Polyvinyl Alcohol Creating Bendable Concrete: The Science Behind It

Literature Review

Discuss About The Polyvinyl Alcohol Creating Bendable Concrete.

Normal concretes almost do not bend having a 0.1% strain capacity which makes them rigid and highly brittle. The featured lack of bendability is the main reason for failure under strain and this factor has pushed for an elegant development of a material known as Engineered Cementitious Composites as well as bendable concrete. The material has the ability to considerably exhibit an improved flexibility. Bendable concrete is reinforced with polymer fibres which are designed micro-chemically whereas Engineered Cementitious Composites is obtained from similar ingredients that are as basic as those of normal concrete. However, it has High Range Water Reducing agents added to it for the purpose of imparting better workability. In ECC, there is no use of coarse aggregates, therefore it is a mortar and not concrete. The amount of Engineered Cementitious Composites powder is high, relatively. Cementitious materials for example fumes of silica, fly ash, blast-furnace slag among others may be added to cement so as to increase the amount of the paste. Engineered Cementitious Composites typically uses 2% of discontinuous short fibres. Engineered Cementitious Composites incorporates silica sand which is very fine and Poly Vinyl Alcohol fibres that covered with a coating of very thin silk. This coating of the surface enables the fibre to begin slipping during over-loading which prevents fracturing.

(Seyhan, John, & Abid, 2018)Conducted a study on synthetic fibres and steel, both available commercially. Deflection and flexural stress relationships have been applied to determine flexural toughness, flexural strength, equivalent flexural strength ratio and equivalent flexural strength. The concrete’s flexural toughness was discovered to be averagely increasing upon the usage of synthetic fibres and steel, however, different fibres of equal dosages did not lead to specimens with similar flexural toughness.

(Recep, Hediye, & Yusuf, 2017)Conducted an investigation study on the flexural behaviour on concrete that self-compacts reinforced with hooked-end and straight steel fibres at 0.5%, 1.0% and 1.5% levels compared to Normally Vibrated Concrete. The tests from the laboratory were determined as per RILEM TC 162-TDF recommendation. The flexural behaviour of SCC appeared comparably similar as Normally Vibrated Concrete, where an increase in the volume ration of fibres led to an increase in post-peak and pre-peak SCC parameters. The type of steel fibres nevertheless, greatly influences this dependency. However, the SCC gains maximum displacement in its crack mouth for lesser deflections as compared to Normally Vibrated Concrete.

Aims and Objectives of the Investigation

(Wei & Yan, 2017)carried out a study to experiment on the probable applications of the Engineered Cementitious Composites reinforced with fibres with less drying shrinkage characteristics in pavements of the concrete with the aim of joint elimination that is used normally to accommodate deformation of shrinkage and temperature. It was realized that composite slab having both normal concrete and LSECC with bars of steel at the interface of concrete/ LSECC and designed procedures of construction was able to localize the tensile cracks into the strip LSECC instead of fracturing in the nearest concrete slab (Viktor, Volker, & Petr, 2017).

(Biswajeet, 2018)Investigated on the self-healing nature of the LSECC with concern on the influence of pre-cracking period and curing condition. A four-point bending test was used to pre-crack beams of ECC at a different age, followed by different conditions of curing. For all the conditions of curing, deflection capacity after self-healing can exceed or even recover those from virgin samples with averagely every pre-cracking age.

Bendable concrete has been noted to be having better features compared to the normal concrete, therefore, this experiment will be investigating the high performance of this bendable concrete in that it will;

• Aim at making and casting beams of ECC to determine the deflection of these beams.
• Aim at performing the separate flexural test, tensile test and compression test to observe the nature of ECC.

