Bending Cement and Concrete PDF

Running head: BENDING CEMENT 1
BENDING CEMENT AND CONCRETE
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BENDING CEMENT AND CONCRETE 2
Nature of PVA fibers and its production.
What are PVA fibers?
Polyvinyl Alcohol (PVA) Fibres are water-soluble compounds. They are polyhydric whose
alternate carbon atoms have secondary alcoholic groups. This compound is soluble in water
because of the many hydroxyl groups that are present in its molecular structure (Shin et al,
2012). To solubilize it in water, use a treatment which has formaldehyde. These fibers are a
monofilament. They disperse all over the concrete matrix hence creating a network of fiber
that is multidirectional. This unique molecular structure enables it to possess alkali and
weather resistance by providing control over shrinkage and limiting the thermal contraction
and expansion (Noushin et al., 2013). This is a good environment-friendly cement reinforced
material. Due to their monofilament nature, the dispersion of fibers can hardly be seen in the
end product hence the name stealth fibers.
Production of Polyvinyl Alcohol
PVA is produced by polymerizing vinyl acetate in methanol with peroxide as a catalyst,
unlike other vinyl polymers which are produced in the process of polymerization of their
corresponding monomers. When vinyl acetate is polymerized, polyvinyl acetate is produced
(Zhifeng and Kun, 2007). Polyvinylacetate in methanol is then converted to PVA by adding
sodium hydroxide (NaOH). Other Chloroacetate groups can be used instead of acetate. The
conduction of the polyester is done by a base-catalyzed transesterification and with ethanol.
[CH2CH(OAc)] n + C2H5OH → [CH2CH(OH)] n + C2H5OAc
The PVA which is in a precipitate from is obtained. It is then pressed and later dried. This
result is then put in the water in which it dissolves and a solution that is 15% the polymer is
obtained. The solution is then extruded in the process of spinning in a spinning bath that
contains 20% sulphuric acid, 50% water, 25% Glauber’s salt and 5% formaldehyde.

BENDING CEMENT AND CONCRETE 3
Physical and chemical proprieties.
The physical properties of PVA vary according to the technology used in their production.
The physical and chemical properties might be slightly different depending on the level of
hydrolysis (Ranger, 1935) because this determines the PVA molecular weight and grade.
Chemical properties Physical properties.
 Biodegradability
 Biocompatibility. Compatible with
human tissues due to its physical
properties.
 Can chemically bound to a
nanoparticle surface.
 Resistance to temperature variation.
 Non-toxicity.
 High modulus elasticity
 Very strong molecular bond
 Ability to create a molecular bond
with concrete and mortar.
 Crystalline structure
 Has a melting point of 230 degrees
for the fully hydrolyzed. For the
partially hydrolyzed it’s melting
point is between 180 and 190
degrees.
 PVA can undergo pyrolysis at high
 Has tensile strength characteristics
 Has gas (e.g. oxygen) and aroma
barrier characteristics
 It is more flexible than other
polymers.
 It is hard.
 It is water soluble.
 It has a film form.
 Stealth nature
 White or yellowish in color and is
granular
 It has chemical resistance. High
alkali, acid and oil resistance.
 Thermal stability. There is no
significant change between the
temperatures of 40 degrees and 160
degrees. Its decomposition
temperature is 200 degrees Celsius
and that is when it starts to get
darker.

BENDING CEMENT AND CONCRETE 4
temperatures.
 It is almost incompressible.
Poisson’s ratio is between 0.42-
0.48.
 Esterification of PVA. Can react
with formylation inorganic acids and
acetylation to produce an ester.
 Etherification of polyvinyl alcohol.
PVA is reacted with sulphuric acid
under the action of an alkali. PVA is
also reacted with epoxy ethane with
the help of a catalyst.
 Storage stability. It can stay for a
long term without being moldy.
However, when stored in an aqueous
solution, some fungicide should be
added.
Effect of the PVA fibers on the environment.
Polyvinyl Alcohol fiber is an environmentally friendly component that is used to reinforce
cement. Due to its molecular structure, it possesses alkali and weather resistance. PVA is
used widely in the fishing industry (Chuangchote et al., 2007). It is used in freshwater sports
fishing. It biodegrades very slowly. Solutions that contain at most 5% PVA are not toxic
hence cannot harm the fish. This product can be used in many areas like buildings and walls
because of it is environmental friendly aspect (Ahmed and Mihashi, 2007).
Australian experience with the PVA fibers.

