Studies on Hemp and Recycled Aggregate Concrete
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International Journal of Concrete Structures and Materials Open Access
RESEARCH
Studies on Hemp and Recycled Aggregate Concrete Samer Ghosn, Nour Cherkawi and Bilal Hamad*
Abstract This paper reports on the first phase of a multi-phase research program conducted at the American University of Beirut (AUB) on “Hemp and Recycled Aggregates Concrete” (HRAC). HRAC is a new sustainable concrete material where hemp fibers are incorporated in the mix, the coarse aggregate content is reduced by 20% of the concrete volume, and 50% of the natural coarse aggregates (NCA) are replaced by recycled concrete aggregates (RCA), thus saving on natural resources and addressing the problem of waste material disposal. The effect of the new material on concrete consistency and hardened mechanical properties was studied. Also, few durability tests were conducted. Variables included percentage replacement of NCA by RCA (0 or 50%), maximum size aggregate (10 or 20 mm), hemp fiber length (20 or 30 mm), and hemp fiber treatment (alkali or silane or acetyl). Fiber characterization tests were conducted including morphology, crystallinity, and thermal analysis. The tests indicated that alkali and acetyl fiber treatments were better than the silane treatment in removing impurities on the fiber surface. Also, alkali and acetyl treatments have increased the crystallinity of the fibers while silane treatment decreased it. Results of mechanical properties tests showed that while HRAC has considerable lower compressive strength and modulus of elasticity than plain concrete, the flexural strength and splitting tensile strength are not significantly affected. The flexural stress– strain behavior of HRAC is ductile as compared to the brittle behavior of the plain concrete beams indicating positive impact on toughness and energy dissipation. The durability tests indicated that whereas HRAC mixes have higher absorption than plain concrete, they have better thermal properties and their resistance to freeze–thaw cycles is comparable to plain concrete. All test results were not significantly affected by fiber length or fiber treatment. Keywords: sustainable concrete materials, recycled aggregates, hemp fibers, mitigation of wastes, characterization, mechanical properties, durability 1 Introduction Similar to other industries, the construction industry is trying nowadays to adapt sustainable practices where the main concern is to reduce the use of non-renewable natural resources. A more sustainable and environmentally friendly concrete material can be produced by reducing the use of natural coarse aggregates (NCA). This reduction can be compensated by the use of recycled materials and “green” construction materials like natural fibers. Construction and demolition wastes (CDW) are *Correspondence: [email protected] Department of Civil and Environmental Engineering, American University of Beirut, P.O. Box 11‑0236, Riad El Solh, Beirut 1107‑2020, Lebanon Journal information: ISSN 1976-0485 / eISSN 2234-1315
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