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Despite the great impact of the stabilizer on SMA quality, few countries have devel­oped testing methods and criteria for the practicality of stabilizers. Some assess­ment methods for the application of stabilizers in various countries are presented in Chapter 5. Practice proves that a reliable stabilizer-effectiveness assessment can be carried out when the same SMA mixture […]

The procedure for the quantitative selection of a stabilizer in a mix is simple, although it may be a little laborious. One of the draindown testing methods described in Chapter 8 may be adopted here. A series of SMA samples of the same composition should be prepared, but with different quantities of stabilizer. If the […]

The second way to counteract the draindown phenomena is to use a binder viscos­ity promoter. The most common agents used to be polymers, either plastomers or elastomers. Test results show, however, that the efficiency of polymers is not as good as that of fibers. Currently in many countries, regardless of the type of applied binder […]

Loose fibers are packed in self-shrinkable plastic bags. They are thrown into a mixer intact and the film melts into the binder during mixing. Granulated cellulose fibers may be bagged like other fibers (Figure 4.7) or packed in big-bags (Figure 4.8). Both loose and granulated fibers can be supplied in autotankers (Figure 4.9). FIGuRE 4.7 […]

Granulated products (Figure 4.6a and b) are produced by coating fibers with a binder or other binder-soluble agents. A binder coating enables control of the forces on fibers during granulation and separation of individual fibers, which is necessary for distributing them evenly in an SMA mix. The granulated form of these products makes dosage at […]

Loose fibers may be pressed into pellets to keep the fibers together without bind­ing agents. Their shape makes metering of the SMA mix during production easier. Pelletized fibers are formed into different shapes; one example is presented in Figure 4.5. Automatic loading with pneumatic feeders is also possible and easy. The pellets are usually supplied […]

Loose cellulose threads (Figure 4.4) have the longest history of application. One of their advantages is that they become effective immediately after mixing them with aggregate and binder. They should be protected from moisture as they are highly hydrophilic and easily absorb water. Wet fibers are not able to absorb the binder and therefore are […]

Binder-absorbing additives are the most popular SMA stabilizing agents. The fol­lowing properties are required of a stabilizing material: • Adequate binder absorbing power—this is the most significant property • Ability to act without weakening the mixture—the stabilizer must not cre­ate glide planes and lessen the grain-interlocking strength. Stabilizers of this type occur in various forms […]

In the 1960s—during the beginning stages of SMA manufacture—the need arose to incorporate stabilizing agents to prevent binder draindown. Such additives are called stabilizers; they stabilize or keep the binder in place. Because of these stablizers, an increase in the binder film thickness on the aggregate is possible. The two main techniques of reducing binder […]

Stone mastic asphalt (SMA) mixtures require a high content of binder, which results in thick binder films on the aggregate grains. To avoid the draindown effect, stabi­lizing additives (drainage inhibitors) are indispensable in most cases. This chapter describes the types of stabilizers and methods of testing them. 4.1 THE DRAINDOWN EFFECT Have you ever seen […]