2.7. Assessment of mixture quality using a salt conductivity method
In the case of P/S and S/S mixtures each 2 g of the sample was
used and diluted to 50 g/L using deionised water and in the case
of O/S mixture each 0.2 g sample was used and diluted to 10 g/L
using deionised water. The conductivity of each of the nine
samples was measured using a conductivity probe. A standard salt
calibration curve was prepared by measuring the conductivity of
salt at different known salt concentrations. From the conductivity
measurements of the samples, the salt concentration in each of
the samples was evaluated by using the slope equation from the
calibration curve. The sample variance (S2) was then evaluated
by inserting these data into Eq. (2).
S2 ¼
P9i
¼1ðCi CaverageÞ2
9 ð2Þ
where
Ci salt concentration in sample i.
Caverage average concentration of salt.
The mixture quality of a binary mixture was assessed by evaluation
of the coefficient of variation (CoV) in Eq. (3).
CoV ¼
S
l ð3Þ
where
S sample standard deviation.
l target composition of salt.
(a)
(b)
1
2
3
4
5
6
7
8
9
Fig. 1. (a) 2 L paddle mixer and (b) mixer showing the nine sampling points.
Table 2
Total mass of powders used for each type of powder mix.
Composition (%w/w) Total mass of
paprika:salt mix (g)
Total mass of
oregano:salt mix (g)
1:99 2000 600
20:80 2000 600
50:50 2000 300
80:20 1000 300
99:1 1000 300
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 1 2 3 4 5 6 7 8 9 10
Unconfined failure strength (kPa)
Major principal consolidation stress (kPa)
Paprika aw=0.35
Salt aw=0.35
Oregano aw=0.35
easy flowing
free flowing
cohesive
very cohesive
non flowing
Fig. 2. Flow function for paprika, oregano and salt at aw = 0.35