Texas Asphalt Pavement Association (TxAPA) 2016 Annual

Meeting

September 2016

Why specify Surface Aggregate Classification ‘A’ (SAC-A) ?

• Reduce wet surface crashes & fatalities

• FHWA mandate issued June 27, 1967

Highway Safety Program Standard 12

• Three components of the program

1. Wet surface crash data analysis – Traffic Operations

Division

2. Aggregate selection guidelines – Construction Division

3. Network level skid testing – Maintenance Division

TxDOT’s Wet Surface Crash Reduction Program (WSCRP)

Texas Asphalt Pavement Association (TxAPA) 2016 Annual

Meeting

September 2016

TxDOT/WSCRP - Aggregate Selection Guidelines (CST/M&P)

Frictional Demand of Roadway Surface Surface Aggregate Classification (SAC)

Texas Asphalt Pavement Association (TxAPA) 2016 Annual

Meeting

September 2016

Where are SAC-A sources available in Texas?

- SAC A

- SAC B

(5)

(11)

(4)

New Mexico

Oklahoma

Arkansas

Amarillo

Corpus

Christi

Austin

San Antonio

Fort WorthDallas

Waco

Yoakum

Bryan

Lubbock

Childress

Abilene

Brownwood

San Angelo

Odessa

El Paso

Laredo

Pharr

Wichita Falls

Paris

Atlanta

Tyler

Houston

Lufkin

Beaumont

Mexico

(2)

(2)

SAC A 42 Sources (45%)

SAC B 52 Sources (55%)

Texas Asphalt Pavement Association (TxAPA) 2016 Annual

Meeting

September 2016

When will TxDOT Implement a SAC ‘B+’ Rating Classification?

- SAC A

- SAC B

- Dolomite

(5)

(11)

(4)

New Mexico

Oklahoma

Arkansas

Amarillo

Corpus

Christi

Austin

San Antonio

Fort WorthDallas

Waco

Yoakum

Bryan

Lubbock

Childress

Abilene

Brownwood

San Angelo

OdessaEl Paso

Laredo

Pharr

Wichita Falls

Paris

Atlanta

Tyler

Houston

Lufkin

Beaumont

Mexico

(2)

(2)

SAC A 41 Sources (45%)

SAC B 43 Sources (45%)

Dolomite 10 Sources* (10%)

* 1 SAC A and 9 SAC B

Texas Asphalt Pavement Association (TxAPA) 2016 Annual

Meeting

September 2016

When will TxDOT use general notes to allow blending of all SAC ‘B’

aggregates?

SAC B Quarries (No Dolomites)

Soundness Rated

Values# of Quarries

10 or Less 10

>10 to 20 21

>20 12

- 10 or Less

- <10 to 20

- > 20

Texas Asphalt Pavement Association (TxAPA) 2016 Annual

Meeting

September 2016

TxDOT SAC ‘A’ Estimated Letting Quantities

Year Total Seal Coat* HMA**

2013 417,987 58,915 359,072

2014 954,903 159,392 795,511

2015 1,579,229 318,278 1,260,952

2016(Jan – Sept)

1,095,553 96,647 998,906

* - Seal coat aggregate conversion factor of 1.20 Tons per CY. No quantities included from item description

codes for Tiers I, II, or III aggregate from seal coat material selection table; SAC not specified.

** - Includes assumptions for percentage of mix and bin percentages for each mix type.

Texas Asphalt Pavement Association (TxAPA) 2016 Annual

Meeting

September 2016

TxDOT Aggregate Research and Testing

DFT

• Dynamic Friction Tester (DFT)

• Measures Coefficient of Friction on wet surface

• Platform speed starts at 50 mph (80 km/h) and

measures friction continuously to 6 mph (10 km/h)

• Maryland DOT has specifications for aggregate

blending

AIMS

• Aggregate Image Measurement System (AIMS)

• Measures aggregate characteristics for texture,

angularity, and shape (round or flat)

• Image based analysis, investigating use of optical

sensors for a laser based system for texture only

Long term (3-5 years) research efforts to quantify microtexture and to predict friction

Texas Asphalt Pavement Association (TxAPA) 2016 Annual

Meeting

September 2016

0

200

400

600

800

1000

0 10 20 30 40

Maxim

um

Load

, lb

s

Number of Cycles

First Crack

Retardation Rate

Power equation

representing load

reduction curve

y = axb , a=1

The fracture energy and crack retardation rate are plotted together

on a design interaction plot

-800

-400

0

400

800

1200

0.00 0.01 0.02 0.03

Lo

ad

, lb

s

Displacement, in.

Maximum LoadArea used for

Fracture Energy

𝑮𝒇 =𝑾

𝑨

OT Data Analysis

Texas Asphalt Pavement Association (TxAPA) 2016 Annual

Meeting

September 2016

Overall View of All Mixtures

9

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0.00 0.25 0.50 0.75 1.00 1.25

Cri

tica

l F

ract

ure

En

ergy, lb

s-in

./in

.2

Crack Progression Rate

CAM

TOM-F

TOM-C

SMA-C

SMA-D

SMA-F

SMAR-C

SMAR-F

SP-C

SP-D

SP-B

Type D

Type C

Type B

TO

UG

HN

ES

S

FLEXIBILITY

Texas Asphalt Pavement Association (TxAPA) 2016 Annual

Meeting

September 2016

Binders with DTc > 6oC

Temperature

log (

Stiffness o

r S

)

Temperaturem

-valu

e (

abili

ty t

o r

ela

x)

S =

300MPa

‘S’ based

continuous

grade

m = 0.3

‘m-value’

based

continuous

gradeDifferen

ce =

DTc

DTc using BBR