Some mechanical and thermal properties of vegetable aggregates cement composites : Evaluation of a new binder based on lime

Abstract

Composite materials incorporating vegetable matter have known an increasingly interest during the past decades. These environmental friendly materials offer advantages such as low-cost and reduction of electrical consumption by air conditioning. This research investigates and compares some physical, thermal and mechanical properties of (1) a cement and sugar cane bagasse ashes binder and (2) an eco-friendly binder based on bagasse ashes and hydrated lime Ca(OH)₂. These binders are mixed with vegetable aggregates of bagasse and coconut (various contents - 5 to 20 wt%). The lightweight eco-friendly binder is performed with low energy consumption and low CO₂ emission materials, compared to cement. Before their incorporation in the binder, the bagasse and coconut aggregates were characterized and compared by using optical microscopy, thermal degradation, apparent and specific density, water absorption and granulometry. The analysis of these characteristics allowed to predict the influence of these aggregates on apparent density, flexural and compressive strengths (28 days) and thermal conductivity (56 days). Experimental investigations showed that the incorporation of vegetable aggregates into an inorganic matrix results in a decrease in the compressive and flexural strengths of the composite.Flexural and compressive strengths of cement – bagasse ashes binder are higher by a factor 2 to 4 than that of bagasse ahes - lime binder. But after addition of aggregates, the decrease of strength is less marked in case of bagasse ashes - lime binder: decrease by a factor 4 in bagasse ashes - lime binder and reduction by a factor 8 to 10 in cement – bagasse ashes binder. The vegetable aggregates allow a reduction of the density of the coumpound binder by up to 57% and their presence induces thermal insulation properties to the composite, specially in case of composite materials made of bagasse ashes - lime binder.