Wednesday, July 6th, 2022
CECR

Studies On Mechanical And Durability Properties Of Lathe Waste In Concrete

 A Sofi
 Associate Professor
 Department of Structural and Geotechnical   Engineering, School of Civil Engineering
 VIT Vellore
 Sanu Peter Thobiyas
 M. Tech Structural Engineering
 VIT Vellore

With time, it has been proven that the use of fibre reinforced concrete will fortify reinforced concrete structures’ structural performance. Fibre-reinforced concrete improves the mechanical and structural properties of concrete. Various fibres and natural, synthetic, glass, steel, and others are used to enhance mechanical property concrete. The manufacture of steel items is increasing, and the accumulation of waste steel fibre is negatively affecting the environment. Therefore, effective and economical methods to convert this waste material to a building material is necessary. Different experimental and mathematical studies were conducted to study the feasibility of the use of waste in concrete.

In the modern construction world, the efficiency and the quality of the concrete cannot be compromised. Thus, the concrete should meet the structure’s demands. The concrete’s main problem is its weak tensile and ductile property. Effective use of fibre can overcome this issue and form a modified concrete. As mentioned earlier, there are many kinds of fibres; mild steel fibre from lathe waste can also be included in it. The addition of fibre can modify the crack propagation and failure crack under loading.

Mainly failure in fibre reinforced concrete will occur due to failure in bonding between the fibre and the concrete. The existing studies show that the changes in concrete properties are directly linked to the shape, length, aspect ratio, amount of addition, etc.[1–5]. For the cases of mechanical properties, remarkable improvement in the tension, and flexural behaviour have been observed. Under the loading, after the formation of the crack, the fibre starts its function.

The objective of the fibre is to resist the propagation of the crack and prolong the failure load. It was observed that fibre-reinforced beam, even after the formation of the crack, the beam won’t fail, and the load will reach the peak value depending on fibre content[8,12,13]. Beyond peak value, applied load decreased due to the failure of fibre and stress transformation from bottom to top of the section. The fibre reinforcement shows an improvement in stress-strain behaviour also [24-26]. Normally, the ultimate strain of reinforced concrete is 0.0035. But under the case of FRC, the strain value is increased to 0.012 and 0.018 at 1.6% and 3% of the fibre. This is an improvement in strain corresponding to peak stress with an increase in fibre content.

It is evident that the steel fibre uplifts the concrete’s structural integrity, and the usage of the steel fibre in concrete can be implemented in the construction. Due to the increase in steel usage, the accumulation of steel scrap increased and caused a lot of environmental issues. Various researches have been conducted to study the use of waste fibre as an alternative to the manufactured steel fibre. Some studies support the use of the lathe scraps, and from there, improvements in the mechanical properties were observed [19 – 21]. The effective usage of the lathe scraps paves the way to the production of economic and modified concrete.

The current research looks into the change in mild steel fibre reinforced concrete’s mechanical property and compares it with conventional concrete. Mild steel fibres from lathe waste are used as a substitute for the manufactured steel fibre. Lathe wastes are added at various percentages (0.0%, 0.5%, 1.0%, 1.5%, and 2.0%) by weight of concrete. For the experimental studies, concrete cubes, cylinders and beams are cast. Cubes and cylinders are employed to determine the compressive strength, split tensile strength, stress-strain behaviour, and elasticity modulus. Flexural strength is studied by testing the concrete beam.

Material Characteristics
The study’s aim is to understand the change in the properties of lathe waste added fibre in the concrete. Lathe waste fibre of the same material collected from a mechanical workshop was used for testing. Mild steel fibres with spiral cross-section were selected as the fibres. For the analysis, the fibre volume was kept as a variant, and the length was kept constant. The changes in mechanical and durable properties of concrete due to the change in the fibre volume were studied. The materials used for the casting works are:

  • Cement: Ordinary Portland cement of grade 53 was used for the study. The initial and final setting time obtained was 30 minutes and 240 minutes. Cement has a specific gravity of 3.15 and of consistency of 33% was used for testing.
  • Fine Aggregate: Dry sand, which passes through a 2.36mm sieve and retains 150 microns, was used. Specify gravity obtained was 2.67.
  • Coarse Aggregate: Locally available coarse aggregate of size between 10-20mm was adopted. The specific gravity of coarse aggregate was 2.76.
  • Lathe Waste: Mild steel fibre from the lathe waste was used as the fibre material. Spiral shaped fibres were selected for the casting. The fibre length was kept as a constant parameter and the volume of fibre addition as a variant. The length and width of the fibre will affect the concrete property, so careful selection of material should be done. The length of the fibre was maintained at 80mm, as shown in Fig 1.
  • Water: Normal tap water was used for casting and curing. The water was free from salt content.

