Effect of freezing-thawing cycles on the physical and mechanical properties of fired and unfired earth bricks

This paper presents the results from a campaign of unconfined compression tests on unfired and fired earth bricks exposed to freezing-thawing cycles. Three types of unfired earth bricks were manufactured by (a) light compaction of unamended earth at the standard Proctor optimum, (b) hypercompaction of unamended earth at a pressure of 100 MPa and (c) hypercompaction of amended earth with hemp fibres at a pressure of 100 MPa. For sake of comparison, the same tests were also performed on standard fired earth bricks exposed to freezing-thawing cycles. All bricks were equalised at a temperature of 23 °C and a relative humidity of 95% before being exposed to 0 (i.e. no freezing at all), 1, 3, 6, 9 and 12 freezing-thawing cycles under dry conditions. The bricks were subsequently subjected to unconfined compression tests to measure the changes of stiffness and strength. Results show that freezing-thawing hardened the unfired earth bricks (especially the lightly compacted Proctor bricks), which exhibited an improved mechanical performance with increasing number of cycles. Only negligible changes of mechanical response were instead measured for the fired bricks after exposure to freezing-thawing. These results suggest that unfired earth bricks can be used for construction in cold regions with sub-zero temperatures without loss of mechanical performance, provided that water uptake close to saturation is prevented by an appropriate architectural design.