
Main minerals
Lime (CaO)
 Silica (SiO2)
 Alumina(Al2O3)
 Iron Oxide (Fe2O3)


Main component is lime (60-65%)
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


Raw materials ground up, mixed and burned
in kiln
Kiln reaches 1500 degrees C
Produces particles called clinker
Clinker is add to 5% gypsum

Consider a hydraulic cement
Sets or hardens with the addition of water
 Chemical process occurs
 This process is called hydration

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Total amount of water to hydrate cement is about
25% of the mass of cement
Page 278 book for types of cement compounds
Hydration produces heat called heat of hydration
Massive structures causes problems
About 50% of the total heat is released in first 3
days.

Type 1 – Normal Portland Cement


Type III – High early strength


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Smaller amounts of C3S and C3A
Type V – Sulfate Resisting


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Cost 10-20% more
90% stronger one day
Same strength after 90 days
Contains more C3S
Cement is also ground finer so water can reach cement particles faster
Type IV – Low Heat


Most common (90-95%)
Used when groundwater contains sulphate
C3A is about 1/3 that of Type I
Type II –Moderate

Used when moderate resistance to sulphate is present

Fineness

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Setting

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Time required for cement to turn from paste to solid state
Compressive strength
Tensile strength
Relative density -3.15 for portland cement
Soundness


Controls hydration – smaller particles absorb water faster
Ability of the paste to retain volume after setting
Air content of the mortar

Paste

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Portland cement
Water
Air
Aggregate

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Fine aggregate
Course aggregate
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
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Ratio of water mass to cement mass
Example 190kg of water and 340g of cement = .56
w/c ratio is usually between .4 and .7
w/c ratio of .5 is 5.64 us gallons (8.33 lb/gallon)
per 94 Ib sack of cement
Water is required for
React chemically with cement to harden
 Make the mix plastic to work


1kg of water is required for 4kg of cement for
hydration (w/c of .25) but this would not give
necessary workability (see chart page 287)



Protects against freeze thaw cycles
Been used since 1940’s
Small bubbles of air are form in concrete by special
chemicals called air-entraining agents



These air bubbles relieves the pressure developed by freezing
of water in pores
9% air provides(paste plus fine aggregate) adequate
protection –except concrete subject to deicing
chemicals
Concrete made with small size coarse aggregates
requires more mortar to fill spaces between the coarse
particles

Proportion of whole mix increases as the size of the largest
particles decrease

Expressed in MPa (psi)




Obtain by dividing total failure load by cross
sectional area
Normal concrete strength at 3,7,14 days is
40%,60,75% of total strength
Strength will vary based on w/c ratio
Air entrain reduces strength of concrete,
however less w/c is necessary with air-entrain
and as a result strength is very similar (see
page 289)

Tensile strength

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Flexural strength or modulus of rupture
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Reactive aggregates
Cycles of freeze thaw
Deicing chemicals create hydraulic pressure
Ground water with high sulphates levels can cause disintegration
Seawater as well
Permeability


Strength of pavement concrete
Tensile stress at bottom of beam
Usually about 15% of compressive strength
Durability


Very low about 10% of compression strength
High w/c ratio will have more air voids and be less water tight
Abrasion resistance


Depends on aggregate choice
Concrete strength

Workability

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Consistency or plasticity of placing and molding concrete
without segregation
Increase water content increase workability
Air entrainment also increases workability
To much w/c can cause bleeding and segregation
Bleeding – movement of water to the surface
 Causes week layer

Segregation –coarse aggregates separate from cement paste
 Dropping concrete from heights and excess vibration


Workability is measured by slump test
Harshness


Finishing quality of concrete
Harsh mix will have too much coarse aggregate and will not
finish well

Temperature change

Varies with type of aggregate
 Average value for coefficient of expansion is 10um/m per
degree C

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Shrinkage

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Example problem in book page 294
During curing moisture escapes
Range is 400 to 800 u/m
Example problem in book page 294
About 1/3 shrinkage occurs first 30 days – 90% first year
Reinforce concrete rate drops to 200 to 300um/m
Concrete creep

Change in volume due to continuously applied load
 Only important in prestressed concrete
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

Problem page 295
Problem page 295
To find 28 day results sooner
Submerge cylinder in boiling water for period of time
 Cure cylinder in autogenous curing box
 Both methods cylinder can be tested at 2 days to give 28
day strength


Concrete subject to bending loads
Concrete bean 150mm x 150mm and 900 mm long is cast
 Load beam at three points to find flexural strength
 Problem page 296

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Cone 300mm high –three levels tamp at each
level 25 times cone removed slump measured
Ordinary structural concrete is usually 50100mm (2-4in)
High slump concrete – 100-150mm(4-6 in)
Zero slump – 0-30mm (0-1 in)

Volumetric method or pressure method
Known volume is filled
 Top part of apparatus is clamped on
 Standpipe is filled with water apparatus is inverted
 Drop of water level is calibrated to give air content
as percentage





80% concrete produced in North America has
chemical additives
Used since 1900’s
Small quantities up to 1% to 2% of mass of cement
ASTM Standard

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Type A-water reducing
Type B- retarding
Type C –accelerating
Type D – water reducing and retarding
Type E –water reducing and accelerating
Type F – high range water reducing (HRWR)
Type G- high range water reducing and retarding

Type A – can reduce amount of water by 20% -30%
Type A – also known as superplasticizers
 Increase slump and workability
 Better flow through pumping




