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. 2024 Mar 25;17(7):1486.
doi: 10.3390/ma17071486.

Utilizing Crushed Limestone as a Sustainable Alternative in Shotcrete Applications

Elamin Mutaz  1 , Muawia Dafalla  2 , Ahmed M Al-Mahbashi  2 , Mehdi Serati  1
Affiliations

Utilizing Crushed Limestone as a Sustainable Alternative in Shotcrete Applications

Elamin Mutaz et al. Materials (Basel). .

Abstract

Solving the challenges facing the mining industry is crucial for shaping the global attitude towards clean energy technologies associated with critical minerals extracted from depth. One of these challenges is the well-known explosion-like fractures (rockbursts) or spalling failures associated with the initiation of internal cracks. To prevent such catastrophic failure, shotcrete, as a cement grout, is widely used in tunnel support applications. In areas where the tunnels are constructed within the limestone strata using tunnel boring machines (TBM), drilling, and/or blasting, millions of cubic meters of crushed limestone (CL) in powder form are extracted and landfilled as waste. Given the fact that natural sand consumption as a raw material in the construction industry exceeds previous records, recycling of such excavation material is now becoming increasingly needed. From this perspective, this study aims to utilize crushed limestone as a potentially sustainable alternative to natural sand in shotcrete applications in deep tunnels. Accordingly, several strength characterization and crack initiation determinations through various stress-strain-based models were carried out on cylindrical samples containing different proportions of crushed limestone. By increasing the crushed limestone content in the shotcrete mix, the crack initiation stress (as a measure of the in situ spalling strength) increased as well. The results suggest that the crushed limestone has good potential to replace the natural sand in the shotcrete mixture used in tunnel support applications.

Keywords: crack initiation; crushed limestone; shotcrete; tunnel support.

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Conflict of interest statement

The author declares no conflicts of interest.

Figures

Figure 1
Figure 1
Mining depth variation over the past century for different ores [7].
Figure 2
Figure 2
Crack closure, crack initiation, and crack damage identification based on the stress–strain response [7].
Figure 3
Figure 3
Determination of CI under uniaxial loading condition via (a) volumetric strain method, (b) lateral strain method, (c) extensional strain method, and (d) Poisson’s ratio method [7].
Figure 3
Figure 3
Determination of CI under uniaxial loading condition via (a) volumetric strain method, (b) lateral strain method, (c) extensional strain method, and (d) Poisson’s ratio method [7].
Figure 4
Figure 4
Shotcrete spraying around a tunnel sidewall.
Figure 5
Figure 5
Supporting systems failure in underground tunnels following violent rockbursting and spalling due to instability of the reinforcement elements [46].
Figure 6
Figure 6
The grain size distribution of crushed limestone material.
Figure 7
Figure 7
The grain size distribution of sand.
Figure 8
Figure 8
UCS shotcrete specimens prepared on 100 mm height and 50 mm diameter molds.
Figure 9
Figure 9
Strain and elastic parameter measurements: (a) strain gauge arrangements around the UCS sample, (b) close-up view of two-element strain gauges.
Figure 10
Figure 10
A Toni/Technic compression loading frame used in the study [48].
Figure 11
Figure 11
Stress–strain curves of the shotcrete samples with different mixtures: (a) 1 Cement:1 Sand, (b) 1 Cement:1 CL, (c) 1 Cement:1.2 CL, and (d) 1 Cement:1.4 CL.
Figure 11
Figure 11
Stress–strain curves of the shotcrete samples with different mixtures: (a) 1 Cement:1 Sand, (b) 1 Cement:1 CL, (c) 1 Cement:1.2 CL, and (d) 1 Cement:1.4 CL.
Figure 12
Figure 12
Determination of CI for control shotcrete mixture through the (a) volumetric strain method, (b) lateral strain method, (c) extensional strain method, and (d) Poisson’s ratio method.
Figure 13
Figure 13
Determination of CI for 1 Cement: 1CL shotcrete mixture through the (a) volumetric strain method, (b) lateral strain method, (c) extensional strain method, and (d) Poisson’s ratio method.
Figure 14
Figure 14
Determination of CI for 1 Cement: 1.2 CL shotcrete mixture through the (a) volumetric strain method, (b) lateral strain method, (c) extensional strain method, and (d) Poisson’s ratio method.
Figure 14
Figure 14
Determination of CI for 1 Cement: 1.2 CL shotcrete mixture through the (a) volumetric strain method, (b) lateral strain method, (c) extensional strain method, and (d) Poisson’s ratio method.
Figure 15
Figure 15
Determination of CI for 1 Cement: 1.4 CL shotcrete mixture through the (a) volumetric strain method, (b) lateral strain method, (c) extensional strain method, and (d) Poisson’s ratio method.
Figure 16
Figure 16
Variation of UCS in shotcrete samples.
Figure 17
Figure 17
Variation of crack initiation in shotcrete samples.
Figure 18
Figure 18
Variation of crack initiation ratio in cement grout samples.
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