64
In day 28, the highest value of the density is in the percentage of both metakaolin and silica fume as much as 25:5. The value is 1.9287 grcm
3
. The complete value can be seen in Table 5.9 and the chart can be seen in Figure 5.2.
Tabel 5.9 Average Weight Density in 28 days Pozzolan
Weight Density grcm
3
Average of Weight Density grcm
3
Metakaolin : Silica Fume 25:5
1.8616 1.9287
1.9902 1.9344
50:5 1.7159
1.8051 1.8512
1.8483
75:5 1.6783
1.6939 1.7351
1.6683
Figure 5.2 Weight Density in 28 Days Chart
1,5500 1,6000
1,6500 1,7000
1,7500 1,8000
1,8500 1,9000
1,9500
25:5 50:5
75:5 W
e ig
h t
D e
n si
ty g
r cm
3
Precentage of Metakaolin and Silica Fume
28 days
65
The value of weight density is depends on the sample. It is because of the process of the compaction from the sample itself. Based on the table above,
weight density of the geopolymer concrete is belongs to lightweight concrete. The biggest value of the average weight density of concrete comes from the
geopolymer concrete with the proportion of the metakaolin and silica fume; 25:5 in 14 days. The value is 1.9519 grcm
3
5.4. Compressive Strength of Concrete
Compressive strength test is done at the age of 14 days and 28 days. The test is done by machine UTM with Shimadzu brands. The test results from the
small cylinder day 14 are already change into the normal size of the concrete 150 mm x 300 mm. The compressive strength value of the research can be seen
in Table 5.10 and the chart of compressive strength test can be seen in Figures 5.3 and 5.4.
Table 5.10 Compressive Strength Test
Pozzolan Compressive Strength Mpa
Metakaolin Silica Fume 14 days
28 days
25 5
2.30729 2.071743
1.10814 1.149566
2.02273 1.20311
1.88520 1.13744
50 5
1.37959 1.229189
0.68563 0.641213
1.21979 0.61374
1.08817 0.62426
75 5
0.69916 0.675865
0.15911 0.178246
0.63963 0.19685
0.68879 0.17876
66
Figure 5.3 Compressive Strength Column Chart
Figure 5.4 Compressive Strength Line Chart
Based on the test, the highest value of the compressive strength is 2.071743 MPa in day 14 with the ratio of metakaolin and silica fume as much as 25:5.
From the test, it is known that the highest proportion of metakaolin, the lowest value of the test.
0,5 1
1,5 2
2,5
25 : 5 50 : 5
75 : 5 C
o m
p re
ss iv
e S
tr e
n g
th V
a lu
e
M P
a
Precentage of Metakaolin and Silica Fume
14 days 28 days
0,5 1
1,5 2
2,5
25 : 5 50 : 5
75 : 5 C
o m
p re
ss iv
e S
tr e
n g
th V
a lu
e
M P
a
Precentage of Metakaolin and Silica Fume
14 days 28 days
67
The value of the mixture should be higher because both metakaolin and silica fume have higher percentage of SiO2 Silica and both of them also contain of
Calcium Oxide CaO. CaO will has a reaction with NaOH become CaOH
2
. SiO
2
will be react with CaOH
2
become Calcium Silicate Hydrate CSH that will be used as a paste. The mixture should be strong enough.
Na2SiO3 also used as alkali of the geopolymer. The Na2SiO3 will react with NaOH and make a
strong binder. From the result, the values of the concrete are very low. According to the
author, the values are low because they do not have a good proportion of CaO. So, the reaction is not properly. From the table below, it is known that all of the
materials only have a good proportion in Silica, but not in Calcium Oxide while the composition of CaO in cement is really big; 64.67. The composition of the
contents can be seen in Table 5.11. Table 5.11 Composition of the Contents
Content Name
cement Metakaolin
Silica Fume
SiO
2
Silica 21.03
66.39 85
CaO Calcium Oxide
64.67 3.08
1 Fe
2
O
3
Iron Oxide 2.58
5.00 -
MgO Magnesia
2.62 9.64
- Na
2
O Alkali
1.34 2.97
8,72
5.5.1. Research Comparison
Research comparison is used to show the effect of the material in the concrete. Every research has its own result that depends on the material preparation,
68
temperature, type, and environment. This research will be compared with the research from Lisantono and Hatmoko 2009 that also use metakaolin and
bagasse ash as the materials. The tables of the comparison value can be seen in table 5.12 and table 5.13.
Table 5.12 Compressive Strength of the Test
Combustion of
Metakaolin Time
minute Molarity
of NaOH
Pozzolan Compressive Strength Mpa
800°C 40 min’
12M Metakaolin
Silica Fume
14 days 28 days
25 5
2.307 2.071
1.108 1.149
2.022 1.203
1.885 1.137
50 5
1.379 1.229
0.685 0.641
1.219 0.613
1.088 0.624
75 5
0.699 0.675
0.159 0.178
0.639 0.196
0.688 0.178
Table 5.13 Compressive Strength of Lisantono and Hatmoko Research
Combustion of Metakaolin
Time minute
Molarity of
NaOH Pozzolan
Compressive Strength Mpa
500°C 25 min’
8M Metakaolin
Bagasse Ash
14 days 28 days
50 -
0.715 0.560
0.759 0.721
0.467 0.507
0.497 0.898
50 50
0.427 0.380
0.720 0.852
0.473 0.950
0.239 0.886
- 50
0.336 0.325
0.366 0.344
0.425 0.329
0.213 0.336
Source: Lisantono and Hatmoko, 2009