BENDING CEMENT AND CONCRETE 5
PVA has been accepted and used widely in Australia. Some Australian companies like
BOSFA which is leading and largest supplier of concrete reinforcement fiber in Australia
have admitted having used PVA in its products to enhance and reinforce the concrete.
Superplasticizer (Melamine Formaldehyde Sulphonate)
Properties in bendable concrete
 Physical properties
The Melamine formaldehyde sulphonate is very hard and durable. It has a versatile
thermosetting plastic which has good fiber and is resistant to heat (Erdogdu 2000).
They also have improved moisture chemical and scratch resistance.
 Chemical properties
Consists of two monomers; melamine and formaldehyde. These two components are
condensed together hence the final product Melamine Formaldehyde Sulphonate.
It releases nitrogen gas when burnt hence the reason for its fire retardant properties. They
provide heat resistance properties to cement.
Melamine Formaldehyde Sulphonate is similar and fully compatible with urea formaldehyde
resins(Yilmaz and Glasser, 1991). For this reason, they can be reacted to reduce the emission
of formaldehyde from particle boards. This also is done to prevent degradation of glue bonds.
Can be converted to form structures which have very distinct pore structures. These structures
are very hard and they have insulation and soundproofing in cement.
A chemical reaction with the cement.

BENDING CEMENT AND CONCRETE 6
Superplasticizers belong to a group of chemicals that are called dispersants. They do not
allow the flocculation of cement’s fine particles. They are chemicals that are active and act on
the surface. They are made of a long chain of organic molecules. They have a polar water
attracting group also known as hydrophilic like COO-, -SO3-, -NH4+ (Singh et al., 1992). This
polar group is bonded to the non-polar water repelling organic chain which is also called
hydrophobic and hydroxide. The polar group is what is absorbed by the cement particles at
the surface. The water repelling end and water attracting groups project outwards from the
cement grains (Olie et al., 1977). The hydrophilic group reduces the water on the surface.
Through electrostatic repulsion, the polymer that has been adsorbed ensures the cement
grains are kept separate. When cement is ground, a charge called zeta potential is produced.
When the admixture is adsorbed, the zeta potential is reduced and eventually negative
charges are caused by the cement particles. As hydration progresses, the electrostatic charge
reduces until it is diminished. Superplasticizers work on lowering zeta potential (Davison et
al.,1974) which eventually leads to electrostatic repulsion.
Characteristics of cement used
Characteristi
c
SiO2 Al2O3 CaO Fe2O3 MgO SO3 Na2O Loss
Mass% 25.32 6.62 57.64 2.07 1.73 - 0.31 6.21
Melamine-formaldehyde is formed from reacting melamine and formaldehyde (crosslinker).
They react to form a number of methylolmelamines mixtures. When heated further, the
methlolmelamines confidence: The hexamethylolmelamine and the Melamine-formaldehyde
resins crosslink various polymeric materials which could be either water- and solvent bore
(Anderson and Berke, 2014). Etherification of melamine formaldehyde resins and the

BENDING CEMENT AND CONCRETE 7
hexamethylolmelamine is done with alcohols so as to enhance the solvents’ solubility. They
react with hydroxyl, carboxyl, thiol, and amide groups after acidifications. They end up
forming thermoset polymer networks that are three-dimensional (Spitz and Valk.,1986).
three-dimensional. The order of - SH > - OH > - CONH2 > - COOH is followed by the
reaction rate of the above mentioned functional groups.
The structure of Melamine Formaldehyde Sulphonate is:
Advantages
Superplasticizers help in improvement of the rheological properties of fresh cement or
concrete.
They increase workability. These additives are advantageous in that they disperse
constituents of concrete uniformly throughout the mix.
Melamine formaldehyde sulphonates are great in achieving a high initial slump property from
5cm to 30cm even without adding water (Saiidi et al., 2009). This reduces the water in use by
15 to 30 percent. Due to this, density and water tightness are improved.
Result
They are also good for precast concrete especially when the concrete time is short.
They are suitable for use in places with cold climates like the polar regions.

BENDING CEMENT AND CONCRETE 8
Australian experience with super plasticizer
Australia has embraced super plasticizers greatly and produces concrete that has these
additives. For this reason, many Australian companies produce bendable concrete that is ideal
for durable, hard and quality structures.
Fine aggregate in bendable concrete
Fine aggregate defines grains that at most 4.75 mm and at least 75 μm.
Properties of Fine Aggregate
The fine aggregate has many properties, and they include:
Absorption capacity. This refers to the total amount of moisture that one must use so that the
aggregate can be said to be Saturated-surface dry condition but not oven dry condition
(McDonald et al., 1998). SSD condition is when all the pores which are permeable get filled
with water yet but no film of water can be seen on the surface.
Specific gravity. This is how dense the material is in terms of density with the inclusion of
the internal pores.
Bulk density. This defines how much of the aggregate filaments are required per unit volume.
It is the mass/volume.
Soundness. This refers to how much the volume of the aggregate changes due to weather
changes and resulting deterioration of the concrete.
IS limit:
Fine Aggregate = 10% (weight loss of five cycles with Na2SO4)
Fine Aggregate = 15% (weight loss of five cycles with MgSO4)
Shape:

