HOT MIX ASPHALT (HMA) DESIGN CRITERIA

Overview of the HMA Mixture Design Criteria Chart (Table 1)

The HMA Mixture Criteria chart identifies the aggregate, mixture volumetric, and laboratory density requirements for mixtures designed under the gyratory mix design system. The chart is formatted to correspond with the bid item designations. The bid item designations classify each mixture by the maximum 20-year traffic load (ESAL), the intended pavement layer (surface, intermediate, base), the mixture size (based on nominal maximum aggregate size), and the surface layer friction requirement. A designation of “HMA 3M S ½ L-3” describes the HMA mixture for up to 3 million ESALs, surface layer, ½-inch mixture size, with level 3 friction aggregate.

The columns to the right of the mixture designations define the required level of compaction (N values) and the maximum or target density (expressed as percent of G_mm) associated with each level of compaction. Note that the required density of a given level of compaction varies for different traffic levels and pavement layers. For example, the 1M ESAL surface/intermediate 7-76-117 mixture requires 96 percent of G_mm (4.0% air voids) at N-design. The 7-76-117 base mixture for 3M ESALs requires 96.5 percent of G_mm (3.5% air voids) at N-design.

The middle columns identify the volumetric properties of the compacted HMA mixture when analyzed at the target air voids at N-design.

The aggregate properties are defined in the right columns. The quality of the aggregate (Type A or B) is further specified in Standard Specifications 4127. The crush value specifies the minimum amount of crushed aggregate required. The Fine Aggregate Angularity and Sand Equivalent values are consensus properties of the fine aggregate portion of the mix. The friction columns specify the minimum amounts of friction quality coarse aggregate (Type 4, 3, 2) as defined in Materials IM T203. The details of the friction criteria are specified in Standard Specification 2303. Table Note 3 defines the allowable quantity of flat and elongated aggregate for all mixtures.

For any specified HMA mixture, the mix design criteria are found by reading across the table. The HMA mixtures are grouped by ESAL levels.

Gradation Requirements

The individual aggregate gradation requirements for HMA mix designers are contained on Form 955.

The combined aggregate shall meet the gradation requirements on Table 2.

VMA Requirements

The VMA requirements are shown on Table 3.

Table 1

Mix Designation	Gyratory Density						VFA	Film Thickness	Filler/ Bit	Friction ⁽²⁾				Aggregate ⁽³⁾
	N _ini	N _des	N _max	Initial	Design (Target)	Maximum				Type 4 (min)	Type 3 (min)	+4 Type 2 (min)	-4 Type 2 (min)	Quality Type	Crush (min)	FAA (min)	Sand Equiv. (min)
				% G_mm	% G_mm	% G_mm
HMA 100K S-I-B	7	68	104	92.5	97.0	98.5	75-85	8.0-13.0	0.6-1.4					B ⁽¹⁾	45 ⁽¹⁾	--	40
HMA 300K S-I	7	68	104	92.0	96.5	98.0	70-80	8.0-13.0	0.6-1.4					B ⁽¹⁾	45 ⁽¹⁾	--	40
HMA 300K B				92.5	97.0	98.5	75-85
HMA 1M S L-2	7	76	117	90.5	96.0	98.0	65-78	8.0-15.0	0.6-1.4	80		25		A ⁽¹⁾	60 ⁽¹⁾	40	40
HMA 1M S L-3										80	45	(25)
HMA 1M S L-4										50
HMA 1M S
HMA 1M I														B ⁽¹⁾	45 ⁽¹⁾
HMA IM B	7	68	104	92.0	96.5	98.0	70-80									--
HMA 1M B (shld pav sep)				92.0	97.0	98.0	75-85									--
HMA 3M S L-2	7	86	134	89.5	96.0	98.0	65-78	8.0-15.0	0.6-1.4	80		25		A ⁽¹⁾	75 ⁽¹⁾	40	40
HMA 3M S L-3										80	45⁾	(25)
HMA 3M S L-4										50
HMA 3M S
HMA 3M I															60 ⁽¹⁾
HMA 3M B	7	76	117	90.5	96.5	98.0	65-78							B ⁽¹⁾	45 ⁽¹⁾
HMA 10M S L-2	8	96	152	89.0	96.0	98.0	65-78	8.0-15.0	0.6-1.4	80		25		A ⁽¹⁾	75 ⁽¹⁾	43	45
HMA 10M S L-3										80	45	(25)
HMA 10M S L-4										50
HMA 10M I
HMA 10M B	7	86	134	89.5	96.0	98.0	65-78							B ⁽¹⁾	75 ⁽¹⁾	40
HMA 30M S L-2	8	109	174	89.0	96.0	98.0	65-75	8.0-15.0	0.6-1.4	80		30 ⁽⁴⁾	25 ⁽⁴⁾	A ⁽¹⁾	85 ⁽¹⁾	45	45
HMA 30M S L-3										80	45	(25)
HMA 30M I
HMA 30M B	8	96	152	89.0	96.0	98.0	65-75							B ⁽¹⁾	75 ⁽¹⁾	40
HMA 100M S L-2	9	126	204	89.0	96.0	98.0	65-75	8.0-15.0	0.6-1.4	80		30 ⁽⁴⁾	25 ⁽⁴⁾	A ⁽¹⁾	85 ⁽¹⁾	45	50
HMA 100M I
HMA 100M B	8	109	174	89.0	96.0	98.0	65-75							B ⁽¹⁾	75 ⁽¹⁾	43
3/8 HMA Special ⁽⁵⁾	--	50	--	--	98.0-99.5	--	70-95	≥8.0						A ⁽¹⁾	45 ⁽¹⁾	40	50
Note (1) On local agency projects, the minimum percent crushed type shown above shall be used unless specified in plans.
Note (2) See Iowa DOT Standard Specification 2303.02, B, 1, b
Note (3) Flat & Elongated 10% maximum at a 5:1 ratio.
Note (4) On interstate mixes, if 40% or less of the combined aggregate is not limestone, 25% of the +4 shall be Type 2 with no requirement on the -4. All interstate L-2 mixes require a Fineness Modulus of ≥1.0 for the Type 2 Material.
Note (5) Highly modified thin lift as specified in plans. See Table 4 for additional requirements.

