Engineered Cementitious Concrete: A Comparative Study On Properties And Usage

Properties of ECC

Discuss about the International Scientific Conference Energy Management.

Engineered Cementitious Concrete is a construction material that has an improved flexibility to a considerable level to be used in building construction. The strain capacity of an ECC is greater compared to normal concrete. ECC, therefore, becomes more ductile rather than being brittle like its counterpart. The ingredients in a bendable concrete are same as the normal concrete, however, it lacks the crushed stones or the coarse aggregate and has a reinforcement from polymer fibres. The ECC which can also be called the bendable concrete is categorized as an ultra-ductile fibre composite that is reinforced with considerable flexibility. The strain capacity of ECC is a bit great in that it falls in between 3 – 5 % more compared to the normal concrete’s 0.01%. The polymer fibres used in ECC is the PVA fibre, an abbreviation of Polyvinyl Alcohol fibre. This fibre has the best polymer properties suitable for building concrete. The PVA used in this type of concrete helps in increasing the strength of the concrete in that it acts as a reinforcement. PVA has an extensive hardened strain behaviour as a composite. Also, the polymer has more advantages such as reduction of the funds and resources in structure rehabilitation. In the initial cost of construction, the use of PVA fibres leads to a doubled cost when compared to the initial cost of the construction of conventional concrete. However, considering that the concrete developed using PVA fibre lasts longer than conventional concrete, concrete developed using PVA fibre would become less costly in the long run. The unbendable nature of conventional concrete due to the 0.1 % strain capacity makes these concrete rigid and brittle. Most buildings would fail due to the inexistence of bendability when exposed to strain. Such feature would result due to the very low ductility, tensile strength as well as little cracking resistance. Concrete usually have internal micro-cracks coming from the drying shrinkage. Propagation of such internal micro-cracks leads to reduced tensile strength. In the long run, the concrete becomes brittle and fails. This proposal presents a comparative study on ECC and conventional concrete regarding the concrete properties that include; young modulus and workability together with hardened properties of concrete such as compressive strength, flexural strength and split strength taking note that the latest research scenarios have been concentrating of the properties of PVA.

Comparison of ECC and Conventional Concrete

This proposal discusses the investigative research that would be performed to fulfil the following aims;

• Finding ted flection of beams.
• Checking the features of ECC when put under compression, flexural test, and split tensile test.

The unbendable nature of conventional concrete due to its % strain capacity makes this type of concrete very rigid and brittle. The absence of the ability to bend is one of the main factors that has led to the failure of structures that utilize this design when under strain. Such failure occurrence has led to the development of better-improved materials of construction. One of the improved materials used in construction is the ECC. This material exhibits the capability of improved flexibility. When put under strain, the ECC has a % more chance of withstanding the forces making it behave like a ductile material. The ingredients used in bendable concrete include similar ingredients in the conventional concrete only that it lacks coarse aggregates and has an addition of PVA fibre. The included PVA fibre is soluble in water. Also, this fibre has a high flexibility and tensile strength. Before being included in the ECC to be developed, this ingredient is slick-coated. In spite of the coating, there will still be some friction since it would not completely eliminate friction. Friction has to be reduced to maximum utilise the PVA properties. Properties of the PVA include; high flexibility and tensile strength making it better suited to ECC construction. PVA is adhesive at its basic nature, therefore, has been used in making glue. ECC structures are supposed to be flexible and strong to increase its applicability in numerous structures. Hence the development of fibre reinforced concrete (Recep, Hediye and Yusuf 2017).

This development is the latest invention in that there are more studies that are still being conducted on it. The materials that have been used in the ECC development can be listed as follows; fibre, water, and, cement, chemical additives. Compared to the fibre reinforced concrete, the developed ECC does not include the substantial fibre volume used. The procedure of mixing ECC has similarity to the one used in conventional concrete. The economization of ECC come in in the reduced fibre usage but with a maintained desired features in ductility and strength. The difference between fibre reinforced concrete also exists in the properties in that once ECC cracks, it hardens whereas fibre reinforced concrete fails to do so. The development of a crack in fibre reinforced concrete continues with the fibre rapture leading to a decrease in the capability to bear stress. The high amount of cement in ECC as there lacked coarse aggregate in the proportion of the mixture compared to reinforced concrete (Qin and Hao 2017).

Potential Applications of ECC

(Alexander 2017) performed an experiment that focused on the commercially obtained synthetic fibres and steel. Relationships in the deflection of flexural stress can be used in determining the flexural toughness, flexural strength, equal flexural strength ratio and equal flexural strength. concrete flexural toughness was discovered to rise considerably with the addition of synthetic fibres and steel. On the other hand, similar addition of various fibres missed to end in the specimens having identical flexural toughness.

(Baoguo, Liqing and Jinping 2017) perfume a research that experimented with the investigation of the flexural behaviour of the reinforced concrete self-compacting with hooked and straight end steel fibres on the levels of, and % with a comparison to Normally Vibrated Concrete. The test coming from the laboratory determined the recommendation of the RILEM TC - TDF. SCC flexural behaviour was seen to be compared with the NCV in that the fibre volume ratio increase led to an increased pre and post peak SCC parameters. However, the steel fibre types greatly determined the dependency. SCC attained highest crack mouth displacement for least deflection compared to NVC.

(Biswajeet 2018) developed an experiment that studied the potential applications of ECC with features of least drying shrinkage regarding the concrete pavement to eliminate the joints that are commonly used to considered shrinkage deformation and temperature. The study realized the composite slab with the plain concrete and the reduced shrinkage property with an interfaced steel bar was possible. The tensile cracks can be localized without cracking the nearby slabs of concrete.

