1. Final Project - Materials - Concrete Flashcards
1
Q
Formwork
A
Shapes and supports concrete until it cures enough to support itself
- Formwork for a beam or slab is also a temporary working surface during construction
- Must be strong enough to support weight concrete without deflection
- Usually repeatedly used and must be protected
- Coated with a form release compound that prevents adhesion of concrete to the form
- Formwork is basically an entire temporary building that has to erected and demolished to construct the actual building. It’s a major cost of the project.
2
Q
most common form of forming material
A
plywood
- usually 3.4” thick
- coated with oil and water resistant glue or plastic to prevent water penetration into wood; help reusability of formwork
3
Q
form ties
A
metal wires or rods used to hold opposite sides of the form together and also to prevent their collapse
-when the forms are removed the wires remain in the conrete; ecess wire is twisted or cut off
4
Q
flying forms:
A
large fabricated sections of framework that are removed, once the concrete has cured, to be resued in forming an identical section above
-used in constuctung buildings with repetitive elements (e.g. hotels and apartments)
5
Q
Form liner
A
conrete is shaped with liners of plastic, wood, or metal
- parallel rib liners are common type
- joints and form tie holes are treated as desired-either left exposed or patched
6
Q
What are form ties? List 2 types
A
SNAP TIES
- have notches or crimps so they can be snapped off after forms are removed
SHE BOLTS
- waler rods (reused) threaded into inner rod which is left in concrete
7
Q
formwork costs for self consolidating concrete may be higher than those for conventional concrete because
A
the greater fluid pressures exerted by the concrete require stronger and stiffer formwork
8
Q
Concrete: why reinforce it? (5)
A
- Concrete resists compression very well, however it must be reinforced with steel so that it is more resistant to tension and shear.
- Attach vertical and horizontal elements
- Reinforce edges around openings
- Reduce cracking due to shrinkage
- Stabilize thermal expansion and contraction.
9
Q
Concrete: advantages (4) and disadvantages (2) ?
A
Advantages :
- It can be given almost any possible shape.
- It can be provided with the most varied finishes and textures.
- Concrete frames are relatively cheap
- Concrete frames are fire resistant
Disadvantages:
- Density (2240kg/m3)
- Formwork necessary before setting it in place so that it sets and hardens.
10
Q
Concrete = mixture of…? (3)
A
- Cement
- Various mineral aggregates
- Sufficient amount of water for the cement to set and bind the entire mass.
11
Q
Concrete: why add admixtures?
Name 5 types of admixtures.
A
Admixtures can be added to a concrete paste to modify these properties or those of the cured product.
- Air-entraining admixture
- Accelerator or retarder
- Surface admixture
- Water reducer
- Dye
12
Q
Concrete: what is an air-entraining admixture? Roles (3)?
A
Disperses microscopic spherical air bubbles in the concrete paste to:
- increase maneuverability
- increase the resistance of the cured product to cracking caused by free thaw cycles or to spalling caused by de-icing chemicals
- in larger quantities, to produce lightweight, insulating concrete.
13
Q
Concrete: why add an accelerator and a retarder?
A
- Accelerator: catalyzes the setting and the development of the resistance of a concrete paste -
Retarder: slows the setting of the concrete paste, allowing more time for placing and handling the concrete paste
14
Q
Concrete: why add a surface admixture?
A
- Reduces surface tension of water added to concrete paste
- Thus promotes the wetting and penetrating action of water or the emulsifying action and the dispersion of other additives in the dough.
15
Q
Concrete: why add a water reducer (or superplasticizer)?
A
- Reduces the amount of mixing water needed for proper workability of concrete paste or mortar.
- By thus reducing the ratio between the proportions of water and cement, the strength of the concrete is generally increased.
16
Q
Concrete: what determines the ratio between the quantity of water and cement?
Too much water = ?
Not enough water =?
Optimal ratio?
A
Determines: 1. Resistance… 2. durability… 3. waterproofing… … of the hardened concrete
The compressive strength of concrete is inversely proportional to the ratio of water to cement:
- If there is too much water, the concrete paste will be weak and porous after drying.
- If there is not enough water, the dough will be dense, but difficult to set up and handle.
In most cases, the ratio of water to cement should be
Water (L)/cement (kg) = 0.45 to 0.60.
