Creep Behavior in Concrete

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In reinforced concrete designs, what is the Poisson effect?

The result of excessive water usage in concrete mixtures

A type of reinforcement used in columns

A factor that is always considered in the analysis and design process

A phenomenon that must be accounted for in arch dams, tunnels, and some statically indeterminate structures (correct)

How does the Poisson's ratio relate to spiral reinforcing in columns?

It allows for better workability of the concrete mixture

It helps reduce the shrinkage of concrete

It is utilized to take advantage of concrete's properties in columns (correct)

It increases the compressive strength of the concrete

Why is it necessary to use more water than required for cement hydration in concrete mixtures?

To ensure proper bonding of the aggregate materials

To minimize shrinkage and cracking

To accelerate the curing process

To achieve the desired workability for placing concrete (correct)

What happens to the excess mixing water used in concrete after curing?

It evaporates, leading to shrinkage and cracking Signup and view all the answers

Which type of structures require consideration of the Poisson effect in their analysis and design?

Arch dams and tunnels Signup and view all the answers

What is the main purpose of the paste consisting of cement and water in concrete mixtures?

To bond the aggregate materials together Signup and view all the answers

What are dead loads in a structure?

Loads of constant magnitude that remain in one position Signup and view all the answers

Which of the following is NOT considered a dead load in a reinforced concrete building?

Furniture Signup and view all the answers

How are estimated weights of structure parts used in the design process?

For use in structural analysis and design Signup and view all the answers

Why is it important to have reasonable estimates of structure weights during design?

To ensure the safety and stability of the structure Signup and view all the answers

How can an experienced designer estimate weights of most structures accurately?

By referring to similar structures or civil engineering handbooks Signup and view all the answers

What role do tables in civil engineering handbooks play in estimating structure weights?

To provide approximate weights for common building materials Signup and view all the answers

What is the purpose of chemically modifying the surface characteristics of fibers used in concrete?

To increase bonding with the cement paste Signup and view all the answers

What aspect of fibers is crucial for determining the improvement in concrete toughness?

Length Signup and view all the answers

Which ASTM standard is used for determining the toughness of fiber-reinforced concrete?

ASTM C101820 Signup and view all the answers

How do fibers contribute to the toughness of concrete when a crack opens up in a member?

Provide resistance to crack opening Signup and view all the answers

What effect do fibers have on the fatigue life of beams in concrete structures?

Increase fatigue life Signup and view all the answers

Why does the use of fibers significantly increase costs in construction projects?

Because fibers are expensive materials Signup and view all the answers

What is the purpose of retarding admixtures in concrete?

To slow down the setting of concrete Signup and view all the answers

Why are superplasticizers used in concrete?

To reduce water content while increasing slumps Signup and view all the answers

In which situations are retarding admixtures particularly useful?

During large pours with significant temperature increases Signup and view all the answers

According to Section 3.6.3 of the ACI Code, when should calcium chloride not be added to concretes?

In concretes cast against stay-in-place galvanized steel forms Signup and view all the answers

What type of admixture is made from organic sulfonates?

Superplasticizers Signup and view all the answers

Why do some concrete truck drivers keep sacks of sugar on hand?

To throw into the concrete in case of traffic jams or delays Signup and view all the answers

What is the main reason why concretes with the highest percentage of cement-water paste have the highest creep?

The cement-water paste does the creeping Signup and view all the answers

How does the addition of reinforcing to compression areas of concrete affect creep?

Greatly reduces creep Signup and view all the answers

Why do large concrete members experience proportionately less creep compared to smaller thin members?

Smaller distance for water to escape Signup and view all the answers

What percentage of the compressive strength of concrete is the typical tensile strength range?

8% to 15% Signup and view all the answers

Why do cracks in concrete have little effect when the material is under compression loads?

Cracks close and allow compression transfer Signup and view all the answers

How does the presence of reinforcing steel in concrete affect tensile loads?

Reduces tensile strength Signup and view all the answers