EXPERIMENTAL INVESTIGATIONS ON JOINTING
MATERIALS FOR PREFABRICATED CONSTRUCTIONS
by
HEMANTH KUMAR V
roll no 36
PGDIE 42
GENERAL
A
jointing material should have high initial and sustained long term strength and
performance. The material should have good dimensional stability and should not
shrink. It should have excellent bonding characteristics. It should be able to
flow under its own gravity and completely fill the joints.
Two types of new materials were identified as
potential materials to be used as jointing materials.
1. Microconcrete
2. Self compacting concrete
This
study was largely focused to evaluate the properties of the above materials for
use as jointing materials. This chapter describes the materials used for making
the concrete, the mix proportions and the details of tests conducted on the
specimens.
MICROCONCRETE
This is
a dry mixture of cementitious binders, graded fine and coarse aggregates,
superplasticizers, and shrinkage compensating admixtures. Fig. shows the dry
mixture of microconcrete.
Fig 3.1 sample of microconcrete
SIEVE ANALYSIS OF MICROCONCRETE
Sieve analysis is performed,
by dividing the sample of microconcrete powder into various fractions each
consisting of the particles of same size. The grading pattern of Sample of
microconcrete powder is assessed by sieving a sample successively through the
entire sieves mounted one over the other in order of size, with larger sieve on
top.
Table 1 Sieve Analysis of
microconcrete.
IS Sieve Number
|
Weight Retained (g)
|
Cumulative weight retained (g)
|
Cumulative percentage weight retained (g)
|
2.36mm
|
13.44
|
13.44
|
4.48
|
1.18mm
|
5.88
|
19.32
|
6.44
|
600μ
|
2.62
|
21.94
|
7.31
|
300μ
|
52.83
|
74.77
|
24.92
|
150μ
|
33.84
|
108.61
|
36.2
|
75μ
|
12.67
|
121.28
|
40.43
|
Pan
|
179.62
|
300
|
-
|
Total
|
300
|
119.78
|
Fineness modulus = 1.19
|
Through
Sieve Analysis, Fineness modulus of Microconcrete is 1.19. It shows that sample
of microconcrete has more finer particle size and Fig 3.3 below shows the graph
drawn between percent passing vs sieve size.
To find weight of
concrete from the adopted volume use the following formula Weight of concrete =
density of concrete x volume of concrete.
Density of concrete
= weight of concrete / known volume.
= 0.612kg/ 0.000196m³
= 3122.44 kg/m³
From sieve analysis:
Coarse aggregate= 13.4 gm
Fine aggregate = 95.17 gm
cement = 192.326 gm
Proportions 1: 0.49: 0.07
|
• s.p glenium -
20 ml
• Water - 5.5
litre
• Concrete - 35 kg
SELF COMPACTING CONCRETE (SCC)
GENERAL
Self-compacting
concrete (SCC) is an innovative concrete that is able to flow and consolidate
under its own weight, completely fill the formwork even in the presence of
dense reinforcement, whilst maintaining homogeneity and without the need for
any additional compaction. The hardened concrete is dense, homogeneous and has
the same engineering properties and durability as traditional vibrated
concrete. Self-compacting concrete offers a rapid rate of concrete placement,
with faster construction times and ease of flow around congested reinforcement.
The fluidity and segregation resistance of SCC ensures a high level of
homogeneity, minimal concrete voids and uniform concrete strength, providing
the potential for a superior level of finish and durability to the structure.
SCC is often produced with low water-cement ratio providing the potential for
high early strength, earlier demoulding and faster use of elements and
structures. The elimination of vibrating equipment improves the environment on
and near construction and precast sites where concrete is being placed,
reducing the exposure of workers to noise and vibration. The improved
construction practice and performance, combined with the health and safety
benefits, make SCC a very attractive solution for both precast concrete and
civil engineering construction. A brief description on the important
characteristics of the materials used for developing self compacting concrete
is given below.
