
This study concluded use of PFA in precast concrete is not recommended for reasons of cost, technical and practical considerations.
With the exception of shrinkage and elastic modulus, the engineering properties of LWAC including strength, workability, bonding strength and water permeability are not obviously different with those of NWC. The flexural and shear behaviors of the reinforced/precast composite slab prototype have been provided in stable and reliable performance and complied with the theoretical calculation. The LWAC can meet the requirements for structural applications.
This report presents the test results and findings of the testing programme, which forms the basis for further application at project level. This report provides recommendations of adopting structural LWAC in precast systems as an alternative to normal weight concrete for high-rise structures.
2. Final Results and Findings
2.1 Properties of lightweight aggregate concrete compared with normal weight concrete