Comparing the performances of bricks made with natural clay and clay activated by calcination and addition of sodium silicate

The mix between 4 M to 12 M NaOH solution and aluminosilicate material forms a thick paste that can be compacted in a mold in order to manufacture bricks at relatively low temperatures (< 100 °C). Starting materials available in Senegal consist of soils that primarily contain kaolin. In this study, we compare the performance of clay from the Niemenike deposit and clay pre-treated at 700 °C. The performance of the two clays depends on the temperature of curing and on the time of curing. In long-term tests (1 week to 3 months), for bricks kept at 40 °C/60% RH, strength did not increase with time for both clays (natural and calcined) activated with sodium hydroxide but this depends on the NaOH concentration. The maximum strength is obtained after 14 days for all concentrations. For all concentrations and periods, strength obtained with natural clay is greater.For short-term tests (6 h, 12 h, 24 h), with bricks kept at 120 °C/0% RH, the situation changed. The calcined clay gave the best mechanical performances. For all cases, long-term or short term, calcined or not, strength increased with concentration. The bricks produced in this fashion are durable and relatively inexpensive to make.

► Mix clay-concentrated NaOH solutions enables to manufacture by geolymerization.
► In long-terms (1 week to 3 months), natural clay gives always higher strength.
► In short-terms (6 h to 24 h), the clay thermally pre-treated gives the best strength.
► For all cases, thermally pre-treated or not, strength increased with concentration.
► The bricks produced in this fashion are durable.