ACARP 34018: Carbolt™: Pre-Commercial Fixed Length Carbolt Prototype

ACARP 34018: Carbolt™: Pre-Commercial Fixed Length Carbolt Prototype

This project aimed to advance the carbon-fibre rock bolt, Carbolt™, prototype by refining its manufacturing process and enabling the testing of a full-length roof bolt. The development required specialized tools, including a braiding machine and a custom mould for resin curing, to ensure uniform diameter and create features such as ribs and threads. A standard nut and bolt locking mechanism was integrated to maintain compatibility with existing roof bolting systems.
Several design iterations were produced and tested against industry standards for steel rock bolts, evaluating shear strength, pull-out resistance, and tensile performance. The results indicated that, while comparing bolts of the same diameter, the direct tensile strength of the Carbolt was lower. However, after accounting for the reduced effective cross-sectional area due to the inclusion of the core, the Carbolt’s tensile strength is comparable, and in some cases higher, of both steel and fiberglass rock bolts. In addition, the Carbolt is significantly lighter—by approximately 80%—than steel rock bolts of equivalent tensile strength.
In shear tests, the Carbolt performed less than steel rock bolts. The braided carbon-fibre structure enhanced load-bearing capacity and energy absorption, making its single shear strength higher but its double shear strength was still lower than that of high-modulus fiberglass rock bolts, indicating room for improvement with higher-modulus carbon fibre. The ribbed design exhibited suboptimal pull-out performance, suggesting that further refinement is needed to improve grout adhesion and match the effectiveness of steel rock bolts.
A major advantage of the Carbolt is its corrosion resistance, making it well-suited for harsh mining environments where steel rock bolts are prone to rust and degradation. While flammability testing was not conducted, carbon fibre’s inherent inert properties suggest similar behaviour to fibreglass rock bolts in high-temperature conditions.
From a commercial perspective, the current braiding process speed may be sub-optimal for large-scale production. A more practical manufacturing approach would involve a wound or twisted fibre configuration, which would require collaboration with international partners due to Australia’s limited composite manufacturing capabilities.
Overall, the Carbolt shows strong potential as a lightweight, corrosion-resistant alternative to steel rock bolts. Further development in areas such as rib design, diameter optimization, underground field trials and scalable production methods is necessary before it can be commercially viable. With these refinements, the Carbolt could provide a practical, high-performance solution for mining operations, improving safety and durability while reducing maintenance costs in corrosive environments.

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