421 Microsurfacing

1. Specification:

Item 421.02 C&MS

2. Sampling and/or Inspection Requirements:

Test Strip:

Construct a test strip for the Engineer to evaluate. Construct this test strip 1000 feet (300 m) long and include all of the application courses specified. Construct the test strip at the same time of day or night the full production will be applied. The Contractor may construct the test strip in 2 days or nights if multiple course applications are specified.

The Engineer will evaluate the completed test strip after 24 hours of traffic to determine if the mix design is acceptable. The Contractor may begin full production after the Engineer accepts the test strip.

If microsurfacing is not being applied between September 30, and May 1, the Department will waive the test strip if the Contractor has constructed a Department approved test strip this construction season with the same materials and mix design.


Maintain continuous control of the Binder to Dry Aggregate proportions to conform to the approved mix design within a tolerance of 2 gallons per ton ( 8.5 L/metric ton).

Control the spread rate to not less than the specified quantity of aggregate per square yard (square meter) on a dry weight basis.

The Engineer will base acceptance of the Binder to Dry Aggregate proportion and spread rate on the Engineer's summary fo quantities used each day. The Engineer will approve and accept a day's application of microsurfacing provided the Engineer's summary indicates conformance with the above control requirements for proportions and spread rate.

The spread rate requirement does not apply to rut fill courses if the Contractor filled the wheel paths according to this specification.

3. Method of Tests:

AASHTO T53, T202