Cement is one of the most popular soil stabilizers because it is readily available and generally can be applied to a wide range of materials. It is considered to have advanced properties. The unit price of cement varies greatly depending on the distribution network and the proximity of the cement manufacturing plant but in many parts of the world is one of the cheapest binders available.
Application of cement in soil stabilization starts with determining needed quantities of cement and water. The moisture of the soil-cement mixture needs to be carefully controlled. Sufficient moisture is necessary for the cement to fully hydrate but no excess water is allowed as it would reduce the final density, increase porosity, increase the water/cement ratio, reduce final strength and contribute to shrinkage cracking. Unless properties are known from previous projects which utilised the same pavement materials, the amount of cement to be added is normally determined by laboratory testing. Water levels are usually controlled in the field at the time of construction using simply field-based test.
The cement is usually delivered by specialised cement spreaders or hopper trucks and evenly spread over the pulverized soil. Moisture contents are normally targeted at being 1 to 2 % lower than the optimum required for compaction.
Compaction of the mixture has to be performed before the mixture begins to set. The time between the addition of water and the compaction will depend on the characteristics of the cement being used and can typically vary between one and four hours.. The mixture is first compacted by sheepsfoot and then followed by steel drum and pneumatic-tired rollers. It is important that the impressions made by the sheep foot are worked up with the use of a grader and steel drum roller. The pneumatic-tired roller use used to provide a tight surface texture.
Hydration of cement results in gel-forming around cement particles and growing into an interlocking matrix which coats soil particles. The effect of the use of cement in soil stabilization may be to lower the plasticity of the material and make it more moisture insensitive or to create an agglomerated structure of calcium silicate hydrates and calcium hydroxide which bound surrounding particles. The later can result in increased tensile strength which can be susceptible to cracking if overloaded as well as shrinkage cracking as the cement hydrates.
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Shrinkage cracking is seen as an undesirable outcome by many road asset owners.
If there is a significant percentage of particles smaller than 425 microns within the material being stabilized, application of cement in soil stabilization is not an optimal solution, as these fine particles hinder the cementitious process.
Although considered as proven solution cement in soil stabilization has numerous drawbacks. It is not effective in all soil types, if dosage rates are high the failure mechanism can be brittle in nature, it can be susceptible to unsightly shrinkage cracking which allows the entry of moisture and the damaging effect under oversize or overloaded vehicles are much higher than flexible materials.
When used in combination with cement GRT’s PCM overcomes a lot of these inadequacies and provides a more reliable solution with improved performance and properties.
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