Fig.1: Mild Steel Fibre from Lathe Waste

Mix Design
A concrete mix design was done for M25 grade concrete and the Mix proportion is listed below in Table 1. The mix design was designed based on IS 10262, with a water-cement ratio of 0.5. Spiral shaped fibres are added at various percentages by weight of the concrete. Cubes, cylinders and beams of standard size are cast for the various percentages and kept curing for 7, 14 and 28 days.

Experimental Detail
The project’s main aim was to understand the change in the properties of lathe waste fibre reinforced concrete. By considering the fibre volume as a variant, parameter casting works for all the percentages were done. Concrete specimens of cubes, cylinders and beams were cast based on Indian standards.

Compression Test: Cubical specimen of size 100x100x100mm was cast for all the percentages, and they were tested in the universal testing machine at a loading rate of 140 kg/cm2. Concrete mixes for all percentage of fibre were prepared, and it was compacted inside the mould. The samples were demoulded after 24 hours and kept in the curing tank for 7, 14 and 28 days. The test specimen was stored in a place free from vibration and cured in fresh water, the water was renewed every 7th day, and the water was at a temperature of 27º ± 2º C. On the day of testing, the samples were taken out of the tank, and the surface moisture was wiped off before testing. The specimen was loaded in the universal testing machine, and the compressive strength was found using the formula

Split Tensile Strength: Standard size cylinders of diameter 100mm and height 150mm were cast for all percentage of fibre and kept under curing for 7, 14 and 28 days. On the day of testing, the samples were taken out of the tank, and the surface moisture was wiped off. The cylindrical specimens were loaded in the universal testing machine at 140kg/cm2 per minute. The failure load was determined and the specimen’s split tensile strength was determined by using the formula.

Flexural Strength Test: Prismatic samples of size 10x10x50cm were cast for all the mixes and tested using a digital flexural testing machine with a loading rate of 180 kg/cm2/min after a curing period of 7,14 and 28 days. A similar method of casting and curing was adopted as done for compression testing. After the required curing, the samples were loaded in the digital flexural testing machine, and the flexure strength of the sample was displayed in the testing machine. The formula used for calculating the strength is

Where P is the load at failure and l is the length.

Modulus Of Elasticity
Cylindrical specimens of size 150mm diameter and 300mm height were cast to determine the modulus of elasticity, and the specimens were kept curing for 28 days. On the day of testing, the samples were taken out from the curing tank, and the surface moisture was wiped off. The strain measuring cage was attached to the cylindrical specimen after leaving a space of 50mm from bottom and 50mm from the top of the specimen. The specimen was loaded into the universal testing machine. From the test results, the load-deflection pattern and stress-strain behaviour of concrete can be studied. Load up to 200kN was considered for the study. A deflection dial gauge was attached to study the load-deflection pattern. Based on the load-deflection pattern stress-strain, values were determined. From the stress-strain curve, the change in the modulus of elasticity with the fibre content was determined by the formula

Water Absorption: For checking the concrete’s water absorption, concrete cubes of size 100x100x100mm were cast and cured for 28 days. After 28 days of curing the samples, air-dried and then placed inside the oven at 110°C for 24 hours. After 24 hours, the samples were weighed and recorded as dry weight. The samples were then kept submerged underwater for 24 hours, and they were weighed again and recorded as wet weight. Water absorption was expressed in percentage:

Sorptivity Test: The Sorptivity test was done to study the rate of water absorption of the concrete. For that concrete cylinder of diameter 100mm and height 150mm were cast, and it was cured for 28 days. After 28 days of curing, the cylinder was cut into a smaller size of the height of 50mm. The inner part of the cylinder was selected for the study, and the samples were kept inside the oven at 110°C for 24 hours. Using insulation tape, the top and sides of the cylinder were covered, and the bottom part was left open. After the sample preparation, the sample was immersed in water with 5mm height from the bottom. Weights of the samples were measured at 30, 45 and 60 minutes. This test measured the rate of water absorption through the capillary rise.

Where,
W1 – Dry weight of the sample in kg
W2 – Wet weight of the sample in kg
A – Surface area of the cylinder which is exposed to water
δ – Density of water in kg/m³
T – Square root of time during the measurement in minutes

Non- Destructive Test: Non -Destructive Test (NDT) consists of a wide range of testing to assess the quality of the concrete without causing any damage to the specimen. In this research, an ultra-sonic pulse velocity test and rebound hammer test was conducted.

