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

(ii)For class A4 rapid setting and K3 emulsions, only special mobile mixing machines should be
used.
(iii)These carry supplies of aggregate, emulsion, water and filler (e.g. ordinary Portland cement or
hydrated lime) and are fitted with metering devices to feed the ingredients in their correct
proportions to a mixer fitted to the rear of the machine.
(iv)From the mixer the slurry is fed into the screed box towed by the machine.
(v)For all other emulsions, mixing may be by hand, concrete mixer or other mixer which
effectively coats the aggregate uniformly and produces a slurry seal of suitable consistency for
satisfactory laying.
(vi)For large areas, a bulk transit concrete mixer may be used into which the ingredients
(including water) are measured and mixed as the mixer travels to the area to be treated. (vii)A
screed box fitted with an adjustable rubber screed should be towed by the mixer which feeds it
during laying.
(viii)The special mobile mixing machine, when used, shall be capable of uniform application to
provide a continuous surface without ridges or segregation.
(ix)Before laying begins, the Contractor shall provide the Engineer in charge with a test certificate
showing test results for rate of application carried out under the supervision of a competent
authority, demonstrating that the machine has been tested, using the system to be used in the
Contract, not more than six weeks before the commencement of the work.
(x)Where the material is to be hand laid, the slurry may be supplied to site pre-mixed in suitable
containers and steps shall be taken to ensure that the material in each container is of an even
consistency throughout the container immediately prior to use.
516.4.5. Application:
(i)Transverse joints for machine laid areas shall be formed with spreading, starting and finishin g
on a protective strip not less than 100 mm wide at each end of the lane length being treated.
(ii)Transverse joints shall be formed such that there shall be no ridges or bare strips.
(iii)Unless otherwise approved by the Engineer in charge, longitudinal joints shall coincide with
lane markings.
(iv)Longitudinal joints shall be formed such that there shall be no ridges or bare strips.
(v)Hand work around street furniture and other obstructions should meet the same performance
requirements and form a homogeneous surface with the rest of the treated carriageway.
(vi)Footways and other confined areas may be spread by hand using squeegees and brooms.
(vii)Transverse joints shall be formed with spreading, starting and finishing on a protective strip
not less than 100 mm wide at each end of the lane length being treated. (viii)Transverse joints
shall be formed such that there shall be no ridges or bare strips. (ix)Kerb edges and other areas
not being treated shall be suitably masked with self adhesive masking material. Footways shall
be finished by dragging a dampened broom transversely over the footway under its own weight.
(x)All voids, cracks and surface irregularities shall be completely filled, In warm dry weather the
surface, immediately ahead of the spreading, shall be slightly damped by mist water spray
applied mechanically, or for hand laying by a hand operated pressure sprayer, unless otherwise
approved by the Engineer in charge.
516.4.6. Rolling:
(i)The need for rolling shall be as instructed by the Engineer in charge.
(ii)Where rolling is required, a pneumatic-tyred roller having an individual wheel load between
0.75 and 1.5 tonnes shall be used, or as may be directed by the Engineer in charge.
(iii)Rolling shall commence as soon as the slurry has set sufficiently to ensure that rutting or
excessive movement will not occur.
516.5. Opening to Traffic
(i)Masking shall be removed after the slurry seal has been applied, without damage to the edge of
the surfacing, and before opening the road or footway to traffic.
(ii)The Contractor shall remove surplus aggregate from the treated areas using a method agreed
by the Engineer in charge.