17
Q
When specifuing small batches of conrete what does 1:2:5 mean?
A
it is the ratio of cement:sand:aggregate
C:S:A
18
Q
concrete components
A
- cement
- fine and course aggregate
- water
portalnd cement: binder; made of lime, silica, iron oxide, alumina
19
Q
5 types of cement
A
type I: standard or normal cement (used for most construction)
type IA: Normal, air entraining
type II: modified cement; used in places when in contact with water with a high concentration of sulfates
type IIA:Moderate resistance, air entraining
type III:High early strength (hardens more quickly, used when reduced curing time is required)
type IIIA:High early strength, air entraining
type IV:Low heat of hydration (used in massive structures like dams, where heat emitted might raise the temperature of the concrete to damaging levels)
type V:High resistance to sulfate attack (used when in contact with water with a high concentration of sulfates) !
20
Q
Air Entraining Admixtures
A
Improved workability during placement
Increase the resistance of the cured concrete to damage caused by repeated cycles of freezing and thawing
Can create very lightweight non structural concretes with thermal insulating properties
21
Q
Air Entrained Cements
A
Contain ingredients that cause microscopic air bubbles to form in the concrete during mixing which give improved workability during placement, and greatly increases the resistance of the cured concrete to damage caused by repeated cycles of freezing and thawing
- Commonly used for pavings and exposed architectural concrete in cold climates
- Can reach the same structural strength a regular concrete
22
Q
concrete strength
A
• Concrete cures/hardens due to hydration, where considerable heat is given off as the
cement combines with water to form strong crystals that bind the aggregates together
Concrete shrinks lightly during the process
• Designed on the basis of the s strength that is reaches after 28 days
7 day strength should be about 75% of the designed 28 day strength
- Early strength concrete can reach normal 28 day strength in 7-14 days
- Typical strength ranges from 3,000 psi - 10,000 psi
- Nominal weight is 150 lbs per cubic foot
23
Q
Aggregates
A
Take up about 3/4 of the volume of concrete
• Structural strength is heavily dependent on the quality of its aggregates
• Must be stone, clean, resistant to freeze-thaw deterioration, chemically stable, and
properly graded for size distribution
• A range of sizes must be included and properly proportioned to achieve close packing of the particles
• The largest particle in a concrete mix must be small enough to easily pass between
the most closely spaced reinforcing bars and to fit easily into the formwork
• Maximum aggregate size should not be more than 3/4 of the clear spacing between
bars or 1/3 the depth of the slab
• 3/4” or 1 1/2” maximum is common for most slab and structural work
• Structural lightweight aggregates are made from minerals like shale and reduce the
density of concrete by about 20%
• Vermiculite or perlite used in non structural lightweight concrete (used for insulating
roof toppings) are less dense than expanded shale
24
Q
The size of the aggregates in concrete is determiend by…
A
…the size of the forms and the spacing between the reinforcing
-in most cases, it should not be larger than 3/4 of the smallest distance between reinforcing bars or larger than 1/5 of the smallest dimension of forms, or more than 1/3 the depth of slabs
25
Methods used to specify the proportions of concrete mix:
- ratio of **cement to sand to gravel**, such as 1:2:4; amount of water also has to be specified
- specify weight of materials, including water, per 94 lbm bag of cement
- for large batch quantities, define the weight of materials needed to make up one cubic yard of conrete
26
Strength of final mix is specified by...
**the compressive strength** of concrete after it has cured and hardened for **28 days** (known as the design strength of concrete)
-typical specified design strengths are indicated as 2000 psi, 3000 psi, and 4000 psi; 12000 is available but it's more expensive
27
Admixtures...
