05-10-2012, 05:20 PM
A Study on the Shrinkage Control of Fiber Reinforced
Concrete Pavement
A Study on the Shrinkage Control.pdf (Size: 400.1 KB / Downloads: 68)
Abstract
Cement concrete pavement provides durable service life and remarkable applicability for heavy traffic. Its purchase
being easier than asphalt, cement concrete pavement offers excellent advantages in terms of durability and economic
efficiency. However, adequate repair of this pavement is harder than asphalt concrete in case of degradation or
damage. Cracking in the concrete pavement is the major cause of such disadvantages and the demand of repair on
road sites is growing every day. This emphasizes the urgency to secure technologies for the control of early and longterm
cracking. Accordingly, this study evaluates the drying and autogenous shrinkage strains regard to fiber
reinforcement in order to reduce cracking of the concrete pavement mix so as to control the damage of the pavement
by means of fiber reinforcement. The results show that the drying shrinkage strain can be significantly reduced to
about 1/4 through the admixing of 0.2% volume ratio of NY fiber compared to the non-reinforced plain concrete, and
that the hybrid fiber reinforcement mix H-N1-ST1 can realize remarkable reduction of the autogenous shrinkage.
Introduction
Two techniques are generally used for road pavement: the asphalt concrete pavement that is ductile
pavement and the cement concrete pavement that is rigid pavement. Cement concrete asphalt offers longterm
service life and excellent applicability for heavy traffic. Its purchase being easier than asphalt, this
pavement technique presents remarkable cost-effectiveness and durability. However, adequate repair of
the cement concrete pavement is more difficult than the asphalt pavement in case of degradation or
damage and demands works with a larger scale (Yang 2000; Um 2000).
The typical causes of cracks in concrete pavement are the hydration cracking at early hydration state
of concrete, the plastic shrinkage cracking, the environmental cracking caused by thermal changes at the
top of the pavement, the drying shrinkage cracking according to the hardening of concrete, and the
cracking caused by the long-term process of alkali-silica reaction. The Korean research community has
and is developing various solutions for the control of cracks.
The fundamental cause of the occurrence of cracks in concrete pavement is the poor resistance of the
concrete pavement to bending, tension and cracking. Fiber reinforcement is a representative method for
supplementing the bending tensile performance of concrete. To date, research on fiber reinforcement has
been steadily conducted. The recent trend of research on fiber reinforcement focuses on studies dedicated
to the plastic shrinkage cracking of fiber reinforced concrete with hybrid type of fibers and the tensile
strength performance of steel fiber reinforced concrete (Won 2004; Kim 2005).
Research devoted to fiber reinforcement focuses mainly on the evaluation of the change of the
mechanical performances according to the content and type of fibers in ordinary concrete and high
strength concrete. However, poor interest is given to the fiber reinforcement effect with respect to the mix
proportions of concrete. Especially, the quasi-absence of thorough study on the fiber reinforcement effect
on concrete pavement of which the mix proportion is limited to a specific weight and is prescribed to
adopt coarse aggregates with granulometry different to that of concrete pavement is noteworthy.
Accordingly, this study intends to evaluate the drying shrinkage and autogenous shrinkage strains
with respect to the fiber reinforcement in order to reduce cracking of the concrete pavement mix. Fiber
reinforced concrete specimens are fabricated with the type and content of fiber chosen as test variable to
select the type and quantity of fiber effective for shrinkage control. To that goal, the shrinkage strain of
concrete is measured. Three types of macro fibers with length longer than 30 mm and small aspect ratio
together with micro nylon fibers with length of 12 mm and aspect ratio larger than 1000 are selected for
the tests. Both reinforcement with a single type of fiber and hybrid reinforcement involving micro and
macro fibers were executed, and the fiber volume ratio was set to 0.2 to 0.3% of the concrete pavement
mix. Using the so-fabricated specimens, the change of the length caused by drying shrinkage and
autogenous shrinkage of concrete is analyzed comparatively.
Test
Test planning and test variables
The detailed mix proportions of the concrete pavement in this study are listed in Table 1. Fig. 1
describes the designation of the variables, and Table 2 presents the test variables and their explanation.
Table 3 arranges the experimental setup.
In the tests on fresh concrete, the slump was measured in compliance with KS F 2402, the air content was
measured according to the specifications of KS F 2421, and the change of length by drying shrinkage and
autogenous shrinkage was measured in compliance with the stipulations of KS F 2424 and KS F 2586.
Conclusions
This study analyzed comparatively the shrinkage performance of concrete pavement according to fiber
reinforcement. It was seen that mix S-N2-00 with single fiber reinforcement provides the largest
reduction of the drying shrinkage while mix H-N1-ST1 with hybrid fiber reinforcement developed the
smallest shrinkage. The most remarkable performance for the autogenous shrinkage was provided by
specimen S-00-PV2 with single fiber reinforcement and mixes H-N1-ST1 and H-N1-PP1 with hybrid
fiber reinforcement.