A few years ago, at the beginning of the work on this book about SMA, I did not suppose it would take on such imposing proportions. Meanwhile, over the course of work on the publication, it turned out that the quantity of accessible materials on SMA was really spectacular, and the range of SMA-related subjects was enormous. While carrying out a survey on relevant publications, it became noticeable that SMA was still a fascinating asphalt mixture to many process engineers the world over.
All in all, it would be appropriate to finish briefly, in contrast to the content of the book, which might seem to be a bit verbose here and there. Nevertheless, I do hope that it will help its readers comprehend SMA and clear up any problems that might arise.
It is a matter of course that the examples quoted in the book cannot fully correspond with personal experiences of each individual reader. Should anybody like to exchange views about SMA mixture, please get in touch with me by e-mail at sma@ road. pl.
* Road binders (bitumens) B65 and B80 were based on Pen@25°C range according to German DIN standard: B65 was 50-70 dmm, B80 was 70-100 dmm.
[2] Germany, Patent No. 1926808 (1969); United States, Patent No. 3797951 (1971); Sweden, Patent No. 7110151-3 (1972); France, Patent No. 71.28874 (1971); Luxembourg, Patent No. 63688 (1971).
[3] This subject will be discussed in Chapter 7.
[4] When arranging spheres and circles as in Figure 2.6a and b, the passive grains cannot be bigger than 0.41 R. So, in an SMA 0/12-mm mixture. Assuming that the active grains are 8/12 mm, the next smaller size fraction should be just 2/5 mm to prevent shoving the active grains apart. The desired gradation discontinuity is developed by the absence of the 5/8 mm fraction.
[5] For more information, see the discussion of Kjellbase in Chapter 13.
* It is a requirement regarding an SMA surface course after its incorporation; for more information, see Chapter 10.
[7] AASHTO is the standards setting organization; founded in 1914, it was known as the American Association of State Highway Officials (AASHO) before 1973.
[8] See Chapter 11.
[9] In this book definitions of the mastic and mortar will be used as presented here. However, in numerous countries these definitions differ from those adopted in this book; for example, in the United States mastic is called total mortar and mortar is called fine mortar (and contains drainage inhibitor, which is a stabilizing additive). f BBR — Bending Beam Rheometer.
[10] The flow rate method, similar to the European concept, is not standardized in the United States Comparison tests have been conducted and are published in (Tayebali et al, 1996).
[11] Filler grains smaller than the bitumen film on aggregates can behave like a carrier (binder extender); very fine filler makes the mix behave as if there is even more binder present, which may result in such problems as the loss of surface course stability, rutting, binder bleeding, and fat spots.
• Filler grains bigger than the binder film on aggregates behaves like a filling aggregate, forming mastic, and taking part in filling up the voids among chippings.
• An excess of filler leads to mastic stiffening and the increase of cracking susceptibility.
• The affinity between filler and binder influences the durability of the mix (i. e., its sensitivity to water).
• The appropriate ratios of binder and filler, combined with their properties, have an influence on an SMA mixture’s workability and, continuing from that, influence the SMA compaction (or final field density).
[12] Blaine’s test is not very accurate for it does not take into account fine voids (area textures); more precise measurements can be performed with laser devices (Grabowski and Wilamowicz, 2001).
[13] In this example, the content of voids in dry-compacted filler is being tested after Rigden’s method or Rigden’s method modified by Anderson (see Chapter 8).
[14] That state might be called a colloidal system of grains (solid bodies) suspended in binder (fluid body). A blend of binder and filler may be regarded as something in between a gel and an alloy at the working temperature of a road pavement (Harris and Stuart, 1995).
[15] DSR — Dynamic Shear Rheometer. t According to the EN 13043 standard.
[16] According to the EN 12597 standard Bitumens and binder products. Terminology, “hot” applied bitumens may be divided into road bitumens (soft and hard), modified (including polymer modified) and special.
