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MIX DESIGN OF SELF.pdf (Size: 1.35 MB / Downloads: 102) ON STUDY OF MIX DESIGN OF SELF COMPACTING CONCRETE ON M30 GRADE
MIX DESIGN OF SELF.pdf (Size: 1.35 MB / Downloads: 102)
ABSTRACT
Concrete occupies unique position among the modern construction materials, Concrete is a
material used in building construction, consisting of a hard, chemically inert particulate
substance, known as a aggregate (usually made for different types of sand and gravel), that is
bond by cement and water.
Self – compacting concrete (SCC) is a high – performance concrete that can flow under its own
weight to completely fill the form work and self consolidates without any mechanical vibration.
Such concrete an accelerate the placement, reduce the labor requirements needed for
consolidation, finishing and eliminate environmental pollution. The so called first generation
SCC is used mainly for repair application and for casting concrete in restricted areas, including
sections that present limited access to vibrate. Such value added construction material has been
used in applications justifying the higher material and quality control cost when considering the
simplified placement and handling requirements of the concrete.
GENERAL
Self – compacting concrete (SCC) is a fluid mixture, which is suitable for placing difficult
conditions and also in congested reinforcement, without vibration. In principle, a self –
compacting or self – consolidating concrete must:
Have a fluidity that allows self – compaction without external energy
Remain homogeneous in a form during and after the placing process and
Flow easily through reinforcement
Self – consolidating concrete has recently been used in the pre – cast industry and in some
commercial applications, however the relatively high material cost still hinders the wide spread
use of such specialty concrete in various segments of the construction industry, including
commercial and residential construction.
DEVELOPMENTS OF SELF – COMPACTING CONCRETE
For several years beginning in 1983, the problem of the durability of concrete structures was a
major topic of interest in Japan. The creation of durable concrete structures requires adequate
compaction by skilled workers. The designs of modern reinforced concrete structures become
more advanced, the designed shapes of structures are becoming increasingly complicated and
heavy reinforcing is no longer unusual. Furthermore, the gradual reduction in the number of
skilled workers in Japan‟s construction industry has led to a similar reduction in the quality of
construction work. One solution for the achievement of durable concrete structure independent
of the quality of construction work is the employment of self – compacting concrete, which can
be compacted into every corner of a form work, purely by means of its own weight and without
the need for vibrating compaction. Okamura proposed the necessity of this type of concrete in
1986. Studies to develop self – compacting concrete, including a fundamental study on the
workability of concrete, have been carried out by “Ozawa and Maekawa” at the university of
Toky
A high volume of the fine particles (<80 µm)
In order to ensure sufficient workability, while limiting the risk of segregation or bleeding. SCC
contains a large amount of fine particles (around 500 kg/m3). Nevertheless, in order to avoid
excessive heat generation, the Portland cement is generally partially replaced by mineral
admixtures like limestone filler or fly ash or GGBS (Cement should not be used as a filler). The
nature and the amount of filler added are chosen in order to comply with the strength and
durability requirements
The possible use of a viscosity agent (water retainer)
These products are generally cellulose derivatives, polysaccharides or colloidal suspensions.
These products have the same role as the fine particles, minimizing bleeding and coarse
aggregate segregation by thickening the paste and retaining the water in the skeleton. The
introduction of such products in SCC seems to be justified in the case of SCC with high water to
binder ratio. On the other hand, they may be less useful for high performance SCC (strength
higher than 50Mpa) with low water to binder ratio. For intermediate SCC, the introduction of
viscosity agent has to be studied for each case. Viscosity agents are assumed to make SCC less
sensitive to water variations in water content of aggregate occurring in concrete plants. Because
of the small quantities of viscosity agents required, however, it may be difficult to achieve
accuracy of dosage.
SLUMP FLOW &T50 TEST
Slump flow is one of the most commonly used SCC tests at the current time. This test involves
the use of slump cone used with conventional concretes as described in ASTM C 143(2002).The
main difference between the slump flow test and ASTM C 143 is that the slump flow test
measures the “spread” or “flow” of the concrete sample once the cone is lifted rather than the
traditional “slump” (drop in height) of the concrete sample. The T50 test is determined during
the slump flow test. It is simply the amount of time the concrete takes to flow to a diameter of 50
centimeters .Typically, slump flow values of approximately 24 to 30 inches are within the
acceptable range; acceptable T50 times range from 2 to 5sec.
J RING TEST
Introduction
The principle of the J ring test may be Japanese, but no references are known .The J ring test
itself has been developed at the University of Paisley. The test is used to determine the passing
ability of the concrete. The equipment consists of a rectangular section (30mm×25mm) open
steel ring, drilled vertically with holes to accept threaded sections of reinforcement bar. These
sections of bar can be of different diameters and spaced at different intervals; in accordance with
normal reinforcement considerations,3x the maximum aggregate size must be appropriate .The
diameter of ring in vertical bars is 300 mm and the height 100 mm.
The J ring can be used in conjunction with the slump flow, the Orimet test, or eventually even
the V-funnel. These combinations test the flowing ability and (the contribution of the J ring) the
passing ability of the concrete. The Orimet time and/or slump flow spread are measured as usual
to assess flow characteristics .The J ring bars can principally be set at any spacing to impose a
more or less severe test of the passing ability of the concrete . After the test, the difference in
height between the concrete inside and that just outside the J ring is measured .This is an
indication of passing ability, or the degree to which the passage of concrete through the bars is
restricted.
Interpretation of result
It should be appreciated that although these combinations of tests measure flow and passing
ability ,the results are not independent .The measured flow is certainly affected by the degree to
which the concrete movement is blocked by the reinforcing bars .The extent of blocking is much
less affected by the flow characteristics ,and we can say that clearly ,the greater the difference in
height ,the less the passing ability of the concrete, Blocking and/or segregation can also be
detected visually ,often more reliably than by calculation.
Note: The results of the J ring are influenced by the combination method selected and results
obtained with different combinations will not be comparable.
Compressive strength of concrete
Compressive strength of concrete is defined as the load, which causes the failure of a standard
specimen.(Ex 100 mm cube according to ISI)divided by the area of crossection in uniaxial
compression under a given rate of loading. The test of compressive strength should be made on
150mm size cubes.
Place the cube in the compression-testing machine. The green button is pressed to start the
electric motor. When the load is applied gradually, the piston is lifted up along with the lower
plate and thus the specimen application of the load should be 300 KN per minute and can be
controlled by load rate control knob. Ultimate load is noted for each specimen. The release valve
is operated and the piston is allowed to go down. The values are tabulated and calculations are
done.
SCOPE FOR FURTHER WORK:
Since a rational mix design method and an appropriate acceptance testing method at the job site
have both largely been established for self compacting concrete, the main obstacles for the wide
use of self compacting concrete can be considered to have been solved. The next task is to
promote the rapid diffusion of the techniques for the production of self compacting concrete and
its use in construction. Rational training and qualification systems for engineers should also be
established. In addition, new structural design and construction systems making full use of the
self compacting concrete should be introduced.
When self compacting concrete becomes so widely used that it is seen as the “Standard concrete”
rather than a “Special concrete”, we will have succeeded in creating durable and reliable
concrete structures that require very little maintenance work.