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The principal function of edge courses is to form a retaining structure with concrete bedding and haunching to resist sideway movement arising from traffic loads. Other functions of edge courses include:
(i) It serves as level guides when carrying out screeding of sand bedding.
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In pavement made up of paving blocks, the edge courses are normally designed to sit on concrete bedding and haunching. The reason of such provision is to prevent lateral movement of paving blocks when subjected to traffic loads. In essence, the edges formed by edge courses tie the body of the paving blocks as a single unit and they have to rely on concrete bedding and haunching to resist the sideway forces generated by moving traffic.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
Cement sand is a mixture of cement and sand and it acts as a cohesive mass once mixed. Normally, a 20mm to 30mm sand layer is laid underneath precast paving block units. However, in locations of steep gradients where it stands a high possibility that rain runoff will wash out infilling sand and sand layers, cement sand should be sued instead. Similarly, when high pressure jetting is anticipated to be employed frequently in routine maintenance, sand layers beneath precast paving block units is not preferable owing to the reason of potential washing out of sand.
In the paving block pavement, it normally consists of the following main elements: sub-base, sand bedding and paving blocks. Sub-base is the main structural element to take up traffic load and spread it into larger area so that the traffic stress is small enough for subgrade to sustain. Sand bedding is used for providing correct line and level for paving blocks to lie on. To achieve this, screeding of bedding layer is implemented so that the paving blocks could be laid directly on it without the need of further leveling.
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Normally after the laying of sub-base layer of the paving slab/interlocking blocks, a 30mm thick sand bedding is screeded and tamped over the pavement area. Then paving slabs are laid horizontally with joints of 2-3mm wide and are laid in uphill direction. After completing the laying of paving slabs, sand used for filling joints is spread over the surface of the units and brushed into the joints such that all joints are completely filled. The paving slabs are then bedded into final position by using plate vibrators.
The sand layer serves the same purpose of normal blinding layer under concrete structure:
In Hong Kong, footway is normally designed with paving slabs/interlocking blocks instead of concrete because the extensive use of concrete in pavement is boring. Moreover, poor appearance will result in concrete pavement due to frequently trench openings for utility work. In addition, owing to the prolonged setting and curing time of concrete, the use of concrete pavement inevitably generates disturbance to the general public.
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The paving for concrete blocks consists of closely packed paving blocks in pre-determined patterns and the tiny joint spaces between individual blocks are filled with sand. The presence of sand avoids the displacement of a single block unit from the remaining blocks. Moreover, the horizontal interlocking provided by the arrangement of paving blocks in special patterns (e.g. herringbone pattern) prevents any single block from moving relative to one another. For instance, vertical loads acting directly on one concrete paving block are not only resisted by the block itself, but also by the blocks adjacent to it.
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Concrete road belongs to rigid pavement and they do not deflect under traffic loads. On the contrary, bituminous pavement deflects when subjected to vehicular load.
The purpose of surface regularity test is to measure the riding quality of pavements and the same requirement and standard is applied to both concrete and bituminous carriageway.
Ten percent fines value is a measure of the resistance of aggregate crushing subjected to loading and it is applicable to both weak and strong aggregate. Fine aggregates are defined as those passing 2.36mm sieve.
The test aims at looking for the forces required to produce 10% of fine values (i.e. weight of fines aggregates/weight of all aggregates = 10%). This test is very similar to Aggregate Crushing Test in which a standard force 400kN is applied and fines material expressed as a percentage of the original mass is the aggregate crushing value.
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