Physical,mechanical and microstructural properties of alkaline and acid-activated mixtures of calcined laterite-volcanic ash based inorganic polymers: Effects of reciprocal substitution

This study determines certain characteristics of inorganic aluminosilicate polymers synthesized by alkaline and acid activations of three calcined laterites and powder of volcanic ash obtained by reciprocal progressive partial replacements, in order to compare their characteristics as earthen building materials. Firstly, the calcined laterites were partially replaced with volcanic ash before activation in the ideal alkaline and acid solutions to obtain inorganic polymer composites. Secondly, reverse replacements and activations were achieved. The results have shown that both the reactive phase content in the aluminosilicates along with the presence of certain oxides (Fe₂O₃ and Al₂O₃) are the main parameters that influence the optimization of the characteristics of the obtained composites. Hence, the partial replacement of calcined laterites by volcanic ash is detrimental to the properties of the obtained products. Compressive strength reduces averagely by 57.6% and 36.7%, respectively for alkaline and acid-activated inorganic aluminosilicate polymers obtained by substituting calcined laterites with up to 50% volcanic ash. Conversely, partial replacement of volcanic ash with calcined laterites leads to 28 days compressive strength increase from 2.0 to 12.2 MPa (alkaline medium) and from 12.5 to 23.9 MPa (acidic medium). To get the best earthen building materials, activation of calcined laterite/volcanic ash mixtures is more effective in acidic medium than in alkaline one. Also, to obtain reliable products, only an aluminosilicate material with greater reactive phase content should be used as a substitute to partially replace the one with lesser reactive phase, not the reverse.