Agriculture Reference
In-Depth Information
Microscopic examination showed that most of the bricks contain a reac-
tive chert temper (microcrystalline silica), which at some time has reacted
with the surrounding matrix, resulting in reaction haloes and the generation
of cements. The temper (defined as those phases with a diameter of
15
μ
m)
varies in size, from 50
m to 1.5 mm. The calcium-bearing bricks tend to fea-
ture the finest temper (50-100
μ
m), whereas the haematite-rich bricks contain
coarser temper (up to 1.5 mm in sample 10), and hence exhibit a more porous
and open microscopic texture.
The petrography shows that the historic rubbers were probably fired at a
temperature of 750-900ºC, whereas the modern rubbing bricks were more
likely to have been fired around the 900ºC mark.
The measured porosity, water absorption, and water suction of the rubbing
brick samples are given in Table 8.
μ
Table 8
Properties of the rubbing bricks related to the presence and movement of water.
Water suction (gcm
2
/min)
Sample
Porosity (%)
Water absorption (%)
Calcium-bearing
3
42.73
18.60
0.73
bricks
4
38.82
17.16
0.52
5
38.05
21.24
0.55
Mean
σ
39.87
2.51
19.00
2.10
0.60
0.11
1
32.41
14.00
0.47
Haematite-rich
2
34.26
12.44
0.19
bricks
6
35.65
15.07
0.40
7
32.68
14.04
0.30
8
32.15
11.99
0.30
9
30.15
11.33
0.43
10
35.56
15.07
0.44
Mean (
σ
)
33.27
2.00
13.42
1.50
0.36
0.10
Even though the haematite-rich rubbing bricks show a more porous and
open microscopic texture, the results show that the calcium-bearing bricks
have a significantly higher effective porosity (volume accessible to water) and
water absorptivity, and a slightly higher ability to absorb water by capillary
