Exam 2 Vocab Flashcards
What does paste consist of
Air, water, cementitious materials
What does mortar consist of?
Paste and fine agg.
What does concrete consist of?
Coarse agg., and mortar (air, water, cement materials, and Fine agg.)
What is workability
How easy or difficult it is to place in forms, consolidate and to finish.
What does an air entraining agent do.
Adds microscopic air bubbles, protects concrete from freeze thaw, increases slump (more stiff)
A larger w/c ratio means what
It has more water and has less compressive strength
Concrete with more of its volume coarse agg will have a higher or lower bulk volume fraction (b/b0)
Higher
Advantages of concrete over steel
More readily available, cheaper
Disadvantages of concrete?
Low tensile strength(needs reinforcement for tension), Low ductility (cannot withstand large deformations before failure), Instability in volume (expands and shrinks), Low strength to weight ratio
What is Portland cement composed of
Ground clinker and gypsum
C3S
Tricalcium silicate, Primary strength in portland cement, moderate rate in strength gain, gives off high heat
C2S
Dicalcium silicate, gives some strength, Slow rate of strength gain, gives off low heat
C3A
Tricalcium aluminate, “bad guy”, Gives no strength, Very fast rxn, Gives off very high heat
C4FA
Iron, turns grey, no strength
Gypsum
Primary prevent C3A from reacting, gives no strength
Type 1 cement
General use anywhere that theres not specific requirements. Ex. highways, inland bridges, floors and buildings
Type III cement
Same as Type one but finer so it reacts faster (sets faster). Uses - Precast concrete, cold weather paving, paving to minimize traffic stoppage
Type IV
Reduced amounts of C3S and C3A, Low heat and slow strength gain, Moderate resistance to sulfate. Used for Mass concrete pours (dams, large concrete)
Type V
Lower amounts of C3A than Type 4, High!! resistance to sulfate attacks, used on ocean
Type II
Reduced C3A, Moderate resistance to sulfate. Low heat from rxns, used in high sulfate soils
What are the five most important compounds in portland cement
C3S, C2S, Iron, C3A, Gypsum
Important rxn products
CSH (calcium silicate hydrate), CH (Calcium hydroxide, Sulfoaluminates (all bad)
CSH
Calcium silicate hydrate, “glue” primary strength of hydrated cement
CH
Calcium hydroxide, flat hexagon crystals, water soluble, High pH
Ettringite
Hexagon needle like shape, reduced workability. Too much of this causes “False set”
Monosulfoaluminates (MSA)
Cluster of irregular plates “rosettes” Vulnerable to sulfate attacks
What is causes by too little gypsum
Flash Set, Sets too fast creates alot of heat
What is caused by too much gypsum
Setting delayed too long
Stage 1 of hydration
First contact of cement and water, initial hydration products form around C3S and the process slows
Stage 2 of hydration
Cement remains workable for hours. concrete is places in forms and consolidated (vibrated)
Stage 3 of hydration
CSH begins forming around C3S, ettringite forms “initial set” water can not longer easily reach C3S, DIFFUSION CONTROLLED
Stage 4 of hydration
CSH continues to get thicker around C3S and rxns become slowS
Stage 5 pf hydration
Hydration nearly complete
What kind of water can be used in concrete
If its good enough to drink it can be used
Air entraining admixtures
Freeze thaw resistance, used in saturated concrete, bubbles in concretes, increased air content, reduced strength
Water reducing admixtures (as water reducer) Given ( Same cement, less water)
Same slump, lower w/c, f’c increases
What does set retarding admixtures do?
Slows down set times to remain workable for longer
What do mineral admixtures do?
Replace cement with waste products such as pozzolans. reduces cement used and improve durability
Types of pozzolans
Fly ash, silica fumes.
Mineral admixtures effect on hardened concrete
reduces porosity, and has higher strength later on
Why is silica fumes added to concrete?
Creates more CSH to increase compressive strength and reduces porosity
What is durability
the ability to resist weathering, chemical attack, and abrasion
What are deterioration mechanisms of concrete
ASR, chemical attacks (sulfate, seawater, acids), corrosion from rebar, freeze and thawing
What does a high w/c ratio do to permability
increases, more capillary pores
What does a sulfate attack do?
rxn of MSA, expansion causes cracking
How to control sulfate attack?
Use low C3A cement, add pozzolan or slag, use a lower w/c to reduce permeability
What does ASR do? and how to avoid it?
forms a gel that expands in the concrete. Use a blend of agg. to reduce amount of reactive silica
Limit distance concrete can fall,
3 to 5 feet
What is Rheology
The science of flowability
What is Thixotrophy
A property of becoming fluid when shaken and returning to a semisolid when standing
Factors to concrete segregation
Larger agg., mixes is way to wet or way to dry
What is bleeding
Upward movement of water after the concrete is consolidated, has a negative effect of strength and ductility
How to reduce bleeding
Increase fineness, increase hydration (air entrained), reduce water content
What does too much coarse agg cause
A harsh mix (less workability)
What does too much fine agg cause?
Oversanded mix, permable, more workable
What is initial set
Begining of stiffening can no longer be molded
What is final set
When the cement has hardened some and can sustain load
What is false set
Formation of ettringite soon after mixing but can still be restored to a fluid
What is flash set
Occurs from C3A forming large amounts of MSA. Sets too fast cannot be reversed
