Pavement Course Tolerance
Wearing Course Binder Course Roadbase Sub-base
+ 5 mm + 5 mm + 0 mm to - 20 mm + 10 mm to - 20 mm
The combination of permitted tolerances in the levels of different pavement courses shall not result in a pavement thickness less than that shown on the Drawings. Each pavement course shall have an average thickness not less than that shown on the Drawings.
4.5.3 Surface Regularity
4.5.3.1 Description
Riding quality on a road surface is positively correlated with roughness of the surface. Low roughness corresponds to good riding quality and vice versa.
Roughness of a pavement surface is brought about by uneven settlement, short and long wave undulations, rutting, wide cracking and other surface defects such as potholes, delamination etc..
The International Roughness Index (IRI) is used internationally to measure the degree of roughness of a pavement surface. It is representative of the vertical motions induced in moving vehicles for the frequency bandwidth which affects both the response of the vehicle and the comfort perceived by the occupants
The IRI describes a scale of roughness which is zero for a true planar surface, increasing to about 6 m/km for moderately rough paved roads, 12 m/km for
S4-44
extremely rough paved roads with potholes and patches, and up to about 20 m/km for extremely rough unpaved roads.
4.5.3.2 Measurement of IRI
The regularity of the completed pavement surface shall be measured before traffic is allowed on it and is measured in terms of its lane IRI. Lane IRI shall be measured using the ARRB Walking Profiler (WP) following the procedures as outlined in AUSTROADS PAT 01:2001 (Appendix 1)
Other types of equipment may be used to measure lane IRI provided that the output from the equipment correlate strongly with the output from WP (R2 > 0.95).
4.5.3.3 Acceptance criteria
The Contractor shall make available lane IRI values for the whole road length as well as for each 100 meter section of the completed pavement surface.
The lane IRI measured for the whole road length and each 100 meter section shall be less than 2.0 m/km.
4.5.3.4 Rectification work for non-compliance
In case of non-compliance, the Contractor shall carry out rectification works on any part of the completed pavement surface so that the lane IRI values for the whole road length and for each 100 meter section are less than 2.0 m/km.
Porous Asphalt
Porous asphalt is a special-purpose wearing course. It is produced using open-graded aggregate mixed with polymer modified binder and contains a relatively high air voids after compaction. The design and in-place air voids shall be in the range of 20 to 25 percent to ensure drainability.
It offers the following benefits;
i. Improved skid resistance at high speeds, especially during wet weather.
ii. Reduced hydroplaning effects.
iii. Reduced splash and spray.
iv. Reduced headlight reflection and glare on wet pavement surface.
v. Reduced rolling tyre noise levels.
Porous asphalt shall be laid on impermeable and relatively even bituminous surface with adequate cross fall. A minimum cross fall of 2.5 percent is recommended. Existing cracks and depression shall be sealed and patched prior to application of porous asphalt.
A minimum thickness of 50 mm is essential to provide adequate drainage within the porous asphalt layer.
Porous asphalt shall be compacted using static steel wheel tandem rollers only.
Vibratory rollers are not permitted because they lead to excessive compaction and the possibility of aggregate crushing. Pneumatic tyre rollers are not permitted because they knead and close the surface, affecting the drainability of porous asphalt. They also cause stripping of aggregates that stick to their tyres. Three wheel rollers are also not permitted because they leave roller marks that can be difficult to remove.
Porous asphalt shall not be laid in areas where;
i. The pavement structural strength is sub-standard.
ii. There is considerable traction due to sudden acceleration, braking and turning like at major junctions.
iii. There are tight radius curves, loops of radii less than 75 meters.
iv. The gradient exceeds 10 percent.
v. Excessive deposits of debris, oil and fuel may be experienced.
vi. Free drainage cannot be
accommodated along the road shoulders.
vii. Length of roads less than 100 meters because of spray carry-over from adjacent surfacing.
viii. There is high flexibility like on bridges.
ix. Frequent excavations by statutory undertakers may occur.
x. Traffic levels exceed 4000 commercial vehicles per lane per day at opening.
xi. Slow moving traffics are expected as there is no beneficial reduction in spray or noise levels achieved at speeds below 40 km/h.