PROPERTIES OF SELF COMPACTING CONCRETE
Self-compacted
concrete is defined as a category of high performance concrete that has
excellent deformability in the fresh state and high resistance to segregation,
and can be placed and compacted under its self weight without applying
vibration. The properties of self compacting concrete are as follows.
(a) Filling Ability
The
concrete must have the ability to flow and completely fill all parts within the
formwork under its own weight without leaving voids. As it is highly fluid it
has the ability to flow considerable distances both horizontally and upwards
and fill vertical elements from the bottom.
(b) Passing Ability
The
concrete containing the required aggregate size must have the ability to flow
through and around restricted spaces between steel reinforcing bars and other
embedded objects under its own weight and without blocking or segregation.
(c) Resistance to Segregation
The
property of self-compacting concrete to flow without segregating.
INGREDIENTS OF SELF COMPACTING CONCRETE
Ordinary Portland Cement
Cement
is the individual unit of fine and coarse aggregate into a solid mass by virtue
of its inherent properties of setting or hardening in combination with water.
It helps to fill the voids and gives density to the concrete. Ordinary Portland
Cement-Grade 53, having been certified with IS: 12269 – 1987 [17] standards,
Grade 53 is known for its rich quality and is highly durable. Hence it is used
for constructing bigger structures like building foundations, bridges, tall
buildings, and structures designed to withstand heavy pressure. As such,
Ordinary Portland Cement is used for quite a wide range of applications in
pre-stressed concrete are dry-lean mixes, durable pre-cast concrete, and ready
mixes for general purposes. The chemical components of Ordinary Portland Cement
are Magnesium (MgO), Alumina (AL2O3), Silica (SiO2), Iron (Fe2O3), and Sulphur
trioxide (SO3).
In
this present study, locally procured Ordinary Portland Cement of grade 53
conforming to IS: 12269 – 1987 was used. The standard consistency of the cement
tested according to IS: 4031 (Part 4) – 1988 [18] was 35%, the initial and
final setting times of cement tested according to IS: 4031 (Part 5) – 1988 [19]
was 130 and 290 minutes respectively. Compressive strength of cement determined
as per IS: 4031 (Part 6) – 1988 [20] was 54 MPa. The physical characteristics
of the tested cement are given in Table 3.2.
Table 2 Properties of Ordinary Portland Cement
Type of cement
|
Ordinary Portland Cement, 53 Grade
|
Conforming
code
|
IS: 12269-1987
|
Fineness(retained
on 90-m sieve)
|
0.85
|
Normal
Consistency
|
35%
|
Vicat
initial setting time (minutes)
|
130
|
Vicat final
setting time (minutes)
|
290
|
Compressive strength
3-days (MPa)
|
20
|
Compressive strength
7-days (MPa)
|
36
|
Compressive strength
28-days (MPa)
|
52
|
Specific
Gravity
|
3.125
|
Bulk
Density(kg/m3)
|
1610
|
Flyash
Flyash
is one of the numerous substances that cause air, water and soil pollution,
disrupt ecological cycles and set off environmental hazards. The combustion of
powdered coal in thermal power plants produces fly ash. Fly ash produced thus
possesses both ceramic and pozzolanic properties. Fly ash is of two basic types
namely, Class F type and Class C type. Both Class F and Class C fly ashes
undergo a pozzolanic reaction with the lime (calcium hydroxide) created by the
hydration of cement and water, to create the same binder (calcium silicate
hydrate) as cement. Class F fly ash, with particles covered in a kind of melted
glass, greatly reduces the risk of expansion due to sulfate attack. Class F fly
ash which is provided for use in concrete applications will meet or exceed the
performance requirements of ASTM C 618 [21]. Class F fly ash is particularly
beneficial in high performance concrete applications where high compressive
strengths are required or where severe exposure conditions demand highly
durable concrete. Class F fly ash is also very effective at mitigating problems
associated with alkali-silica reactions.
