Materials and Assemblies for the Envelope Flashcards
What are two most common types of soil tests for bearing capacity?
- borings
2. test pits
What is the most common type of borehole test?
Standard Penetration Test = A type of borehole test that measures the density of granular soils and some clays.
A 2 in. diam. sampler is driven into the bottom of the borehole by a 140 lbm hammer falling 30 in. The number of blows (N) is recorded to drive the cylinder 12 in. Samples are tested in the lab.
What are Test pits?
A type of soil test that uses trenches dug on site to allow visual inspection of the soil strata and direct collection of undisturbed samples. Practical limit on depth is 10 ft
What are wash borings?
A type of soil test in which samples are gathered via 2 in to 4 in pipe through which water jet is forced to push up soil. Most useful for soils too hard for an auger test. Can extend to 100 ft or more.
What are auger borings?
A type of soil test in which an auger is used to pull up soil samples. Best used in sand or clay for shallow or intermediate depths since the auger cannot penetrate hard obstructions like bedrock or hardpan soil.
What are soil load tests?
a platform is built on site and incremental loads are placed on it. The amount of settlement during a given period is observed until settlement becomes regular after repeated loading.
What is a Karst?
Karst = landscape in which soluble rocks such as limestone, dolomite, and gypsum have dissolved and formed caves/voids below the surface, which can cause sinkholes.
What are 8 methods to increase bearing capacity and/or decrease settlement of the soil?
- Drainage
- Fill
- Proctor test
- Compaction
- Densification
- Surcharging
- Mixing
- Geotextiles
How can drainage help to increase bearing capacity and/or decrease settlement of the soil?
draining water from soil can increase soil strength and prevent hydrostatic pressure
How can fill help to increase bearing capacity and/or decrease settlement of the soil?
removing poor soil and replacing with fill. Fill needs to be compacted
How can a Proctor test help to increase bearing capacity and/or decrease settlement of the soil?
determines standards for compaction
How can compaction help to increase bearing capacity and/or decrease settlement of the soil?
compacting existing soil makes it stronger
How can densification help to increase bearing capacity and/or decrease settlement of the soil?
type of on-site compaction involving vibration, dropping heavy weights, pounding piles into the ground and filling voids with sand.
How can surcharging help to increase bearing capacity and/or decrease settlement of the soil?
preloading the ground with fill material to cause consolidation and settlement before building. Often costly and takes time.
How can mixing help to increase bearing capacity and/or decrease settlement of the soil?
mixing a layer of sand or gravel with existing less stable soil.
How can geotextiles help to increase bearing capacity and/or decrease settlement of the soil?
used to stabilize engineered fill below footings, stabilizing marginal soils under paving, and erosion control
Where should building footings be located in relation to the frost line?
footings should be located below the frost line to prevent the structure from lifting up.
When should you use a mat slab (raft) foundation?
when soil bearing is low or where loads are heavy in relation to soil pressures.
When should you use pile footings?
When soil near grade level is unsuitable for spread footings. They transmit building loads through the unsuitable soil to a more secure bearing with end bearing or side friction.
When should you use grade beam foundation?
Where expansive soils or clay (such as bentonite) are encountered near the surface
What is the difference between a pile and a pier?
pile = timber, steel, or precast concrete that are driven into the ground with hammers piers = drilled hole that is filled with concrete
What is grading? What is the difference between rough grading and finish grading?
Grading = the modification of contours of the site according to the grading plane.
Rough grading = the moving of soil prior to construction to approximate levels of final grades. Also includes adding or removing soil after construction to the approximate final grades, within 6”-12”.
Finish grading = the final moving of soil prior to landscaping or paving, where level of earth is brought to within 1” of desired grades
What are two common methods of excavation if excavation is too deep for a slope cut? What is the main difference between the two?
- shoring (soldier piles)
- braced excavation
Shoring with soldier piles uses wide flange and breast boards to hold up the earth. The wales are reinforced with tiebacks into the earth.
Braced excavation uses wood or steel sheathing to hold up the earth. The wales are reinforced with diagonal rakers that are anchored to the bottom of excavation.
What is underpinning?
a method to temporarily support existing foundations while they are being repaired or strengthened or when they are being extended to a lower level. Uses needle beams supported by adjacent grade and hydraulic jacks to support the building.
