HomeMy WebLinkAbout23- Workshop SLURRY
WHAT IS IT?
Emulsion-aggregate slurry is a mixture of emulsified asphalt, mineral aggregate,
water and when specified, asphalt modifiers. It is specified in the Standard
Specifications for Public Works Construction as generally a Type I or Type H.
Type I is applied between 8 and 11 pounds per square yard, has finer aggregate
than Type II and has 10% residual asphalt as a percentage of dry aggregate
weight. Type II uses course aggregate, is between 11 and 15 pounds per square
yard and has a minimum of 7.5% residual asphalt as a percentage of dry aggregate
weight. The asphalt, water (for emulsification), aggregate and modifiers are mixed
in the machine and dumped into a spreading box as it moves down the street.
WHAT DOES IT DO?
Slurry is used to waterproof and seal the surface of existing asphalt, restore some
of the fine aggregate material lost from the original asphalt surface, restore some
of the asphalt oil lost from the upper surface of the pavement and increase the
useful life of existing pavements. It is not structural in that it adds no additional
capacity to the street to resist traffic loads nor can it patch holes.
WHY IS IT USED?
It is used to extend the life of pavement and preserve the original pavement section
at a moderate cost. Much like you might re-stucco a house, a new coat of stucco
does not make a new house out of a 40 year old one but it does preserve it,
improve the looks and extend its life. It does not however fix the plumbing or the
foundation. Slurry is approximately 1/6th the cost of a one inch overlay of
pavement and approximately 1/20th the cost of reconstruction of pavement section.
It does not require the adjustment of manholes, water valves, utility vaults or
adjustment of driveways to meet a new grade. It does not require grinding of old
pavements to achieve a satisfactory grade and does not change the profile of the
streets. It is a cost effective tool to preserve pavement and allows a return
frequency to streets that keeps them in good condition rather than allowing them
to fall apart before being repaired. It use covers 6-20 times more area than a one
inch overlay or reconstruction. A street may receive more than one slurry and still
not require any adjustments. It may be combined with other treatments to build
up a good wearing surface over time.
#z �
WHERE SHOULD IT BE USED?
It can be used on just about any street or highway that has not reached a point of
deterioration that requires major rehabilitation or reconstruction. However, staff
is presently recommending its use for residential or low volume streets (under
3500 vehicles per day and averaging approximately 100-150 vehicles per day) and
streets that rate 3 or better on the City street rating system. Further, staff has
been and continues to recommend complete preparation of the streets prior to
slurry. This is done by cleaning the cracks, grinding the cracks with a pavement
grinder to level the street and eliminate bumps, filling cracks with a rubberized
crack sealant, sweeping the pavement and then applying a latex modified slurry
seal. The latex additive provides additional flexibility and aggregate retention as
well as providing a black appearance.
WHY NOT USE ASPHALT OVERLAY?
There is no reason to not consider overlay. Staff will still be using overlay where
appropriate and cost effective. Overlay is only one of the tools available to staff
to address street conditions and is presently being used on many of the
rehabilitation projects (i.e. Mill and Sierra Way). Grinding and overlay is by far
the most common method of rehabilitation on major streets.
By State code, maintenance is defined as one inch or less of asphalt overlay. A
one inch overlay over a cracked street without additional preparation will reflect
the cracks through to the surface in one year or less depending on traffic loads.
Additional thickness of asphalt may delay the cracking process but eventually it
does reflect all cracks unless other actions are taken. A one inch overlay adds
additional costs for the adjustment of all manholes, valves and vaults, may cause
excessive grades on the pavement, reduces the curb face unless the overlay is
tapered to the gutter (this requires 5-10 feet that does not receive the full overlay)
and may affect street drainage. It costs significantly more and depending on what
other methods are used, may leave the maintenance category and fall into
reconstruction which in turn adds additional cost for disabled access requirements.