The Effect of Clay, Cement and Fibers on the Strength and Durability of Compressed Earth Blocks

This Thesis examines the effect of soil characteristics, cement content and fibers on the strength and durability of compressed earth blocks (CEBs). This work expands on the available information regarding the constituent properties which affect the compressive and tensile strengths and durability of CEBs. Additionally, little research on the subject of synthetic fibers and their effect on strength and durability of CEBs is available and this work provides an initial study in this area. To study the effects of fibers, as well as confirm the trends of previous research regarding the effects of clay and cement, 27 unique batches of CEBs were pressed and tested using a Vermeer BP 714 block press. Three different soil types and two fiber types were utilized. The compressive strength, modulus of rupture (MOR), absorption, and durability were measured on over 185 specimens. The strength and absorption tests were adapted from common ASTM International test methods for similar materials, while the durability test was a uniquely developed method to quantify durability by measuring mass loss during drying and wetting cycles. After the testing regimen was completed, a trend between clay content and strength could not be determined. Durability testing suggested that as clay content decreases, durability increases. A linear relationship was found between cement content and strength, which was confirmed during durability testing. The addition of different fibers did not have an effect on the peak strength of CEBs, although it appears they may decrease the durability. The gross versus net unit strengths of CEBs were examined due to the unique shape of the CEBs utilized. Additionally, a mathematical expression relating the MOR to the compressive strength was developed