What is the most common forming material for cast in place concrete?
plywood
What are alternate forming materials for plywood for cast in place concrete?
prefabricated steel forms - strength and reusability. Good for one-way joist systems, waffle slabs, and other special shapes
glass-fiber-reinforced plastic, etc - can be manufactured with patterns embedded within.
What is slip forming?
A type of concrete formwork that moves as the concrete cures. It is used to form continuous surfaces (tunnels or high rise building cores).
What are flying forms?
A type of concrete formwork made from large fabricated sections of formwork that are removed once the concrete has cured and reused in forming an identical section above. Used in buildings with highly respective units (hotels or restaurants).
What are insulating concrete forms (ICFs)? What is their main benefit? Where are they commonly used?
Insulating concrete forms (ICFs): polystyrene foam forms that provide the formwork for poured concrete and remain in place after the concrete cures.
They speed construction and provide insulation in one operation.
Often used in single family residential and small commercial. Can be used for the basement portion of the building only, or up to 2 stories above grade.
What are three basic varieties of ICF systems?
Blocks = foam blocks the size of concrete blocks
Panels = flat foam panels 4 ft x 12 ft
Plank systems = flat forms 12 in. high and from 4 ft to 8 ft long
What is one of the biggest expense for CIP concrete?
the formwork
What is the construction tolerance for columns, piers, walls?
1/4” in any 10’ length
What is the construction tolerance for ceilings, beam soffits, and slab soffits?
1/4” in any 10’ length
What is the construction tolerance for elevated, formed slabs?
3/4”
What are 2 methods to implement if hydrostatic pressure is an issue?
Place a layer of gravel against the wall
Place a geotextile material against the wall
Where should the vapor barrier be placed in a slab on grade assembly? why?
Below the slab and on top of the sand/gravel cushion layer/subbase. To avoid moisture migration through slabs on grade.
When should you specify low water-cementitious materials ratio (w/cm ratio)?
to reduce water problems inside the building.
What is the min and max w/cm ratio?
Min w/cm ratio = 0.30 to 0.35 (to produce workable mix)
Max w/cm ratio = 0.45 to 0.50 (to avoid being watery)
For how long should concrete slabs dry/cure before sealants or resilient flooring is installed?
min six weeks
What will occur in cement if too much water is added?
laitance = chaulky surface deposit of low-strength concrete. Must be removed if new concrete is to be poured on top of it.
when can you use a w/cm ratio of 0.25?
w/cm ratio of 0.25 is used where high strength is required, but it must be with a superplasticizer to make the mix workable
when can you use a w/cm ratio of 0.55?
w/cm ratio of 0.55 is workable for common residential walks and driveways
What 4 types of rebar should you use if corrosion presents a problem, such as in highways or high voltage transformer vaults?
- Stainless steel = use in conditions of extreme corrosion resistance or nonmagnetic characteristics are needed. High cost
- Galvanized steel
- Epoxy-coated rebar = use where corrosion presents a problem (road, parking, marine). Less expensive than stainless steel.
- Glass-fiber-reinforced polymer rebar (GFRP) = use where corrosion is present or nonferrous reinforcement is needed. Cannot be used in primary structural members since it has different properties than steel.
What are the 3 ingredients in concrete?
cement
fine and course aggregates
water
What will be the result of too much water in concrete mix?
it will decrease the concrete’s strength. excess water remains in the paste and forms pores that cannot resist compressive forces.
What are the 5 types of cement?
Type I = standard / normal cement
Type II = modified cement
Type III = high-early-strength cement = sets quickly with higher heat hydration (good for cold-weather)
Type IV = low-heat cement = very slow setting, not commonly used
Type V = sulfate-resisting cement = used for structures that will be exposed to water or soil with high alkaline content
What is welded wire fabric? When should you use it for reinforcement?
cold-drawn steel wires set at right angles and welded at intersections. Use for temperature reinforcement in slabs.
What percentage of concrete mix is aggregate? What is the goal for deciding how much aggregate to use?
65-75%
Goal is use min amount of cement (because it’s expensive) with a combination of aggregates sizes that fill the most of the volume and still achieve the desired strength
What are aggregates typ made of?
Aggregates are usually made of sand and gravel, but may also include expanded clays, slags, and shales in lightweight structural concrete
How much does standard concrete weight in lbm/ft3? Lightweight concrete?
150 lbm/ft3
50 lbm/ft3
What are the 5 factors that determining proportions in a concrete mix?
Strength Workability Durability Economy Sustainability
What is the design strength of concrete?
