Two iron-rich clayey materials (L1 and L2, with the main difference being the level of iron accumulation) have been studied for their suitability as solid precursors for inorganic polymer composites. L1, with the lower iron content, was calcined at 700°C for 4 h and used as replacement, in the range of 15–35 wt%, for both raw laterites in the formulations of geopolymeric composites. The different mixtures were activated with a highly concentrated alkaline solution containing sodium hydroxide and sodium silicate. River sand with semi-crystalline structure was added to form semi-dry pastes which were pressed to appropriate shape. X-ray diffraction, Infrared spectroscopy, Scanning Electron Microscopy and Mercury Intrusion Porosimetry results demonstrated the effectiveness of the calcined fraction of L1 to act as nucleation sites and extend the geopolymerization to the matrix composites. A highly compact matrix with low porosity and good stability in water, together with a strength comparable to that of standard concretes was obtained allowing for conclusions to be made on the quality of laterites as promising solid precursor for sustainable, environmentally-friendly, and cost-efficient structural materials.

Lateritic soils are formed in the tropics through weathering processes that favor the formation of iron, aluminum, manganese and titanium oxides. These processes break down silicate minerals into clay minerals such as kaolinite and illite. Iron and aluminum oxides are prominent in lateritic soils, and with the seasonal fluctuation of the water table, these oxides result in the reddish-brown color that is seen in lateritic soils. These soils have served for a long time as major and sub-base materials for the construction of most highways and walls of residential houses in tropical and sub-tropical countries of the world. Civil engineering applications of these lateritic soils are continually being developed with the use of different types of stabilizers. The stabilized soil-based products are as such viewed as environmentally-friendly and low-cost energy materials for sustainable building applications. This work aims at presenting a global view of what has been done in the field of lateritic soil improvement for construction purposes in tropical countries such as Cameroon. This shall be discussed through the presentation of the structure, composition and properties of lateritic soils, the various ways of improving their properties for construction purposes, the properties of products obtained and other prospects.

The reactivity of calcium dialuminate CaAl₄O₇ refractory cement containing little amount of gehlenite Ca₂Al₂SiO₇, belite Ca₂SiO₄, calcium aluminum iron oxide Ca₃(Al,Fe)₂O₆ and calcium iron aluminum oxide Ca_3.18Fe_15.48Al_1.34O₂₈ was studied with and without Li₂CO₃. The granularity of the cement is d₉₇ = 112.58 µm, d₅₀ = 9.72 µm and d₁₀ = 1.41 µm with water cement ratio W/C = 0.375. Little amount of Li₂CO₃ from 0.1wt.% to 0.6wt.% was added to the cement paste, and the result from calorimetry showed hydration mean peak time reduced from 17 h to 32 min and showed that the hydration heat of CA₂ cement paste with Li₂CO₃ was 123 J/g lower than the one without Li₂CO₃ of 168 J/g. XRD of stabilized hydrates show that CaAl₄O₇ and Ca₃(Al,Fe)₂O₆ participate in the hydration reaction to form C₃AH₆, AH₃ and Ca₃Al_1.54Fe_0.46(OH)_12. The results from SEM images show nucleation site with plate-like crystal of CAH₁₀ and small particles of AH₃ forming a membrane on the cement surface.