Expt 2. Flexural Strength Test of Concrete Beam
Summary
TLDRThis video demonstrates the flexural strength test of concrete according to IS 516 standards. The test assesses the concrete's ability to resist failure under bending, using a plain concrete beam subjected to two-point loading. It outlines the steps from preparing the concrete mix, curing the specimen, to testing the beam by applying a gradual load. The video explains the two types of beam failures, Type A and Type B, and how the modulus of rupture is calculated based on these failure types. The final flexural strength is expressed as the modulus of rupture.
Takeaways
- 🧪 The flexural strength test evaluates the bending strength of concrete indirectly.
- 🔨 It assesses the ability of an unreinforced concrete beam or slab to resist failure in bending.
- 📏 The test can be conducted using either a third-point load test or a two-point load test.
- 🧱 The concrete specimen size for testing is standardized: 150mm width, 150mm depth, and a span of 700mm, or 100mm width, 100mm depth, and a span of 500mm.
- 🔧 For sample preparation, mix cement, sand, aggregate, fly ash, and water by hand or with a mixing machine.
- 🛠️ The fresh concrete is poured into molds, compacted in three layers, and cured at 27°C for 24 hours.
- 🕒 After curing, the specimen is moist-cured at the same temperature until the testing time.
- 📊 During the test, the specimen is placed correctly, and the load is applied continuously at a constant rate until the beam fractures.
- ⚠️ Two types of failure are noted: Type A failure (fracture in the middle third of the span) and Type B failure (fracture outside the middle third but within 5% of the span).
- 🧮 The modulus of rupture is calculated using different formulas depending on the failure type, as per IS 516 standards.
Q & A
What is the purpose of the flexural strength test on concrete?
-The flexural strength test evaluates the tensile strength of concrete indirectly by testing the ability of an unreinforced concrete beam or slab to withstand failure in bending.
Which two methods can be used to conduct a flexural strength test on concrete?
-The flexural test on concrete can be conducted using either the third-point load test or the two-point load test.
What are the dimensions of the concrete specimen used in this test according to Indian Standard IS 516?
-According to IS 516, the dimensions of the concrete specimen are either 150 mm width, 150 mm depth, and 700 mm span, or 100 mm width, 100 mm depth, and 500 mm span. In this test, a 100 mm x 100 mm x 500 mm plain concrete beam is used.
What materials are used to prepare the concrete mix for the test?
-The materials used for the concrete mix include cement, sand, aggregate, fly ash, and water.
What steps should be followed after preparing the concrete mix before testing?
-Once the concrete mix is prepared, it should be poured into lubricated molds in three layers, each layer compacted on a vibrating table. After compaction, the molds should be left undisturbed for 24 hours at 27°C, followed by moist curing of the specimen at the same temperature until testing.
How is the specimen positioned in the machine for testing?
-The test specimen should be placed in the machine correctly, centered with the longitudinal axis of the specimen at a right angle to the longitudinal axis of the upper and lower rollers.
What is the rate of loading applied during the flexural test?
-The load should be applied without shock and increased continuously at a constant rate. For a smaller beam, the rate is 30 Newtons per minute, and for a larger beam, it is 67 Newtons per minute.
What are the types of failure observed in flexural strength testing?
-The two types of failure are: Type A, where the fracture initiates in the tension surface within the middle third of the span between the loading points, and Type B, where the fracture initiates in the tension surface outside the middle third of the span but within 5% of the span length.
How is the modulus of rupture calculated in case of Type A and Type B failure?
-In Type A failure, the modulus of rupture (fcr) is calculated using the formula: fcr = PL / BD², where P is the failure load, L is the span length, B is the width, and D is the depth. In Type B failure, the formula accounts for the distance from the fracture line to the nearest support.
What should be done if the fracture occurs outside the acceptable range?
-If the fracture initiates outside the middle third of the span length by more than 5% of the span length (unsatisfactory failure), the test results should be discarded.
Outlines
🛠️ Introduction to Flexural Strength Test on Concrete
The flexural strength test assesses the tensile strength of concrete indirectly by evaluating its ability to resist bending failure. This test is usually performed on unreinforced concrete beams or slabs using either the third-point or two-point load method. The script introduces the standard dimensions for the concrete specimen based on Indian Standard IS 516, where the experiment uses a 100x100x500 mm concrete beam.
🔬 Preparing the Concrete Specimen for Testing
Details on the preparation of the concrete specimen are provided, including selecting materials like cement, sand, aggregate, fly ash, and water, followed by mixing them either by hand or with a machine. The fresh concrete is poured into molds, compacted in three layers, and allowed to set for 24 hours at 27°C. After curing, the specimen is kept moist until testing time.
📏 Setting Up the Concrete Specimen for Testing
Before testing, the concrete specimen is cleaned and aligned properly in the machine. The setup must be precise, with the longitudinal axis of the specimen perpendicular to the loading rollers. The loading should be gradual, with different rates of loading for beams of varying sizes. After reaching the maximum load, the failure type and details are recorded.
🧪 Recording and Analyzing Beam Failure
The script explains the classification of failure types: Type A, where the fracture occurs in the middle third of the beam, and Type B, where the fracture is slightly outside this range. Specific guidelines for the allowable distance of the fracture for different beam sizes are provided, along with conditions for discarding unsatisfactory results.
