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of fly ash. Besides that, because of the present of high
quantity of material with fine sediment (fly ash) the
specific surface of the sample increase.
From the point of view of different type of fly
ash (with each different initial characteristic), we can
observe that, at teen age curing time (7-28 days)
sample with fly ash FA_1 shows higher compressive
strength value than sample with FA_2. As mentioned
in previous paragraph that at 7-28 days of curing age,
the most important role of binder is as a filler. This
filler effect is very influenced by the particle size of
the binder (fly ash). Compared the result of particle
size distribution and Unconfined compressive
strength test (presented in table 2 and 5), we can
conclude that, the sample possess the particle size
with greater quantity of particle with size of <2 µm
(FA_1) produces higher compressive strength.
Silitonga in his research working on fly ash with
different particle size (Silitonga, Matondang, 2018).
This result of this study done by Silitonga, shared the
same patterns with the result above. Pozzolanic
binder with higher percentage of particle size <2 µm
produces higher strength (especially compressive
strength).
The unconfined compressive strength result at
60-90 days curing age presents different pattern than
the previous curing age. (7-28 days). At 60 days, the
pozzolanic reaction assumed already reach its
maximum reaction. At this age, the sample with fly
ash content produces higher compressive strength
value than sample consist only with cement (CMT).
The pozzolanic reaction need more time to reach its
maximum reaction, on the opposite the cement
hydration already finish reacts, because there is no
more calcium and the silicate available in the cement.
On the other hand, due to its pozzolanic reaction, the
produced of C-S-H and C-A-H, that enhance the bond
between the particle and automatically provide
additional strength of the admixture. As long as the
pH of the environment reach 9 or more, the
pozzolanic reaction can always proceed. The pH
value 9 release the calcium and the silicate that
available in the soil, and with the help of CaO then
form C-S-H and C-A-H, which plays an important
role on increasing the strength by strengthen the
microstructure of the sample.
Unlike at teenage curing time (7-28 days), the
mineralogical characteristics of the fly ash plays
important role at this age of curing (60-90). At
previous chapter (table 3) we can observe that the
named FS_1 has more SiO
2,
Fe
2
O
3
and Al
2
O
3
than
FS_2. On the other hand, FA_2 consist more CaO
total then FA_1. The unconfined compressive
strength result proves that the sample with FA_2
possess higher strength value than FA_2. This result
confirms that the present of SiO
2,
Fe
2
O
3
and Al
2
O
3
promotes the pozzolanic reaction better than the CaO
content. The present of the SiO
2,
Fe
2
O
3
and Al
2
O
3
on
fly ash, provides substance to initiate the pozzolanic
reaction. Beside the amount of SiO
2,
Fe
2
O
3
and Al
2
O
3
that available in the soil, the present of SiO
2,
Fe
2
O
3
and Al
2
O
3
on the fly ash helps to provides for
pozzolanic reaction. The CaO content also provides
CaO for initiate the pozzolanic reaction. Based on this
result we can confirm that the content of the SiO
2,
Fe
2
O
3
and Al
2
O
3
on the binders has greater influence
than the present of CaO.
4 CONCLUSIONS
The main goal of this study is to determine which
initial characteristics that affect the pozzolanic
reaction on enhancing the engineering properties of
the sample. The physical characteristic is represented
by particle size distribution and the mineralogical
characteristic is identified by XRD test. The physical
properties show that, due to its finer particle size, the
fly ash (FA_1) has a higher possibility to increase the
strength than FA_2. According to the mineralogical
test, FA_1 has more SiO
2,
Fe
2
O
3
and Al
2
O
3
than
FA_2, on the opposite the FA_2 has more CaO
content than FA_1. Each result has a possibility to
increase the engineering performance. In order to
confirm this theory, unconfined compressive strength
is realized. The Analysis of this compressive strength
devised in two period of time, teen age of curing time
)7-28 days and long-term condition (60-90 days). The
result demonstrates that, binder with finer particle
size distribution has higher engineering performance
(compressive strength) than other. The result of long-
term period of time demonstrate that, the present of
SiO
2,
Fe
2
O
3
and Al
2
O
3
on the mixture plays more
important role to enhance the strength than the
content of CaO. We can conclude also that with
addition of fly ash, the soil utilized can be used and
fulfil the criteria to be reused in as material in road
construction.
REFERENCES
Bernal, S. A. et al. (2011) “Effect of binder content on the
performance of alkali-activated slag concretes,”
Cement and Concrete Research. doi:
10.1016/j.cemconres.2010.08.017.
Fernández-Jiménez, A., Palomo, A. and Criado, M. (2005)
Effect of Initial Characteristic on Promoting the Pozzolanic Reaction in Soil Solidification Work
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