Australian Experience With PVA Fibers And Superplasticizer For Bendable Concrete

1. PVA fibers in bendable concrete

1.1 Nature of PVA fibers and its production.( what is PVA fibers and its production)

1.2 Physical and chemical proprieties.( what are the physical and chemical proprieties…. Make sure that you but tables )

1.3 Effect of the PVA fibers on the environment.( clear the effect of the PVA fibers)

1.4 Australian experience with the PVA fbers.( also clear Australian experience with PVA fibers and if had been used in asutralia )

4.1- Proprieties ( chemical and physical)  in bendable concrete

4.2- Chemical reaction with the cement.( tables and equations)

4.3- Advantages

4.4- Australian experience with super plasticizer

1.5 Fine aggregate in bendable concrete

5.1- Properties of Fine aggregate and its function in bendable concrete 

1.6 PVA fibers and fly Ash in bendable concrete.

6.1- Advantages

6.2- Disadvantages

Properties of Fine aggregate and its function in bendable concrete

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.

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 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.

· 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. · 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).

Nature of PVA Fibers and its Production

Australian experience with the PVA fibers.

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.

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

 

Characteristic	SiO2	Al2O3	CaO	Fe2O3	MgO	SO3	Na2O	Loss
Mass%	25.32	6.62	57.64	2.07	1.73	-	0.31	6.21

Effect of the PVA fibers on the environment

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 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:

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.

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 defines grains that at most 4.75 mm and at least 75 µm.

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.

Australian experience with the PVA fibers

IS limit:

Fine Aggregate = 10% (weight loss of five cycles with Na2SO4)

Fine Aggregate = 15% (weight loss of five cycles with MgSO4)

Shape:

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. 

• 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. 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 concrete. · Chemical bonds with concrete

· 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.

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.

 

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.

Superplasticizer (Melamine Formaldehyde Sulphonate)

Reference:

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