Influences of Fibers on Expansive Shotcrete Mixture Consisting of Calcium Sulfoaluminate, Portland Cement, and Calcium Sulfate

• Author / Creator

  Yu, Hau

• Shotcrete is often used by the mining industry as rock support, tunnel lining, and concrete repair. However, cracking within shotcrete is common, which delays production schedules and increases maintenance costs. To reduce cracking, expansive shotcrete mixtures are often used. While several commercial expansive cements / shotcrete mixtures are available, the ingredients of these products are usually confidential. To optimize the effects and usages of expansive shotcrete mixture, mixture with known compositions should be studied. Possible expansive shotcrete mixtures can be developed by combining calcium sulfoaluminate cement (CSA), ordinary Portland cement (OPC), and calcium sulfate (CS) in the binder. Furthermore, fibers can be added to the mixture to restrain expansion and impede cracking. The objective of this thesis is to identify expansive shotcrete mixtures consisting of CSA, OPC, and CS, and study the effects of nylon fiber, glass fiber, and steel fiber on the identified mixture so that better crack resistance can be achieved. In this study, parameters such as density, water absorption, volume of permeable voids, unconfined compressive strength (UCS), splitting tensile strength (STS), and volume change of the mixtures were determined at different time periods (i.e., the mechanical strengths on the 28th day, and the volume changes on the 1st, 7th, 14th, 21st, and 28th days). Five expansive shotcrete mixtures, along with five strength-enhanced mixtures, that contained CSA, OPC, and CS in the binder were identified. The expansive mixture showing enhanced UCS (mixture with 40%CSA+20%OPC+40%CS) was selected for fiber additions in this study. Results have presented that the addition of fibers improved mixture durability, in the form of decreased water absorption and reduced permeable pore space content. Moreover, the expansion of the CSA-OPC-CS mixture was controlled by fiber reinforcement. Glass fiber restrained up to 50% of the expansion, while nylon fiber restrained up to 43% and steel fiber restrained up to 28% of the expansion. The results showed that STS was improved by 57% with glass fiber addition, 43% with steel fiber addition, and 38% with nylon fiber addition. The UCS also increased at a percentage of 31% after steel fiber addition, 26% after nylon fiber addition, and 16% after glass fiber addition. Based on the results, it is concluded that fiber additions to expansive shotcrete mixtures improve durability and mechanical strengths, while controlling expansion. The results in this thesis provide alternative options of expansive and strength-enhanced shotcrete mixtures consisting of CSA, OPC, CS, and fibers. These options could better mitigate the cracking in shotcrete, thereby reducing the costs on repair and replacement.

• Subjects / Keywords

  • Restrained expansion
  • Fibers
  • Calcium sulfate (CS)
  • Shotcrete
  • Calcium sulfoaluminate cement (CSA)

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3BG2HQ62

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.