Page 125 - RoadCem Manual - PCT BV

has become increasingly recognized worldwide that, under favorable circumstances, or when using appropriate material property modifiers such as RoadCem, almost all such materials can and, indeed, have been used successfully. However, this requires an in-depth knowledge and experience of the properties of such materials and the conditions necessary for successful performance.
It should be noted that the concept of “non-standard” in relation to materials is specific to a particular time and place associated with our level of understanding of the behavior of the material and knowledge of how to use it.
For example, forty or fifty years ago, gravel was considered as a nonstandard material because crushed stone, the “standard” material, was used in the construction of Macadam and Telford pavements.
5.2.4 Characteristics of Pavement Materials
Materials used in pavement layers can be classified into three categories as follows:
• Unbound granular:
• Unprocessed (naturally occurring, as dug).
• Processed (screened, mechanically stabilized).
• Highly processed (crushed to specified grading).
• Bound granular.
• Cement, lime, bitumen or pozollanic material.
The material types described above derive their strength from a combination of the following intrinsic
properties:
• Inter-particle friction.
• Cohesive effects from fine particles.
• Soil suction forces.
• Physic-chemical (stabilization) forces.
The relative dependence of a material and the influence of moisture on each of the above components of shear strength will significantly influence the manner in which they can be incorporated within a pavement. For example, unbound/unprocessed materials (e.g. calcrete or ferricrete) are highly dependent on suction and cohesion forces for development of shear resistance that will only be generated at relatively low moisture contents. Special measures therefore have to be taken to ensure that moisture ingress into the pavement is prevented. Otherwise suction forces and shear strength will be reduced as illustrated (notionally) in Figure 5.21, possibly resulting in failures.
125