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Item 346. Item 346 is a QCQA specification for Stone-Matrix Asphalt (SMA) and Asphalt Rubber Stone-Matrix (SMAR) mixtures. Typical Use. Used as surface mix or intermediate layer Often used as intermediate layer for PFC

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Item 346 l.jpg

Item 346

Item 346 is a QCQA specification for Stone-Matrix Asphalt (SMA) and Asphalt Rubber Stone-Matrix (SMAR) mixtures.

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Typical Use

  • Used as surface mix or intermediate layer

  • Often used as intermediate layer for PFC

  • Standard SMA contains PG76-xx and fiber and is recommended for the vast majority of applications

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Typical Use

  • Asphalt Rubber SMA is used:

    Where a high degree of noise reduction is desired

    Where it is being placed as an overlay of a pavement with a

    high degree of cracking.

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  • Is rut resistant and crack resistant

  • Has high concentration of CA which gives more stone on stone contact

  • Voids in CA are filled with fibers, mineral filler, and polymer modified asphalt making a rich mixture that is rut and crack resistant.

  • Considered impermeable

  • High degree of surface texture

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  • Higher initial cost (More Asphalt)

  • Additives required such as mineral filler, fibers (not required with SMAR), polymer or asphalt rubber binder add to the initial cost and often requires producers to modify the production process.

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  • Requires high compactive effort to produce required higher densities.

  • Difficult to compact in cooler weather

  • Handwork is difficult

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Item 346 Page 364

346.1 Description. Construct a pavement layer composed of a compactedstone-matrix asphalt (SMA) or stone-matrix asphalt rubber (SMAR) mixture of aggregate, asphalt binder, and additives mixed hot in a mixing plant

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D. Asphalt Binder.For SMA mixtures, furnish the type and grade of PG binder and fibers specified on the plans. For SMAR mixtures, provide the A‑R binder specified on the plans. Provide asphalt binder that meets requirements of Item 300, “Asphalts, Oils, and Emulsions

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  • PG Binder. When SMA is specified, provide an asphalt binder with a high-temperature grade of PG 76 and low-temperature grade as shown on the plans in accordance with Section 300.2.J, “Performance-Graded Binders.”

  • A‑R Binder. When SMAR is specified, provide A‑R binder that meets the Type I or Type II requirementsof Section 300.2.I, “Asphalt-Rubber Binders,” unless otherwise shown on the plans.Use at least 15.0% by weight of Crumb Rubber Modifier (CRM) that meets the Grade B or Grade C requirements of Section 300.2.G, “Crumb Rubber Modifier,” unless otherwise shown on the plans.

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F. Additives. When shown on the plans, use the type and rate of additive specified. Other additives that facilitate mixing or improve the quality of the mixture may be allowed when approved.

1. Fibers.When PG binder is specified, provide cellulose or mineral fibers. Submit written certification to the Engineer that the fibers proposed for use meet the requirements of DMS‑9204, “Fiber Additives for Bituminous Mixtures.”

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DraindownSMA W/O Fibers

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346.4. Equipment. Provide required or necessary equipment in accordance with Item 320, “Equipment for Asphalt Concrete Pavement”. When A-R binder is specified, equip the hot mix plant with an in-line viscosity-measuring device located between the blending unit and the mixing drum.

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D. Mixture Design.

1. Design Requirements. Unless otherwise shown on the plans, use the SMA or SMAR design procedures given in Tex‑204‑F, Part VI or Part VII, to design a mixture meeting the requirements listed in Tables 1, 2, 3, 6, 7, and 8. Use an approved laboratory to perform the Hamburg Wheel test and provide results with the mixture design or provide the laboratory mixture and request that the Department perform the Hamburg Wheel test…….

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The design number of gyrations (Ndes) may be increased from 75 to 100 when allowed by the Engineer.

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Table 6

Master Gradation Bands (% Passing by Weight or Volume) and Volumetric Properties

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Table 7

Laboratory Mixture Design Properties

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Table 9

Operational Tolerances

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Table 10

Compacted Lift Thickness and Required Core Height

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1. Weather Conditions.Place mixture when the roadway surface temperature is 70°F or higher unless otherwise approved. Measure the roadway surface temperature with a handheld infrared thermometer. Unless otherwise shown on the plans, place mixtures only when weather conditions and moisture conditions of the roadway surface are suitable in the opinion of the Engineer.

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Table 11

Suggested Minimum Mixture Placement Temperature

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(2) Asphalt Binder Sampling.Obtain a 1‑qt. (1‑gal. for A‑R binder) sample of the asphalt binder for each sublot of mixture produced. Obtain the sample at approximately the same time the mixture random sample is obtained. Sample from a port located immediately upstream from the mixing drum or pug mill. Take the sample in accordance with the pipeline sampling procedure given in Tex‑500‑C, Part II. Label the can with the corresponding lot and sublot numbers, and deliver the sample to the Engineer.

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  • Production Testing. The Contractor and Engineer must perform production tests in accordance with Table 12. ..

    At any time during production the Engineer may require the Contractor to verify the following based on quantities used:

    • lime content (within ±0.1% of JMF), when PG binder is specified;

    • fiber content (within ±0.03% of JMF), when PG binder is specified; and

    •CRM content (within ±1.5% of JMF), when A‑R binder is specified.

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Table 12

Production and Testing Frequency

Contractor Engineer

Drain-down 1 per sublot 1 per 12 sublots

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  • Fibers.Suspend production if fiber content varies from the design target value by more than 10% on 2 consecutive tests.

    Requirements for:

    Hamburg Wheel Test

    Individual Loads of Hot Mix

    Are the same as previously discussed

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3. Placement Acceptance.

  • Placement Lot. A placement lot consists of 4 placement sublots. A placement sublot consists of the area placed during a production sublot.

    b. Lot 1 Placement. Placement bonuses for Lot 1 will be in accordance with Section 346.6.B, “Placement Pay Adjustment Factors.” However, no placement penalty will be assessed for any sublot placed in Lot 1, when the In-Place air voids are greater thanor equal to2.7%and less than or equal to8.0%.Remove and replace any sublot with In-Place air voids less than 2.7% or greater than 8.0%.

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Table 14

Production Pay Adjustment Factors for Laboratory-Molded Density

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Table 15

Placement Pay Adjustment Factors

For In-Place Air Voids

Maximum Bonus 10.0%

Maximum Penalty 30.0%

Remove and Replace < 2.7% & > 8.0 %