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Following is a question by the Hon Chan Chi-chuen and a written reply by the Secretary for Transport and Housing, Professor Anthony Cheung Bing-leung, in the Legislative Council today (June 15):
Question:
It has been reported that several days before the visit by a member of the Standing Committee of the Political Bureau of the Communist Party of China Central Committee cum Chairman of the Standing Committee of the National People's Congress (the Chairman) came to Hong Kong last month for inspection, contractors engaged by the Highways Department applied glue to seal the joints of the slabs on the pavements along Tim Mei Avenue in Admiralty and Harbour Road in Wan Chai (joint sealing works). It is learnt that as the joints of the slabs had been sealed with glue, puddles of water appeared on the surfaces of the slabs when it rained (including the period during which the Red Rainstorm Warning Signal was issued last month), increasing the chances for pedestrians to slip and fall. In addition, large quantities of white powder on the surfaces of such slabs, allegedly originating from the glue, drifted with the wind from time to time, thereby causing inconvenience to pedestrians. In this connection, will the Government inform this Council:
(1) regarding the joint sealing works, of the area of pavements and expenses involved, the number of workers deployed, as well as the composition and quantity of various types of materials used;
(2) of the objective and effectiveness of the joint sealing works carried out by the authorities;
(3) prior to carrying out the joint sealing works, whether the authorities have taken into account the fact that the drainage capability of the surfaces of the slabs will be reduced by the use of glue; if they have, of the details; whether the authorities have reviewed the effectiveness of such type of glue following the rainstorm last month; if they have, of the details; whether such type of glue has been used in similar works by the authorities;
(4) as there are views that the joint sealing works were related to the security arrangements for the Chairman's visit to Hong Kong, and that the carrying out of such works reflected that the authorities blew up the visit and were too anxious about it, whether the authorities have responded to such views; if they have, of the details;
(5) of the policy bureaux and government departments that participated in making the decision to carry out the joint sealing works; whether the decision was related to the security arrangements for the Chairman's visit to Hong Kong; and
(6) regarding the various joint sealing works carried out by the authorities in each of the past three years, of the respective streets and roads involved, works implementation methods, expenses incurred, numbers of workers deployed, types of materials used and reasons for carrying out such works (set out in a table)?
President,
My reply to the various parts of the Hon Chan Chi-chuen's question is as follows:
Footpaths in Hong Kong are mainly classified into two types: footpaths paved with concrete and footpaths paved with paving blocks (paving block footpaths), as well as some footpaths paved with other materials (such as bitumen). The Highways Department (HyD) is responsible for the maintenance of footpaths under its purview. The HyD will conduct routine inspections and arrange appropriate maintenance work for footpaths to maintain them in good condition, hence ensuring the safety of users.
As regards paving block footpaths, one of the maintenance works conducted by the HyD is to consider whether to conduct paving block strengthening works in light of the actual conditions of the paving block footpaths.
The structure of paving block footpaths consists of four layers: the bottommost layer is soil; on top of soil is a layer of granular sub-base; a layer of sand bedding is laid on the layer of granular sub-base; and paving blocks are laid at the topmost layer. The gaps between paving blocks are filled by sand. In considering whether to conduct paving block strengthening works, the HyD will consider the conditions of paving block footpaths at different locations, including: pedestrian flow, whether underground soil is likely to subject to uneven settlement, whether illegal parking is frequent which increases the chance of settlement and damages, and whether they require frequent use of high-pressure water jets for cleansing (for example, paving block footpaths that are hygienic black spots), causing the loss of sand in the layer of sand bedding and between gaps, whether there are frequent growth of moss and grasses in the gaps between paving blocks due to environmental factors, and whether they are located in crowded areas which may be subject to risk of artificial damages, etc.
