Grouted Macadam: Material Characterisation for Pavement Design

Chapter 2 Review of “Traditional” Road Pavement Types and Design
properties of the job standard mixture either by: (i) the characteristic compressive
strength Rck of specimen (System I); (ii) the characteristic direct tensile strength Rtk
or the indirect tensile strength Ritk and the modulus of elasticity (E) of specimen
(System II). Table 2.3 shows the new classification regarding System I.
Classification according to System II is presented in Figure 2.9 and Table 2.4.
Similar classifications can also be found, for slag and fly ash bound mixtures, in BSI
(2004a, 2004b), as well as for hydraulic road binder bound mixtures (BSI, 2004c).
Table 2.3 – Characteristic compressive strength of CBGM – System I (BSI, 2004)
28 days compressive strength (MPa)
Characteristic strength Rck
Cylinders
H/D a Cylinders or Cubes
= 2.0
H/D a = 1.0 b
Strength class
No requirement C0
1.5 2.0 C1.5/2.0
3.0 4.0 C3/4
5.0 6.0 C5/6
8.0 10.0 C8/10
12 15 C12/15
16 20 C16/20
20 25
a
H/D = ratio between the height and the diameter of the specimen.
C20/25
b H/D = 0.80 to 1.21.
Table 2.4 – Characterisation of CBGM by tensile strength and modulus of elasticity
at 28 days – System II (BSI, 2004)
Category Rt (MPa) for category curve
E (MPa) 1600 2000 5000 10000 20000 40000
Category Rt (MPa)
T5 0.64 0.70 1.00 1.23 1.46 1.59
T4 0.45 0.49 0.68 0.83 0.97 1.09
T3 0.33 0.36 0.48 0.58 0.68 0.75
T2 0.21 0.23 0.32 0.38 0.44 0.49
T1 0.12 0.13 0.18 0.22 0.26 0.29
Note: The table gives the values of R t and E used to draw the curves limiting the categories
T5, T4, T3, T2 and T1 in Figure 2.9
Transverse cracks often occur in the surface of composite pavements as a reflection
of either the cracks in an existing concrete pavement or the naturally occurring or
induced thermal stress cracks in the new CBM base (Figures 2.10 and 2.11).
Cracking in a CBM base is mainly the result of its failure in tension. It is well
established that a pavement layer, whether cement bound, concrete or asphalt, will
crack when the induced stresses, either externally applied or internally developed,
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