ROADS (Causes of deterioration)

Mr Ang Nam Piau asked the Minister for National Development and Communications (a) why so many roads have deteriorated during the recent heavy rains and what are the causes of the deterioration; (b) whether he is satisfied that road surfacing is carried out with proper technique and under adequate supervision; (c) how much money has been spent on the recent road repairs: and (d) whether and what steps he intends to take to minimise damage to the roads during heavy rains in future.

Dr Tan Eng Liang (for the Minister for National Development and Communications): Mr Speaker, Sir, damage to road pavements occur mainly in bus lanes, bus stops, intersections and tight bends. Observations indicate that oil spillage over a period softens and dissolves the asphalt in road pavements resulting in loss of its binding quality. With heavy rainfall, water easily penetrates the asphalt film surrounding the stone aggregate, stripping them from the road pavement thus aggravating the damage. In tight bends, the pavement surfaces are highly stressed by turning vehicles and tend to deteriorate faster than straight road sections. In all instances, heavy vehicles and high traffic volumes tend to hasten the deterioration of road pavements.

The Public Works Department exercises rigid quality control over the materials used for road surfacing and also undertakes strict supervision of the laying of the premixed asphalt concrete. Samples of materials used at every site are taken and sent to the PWD's engineering laboratory for testing. Sub-standard materials are rejected. Financial penalties are imposed for minor departures from the qualities specified. During road resurfacing works, PWD officers maintain standing supervision to ensure that compaction is adequate and the hot mix asphalt concrete has cooled down sufficiently before the road is opened to traffic. Premature opening to traffic will result in some loosening of the surface materials and subsequent deterioration of the road surface.

For the period April to October 1977, the average monthly expenditure on road patching was approximately $85,000. For November 1977, this rose to $113,000 and could be attributed to the heavy rainfall at that time.

In 1976, the PWD reviewed the existing asphalt concrete mix design used and experimented with various mix designs with the aim of improving on the asphalt concrete mix that will be used for future road surfacing. Since the beginning of the current fiscal year, an improved mix has been in use. A stiffer grade of bitumen has also been specified. The PWD is in correspondence with various research and highway authorities in other countries, obtaining useful information on how the problem can be solved. The Department has, in addition, initiated systematic scientific studies to determine precisely the factors affecting road surface deterioration.