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2017SpringShotcreteEMag

These values are higher than measured in the laboratory study (refer to Table 4), but this is because the Field Evaluation mixture had a higher w/cm of 0.45, compared to a w/cm of 0.40 in the laboratory study mixtures shown in Table 2. SUMMARY The comparative laboratory study and field evaluation detailed in this paper has demonstrated that treated natural hemp-based fiber has several beneficial attributes that enhance the performance of wet-mix shotcrete with no detrimental effects. These beneficial attributes include the following: 1. The treated natural hemp-based fiber is hydrophyllic (absorbs water) and as such is compatible with portland cement-based systems. In particular: a. The fiber is readily dispersible in wet-mix shotcrete, providing uniform distribution of the fiber during mixing, pumping, and shooting, without fiber balling or segregation. b. Water absorbed by the fiber during batching and mixing acts as an internal curing aid because water is available to the cement paste during hydration. This is beneficial in helping to mitigate early-age plastic and drying shrinkage-induced cracking. 2. The natural fiber shotcrete displayed a superior CRR in the ASTM C1579 plastic shrinkage cracking test, compared to the microsynthetic fiber-reinforced shotcrete. 3. The natural fiber addition produced a very cohesive wetmix shotcrete, suitable for pumping and shooting without segregation or pump blockages. 4. The natural fiber shotcrete displayed remarkable adhesion characteristics when applied to a vertical plywood form, compared to the plain control shotcrete and shotcrete with microsynthetic fiber. Unlike those two shotcretes, considerable effort was required to dislodge a beehive of natural fiber shotcrete from the plywood form. This has very positive implications for shotcrete applications to vertical and overhead surfaces, where adherence of fresh shotcrete to the substrate surface is an important consideration (for example, in shotcrete repair and restoration works and in tunneling, mining, and rock slope stabilization projects). 5. Because of the very adhesive and cohesive rheology of the natural fiber mixture, it was possible to bench shoot (stack) 18 in. (450 mm) thick structural shotcrete walls to heights up to 6 ft (1.8 m) in a single pass without sagging, sloughing, or fallout. This provides opportunities for accelerating the shotcrete construction schedule. 6. The natural fiber shotcrete displayed superior finishing characteristics to the microsynthetic fiber-reinforced shotcretes because fibers were not drawn to or exposed on the surface by finishing operations. The finishers commented that the natural fiber appeared to act almost like a finishing aid. 7. Because of the stable nature of the just-shot natural fiber shotcrete (resistance to sagging, sloughing, and fallout), finishers could follow closely behind the shotcrete nozzleman. This provides opportunities for accelerating the shotcrete construction process. 8. Tests conducted on cores extracted from the hardened shotcrete demonstrated that the natural fiber had no detrimental effects on properties of the hardened shotcrete, such as compressive strength, BA, and VPV (an indicator of permeability), or rapid chloride penetrability (an indicator of resistance to chloride ion intrusion). In fact, the natural fiber shotcrete displayed slightly higher values of compressive strength and lower values of BA and VPV compared to the plain control shotcrete or shotcrete with microsynthetic fibers. 9. Finally, because the natural fiber is produced from custom-farmed hemp plants, it is a sustainable green product, with much reduced CO2 emissions compared to microsynthetic fibers that are derived from hydrocarbon (oil and gas) feedstock. Based on the studies detailed in this paper, it is recommended that the treated natural hemp-based fiber be added to wet-mix shotcrete at fiber addition rates as follows: a. In favorable ambient environmental conditions with low evaporation rates (cooler temperatures, high relative humidity, and low wind speeds) and thus a low potential for early-age plastic and drying-shrinkage-induced NForce-Fiber® for Performance & Sustainability. Developed by Industry Professionals, Tested by Industry Experts. For the First Time, a Shotcrete Fiber for not Only MIX STABILITY, COHESION, ADHESION, REBOUND & CRACK CONTROL... but A PERFECT FINISH!!! Effective in BOTH Wet and Dry Shotcrete. Technical Info / Expert Reports: www.canadiangreenfield.com Contact: info@canadiangreenfield.com 44 Shotcrete | Spring 2017 www.shotcrete.org


2017SpringShotcreteEMag
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