## 2 Materials and Methods  
### Sample Preparation  
Seventy-two fully grouted rock bolts were fabricated using Stratabinder HS, Australia's widely used cementitious grout containing Portland cement-fly ash, superplasticiser, and ground granulated blast furnace slag (GGBS). Three W/G ratios (30%, 35%, and 40%) and the replacement of grouts with two FA contents (1% and 2%) were incorporated to assess the influence of different admixtures on the performance of fully grouted rock bolts. Also, two different casting boards for placing 23 mm and 50 mm steel confinements (50 mm length) and 16 mm rebars with lengths of 21 mm were built using a CNC machine (Figure 1). For constructing the casting boards, a top layer of polymethyl methacrylate, commonly known as Perspex, with 25 mm and 53 mm holes, was evenly spaced across the board. These holes were cut using a CNC machine to ensure accuracy. The second layer consisted of a medium-density fibreboard (MDF) with a Melamine laminate overlay. This layer had 16 mm holes that were directly centred inside the above layers' holes. A CNC machine was then used to cut these holes to ensure accuracy. Lastly, duct tape was used under the base to seal off the holes. Also, two different sizes of 3D-printed caps, 23 mm and 50 mm, were used to center the rebars within the confinements.  
In addition to the pull-out samples, 72 grout cubes (50 mm \(\times\) 50 mm \(\times\) 50 mm) were prepared according to ASTM C579 [31].  
All samples were cast in the ambient conditions. Batches of grout were mixed for PL samples. Due to the non-Newtonian behaviour of the Stratabinder HS and water mixture, a three-stage mixing process was necessary. First, two-thirds of the amount of total requiredwater was added to the buckets. Second, grout was gradually added while stirring the mixture. The non-Newtonian fluid thickened as it was stirred, requiring intermittent pauses to allow it to liquefy. This process continued until the mixture became challenging to stir. Finally, the remaining water was added to soften the mixture and allow stirring to resume. A slight vibration was subsequently done to avoid any air trapped in the grout. The grout was then placed or poured into pipes and UCS cubes. The 30% water mixture was very thick and required a spade for placement, while the 35% and 40% water mixtures were less thick and could be poured directly into the pipes and UCS cubes. Cubes and rock bolting samples were stored in a curing room with a 25 \({}^{\circ}\)C temperature and 100% humidity. Samples were then cured for 1, 7, 14, 21, and 28 days (Figure 1).  
The prepared UCS samples as shown in Figure 2 were first sanded to ensure the surfaces were smooth (<0.05%), and then the dimensions were measured using a digital calliper. These cube samples as demonstrated in Figure 2 were placed on the lower crosshead of the testing machine, and the load was applied at the rate of 1 kN/s. These cubes used the same W/G ratios, admixtures, and curing times as the rock bolts to investigate the relationship between grout mechanical properties and the PL capacity of fully grouted rock bolts.  
Figure 1: Sample preparation: (**a**) Stratabinder HS; (**b**) grout mixing procedure; (**c**) fully grouted rock bolt sample, ID: 50 mm; (**d**) fully grouted rock bolt sample, ID: 50 mm; view of cast samples, (**e**) 23 mm, and (**f**) 50 mm on the casting boards and (**g**) a view of some of samples, ID: 23 mm, in the curing room.  
Figure 2: A view of some UCS samples in the curing room.  
It should be mentioned that UCS cubes used the same W/G ratios, admixtures, and curing times as the rock bolts to investigate the relationship between grout mechanical properties and pull-out capacity of fully grouted rock bolts (Figure 2).