Ultra-Sonic Pulse Velocity Method: The basic principle of ultra-sonic pulse velocity is to determine the time taken by an electronic wave to passing through the concrete specimen. Based on the received waves, the quality of the concrete was analysed. Electroacoustic transducers produce an ultrasonic pulse, and by transmitting this pulse through the concrete specimen, the quality of the concrete was studied. By a receiving transducer, the fastest waves was detected, and their velocity was measured. Pulse velocity only depends on the elastic property of the concrete, so it is the better method to understand the quality of the material. In this test, after selecting the line of propagation of the wave, the transducer which propagates the wave was placed in one end and the receiving transducer at the other end. As the wave passes the velocity of the wave was displayed in the UPV machine. Based on this value, the quality was determined. For the testing concert cubes of size 100x100x100mm of age 28 days was used.

Rebound Hammer Test: Hardness of the concrete was measured by the rebound hammer test. Based on the rebound hammer number obtained from the test the hardness of the concrete was determined. The test was conducted by the procedure based on IS 13311 (Part 2): 1992. Rebound hammer consists of a tubular housing having spring controlled mass that slides over the plunger within it. During the testing, the plunger was pressed against the test specimen and the spring controlled mass rebounds. The range of the rebound varies with the surface of the specimen. The rebound value number was then compared with the standard values. For testing, concrete cubes of size 100x100x100 were used and rebound hammer number of a surface were taken three times in different points and the average value was compared with the standard values.

Results And Discussion
Workability
The slump height of all the percentage concrete was calculated, and from the test results, it was observed that slump height was decreasing with an increasing percentage of fibre. The slump value is shown in Table 2. The addition of the fibre leads to an increase in the confining pressure between the fibre and the concrete mix, which causes a decrease in the value. The fibre will form a bond between the materials and arrest the falling of the concrete. Some other researches suggest the use of superplasticizers to overcome the decrease in workability. But for this study, no plasticizers were used since there was only a slight decrease in the value of slump height, and the resultant mix was sufficient.

Compression Test
From the compressive test results, it was observed that the fibre addition in the concrete would support the compressive strength properties of concrete. The fibre added in the concrete has helped to prolong the failure of concrete, and as a result, the value obtained for fibre reinforced concrete under compression was greater than conventional concrete. It was observed that the value of compressive strength was increasing with an increase in fibre content, and the maximum value was obtained at 2% of fibre addition. It was also observed that the fibre added concrete shows a different crack pattern in the concrete cube. The values of the compressive strength of the cube are shown in Table 3.

From Table 3, it was observed that there was only a slight increase in strength on the 7th day compressive test, and after that, during the 14th day and 28th day, there was a remarkable improvement in the strength. The result shows a gradual increase in the strength of the 14th and 28th days.

Fig. 2 shows the crack pattern in the cube after compression. The cube was not completely collapsed even after the failure, and the fibre added in concrete shows good resistance in the propagation of the crack. The failure pattern shows a small amount of collapse compared to conventional concrete.

Fig. 2: Cube after Compressive Test

Split Tensile Strength
Fibre-reinforced concrete is mainly adopted for improving the ductile behaviour of the concrete. From the test results, it was observed that the ductile properties of the concrete had been improved with an increase in fibre content [1-4]. The added fibre also takes part in load distribution in the specimen. Due to its ductile behaviour, the fibre can withstand load before its failure, and from the experimental results, the quantity of the fibre increases the load-carrying capacity of the concrete. Maximum tensile strength was obtained at 2% of fibre addition. Test results for all percentages of fibre addition at 7, 14 and 28 days are shown in Table 4.

Based on all the literature review and experimental data, the results show good agreement with the crack pattern and increased strength. Crack width of the cylinder was observed to be decreasing with the increase in the fibre content.

Fig. 3 shows the cylinder at failure. Only a slight crack is formed on the cylinder and it is also observed that the width of the crack decrease with increase in fibre content. For the case of conventional concrete, the cylindrical specimen was split into two pieces and for lathe waste reinforced concrete, the failure load of the cylinder was prolonged by the fibre.

Fig. 3: Cylinder under Split Tensile Strength

Modulus Of Elasticity
Based on the stress – strain values, the value of the modulus of the elasticity was determined. From the test data, it was observed that the value of the modulus of the elasticity was increasing with an increase in the fibre content. As per Indian code IS 456: 2000, Modulus of elasticity (Ec) is calculated by the 5000, where fck is 28th day compressive strength of the concrete. Therefore, as per IS code, the value for modulus of elasticity for conventional concrete should be 25000 kN/mm2. From the experiment, the value obtained for conventional concrete was 25,464 kN/mm2, which shows the adaptability of the test results. The values of modulus of the elasticity are exhibited in Table 5.

