Influence of solfonated melamine formaldehyde condensate on the quality of building blocks production by extrusion of cement–clay pastes

The extrusion of cement–clay pastes to manufacture building blocks by cold stabilization of clays by cement is investigated. Based on the pressure and the torque values measured during paste preparation and extrusion, an operative window of concentration of water and sulphonated melamine formaldehyde (SMF) fluidizer suitable to obtain simple and complex building blocks is identified: for pastes with clay/cement ratio 2.6:1 the water content ranges between 24% and 29% w/w for 6% w/w SMF and between 29% and 33% for 0% w/w SMF. Extruded items have been submitted to bending stress resistance tests to evaluate the mechanical properties of clay stabilized by cement and to identify the paste formulations with the highest resistances. To the best a 25% increase in mechanical properties is achieved by applying a curing treatment at 35 °C and 90% humidity for 96 h. However based on the results of tests of frost resistance and resistance to water contact, the clay–cement blocks do not offer so far an alternative to conventional bricks.