(Edward 2008) developed an experiment that focused its study on the investigation of self-healing ECC feature. The study experimented ion the curing conditions as well as the pre-cracking time. Test on four-point bending were used in ECC beam pre-cracking at various ages. Also, the curing conditions were not identical in every curing condition, the capacity of deflection after self-healing could be recovered. They could further exceed the virgin samples with averagely all the pre-cracking ages. To add on this, there was a promising nanoclay utilization in the distribution of internal reservoir of water that promoted the self-healing feature in ECC without depending on external supply of water.

Due to the ECC better flexibility compared to the traditional concrete, the concrete behaves similarly to metal than glass. The ceramic nature of conventional concrete has proven to be very rigid and brittle. Hence, there could be a possibility of catastrophic failure in exposure to routine overuse or earthquake. The concrete proposed to be having specially coated reinforced fibres that keep the concrete intact (Seyhan, John and Abid 2018). Therefore, ECC that will be developed will be safe and intact with the usable % tensile strain. The fractures of the traditional concrete fail to withstand load s up to % strain capacity builders have been reinforcing concrete structures with the use of steel bars to restrain the cracks to smaller dimensions. However, these cracks would not be very small to heal. The existence of salts and water penetrate to the steel leading to corrosion that makes this structure weaker. The development of a self-healing concrete would eliminate the need for steel reinforcement by keeping the crack restrained and limiting the structure’s corrosion (Jaroslava, et al. 2017)

Experimental Studies on ECC

The proposed methodology for the development of this concrete’s specifications and materials require performing tests as per the standards that are relevant to the technique. The standard would determine the ECC testing and make. Also, conventional concrete would be used as a comparison or the control experiment. The used conventional concrete would be having identical proportions (Joaquim, Liberato and Enzo 2017). Additionally, the cement would be replaced in a proportion of 30% using fly ash in ECC. Taking note of the reviewed literature, there are specified materials to be used in the experiment. This literature also gives a direction on the mix proportions, testing period and as well as the tests to be conducted and the testing period. This paper proposes the use of aggregate, fly ash, PVA fibres, plasticizers an river sand as the materials. Also, water would be used. Specifically, about 0.5 – 2% of PVA fibre, 10 mm aggregate size and conplast30 plasticizer will be used (Vera and Zdenka 2017).

There will be 4 different fibre percentages to be used in the evaluation of the optimum ranging from feasible used of PVA in concrete with regards to strength. The developed conventional concrete having similar fly ash content would then be compared to the tested nixes. The comparison would be on the concrete properties testing. Test mixes would have 2, 1, 0.5, and 1.5% PVA volume fraction in ECC developed. Six cubes of 150 mm dimensions are to be cast along with six cylinders of 150 mm diameter and 300mm height. Additionally, prisms will be cast (Jun and Hao 2018).

This is a normal type of cement that is utilized across the world. In the development of mortar and concrete, this component is the key ingredient. It is composed of ground calcareous and argillaceous materials. OPC has some physical properties that include (Maekawa, Okamura and Pimanmas 2015);

• Consistency which is the ability of the paste developed from cement to flow the consistency of cement paste flow can be found out using Vicat instrument by 10+1 mm plunger penetration along with the water-cement ratio correspondence.
• Setting time that is the elapsed time from instant water addition to the paste behaviour resembling plastic material leading to penetration resistance. The final setting time means the required time for the formed cement paste to reach defined hardness state that can withstand some load. This is tested with the use of Vicat instrument(PANKAJ and MANISH 2011).
• Soundness that is the toughened cement paste ability to maintain its shape once it has set. The samples of cement have excess amounts of free magnesia and lime that lead to changes in volume. Cement soundness is measured using Le chartliars
• Specific gravity which is the density of particles being measured without taking note of the air pores in OPC that is ranged at 3.1-3.25. The cement density is obtained with the use of density bottle instrument and in this case, the experiment recommends using kerosene (Viktor, Volker and Petr 2017).

These fibres were produced but 20 years ago. An addition of these fibres to mortar or concrete led to the development of chemical and molecular bond with the cement in the process of curing and hydration. Generally, the used fibre in ECC has remarkable features in that the fibre would strong bond with the cement matrix. Ca(OH)2 layer is known as the artificial zone of transition that would form around the PVA making a complex cluster with the cement matrix hydroxide. OH- and the Ca+ ions are different and are attracted by the polymer fibre in the cement slurry. A resultant product is the Ca(OH)2. This product would then play an important function in strong bonding between the matrix and the fibre (Mehdi 2017).

Methodology

Proper sand from the banks of rivers is categorized by their lack of organic matter and earthy matter. Their articles are almost angular shaped less than 250mcron and can be retained in a 150 microsieve. The obtained sample can then be washed using water to remove the earthy or any other organic matter before being dried for a period of forty-eight sunlight hours (Nicholas 2017).

The rheological properties of this material improve the fresh concrete properties. It is an additive that helps in the uniform dispersion of the fresh concrete all around the mix. In the long run, the workability of the concrete can then be increased. Along with the slump properties. The slump properties increase from 5 – 30 cm with including water. This feature leads to a reduction of the required amount of water to about 15 – 30%. Furthermore, the vital properties of the concrete such as water tightness, density and workability can be improved without the need for compaction (Milan and Zdenek 2012).

Conclusion

Although the OPC cement is expensive, it is an important concrete ingredient. It is horrible to note the pollution due to its production in that carbon dioxide as well as other gas emissions would lead to greenhouse effects together with global warming (Mohammad, King and Safat 2017). This study tries to make use of partial replacement of cement quantity in concrete but as seen from previously reviewed literature, cement cannot be replaced fully. Various researchers on ECC have been noted to be important when appropriately used in replacing the cement. This proposal tries to include the reviewed researchers for the future development of concrete structures.

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