30 Questions
Which test measures the amount of penetration to determine concrete consistency?
Kelly-Ball test
What is consistency in concrete related to?
The fluidity of the concrete
Which type of concrete class is best suited for trench-filled foundations requiring high flowability?
S3
What is the main factor indicating the workability of freshly mixed concrete?
Shear resistance of the mass
What is the most widely used test to measure concrete consistency?
Slump test
What is the recommended batching method for concrete mixing according to most specifications?
By weight
What is the purpose of mixing concrete thoroughly?
To ensure all ingredients are evenly distributed
Why is careful attention paid to the required mixing time in stationary mixing?
To comply with specifications and ensure proper mixing
In truck-mixed concrete, where is the mixing completed?
Completely in a truck mixer
What does 'bleeding' in fresh concrete refer to?
The rising of free water to the surface due to heavier particles settling
What factor has the most significant influence on bleed water rates?
Water-to-cement ratio
What type of concrete is batched and completely mixed in a stationary mixer at the plant site?
Central-mixed concrete
What is the best water curing method for concrete?
Immersion Method
Which test is used to check the uniformity of fresh and hardened concrete?
Slump Test
What maintains the satisfactory moisture content and temperature inside concrete for proper hydration of cement?
Curing
In which curing method are small rectangular ponds built around the concrete surface?
Ponding Method
Which test is NOT used to check the uniformity of concrete?
Strength Test
What are examples of properties checked in hardened concrete?
Shrinkage & Creep Deformations
What is the term used for the plastic state of concrete starting from the time the materials are mixed until it gains rigidity?
Fresh concrete
Which of these is NOT considered an advantage of concrete as mentioned in the text?
Low tensile strength
What is workability in relation to concrete?
The ease of mixing and placing fresh concrete
Which of these is NOT a class of chemical admixtures for concrete as mentioned in the text?
Volume-stabilizing
What is the main disadvantage mentioned in the text that relates to the strength property of concrete?
Volume instability
What distinguishes fresh concrete from hardened concrete according to the text?
Rigidity gain time
What is the most important property of hardened concrete?
Compressive strength
Which of the following factors does NOT affect the strength of concrete?
Color of the cement
At what age is the compressive strength of concrete typically determined?
28 days
Which method can be used to convert cube strength to cylinder strength?
Testing core specimens drilled from hardened concrete
Besides compressive strength, which other type of strength is mentioned in the text?
Tensile strength
Which operation does NOT affect the strength of concrete according to the text?
Molding
Study Notes
Factors Affecting Workability
- Quantity of mixing water, cement, and mineral admixtures
- Properties of cement, aggregate gradation, and Dmax
- Shape and surface texture of aggregate particles
- Quantity of entrained air and temperature of concrete
Consistency
- Measures the fluidity or degree of wetness of concrete
- Dependent on shear resistance of the mass
- Major factor in indicating workability of freshly mixed concrete
- Measuring methods: flow test, Kelly-Ball test, and slump test
Slump Test
- Measures the ease of concrete flow during placement
- Classes S1 to S5, each suitable for specific applications
- S1 for kerb and pipework bedding, S2 for strip footings and hard-standing slabs, etc.
Batching
- Measuring concrete mix ingredients by mass or volume
- Most specifications require batching by mass
- Within-batch and batch-to-batch variations affect concrete quality
Uniformity of Concrete
- Checked by conducting tests on fresh and hardened concretes
- Tests: slump, unit weight, air content, and strength tests
Curing
- Maintains satisfactory moisture content and favorable temperature
- Methods: immersion, ponding, and spraying or fogging
- Essential for hydration of cement and development of desired properties
Properties of Hardened Concrete
- Strength
- Permeability and durability
- Shrinkage and creep deformations
Mixing Concrete
- Should be mixed thoroughly until uniform in appearance
- Stationary mixing: careful attention to required mixing time
- Ready-mixed concrete: central-mixed, shrink-mixed, and truck-mixed
Transporting Concrete
- Essential to maintain quality of concrete
- Should be transported to the job site before initial setting time
Bleeding
- Process where free water in the mix is pushed upward to the surface
- Factors affecting bleed water rates: water-to-cement ratio
- Excessive bleeding can be problematic
Concrete Constituents
- Cement
- Water
- Fine aggregate
- Coarse aggregate
- Admixtures
Admixtures
- Classified according to function
- Five distinct classes: air-entraining, water-reducing, retarding, accelerating, and plasticizers (super plasticizers)
Advantages and Disadvantages of Concrete
- Advantages: ability to be cast, economical, durable, fire resistant, energy efficient, and on-site fabrication
- Disadvantages: low tensile strength, low ductility, volume instability, and low strength-to-weight ratio
Fresh and Hardened Concrete
- Fresh concrete: plastic state from mixing to gaining rigidity
- Hardened concrete: state from gaining rigidity onwards
Workability
- Ease with which fresh concrete can be mixed, placed, compacted, and finished without segregation
Strength of Hardened Concrete
- Ability to resist strain or rupture induced by external forces
- Factors affecting strength: W/C ratio, mixing water quality, cement properties, aggregate properties, admixtures, and curing conditions
- Test methods: standard test method, testing core specimens, and non-destructive methods (rebound hardness)
Learn about the composition and constituents of concrete, including cement, water, fine aggregate, coarse aggregate, and admixtures like air-entraining, water-reducing, and retarding agents. Understand how these components come together to form the versatile material known as concrete.
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