Modern Quarrying

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October - November 2015 MODERN QUARRYING 29
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brick failed and the force measured at failure was documented. The
compressive strengths obtained were then averaged. The mixture
ratio that gave the highest compressive strength was subsequently
employed to manufacture bricks for water absorption, weight loss,
and leaching rate tests. Unconfined compressive tests were also
done on commercial bricks to provide a basis for comparison.
Water absorption rate and weight loss tests:
Two solutions with different pH values, one acidic and one neutral,
were used for these tests. The tailings bricks were first prepared from
mixture 7 (Table II) and cured in water for 24 hours. Tests were con-
ducted on four samples in each solution. The bricks were immersed
in water baths, one containing water at pH 7 and the other an acidic
solution at pH 4. The solid–to-liquid ratio was maintained at 15. The
saturated weight of the bricks (Ws) was measured every 24 hours
over a five day period. After five days, the bricks were dried at 110°C
for 24 hours and the oven-dried weight (Wd) recorded. The bricks
were again tested for compressive strength. The percentage water
absorption rate was then calculated as:
Water absorption (%) = [(Ws - Wd]/Wd × 100
The weight loss tests were done in the neutral environment only (pH
7). The average weight loss was measured after the bricks had been
soaked in neutral water for seven days then dried overnight at 110°C.
Table II: Different mixtures used in brickmaking.
Results and discussion
Particle size distribution:
Figure 1 shows the particle size distribution of the material used in
the brickmaking process. The results are presented in cumulative
form, in which the total amount of all sizes retained or passed by a
single notional sieve is given for the range of sizes.
The results indicate that most of the particles fell into 90–200 μm
range. 80% of the material passed the 200 μm screen aperture while
about 12% passed the 90 μm screen. The particle size range used in
standard commercial brickmaking includes coarser sand particles as
well as fine particles. The material used in these tests was, in com-
parison, relatively fine.
A cost analysis study done by Roy et al., (2007) showed that
cement-tailings bricks are generally uneconomical compared to
the soil-tailings based bricks, therefore future test work will have
to consider the addition of coarse particles, possibly from mining
overburden.
Different mixtures used in brickmaking
Mixture number Tailings (kg) Cement (kg) Water (ℓ)
1 2 1 0,6
2 14 2 2,65
3 9 6 3,0
4 7 8 2,5
5 10 5 2,5
6 12 3 2,5
7 5 10 3,3
8 10 5 3