Specification Part 3 - Road & Bridge Works - Urban Administration ...

evaporation of water and/or solvent for the development of their curing and adhesion
characteristics. Cold weather, rain and high humidity slow down the rate of curing. Extra
manipulation may be required to remove
TABLE 500-39.
PERMISSIBLE VARIATIONS FROM THE JOB MIX FORMULA
Description
Permissible variation
Base/binder course Wearing course6
Aggregate passing 19mm sieve or larger ±8% ±7%
Aggregate passing 13.2mm, 9.5mm ±7% ±6%
Aggregate passing 4.75mm ±6% ±5%
Aggregate passing 2.36mm, 1.18mm, 0.6m ±5% ±4%
Aggregate passing 0.3mm, 0.15mm ±4% ±3%
Aggregate passing 0.075mm ±2% ± 1.5%
Binder content ±0.3% ±0.3%
volatiles in cool and humid conditions. Wind increases the rate of evaporation.
519.2.3.2. Preparation of the base: The base on which cold mix is to be laid shall be prepared,
shaped and leveled to the required profile in accordance with Clauses 501 and 902 as
appropriate, and a prime coat, where specified, shall be applied in accordance with Clause 502 or
as directed by the Engineer in charge.
519.2.3.3. Tack coat: A tack coat in accordance with Clause 503 shall be applied over the base
on which the cold mix is to be laid where specified in the Contract.
519.2.3.4. Preparation and transportation of the mixture: Mixing can be carried out using one
of the following types of mixer, which is provided with equipment for spraying the binder at a
controlled rate and, if necessary, for heating the binder to a temperature at which it can be
applied uniformly to the aggregate:
(a) Rotary drum type concrete mixer;
(b) Single or twin shaft concrete or macadam mixer;
(c) Batch or continuous type mixer without dryer or screens other than a scalping screen.
(d)A sufficient number of haul trucks with smooth, clean beds should be available to ensure
continuous operation of the mixing plant.
(e)The type of truck used for transporting the mixture from the mixer to the road site must be
suited to the Contractor’s nominated laying procedure methodology.
519.2.3.5. Spreading:
(i)Designed cold mix shall be placed only when the specified density can be obtained. (ii)The
mixture shall not be placed on any wet surface or when weather conditions will otherwise prevent
it proper handling or finishing.
(iii)If spreading by motor grader, the grader must have a blade that is straight and sharp and long
enough to ensure finishing closing, straight, transverse tolerances and all joints and linkages
must be in good condition.
(iv)The grader must be heavy enough to hold the blade firmly and uniformly on the surface while
spreading the mixture.
(v)If climatic conditions and aggregate grading permit evaporation of moisture or volatiles without
aeration by manipulation, a conventional self-propelled asphalt paver shall be used to place
designed cold mix.
(vi)Other methods of spreading may be used as approved by the Engineer in charge.
519.2.3.6. Compaction:
(i)Initial compaction of the laid material shall be carried out using a pneumatic-tyred roller of a
weight appropriate to the layer thickness to be compacted with single layer thicknesses being 25-
100mm and all compaction being in accordance with Clause 501.6 and Clause 501.7.