CE 324 Exam 2

Chemical Admixture

A material other than water, cement, aggregate, SCM's, and fiber reinforcement that is added before or during mixing to modify the properties of the fresh mix, setting, or hardening og the mix.

Plasticizer

A water reducing admixture that increases the slump of a material without increasing the water content. makes it easier to place without affecting the strength and durability.

water reducer

maintains the slump while reducing the water content. reduces w/cm which leads to increased strength and durability.

Type A

Water-reducing admixture that typically produces a 5-10% water reduction. can be used alone or in combination with high-range wr.

Type B

A retarding admixture. causes a decrease in the rate of hydration so it lengthens the time of setting. typically used in hot weather to give longer haul times and keep concrete workable while placing

Type C

An accelerating admixture that increases the rate of hydration. typically used in cold weather or to generate early strength in a repair.

Type D

Water-reducing and retarding admixture.

Type E

Water-reducing and accelerating admixture

Type F

High range water-reducing admixture. 12-30% water reduction, commonly a polycarboxylate, key component of self-consolidating concrete

Type G

High-range water reducing and retarding admixture, similar to type F

Water reducing admixture

type A, D, and E. typical water reduction of 5-10%

Mid-range water reducing admixture

No ASTM classification. typically meets type A and D requirements with a typical water reduction of 6-12%

High-range water reducing admixture

Types F or G. Has a typical water reduction of 12-30%, commonly made of polycarboxylates. Key component of self-reducing concrete but can be used across a range of concretes.

Flocculation

The formations of flocs by the clumping of fine particles

Deflocculation

Dispersion of the flocs to form a stable colloid

Electrostatic dispersion

A polar chain with an anionic hydrophilic head selectively absorbs onto a cement particle and the anionic heads repel the other anionic heads, forming a colloid

Self-Consolidating concrete

Fresh concrete that can flow around reinforcement and consolidate under its own weight without use of vibration

Set Retarding Admixture

An admixture that decreases the rate of hydration and increases the setting time. typically used in warmer weather to increase haul time and workability over time (approximately >80 degrees)

Set Accelerating Admixture

An admixture that increases the rate of hydration and decreases the setting time. typically used in colder climates or in repairs for quick early strength (approximately <50 degrees)

Temperature effect on set time

As the temperature decreases the set time increases. at 20 F the concrete will freeze before it sets.

Phases of Hydration

Induction/Dormant Period
Setting Period
Hardening period

Rigidity increases over time

Induction/Dormant Period

This is when the concrete is workable and has low rigidity. This phases lasts until the initial set

Setting Period

This is when the concretes rigidity begins to sharply increase. Lasts from initial set to final set

Hardening Phase

Starts at final set then continues over time. Rigidity sharply increases and it reaches the beginning of mechanical strength.

Initial set

The time at from which water is added until the paste ceases to be fluid and plastic. mild indentations can still appear

Final Set

Time from moment water is added to where the paste has a certain degree of hardness and no more modifications can be made to the surface.

Effects of temperature on strength gain

At higher temperatures the hydration rate increases and more precipitates are formed (?)

Air-Entraining Admixture

An admixture that causes the development of microscopic materials in mixtures during mixing that increases workability and resistance to freezing and thawing. Required where there are freeze-thaw cycles and especially if exposed to de-icing salts

How Air-Entraining Works

Air bubbles provide space for water as it freezes (water expands) which relieves hydrostatic pressure in the concrete. Air is generated during the mixing process but the high surface tension of water and coalescing bubbles form large voids which are removed during compaction. The admixture reduce the aur water surface tension through an anionic surfactant. Bubbles of air attract the hydrophobic tails of surfactants so the hydrophilic head is oriented toward the water.

Spacing Factor L

The maximum distance of any point in the paste from the periphery of an air void. A L < 0.008" gives good frost resistance.

Specific Surface

The total surface area of all air voids with a volume > 1mm^3

Steel Passivity

Concrete has a pH>13.2 so a passive layer of rust (?) forms on rebar in concrete.

Steel Corrosion

If concrete has a high pH steel is protected from corrosion forever. Chlorides or CO2 penetrating the cover of the concrete will cause corrosion.

Corrosion prevention

Corrosion is prevented with membranes or sealers, low-permeability concrete, coating the steel, or using chemical corrosion inhibitors

Alkali-Silica Reaction (ASR)

The alkalis (Na, K, OH) from the cement react with unstable SiO2 in aggregate and an alkali-silica gel is produced that absorbs the water from the surrounding paste and expands, causing the concrete to crack. Needs reactive silica, sufficient alkali, and sufficient moisture to happen. Having a pH>13.2 makes steel passive but also makes reactive aggregates dissolve forming the ASR gel

Sulfate Attack

Occurs when sulfates in surrounding soil or groundwater penetrates the concrete to attack the cement hydrates (specifically C3A) which deteriorates the cement matrix

Preventing Sulfate Attacks

Using certain fly ashes can help protect, as well as reducing W/CM.

Outer Bark

Outermost layer of the tree

Inner bark

Softer bark layer before the cambium

Cambium

Forms new wood; growing part of the trunk

Sap Wood

Conducts the moisture, minerals, oxygen, and nitrogen

Heart Wood

Dead Cells around the pith of the tree

Pith

Central collection of cells that accesses the root system (?)