📊 Calculating the Modulus of Rupture
The flexural strength of the beam, expressed as the modulus of rupture, is calculated using formulas specific to Type A and Type B failures. For Type A, the modulus is derived using the beam's dimensions and the failure load. For Type B, additional factors such as the distance from the neutral support are considered. The test results are discarded if the fracture occurs outside the acceptable range.
📝 Conclusion: Recording Failure and Strength
Once the test is complete, the failure load is recorded in the observation sheet, and the type of failure is noted. The test sample shows a Type A failure, and the modulus of rupture is calculated accordingly, reflecting the specimen's flexural strength as per IS 516.
📐 Flexural Strength Calculation
The modulus of rupture is the key parameter in expressing the flexural strength of the concrete specimen, summarizing the final output of the test.
Mindmap
Keywords
💡Flexural Strength Test
💡IS 516
💡Two-Point Loading Test
💡Plain Concrete Beam
💡Compaction
💡Curing
💡Modulus of Rupture (fcr)
💡Type A and Type B Failures
💡Rate of Loading
💡Fractured Specimen
Highlights
Flexural strength test on concrete as per IS 516 evaluates the tensile strength of concrete indirectly.
Flexural test checks the ability of unreinforced concrete beams or slabs to withstand failure in bending.
The test can be conducted using either the third-point load test or two-point load test.
A standard plain concrete beam with dimensions of 100x100x500 mm is used for the experiment.
Material proportions include cement, sand, aggregate, fly ash, and water.
Concrete mix is prepared and poured into molds in three layers with each layer compacted.
After 24 hours, the molds are removed, and specimens are moist cured at 27°C until testing.
Before testing, the specimen is placed in the machine with correct alignment, and loading rollers are wiped clean.
The load is applied continuously at a constant rate until the specimen can no longer sustain the load.
For smaller beams, the loading rate is 30 N/min, and for larger beams, it is 67 N/min.
Type A failure occurs when the fracture initiates in the tension surface within the middle third of the span.
Type B failure occurs when the fracture initiates outside the middle third of the span but within 5% of the span length.
Type A failure modulus of rupture (fcr) is calculated using the formula fcr = Pl/BD².
Type B failure modulus of rupture (fcr) involves measuring the distance between the fracture and the support line.
Unsatisfactory failure is when the fracture initiates outside the permissible range, and test results should be discarded.
Transcripts
welcome to Virtual labs today we will
perform flexural strength test on
concrete as per eyes 516
flexural test evaluates the dense size
strength of concrete indirectly
it tests the ability of unreinforced
concrete beam or slap to withstand
failure in bending
the flexural test on concrete can be
conducted using either third-point load
test or two point load test
we are performing The Experiment on a
standard plane concrete beam which is
subjected to two-point loading
Indian Standard determine the size of
the concrete specimen as 150 millimeters
width 150 millimeters depth and span of
700 millimeters
it also states that a size of 100
millimeters width 100 millimeters depth
and span of 500 millimeters
we are using 100 by 100 by 500
millimeters plain concrete beam
for sample preparation
determine the proportions of materials
including cement sand aggregate fly ash
and water
mix the materials either by hands or by
using suitable mixing machine
once the concrete mix is prepared and
the moles are lubricated pour the fresh
concrete into the molds in three layers
compact each layer by placing the molds
on the wide rating table
once the compaction is done remove the
extra concrete from the molds and
smoothen it out using trowel without
imposing any extra pressure
now keep the moles undisturbed for the
next 24 hours at a temperature of 27
degree Celsius
remove the moles and then moist cure
specimen at a temperature of 27 degrees
Celsius till the time of testing
remove the excess moisture from the
surface of the specimen
finally measure the cross section of the
tested specimen and do the markings as
per the specimen size
the bearing surfaces of the supporting
and loading rollers shall be wiped clean
before testing
the test specimen shall be placed in the
machine correctly centered with the
longitudinal axis of the specimen at
right angle to the longitudinal axis of
the upper and lower rollers
the load shall be applied without shock
and shall be increased continuously at a
constant rate until no greater load can
be sustained
rate of loading should be 30 Newton per
minute for smaller beam and 67 Newton
per minute for larger beam size
fractured specimens shall be examined
and appearance of the beam and type of
fracture shall be recorded
type a failure is when the fracture
initiates in the tension surface within
the middle third of the span between the
loading points
type B failure is when the fracture
initiates in the tension surface outside
of the middle third of the span length
by not approximately more than 5 percent
of the span length
in case of type a failure modulus of
rupture fcr is given by the following
formula scr is equal to p l by BD Square
in case of type B failure modulus of
rupture fcr is given by the following
formula
Varys the distance between the line of
fracture and the neural support measured
on the center line of the tensile side
of the specimen
for 150 millimeter specimen a shall be
between 200 and 170 millimeters
for 100 millimeter specimen it shall be
between 133 and 110 millimeters
unsatisfactory failure is when the
fracture initiates an attention surface
outside of the middle third of the span
length by approximately more than 5
percent of the span length
is not in the given range the results of
tests shall be discarded
once the test is performed note down the
failure loads in the observation sheet
and observe the type of failure
failure in our sample is obtained as
type a failure
modulus of rupture can be calculated
with the given formula as per is 5 16.
flexural strength of the specimen is
expressed as the modulus of rupture
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