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Inspector

Any individual who is responsible for inspecting a paving site or production facility. This work may include quality control and troubleshooting when production problems arise.
Figure 1: Thin lift nuclear density gauge.

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 »

Figure 3. Limerock base course undergoing final grading.

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 »

Figure 12: Cutting equipment for one dowel bar slot at a time.

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 »

Figure 2. Dowel bars in slots.

Dowel Bar Retrofit

Dowel bar retrofitting is a method used to restore or provide better load transfer across transverse joints or cracks using dowel bars. Usually, dowel bar retrofits are necessitated by excessive faulting due to a loss of aggregate interlock over time. It is interesting to note that much of the rigid pavement built in the U.S. … Read more »

Figure 2. Large vibratory steel wheel roller (17 tonnes (18.7 tons), 213 cm (84-inch) wide drum).

Compaction Equipment

There are three basic pieces of equipment available for HMA compaction: (1) the paver screed, (2) the steel wheel roller and (3) the pneumatic tire roller.  Each piece of equipment compacts the HMA by two principal means: By applying its weight to the HMA surface and compressing the material underneath the ground contact area.  Since … Read more »

Figure 2. Side tie bar inserter.

Tie Bar Placement

Tie bars are typically placed after PCC placement either by hand or using a tie bar inserter attachment (slipform paving only). When one lane at a time is paved, tie bars are inserted at mid-slab depth and bent back until the adjacent lane is ready to be paved (see Figure 1). On slipform pavers, tie … Read more »

Figure 1: Dense-Graded HMA Up Close

Mix Types

HMA Mix Types The most common type of flexible pavement surfacing in the U.S. is hot mix asphalt (HMA). Hot mix asphalt is known by many different names such as hot mix, asphalt concrete (AC or ACP), asphalt, blacktop or bitumen. For clarity, this Guide makes a conscious effort to consistently refer to this material … Read more »

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Pavement Life-Cycle

This section discusses the basic pavement life-cycle and how maintenance and rehabilitation affect this life-cycle. All pavement deteriorates over time. Typically, pavement deteriorates at an ever-increasing rate: at first very few distresses are present and the pavement stays in relatively good condition, but as it ages more distresses develop with each distress making it easier … Read more »

Oil is very easily apparent on the surface of water.

Key Pollution Concepts

Introduction The connection between pavement and pollution may not be immediately obvious. However, the United States has nearly four million miles of roads. (Low Impact Development Center, Inc. et. al.[1]) In a very simple breakdown, people drive and goods are transported on these roads; burning of fossil fuels in engines creates air pollution, while rain … Read more »

Polished PCC aggregate after 40 years of wear.

Polished Aggregate

Description Areas of pavement (either PCC or HMA) where the portion of aggregate extending above the asphalt binder (in the case of HMA) or cement paste (in the case of PCC) is either very small or there are no rough or angular aggregate particles. Problem Decreased skid resistance Possible Causes Repeated traffic applications. Generally, as … Read more »

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