Type B – delay the time required for setting and
hardening
Type C – retard setting and hardening – used
below 5 degree C (41 degrees F)
Other Admixtures
Corrosion inhibitors
 Pumping additives
 Microsilica



Materials suitable to replace portion of portland cement – reduce
cost
Main types are supplementary cementing materials (SCM)

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Also referred to as mineral admixtures
Fly ash is lighter then cement

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
Improves placing and workability
Easier to pump
Resistance to sulphate attack
Slag by product of blast furnaces

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
Fly ash
Granulated slag
Silica fume
Similar to fly ash benefits
Segregation or bleeding are more of a problem
Silica fume –fills spaces between cement particles


Creates denser mixes with fewer air and water voids
Improves pumping and reduces bleeding

Should be clean, hard, strong and durable

Hardness or resistance to wear
 Important for pavement

Soundness or resistance to freeze thaw
 Ability to withstand weathering
 Water expands 9% when it freezes

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Chemical stability
Particle shape and texture
 Long thin aggregate should be avoid

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
Relative density and absorption
Deleterious substance
Maximum size

Limit coarse aggregate to 1/5 width of forms, ¾ of space
between reinforcing, 1/3 depth of slab


Designed for strength and resist deterioration
Owner or agency specifies proportions required in a mix


Most cases only required strength, exposure conditions and
placing conditions specified
Items to be determined according to standards
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Relative density and absorption of the aggregates
Dry rodded density of coarse aggregates
Fineness modulus of fine aggregates
Slump
w/c ratios for various strengths
Overdesign factors
Harshness or finishing potential
Maximum size of aggregates
Air-entrainment requirements
Use of SCM’s or special admixtures

Page 311
7-6
 7-7
 7-7.3
 7-7.5
 7-8


7-8.1 page 314

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
Choose slump
Choose maximum size of the aggregate
Estimate the amount of mixing water
Select the w/c
Calculate the cement
Estimate the proportion of coarse aggregate
Estimate the mass of fine aggregate using the estimated
Calculate the adjustments required for aggregate
moisture
7-9 page 317



prepared a batch at a time
Aggregates and cement weigh into a stationary mixer
10% of the water place in mixer initially


The rest with the admixtures and aggregates
Three types of mixing can follow
Central mixed – stationary mixer at plant – delivered to site in
rotating drum
 Shrink – mixed – partially mixed at plant- complete mixing in
truck
 Truck mix – concrete is mixed in truck


Mixing requires 70-100 revolutions of drum at 6-18 rpm



Followed by agitating until concrete is placed (2-6rpm)
Mixing time is 1 min for 1 yd/cu plus 15 sec for each additional
yard
Placement of concrete needs to take place within 2 hours



Use of buckets, chutes, pumps and belt
conveyors
In forms place in 8-20 in thick layers
Vibration is used to consolidate and remove
voids

Vibrators place every 18in apart in forms and be
used less then 15s

Proper curing requires
Water
 Good temperature



Hydration stops when water is no longer present
Methods of curing

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Ponding – fogging action – expensive
Wet covering – special types of burlap used kept damp
layed over concrete
Wet hay straw – may discolor concrete
Waterproof paper – consisting of two sheets of paper
with an asphalt adhesive or plastic sheets
Curing compounds – sprayed on surface


Hydration can be accelerated
Methods
Steam curing
 High early strength cement
 Accelerating admixtures


Steam applied about 4-5 hours after pouring
Turned off in about 24 hours
 80% of design strength in three days


Cracks happen from volume change in concrete
Drying shrinkage
 Temperature changes


Control joints used to allow for drying shrinkage



Place no more then 30 times slab’s thickness – both
directions
Construction joints – located at the end of one days
pour – allow load to be transfer from one slab to
next
Isolation joints – used to separate slabs from
structure pour – filler matter used to absorb
expansion of the two concrete units.






Hot weather – danger of low slump , quicker
setting, poor finishing conditions, variable air
content
Concrete should not be placed if mix is more then
90 degrees f (ASTM)
Below 5 degrees c (41 F) slow the rate of hydration
Below -10 degrees c (14f ) hydration stops
ASTM requires placing concrete mix at above 55
degrees c (13 c)
If air temp within or after 24 hours of pour is
below 5 degrees c (41f) precautions need to be
taken


5% of N. America roads use concrete
Volume changes major problem



Slab shrinks as it cures
Expansion and contraction due to temp. changes
Allow for these changes

Plain pavements – sawed or formed joints
 Cracks form beneath joint
 Load transfer between slabs
 Joints place (13-23ft apart)

Dowelled pavements – smooth steel dowel under sawed joint
 Joints place (13-23ft apart)
 Better load transfer between slabs then plain

Reinforced pavements – uses heavy reinforcing steel bars
 Joints place 40-100ft

Continuously reinforced pavement – heavy reinforcement
 No joint built in

Saw joints need to be done within 24 hours after set up

Saw ¼ depth of slab

2 slump test made on first load each day



Sample taken at about 15% and 85% of truck
Consistency must fall with in ½ for low slump and 1
in for medium slump
2 compressive strength test are required




Cylinders not disturbed and protected on site for 24
hours
Then moved to lab
Strength acceptable if the average of 3 tests is equal
to or greater then specified and no individual test is
more then 500 lb/in2 below specified strength
Require one strength test for each 150yd3