InTRoducTion

SPECIAL CONCRETE

Disadvantage of Ordinary Portland Cement Concrete (OPCC):

1. High early strength, long term strength = constant
2. Reduce / lower durability
- corrosion
- ASR (alkali silica reaction)
- Resistance to chemicals, sulphates, chlorides – reduce


Overcome general problems:

5C’s: CONSTITUENTS, COMPACTION, CURE, COVER, CODE


Overcome specific problems:

1. Compared with steel, ratio strength/weight low

a) lower density – LIGHTWEIGHT CONCRETE
(Density 800-1860 kg/m2 and strength 25-60N/mm2)

b) increase strength – HIGH STRENGTH CONCRETE
(Strength 60-100++ N/mm2) – cement, admixtures, pozzolans


2. Heavily reinforced structural members

- HIGH WORKABILITY CONCRETE
- FLOWING, SELF CONSOLIDATING CONCRETE


3. Thin structural members – shrinkage and cracking

- SHRINKAGE – COMPENSATING CONCRETE
- Expensive cement or admixture


4. Improving fracture toughness and impact resistance

- FIBRE REINFORCED CONCRETE
- FERROCEMENT


5. Increasing the imperviousnous of concrete
(Esp. increase durability to moisture and chemical solutions)

- CONCRETE CONTAINING POLYMERS
Impermeability and chemical resistance increase
i. POLYMER CONCRETE
ii. POLYMER PORTLAND CEMENT CONCRETE
iii. POLYMER IMPREGNATED CONCRETE


6. Radiation shielding in nuclear power plan

- mass concrete
- heavy weight / high density concrete = 50% x density OPCC


Important information needed when ‘new’ material added to concrete (aggregates, cement modifiers)

1) a) Improved properties of modified concrete

- justification of using new materials – cost, performance cost, performance based specification and RCPT
- strength and durability

b) Disadvantages in some properties of concrete


2) Collection of data

- shrinkage, creep, E, structural behaviour
- any detrimental effects
- long term effects – conservation of HAC and CaCl

• Control of the production of concrete must be high.


Comparisons with control Ordinary Portland Cement

1. Effects on fresh concrete

- workability, water demand, slump loss
- segregation and bleeding (moving water over the concrete)
- time of set
- temperature (heat of hydration)

2. Effects on hardened concrete

- FCU, E, shrinkage, creep

3. Durability

- permeability, resistance to chemicals
- ASR, corrosion

4. Structural behaviour

- cracking, brittle, ductile, ∆
- long term behaviour