Abstract
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.
Highlights
Laterites and lateritic soils, described as Fe2O3-Al2O3-SiO2-H2O matrices, are made from kaolinite in which a high proportion of Al3+ is replaced by Fe2+ or Fe3+
The final products presented a good stability in water, low water absorption and mechanical properties comparable to that of conventional concretes
The products of the geopolymerization of laterites showed stability in water already after 14 days and good stability after 90 days indicating the effective transformation and induration of the matrices. This stability varies with the content of calcined laterite and the degree of iron accumulation of the laterite used: the higher the calcined laterite in the formulation (35 wt%), the shorter the period of time needed for stability in water
Summary
Laterites and lateritic soils, described as Fe2O3-Al2O3-SiO2-H2O matrices, are made from kaolinite in which a high proportion of Al3+ is replaced by Fe2+ or Fe3+. Ambrost et al [6], described the antagonism between hematite and kaolinite in the matrix of laterite: the corrosion of the kaolinite is followed by a complete destruction of the crystal giving place to hematite or goethite organized into thin lamellar structures; the crystals of Al-rich hematite or Al-rich goethite formed maintain a clear trace of the shapes of former kaolinite platelets They postulated that, in the deep layers of laterites fed by Fe3+ solutions, the protons necessary to dissolve kaolinite are generated by a reaction similar to the oxidation–hydrolysis step of ferrolysis [6]. To the particle size distribution, reactive amorphous/vitreous phase and the Si/Al, key factors governing the suitability of a solid precursor for geopolymerization of classical aluminosilicates, additional elements as the degree of laterization and the form of iron (ferrihydrite, hematite or goethite) should be considered for laterite materials. The present study intends to confirm whether good geopolymeric products can be obtained from laterites or lateritic soils
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