Engineer
Compaction Measurement and Reporting
Compaction reduces the volume of air in HMA. Therefore, the characteristic of concern is the volume of air within the compacted pavement. This volume is typically quantified as a percentage of air voids by volume and expressed as “percent air voids”. Percent air voids is calculated by comparing a test specimen’s bulk density with its … Read more
Nuclear Density Gauge
A nuclear density gauge measures in-place HMA density using gamma radiation. Gauges usually contain a small gamma source (about 10 mCi) such as Cesium-137 on the end of a retractable rod. Gamma rays are emitted from the source and interact with electrons in the pavement through absorption, Compton scattering, and the photoelectric effect. A … Read more
Asphalt Mixture Performance Test
Overview The asphalt mixture performance tester (AMPT) is the companion performance test for use with the Superpave mix design procedure. Although the original SHRP asphalt research program was essentially done by 1993, it did not include a performance test for use with the rest of the Superpave mix design procedure. The AMPT is actually a … Read more
HMA Pavement
HMA pavements are classified as “flexible” pavements because the total pavement structure deflects, or flexes, under loading. A flexible pavement structure is typically composed of several layers of material. Each layer receives the loads from the above layer, spreads them out, then passes on these loads to the next layer below. Thus, the further down … Read more
HMA Weight-Volume Terms and Relationships
Basic HMA weight-volume relationships are important to understand for both mix design and construction purposes. Fundamentally, mix design is meant to determine the volume of asphalt binder and aggregates necessary to produce a mixture with the desired properties (Roberts et al., 1996[1]). However, since weight measurements are typically much easier, they are typically taken then … Read more
Permeable Pavements
Description Permeable pavements allow water to infiltrate through surfaces that would normally be impermeable, such as asphalt or portland cement concrete parking lots. (NCDENR, 2007[1]) Rain and snow may then recharge the groundwater table, and air may pass through to nourish the roots of grass and trees. Pervious surface treatments reduce the risk of stormwater … Read more
Life Cycle Assessment
The International Organization of Standardization (ISO) wrote guidelines for life cycle assessment. Examining manufacturing and construction processes and making comparisons between material and process options has great promise for encouraging positive environmental impacts. Standardization of this process leads to greater opportunity for data sharing and adds consistency to reports from different people and organizations. The … Read more
Asphalt Additives
Additives Asphalt additives are any of a number of substances that can be added to the asphalt binder to alter the characteristics of the final blend of HMA. Sasol Sasol production meets about 30% of South Africa’s transportation fuel needs. There are two major plants in South Africa, one at Sasolburg, which is a natural … Read more
Asphalt Modifiers
Some asphalt cements require modification in order to meet specifications. Asphalt cement modification has been practiced for over 50 years but has received added attention in the past decade or so. The added attention can be attributed to the following factors (Roberts et al., 1996[1]): Increased demand on HMA pavements. Traffic volume, loads and tire … Read more
Dowel Bar Retrofit Construction Practices
Introduction The following describes and illustrates the dowel bar retrofit construction process. In addition, descriptions of critical details for ensuring pavement performance are also included. In general, the dowel bar retrofit process includes the following steps: Using diamond saw blades, sawcut dowel bar slots (three to four per wheelpath). Remove existing concrete within dowel bar … Read more
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