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.

中文翻译：

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麻与再生骨料混凝土的研究

本文报告了在贝鲁特美国大学 (AUB) 进行的关于“大麻和再生骨料混凝土”(HRAC) 的多阶段研究计划的第一阶段。HRAC 是一种新型可持续混凝土材料，在混合物中加入了大麻纤维，粗骨料含量减少了 20% 的混凝土体积，50% 的天然粗骨料 (NCA) 被再生混凝土骨料 (RCA) 取代，从而节省自然资源并解决废物处理问题。研究了新材料对混凝土稠度和硬化力学性能的影响。此外，几乎没有进行耐久性测试。变量包括 RCA 替代 NCA 的百分比（0 或 50%）、最大尺寸聚集体（10 或 20 毫米）、大麻纤维长度（20 或 30 毫米）、和大麻纤维处理（碱或硅烷或乙酰）。进行了纤维特性测试，包括形态、结晶度和热分析。试验表明，碱和乙酰纤维处理在去除纤维表面杂质方面优于硅烷处理。此外，碱和乙酰处理增加了纤维的结晶度，而硅烷处理降低了它。力学性能测试结果表明，虽然 HRAC 的抗压强度和弹性模量明显低于素混凝土，但其抗弯强度和劈裂抗拉强度并未受到显着影响。与素混凝土梁的脆性行为相比，HRAC 的弯曲应力-应变行为具有延展性，表明对韧性和能量耗散有积极影响。耐久性测试表明，虽然 HRAC 混合物比素混凝土具有更高的吸收性，但它们具有更好的热性能，并且它们的抗冻融循环能力与素混凝土相当。所有测试结果均不受纤维长度或纤维处理的显着影响。