Mechanical Performance of Lime-cement Mortar for Straw-bale Construction

Experimental data describing the mechanical performance of Portland cement- hydrated lime mortars used for straw bale construction is presented. Straw bale construction uses stacked straw bales plastered on each side to form load-bearing elements. Mortars used have slumps of approximately 50 mm, compared to slumps up to 279 mm for conventional masonry mortars. Cylinder and cube tests of a range of typical straw bale mortar mixes were carried out. The mortars had compressive strengths ranging between 0.3 MPa and 13 MPa. Empirical equations describing the relationships between compressive strength and curing time, w/cm ratio, proportions of lime, cement and sand, and modulus of elasticity are presented. The data show that cement-lime mortars for straw bale construction will have a higher modulus of elasticity and lower failure strain than a conventional mortar of equivalent compressive strength. The Modulus of Elasticity is on average 818 times the compressive strength of a straw bale mortar, compared to 100 to 200 times as reported in the literature for conventional mortar. The average failure strain for straw bale mortar is 0.00253 compared to 0.0087 to 0.0270 reported in the literature for conventional mortar.