World Academy of Science, Engineering and Technology International Journal of Civil and Environmental Engineering Vol:15, No:9, 2021 Abstract—The purpose of this study is to evaluate the incorporation of hemp fibers (HF) in concrete. Hemp fiber reinforced concrete (HFRC) is becoming more popular as an alternative for regular mix designs. This study was done to evaluate the compressive strength of HFRC regarding mix procedure. HF were obtained from the manufacturer and hand processed to ensure uniformity in width and length. The fibers were added to concrete as both wet and dry mix to investigate and optimize the mix design process. Results indicated that the dry mix had a compressive strength of 1157 psi compared to the wet mix of 985 psi. This dry mix compressive strength was within range of the standard mix compressive strength of 1533 psi. The statistical analysis revealed that the mix design process needs further optimization and uniformity concerning the addition of HF. Regression analysis revealed that the standard mix design had a coefficient of 0.9 as compared to the dry mix of 0.375 indicating a variation in the mixing process. While completing the dry mix, the addition of plain HF caused them to intertwine creating lumps and inconsistency. However, during the wet mixing process, combining water and HF before incorporation allows the fibers to uniformly disperse within the mix hence the regression analysis indicated a better coefficient of 0.55. This study concludes that HRFC is a viable alternative to regular mixes however more research surrounding its characteristics needs to be conducted. Keywords—Hemp fibers, hemp reinforced concrete, wet and dry, freeze thaw testing, compressive strength. I. INTRODUCTION ONCRETE is a mixture of water, aggregate and cement that has been used for thousands of years. It is the most used man-material today with over an estimated 4100 million tons of cement created worldwide in 2019 to make it [5]. The main component in concrete is the binder, cement, which sets and hardens. Various materials such as calcium oxide and crushed volcanic rock have been used throughout history to create cement. Portland cement is widely used today, however dating back to 1824 the creation process entails heating a mixture of limestone, clay, and sand up to 1450 °C in a rotating kiln [4]. Using natural fibers in mix designs has been done with HFRC as an expansion into more green based concrete mix designs to create more sustainable structures. Hemp belongs to the Cannabaceae family and has one of the quickest grow times of approximately 15 weeks [7]. The durable fibers have a variety of uses in both commercial and manufacturing trade creating a 4.7 billion USD industry globally. Data have shown that HF with a mean width of 60 ߤm has an average tensile strength of approximately 310 MPa while the strength at 40 ߤm Chang, Z.* and Williams, M. are Research Assistants and Das, G. is Associate Professor with Civil Engineering, Wentworth Institute of is recorded to be closer to 610 MPa [2]. The inverse correlation creates a unique phenomenon which is ideal for incorporating as a strengthening agent in various materials. HF 23.15 ± 17.6 ߤm wide used to create reinforced concrete have been proven to increase compressive strength by 4%, flexural strength by 9% and flexural toughness by 144% depending on percentage [3]. Hemp reinforced fiber mix is incorporated into two different ways referred to as dry and wet. The proportions of aggregate, cement and hemp are kept constant while the order of materials added is changed to determine potential effects on samples. This is compared to data from concrete mixes made similarly but without hemp referred to as standard or base mixes. The objectives of the research are as follows: 1. Evaluating the impact of HFRC and comparing the compressive strength to standard concrete mixes without HF. 2. Evaluating the HRFC in regards to wet and dry conditions in comparison to standard concrete mixes without HF. 3. Identifying the potential leaching of heavy metals such as cadmium and chromium from standard concrete mixes in comparison to similar leaching potential to HRC mixes. 4. Researching the impact of HF in concrete mix design and how it relates to standard mixes to identify a correlation with compressive strength. 5. Incorporating statistical analysis to determine efficacy of the HF mix design process. II. MATERIALS Hemp Raw natural HF are initially used for this experiment (Fig. 1). The remaining processing is done by hand as the husk from the stem of the hemp plant is stripped leaving only fibers. The fiber widths initially range from approximately 2000 m to 23 m. The fibers are combed through with a quadruple row hackling comb to reduce the width to 50 m (Fig. 3). Hackling combs are traditionally a metal plate with rows of needles used to prepare other natural fibers such as flax for spinning. Three variations of the hackles are created with smaller nails that are closer together. This ensures no fiber is larger than 200 m in width to capitalized on the inverse correlation between strength and size. Research has shown that hemp measuring 23.15 ± 17.60 m has the properties listed in Table I with in a 95% confidence range [3]. Technology, Boston, MA 02115 United States (*e-mail: Chang.zoe.95@gmail.com). Optimization of Hemp Fiber Reinforced Concrete for Mix Design Method Zoe Chang, Max Williams, Gautham Das C 429 International Scholarly and Scientific Research & Innovation 15(9) 2021 ISNI:0000000091950263 Open Science Index, Civil and Environmental Engineering Vol:15, No:9, 2021 publications.waset.org/10012269/pdf