36 Questions
What is the purpose of retarding admixtures in concrete?
Delay the setting time
How are accelerators different from retarding admixtures in concrete?
Accelerators speed up the setting time
What effect does a water reducer admixture have on concrete workability?
Increases workability
When is additional cement usually not needed for lean mixtures with lower f’c and higher w/c ratio?
When air entrainment has a weakening effect
What property of concrete is affected by the reduction in w/c ratio for lean mixtures?
Compressive strength
What is the main purpose of high-range water-reducing admixtures according to the text?
Reduce water content by 12% to 30%
Which characteristic is associated with plasticizers for flowing concrete?
Extended-slump-life to reduce slump loss
What does a superplasticizer do to cement particles dispersion?
Steric inhibition of particle-particle contact
How does mid-range water reducing admixture affect the water content in concrete?
Reduce water content by 6% to 12%
What effect do high-range water-reducing admixtures have on compressive strength of concrete?
Increases compressive strength above 70 MPa
What happens when bubbles approach each other in concrete?
They repulse
In concrete, what is considered the most important parameter related to air spacing?
Air spacing
What is the Spacing Factor (⎯L) in the air-void system of concrete?
The maximum distance of any point from the periphery of an air void
What does ASTM 457 specify about the Spacing Factor (⎯L) related to air voids in concrete?
Less than 0.2 mm (0.008 in.)
How can the spacing of air bubbles in concrete be measured?
By analyzing images with automated image analysis
What is the main purpose of retarding admixtures in concrete?
Increase setting time in hot weather
Which compound is commonly used as an accelerator in concrete?
Calcium chloride
What is the main objective of water reducer admixtures in concrete?
Reduce mixing water and reduce water-cement ratio
What is the range of compressive strength typically associated with HPC (High-Performance Concrete)?
60-100 MPa
How does the addition of water reducer admixtures impact the slump life of concrete?
Decrease slump life
What effect does finely divided materials like silica fume have on air-entraining admixtures?
Decrease the water available for bubble formation
How does the proportion of fine aggregate in total aggregate affect air generation in concrete?
Increases air content
What impact does higher temperature have on the air content in concrete?
Decreases air content
How does a higher slump in concrete affect the air content?
Increases air content
How do retarding and accelerating admixtures affect the workability of concrete?
Retarding admixtures increase workability, while accelerators decrease workability
What is the purpose of water-reducing admixtures in concrete?
Reduce water content
Which component in concrete is responsible for providing strength?
CSH
How do accelerating admixtures affect concrete?
Accelerate early strength development
When are accelerators typically used in concrete construction?
In cold weather
What effect does reducing the water content in concrete have on setting time?
Decrease setting time
What is the primary function of retarding admixtures in concrete?
Delay the rapid heat evolution
How do water reducer admixtures affect the bleeding rate in concrete?
Decrease it
What is the impact of water reducer admixtures on the early strength of concrete?
Decrease it
Which compound is commonly used as a water reducer admixture in concrete?
Lignosulfonates
How do retarding admixtures influence the 28-day compressive strength of concrete?
Increase it significantly
Which type of admixture is developed as water reducers and also act as retarding agents in concrete?
Lignosulfonates
Test your knowledge on the impact of air content and cement content on the performance of concrete in sulfate soil. Explore how different air and cement content levels can affect the durability and strength of concrete over time.
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