| Summary: | The sources of crushed stone and river sand in Cilacap District, Central Java
Province has not been used optimally. There are only the crushed stones in large size
that are used and it is used only for foundation. While the small crushed stones are
not utilized and became waste. The use of river sand from Kesugihan village is also
not optimal because the granules is considered too fine, so it is only used as land fill
of-street and simple house foundation.
This research use crushed stone waste and river sand as materials for making
concrete bricks. Fine aggregate used was a mixture of crushed stone waste from
Jeruklegi Kulon Village and fine sand obtained from Kesugihan Village, Kesugihan
Sub-district, Cilacap District, with maximum size 4.8 mm. Variations in the
composition of crushed stone waste on river sand was 0%, 25%, 50%, 75%, and
100%. The compositions of volume ratio between cement and fine aggregate are 1:4,
1:6, and 1:8. The tests performed included density, compressive strength, flexural
strength, modulus of elasticity, and water absorption.
The results showed that the highest density of the concrete bricks before
mixing crushed stone waste and sand is obtained 1934.71 kg/m
3
in the mixture
volume variation 1:4 with proportion of 100% sand : 0% of crushed stone waste.
After mixing the crushed stone waste and sand, the highest density obtained was
2012.25 kg/m
3
in the mixture volume variation 1:4 with 75% sand : 25% crushed
stone waste. The highest value of the compressive strength of concrete bricks before
mixing is 9.96 MPa in the mixture proportion of 1:4 with 0% sand : 100% crushed
stone waste. Then after mixing, the highest compressive strength of concrete bricks
is 9.26 MPa in the mixture volume variation 1:4 with 75% sand : 25% crushed stone
waste. The highest value of the flexural strength before mixing is 1.80 MPa in the
mixture volume variation 1:4 with 100% sand : 0% crushed stone waste. After
mixing, the highest flexural strength obtained is 1.93 MPa in the mixture volume
variation 1:6 with 50% sand : 50% crushed stone waste. The highest water
absorption before mixing is 12.99% in the mixture volume variation 1:8 with 100%
sand : 0% crushed stone waste. After mixing, the highest water absorption is
obtained 13.68% in the mixture volume variation 1:8 with 75% sand : 25% crushed
stone waste. The highest modulus elasticity before mixing is 1738.20 MPa in the
mixture volume variation 1:4 with 100% sand : 0% crushed stone waste. After
mixing, the highest modulus elasticity is 1481.70 Mpa in the mixture volume
variation 1:8 with 50% sand : 50% crushed stone waste. The price of making
concrete bricks with research materials was cheaper than making concrete bricks in
Cilacap District. Concrete bricks that met the quality requirements with minimum
average of compressive strength based on SNI 03-6861.1-2002 for quality II used
mixture of 1:6 with 25% sand : 75% crushed stone waste, and for the quality III it
used mixture of 1:8 with proportion 0% sand : 100% crushed stone waste.
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