Hardened Concrete (Lecture 6)

Question 1

What is the typical range of 28 day compressive strength on normal concrete?

Answer 1

2000-6000 psi

15-40 MPa

Question 2

What are the relationships between tensile strength, flexural strength, and elastic modulus with the compressive strength of concrete?

Answer 2

Tensile strength- 10% of compressive strength
Flexural strength- 15-20% of compressive strength
Elastic modulus-Strength between stress and strain to measure stiffness. 15-40 GPa

Question 3

What is the most important mix parameter effecting the strength of concrete?

Answer 3

Water cement ratio: lower water/cement = higher strength

Question 4

What other parameters effect the strength of concrete?

Answer 4

Age- strength increases with curing time
Curing conditions- longer moist curing & higher temp= higher strength
Type fo cement and admixture- can affect rate of strength gain and ultimate strength
Strength of aggregate
Moisture content- higher moisture = lower strength

Question 5

What is the creep property

Answer 5

Continuing yield under sustained stress.

Creep of concrete under sustained stress can cause reduction of prestress in prestressed concrete structures

Question 6

What are the effects of concrete permeability on its performance?

Answer 6

Ease of flow of a fluid or gas through the concrete.
low permeability is needed to prevent disintegration caused by freezing of saturated porous concrete, dissolving of soluble concrete components, and chloride intrusion causing rebar erosion.

Question 7

What is the density of normal concrete?

Answer 7

150 pdf

2.4 Mg/m^3

Question 8

What is the density of florida limestone?

Answer 8

140pcf

2.24 Mg/m^3