Porous asphalt is a non-structural layer.
Therefore, it shall not be applied on pavements which are experiencing structural deficiency.
S4-46 4.6 SPECIALTY MIX 1- POROUS ASPHALT
4.6.1 Description
This work shall consist of furnishing, placing, shaping and compacting porous asphalt as a wearing course on an existing, impermeable and accepted bituminous pavement course. This Specification shall be read in conjunction with Sub-Section 4.3.3 of the Standard Specification for Road Works of JKR (JKR/SPJ/2007). All requirements in the Sub-Section 4.3.3 shall apply unless stated otherwise in this Specification.
Porous asphalt is a special-purpose wearing course. It is produced using open-graded aggregate mixed with polymer-modified binders and contains a relatively high and interconnected air voids after compaction. It offers the following benefits;
i. Improved skid resistance at high speeds, especially during wet weather.
ii. Reduced hydroplaning effects.
iii. Reduced splash and spray.
iv. Reduced headlight reflection and glare on wet pavement surface.
v. Reduced rolling tyre noise levels.
4.6.2 Materials 4.6.2.1 Coarse Aggregate
Coarse aggregate shall be screened crushed hard rock, angular in shape and free from dust, clay, vegetative and other organic matter, and other deleterious substances.
They shall conform to the following physical and mechanical quality requirements;
i. The loss by abrasion and impact in the Los Angeles machine when tested in accordance with ASTM C 131 shall be not more than 25%.
ii. The weighted average loss of weight in the magnesium sulfate soundness test (five cycles) when tested in accordance with AASHTO T 104 shall be not more than 18%.
iii. The flakiness index when tested in accordance with MS 30 shall be not more than 25%.
iv. The water absorption when tested in accordance with MS 30 shall be not more than 2%.
v. The polished stone value when tested in accordance with MS 30 shall be not less than 40.
Notwithstanding compliance with the aforementioned requirements, crushed or uncrushed limestone and gravel shall not be permitted.
4.6.2.2 Fine Aggregate
Fine aggregate shall be screened quarry fines. They shall be non-plastic and free from clay, loam, aggregations of material, vegetative and other organic matter, and other deleterious substances. They shall conform to the following physical and mechanical quality requirements;
i. The sand equivalent of aggregate fraction passing the No. 4 (4.75mm) sieve when tested in accordance with ASTM D 2419 shall be not less than 45%.
ii. The fine aggregate angularity when tested in accordance with ASTM C 1252 shall be not less than 45%.
iii. The Methylene Blue value when tested in accordance with Ohio Department of Transportation Standard Test Method shall be not more than 10 mg/g.
iv. The weighted average loss of weight in the magnesium sulfate soundness test (five cycles) when tested in accordance with AASHTO T 104 shall be not more than 20%.
v. The water absorption when tested in accordance with MS 30 shall be not more than 2%.
4.6.2.3 Mineral Filler
Mineral filler shall be incorporated as part of the combined aggregate gradation. It shall be of finely divided mineral matter of hydrated lime (calcium hydroxide). At the time of mixing with bitumen, the hydrated lime shall be sufficiently dry to flow freely and shall be essentially free from agglomerations. Not less than 70% by weight shall pass the BS 75 um sieve. If hydrated lime is not available, ordinary Portland cement shall be used as an alternative, subject to approval by the S.O. The amount of mineral filler to be added shall be not less than 2% by weight of the combined aggregates. However, the amount shall be limited to not more than 2% if hydrated lime is used.
4.6.2.4 Bituminous Binder
The bituminous binder for use with porous asphalt shall be of performance grade PG 76 or higher in compliance with AASHTO Standard M320-02.
(a) Polymer Modified Binder
The performance grade PG 76 or higher shall be achieved by incorporating an appropriate quantity of polymer additives to conventional bitumen which shall be penetration grade 70-100 conforming to MS 124. The polymer shall be non-carcinogenic. The Contractor shall submit material safety data sheet of the proposed polymer modified binder. The properties of the polymer modified binder (PMB) shall be as given in Table 4.6.1.