Page 188 - AJWEP-22-5

Hou, et al.

Table 2. Particle size distribution for each thorough mixing, the slurry was immediately poured
gradation index (i ) into the mold. The mold was then vertically lifted in a
k
Gradation <1 mm (%) 1 – 3 mm (%) 3 – 5 mm (%) swift, continuous motion to allow the slurry to spread
index (i k ) freely. After 30 s, the maximum diameter of the spread
0.88 74.33 16.68 8.99 slurry on the glass plate was measured. The test was
repeated 3 times, and the average of the three measured
0.89 76.31 12.95 8.23 values was recorded as the flowability of the slurry.
0.90 78.31 14.22 7.47
0.91 80.34 12.95 6.71 2.3.3. Bleeding rate
0.92 82.41 11.63 5.96 The bleeding rate is a critical indicator of the stability
of coal gangue slurry. According to the Technical
fly ash; the balance was deionized water. Except for the Specifications for Tailings Paste Backfill (GB/T 39489
gradation adjustment, the mixing, molding, and curing – 2020), the bleeding rate of paste backfill slurry should
procedures were identical to those in Section 2.2.1. All be controlled within the range of 1.5 – 5%. In this
preparation and testing were conducted at 20 – 25°C study, a 500 mL beaker and a 50 mL graduated cylinder
were used to measure bleeding rate. First, the well-
and 50 – 60% relative humidity to ensure consistent mixed slurry was poured into the 500 mL beaker and
hydration and rheological measurements. allowed to stand for 2 h. Subsequently, the clear water

2.3. Testing methods that separated on the surface of the slurry was drawn
using a syringe and transferred to a graduated cylinder
2.3.1. Slump flow for volume measurement. Finally, the bleeding rate
Slump flow is a critical parameter for evaluating was calculated according to Equation II to assess slurry
the flowability of coal gangue slurry for backfilling stability.
applications. In this study, an XN-type slump flow
testing apparatus (Shanghai Jingke, China) with W V 1 100% (II)
dimensions of 50 mm (inner diameter) × 100 mm (top V 2
diameter) × 150 mm (height) was used, and the test was Where W is the bleeding rate of the slurry, and V and
1
conducted in accordance with the Technical Code for V represent the volume of separated water and the total
2
Concrete (GB 50119 – 2013). During the test, the slump slurry volume (cm ), respectively.
3
flow plate was first placed horizontally and wiped with
a damp cloth along with the slump cone and tamping 2.3.4. Segregation index
rod to ensure surface moisture. The cone was positioned The dynamic stability of the slurry during transportation
at the center of the test plate and covered with a damp can be characterized by the segregation index (SI).
cloth to prevent moisture loss. The slurry was poured Slurries with high segregation rates are prone to particle
into the cone in two layers, each approximately half the separation and pipeline blockages, which may pose
cone’s height. Each layer was tamped 15 times from the safety hazards. While no unified standard exists for coal
cone wall to the center using the tamping rod to ensure gangue slurry, the Technical Code for Self-Compacting
uniform distribution. After tamping, excess slurry was Concrete Applications (JGJ/T 283 – 2012) recommends
leveled off with a scraper. The cone was then lifted segregation below 20% during pipeline transport.
vertically at a steady rate, and the slurry was allowed Therefore, maintaining the segregation rate of the coal
to settle for 10 s. A steel ruler was used to measure gangue slurry below 20% is considered reasonable for
the maximum spread diameters in two perpendicular ensuring transport stability.
directions, and the average value was recorded as the In this study, the segregation rate was measured
slump flow. This method effectively characterizes the using a segregation tester (Shanghai Jingyi Co., Ltd,
slurry flowability and provides an experimental basis China), following the procedures outlined in JGJ/T
for optimizing the mix design of backfill materials. 283 – 2012. First, the coal gangue slurry was poured
into a cylindrical mold, which was then placed on an
2.3.2. Slurry flowability electric vibration table and vibrated 25 times. Next, the
Slurry flowability was evaluated using a glass plate and slurry was removed from the mold and passed through a
a truncated cone mold with an upper diameter of 36 mm, 5 mm mesh sieve to separate the coarse aggregates. The
a lower diameter of 64 mm, and a height of 60 mm. After separated coarse aggregates were dried until the surface

Volume 22 Issue 5 (2025) 182 doi: 10.36922/AJWEP025200154