Page 126 - RoadCem Manual - PCT BV
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      Figure 5.21 Illustrative soil strength/suction relationship
RoadCem approach is actually based on the ability of RoadCem, in tandem with Cement, to modify the characteristics of pavement materials and in so doing enhance those desirable characteristics and reduce the characteristics which could be responsible for the failure of the pavement structure.
Working of RoadCem
As the grain size of a fine-grained material decreases, the total exposed surface area becomes very large in relation to the volume of voids within it. Under these circumstances, molecular forces, which are only effective for very short distances from the surface, begin to play an increasingly important role. They are essentially attractive in nature and can provide significant additional strength. The forces are equivalent to, and can be described by, a reduction in pressure in the “pores” or voids in the material.
This is referred to as suction. As the magnitude of soil suction can be very much greater than normal atmospheric pressure, the effective pressure can become highly negative. Its value depends not only on the amount of fluid in the pores (voids) but also on its nature, i.e. dissolved salts. As the pores fill with water, the magnitude of the suction decreases rapidly.
RoadCem/Cement modified materials are essentially water proof and have a highly reduced porosity as a result of treatment so suction forces can never develop to significant level.
The shear strength of granular materials and normally consolidated fine-grained soils is described by the well known effective stress equation:
Shear strength = (cohesion) + [(normal stress) – (pore pressure)] Tan (angle of internal friction)
The strength and stiffness of a pavement layer are reduced if pore pressure is increased (at high moisture contents) and conversely are increased when pore water pressure is decreased (at low moisture contents). When the pore pressure equals the total stress, internal friction becomes negligible and the shear strength is directley proportional to cohesion.
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