Construction and Building Materials Accepted manuscript This manuscript version is made available under the CC-BY-NC-ND 4.0 --------------------------------------------------------------------------------------------------------------------------- 1 Mechanical properties of organic-based light- 1 weight concretes and their impact on economic 2 and ecological performances 3 Daia Zwicky 4 Professor, Dr. sc. techn., dipl. Bauing. ETH, Institute of Construction and Environmental Technolo- 5 gies iTEC, School of Engineering and Architecture Fribourg HEIA-FR, University of Applied Sci- 6 ences and Arts Western Switzerland HES-SO, Boulevard de Pérolles 80, CH-1700 Fribourg, 7 daia.zwicky@hefr.ch 8 9 Abstract – The study presented here aimed at improving mechanical properties of wood-cement com- 10 pounds, basically consisting of Portland cement and of up to 60% of untreated sawdust, through an 11 aggregate skeleton made of organic aggregates (fruit pits, crushed nut shells) and lightweight aggregates 12 (expanded clay and glass). Experimental results show that workability and strength development can be 13 notably improved. Compressive strength can be doubled, and elastic modulus can be tripled. All prop- 14 erties exhibited a marked influence of organic aggregate content. Contextualized comparisons show that 15 the developed alternative lightweight concretes (LC) can be economically competitive with regular LC 16 while the eco-balance is reduced by 70-80%. 17 Keywords: Lightweight concrete, Organic aggregates, Lab tests, Fresh-state properties, Strength de- 18 velopment, Mechanical properties, Analytical predictions, Economic competitiveness, Ecological per- 19 formance. 20 Declaration of interest – As further developments may involve spin-off activities, some degree of con- 21 fidentiality is applied to the results presented here. Specific organic skeleton components and their over- 22 all percentages are given but detailed recipe compositions incl. individual particle size distributions as 23 well as mixing process details are kept confidential. 24