Softwood

Typically from gymnosperm trees that have needles and produce cones (Evergreen). Seeds are uncoated and dropped to ground. Typically conifers such as cedar, juniper, pine, spruce etc.. 80% of timber comes from softwood

Hardwood

From angiosperm (deciduous) trees and are usually broad leaved. Seeds have a coating, sometimes a fruit or a shell. Typicallt alder, balsa, beech, mahogany, hickory, oak etc.. More likely to be used in furniture, decks, flooring and is much more fire resistant

Hardwood vs. Softwood composition

Softwood has many more vertical cells closer together while hardwood has fewer that are farther apart. Hardwood has more visible pores and a much higher solids content so it is more durable. Porosity and strength are inverses.

Anisotropic

Wood is anisotropic with different properties in each direction; longitudinal, radial, and tangential

Longitudinal

Parallel to the grain (upward, z) is the strongest direction with the least shrinkage

Radial

Perpendicular to the grain directed outward

tangential

tangent to the growth rings; weakest with the most shrinkage

FSP

Fiber saturation point. Zero shrinkage past this point

Shrinkage

as wood shrinks the distance from solid to solid decreases so the hydrogen bonds become stronger which makes the wood stronger

Cellulose

Polymer that forms the strands that make up cell walls; crystalline

Lignin

Glue that is amorphous and 3-D

Center-Point Bend Test

Wood cracks in compression on top first since the tensile strength is much less than tensile. As the neutral axis moves down the ultimate failure eventually occurs in the section in tension at the bottom of the beam

Stress vs. Strain of wood

the modulus of elasticity is 1-2E6 psi for compression parallel to the grain. The graph is linear to proportional limit then has a small non-linear curve

Wood vs. Timber

Wood is small individual specimens with no defects. Timber is sawn structural members that can have defects

Engineered Wood Products

Made by bonding together wood strands or forms of fibers to produce large units. Can significantly reduce anisotropy. Easier to manufacture and minimizes defects

Particle Board

Formed by gluing sawdust sized particles together with resin

Chip Board

Randomly oriented wood chips glued together by resin

Oriented Strand Board

Specifically oriented wood chips and strands glued together with resin

Plywood

Thin sheets (piles) that are glued together with the grains at right angles to each other so it has same properties in both directions.

Laminated Wood

Piles are glued together with the grains in parallel directions

Mass Timber

Can be cross laminated, glue laminated, dowel laminated, or nail laminated.

IBC

As of 2018 buildings could be up to 18 stories (?)

Asphalt

Created during the distillation of crude petroleum (residue)

Asphaltenes

Dark brown friable (solids that breaks down under duress or contact) solids that are responsible for viscosity and adhesive properties

Maltenes

Resins that help to disperse the asphaltenes in oils (clear or white liquids)

Asphalt Cements

A refinery produced material that is usually hot

Cutbacks

Asphalt cut with petroleum solvents

Emulsions

Mixture of asphalt cement, water, and an emulsifying agent

Hot Mix Asphalt conrete

Asphalt cement and aggregates are mixed between 275F and 325F that is transported at a high temperature and solidifies as it cools. Opens to traffic much faster than cement

Aggregate in Asphalt

Asphalt is typically 95% aggregate and it must be well packed to minimize the binder content. Also must have crushed faces to bond with the asphalt

Asphalt Aging

Reacts with oxygen and hardens, can rack due to volatile compounds during the construction process, or over long term use. Can also crack due to fatigue and low temperatures

Asphalt Compaction

Done to reduce further compaction, provide shear strength and resistance to rutting, ensure waterproof mixture, and prevent excessive oxidization

Rapid Cure

Gasoline is used in cutbacks for rapid curing but it is highly volatile. Typically used for surface treatments and tack coats.

Medium Cure

Kerosene is used for medium cure for moderate volatility Used for stockpile patching mix

Slow Cure

Uses a low viscosity oil for low volatility and acts as a prime coat for dust control

Emulsions

Emulsifier gives a surface charge to the asphalt droplets in the water medium. Anionic means alkaline which is good with limestones. Cationic is an acid and good with silica gravel

Chip Seals

When asphalt binder is placed on pavement which is then covered with aggregate chips and rolled over to embed the aggregate into the binder.

Permeable Friction Course

Open or gap-graded aggregate with 10-15% more voids than a typical impermeable base. Reduces risk of hydroplaning and pavement noise while increasing night visibility and friction on the surface. Also makes clean runoff water.

Production of Steel

Iron ore is reduced to pig iron which is then refined through oxidation to remove excess carbon, then deoxidized with aluminum and other minerals. The steel is cast into ingots that can be re-melted and re-shaped

Phase

When a material has the same structure of atomic arrangement, composition, and properties throughout. Typically refers to solid and liquid.

Component

A distinct chemical substance from which a phase is formed. Water can form 2 phases ice and water (solid and liquid)

Heat Treatment of Steel

Refines grain structure, removes gases and internal stresses, and changes electrical and magnetic properties. 4 types; annealing, normalizing, hardening, and tempering.

Annealing

Heating steel then slowly cooling to room temperature; steel gets softer and more ductile so toughness increases.

Normalizing

Steel is heated higher than annealing and then air cooled; gains a uniform, fine-grained structure that provides high fracture toughness. more so a corrective process than strengthening or hardening

Hardening

Heated high then rapidly cooled through quenching; the steel is harder and more brittle and must be tempered afterward

Tempering

Reheating steel to a lower temperature then quenching; increases ductility and toughness after both effects were hardened.

Steel Alloys

Steel + Alloying metal to change a physical property. Construction steels are low and medium carbon plain steels

Structural Steel

Hot rolled shapes used in construction; graded by mechanical properties (tensile strength, yield strength, and percent elongation) and chemical composition (percent carbon and limits of other chemicals)

Cold Forming

Results in plastic deformation that causes strain hardening which increases yield strength (50-70%), tensile strength(20-30%), and hardness while reducing ductility