... are ingredients _other than_ cement, aggregates, and water that are added to the mix to alter it in various ways
28
Accelerating admixtures:
cause concrete to **cure more rapidly**
29
Hydration:
**chemical reaction** between water and cement which creates **heat**
30
High range **water reducing** admixtures (_Superplasticizers_):
**Organic** compounds that transform a stiff concrete mix into one that **flows freely** into forms, used to help place concrete in challenging circumstances, or to **reduce the water content** in a mix in order to increase its strength
31
Water reducing admixtures:
Allow a **reduction in the amount of mixing water** while
retaining the same workability, results in a **higher strength** concrete
32
Retarding admixture:
**Slow curing** to allow _more time for working_ with wet concrete
help reduce the heat of hydration
33
Waterproofing admixtures:
**decrease the permeability** of the conrete
34
Fly ash:
A **fine powder** that’s a _waste product_ from coal-fired power plants, which
**increases concrete strength**, **decreases permeability**, **increase sulfate resistance**, **reduces temperature rise** during curing, **reduces mixing water**, and **improves workability**
35
Silica fume (microsilica):
A **powder** 100x finer than portland cement, a _byproduct of electronic semiconductor chip manufacturing_ that when added produces extremely **high strength** and **low permeability**
36
Blast furnace slag:
Byproduct of _iron manufacture_ that **improves workability**, **increases strength**, **reduce permeability**, **reduce temperature rise** during curing, and **improve sulfate resistance**
37
Pozzolans:
**varicose** natural/artificial material that react with calcium hydroxide in wet concrete to **form cementing** compounds
38
Workability agents
Improve the **plasticity** of wet concrete to make it easier to place in forms and finishes
39
Corrosion inhibitors:
Used to **reduce rusting of rebar** in structures that are exposed to _road deicing salts_ or other corrosion causing chemicals
40
Fibrous admixtures:
**Short fibers** of _glass or steel_ added to a concrete mix to act as **microreinforcing**
41
Freeze protection admixtures:
allow concrete to cure at temperatures as low as -6 C
42
Extend set control admixtures:
used to **delay the curing** reaction in concrete for up to 7 days.
43
Coloring agents:
**dyes and pigments** used to alter the **color** of concrete
44
True or false.
Water used to mix with concrete must be potable
True.
Mixing water for concrete must be free of harmful substances, clay, salts, etc. If it’s good
enough to drink, it’s good enough to be in concrete.
45
Self consolidating concrete (SCC)
can be placed purely by **means of its own weight** _without_ the use of _vibration_
- made posible with the use of **superplasticizer** admixture called polycarboxyplate polymer
- placement is increased, less labor required, **productivity increased**
- uniform smooth surface
46
carbon fiber conrete
Uses _epoxy coated carbon fiber mesh_ in place of standard steel meash
- carbon fiber is **less corrosive** requiring **less conrete** cover
- resulting panels require smaller foundation and support structures
- carbon fiber are bundled together to form pieces resembling yarn, called tows; tows laid perpendicular to each other, forming a grid; grid could have nearly seven times the tensile strength of standard steel mesh
47
poured gypsum deck
used for roofs and similar to conrete in that **liquid is poured on a reinforcing form board**
-Poured gypsum and concrete deck fill insulation are **economical** & applied directly to the **corrugated steel decking** and rough concrete decks, easily tapered during installation
48
**alkalinity** in concrete can cause problems in two ways
high alkalinity on the surface of a slab can damage a tile installation by causing the **adhesive to reemulsify**
also responsible for the phenomenon known as **alkali silica reaction (ASR)**; high alkaline cement begins to **dissolve sand and rock within the concrete.** this reaction produces a gel like materal that creates _pressure_ in the pores of the conrete surface
-ASR can be reduced by specyfiying aggregates not suceptible to ASR, using low lime cement, proper curing not finishing conrete with a hard trowel surface
49
What cement would be used in slip form construction
type 1
type 2
type 3
type 4
**type 3**
type 3 is high early strength --the type needed for rapid slip form construction
type 1 is normal cement
type 2 is low heat and sulfate resistant
type 4 is slow setting and low heat for massive structures
50
true or false.
the strength of concrete increases as the water cement ratio decreases
true
51
**calcium chloride** is used as an admixture for concrete in order to...
**accelerate the strengthening** of concrete
52
What is concrete mix comprised of?
+ CEMENT (PORTLAND)
+ WATER
+AGGREGATE
53
Relationship of water-cement ratio to strength & ideal range
* Compressive strength **inversely proportional** to ratio of water to cement.
* IDEAL RANGE .45-.60
54
Concrete mix contains \_\_-\_\_% aggregate.
60-80%
(Key to FR, Strength, Weight)
55
Lightweight concrete made with _______ OR \_\_\_\_\_\_\_\_\_\_\_.