[17] Additives that absorb part of the binder (the surplus that is likely to draindown)
• Additives (polymers) that increase binder viscosity at high temperatures, which in turn reduce the risk of its draindown
[18] Cellulose—the most popular (Shown in Figure 4.1)
• Pseudocellulose—made of milled or fragmented waste paper
• Mineral fiber—developed through melting rocks and subsequently processing the melted rock to form threads (like rock wool)
• Cellulose-mineral—a blend of cellulose and mineral fibers occurring in various compositions (proportions)
• Cellulose-polymer—a blend of cellulose fibers and different types of polymers occurring in various compositions (proportions)
• Cellulose-wax—a blend of cellulose fibers and synthetic waxes, which not only stabilizes but changes the binder viscosity-temperature relationship as well
• Textile—threads of processed and fragmented textile waste products
• Plastics—for example, polypropylene (Shown in Figure 4.2)
[19] This method, which is described in European Standard EN 1097-1, could also be performed without water. In the United States the Micro-Deval method is based on AASHTO T327 (ASTM D6928).
[20] The notation Declared exclusively denotes the necessity of giving a test result without determining any threshold limit for that requirement.
• The notation Category refers to the following:
• An absolute numerical value for a given category in the system presented in EN 13043: the numerical limit is shown in the table following a letter symbol for a given category (see also Table 5.1 for explanations)—for example, a category MBF10 means the requirement is MBF is less than or equal to 10 g/kg according to test method EN 933-9 or PSV50 means requirement PSV is great than or equal to 50 according to test method EN 1097-8).
• A declared value, which means the result of the test is outside the bounds of the last category with a specified numerical value—for example, category MBFDeclared is used when test result is larger than 25 g/kg. For two specified properties: resistance to polishing (PSV) and resistance to abrasion from studded tires (AN), declared values mean both—result of the test outside the limit or any intermediate value.
[21] Council Directive 89/106/EEC of 21 December 1988 on the approximation of laws, regulations, and administrative provisions of the Member States relating to construction products.
[22] Fiber length: maximum 6 mm
• Thickness or diameter of mineral fibers: maximum 0.005-mm mean test value
• Gradation of cellulose fibers
• Passing a 0.15-mm Alpine sieve (method A): 70% ± 10%,
• Passing 0.85-, 0.425-, and 0.106-mm mesh screen sieves (method B): 85% ± 10%, 65% ± 10% and 30% ± 10%, respectively
[23] SMA position (in a wearing course or in an intermediate course)
• Design thickness of the course after compaction
• Traffic load and the location of the road section (e. g., rural or urban)
• Additional requirements for the SMA course
[24] All four variants have preserved a fixed content of chippings at a level of 75%.
[25] A finer graded coarse fraction is characterized by a greater amount of smaller pores more evenly distributed through the mix, which brings about better interparticle contact and, in contrast, increases the risk of shoving grains aside by larger particles of the sand fraction.
• A coarser graded coarse fraction is characterized by a smaller amount of larger-sized pores unevenly distributed over a mix.
[26] The contents of air voids in the aggregate mix (i. e., VMA), causing a substantial rise in the optimum quantity of binder—the very high volume of air voids in the coarse aggregate skeleton must be filled in with binder
• The SMA resistance to permanent deformation, which is an advantageous effect
[27] These values are of TL-Asphalt 07 and come from the new methods of density measurements (according to EN); in the old ZTV StB 01 corresponding values were 3-4% (v/v).
Designations used in German guidelines for SMA: N = low and medium traffic, S = heavy traffic (e. g., SMA 11S).
[28] Selecting an aggregate
• Designing a gradation curve that secures the desired interparticle contact (stone-to-stone contact)
• Selecting the gradation corresponding with the criterion of a minimum of air voids in an aggregate mix (minimum VMA)
• Selecting an amount of binder for a target content of air voids in compacted specimens of the asphalt mixture
• Checking for draindown and water susceptibility
Next we will follow the U. S. cycle of design through its successive stages.
