Rebuilding with sand roses: Cold sintering of sand-gypsum mixture for sustainable brick production

In the arid climate of the Sahara Desert, several historical cities dating back to the 16th century were constructed using bricks made from sand roses, a rosette-like rock composed of sand and gypsum. This study proposes the cold sintering of sand – dihydrate gypsum (uncalcined) mixtures as a sustainable approach to develop geomimetic sand roses with satisfactory mechanical performance. The results showed that crucial factors for enhancing the unconfined compressive strength (UCS) of the cold-sintered sand-gypsum mixtures are reducing gypsum size, utilizing cyclic loading, and applying higher pressures. Reducing sand size or introducing lubricant has minimal or negative effects. Cold-sintered sand-gypsum mixtures containing over 30 % micron-sized gypsum, subjected to cyclic pressures of 100 MPa for 15 minutes, can achieve superior UCS values compared to equidimensional concrete bricks. In addition, coating the mixture with calcium carbonate can be a viable approach for protecting against weathering agents. Coating and recycling the sand-gypsum mixture do not compromise the mechanical performance of the bricks. The proposed integration of sustainable materials and manufacturing practices has the potential to reduce costs, energy consumption, and industrial emissions, while promoting a circular economy and resource preservation. The proposed brick is referred to as “sand rose brick.”