A Study of Engineered Cementitious Composites by Investigating its Compressive and Flexural Strength

Concrete has become an essential material as a part of construction eld. Its behavior is weak in tension and strong in compression. The demand for tensile strength is high for concrete because higher loading requires more than 10% of compressive strength which make a critical issue for engineers. Another major issue faced by normal concrete is lack in ductility and strain capacity. Engineered Cementitious Composites (ECC), also known as Bendable Concrete, has been designed to overcome the brittleness of concrete. It has tensile ductility of 3–5% and its self-controlled tight crack width is less than 100µm.It is a unique type of cement mixture with composition of low volume bers (~ 2%) so as to impart ductility, ability to repair and high tensile strength besides. It also has low maintenance and is environment friendly in nature.The ECC composition does not contain coarse aggregate because they develop larger crack width which tend to have a negative effect on ductile behavior of ECC. This paper demonstrated a detailed review on properties of ECC and experimentally identied the best ECC mix by analysing the compressive the exural strength at different ratios: 0.5%, 1%, 1.5%, 2% and 2.5% of PVA bre. Fifteen cubes (150mm x 150mm x 150mm) were casted for compressive strength test and fteen beams (500mm x 100mm x 100mm) were casted for exural strength and tested at the age of 28 days. Workability test have been conducted to access the fresh properties and consistency of the concrete.


Introduction
Concrete is one of the commonly used construction material throughout the world. In spite of its high compressive strength, it has low bending nature and the strain capacity of concrete is only up to 0.1 percent which is one of the main reasons for its rigidity and brittleness which leads to its failure under strain. Therefore, an improvement of a more e cient material is a speci c requirement of concrete structure which leads to the evolution of a material namely, Engineered Cementitious Composites (ECC), which is also called as Bendable concrete. It belongs to a family of ductile concrete. The tensile strain capacity of ECC can ranges from 3-5%, and thus the material can exhibit considerably enhanced exibility. This results in 300 to 500 times the tensile strain capacity as compared to normal concrete and ber reinforced concrete. It is a highly ductile composite with tight crack width control property, more

Methodology And Material Used
The material used in this work includes cement, M-sand, Fly ah, PVA ber, super plasticizer, and water.
Ordinary Portland Cement 53 grade is used in this study. The physical properties of cement are determined by conducting various laboratory tests. The M-sand used in the experiment is ne aggregates which passing through 150µm and retained in 90µm sieve. Class F y ash is used in the experiment. Fly ash is produced in thermal power stations. The water reducing agent used is Modi ed Polycarboxylate ether (PCE). The polycarboxylate based super plasticizers are made of HI-PCE HR50 which is Polycarboxylate ether. It has excellent water reduction by dispersing effect, high retardation and good ow-ability. In this work, PVA bre is used for making ECC at a different volume fraction of 0.5%, 1%, 1.5%, 2% and 2.5%. The dimensions of PVA bre used in the study are 6mm length and 39µm diameter.
And the density of bre is 1500 kg/m3. The PVA bre used in the experimental investigation is shown in Fig. 1. The quality of water used for this study was potable water.

Mix Proportioning
A regular ECC mix as found in Thermal behaviours of CFRP-ECC Hybrid under elevated temperatures [9] is used in this study. The mix proportion of ECC is shown in Table 1.

Mixing and Curing
A mixer with 30L capacity is used to prepare the ECC mixtures. Firstly, the solid ingredients like cement, sand and y ash are dry mixed for 6 minutes. Then water and HRWR admixture are mixed together and then added slowly into the dry mixture and mixed for next 4 minutes. The mixture was then checked and any clamping found in the mixture was broken to ensure a complete homogenous paste. The mixing is continued for another 3 minutes in order to attain a good uidity. The PVA bers were added slowly into the mortar mix and mixed until the bers were well dissipated. The fresh ECC was casted into cubes of 150×150×150mm that were moderately vibrated using a concrete vibrator. The beams of 500×100×100mm were also casted and compacted using a vibrator. Specimens were remoulded after 24 hours. After remoulding the specimen were cured and the values of compressive strength and exural strength are taken at 28days. Slump test is also carried out to determine the workability of ECC.

Slump Test
The slump test was conducted to check the consistency of ECC mix for .25 water/binder ratio. The slump value of ECC mix for different ratios of PVA bre is shown in Table 2.

Compression Test
Compressive strength is measured using compression testing machine and the maximum compressive load a material can bear before fracture was measured. In this study, cube of size 150 mm×150mm×150mm were used and it is shown in Fig. 2. The specimen is placed in the machine and load was applied. The maximum load at which specimen fails is noted. The maximum load divided by the original area of the specimen gives the compressive strength. Compressive strength of the cube was evaluated after 28 days and the obtained compressive strength value of ECC mix is shown in Table 3.
Compressive strength is calculated by the following formula: P = Maximum load in N applied to the specimen A = Area of a cross section in mm 2

Flexural Strength Test
Flexural strength is measured using a exural testing machine and it is shown in Fig. 3. Beam specimen of 500mm×100mm×100mm was used for the study. The bed of testing machine must be provided with two rollers, and all rollers shall be mounted in such a way that the load is applied axially without any torsional stresses or restraints. Flexural strength of the beam was evaluated after 28 days and the obtained values are shown in Table 4

Conclusion
This paper experimentally analysed the compressive and exural strength of ECC with 0.5%, 1%, 1.5%, 2% and 2.5% of PVA at 28 days of curing. Conclusion can be drawn as follows: 1. The compressive strength and exural strength of ECC was found to be high with ECC mix of 1.5% of PVA content and hence chosen to be the best ECC mix.
2. ECC have good workability and lies between the standard values of concrete. The value slump was increased without changing water/cement ratio because of superplasticizer ( High Reducing Water Reducing agent) 3. The ECC specimen beams produced greater exural strength than what would be normally produced by conventional concrete beams.
4. The ECC specimen cubes produced slightly lesser compressive strength than that which would have been produced by conventional concrete. 5. ECC technology focuses more on increasing the exural strength of the concrete and does not signi cantly increases the compressive strength of the concrete.
The contrivance of ECC emphasis civil engineers to provide a safer, lighter, more durable, economic and sustainable construction environment for society. ECC also have self-healing and self-consolidating properties. The results from life cycle assessment modelling con rmed that the use of ECC technology leads to a reduction of carbon and energy footprints of constructed facilities. The various investigations are done by several engineers for further development of Engineered Cementitious Composite (ECC) and its applications in the real eld proves to be one of the best alternative and sustainable concrete materials of the future decades.

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Availability of data and materials All the data generated or analyzed during this study are included in this published article  Compression testing on cube Flexural strength test