From Fig. 4, it is evident that the strain value of the concrete specimen was decreasing with the increase in the fibre content. From various literature reviews and the experiment conducted, we can say that the fibre resists the deformation of the concrete under loading and prolong the stress value. Therefore, the concrete can yield heavy loading with low deformation, and due to a decrease in the strain value, the value of modulus of elasticity will increase.

Fig. 4: Stress-Strain Behaviour

Flexural Strength
Fibre-reinforced concrete was mainly adopted to improve the ductile and bending behaviour of the concrete. From the test results, it was observed that the addition of mild steel fibre in concrete shows a progressive behaviour in the bending behaviour of concrete. Improvement in the flexural strength of the concrete with an increase in the amount of mild steel fibre was observed. Mild steel fibre added in concrete will take part in load distribution in the concrete beam
and the fibre will support yielding under loading. During testing, all the concrete beam has undergone brittle, but for fibre reinforced concrete, the failure load was increasing with an increasing percentage of mild steel fibre. The value of the flexural test of fibre reinforced concrete is shown in Table 6 below.

From the results, it is evident that an increase in the amount of steel fibre has a positive impact on flexural behaviour. The change in strength is observed from the 7th day onwards.

Water Absorption
The water absorption test was conducted under the study of the durability of concrete. The amount of water undergone absorption depends on the porosity of the concrete specimen. Thereby, an idea regarding the porosity in the concrete can be made. The addition of mild steel fibre helps to reduce the porosity in concrete by filling the voids and by providing strong bonding in concrete. From the test results, it was observed that the amount of water absorption was reduced with the increase in the amount of fibre. Table 7 shows the results, which reflect the decrease in the percentage of water absorption.

Sorptivity Test
It was observed that the rate of water absorption was decreased with an increase in fibre content. The value shows good agreement with the water absorption value because the value of water absorption was also decreasing with an increase in fibre content. The results from the sorptivity test are shown in Table 8.

It was observed that the rate of water absorption was increasing with time, but it was decreasing with increase in fibre content.
The maximum rate of absorption was obtained for conventional concrete (4.18X104 mm/min0.5 at 60 Min), and the minimum value was obtained for concrete with 2% fibre (2.93X104 mm/min0.5 at 60 Min).

Ultra-Sonic Pulse Velocity (UPV)
The UPV test was conducted, and the average values are recorded in Table 9. As per Indian standards, the values greater than 4 km/sec come under excellent quality concrete.

Both lathe waste reinforced concrete and conventional concrete come under good quality concrete, and the value of UPV was observed to be increasing with an increase in fibre content

Rebound Hammer Test
As per Indian standards, for very good and hard layer concrete, the value of the rebound hammer number should be greater than 40. Here, all the specimen have a value greater than 40, so all specimen comes are of good quality. The average value of all the specimens is shown in Table 10.

Conclusion
From the experimental study, the results indicate that:

From the slump test, it was observed that the addition the mild steel fibre increases the confining behaviour between the fibre and concrete materials, leading to a decrease in the value of slump height. For 2% fibre addition, the value of slump height was dropped to 54mm from 64mm at 0% addition.

The value of compressive strength was observed to be increasing with the increase in fibre content. For 2% fibre addition, the value of compressive strength obtained was 42 MPa, whereas, for conventional concrete, the compressive strength was 33.1MPa.

Remarkable improvement in the split tensile strength was observed in the fibre reinforced concrete. Due to the internal bonding provided by the fibre, the width of the failure crack was decreasing with an increase in the fibre content. The maximum value was obtained at 2% of fibre addition was 3.53 MPa.

Flexural strength was also improved with an increase in fibre content. The addition of the fibre resists the propagation of the crack and prolongs the failure load of the beam. The maximum value was obtained at 2% was 5.55 MPa.

The effect on modulus of elasticity of concrete was also observed to be increasing with the increase in the fibre content. From the test, it was observed that the fibre reinforced concrete could resist more stress with less strain value. At 2% fibre addition, the value obtained for modulus of elasticity was 42,441 MPa, and for convention concrete, the value was 25,464 MPa.

Due to the internal bonding provided by the fibre, the pore space inside the concrete was reduced. Therefore, from the test results, the value of water absorption was decreasing with the increase in fibre content. The rate of absorption measured from the sorptivity test shows a good correlation with this.

The sorptivity test results show that the rate of absorption was decreasing with the increase in fibre content.

From the NDT test, it was observed that the casted specimen was of good quality.

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