Types of Additives Used The various additives used fall under the following categories:
(i) Cementing materials: Increase in strength of the soil is achieved by the cementing
action of the additive. Portland cement, line, fly-ash and sodium silicate are examples
of such additives.
(ii) Water-proofers: Bituminous materials prevent absorption of moisture. These may
be used if the natural moisture content of the soil is adequate for providing the
necessary strength. Some resins also fall in this category, but are very expensive.
(iii) Water-retainers: Calcium chloride and sodium chloride are examples of this category.
(iv) Water-repellents or retarders: Certain organic compounds such as stearates and
silicones tend to get absorbed by the clay particles in preference to water. Thus,
they tend to keep off water from the soil.
(v) Modifiers and other miscellaneous agents: Certain additives tend to decrease
the plasticity index and modify the plasticity characteristics. Lignin and
lignin-derivatives are used as dispersing agents for clays.
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