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Durability
Durability is a measure of how asphalt binder physical properties change with age (sometimes called age hardening). In general, as an asphalt binder ages, its viscosity increases and it becomes more stiff and brittle. Age hardening is a result of a number of factors, the principal ones being (Vallerga, Monismith and Grahthem, 1957[1] and Finn, … Read more
Design Parameters
When designing pavements (both mix design and structural design), there are three fundamental external design parameters to consider: the characteristics of the subgrade upon which the pavement is placed, the applied loads and the environment. First, the subgrade upon which the pavement is placed will have a large impact on structural design. Subgrade stiffness and … Read more
Design Life
Pavements are typically designed for a specified “design life”. Design life (or “design period”) is the time from original construction to a terminal condition for a pavement structure. A terminal condition refers to a state where the pavement needs reconstruction. Structural design is carried out so that the pavement structure is sufficient to withstand the … Read more
Cutback Asphalt
A cutback asphalt is simply a combination of asphalt cement and petroleum solvent. Like emulsions, cutbacks are used because they reduce asphalt viscosity for lower temperature uses (tack coats, fog seals, slurry seals, stabilization material). Similar to emulsified asphalts, after a cutback asphalt is applied the petroleum solvent evaporates leaving behind asphalt cement residue on … Read more
Crack Seals
Crack seal products are used to fill individual pavement cracks to prevent entry of water or other non-compressible substances such as sand, dirt, rocks or weeds. Crack sealant is typically used on early stage longitudinal cracks, transverse cracks, reflection cracks and block cracks. Fatigue cracks are most often too extensive to warrant filling with crack … Read more
Compressive Strength
PCC is most often known by its compressive strength. This is because PCC is much stronger in compression than it is in tension and thus, is often used in compression. The ACI Concrete Code gives some rough rules-of-thumb for converting compressive strength to tensile and flexural strength: where: = compressive strength Description Compressive strength is … Read more
Capillary Rise
Capillary rise is the rise in a liquid above the level of zero pressure due to a net upward force produced by the attraction of the water molecules to a solid surface (e.g., soil or glass). Tabor, in 1930, recognized that frost heaving required substantially more water than was naturally available in the soil pores … Read more
Central Mixed PCC
Central mixed PCC is usually proportioned by batching the separate ingredients into a central plant mixer (see Figures 1 through 4) where they are completely mixed before discharge into a transport vehicle. Transport vehicles can be concrete mixing trucks or conventional end and bottom dump trucks depending upon travel distance and other requirements. About 20 percent … Read more
Bottom Dump Truck
Bottom dump trucks, most often used for HMA in more rural settings, (Figure 1) unload their payload by opening gates on the bottom of the bed. Internal bed walls are sloped to direct the entire payload out through the opened gates. Discharge rates can be controlled by the degree of gate opening and the speed … Read more
Aggregate Specific Gravity
Aggregate specific gravity is useful in making weight-volume conversions and in calculating the void content in compacted HMA (Roberts et al., 1996[1]). AASHTO M 132 and ASTM E 12 define specific gravity as: “…the ratio of the mass of a unit volume of a material at a stated temperature to the mass of the same … Read more
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