Effect of Compaction Pressure on a Stabilized Rammed Earth Behavior

The current work addresses the effect of compaction pressure on durability against water ingress, compression behavior, and thermal conductivity of rammed earth specimens stabilized with fly ash geopolymer. These properties were investigated for specimens made from 25 % fly ash and proportions of sand, silt, and clay. The fly ash was activated with 2M sodium hydroxide solution, and the specimens were compacted statically to 5, 10, or 25 MPa. Reference mixtures containing the raw material (i.e., sand, silt, and clay) were also prepared for comparison. The results of the durability test on stabilized specimens indicated excellent resistance to deterioration caused by water ingress, unlike those made from raw materials which almost failed completely. The materials elastic stiffness and compressive strength were both improved substantially with the inclusion of fly ash geopolymer and with compaction pressure increase. The inclusion of geopolymer resulted in 6 to 10 folds improvement in the compressive strength. For instance, the stabilized specimens provided a compressive strength of 2,7 MPa when compacted to 5 MPa, compared to only 0,3 MPa provided by the unstabilized specimen. Likewise, an increase in compaction pressure from 5 to 25 MPa, resulted in an increase of 56 % in the compressive strength. The thermal conductivity of the stabilized material was in the order of 0,4-0,5 W/ (m.K) and was considered relatively low comparing to that of other competitors such as normal concrete and even lower than that of the raw material by about 18 %. The thermal conductivity increased by about 20 % with compaction pressure increase from 5 to 25 MPa. It seems that the increase in the stiffness and strength with compaction pressure increase can compensate the small undesirable increase in the thermal conductivity