During my original post which generated a lot of discussion mention was made to RoadCem as ‘Pixy Dust’ which I believe was originally a reference to our claim to be introducing Nano Technology into soil stabilisation.
Perhaps an explanation could be useful.
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.
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.
If these pores fill with water, the magnitude of the suction decreases rapidly.
RoadCem/Cement modified materials are essentially waterproof and have a highly reduced porosity after 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 Mohr-Coulomb 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 decreased 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 directly proportional to cohesion.
As the pores fill with water, the magnitude of the suction decreases rapidly. RoadCem/Cement modified materials are essentially waterproof and have a highly reduced porosity. The pores with RoadCem are normally of a size range 2.5 to 20 Nano meters (nm) (or 0.0025 to 0.02 microns) and are considered harmless pores.
Pores in cement stabilised soils without RoadCem will normally be larger decreasing the mechanical strength, density, as well as the ability of the stabilised soil to resist degradation and long-term saturation. With RoadCem the voids in the stabilisation are generally filled by the increased crystallisation, the mechanical strength, density and life span of the structure increases substantially.as a result of treatment so suction forces can never develop to significant level.
The effective stresses in subgrade could be reduced due to increased pore water pressure, and as a result, reduce stiffness and strength of the subgrade. The change in moisture content and pore water pressure could significantly impact the load-bearing capacity and performance of pavement structure.