| Abstract | This study is aimed at investigating the feasibility of using concrete rubble from the
old buildings in coastal areas as coarse aggregate in making concrete. The rubbles are
classified into two groups namely, 5-years concrete rnbble and 15-years concrete rnbble. Mix
proportions of concrete possessing the required workability and strength are designed. The
mechanical properties and percentage replacement of concrete rnbble are the dominant factors
in concrete mixture. Each type of concrete rubble is tested for their physical and mechanical
properties namely absorption, unit weight, moisture content, specific gravity, gradation,
compacted void content, aggregate impact value, abrasion resistance and chloride content.
The rnbble is used to replace the natural coarse aggregate in the following percentages: 0, 30,
50 and 100 by volume of coarse aggregate. Fly ash from Mae Moh Lignite Power Plant is
used to replace of 20% by weight of cementitious materials and superplasticizer having a
fixed dosage of 1.2% by weight of cementitious materials is also used. Two main variables
considered in the experimental program are the percentage replacement of concrete rubble
and age of concrete rnbble. Concrete containing limestone aggregate is used to be controlled
concrete. The physical and mechanical properties investigated are slump loss, compressive
strength at 3, 14, 28 and 90 days, permeability at 28 and 90 days, autogeneous shrinkage up to
90 days and drying shrinkage up to 90 days.
Test results indicated that the abrasion resistance of 15-years concrete rubble was
lower than that of 5-years concrete rubble. The compressive strengths of all specimens
differed slightly at the early age. The difference of compressive strengths increased as the age
increased. At 90 days, the compressive strength of concrete containing 5-years concrete
rubble was higher than that of concrete containing 15-years concrete rnbble and lower than
that of concrete containing limestone aggregate. The lowest case was concrete containing
100% replacement of 15-years concrete rnbble. It can be observed that the compressive
strength of the lowest case was about 75% of conventional concrete. The permeability,
autogeneous shrinkage and drying shrinkage had the same trend. When the percentage
replacement of concrete rubble was up to 50%, the permeability, the autogeneous shrinkage
and the drying shrinkage of recycled concrete were 1.4 times, 2.5 times and 2.25 times of
conventional concrete, respectively. The concrete properties containing concrete rnbble were
found to be much worse than conventional concrete as the percentage replacement of concrete
rnbble was higher than 50%. Thus, the percentage replacement of concrete rubble from the
old buildings in the coastal area should not be higher than 50% provided that fly ash and
superplasticizer are incorporated in the mixture. |