Advantages of Fly ash
(a) Higher
ultimate strength
(b) Increased
durability
(c) Reduced
bleeding
(d) Reduced Heat
of Hydration
(e) Increased
resistance to sulfate attack
(f) Reduced
shrinkage.
(g) Reduced Efflorescence
The
present investigations were carried out using Class F fly ash which was
obtained from the Ennore Thermal Power Station near Chennai, India. The
physical properties of fly ash are given in Table 3.3
Table 3 Properties of Class F Fly ash
Mineral Admixtures
|
Fly Ash (Class F)
|
Specific
gravity
|
2.13
|
Fineness(cm2/g)
|
3500(Blaine)
|
Silica(SiO2)%
|
58.55
|
Iron Oxide (Fe2 O3) %
|
3.44
|
Alumina (Al2 O3) %
|
28.20
|
Calcium Oxide (CaO) %
|
2.23
|
Magnesium Oxide (MgO)
%
|
0.32
|
Sodium Oxide (Na2O) %
|
0.58
|
Potassium Oxide (K2O)
%
|
1.26
|
Total Sulphur (SO3) %
|
0.07
|
Insoluble Residue
|
-
|
Bulk Density (kg/m3)
|
995
|
Normal Weight Aggregates
Aggregate
is a material which is mixed with cement to create concrete which is hard,
strong, and long-lasting. Using aggregate makes concrete much stronger, with
the aggregate acting as a type of reinforcement. The aggregate occupies the
three-quarter of the volume of the concrete, it contributes significantly to
the structural performance of concrete, especially strength, durability and
volume stability. The influence of fine aggregates on the fresh properties of
the SCC is significantly greater than that of coarse aggregate. The high volume
of paste in SCC mixes helps to reduce the internal friction between the sand
particles but a good grain size distribution is still very important. The
reinforcement spacing is the main factor in determining the maximum aggregate
size. The particle size distribution and the shape of coarse aggregate directly
influence the flow and passing ability of SCC and its paste demand. The maximum
size actually used varies but, in any mix, particles of different sizes are
incorporated, the particle size distribution being referred to as grading. The
alternative always used in the manufacture of good quality concrete, is to
obtain the aggregate in at least two sizes groups, the main division being
between fine aggregates often called sand, not larger than 4.75 mm and coarse
aggregate, which comprises material at least 4.75 mm size.
In this study, locally available
river sand and crushed granite were used as normal weight fine and coarse
aggregates.
Super plasticizer
Super
plasticizers are linear polymers containing sulfonic acid groups attached to
the polymer backbone at regular intervals. Super plasticizers are high range
water reducing admixtures that meet the requirements of ASTM C 494 – 08 [24].
The
super plasticizer used for the present study is Glenium B233. Glenium B233 is
an admixture of a new generation based on modified polycarboxylic ether. The
product has been primarily developed for applications in high performance
concrete where the highest durability and performance is required. Glenium B233
is free of chloride & low alkali and compatible with all types of cements.
Glenium B233 consists of a carboxylic ether polymer with long side chains. At
the beginning of the mixing process it initiates the same electrostatic
dispersion mechanism as the traditional superplasticizers, but the side chains
linked to the polymer backbone generates a steric hindrance which greatly
stabilizes the cement particles ability to separate and disperse. With this
process, flow able concrete with greatly reduced water content is obtained. The
properties of Glenium B233 are given in Table 3.4.
