Long-Term Compressive Strength Development of Steel Fiber Shotcrete from Cores Based on Accelerator Types at Tunnel Site

Abstract

In this study, cement minerals, aluminates, and alkali-free accelerators incorporated with steel fiber were used to scrutinize the influence of accelerating agents on the long-term performance of tunneling shotcrete. Performance tests were identified based on the core compressive strength of mix shotcrete specimens with different types of accelerating agents throughout timeframes of 1, 3, 6, and 12 months. Here, 37 kg of steel fiber was incorporated into the cement mineral and aluminate mixes, and 40 kg of steel fiber was incorporated in an alkali-free mix for the shotcrete mix design. The KSF 2784 and ASTM 214 standards were followed for specimen fabrication and core cutting. For all specimens, shotcrete test panels of 250 × 600 × 500 mm were manufactured for core compressive strength tests conducted using 100, 75 and 55 mm diameter cylindrical molds and a length-to-diameter ratio of 2. The 1-month compressive strength of all test variables satisfied the Korea Expressway Co. standard of 21 MPa. The core compressive strength of the shotcrete specimens showed a tendency to increase with age, but a strength reduction occurred in 6 months and increased again at 12 months. Moreover, the impact of the diameter changes in the shotcrete core specimens was analyzed based on the mixing. For 12 months, a large increase in the core compressive strength occurred, particularly in the alkali-free specimens. The comparison also focused on the relative strength compared with a cast concrete mold and shotcrete core specimens. It is necessary to use alkali-free accelerators considering the long-term performance of tunnels and worker safety.

Performance of engineered fibre reinforced concrete (EFRC) under different load regimes: A review

“…Yun et al observed that steel fibres incorporated with accelerators increased the strength of concrete in the long and short term. However, alkali-free accelerator was safer than cement mineral and aluminate for workers and the environment [61]. In another study, the use of accelerators had a great impact on the mechanical properties of FRC [62].…”

Early age dynamic mechanical properties of basalt fiber reinforced early strength concrete

“…In an actual construction process, the construction of supporting structural concrete and blasting excavation are often done alternately, and blasting excavation is often carried out soon after concrete construction 8–10 . When the supporting structure is very close to the source of explosion, the blasting excavation may cause impact damage to nearby structural concrete that have not reached the standard curing age, which affects the long‐term strength of the supporting structure 11–14 . Therefore, the influence of early impact on concrete has attracted much attention, and a large number of scholars have carried out experimental studies on the influence of vibration disturbance on concrete with early age 15–18 …”

“…[8][9][10] When the supporting structure is very close to the source of explosion, the blasting excavation may cause impact damage to nearby structural concrete that have not reached the standard curing age, which affects the long-term strength of the supporting structure. [11][12][13][14] Therefore, the influence of early impact on concrete has attracted much attention, and a large number of scholars have carried out experimental studies on the influence of vibration disturbance on concrete with early age. [15][16][17][18] In order to reflect the engineering practice, people have begun to study the dynamic response of concrete with early age under high strain rate by the split Hopkinson pressure bar (SHPB).…”