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Questions and Answers
What is the most commonly used method of measuring consistency of concrete?
What is the most commonly used method of measuring consistency of concrete?
What is the height of the metallic mould used in the slump test?
What is the height of the metallic mould used in the slump test?
What type of slump occurs when the concrete collapses completely?
What type of slump occurs when the concrete collapses completely?
What is the diameter of the tamping rod used in the slump test?
What is the diameter of the tamping rod used in the slump test?
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What is the main limitation of the slump test?
What is the main limitation of the slump test?
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What is the purpose of the slump test?
What is the purpose of the slump test?
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What is the effect of a higher curing temperature on concrete?
What is the effect of a higher curing temperature on concrete?
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What is the primary function of isolation joints?
What is the primary function of isolation joints?
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Why are contraction joints used in concrete construction?
Why are contraction joints used in concrete construction?
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What happens if contraction joints are too widely spaced in slabs on ground?
What happens if contraction joints are too widely spaced in slabs on ground?
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What is the purpose of construction joints?
What is the purpose of construction joints?
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What type of joints are used to isolate slabs-on-ground from fixed foundation members?
What type of joints are used to isolate slabs-on-ground from fixed foundation members?
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What is bleeding in concrete?
What is bleeding in concrete?
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What is the primary cause of bleeding in concrete?
What is the primary cause of bleeding in concrete?
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What can happen if finishing operations take place while bleed water is present?
What can happen if finishing operations take place while bleed water is present?
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What is one benefit of some bleeding in concrete?
What is one benefit of some bleeding in concrete?
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What is one way to reduce bleeding in concrete?
What is one way to reduce bleeding in concrete?
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What is the process of measuring quantities of concrete mixture ingredients called?
What is the process of measuring quantities of concrete mixture ingredients called?
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What is the purpose of retempering of concrete?
What is the purpose of retempering of concrete?
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Which of the following is not a method of transporting concrete?
Which of the following is not a method of transporting concrete?
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Why is it important to maintain homogeneity while transporting concrete?
Why is it important to maintain homogeneity while transporting concrete?
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What is sometimes added to the concrete during retempering?
What is sometimes added to the concrete during retempering?
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What is the main precaution to be taken while transporting concrete?
What is the main precaution to be taken while transporting concrete?
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What is the primary requirement for producing concrete of uniform quality?
What is the primary requirement for producing concrete of uniform quality?
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Why is it desirable to add 10 per cent more cement when using hand mixing?
Why is it desirable to add 10 per cent more cement when using hand mixing?
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What is the characteristic of a well-mixed concrete?
What is the characteristic of a well-mixed concrete?
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What is the primary difference between hand mixing and machine mixing?
What is the primary difference between hand mixing and machine mixing?
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What is the characteristic of ready mixed concrete?
What is the characteristic of ready mixed concrete?
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What is central-mixed concrete?
What is central-mixed concrete?
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Study Notes
Curing Temperature and Strength Gain
- Higher curing temperature leads to earlier strength gain in concrete, but may decrease 28-day strength
- Lower curing temperature results in slower strength gain
Types of Joints in Concrete Construction
- Isolation Joints: permit horizontal and vertical differential movements, used around perimeter of floors, columns, and slabs-on-ground
- Contraction Joints: provide for movement in the plane of a slab or wall, induce controlled cracking due to drying and thermal shrinkage
- Construction Joints: stopping points in the construction process, bond new concrete to existing concrete, and permit no movement
Measuring Workability of Concrete
- Common tests to measure workability: Slump Test, Compacting Factor Test, Flow Test, Kelly Ball Test, and Vee Bee Consistometer Test
- Slump Test: most commonly used method, measures consistency of concrete, not suitable for very wet or very dry concrete
Slump Test
- Apparatus: metallic mould in the form of a frustum of a cone with specific dimensions
- Types of Slump:
- Collapse Slump: concrete collapses completely, indicating too wet or high workability mix
- Shear Slump: top portion of concrete shears off and slips sideways
- True Slump: measures the deformability of concrete
Bleeding and Settlement
- Bleeding: development of a layer of water at the top or surface of freshly placed concrete
- Caused by sedimentation of solid particles and upward migration of water
- Excessive bleeding increases water-cement ratio near the top surface, creating a weak top layer with poor durability
Reducing Bleeding in Concrete
- Reduce water content, water-cementitious material ratio, and slump
- Increase the amount of cement, finer cementitious materials, and supplementary cementing materials
- Use blended hydraulic cements, air-entrained concrete, or increase the amount of fines in the sand
Process of Manufacture of Concrete
- Batching: measuring quantities of concrete mixture ingredients by mass or volume and introducing them into the mixer
- Mixing: thorough mixing of materials is essential for uniform concrete, can be done by hand or machine
Mixing Concrete
- Hand Mixing: practised for small scale, unimportant concrete works, with 10% more cement added to cater for inferior concrete
- Machine Mixing: ready mixed concrete is batched and mixed at a concrete plant and delivered to the project
Retempering (Remixing) Concrete
- Remixing concrete with addition of required quantity of water, and sometimes a small quantity of extra cement
Transporting Concrete
- Methods of transportation: mortar pan, wheelbarrow, crane, truck mixer, belt conveyors, chute, pump and pipeline, skip and hoist, and helicopter
- Precaution: maintain homogeneity obtained at the time of mixing while transporting to the final place of deposition
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Description
This quiz covers the effects of temperature and moist curing on concrete strength, as well as different types of joints used in concrete construction. Understand the role of isolation, contraction, and construction joints in building structures.
