Microstructure and physical properties of lime-clayey adobe bricks

Microstructural changes of adobe bricks made of lime-clayey raw material mixes were investigated by X-ray diffraction, infrared spectrometry, differential thermal analyses, scanning electron microscopy and energy dispersive spectrometry. The impact of these changes on the mechanical resistance and water absorption of adobe bricks was evaluated. It is found that lime additions resulted in the development of calcite and poorly crystallized calcium silicate hydrate (CSH). The latter compound is mainly originated from the reaction between fine filiform quartz and lime. The contribution of the pozzolanic reaction, involving kaolinite (the unique clayey constituent of the raw material), to CSH formation seems to be insignificant. The development of CSH together with the formation of minor amounts of calcite, in <10 wt.% lime samples, improved the mechanical strength and the compactness of adobe bricks. However, the quasi-absence of CSH and the excessive contents of portlandite (Ca(OH)2) and calcite, observed for >10 wt.% lime, had a slight detrimental effect on the measured physical properties. In all cases, lime amended adobe bricks are suitable for rural building construction in tropical countries.