TxDOT is proposing to implement the Superpave Binder Specification
in a two-tiered approach. One tier involves "immediate"
implementation using the current system of sampling, testing and
approving binders at the source. This will allow full implementation
of Superpave binders for all HMAC projects beginning on June 1,
1997. Concurrently, work will continue on the development of
a QC/QA Superpave Binder Implementation Specification which should
ultimately replace the source approval mechanism for HMAC binders.
Superpave Using Source Approval
The Superpave Binder Specification can be implemented "immediately"
by using a modification of the system currently in place for sampling,
testing and approval of binders under the viscosity-penetration
specifications now used. This implementation would be transparent
to contractors, but would affect the quality control plans of
asphalt suppliers.
Since Superpave testing takes longer than conventional specification
testing, a modification must be made to accommodate both suppliers'
need for fast approval and TxDOT's limited resources in equipment
and personnel. To this end, TxDOT will no longer be able to completely
analyze binders for suppliers. TxDOT must move to a verification
role. This requires that suppliers must test their own products
prior to submission for TxDOT approval, and supply a copy of their
test results with the sample. This will allow TxDOT to verify
supplier data on a monitoring basis and approve materials in a
timely manner. This change in the binder quality direction will
cover all binders under Superpave and conventional specifications
for HMAC and Surface Treatment binders (PG grades for HMAC, as
well as AC asphalts and asphalt emulsions and cutback asphalts
under current specifications).
A key to rapid Superpave implementation will be to provide a driving
force for suppliers to enact a change from current to Superpave
specifications. This will take the form of a blanket field change
allowing asphalt suppliers for existing HMAC projects to supply
either an AC asphalt or an "equivalent" PG binder.
As more PG binders are bid in projects suppliers will have the
choice of supporting two different binder specifications or supplying
only PG binders.
Superpave Using QC/QA
TxDOT, through the efforts of an internal Technical Working Group,
has developed a QC/QA implementation specification for HMAC Superpave
binders. This program has been presented to industry in several
presentations. TxDOT has also received industry comments in several
TxDOT-Industry meetings. This QC/QA approach for HMAC is currently
undergoing field trials in 5 districts. Required equipment has
been ordered and delivered to 11 districts. The intent is to
ultimately move to the QC/QA approach for HMAC Superpave binders.
The current specification contains both preconstruction and construction
testing requirements. Preconstruction requires a sample and supporting
test report from the contractor for the proposed binder which
will be verified by TxDOT testing. The construction testing requires
random sampling at every sublot or 4 times per day. One of these
samples will be chosen for the Contractor to provide RTFOT/DSR
testing (high temperature properties). Every 12 sublots or 3
days TxDOT will verify contractor results. Every 36 sublots or
9 days TxDOT will verify high and low temperature properties.
The specification has provisions for penalties and bonuses, but
these have been disabled for initial use.
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