Lec 9 Flashcards
Pozzolanic material
2S + 3CH -> C3S2H3 (C-S-H)
S is active silica
CH is calcium hydroxide
CSH is cementitious compunds
Limitation amount of pozzolanic material
- fly ash or other pozzolanic -> 25
- slag -> 50
- silica fume -> 10
- (1) + (2) -> 50
- (1) + (3) -> 35
types of Cement Replacement Materials (slide 7 ppt)
pfa (class C largest Fe2O3), ggbs (largest MgO), csf (largest SiO2), metakolin (largest Al2O3 and pozzolan reacitivity), portland cement (largest CaO)
Types of chemical admixtures
- plasticizer: water-reducers without affecting the workability and increasing strength with the same cement
- Superplasticizer: more powerful than plasticizer to increase in fluidity and workability
- Accelerators: increase the rate of hardening of cement paste -> enhancing early strength (CaCl2)
- Retarders: delay the setting time of a mix
- Air entraining agent: entrain a controlled quantity of air in the form of small bubbles in the cement paste (act at air-water interface)
ASTM C494-92 functional classification
Type:
A - water reducing
B - retarding
C - accelerating
D - water reducing & retarding
E - water reducing accelerating
F - superplasticizIng
G - superplasticizing and retarding
Explain type A - water reducing
purpose: less water, more workability
mechanism: is a surfactant and acts on the solid and liquid interfaces to uniformly disperse the particle
material: ligninsulfonate and formic acid
Explain type B - retarded
purpose: to slow the setting time
mechanism: retarding of C3S, inhibition of Ca(OH)2, has ligninsulfonate
function: reduce hydration heat, delayed concrete setting and hardening time, avoid cold joints, long working time at high temp, increased workability due to plasticizing
Explain type C - Accelerating
purpose: to accelerate the hydration of cement, shorten setting time, increase early strength
mechanism: the acceleration effect on C3S shortens the incubation period, acidification accelerates the dissolution of lime, silicic acid, aluminate in cement, suitable for spraying or cold weather
precautions: CaCl2 is good and cheap. BUT, it will damage the passive film and accelerate corrotion rate of steel (amount must <2%)
CaCl2 should not be used when prestressed concrete and nuclear protective concrete, sulfate reaction possible, containing aluminium or hot weather
Explain plasticizer
purpose: 15-30% water reducing, avoid bleeding and segregation
mechanism: mechanism action is similar with water reducing, but no bleeding or segregation, can be added 0,5-3% of cement weight and the water reduction rate must be >12%, IMPORTANT -> reducing the surface tension, make cement particle with isoelectric potential, form a lubricant film on the surface
Precautions: cement hydration and PH >12 will break the chemical of plasticizer, C3A will adsorb the plasaticizer so add it several minutes after
Explain air entraining agents
purpose: make stable air bubbles into fresh concrete to increase workability and frost resistance
mechanism: Hydrophilic (bulat kecil) and Hydrophobic (segiempat) are used to form independent micro-bubbles at the gas-liquid, belong to air and liquid surfactant
Heavy Weight Concrete (special concrete)
- density between 3300 to 3800 kg/m^3
- to block x-ray, gamma rays, neutron radiation
- the higher the density, the higher the shielding efficiency
- compressive strength used in the prestressed concrete of the nuclear reactor containment building wall must reach 550-650 kgf/cm2 (7days) and 650-800 kgf/cm2 (28 days)
High Strength Concrete HSC (special concrete)
- compressive strength > 420 kgf/cm2
- applicaiton is between 560 and 700 kgf/cm2
- economic benefits, less costs, less maintenance cost, increase life building
- 7 days strength (294 kgf/cm2) and cement amount is 300-450 kg/m3
- silica fume 5% and 60% slag usually added, aggregate need to consider every aspects
High Performance Concrete (special concrete)
- superior properties: high flowability, strength, durability
- Based on Japan: High-strength High Performance concrete, Self Compacting Concrete (achieve uniform filling concrete without tamping), HPC with special functions or properties
- High-flow high performance concrete or SCC does not require tamping , automatic pouring, and reducing construction noise
HPC stricter requirements
- Cement: I, III cement -> fly ash and slag substitute cement to reduce the cement and reduce heat of hydration
- Aggregates: make sure no harmful substances, FM = 2,8-3,2, maximum particle size of coarse 3/4” (19mm), preferably 1/2” (12,7mm)
- Chemical admixture: plasticizer is the most important and most used
- Mineral admixture: slag, fly ash, and silica fume is thinner than cement -> increasing strength (denser cement and higher durability) at late stage (28days). It can reduce the use of chem admixture, less hydration heat, and less temperature cracks
Self Compacting Concrete SCC (part of HPC)
Fill without any vibration and tamping during the pouring process, and completely fills the narrow gaps between the reinforcement and corners of the framework with the filling.
- automatic pouring and less noise
