EVALUATION OF SUSTAINABLE CONCRETE PRODUCED WITH INDUSTRIAL HEMP FIBERS AND RECYCLED AGGREGATES USING MULTI-SCALE TESTING AND LIFE-CYCLE ANALYSIS

Abstract

Hemp and Recycled Aggregate Concrete (HRAC) is a sustainable concrete material prepared by partial substitution of natural coarse aggregates with a combination of recycled concrete aggregates (RCA) and industrial hemp fibers.

The application of HRAC offers multiple benefits related to sustainable development. The new material would help in resolving the depletion of natural aggregate resources, mitigate the negative environmental impact of the construction and demolition waste (CDW) material of concrete-based structures, incorporate renewable and agricultural industrial hemp fibers as partial substitute of natural aggregates, and would solve socio-economic problems associated with the farming of hashish, the sister plant of Hemp, in Hermel-Bekaa (Lebanon) and elsewhere.

The proposed research was planned to be completed through tasks distributed across three phases. The objective of the first phase was to achieve a concrete mix that incorporates RCA and is reinforced with industrial hemp fibers while assuring that the designed mix meets the requirements of high-performance concrete including workability and durability. Tests on trial batches included plastic state slump; hardened state mechanical properties such as compressive strength, tensile splitting strength, modulus of elasticity, flexural strength of standard beams; and several durability tests. Results showed that while HRAC has considerably lower compressive strength and modulus of elasticity than plain concrete, the flexural strength and splitting tensile strength are not significantly affected. 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.

The objective of the second phase was to assess the structural performance of reinforced concrete beams prepared using the HRAC’s optimal batch achieved in the first phase. By investigating the difference in strength and behavior between conventional and HRAC structural concrete elements, the hypothesis to be tested was whether the substitution of natural aggregates with a combination of RCA and hemp fibers to produce HRAC would lead to reduction in the flexural, shear, and bond splitting characteristics of the structural elements, or would affect the ductility of the mode of failure and the load-deflection history. The testing of large-scale specimens would serve as a validation study of the proposed mix. Test results of the second phase indicated that the HRAC beam with optimal combination of constituents, including hemp fibers and RCA, had a peak load comparable or higher than that of the control beam for the three tested mode of failures, despite the HRAC mix having a significantly lower compressive strength than the control mix.

The significance of the third phase was to conduct a life cycle analysis to quantitatively assess the benefits of HRAC over regular concrete from environmental aspects. The life-cycle assessment quantitively proved that HRAC is indeed a sustainable concrete, having better structural properties and lower environmental impact as compared to ordinary concrete.