Because ECC is flexible more than the traditional concrete, it is considered more of a metal than glass. Traditional concrete is considered to be rigid, brittle and ceramic. It may experience the greatest failure by routine overuse and when under strain.it is studded with specially coated fibre reinforcements which hold it together thus ECC remains safe and intact to be at a tensile strength of up to 5%. Traditional concrete cracks may not be in a position to withstand a load with a tensile strain of 0.01%. Today, constructers reinforce concrete buildings with bars of steel so that if cracks would exist, they would only be small fractures. However, these fractures are not as small as such to heal adequately. Deicing salts and water that penetrate the concrete to the steel results in corrosion of the steel which makes the building weaker. The self- healing concrete will not face corrosion as it does not require reinforcing with steel for the concrete to maintain the width of the fractures intact (Zongjin, 2011).

• PVA

 Polyvinyl Alcohol fibres.

• Permeability

 The rate at which fluid flows through a porous medium, in this case, concrete.

• Flexural strength  

This is the material’s bendability strength in its effort to withstanding the imposed pressure on it.

• Self-curing

It is the feature of bendable concrete of refilling the fractures which exist as a result of reactions that happen. The concrete’s point of failure is extended.

• Workability

Importance of the Project

This is the relativity ease of concrete being allowed to be transported, compacted, mixed and moulded.

• Durability

This is the feature of the concrete to withstanding damage, wear and pressure.

The engineered cementitious composite is comprised of fly ash, optimal contents of fibres, sand, cement, and small contents of admixtures. In the mixture, coarse aggregates are eventually not applied due to the ECC property of forming small cracks with deflections that are large. Coarse aggregates increase the width of the fractures this being the opposite of the property of the ECC concrete (Mohammad, King, & Safat, 2017).

CEMENT

Portland ordinary cement is the cement used. Cement is defined as the many organic compounds applied for fastening or adhering material. However, these are categorized as adhesives and the word cement on its own stand for material for construction. The blast furnace is also important that they are applied in some cement where it is referred to as Portland slag cement.  The cement’s colour is highly influenced by the existence of iron oxide and in the cases that there were no impurities the cement would be white in colour. The cement normally used is the ordinary Portland cement grade 53 (Edward, 2008).

SAND

Sand is applied in concrete and mortar making and also in sandblasting and polishing. Sands with some amounts of clay are applied in foundries for making moulds. The weight differs from 1,538 – 1,842kg/m3 depending on the grain’s size and composition. The passing of the fine aggregate through a sieve of 4.75mm with 2.68 special gravity is applied most of the times (Vera & Zdenka, 2017).

Fly Ash

 The type of fly ash applied is known as pozzocrete dirk 60 and specification are given by the supplier in the table below. In the construction of RCC, there has been a successful use of the fly ash in lowering generation of heat with no strength loss, increasing strength that is averagely above 180 days and producing other fines for compaction. Levels of replacement of a primary classed fly ash is in the range of 30% to 75% of cementitious material’s solid volume. In mixture proportioning, for minimum paste volumes, one major role of fly ash is to ash is to fill empty spaces that would have been instead filled with water or cement. The filling of the empty spaces by water would lead to concrete’s strength reduction (Joaquim, Liberato, & Enzo, 2017).

Table 1

Definition of Terms

  (Qin & Hao, 2017)

WATER

Water that is fit for consumption is considered generally fit for concrete making. Water should be free from impurities such as vegetables, alkalis, oils acids and other organic impurities. Soft water generates concrete that is weaker. Water plays two roles in the concrete mixture first, it chemically reacts with cement to produce cement paste in which unreactive aggregates suspended until the hardening of the cement paste. Second is that it acts as a lubricant or vehicle in the mix of cement and fine aggregates (Jun & Hao, 2018).

The polyvinyl Alcohol fibres have an important feature that is, reinforcement materials for cementitious composites. Other suitable features include; high elasticity modulus, high bonding strength with the concrete matrix, high tensile strength and durability. Polyvinyl Alcohol fibres have high elasticity modulus and a high strength of about 25pa -40pa than other normal organic fibres which are used on a wide range for cement reinforcement. Enlargement fibre is almost 6% to 10%. The fibre tensile strength ranges from 880Mpa -1600Mpa.  One important feature of PVA fibre is the high bonding strength with cement matrix (Baoguo, Liqing, & Jinping, 2017).