Table 2

Aggregate Gradation Control Points
Sieve Size	Mix Size – Control Points (% Passing)
	1 inch (25 mm)		3/4 inch (19 mm)		1/2 inch (12.5 mm)		3/8 inch (9.5 mm)		3/8 inch ⁽³⁾ (9.5 mm)
	min.	max.	min.	max.	min.	max.	min.	max.	min.	max.
1 1/2 inch (37.5 mm)	100
1 inch (25 mm)	90	100	100
3/4 inch (19 mm)		90	90	100	100
1/2 inch (12.5 mm)				90	90	100	100
3/8 inch (9.5 mm)						90	90	100	100
No. 4 (4.75 mm)								90	80		100
No. 8 (2.36 mm)	19	45	23	49	28	58	32	67	60		85
No. 16 (1.18 mm)⁽¹⁾				28		32			40		70
No. 30 (600 μm)⁽²⁾				24		25			25		55
No. 50 (297 μm)									15		35
No. 100 (297 μm)									8		20
No. 200 (75 μm)	1	7	2	8	2	10	2	10	6		14

(1) Only applies to surface and intermediate mixtures for HMA 30M and above.

(2) Only applies to surface and intermediate mixtures for HMA 10M.

(3) Applicable only for 3/8 HMA Special

Table 3

Minimum VMA Criteria^(1,2)
Mix Designation	Mix Size
	1 inch (25 mm)	3/4 inch (19 mm)	1/2 inch (12.5 mm)	3/8 inch (9.5 mm)

HMA 100K	12.0	13.0	14.0	15.0
HMA 300K
HMA 1M
HMA 3M
HMA 10M
HMA 30M	11.5	12.5	13.5	14.5
HMA 100M
3/8 HMA Special				16.0

(1) Applies to all layers in the pavement structure (surface, intermediate and base).

(2) Minimum VMA criteria may be waived if the design Asphalt Film Thickness (AFT) is greater than or equal to 9.5 microns. If the AFT of the plant produced material falls below 9.0 microns, the minimum VMA criteria will be re-instated. The price adjustment schedule for AFT will not change.

Table 4

Performance Requirements for 3/8 HMA Special Thin Lift ⁽³⁾

Test

Requirement

Notes

AASHTO T-321

Minimum 100,000 cycles to failure

AASHTO T-324

< 12 mm @ 10,000 passes

SIP > 10,000 passes

(1) Failure criterion at 2,000 microstrain shall be 50% of the initial flexural stress measured at the 200^th load cycle.

(2) Applicable when exposed to traffic. Test at 50°C. Stripping Inflection Point and rut depth are determined by the Iowa DOT Hamburg software analysis.

(3) An alternate binder grade may be selected by the contractor at no additional cost to the contracting authority to meet the above criteria provided it exceeds the performance grade specified on the contract. All testing shall be submitted by contractor for JMF approval. Testing may be verify by the Engineer on field produced mix.