Expanded shale or slate aggregate
56
5 Types of concrete
TYPE I - normal
TYPE II - moderate portland cement
TYPE III - accelerated cure (cold weather)
TYPE IV - low heat
TYPE V - sulfate resistance (salty acidic soil)
57
What kind of cement is portland cement and how is it made?
• HYDRAULIC CEMENT
1 - Burn clay & limestone in a kiln
2 - Pulverize into fine powder
58
Insulating concrete made with \_\_\_\_\_\_\_\_\_
Prelite aggregate or foam agent.
59
Size of fine & coarse aggregate.
What is the appropriate depth & thickness for a slab / walls?
FINE:
sand \< 6mm
COARSE: (Abram's Law)
must be \<1/3 slab depth
must be \<1/2 wall thickness
60
Rule of thumb for estimating depth/width of a concrete beam:
**Span / 16**
Width: **1/3 to 1/2 of beam depth** \*equal or greater than width of column
\*beam measured from top of slab
61
One-way slab
Uniform thickness, reinforced in one direction, cast with parallel supporting beams
_Short spans_ : **6'@18'**
Slab thickness: **span/30**, 4" min, roof slabs span/36
62
One-way joist slab
Joist or ribbed slab with perp beams
**Spans** : **15'@36'**
_Light to medium live loads_
Slab thickness: **span / 24**, 3" - 41/2"
Joist width 5"-9"
Reusable pans 20" or 30"
Distribution rib for spans between 20'-30'
63
Two way slab and beam
Reinforced in two directions, nearly square bays
\*usually built as flat slabs without beams
**Medium Spans** : **15'@40'** square
_Heavy live loads, high resistance to lateral forces_
Slab depth: min 4", **slab perimeter/180**
64
**Two way flat plate**
Reinforced in two or more directions, columns _without_ beams
Simple to form, low floor-to-floor height, flexibility in column placement : apartment / hotel
**Short Spans** : **12'@24'** square
_Light to moderate loads_
Slab depth: 5"-12", **span/33**
_Punching shear_ @ columns
65
Two way flat slab
Flat plate thickened at column supports (drop panels)
**Long Spans** : **20'@40'** square
_Heavy loads_
Slab depth: 6"-12", **span/36**
_Drop panels_ @ columns : 0.25xslab thickness projection, 0.33 span = width
66
Two way waffle slab
Reinforced by ribs in two directions
**Long Spans** : **24'@54'** square
_Heavy live loads_
Slab depth: 3"-4 1/2", **span/24**
Square dome forms 19" or 30" - 2' or 3' module
Solid heads at column supports
Cantilever : 1/3 span
67
What is prestressed concrete?
**Pretensioning** or **posttensioning** high-strength steel tendons to actively resist a service load.
Tensile stresses transferred to the concrete, placing entire member in _compression_
- deflect less
- carry greater load
- span greater distance
68
What is **pretensioning**?
Pretensioning is done in a precast **plant**.
**Stretch the tendont before concrete is cast**.
Member bents upwards & deflection makes it flat.
69
What is **posttensioning**?
Pretensioning is done on **site**.
**Stretch the tendont after concrete is cast**.
Member bents upwards & deflection makes it flat.
Tend to shorten over time = expansion joints required
70
What is needed on top of pre-cast slab units?
2"-3 1/2" concrete topping with steel fabric is required on top of pre-cast slabs.
71
Grids for concrete columns:
12"
16"
20"
12" - 2000 sq.ft. - 44'x44'
16" - 3000 sq.ft. - 54'x54'
20" - 4000 sq.ft. - 63'x63'
\*Note that span of floor would most likely dictate spacing
72
Minimum concrete cover to protect reinforcement from fire & corrosion
1 1/2"
73
epoxy coated reinforcing bars are used when ...
...the concrete will be exposed to cholrides (**salts**) such as deicing salts and those in sea water.
