Chip seal design (McLeod method)

ASTM D5360 · MnDOT Seal Coat Handbook · TxDOT Seal Coat Manual

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Chip seal design (McLeod method)

ASTM D5360 · MnDOT Seal Coat Handbook · TxDOT Seal Coat Manual

From the chips’ size, shape, unit weight and specific gravity, the road’s traffic and its surface, the cover aggregate and binder rates for a one-stone-thick seal.

Units US customary SI (metric)

Aggregate

Median particle size

Median particle size, M, in.

The sieve size 50 percent of the chips pass.

Gradation
Sieve	Sieve opening, mm	Percent passing, %
1
2
3
4
5
6
7
8
9
10

Sieve openings in millimeters (12.5, 9.5, 6.3, 4.75 for No. 4, 2.36 for No. 8, …) and percent passing. Two sieves must bracket 50 percent.

Flakiness index, FI, %

Percent by mass of flat chips (they pass the slotted plate). The example is MnDOT’s design example except here: its chips measured 28.6 percent, over MnDOT’s 25 percent limit, so the example uses 20 percent.

Loose unit weight, W, pcf

Dry loose unit weight (ASTM C29, loose fill).

Bulk specific gravity, G

Absorption correction, A, gal/yd²

McLeod suggests 0.02 gal/yd² (0.09 L/m²) for absorptive chips; MnDOT applies it at 1.5 percent absorption or more.

Road

Traffic

Allowance for whip-off and handling, %

About 5 percent for low-volume roads, 10 percent for faster ones (TxDOT).

Existing surface

Binder

Residual binder in the emulsion, R, %

From the supplier. 100 for a hot asphalt cement.

Specification

Maximum flakiness index, % (optional)

MnDOT Seal Coat Handbook: chips with a flakiness index over 25 percent should not be used for chip sealing. Blank to skip.

Example values: the MnDOT Seal Coat Handbook’s design example (a granite chip, 850 vehicles a day, a CRS-2 emulsion) with the flakiness index lowered to 20 percent so the chips pass. Test strips set the final rates.

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