In general, the HyD will adopt the following two methods in conducting paving block strengthening works:
(i) The use of joint stabilising sealant (JSS) to seal up the gaps between paving blocks. This is the "joint sealing works" stated in the Hon Chan's question where glue was applied to seal the joints of the slabs on paving block footpaths. The JSS will be filled in the gaps between paving blocks, through which the blocks will be adhered together, thus reducing the loss of sand in the gaps between paving blocks, and thereby strengthening the stability of the paving block footpaths and reducing the chance of settlement.
The major component of JSS is a non-water-based epoxy, which is a chemical commonly found in the commonly-known "superglues". JSS is a light brown viscous liquid which is commonly known as glue. When compared with the glue for everyday use, the JSS has a higher viscosity. When using JSS in strengthening paving blocks, it is not necessary to excavate the existing paving block footpath. JSS is first filled in the gaps between paving blocks, and is left until the JSS is completely dried and hardened, during which the filled JSS needs to be appropriately protected. For instance, by temporarily covering it up using a curing material in the form of white powder called quartz sand for relatively large scale works, and by temporarily fencing off or temporarily covering it up by wooden or plastic plates for relatively small scale works, in order to avoid damages to JSS from the outside (e.g. being stepped on by pedestrians) before it is fully dried and hardened. Once the JSS is completely dried and hardened, it will fully fill the original gaps between paving blocks, and adhere the blocks together. The HyD will then clear up or remove the temporary protective measures.
(ii) The use of sand mixed with cement to construct the layer of sand bedding under paving blocks: this method aims to increase the strength of the layer of sand bedding under paving blocks, thus increasing the stability of paving block footpaths and reducing the chance of settlement. When carrying out the works, the existing paving block footpaths will first be excavated (including the sand bedding layer). The sand bedding layer will be constructed using sand mixed with cement, and the gaps between paving blocks will also be filled with sand mixed with cement to assist in stabilising the paving blocks. When compared with the use of JSS, this method involves more procedures and takes longer time to complete. Therefore, this method is usually adopted for relatively large scale reconstruction of paving block footpaths. However, in terms of sealing up the gaps between paving blocks and adhering paving blocks together, this method performs less effectively than the use of JSS.
Both of the above two methods in strengthening paving blocks do not affect the drainage function of footpaths.
Over the past three years (from April 2013 to April 2016), the HyD has conducted joint sealing works in 16 districts in Hong Kong (including Central and Western District, Wan Chai District, Kowloon City District, Kwun Tong District, Wong Tai Sin District, Yau Tsim Mong District, Sham Shui Po District, Islands District, Kwai Tsing District, North District, Sai Kung District, Sha Tin District, Tai Po District, Tsuen Wan District, Tuen Mun District and Yuen Long District). The works involve a total of 167 sections of paving block footpaths (details at Annex), with a total cost of works of about $13 million. Since these joint sealing works are mostly of relatively small scale and the number of works involved is large, the HyD is unable to provide information related to cost, manpower, etc. of individual joint sealing works.
As regards the joint sealing works conducted by the HyD in certain paving block footpaths in Admiralty and Wan Chai in early May this year, in order to meet the security requirements of the Police, the HyD conducted joint sealing works at six sections of paving block footpaths in the aforementioned locations. As the works area was relatively large, the HyD used quartz sand as curing material.
The aforementioned joint sealing works conducted by the HyD involved footpaths of a total area of about 12,000 square meters. The contractor deployed about 40 workers to conduct the works on the aforementioned footpath sections, and used about nine cubic meters of JSS. The HyD is still finalising the cost of works. The works were completed in mid-May this year, and the paving blocks of the footpaths concerned have been strengthened properly.
On May 10 this year (the day when the Red Rainstorm Sign was hoisted), after the HyD learnt from the internet and the media the situation of the sites concerned of the aforementioned joint sealing works, the HyD conducted a site visit to the concerned sites in the morning of the same day, and confirmed that the white materials flushed by rain was quartz sand. The HyD then conducted another site visit in the afternoon when it was less rainy, and confirmed that there was no ponding water on the concerned paving block footpaths. The HyD cleared up the quartz sand on the same day.
Ends/Wednesday, June 15, 2016
Issued at HKT 14:39
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