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In Hong Kong, the majority of buildings are over 20-year old and most of them are facing different degrees of aging. An investigation on building population shows that about 13,000 private buildings were built in 1970's and the number is expected to increase to 22,000 in the next ten years. A recent inspection carried out by the Buildings Department (BD, 2010) on buildings aged 50 years or above states that about 26% of the investigated buildings exhibit different extents of defects and need to be repaired in the near future.
As is known, the traditional construction materials such as steel and concrete will show signs of deterioration in their life of use. For RC structure members, the reasons for reduction of loading capacity and ductility can be attributed to either the aging of materials such as deterioration of concrete and corrosion of steel reinforcement, or even the poor resistance to adverse environmental conditions or natural disasters. Other causes such as substandard workmanship during the construction process or improper use after the completion of the building will also lead defects to the structures. Even all of the above aspects are properly followed, for those concrete structures designed and constructed in accordance with early building standards, maintenance and upgrading works also need to be carried out to meet the more stringent requirements imposed by the existing design codes.
Although the deterioration problems can be overcome by demolition or reconstruction of buildings, a large amount of construction waste will be generated and the financial cost will be extremely huge. Over the past decades, building maintenance works have become more and more popular in construction industry. Given by BS 3811 (1984), "maintenance is a combination of any actions carried out to retain an item in, or restore it to an acceptable condition." By upgrading and retrofitting the aged buildings into a satisfactory condition, both the environmental impact of demolition works and cost involved of reconstruction could be significantly reduced.
Although ferrocement has been widely used in construction and repair works of RC structures, some shortcomings are observed by the recent researches. As Ohama (1995) indicated, the conventional ferrocement may easily form cracks because the cement mortar with low tensile strength has been used as the matrix of ferrocement. To improve the mechanical behavior and the durability of ferrocement, polymer-based ferrocement has been developed using latex-modified mortars instead of the ordinary cement mortar as matrixes.
It is quite important to understand the existing conditions of the building before any maintenance works are carried out. Referring to Section 4.4.3 of the Building Maintenance Guidebook (BD, 2002), a condition survey on the existing building should be firstly carried out. The main purposes of this condition survey are to understand the current conditions and degree of deterioration of the building then identify the causes of the deterioration and determine the appropriate repair methods. Other aspects, such as budget plan and preparation of contract are also base on the results of this condition survey.
One of the most important issues in the condition survey is to check the in-situ concrete strength of the existing building. Under Section 63(1) of the Buildings (Construction) Regulations, "when the concrete is considered form visual inspection to be suspect or when the specified grade strength has been deemed not be attained under regulation 59 the compressive strength of the concrete in the structure may be determined by drilling a sufficient number of cores form the concrete at suitable locations." Detailed standards and requirements are stated in Section 63(2), (3) and (4) of the regulation.
Health and safety issues are always the most concerned aspects in all kinds of construction works. As the maintenance technique varies, different strategy may have different in site requirements and health / safety impacts. For example, if the working site located in a crowed urban area, welding should be avoided as the spark and glare generated will either pose a potential risk in fire safety or cause a nuisance to the public. Therefore, a detailed assessment on health and safety aspects should be carried out based on the condition survey report prior to the determination of maintenance strategy.
Financial cost may be probably the most determining factor in choosing the maintenance strategy. Although those newly developed maintenance techniques provide a lot of attractive benefits, the costs are raised accordingly. Not only the cost of material itself, but also some potential aspects such as logistics fee, rental of equipment, salary of workmanship and etc. As the financial cost significantly affects the selection of maintenance technique and its further performance, a wise and clear budget assessment is definitely needed in help of seeking the most cost-effective technique.
"Prevention is better than cure." According to Ho et al. (2008), the differences in building management systems caused most of the variations in building health and safety conditions rather than building design. It is a responsibility of the building owners or owners' cooperation (OC) to maintain and make sure the building is in a safe state for both the residence and the public. Some legal provisions and statutory orders have been made to define this responsibility,
Statutory Orders issued by the Buildings Department also impose the investigation and repair responsibilities on the building owners or OC. Under Section 26A of the Buildings Ordinance (BO), an order in writing will be served upon building owners or OC to engage an Authorized Person to carry out investigation on the building where early signs of building defects are detected.
To meet these requirements, some proactive approach has been made by the government to maintain the buildings under a safe condition. A preventive maintenance scheme called Building Safety Inspection Scheme (BSIS) was introduced by the BD in 1997. It requires the owners of the building to engage building professionals to carry out regular systematic inspection to prevent danger from arising. The Mandatory Building Safety Inspection Scheme (MBSIS) was put in place in 2007 to legislate the obligation of building owners to carry out preventive maintenance on their buildings.
Previous study carried out by other researcher showed that about 90% of the building owners and OC thought that public education the most essential and effective means of improving the state of buildings in Hong Kong so as to prevent them form deterioration (Chan, 1994). Besides promoting the preventive maintenance schemes, the government and related departments have also issued a lot of posters and advertisements both in newspaper and television to notify the public the obligations of the building owners and OC.