Influence of mineralogy and firing temperature on the porosity of bricks


The changes in brick porosity upon firing (700 up to 1100 C) and its relation to the mineralogical composition were examined using two types of raw clay, one containing notable  amounts of carbonates, with a grain size of under 1 mm, and the other being predominantly quartzitic and lacking in carbonates. Carbonates in the raw clay promoted the formation of fissures and of pores under 1 micron in size when the bricks were fired between 800 and 1000 C. The absence of carbonates resulted in a continuous reduction in porosity and a significant increase in the pore fraction with a radius > 1 micron as the firing temperature rose and smaller pores coalesced. Porosity and pore size distribution  results obtained from the combined use of hydric tests, mercury intrusion porosimetry and digital image analysis of SEM photomicrographs were compared. A clear correlation existed between the water absorption and drying behaviour of  the bricks and the porosity plus pore size distribution. These results as well as a study of the evolution of the speed of ultrasound waves vs. time yielded useful information to evaluate the physical-mechanical behaviour and durability of the bricks. The relevance of these findings in the conservation of historic buildings is discussed.  70 refs.

Primary author(s): Cultrone G; Sebastian E; Elert K; de la Torre M J; Cazalla

                            Granada,University; Jaen,University

Source: J.Eur.Ceram.Soc.


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