BENDING CEMENT AND CONCRETE 9
Flakiness index. Should be 0.6 times their mean dimension hence more surface area per
unit volume.
Elongation index. Greatest elongation should be 1.8 times their mean dimension for the
maximum surface area to volume ratio.
Porosity. Influences the crushing strength, elastic modulus and the impact value abrasion
resistance.
Size and grading. The grading limits and the maximum aggregate size should be specified
since they influence workability and cost. Fine aggregates increase the water requirement.
Fineness Modulus. This is the empirical factor and it is got from screen analysis data by
getting the total of cumulative percentages of aggregate collected from all the specific
series then divide it by 100. Fine aggregate with Fineness Modulus of 2.4 to 2.6 is best
used in plaster application and fineness modulus between 2.6 to 3.0 are best for the
concrete application (Bell et al., 2012).
Silt content. This affects the workability, therefore, water demand increases.
The function of fine aggregate in bendable concrete
 Provide stability of the volume
 Makes the material harder
 Reduce the changes in volume
 Provide resistance to abrasion
 They are cheap fillers.
PVA fibers and fly Ash in bendable concrete.
Fly Ash is an additive that is used as an instead of cement, partially when producing bendable
concrete. It contributes to the hardening of cement through hydraulic or pozzolanic activities.

BENDING CEMENT AND CONCRETE 10
It has spherical glassy particles that are in powder form and is obtained for burning
pulverized coal.
Advantages
Both PVA fibers and fly Ash have advantages.
PVA fibers Fly Ash
 It is a stealth fiber
 Is hard hence stronger concrete, It
also has low elongation which is a
great mechanical property.
 Increased ductility hence concrete
can move and absorb more energy
hence limited cracking.
 Panels can be cast thinner hence
saving the amount of the material
used and reduce the weight.
 Easier to work with since they are
shorter i.e. 3/8 inch.
 Resistant to alkali
 Corrosion resistant
 Vibration and impact resistance.
This helps in effective absorption of
impact energy hence improve
seismic capacity.
 Improves the resistance and frost of
 Has very fine and small particles.
This makes the concrete very dense
hence reduces the permeability of
the concrete.
 Adds greater strength to the concrete
and building.
 It is extremely affordable and
economical.
 It is environmentally friendly since
its waste are used to create building
materials.
 Helps prevent thermal cracking since
the concrete mixture generates very
minimal and low heat of hydration.
 It is resistant to chemical attacks i.e.
acid and sulfates.
 Limited shrinkage.
 Gives durability, good workability
and quality end product.

BENDING CEMENT AND CONCRETE 11
concrete.
 Chemical bonds with concrete
Disadvantages
PVA fibers Fly Ash
 It is difficult to formulate mixes with
PVA fibers at higher dosage rates
and use. this is because of the
monofilament fiber nature.
 The hairball effects. The PVA fibers
bind and clump to each other in the
process of mixing.
 PVA is expensive.
 Its properties are diminished under
wet conditions.
 The comprehensive strength is low
in the early days.
 In case of poor quality fly Ash,
permeability will increase.
 The quality of the fly ash always
affects the quality of the bendable
concrete.
 It is nonresistant to changes in the
weather an erosion.
Comparison between fly ash and cement of bendable concrete
The following table is used to show the analyses for different types of fly ashes and ordinary
cement (Minard,2009). Similar compounds are found in cement and fly ash. Due to rapid
cooling, the compounds in fly ash are glassy while the ones in cement are crystal in nature
because the cooling process is slower.

BENDING CEMENT AND CONCRETE 12
Chemical
compound
Class N Class C Class F Cement
Al2O3 18.40 16.70 25.80 4.30
MgO 3.90 4.60 1.80 2.10
Fe2O3 9.30 5.80 6.90 2.40
Na2O & K2O 1.10 1.30 0.60 0.60
SO3 1.10 3.30 0.60 2.30
CaO 3.30 24.30 8.70 64.40
A big difference between cement and fly ash is the amounts of the above elements in each
substance. Cement has a lot of CaO(lime) which is low in fly ash which instead has high
amounts of silicates. Cement has very low levels of sulfates. Cement is produced with lime.
A little of the CaO, which is in a free state, is released during the process of hydration
(Kazem and Mohammad,2008). This released lime becomes the ingredient needed for the
reaction of silicates found in fly ash which results to strong bonds and long-lasting cementing
compounds. A blend of the fly ash and cement, therefore, makes the concrete better and
incorporates the properties of the two elements.

BENDING CEMENT AND CONCRETE 13
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