Lab/Field Technician
Mixture Characterization Tests
Mixture characterization tests are used to describe fundamental mixture parameters such as density and asphalt binder content. The three primary mixture characterization tests discussed here are: Bulk specific gravity Theoretical maximum specific gravity Asphalt content/gradation Bulk Specific Gravity Bulk specific gravity is essentially the density of a compacted (laboratory or field) HMA specimen. The bulk … Read more
Dense-Graded
A dense-graded mix is a well-graded HMA mixture intended for general use. When properly designed and constructed, a dense-graded mix is relatively impermeable. Dense-graded mixes are generally referred to by their nominal maximum aggregate size. They can further be classified as either fine-graded or coarse-graded. Fine-graded mixes have more fine and sand sized particles than … Read more
Resistance Value
The Resistance Value (R-value) test is a material stiffness test. The test procedure expresses a material’s resistance to deformation as a function of the ratio of transmitted lateral pressure to applied vertical pressure. It is essentially a modified triaxial compression test. Materials tested are assigned an R-value. The R-value test was developed by F.N. Hveem … Read more
HMA Performance Tests
Performance tests are used to relate laboratory mix design to actual field performance. The Hveem (stabilometer) and Marshall (stability and flow) mix design methods use only one or two basic performance tests. Superpave is intended to use a better and more fundamental performance test. However, performance testing is the one area of Superpave yet to … Read more
Workability
Workability is a general term used to describe the basic rheological aspects of fresh PCC (e.g., PCC in a wet, plastic state). Workability is instrumental in the proper placement and compaction of fresh PCC. In general, excessively stiff (or harsh) fresh PCC can be difficult to place and compact resulting in large void spaces and … Read more
Aggregate
“Aggregate” is a collective term for the mineral materials such as sand, gravel and crushed stone that are used with a binding medium (such as water, bitumen, portland cement, lime, etc.) to form compound materials (such as asphalt concrete and portland cement concrete). By volume, aggregate generally accounts for 92 to 96 percent of HMA … Read more
Ductility
The ductility test (Figure 1) measures asphalt binder ductility by stretching a standard-sized briquette of asphalt binder (Figure 2) to its breaking point. The stretched distance in centimeters at breaking is then reported as ductility. Like the penetration test, this test has limited use since it is empirical and conducted at only one temperature (25° … Read more
Acceptance Plan Basics
In general, a statistical acceptance specification is simply an acceptance procedure. An acceptance procedure is a formal procedure used to decide whether work should be accepted, rejected, or accepted at a reduced payment (Freeman and Grogan, 1998[1]). This makes acceptance procedures a form of quality assurance. Specifically, they are monitoring methods used to determine whether … Read more
Marshall Method
Most private laboratories use the Marshall method because it is a proven method and requires relatively light, portable and inexpensive equipment. Like the Hveem and Superpave methods, the Marshall method has been proven to produce quality HMA from which long-lasting pavements can be constructed. This section briefly discusses the Marshall mix design method. The basic … Read more
Asphalt
“Asphalt” is a dark brown to black, highly viscous, hydrocarbon produced from petroleum distillation residue. This distillation can occur naturally, resulting in asphalt lakes, or occur in a petroleum refinery using crude oil. In 2001, the U.S. produced almost 35 million tons of asphalt at a rough value of around $6 billion. Roads and highways … Read more
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