Concrete Structures

Question 1

Nature of concrete

Composite material composed of three basic ingredients.

What are the ingredients.

Answer 1

Aggregate
Binder (cement and water)
Additives.

Question 2

Aggregate

Answer 2

This is a hard material that is responsible for the compression strength and stiffness of the concrete.
This must be washed in fresh water to remove salt.

Question 3

Binder

Water and cement
Two diffeeent types. Hydraulic and non hydraulic

Hydraulic is most common.

Answer 3

Hydraulic cements react with water this process is called hydration

The pouring on concrete is called placement

Question 4

Plastic shrinkage cracking in concrete

Answer 4

This is when water content is to night and excess water migrated to the surface leaving a volume shrinkage and the sub surface layers firing a skin of tensile stress.

Question 5

Thermal cracking.

Answer 5

This is when a large amount of concrete is poured all at once the heat produced during hydration process causes the sub surface material to expand and cooling the surface with causes contraction and the skin of the tensile stress is formed.

This is thermal cracking.

Question 6

Ph level of concrete

Answer 6

Ph 12.5

Question 7

Curing phase

Answer 7

This phases could last from a number of days to a number of weeks this is when the temperature and evaporation levels must be controlled.
The concrete continues to harden and gain strength. It will react about 70% of its final strength during the cure. And 90% of its final strength around a month after

Question 8

Additives ( admixtures)

Plasticisers
Accelerators
Others.

Answer 8

These are chemicals that are added to the mix to enhance properties or to change workability or rate of hydration.

Question 9

Types of concrete.

Answer 9

Grout

Mortar
Plain
Reinforced
Pre stressed.

Question 10

Grout

What is it and what is it used for

Answer 10

Grout is a mixture of cement and water

Used to deal joints pack in materials between steel pipes and repair work

Question 11

Mortar

What is it and what is t used for.

Answer 11

Mixture of aggregate (sand) cement and water

Stronger then grout but not as strong as concrete

It is used when some flexibility is needed. Repair work between two stiffer components.

Question 12

Applications for mortar

Answer 12

Jointing
Sealing
Filler
Repair work

Same as for grout mortar is not used for structural material

Question 13

In service defects

Three category’s

Answer 13

Defects

Areas of concern

Blemishes

Question 14

Category A defects

Answer 14

Cracks
Impact damage 
Pop outs 
Delamination
Exposed reinforcement 
Tearing
Poor repairs

Question 15

Category B

Areas of concern

Answer 15

Embedded objects 
Recessed metal plates 
Cast in sockets
Abrasian 
Water jet damage 
Honey combing.

Question 16

Category C

Blemishes

Answer 16

Construction joints 
Blowholes
Scabbing
Good repairs
Resin repair
Sealant runs 
Framework misalignment 
Vertical drag marks