-epoxy coating helps keep that salts from corroding the steel by chemical reaction
74
Reinforcing
Is required because concrete has **no useful tensile strength**
* Steel rebar is placed where there are tensile forces in a structural member, and concrete resist the compressive forces
* Rebar is hot rolled like structural shapes, round in cross section with ribs for better bonding to concrete
* Bars are numbered based on the number of eights of an inch the bar’s diameter is (Ex: number 6 rebar is 6/8” (or 3/4”) in diameter, number 8 rebar is 8/8” or 1”)
• Structural engineer knows how to calculate the amount of rebar required
for a given cross section and can be achieve with a few big bars or many small bars
• Rebar in structures exposed to salts like seawater are prone to rust
75
two types of reinforcing steel for cast in place concrete
1 deformed bars
2 welded wire fabric
76
rebar comes in 2 common grades
**grade 40** and **grade 60**
- these numbers refer to _kips per square inch_
- **grade 60** is the type **most used** in construction
77
How to read rebar
- top symbol: producing mill
- second marking: size (given in eights of an inch)
- Third marking: Manufacturing material ( "S" for carbon-steel or "W" for low- alloy steel)
- bottom marking: Grade marking
78
how to read welded wire fabric designations
example 6 x 6 -W1.4 x 1.4 means that the grid is 6 in by 6 in and the size of the wire is 1.4 hundredths of a square
-the letter preceding the gage is either W for smooth wire or D for deformed wire
79
the designation for america standard sizes of rebar is based on...
...the number of **eights of an inch** in the nominal diameter of a bar, up to 1 inch
80
In **post tensioned** concrete construction, what does it mean to **drape reinforcing**
reinforcing is draped (curved) along the length of a beam;
after tensioning, the drape creates for structural efficiency
81
Minimum concrete coverage for reinforcement when exposed to earth?
3" min
82
The best way to stop the **migration of moisture** though a conrete slab is with a vapor barrier placed...
directly below the conrete slab and on top of any sand cushion layer or subbase.
83
vapor barrier
a thin sheet material, generally plastic, designed to prevent water vapor from passing though it.
permeance (measure of a materials resistance to water vapor transmission) **not exceeding 0.04 perm**
**10 mils** thick
perm is the passage of one grain of water vapor per hour through one square foot of material at a pressure differential of one inch of mercury between the two sides of the material
84
vapor retarder
is not vapor proof; **allows vapor to pass**
it _slows the rate_ of water vapor transmission
- is a membrane of metal foil, plastic, or treated paper placed on the **warm side of thermal insulation** to prevent water vapor from entering the insulation and condensing into liquid
- essential in colder climates to prevent moisture from accumulating within the insulation
85
Capillary break
crused stone placed over compacted subsoil and serves as a drainage layer
86
How to adequately place conrete?
If concrete slurry is _vibrated excessively_, _dropped_ from a height, or _moved too far horizontally_ in formwork its likely to **segregate**
• Aggregate works it way to the bottom of the form and water/cement to the top
• Result is non uniform and unsatisfactory, and typically has to be redone
• Segregation is prevented by **depositing fresh from the mixer** as close as possible to
the **final position**
• Should not be dropped more than **3’ - 4’**
• If it must be moved to an inaccessible location, it should be **pumped** through hoses or
conveyed in buckets
87
for concrete columns, piers, and walls, the maximum variation in plumb will be
plus ot minus 1/4 in in any 10 ft length.
-the same tolerances applies for horizontal elements
88
the maximum variation out of plumb for the total height of the structure is
1 in for interior columns
1/2 in for corner columns for buildings up to 100 ft tall
89
Ideally, concrete slabs should be allowed to cure and dry for a minimum of
**six weeks** before resilient flooring is installed
90
If too much water is placed in a concrete mix, which of the following problems might develop:
laitance
efflorescence
hydration
segregation
**laitance**
laitance is the **surface deposite of low strength material** containing cement and fine aggregates (sand) **brought to the surface** of concrete. it is caused by having to much water in the concrete mix, which results in water bleeding to the top
91
efflorescence
• Sometimes appears on the surface of a wall of brick, stone, or concrete masonry
• Consist of one or more **water soluble salts** that were originally present in the
masonry unit or in the mortar
• **Brought to the surface** and deposited there by water that seeped into the masonry,
dissolved the salts, then migrated to the surface and evaporated
• Can be avoided by choosing masonry units that are lab tested and don’t contain water soluble salts
• Will eventually diminish and disappear with time as the salt is gradually leached out of the wall
92
**expansion joints** in concrete walks should be located at a maximum spacing of
expansion joints with a joint filler are placed a maximum of **20 ft**
**control joints** placed where spearate sections of concrete are poured and in walks are placed **5 ft** apart
93
what is used to minimize **cornner chipping** of a concrete
**chamfer strips**
a chamfer strip is a small, triangular piece of material placed in the corners of forms to prevent sharp 90 corners, which are difficult to cast and have a tendency to break off during use or when the forms are removed
94
at what temperature doe workers need to to take to protect concrete when **cold weather** is predicted?
