Development of inorganic polymer by alkali-activation of untreated kaolinitic clay: Reaction stoichiometry, strength and dimensional stability

• Kaolinite can be alkali activated resulting in hydroxysodalite.
• Reaction product is a strong and stable building material.
• Maximum mechanical strength (50 MPa) is obtained at about 50% of kaolinite conversion.

An environmental friendly building material was developed by alkali-activation of untreated kaolinitic clay using sodium hydroxide. The reaction was studied using differential scanning calorimetry. The chemical structure of the produced inorganic polymer was deduced from infrared spectroscopy, X-ray powder diffraction, thermogravimetric analysis, and scanning electron microscopy to be the tetrahydrate phase of hydroxysodalite with a Na/Al ratio of 4/3. Its strength and stability were evaluated in terms of compressive strength under dry and saturated conditions using different ratios of mixing water and NaOH. The compressive strength of dry samples ranges between 45 and 50 MPa. The wet samples after soaking in water show a strength between 20 and 25 MPa, and the wet samples after alternating cycles of drying and wetting also show a strength of 20–25 MPa.