8 - Experimental Investigation Techniques
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Creep Test Setup
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Today, we're going to learn about the creep test setup. Can anyone tell me what kind of specimens we typically use?
Are they cylindrical or prismatic specimens?
Exactly! We usually use cylindrical or prismatic specimens. The standard size is typically 100 × 200 mm. Now, we need to apply a stress. Who can tell me what percentage of the cube strength we should use?
Isn’t it about 30%?
Correct! Applying around 30% of the cube strength allows us to measure creep effectively. We use various tools for measurement. What tools can you think of?
I think we can use strain gauges and dial gauges!
Spot on! And we can also use digital extensometers for more precise measurements. Remember, accurate measurement is essential for understanding and mitigating creep in concrete structures. Let's recap: we use cylindrical or prismatic specimens, apply 30% of cube strength stress, and utilize several measurement tools.
Shrinkage Test Setup
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Moving on to shrinkage, can anyone explain what distinguishes sealed specimens from unsealed ones?
Sealed specimens measure autogenous shrinkage, while unsealed specimens measure drying shrinkage, right?
Absolutely correct! Sealed specimens prevent moisture movement, capturing only the internal chemical effects. What about the conditions in which we conduct these tests?
We need to control the humidity and temperature using an environmental chamber!
Exactly! An environmental chamber is critical for achieving accurate shrinkage data. We reference standards like ASTM C157 and IS 1199 to ensure reliable results. Let's summarize: we use sealed and unsealed specimens to test different shrinkage types, and we manage environmental conditions for accuracy.
Introduction & Overview
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Quick Overview
Standard
Experimental Investigation Techniques covers the setup and methodology employed in measuring creep and shrinkage in concrete. It details procedures for conducting tests, including the necessary equipment and conditions required for reliable results. Understanding these techniques is crucial for engineers to mitigate the effects of these time-dependent deformations on concrete structures.
Detailed
Experimental Investigation Techniques
This section examines the experimental methodologies for investigating two critical phenomena in concrete: creep and shrinkage. The understanding of these techniques is essential for civil engineers who design structures that must withstand time-dependent changes.
Creep Test Setup
- Specimen Type: The test commonly involves cylindrical or prismatic specimens, typically sized at 100 × 200 mm.
- Applied Stress: To initiate the creep test, a stress of approximately 30% of the cube strength of the concrete is applied.
- Measurement Tools:
- Mechanical Dial Gauges: Used for manual measurements of deformation.
- Strain Gauges: Electronic devices that provide precise measurements of creep over time.
- Digital Extensometers: Highly accurate instruments for recording elongations and contractions during tests.
Shrinkage Test Setup
- Specimen Conditions: Tests include both sealed and unsealed specimens to differentiate between autogenous and drying shrinkage effects.
- Environmental Control: An environmental chamber simulates controlled humidity and temperature to standardize the testing conditions.
- Standard References: The methods referenced include ASTM C157 and IS 1199, which provide protocols for drying shrinkage measurement.
Understanding these experimental techniques is imperative for addressing the potential long-term impactful deformations in concrete structures due to creep and shrinkage.
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Creep Test Setup
Chapter 1 of 2
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Chapter Content
- Cylindrical or prismatic specimens (100 × 200 mm typical)
- Applied stress ~30% of cube strength
- Measurements taken with:
- Mechanical dial gauges
- Strain gauges
- Digital extensometers
Detailed Explanation
The creep test setup primarily involves preparing cylindrical or prismatic concrete specimens, typically measuring 100 by 200 mm. These specimens are subjected to a specific stress level, usually around 30% of their compressive cube strength, which helps simulate real-world conditions for long-term loading. During the test, deformation or strain is measured using various instruments. Mechanical dial gauges provide a straightforward way to read displacement, while strain gauges and digital extensometers offer precise measurements, crucial for assessing concrete's time-dependent deformation behavior.
Examples & Analogies
Think of this setup like testing a sponge soaked in water. Imagine squeezing the sponge - if you press it lightly, it will deform a little, but if you press harder, it deforms more. Similarly, in the creep test, we're examining how concrete deforms over time under a constant 'squeeze' or stress to understand its durability.
Shrinkage Test Setup
Chapter 2 of 2
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Chapter Content
- Sealed and unsealed specimens for autogenous vs drying shrinkage
- Environmental chamber used to simulate controlled humidity and temperature
- Standard reference: ASTM C157, IS 1199
Detailed Explanation
For measuring shrinkage in concrete, two types of specimens are set up: sealed and unsealed. Sealed specimens are used to study autogenous shrinkage, where the concrete shrinks internally due to chemical processes, while unsealed specimens are exposed to the environment to observe drying shrinkage, caused by moisture loss. An environmental chamber is utilized to ensure that humidity and temperature are controlled during the test, creating conditions that are consistent and reliable. The tests follow standards such as ASTM C157 and IS 1199 to ensure comparability and accuracy in results.
Examples & Analogies
Consider cooking pasta. If you cover the pot tightly (sealed), the steam can't escape, mimicking sealed specimens which retain moisture. If you leave it uncovered (unsealed), the water evaporates, similar to how unsealed concrete specimens lose moisture to the environment. This analogy helps visualize how different conditions impact the shrinkage of concrete.
Key Concepts
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Creep Test: A method to measure time-dependent deformation under constant load.
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Shrinkage Test: A method to assess the volume reduction of concrete over time.
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Environmental Chamber: A controlled facility for simulating precise testing conditions.
Examples & Applications
In a creep test, cylindrical specimens are carefully monitored under a set load to determine how much they deform over a specific period.
During shrinkage testing, environmental chambers are utilized to replicate varying humidity levels to study their effects on concrete shrinkage.
Memory Aids
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Rhymes
To measure creep, don't be late, 30 percent is the stress rate.
Stories
Imagine a scientist with two buckets: one sealed and one open, testing how much water evaporates while they sit. The sealed bucket stays full longer, just like sealed concrete shrinks differently than open concrete does!
Memory Tools
Creep Test: 'SAS' - Specimen, Apply stress, Spot measures.
Acronyms
ECR - Environmental Control essential for Reliable results.
Flash Cards
Glossary
- Creep Test
A testing method used to measure the time-dependent deformation of concrete under a constant load.
- Shrinkage Test
An experimental setup to measure the decrease in volume of concrete over time due to moisture loss or chemical reactions.
- Environmental Chamber
A controlled environment facility used to simulate specific humidity and temperature conditions during concrete testing.
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