around 4 deg C
A concrete pour can proceed at temperature below 4C. However the **water and sand must be heated** to ensure that none of the constituents have frozen, and the concrete must be **heated for at least 7 days after placement**, during the early curing stage
95
during which period in the curing process does concrete gain the most compressive strength
**0 to 3 days**
- concrete gains the most compressive strength during the first few days of curing
- most critical time in curing process
- the compressive strength of concrete is always referred to as its strength 28 days after it is palced
96
chairs
small wire supports that help to keep rebar a specified distance from the outside of the concrete and help ensure adequate concrete cover
97
four primary types of **concrete joints**:
1) **control joints**: joints that allow for shrinkage of large areas, and controls and inducescracking to occur along the joint: cut to a depth of 1/4 the slab thickness; intentionally created cracks that can open to accommodate shrinkage in surfaces made of concrete masonry
2) **construction joints**: occur wherever thera are two successive pours ( a new pour against a cured section of concrete); should be located at point of minimum shear; suceptible to water leakage, thus wa waterstop should be cast into the first pour
3) **expansion joints**:joints that allow free movement of adjacent parts due to expansion or contraction of concrete. Typically waterproof, watertight, filled with an elastic filler; Required at buildings over 200’ long, at joints of building wings, and additions
4) **Isolation Joints**: joints located at slab on grade, columns, or walls to allow for independent movement
98
List the 3 most common precast concrete wall types
SOLID - 8' width typ.
(max height 7m)
COMPOSITE - Rigid Foam @ center
(max height = 7m)
RIBBED - max rib depth 305mm
(max height = 14m)
99
Autoclaved aerated conrete (AAC)
**Precast concrete** product manufactured by adding _aluminum powder_ to conrete hardening it in molds, and then curing the molds in pressurazed steam chambers (autoclaves)
- 1/5 the _density_ of regular conrete
- has _good sound control_ qualities and thermal mass
- **_not as strong_** thefore should only be limited to non load bearing application and low rise buildings
- must be _protected from weather_
100
Dimensions of three types of precast wall panels?
1. **Solid panels**:
height: 24' max, thick: 3 1/2"-10", width: 8' typ.
2. **Composite panels**:
height: 24' max, thick: 5 1/2"-12", rigid foam insulation core with wire shear ties between concrete layers
3. **Ribbed panels**:
height: 48' max, thick: 12"-24", width: 8' typ.
101
what is the primary purpose of the **voids** in a cored slab?
a. to allow electrical services to be concealed in the slab
b. to make a more efficient load carrying member
c. to make erection easier
d. to minimize weight
b. to make a more efficient load carrying member
as with any beam, the deeper the member, the more efficient the beam. using a cored slap rather than a solid slab allows **the depth to be increased without increasing the weight** in the center of the beam where it is not needed
option A and D are also correct but B is the best choice
102
Which of the following statements if FALSE?
a. type iii cememnt is often used for precast concrete members
b. precast concrete members can be a maximum of 14 ft wide
c. concrete used in precast members is typically 300 psi
d. conditions ar emosre controlled during the production of precast concrete members than they would be for similar structural systems
c. concrete used in precast members is typically 300 psi
concrete used in **precast members** is generally **higher strength mix** than the 300 psi concrete typically used for site cast applications
103
How do you make precast panels on site?
Tilt-up construction
Pour on site & lift in place.
