Abstract:
Significant amount of concrete waste generates every day from construction and
demolition (C&D) works and has become a global concern from environmental
perspective. Recycled aggregate produced from these C&D waste can be used as an
alternative material for natural aggregate (NA) which has finite resources. Recycled
aggregate (RA) has lower density, higher water absorption, lower mechanical properties
compared to normal aggregate (NA). Inclusion of fiber along with RA in concrete mixes
improves the mechanical properties of concrete. This study investigates the fresh and
hardened properties of normal aggregate concrete (NAC) and recycled aggregate concrete
(RAC) made with locally available low-cost galvanized iron (GI) fiber, as an alternative
to steel fibers, and polypropylene (PP) fibers. The objective of this study is to explore the
effect of GI fiber and PP fiber in terms of compressive strength, stress-strain behavior,
splitting tensile strength, and flexural strength. The study has been completed in two
phases. In the first phase, GI fiber and PP fiber with 0.5%, 1% and combination of GI and
PP fiber are used to prepare NAC to find out the optimum fiber type and percentage.
From test results it has been observed that concrete with 0.5% GI fiber produced best
results in terms of strength and ductility than the concrete with PP fiber, other GI fiber
content and combination of GI and PP fibers. In the second part of the study, diameter
and length of the GI fiber has been varied while keeping the fiber percentage of 0.5%
constant. From local market three different diameters of GI fibers, such as 0.51 mm, 0.70
mm and 1.21 mm, have been used in NAC to evaluate the effect of GI fiber diameter on
the properties of NAC. In terms of the performance against workability, compressive and
splitting tensile strength, 0.51mm diameter GI fiber has chosen for the next part of the
study. Finally, GI fiber of 0.51 mm diameter considering three different aspect ratios,
such as 30, 50 and 70, for which the fiber lengths were 15, 26, and 36 mm respectively,
have been incorporated in both NAC and RAC. For NAC, GI fiber of length 26 mm and
for RAC, GI fiber of length 36 mm showed the highest compressive strength. In general,
the test results have showed that RAC has lower strength than NAC at 28 days. However,
at 56 days RAC have showed better strength compare to NAC. Inclusion of GI fiber has
improved the mechanical properties of both NAC and RAC. On the other hand,
incorporation of PP fiber has very little effect on the compressive, tensile and flexural
strength of NAC and RAC.PP fiber showed reduced compressive and split tensile
strength. But PP fiber performed better at lower fiber content. At 0.5 % PP fiber content,
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concrete had low air content. However, against flexural loading concrete with PP fiber
showed better ductility. PP fiber performed better with RAC than the NAC.
