The FHWA test road: construction and instrumentation

Public Roads, June, 1992 by Kevin Black, William Kenis

Instrumentation

The Test Road's experimental sections were designed to collect primary response measurements (deflection, strain) and environmental data (moisture, temperature). These parameters are typically needed to verify the use of mechanistic models in pavement design and life-cycle analysis. The baseline pavement profile was measured at completion of each layer to determine the variability of construction operation and provide initial elevation measurements for layer theory analysis. Table 1 shows the gauges installed, the parameters they measure, and the experiments in which they are used.

Pavement response is measured with strain gauges and deflectometers. The gauges installed were either the H-type (Kyowa) or a variety made by the Alberta Research Council (ARC). The deflectometers consisted of both single-layer and multilayer types and were installed in each section. The locations of the various instruments are shown in figure 5. A graphic display of each gauge is given in figure 6 a through f.

The H-type gauges were installed to measure the dynamic loading of the thick pavement section. To ensure their adherence to the underside of the asphalt pavement while retaining alignment along the path, the gauges were modified at the TFHRC Highway Electronics Laboratory. They were installed in a line of 36 gauges set 0.305 m (1 ft) apart.

The ARC strain gauges were placed to study strain in the pavement under controlled loading conditions. These gauges were placed in a pattern to cover the vehicle wheel print. A configuration of two rows of two in each section was used for redundancy. Deflectometers were installed to evaluate the degree to which the pavement layers deflect. The single-layer or single-point deflectometers, also supplied by ARC, were used in coordination with the ARC strain gauges. Multidepth deflectometers were used to evaluate the compressive strains occurring in the lower structural layers. These instruments were fabricated at Texas A&M University. Both types of deflectometers are linear variable differential transformers; they were anchored at a depth of about 3 m (10 ft) to isolate them from vibration, noise, and settlement.

The environmental gauges were used to correlate the weather and climatic conditions to the responses measured. Soil moisture was measured using gauges placed 152 mm (6 in) and 305 mm (12 in) into the subgrade under each section.

Thermocouples were installed to measure the temperature changes in the pavement during testing. Each section contained one set of instruments; these provide temperature information at seven locations from the pavement surface to a depth of 1.3 m (4 ft).

Truck-Pavement Interaction

The Test Road was developed to support the overall goals of the FHWA's high priority area on Truck-Pavement Interaction. The three phases are summarized:

* Load Equivalency Factors (LEF's).

* Primary Response Analysis.

* Vehicle/Pavement Interaction.

Accomplished work in each phase will depend on the results from test conducted on the Test Road, ALF, PITS, and DYNTRAC.