Technical Paper


packing in all types of castables. In the present study, the q-values for shotcreting and dry-gunning mixes are 0.27 and 0.22, respectively.


Table 1 shows the composition of bauxite based mixes for shotcreting and dry-gunning. Bauxite, brown sintered alumina (BSA), kyanite and calcined alumina with different particle size fractions were selected as aggregates. Calcined alumina, cement and other additives were used in the matrixes. SioxX-Flow (Elkem, Norway) was used as specialty dispersant in the shotcrete recipes, and SioxX-Set (Elkem, Norway) was used as accelerator in the dry-gunning recipes.


2.2 Laboratory test procedures To develop shotcrete


recipes,


Figure 1: Panel and cut specimens of NCC-G. a) Panel (500x500x100mm)


the flow and setting-behaviour were


evaluated in the lab. Self-flow and vibration-flow were measured using the 50mm high flow-cone described in ASTM C230. The self-flow value is the % increase of the diameter of the fresh mix measured 90 seconds after removing the cone.


To design the dry-gunning mixes, the following test procedure was used for lab evaluation: i) mix it in a Hobart mixer; ii) stop mixing as soon as the dry mix starts to wet; iii) make a ball in hand to evaluate its consistency and iv) throw the ball onto a glass wall. If it sticks, it passes the test; if it slips, it fails.


Shotcrete %


Bauxite, 0.5-6 mm BSA 96, 0-0.5 mm TA 60, 0-0.3 mm


Calcined Al2O3 fines


CA cement, 70% Al2O3 Elkem Microsilica 971


EMSIL-DRY SioxX-Flow


Reactive alumina


Raw kyanite, 35 mesh Betonite SioxX-Set Water


NCC-S 52


15.5 15 10


0.5 6


0.1 1


LCC-S 52 16 15 5 5 6


0.1 1


Dry-gunning


NCC-G 37.5 23 5


12.5 0.5 6.5 0.1


7.5 5


0.5 2


4.5 5.0 8.0 Table 1: Bauxite based NCC and LCC for shotcreting and dry-gunning


2.3 Industrial-scale shotcrete and dry-gunning trials Based on the results from the laboratory, full-scale shotcreting and dry- gunning trials were carried out in cooperation with industrial partners. The water addition for dry-gunning mixes was 8-9%, and the water in NCC-S and LCC-S for shotcreting was 4.5-and 5.0%, respectively. The mixes were sprayed without complications and test panels produced. The rebound for both shotcreting and dry-gunning was considered low by the installation crews.


No lamination was observed in the centre of the panels and samples were cut for further characterisation. Figure 1 shows a test panel and cut specimens. The cut specimens were fired at various temperatures before cold crushing strength (CCS), cold modulus of rupture (CMOR) and hot modulus of rupture (HMOR) measurements.


Figure 3: Vibration-flow testing of microsilica-gel bonded NCC-S. The LCC-S looked similar


LCC-G 37 22 5


10 5


7.5 0.1


7.5 5


0.5 0.5 9.0


Figure 2: Self-flow (SF) and vibration-flow (VF) b) Cut specimens (25x25x150mm) for HMOR test 3. Results and discussion


3.1 Evaluation of NCC and LCC shotcrete Self- and vibration-flow values of lab-scale samples are shown in Figure 2. The NCC-S had similar flow values at 4.5% water addition as the LCC-S at 5.0% water. The self-flow value of NCC-S was 52% and the vibration-flow was 112%. The consistency of NCC-S looked fine, no bleeding or separation was observed as seen in Figure 3.


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ENGINEER THE REFRACTORIES


January 2018 Issue


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