CHAPTER 16 PAVING OPERATIONS AND EQUIPMENT

The modern use of asphalt for road and street construction began in the late 1800s and grew rapidly with the emerging automobile industry. Today, asphalt technology is complex, and the equipment and techniques, used to build asphalt pavement structures, are highly sophisticated. This chapter presents only the basic components, procedures, and principles of paving _operations. The extensive knowledge and skills, required to perform the operations, must be gained through formal training and on-the-job-training experience.

NOTE: One rule that has remained constant throughout the long history of the use of asphalt in construction is this: a pavement is only as good as the materials and workmanship that go into it. No amount of sophisticated equipment can make up for the use of poor materials or poor construction practices.

PAVEMENT CONSTRUCTION

Modern paving is broadly divided into rigid paving and flexible paving. Both types consist of an aggregate blend (sand, gravel, crushed stone, etc.), bound together by a hardening or setting agent, called a binder. The primary difference between the two types of paving, from the standpoint of ingredients used, lies in the character of the binder.

The binder for most rigid paving is portland cement, and for this reason, rigid paving is often referred to as concrete paving. In flexible paving, the binder consists of bituminous material. Paving mixes, containing bituminous material, are referred to as asphalt-paving mixes.

ASPHALT-PAVING MIXES

Asphalt-paving mixes may be produced from a wide range of aggregate combinations, with each combination having its own characteristics and being suited to specific design and construction uses. Aside from the asphalt content, the principal characteristics of the mix are determined by the relative amounts of aggregates. The aggregate composition may vary from a coarse-textured mix to a fine-textured mix, depending on aggregate size and design specifications.

The selection of bituminous material depends upon the type of pavement, temperature extreme, rainfall, type and volume of traffic, and type and availability of equipment. In general, hard penetration grades of asphalt paving are used in warm climates and softer penetration grades in cold climates. Heavier grades of asphalt cutbacks and tars are generally used in warm regions.

Asphalt materials are produced by the refining of petroleum (fig. 16-1). Asphalt is produced in a variety of types and grades, ranging from hard, brittle solids to almost water-thin liquids. The semisolid form, known as asphalt cement, is the basic material.

Liquid asphaltic products are generally prepared by cutting back (blending) asphalt cements with petroleum distillates or by blending with an emulsified agent and water known as asphalt emulsion. Types of liquid asphaltic products are shown in figure 16-2.

Table 16-1 indicates various uses of asphalt for different types of construction.

BASIC CONCEPTS

The basic idea in building roads, airfields, or parking areas for all-weather use by vehicles is to prepare a suitable foundation, to provide necessary drainage, and to construct a pavement that has the following characteristics:

1. Has sufficient total thickness and internal strength to carry expected traffic loads.

2. Is capable of preventing both the penetration and accumulation of moisture.

3. Has a top surface that is smooth and skid resistant.

4. Is resistant to wear and distortion.

5. Is resistant to deterioration caused by weather conditions or by deicing chemicals.

The foundation ultimately carries all traffic loads. Therefore, the structural function of pavement is to support a wheel load on the pavement surface and to transfer and spread that load to the foundation without

Figure 16-3 shows the wheel load (W) transmitted to the pavement surface through the

Figure 16-1.-Petroleum asphalt flow chart.

overloading either the strength of the subgrade or the internal strength of the pavement itself. Being Figure 16-3 shows the wheel load (W) tire at transmitted to the pavement surface through the an approximately uniform vertical pressure (P405). The pavement then spreads the wheel load to the foundation, so the maximum pressure on the foundation is only P415. By proper selection of pavement materials and with adequate pavement thickness, P415 will be small enough to be easily supported by the subgrade.