Design strength = Strength of concrete is specified by its compressive strength after it has hardened/cured for 28 days
What are 4 typical design strengths?
2000 psi
3000 psi (most common)
4000 psi
12,000 psi available for special applications
What are admixtures?
= chemicals added to concrete to impart certain qualities
Air-entraining agent
an admixture that increases workability and durability of the concrete, and improves its resistant to freezing and thawing cycles
Accelerator
an admixture that speeds up hydration of the cement so that the concrete achieves strength faster. Allows faster construction and reduces the length of time needed for protection in cold weather.
Plasticizer
an admixture that allows for higher-strength concrete by reducing the amount of water needed while maintaining the needed consistency
Retarder
an admixture that slows down the setting time to help reduce the heat of hydration. Counteracts the accelerating effect of hot weather on concrete setting.
Waterproofing agent
an admixture that decreases the permeability of the concrete
What are Supplementary cementitious materials (SCMs)?
added to concrete as part of total cementitious system and also impart desirable qualities to the mix
Fly ash
a supplementary cementitious materials (SCMs) that improves workability, reduces temperature rise, reduces quantity of total cement needed, minimizes bleeding, reduces permeability, inhibits alkali-silica reaction (ASR), and enhances sulfate resistance.
Ground-granulated blast-furnace slac (GGBFS)
a supplementary cementitious materials (SCMs) that is substituted for portland cement in different ratios. Good for large pours in hot weather.
What are 4 attributes of Ground-granulated blast-furnace slac (GGBFS)?
- Improves workability
- Decreases need for water
- Increases setting time of concrete
- Slower setting time – continues to gain strength after 28 days and ultimately has higher compression strength than portland cement concrete
Silica fume
a supplementary cementitious materials (SCMs) that:
- Decreases permeability
- Increases compressive strength
- Improves abrasion resistance
- Reduces bleeding
Pozzolan
a supplementary cementitious materials (SCMs) that is used as partial replacement for portland cement:
- Decreases permeability
- Increase strength
- Improve resistant to ASR and sulfate attack
- Can be made from shale, clay, volcanic ash
What are autoclave aerated concrete precast concrete blocks?
Sustainable alternative to concrete in nonbearing walls and low rise structures
- 10 in. tall x 25 in. long and thicknesses 4 in, 8 in, 10 in, made with aluminum powder
- 1/5th density of conventional concrete
What is self-consolidating concrete (SCC)?
A concrete product in which no vibration needed, can be used with a superplasticizer admixture
- Finishes faster, requires less labor, and increases productivity
- Used for cast-in-place conditions
What is Carbon fiber concrete?
A concrete product that uses epoxy-covered carbon fiber mesh instead of standard steel mesh for secondary steel reinforcement.
- Used to make precast concrete panels thinner and lighter
- Require smaller foundations
- Reduces transportation costs
- Speeds erection process
What is ultra high performance concrete?
A concrete product that is high strength, low water absorption, and high resistant to chemical degradation
- Compressive strength = 17,500 psi to 25,000 psi
- Cement, sand, water, silica fume, plasticizers, and alkali resistant glass fibers or steel fibers
- Typically precast
What is the slump test?
Measures the consistency of concrete
- On-site test that poures concrete into a cone shaped form, removes the form, and measures how much the concrete slumps in inches.
- 2”-6” of slump is ideal.
- Too much slump = excessive water in the mix
- Too little slump = mixture will be difficult to place properly
What is a K-slump test?
measures consistency of concrete
Similar measure to traditional slump test, but with tube containing a floating scale on poured concrete
What happens if concrete dries/cures too fast?
It can lose up to 35% or more of its strength
What is heat of hydration?
the heat that concrete produces while it cures.
What is the Kelly ball test or ball penetration test?
measures consistency of concrete
a steel ball is drop onto a slab of freshly laid concrete.
Amount of penetration of ball is measured and compared to 1/2 of the values of the slump test
What is the Cylinder test?
measures compressive strength
as concrete is placed, samples are put in a cylinder mold and tested in the laboratory.
What is the Core cylinder test?
= used when the structure is in place and cured but needs to be tested
Cylinder is drilled out of concrete and tested in the lab
What is the Impact hammer test?
Tests concrete strength after it has hardened. An on-site, nondestructive test that measures strength through rebound of hammer.
When should testing concrete for moisture content and alkalinity be done?
before flooring can be laid on top of concrete