SUPERPLASTICIZER

The type of plasticizer used is called Melamine Formaldehyde Sulphonate. It is used in order to regulate rheological features of fresh concrete. Basically, they are additives to the concrete and used to uniformly spread the cement in the mixture. This is attained by the action of deflocculating on cement agglomerates whereby water trapped in the cement grains groups is released ready for workability. Superplasticizers typically lead to slump increase from 5cm – 18 or 20cm with no water being added. Although when applied to attain in reducing the amount of water used for mixing, water can be reduced to about 15 to 20% therefore, the ratio of water or cement is averagely reduced by the same amount. This leads to strength increase and increases in other features such as tightness of water and density (Milan & Zdenek, 2012).

Mixture proportion initially was 1:8004:1.996, the dosage of superplasticizer was 1040.47 ml/bag, PVA fibres 1% and the ratio of water to cementitious components was 0.274. Therefore, for the 2^nd trial the proportion of the mixture changes were made to be 1:0.9:1.1, increasing the water ratio and of the cementitious components to 0.3048, by retaining the similar dosage of superplasticizer and the amount of PVA fibre increased to 1.2%. In the 3^rd trial, the proportion of the mixture was 1:1:1 hence, lowering the superplasticizer dosage to 600ml bag, the percentage of PVA fibre was 1.2% and the ratio of cementitious material to water was 0.33. In the 4^th trial, the proportion of the mixture was 1:0.9:1.1, a dose of superplasticizer was a 600ml bag, the percentage of PVA was 1.2% and the ratio of cementitious materials to water was 0.3118. So as to attain workability a number of trials were conducted and as for the 4^th proportion mix, the dosage of superplasticizer was lowered in order to achieve workability. For every trial mixture, three cubes were introduced then cured by the use of the accelerated tank for curing then later tested to achieve the desired requirement for strength. After cubes for every trial were tested, the mixture of the trial number three was seen as the most appropriate and therefore the final proportion mixture (Mehdi, 2017).

Ingredients of Bendable Concrete

Mixing influences the performance of the ECC it, therefore, implies that a suitable and better mixing practice results in quality and improved performance of the ECC concrete. The flexural test was done on the slab at the time of mixing and after putting off the fresh concrete, homogeneity of the mixture materials also has an influence on the quality of the concrete.  It is, therefore, important to properly mix the concrete for the concrete to achieve the desired strength and for the cement to bond well with the PVA fibres. Upon the mixture design of concrete being finalized mixing is therefore conducted by the use of a hand mixer. The hand mixing procedure is as follows: place sand, cement, fly ash a percentage of 50%, superplasticizer and amount of water of 50%. Slowly add the entire amount of fly ash, superplasticizer and water. After the homogenous mix is fed, slowly add the PVA fibres and mix all the contents until all fibres are mixed homogeneously in the matrix (Maekawa, Okamura, & Pimanmas, 2015).

Before concrete is placed, it is important to oil the concrete mould for easy stripping of the concrete specimens. The oil applied is a mix of kerosene and diesel. Reasonable care is observed at the time of oiling the moulds to ensure that there are no stains of the concrete on the moulds. After the ECC’s workability test has been conducted the fresh concrete must be put in concrete moulds for the test of hardened properties. At the time of putting off the fresh concrete into the moulds, tamping is conducted by use of a tamping rod so as to minimize honeycombing (Nicholas, 2017). Vibrations are conducted by using a table vibrator after the placement of the concrete into moulds. Concrete vibration enables complete compaction of the fresh concrete so as to remove any entrained air spaces present in the concrete. If the concrete is not properly compacted, the desired strength may not be attained. After the operation of vibration, concrete levelling is conducted on the concrete’s surface. Levelling is the first operation conducted after placement and compaction of concrete. After the fresh concrete has been levelled the concrete in the moulds is by the overnight left to enable the fresh concrete to set (Alexander, 2017).

