Clay Aggregates

One of the major factors limiting the development of paved roads in Guyana is the exorbitant cost of stone aggregate and binding materials (such as bitumen). Aggregates are typically mined in the interior of the country, and must be transported at great cost to the coast. Binding materials used on the wear layer of the road surface, such as bitumen, is imported at prohibitive cost, as the country does not yet have a local petrochemical industry.

During the periodic rainy seasons in Guyana, the agricultural access roads and the roads in rural villages are transformed into muddy morasses, which impacts not only the comfort of the villagers, but significantly impedes the transportation to Georgetown and other urban centers.
Fired clay aggregates have been used in Guyana since the early 1800’s, particularly by the sugar industry, as a road surfacing material. The process used has changed little since then, and represents a costly solution to the coastal lack of quarried material. The bulk of the costs incurred in firing clay (known as burnt-brick) are primarily due to the need to utilize expensive walaba and other woods as fuel. In addition, the process is conducted in open pits, resulting in significant losses of heat to the environment and as well in an un-equal application of heat to the clay material, resulting in consequential heterogeneity in the strength of the fired material.
A final consideration is that the size of the clay particles is generally not controlled and there is a lack of effort in manipulating the composition of the fired clay so as to include materials which may act as binders.
Puzzolanas are materials containing constituents which combine with lime at ordinary temperature in the presence of water to form stable insoluble compounds possessing cementing properties. These materials may be natural or artificial. Natural puzzolanas are of volcanic origin e.g. volcanic glass, volcanic ash, etc., but artificial puzzonlana may be prepared by heat treating clays, shales, etc.
Work has been conducted by the U.S. Army Engineer Corp where they have used alkali-activated alumino-silicate binders for the construction of military roads. In such work, potassium or sodium hydroxide (rather than lime) is mixed with a fine-grained non crystalline alumino-solicate (such as from fired clay). The resulting reactions are capable of producing a hardened binder which is an excellent road wear surface, similar to cement. Other forms of excellent alumino-silicate materials include rice husk ash, which is in plentiful supply on the coast of Guyana.
The development of effective, cost-competitive puzzolanas using materials available on the coast of Guyana would certainly have a significant effect on the commerce of agriculture and the quality of life of citizens residing in the rural areas of the coast.
It also has significant uses in the housing construction industry as a low-cost, durable and aesthetic alternative for for home building.
Both the production of clay aggregates and puzzolanic materials as binders would also impact heavily on low-cost housing construction. Therefore, the IAST has a major, multi-year project focused on the firing of coastal clays for the production of aggregate materials and for combination with lime, fired rice husk, and other binder materials to produce wear-resistant concrete-like binders.
Please view slide show to see the construction of the kiln built by the IAST and the production process in preparing clay aggregates.



A few rural roads in Guyana: