defining_pavement_b_1 B. the word "pavement" does not only refer to the smoothe driving surface. 1 - RIGHT: the "real pavement" (example is a typical pavement for an asphalt driving surface roadway):
note above that:   (i) only the top 1-2 inches of "the pavement" is the applied asphalt driving surface.  (ii) and that most of "the pavement" entails various other strates and courses, per geotechnical and/or pavement engineer's specifications and design; [In figure 6.1 above: this typical example of a civil asphalt roadway, the asphalt "smoothe driving surface" layer makes up only 2.857% up to 11.111% of the entire pavement.] (iii) and that the various non-asphalt (compacted aggregate) strata and courses are required in order to achieve various engineering functions, design components which derive from, and are dependant upon, the known physical weaknesses of the finished driving surface: in this example asphalt . In the example above, the known physical weaknesses of the asphalt driving surface which must be compensated for in the design include: (a) Extremely low tensile strength: lack of horizontal connectivity. in section (a) above: because the [relatively] rigid concrete or asphalt conventional paving cannot flex and recoil back to position, when exposed to severe dynamics of moving heavy loads; the tension on the driving surface forms submicroscopic or visible fissures, flaws and faults. These faults expand rapidly when exposed to further torsional and/or rotational [horizontal] forces. (b) Rigidity [relative to ecoraster]: prone to fractures and cracks, caused when the traffic axles create traveling waves of surface tensions. in section (b) above: when even submicroscopic fissures or pores are created on the asphalt of concrete surface, precipitation exploits and penetrates these flaws. During winter freeze/thaw cycles, this degeneration of the conventional paving surface is rapidly accelerated. (c) Impermeabililty: conversion of precipitation into surface sheetwater, as opposed to infiltration into the earth: Thereby creating a hydrologic void (vacuum of water) within the compacted compacted aggregate roadbase and subsoil. This hydrolologic void resists the most irresistable and destructive force majeur in the earth: the flow of water following the path of least resistance. Across time - the flow of water will:  fill the hydrologic void, penetrating into the suboil, migrating the subsoil, decaying the compacted roadbase at its foundation. Extraordinary pavement engineering is required to [temporarily] stave off the the deconstructive force majeur: the flow of water following the path of least resistance.
Those pavement design function requirements [of conventional rigid + impermeable pavements], which are demanded by the choice of conventional vehicular traffic surfaces, will also  include: (a) that the "natural subghrade" earth may support the vehicular traffic weights when stationary (this is a minimal requirement in most soil types, and is true for all vehicular traffic designers, regardless of the type of "finish" applied for smoothe driving surface); (b) to prevent subsurface horizontal migration of groundwater beneath and into the pavement (this is required in order to retain + stabilize the "hard compacted aggregat roadbase" that the driving surface requires in order to retain its shape + size; and is specifically required in order to compensate for the known physical weaknesses of the asphalt, per se its absence of horizontal connectivity); (c) to prevent subsurface shifting of the base across time (most often due to the subsurface migration of groundwater seeking the path of least resistance + seeking to "fill the vacuum of moisture content" created by the compacted roadbase); (d) to provide a "hard solid base" to support the asphalt surfacing (i.e. to prevent the deconstruction of the asphalt into broken slabs or chunks); (e) and an impermeable roadbase, to counteract asphalt's susceptibility to damage/decay resulting from ground surges and upheavals during winter freeze/thaw cycles.