| Summary: | Geothermal sludge is an undesired product from operation of geothermal
power plants. Geothermal sludge contains amorphous silica in an amorphous
form. In the present study, geothermal sludge from Dieng power plant was treated
to produce an alternative pozzolan material.
The work was conducted in three stages. The first aimed at finding the
best composition of geothermal sludge-hydrated lime mixture as pozzolan
material. The geothermal sludge-hydrated lime mass ratio was varied which
values were 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, and 3:1. The second stage was to use the
best composition of the pozzolan resulted from the the first phase to partly
substitute white Portland cement. Composition of the pozzolan material in its
mixture with white Portland cement was varied at values of 0%, 5%, 10%, 15%,
20%, 25%, and 30%(w/w). Cylinder specimens for compressive stress tests that
had a dimension of 3 cm x 6 cm were prepared at these stages. The third stage was
to compare the compressive strength of the resulting pozzolan with the respective
SNI standard in the form of mortar. The procedure of specimen preparation and
testing followed SNI 15-2049-2004 (portland cement) and SNI 15-0301-1989
(lime pozzolan cement). The composition of pozzolan in its mixture with white
Portland cement in the specimens tested were 0%, 10%, 20%, 30%. In addition, a
mortar specimen made of pozzolan without addition of white Portland cement was
also tested.
The experimental work showed that the best composition of pozzolan
resulted in the first stage had a geothermal sludge-hydrated lime ratio of 1:1 . The
pasta compressive strength at curing age of 28 days was 55.77 kgf/cm
2
. The
compressive strength still develop until the curing age reached 56 days for
specimens with pozzolan-lime ratio of 1:1, 1,5:1 and 2:1. In the second stage,
substitution of white Portland cement with pozzolan-lime lead to compressive
strength decrease. Meanwhile, the third stage of the study indicated that
substitution of white Portland cement with 10%, 20% and 30% pozzolan did not
fulfill the minimum white Portland cement compressive strength according to SNI
15-0129-2004. However, the mortar with those substitutions still qualified other
types of cement those are portland pozzolanic cement, portland composit cement,
and masonry cement for specific purposes.
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