Minnesota Department of Transportation

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Road Research

Strain [Asphalt]

Staff member installing sensors

Strain [Asphalt]

AE Sensor

Description

An "AE" sensor measures hot-mix asphalt strain response due to dynamic loads. The Angled Asphalt Strain (AE) sensor is an electrical resistance (full bridge) strain transducer, utilizing a nylon rod with transverse steel anchors at each end to form an H-shape.

Manufacturer

AE sensors: Model ASG 152, manufactured by CTL Group.

Location

AE sensors are located at the bottom of the hot-mix asphalt layers. They are oriented at a 45 angle to direction of traffic.

Current Status

Some AE sensors are still in service as of February 2011.

MnROAD Database Tables

Data has been collected during various load response testing sessions, and some has been processed and loaded into the MnROAD database. Data is located in database tables named: MNR.DYNAMIC_LOAD_TEST_VALUES and MNR.DYNAMIC_LOAD TEST DESCRIPTIONS.

Biaxial Strain Gauge - BS (BL/BT)

Description

A "BL/BT" sensor measures hot-mix asphalt strain response due to dynamic loads. The Biaxial Strain (BL/BT) sensor consists of four electrical resistance strain gauges embedded in an asphalt mastic mix. Two of the strain gauges within a biaxial strain sensor are orientated in the longitudinal direction (with traffic) and designated as "BL". The remaining two gauges are oriented in the transverse direction (90º to traffic) and designated as "BT". Data is stored in the database under the designations "BL" and "BT". Physical dimensions of the biaxial strain sensor are: 152.4mm x 152.4mm x 12.7mm (6" x 6" x 1/2").

Manufacturer

BL/BT sensors were manufactured by the Alberta Research Council.

Location and Quantity

BL/BT sensors are located at the bottom of the hot-mix asphalt layers. They are mounted on top of the base layer and paved over with the asphalt layer, to become embedded into the bottom of the asphalt layer.

There were originally 40 Biaxial Strain sensors installed into test cell 26.

Current Status

Due to reconstruction of Cell 26 in 2000, these sensors were removed.

MnROAD Database Tables

Data was collected during various load response testing sessions, and some has been processed and loaded into the MnROAD 29 database. Data is located in database tables named: MNR.DYNAMIC_LOAD_TEST_VALUES and MNR.DYNAMIC_LOAD TEST DESCRIPTIONS. 

Bituminous Longitudinal Embedment or Transverse Embedment Strain Gauge - LE or TE

Description

A "LE" or "TE" sensor measures strain response in hot-mix asphalt due to dynamic loads. Sensor designation "LE" indicates a strain sensor was mounted longitudinally or parallel to the direction of traffic. A sensor designation "TE" indicates a strain sensor was mounted transversely or perpendicular to the direction of traffic. Two different sensor models have used the designation "LE" or "TE". Prior to 2008, the LE and TE strain sensors were an electrical resistance strain gauge embedded within a strip of glass-fiber reinforced epoxy, with transverse steel anchors at each end of the strip to form an H-shape. After 2007, the LE and TE strain sensors are an electrical resistance (full bridge) strain transducer, utilizing a nylon rod with transverse steel anchors at each end to form an H-shape.

Manufacturers

Pre 2008: Dynatest model PAST-2AC. Post 2007: CTL Model ASG152.

Location and Quantity

LE and TE sensors are positioned at the bottom of the hot-mix asphalt layers near wheelpaths.

Current Status

These sensors have performed very well, with a demonstrated life span of approximately 2 years. Original (1993) sensors have either ceased to function, or have been removed due to reconstruction of a test cell. Newer sensors remain in service.

MnROAD Database Tables

Data continues to be collected during various load response testing sessions, and some has been processed and loaded into the MnROAD database. Data is located in database tables named: MNR.DYNAMIC_LOAD_TEST_VALUES and MNR.DYNAMIC_LOAD TEST DESCRIPTIONS.