104
Slump test
measures the **consistency** of the conrete
- conrete is placed in a 12 in high cone and compacted with a rod
- the distance the conrete slumps from the original 12 in is measured in inches
- the amount of slump depends on how the conrete will be used (typically 2-6 in)
- too much slump indicates too much water in the mix
105
cylinder test
measures **compresive** strength
- concrete is placed samples are put in cylinder molds that are 6 in diamter and 12 in high, and are moist cured and tested in the lab
- cylinders are tested at specified number of days, normally 7 - 28 days; seven days are suually about 60-70% of the 28 day strength
106
core cylinder test
- used when a portion of the structure is _placed and cured but needs to be tested_
- cylinder is drilled out of the conrete and tested in a lab to determie **compressive** strength
107
kelly ball test
- also known as the ball penetration test
- a hemispheric mass of steel with a calibrated stem is dropped onto a slab of freshly laid concrete
- the amount of penetartion of the ball into the concrete is measured and compared to one-half the values of the slump test
108
impact hammer test
- nondestructive way to test concrete strength after is has hardened
- spring loaded plunger is smalled against a conrete surface, and the _amount of rebound_ is measured.
- the rebound gives an apporoximate measure of **conrete strength**
109
k slump test
- uses a 3/4 in tube that contains a floating scale
- the tube is palced on the wet concrete and the scale is pushed into the mixture and released.
- the distance the scale floats out is read directly and is a measure of the **consitency** of the conrete, comparable to the slump
110
calcium chloride test
sometimes called the moisture dome test
- used to measure **moisture emission** from conrete
- a standard mass of calcium choloride is placed below a plastic cover and sealing it to the concrete floor
- after the 60 to 72 hours the calcium chloride is weighed and compared to its pre test weight
111
hygrometer
- sometimes called the relative humidity test
- determines the **moisture emission** by measuring the relative humidity of the atmosphere confined adjacent to the concrete floor
- a pocket of air is trapped below a vapor impermeable box and a probe in the box measures RH
- moisture sensitive flooring shouldn't be installed unless RH is 75% or less
112
polyethelene sheet test
qualitative test conducted by sealing an 18 in by 18 in sheet of plastic to the floor to trap excessive **moisture**
- after a min. of 16 hours a visual inspection of the floor and sheet is performed
- the presence of visible water indicates the concrete is insuficiently dry
113
mat test
similar to polyethelene sheet test
a 24 in x 24 in smaple of vapor retardant floor finish is applied to floor with adhesive and edges are sealed with tape
- after 72 hours, is floor is firmly bonded or difficult to remove, conrete is considered sufficiently dry
114
electrical impedance test
-uses proprietary meaters to measure **moisture** by measuring conrete conductance and capacitance
115
titration test
used to determine level of **alkalinity** in concrete
-involves grinding portions of the concrete, mixing with demineralized water and performing lab analysis to determine PH level
116
scrubbed finish
the surface of the conrete is **wetted and scrubbed** with a wire or fiber bush to remove surface mortar and expose the coarse aggregate
117
acid wash finish
the surface of the conrete is w**etted with muriatic acid** to expose and bring out the full color of the aggregate
118
water jet finish
a **high pressure water jet mixed with air** is used to remove some of the mortar and expose the aggregate
119
brush hammering
a brush hammer finish gives a **rugged, heavy texture** by removing a portion of the surface made with form liners
120
grinding
finishing technique that **smoothes out** the surface of the concrete, similar to terrazzo in appearance
121
applied finishes
appication of **other materials**, such as stucco
122
sand blasted finish
produced by **removing surface material** of conrete
-exposes the fine and course aggregate to varying degrees
123
smooth rubbed finish
concrete surface is **wetted and rubbed with carborundum brick** to produce a smooth uniform color
124
grout cleaned
**grout** is applied over concrete and smoothed out
-conceals defects
125
float finish
- **sandpaper** like texture
- appropriate of exterior surfaces
126
light steel troweled finish
achieved by using a **steel trowel** several hours after floating
127
hard steel troweled finish
continues the consolidation of the conrete and **greatly densifies the top 1/8 in**, making a very smooth surface
128
broom finish
- achieved by **running a broom** over the surface of the conrete
- process dislodges fine aggregate and produces slip resistant surface on outdoor slabs
129
super flat floor finish
- **hard steel trowl finish**
- used in **industrial warehouses** where forklift vehicles are used
- vehicles must travel on very smooth and level floors.
130
temperature sensitive materials, such as sealants should not be applied when the temperature dips below..
...4 C deg
