hydration of cement

-Setting time

1. The time taken from additionn of water to initial set and final set
2. Vicast Test-to test cement setting time

Hardening

1. Hardening also means useful strength development

hydration of cement

Hydration=the chemical combination of cement and water

1. Will produce a very had and strong binding medium for aggregate particles in concrete
2. Hydration may continue over a period of a month
3. The heat generated during hydration will affect the durability of concrete due to micro cracking

Learning outcome

-Upon completion of this chapter , you should be able to:

1. Describe hydration of cement
2. discuss factors affecting cement setting
3. Outline the Vicat Test

Concrete

Cement
-Hydration of cement

Moisture

-Saturated , surface dry

1. Ideal state
2. Do not require alteration to mixing water

-Wet

1. Surface moisture is pressent
2. Most common
3. Require deduction of water when mixing

Moisture

-4 states which aggregate may exist in:
-oven-dry

1. on heating to 105 celcius , no loss of weight
2. seldom occur
3. require extra water when mixing

-Air-dry

1. No free moisture and surface are dry
2. Occur at upper part of stockpiles in dry wheather
3. Require extra water when mixing

Strength

-Strength of aggregate generally higher than compressive strength of concrete:
-Factors affecting strength of concrete:

1. Aggregate size
2. Aggregates shape and texture
3. Cleanliness