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Enhanced Flexible Base Test Procedures Improve Consistency

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The Texas Department of Transportation (TxDOT) and AGC members agree that high quality construction materials are essential to the success of every job. Ensuring that materials meet design specifications accomplishes that goal.

TxDOT recognizes that consistency of testing procedures is also essential to the process, so contractors and material suppliers know exactly what is expected to meet specification requirements.

Recent changes to TxDOT test procedures governing sampling, laboratory compaction, and strength testing of flexible base material have significantly improved consistency among laboratories and reduced construction delays. One key element of the changes is the requirement that laboratory compactors are controlled by a Soil Compactor Analyzer (SCA).

The SCA measures and controls the amount of compaction energy delivered to a flexible base sample during molding. The SCA attaches to the automatic tamper specified in test method Tex-113-E and measures hammer impact velocity.

Using the mass of the hammer and the velocity, the SCA calculates the energy of each hammer drop applied to the sample. When the layer being compacted receives the required 750 feet per pound of energy, the SCA stops the compactor. The technician prepares the next layer, starts the SCA, and repeats the process until all four layers have been compacted.

Prior to development of the SCA, the compaction energy delivered to the sample was controlled by specifying the weight of the hammer, the drop height, and the number of blows per layer. Although mathematically correct, this method does not take into account the loss of energy caused by friction that occurs during operation of the automatic tamper. By measuring the actual energy delivered to the specimen and allowing the number of drops to vary, the SCA eliminates equipment variability and significantly increases uniformity of each specimen.

All twenty-five TxDOT district laboratories are equipped with SCAs. In addition, several industry laboratories have acquired SCAs and are listed on TxDOT’s Material Producer List, “Laboratories Approved to Perform Compaction and Triaxial Compression Testing,” located on the TxDOT website at http://www. txdot.gov/business/contractors_consultants/producer_list.htm. The SCA is commercially available from Schmitz Engineering and Innovation, LLC and Rainhart Co.

Specific questions regarding the SCA and test procedure changes or recommendations for future changes should be directed to Caroline Herrera, P.E. or her staff at the Geotechnical, Soils, and Aggregates Branch of the Construction Division. 512.506.5907 or This email address is being protected from spambots. You need JavaScript enabled to view it..

The strong working relationship between TxDOT and AGC serves as the foundation of our goal to provide safe and reliable transportation solutions for Texas. Thank you for your dedication and continuous commitment to setting the bar higher each year.

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