After the fresh concrete is left in the moulds by overnight to set, the specimens of the concrete in the moulds stripped. Concrete specimen identification was conducted and after twenty-four hours, all specimens of the concrete were put into the tank for curing at a regulated temperature of 250C and further for twenty-eight days for the test of hardened properties of concrete (PANKAJ & MANISH, 2011). The process of curing is very important in protecting the specimens of the concrete from moisture loss as it attains the strength that is required. If curing is not done it will result in the attainment of improper strength. After curing for twenty-eight days, the specimens of the concrete are removed from the tank used for curing so as a test for hardened properties of engineered cementitious composites concrete is conducted (Jaroslava, Jan, Pavel, & Karel, 2017).

property	Normal concrete	ECC
durability	Has a less durable structure	Has a more durable and flexible concrete structure
Earthquake resistance	These structures are susceptible to earthquakes they may collapse or crack during earthquakes.	Its concrete is flexible hence resists cracking or failure during earthquake motion.
Self-healing property	This concrete has a much-reduced level of self-healing property since the free cement concrete is low.	This concrete has a higher level of self-healing property since the micro-cracks are self-healed by water carbon dioxide reaction.
Repair and maintenance	The cost of repairing and maintaining is high in these concrete structures due to developing defects and cracks.	The cost of repairing and maintaining is less in these concrete structures as it fails reduces crack development.

 

Conclusion

Although the ordinary Portland cement is expensive and intensive energy, it is the ingredient used most widely required in the concrete mixture production. It is unfortunate that cement production involves releasing carbon dioxide in amounts that are large into the atmosphere which contributes greatly to global warming and greenhouse effects. However, it cannot be avoided nor can another material be used instead of or be replaced partly. Numerous investigations conducted by researchers in relation to the design of engineered cementitious composites and its usage in reality in the field has proven to be the best sustainable and an alternative material for concrete in the nearby future. The process of curing is very important as it prevents the specimen of the concrete from losing moisture thus helping it gain the required strength and also vibration process enhances full compaction of the fresh concrete hence removing void spaces in the concrete.

References

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Edward, G. (2008). Concrete Construction Engineering Handbook. Bendigo: CRC Press.

Jaroslava, K., Jan, Z., Pavel, R., & Karel, K. (2017). Concrete and Cement Composites Used for Radioactive Waste Deposition. Sands: Elsevier Limited.

Joaquim, A., Liberato, F., & Enzo, M. (2017). Recent Advances on Green Concrete for Structural Purposes: The contribution of the EU-FP7 Project EnCoRe. Bunbury: Springer.

Jun, W., & Hao, W. (2018). Multi-layer Pavement System under Blast Load. Bunbury: Springer Singapore.

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Mehdi, S. (2017). Seismic Evaluation of Bridge Columns with Energy Dissipating Mechanisms. Coffs Harbour: Transportation Research Board.

Milan, J., & Zdenek, P. (2012). Inelastic Analysis of Structures. Coffs Harbour: John Wiley & Sons.

Mohammad, M., King, L., & Safat, A. (2017). 08.50: A Study on the Bond Stress?slip Behavior Between Engineered Cementitious Composites and Structural Steel Sections. Bendigo: Wilhelm Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Company.

Nicholas, F. (2017). ICCS20 – 20th International Conference on Composite Structures. Tamworth: Società Editrice Esculapio.

PANKAJ, A., & MANISH, S. (2011). EARTHQUAKE RESISTANT DESIGN OF STRUCTURES. Tamworth: PHI Learning Pvt. Ltd.

Qin, F., & Hao, W. (2017). Concrete Structures Under Projectile Impact. Bunbury: Springer.

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