Advantages of Glenium B233
(a) Elimination
of vibration and reduced labour cost in placing
(b) Marked
increase in early & ultimate strengths
(c) Higher
Young’s modulus
(d) Improved
adhesion to reinforcing steel
(e) Better
resistance to carbonation and other aggressive atmospheric conditions
(f) Increased
durability
(g) Reduced shrinkage and creep
Table 4 Properties of Glenium B233
S.No
|
Property
|
Superplasticizer
(MBT data sheet)
|
1
|
Chemical
type
|
Polycarboxylic
ether
|
2
|
Specific
Gravity
|
1.09
|
3
|
Chloride
content
|
Nil
|
4
|
Approx.
air entrainment
|
1%
at normal dosages
|
5
|
Relative
Density
|
1.09±0.01
at 25°C
|
6
|
pH
|
≥ 6
|
7
|
Dosage
|
500ml
to 1500ml per 100kg of cementitious material
|
8
|
Solid
content
|
30%
|
9
|
Conforming
standard
|
ASTM
C 494 Type F
|
10
|
Colour
|
Light
Brown
|
11
|
Form
|
Viscous
liquid
|
12
|
Transport
|
Not
classified as dangerous
|
13
|
Labeling
|
No
hazard label required
|
Viscosity Modifying Agent
Viscosity
Modifying Admixtures can be used to produce concrete with better robustness
against the impact of variations in the concrete constituents and in site
conditions, making it easier to control. The key function of a VMA is to modify
the rheological properties of the cement paste. VMA’s change the rheological
properties of concrete by increasing the plastic viscosity but usually cause
only a small increase in the yield point.
The viscosity modifying agent used
for the present study is Glenium stream 2. It is a premier ready-to-use,
liquid, organic, viscosity-modifying admixture (VMA) specially developed for
producing concrete with enhanced viscosity and controlled rheological properties.
Concrete containing Glenium stream 2 admixture exhibits superior stability and
controlled bleeding characteristics, thus increasing resistance to segregation
and facilitating placement. Glenium stream 2 consists of a mixture of water
soluble copolymers which is adsorbed onto the surface of the cement granules,
thereby changing the viscosity of the water and influencing the rheological
properties of the mix. It is chloride-free and compatible with all cements and is incompatible for use with naphthalene
sulphonate based superplasticizer admixtures. The properties of Glenium stream
2 are given in Table 3.5.
Advantages of Glenium Stream 2
(a) Increased
viscosity and thixotropic properties
(b) Improved
stability during transport & placing
(c) Controlled
bleeding
(d) Reduced
segregation, even with highly fluid mix
(e) Enhanced
pumping and finishing
(f) Enables flexibility in mixture
proportioning
Table 5 Properties of Glenium Stream 2
S.No
|
Property
|
Viscosity Modifying Agent
(MBT data sheet)
|
1
|
Chemical
type
|
Water
soluble polymer
|
2
|
Specific
Gravity
|
-
|
3
|
Chloride
content
|
Nil
|
4
|
Approx.
air entrainment
|
-
|
5
|
Relative
Density
|
1.09±0.01
at 25°C
|
6
|
pH
|
≥ 6
|
7
|
Dosage
|
50
ml to 500 ml per 100kg of cementitious material
|
8
|
Solid
content
|
-
|
9
|
Conforming
standard
|
-
|
10
|
Colour
|
colourless
|
11
|
Form
|
Viscous
liquid
|
12
|
Transport
|
Not
classified as dangerous
|
13
|
Labeling
|
No
hazard label required
|
Water
Water
is the key ingredient, which when mixed with cement, forms a paste that binds
the aggregate together. The water available in the laboratory which satisfies
drinking standards was used for the concrete making and its subsequent curing.
THE BASIS OF SCC MIX DESIGN
The
behavior of fresh concrete is closely linked to many concrete mixture variables
as follows:
1. The free water content of the
concrete: The water content in a mixture can be classified into
free water and the bound water. Free water is the interstitial water existing
between fines and aggregates. It disperses and lubricates the solid particles
in concrete to create fluidity and plasticity of concrete. Therefore, it is the
quantity and quality of free water that determines much of the rheological
behavior of fresh concrete. On the other hand, flowable concrete, especially
flowable lightweight concrete, requires rich fine content to achieve adequate
cohesion. The fines content in concrete basically determines the amount of the
bound water. It has been found that the appropriate water-to-fines ratio in
selfcompacting lightweight concrete ranges from 0.85 to 1.0 by volume.
