Limult Laterite for Road Construction

Laterite is both a soil and a rock type rich in iron and aluminum and is commonly considered to have formed in hot and wet tropical areas. Nearly all laterites are of rusty-red coloration, because of high iron oxide content. They develop by intensive and prolonged weathering of the underlying parent rock. Tropical weathering (laterization) is a prolonged process of chemical weathering which produces a wide variety in the thickness, grade, chemistry and ore mineralogy of the resulting soils. The majority of the land area containing laterites is between the tropics of Cancer and Capricorn.

The term ‘Laterite’ appeared in academic literature over a century ago. Buchanan (1807) first used this term to denote a building material in the mountainous region of Malabar, India (Maignien, 1966). The term ‘Laterite’ could mean brick earth in some local dialects but the name ‘latérite’ got its meaning from a Latin word later, meaning ‘brick’ and so relating solely to the use of these soils in block making (Prescott and Pendleton, 1952 in Gidigasu, 1974). There have been so many arguments,

Characterisation of laterite for road construction

Lateritic soils exist in many places in tropical regions of Africa and America. They are frequently used for road construction. It is important to use them in an optimized way and attempts are made to improve their description and characterization for road applications. Laboratory work done in Brazil, Senegal and France was aimed at including specific properties of laterites in their classification, especially the degradability of their gravelly and sandy fractions due to weathering and compaction during construction works. The paper presents results of laboratory tests, which highlight the importance of particle size reduction due to compaction and its variability. The link between the grain sizes of raw laterites and those of the same laterite after compaction should be further studied, in order to help the road designer in tropical and equatorial countries.

Structure, Composition and Properties of Lateritic Soils

Laterites vary greatly in structure, but can be reduced to the following three structural patterns:

(a) The indurated elements form a continuous, coherent skeleton;

(b) The indurated elements are free concretions or nodules in an earthy matrix;

(c) The indurated elements cement pre-existing materials. These structural patterns exhibit great variability in relation to the shape and size of the elements involved and the degree of induration. The degree of hardness ranges from products that are practically unconsolidated and scarcely coherent to the hardest blocks which can be broken only with a hammer. Induration is an empirical criterion, as it is impossible to give quantitative expressions to any character related to the mechanical properties of the material. The usual definition of induration is a state in which the hard brittle consistency of the medium is not affected by humidity. Induration, which involves the precipitation of goethite in a reticular network, is influenced by composition and the extent of crystallization of the components in the soil: the higher the sesqui oxide content, the greater the induration. In other words, hardness increases as the iron content increases; the hardest laterites are also the least hydrated.

Laterites vary in color, but are usually brightly colored. The shades most frequently encountered are pink, ochre, red and brown; however, some occurrences are mottled and streaked with violet, and others exhibit green marbling. A single sample may exhibit a whole range of colors merging more or less perceptibly into one another in a variety of patterns and forms. Laterites owe their color to iron oxides in various states of hydration and sometimes also to manganese. Their mineralogy generally involves quartz, kaolinite, hematite, goethite, and sometime maghemite. Kaolinite is always present with iron oxides. The physical properties of lateritic soil vary according to the mineralogical composition and particle size distribution of the soil. The granulometry can vary from very fine to gravel according to its origin, thus influencing geotechnical properties such as plasticity and compressive strength. One of the main advantages of lateritic material is that it does not readily swell with water. This makes it an excellent packing material particularly when it is not too sandy.

Improving Lateritic Soils for Construction Purposes

Stabilization processes are very complex because many parameters come into play. The knowledge of soil properties can help to better consider what changes, the economic studies (cost and time), as well as production and construction techniques to use. The simplest process consists of taking soil and drying it in open-air. It is the ―pise technique, rammed earth, adobe, and brick dried in the sun, widely used in the majority of African countries. More elaborate processes can include heat treatment, or mixing soil with ordinary Portland cement, lime, etc.

Limult Group sells quality Laterite for road constructions_ thus providing for the nation. Feel free to visit our store at www.limult.com/shop to see more products that we make available for the people. For further inquiries, call us on +2347052446249.

by Limult