2. Dispersion characteristics of
solid particles in concrete: Water-reducing admixtures are
dispersion agents that reduce cement flocculation and release bound water in
concrete. On the other hand, a cohesive agent ―thickens‖ the interstitial free
water in concrete, making it more cohesive and thixotropic. Only when the
cohesive agent is properly used together with water reducing admixtures, the
desirable self-compacting property can be achieved.
3. Particle packing
characteristics have significant effects on the concrete workability.
Self-compacting concrete typically contains fine aggregates in the range of
45-50% of total aggregates by volume. The shape and size of coarse aggregates
also have a influence on concrete workability. As concrete flows, the
aggregates will contact each other to impose friction force in resistance.
Thus, concrete containing large and angular aggregates tends to be less
workable.
4. Composition of cementitious
materials is also an important parament. Replacing a portion of the
portland cement with fly ash may remarkably improve the concrete workability.
Cement containing high C3A content usually causes rapid hydration of cement and
consumption of free water in the paste, resulting in loss of slump with time.
Type II Portland cement is typically used.
On
the basis of the previous studies, a number of concrete proportions were
developed for trial batch tests. In essence, the concrete mixtures had
water-to-cement ratios in the range of 0.3 to 0.34.
MIX PROPORTIONS
The mix proportions of
SCC, according to EFNAC guidelines are followed as below.
Mix proportion of M40 concrete
The weight of materials used for making 250 kg of concrete (0.1m³) is as
follows:
Cement - 35kg Flyash - 22 kg
Sand - 85 kg
Coarse Aggregate - 80 kg
Water - 17 litres
Super plasticizer - 410 ml (0.7 % of
binder.)
CONCLUSIONS
The following conclusions are drawn
based on the study:
MICROCONCRETE
The microconcrete had:
·
Very low drying shrinkage. The shrinkage
observed at the end of 7 days is only 0.004mm which is very low.
·
High early age compressive strength .The
strength obtained on the third day is 57 MPa.
·
High 28 days compressive and tensile strength.
The strength obtained on the twenty eighth day was 60.31 MPa and 4.93 MPa
respectively.
·
Modulus of rupture of twenty eight day was
observed to be 5.4 MPa.
SELF COMPACTING CONCRETE
The following properties were
observed. The concrete had:
·
A slump flow of 600 mm.
·
High early age compressive strength .The
strength obtained at the end of one day is said to have 15MPa, The strength
obtained at the end of third day was 21MPa, and the strength obtained at the
end of seventh day was 33MPa.
·
High 28 days compressive and tensile strength.
The strength obtained on the twenty eighth day was 45 MPa and 6.93 MPa
respectively.
·
Modulus of rupture of twenty eight day was
observed to be 5.91 N/mm2.
·
Time taken for the scc to reach 20cm length from
the junction of the L-Box is 1 second and 2 seconds to reach 40cm which shows
that scc has achieved its filling and passing ability.
·
In V- funnel test, scc evacuated the apparatus
in 10 seconds, shows high passing ability of the fresh concrete.
·
In U – Box test, the filling height of the scc
was measured to be 33 cm, resulting in good filling ability of the fresh
concrete.
Hence,
the properties of microconcrete and selfcompacting concrete are satisfactorily
achieved and can be used in the wet connections (or) jointing area of the prefabricated
wall panels.
REFERENCES
Series of Large Panel Residential
Buildings and Block-Sections. Standard designs # 158
Research Institutes TsNIIEP zhilishe
and GP I "Alma -Ata Giprogor", Alma -Ata 1977
SNIP II-A.12-69 Construction in
seismic regions. Standards of design
SNIP II-7-81 Construction in
seismic regions. Standards of design
SNIP RK B.1.2-4-98 Construction in
seismic regions
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