Materials Midterm

Sources of aggregate

natural sand and gravel pits, river rock, quarries

for normal weight concrete

Use normal weight aggregate (manufactured material like steel mill slag - can be a radiation shield or used for sound reduction)

for light weight concrete

use light weight concrete (manufactured material like styrofoam - can be used for insulation)

sand

fine aggregate

gravel

coarse aggregate

Igneous Rock

one time molten and cooled into present form (varying texture, can be glass-like)

Sedimentary Rock

Bedrock sediment deposited by winds, water, glaciers, or remains of sea creatures (deposited at base of ancient seas and lakes

metamorphic rock

sedimentary rock transformed by heat and/or intense pressure

physical, mechanical, and chemical properties of rock

expanded upon by mineralogical examination

Trusted, local suppliers

have a historical performance of providing accurate information. Use them for you materials.

aggregate uses under foundations and pavements

used for stability and drainage (protects structure from frost damage)

Rounded and smooth aggregate

makes concrete more workable

Aggregate acts as a filler in Portland Cement Concrete

more aggregate makes cheaper, higher quality concrete (less paste is required)

Asphalt

Use rough and angular aggregate that fits together to create smooth roads

Load on concrete

cement and aggregate takes the load

load on asphalt

only aggregate takes the load, it is plastic and squishes

Coarse aggregate, or gravel

aggregate retained on a sieve with 4.75mm openings (#4 sieve)

fine aggregate, or sand

aggregate passing through a sieve with 4.75mm opening (#4 seive)

#4 sieve

sieve with 4 openings per linear inch

maximum aggregate size

the largest sieve that allows ALL of the aggregate to pass

nominal maximum

the first sieve to retain some aggregate (less than 10%)

Larger sieves

used for coarse aggregate, designated in inches (3”, 2.5”, 2”, 1.5”, 1”, .75”, .5” 3/8”, 1/4”

Smaller sieves

used for fine aggregate, designated by number (No. 4 No. 10 No. 20 No. 30 No. 40 No. 50 No. 60 No. 100 No. 200)

ASTM

American Society of Testing Materials (published new standards every 5 years)

Aggregate Properties to notes

moisture states, specific gravity, gradation

concrete compressive strength decrease

too much water in concrete mix

high friction aggregate

angular, rough used for strength and stability of asphalt

low friction aggregate

rounded and smooth used for workability of concrete

flaky and elongated aggregate

BAD because of easy breakage and difficulty compacting

Weathering

water expands when freezes, so water in aggregate expands when it freezes and breaks the aggregate

Dry moisture state of aggregate

dried in an oven until mass in consistent (no water present)

Air Dry moisture state of Aggregate

surface voids are full of water

Saturated Surface Dry (SSD) Condition of Aggregate

permeable voids are filled with water but surface voids are dry (assumed state of aggregate in concrete mix)

Moist moisture condition of aggregate

free water on surface of aggregate (in a puddle of water)

why is too much water in concrete mix bad?

It decreases the strength of the concrete because once it evaporates from the concrete mix it leaves many voids, or failure points

absorption

moisture content in SSD condition (weight of water over weight of solid)*100

free moisture

moisture in excess of SSD condition

negative free moisture

aggregate absorbs water to fill voids (water should be quantified)

positive free moisture

aggregates give water to cement past, but keep voids filled

consolidation

shake or vibrate concrete so aggregate won’t sink to the bottom

weight of aggregate

weight of solids + weight of voids

unit weight of water

62.4 lb/ft³

specific gravity

ratio of the mass to volume of an object to the mass to volume of water at the same temperature (Ms/V)/(Mw/V)

bulk specific gravity of aggregate

uses the weight of solid materials and includes all voids (permeable and exterior) (think fill bucket and there were gaps between aggregate in bucket)

apparent specific gravity

less than bulk specific gravity, uses only dry solids and does not include the exterior voids of aggregate

Bulk SSD

all surface voids are filled with water

bulk unit weight of an aggregate

the weight of aggregate required to fill a “unit volume”

percent voids

100 - (bulk unit weight/(bulk specific gravity * water unit weight) *100)

Gradation

the size distribution of particles in aggregate

Fines (not fine aggregate)

particles finer than the No. 200 sieve (silts and clays) (pass through the 200)

sieve analysis

used to evaluate the gradation of an aggregate sample.

Well-graded (high density gradation)

soil grains are equally distributed over a wide range of sizes… less cement is needed

poorly graded (uniformly graded)

most of the soil particles are the same size (nearly vertical gradation curve

gap graded

certain particles sizes are missing (especially middle sizes) (missing smaller aggregate particle sizes that fill in the voids between large aggregate particles)

fineness modulus (of sand)

a measure of the relative fineness or coarseness of a fine aggregate sample (range of 2.3-3.1)

silica

in some aggregate reacts with the alkalis in portland cement

Carbonates

in aggregate can react to the alkalis in Portland cement as well

control joint

control cracking

expansion joint

used to account for masonry expanding over time

PC

Portland Cement

Portland Cement is named after

the limestone and chalk cliffs on the isle of Portland, where it was first made in the early 1800s. All cement in construction is assumed to be portland cement

Cement past

cement + water (the lubricant in concrete)

mortar

cement, water, and sand

concrete

cement, water, sand (fine aggregate), and gravel (coarse aggregate)

Cement specific gravity

3.15

weight

what cement is ordered and measured by (because volume of cement will shrink and consolidate over time)

Raw materials present in cement

Calcium Oxide (limestone, chalk, oyster shells) and Silica and Alumina (clay, shale, blast furnace slag)

Cement clinker

the heating and melting at a high temperature of raw materials in cement

Gypsum

delays set time

tricalcium silicate (C3S) and dicalcium silicate (C2S)

main chemical compounds in PC

Alkalis (Na2), K2O)

minor compound in PC… reacts with silica causing disintegration and expansion of concrete

Cement Fineness

controls rate of hydration (smaller particles have more surface area to react with water)

exothermic reaction

cement curing (releases heat)

Hydration

chemical reaction of cement with water

hardening

happens over time

drying

evaporation = no water

C-S-H

calcium-silicate-hydrate (produced from hydrating C2S and C3S). It is the primary chemical reaction that hardens cement paste, the “velcrow”

final set of concrete

harden after 28 days

timeline for concrete in field

initial set, final set (broom, trowel, cure), strength gain

low water over cement ratio

high compressive strength

trapped voids

large air pockets that can be consolidated via vibration table (decrease strength, increase permeability)

entrained air

microscopic bubbles added to concrete mixture, increases permeability, decreases strength, increases durability (prevents cracks due to thermal expansion)

concrete setting

stiffening or change from plastic to solid state

hardening

strength gain of cement paste over time

soundness

ability for concrete to retain its volume after setting

Typical w/c ratio for PC

between 0.4 and 0.7

w/c ratio

water over cement ratio, the most important property of hydrating cement

Extra Water

increases:

• workability

• permeability

decreases:

• strength

• durability

• bonds

Type I PC

Normal

Type II Portland Cement

Moderate Sulfate Resistance

Type III Portland Cement

High Early Strength (finer, faster reaction, common and cheap)

Type IV PC

Low Heat of Hydration (for large, massive pours to control heat released during hydration)

Type V PC

High sulfate resistance

allowable mixing water

drinking water, sea water, stabilized concrete wash water

Prevented concrete wash water disposal areas

dumping at jobsite, dumping at landfill, dumping into ready mix at plant

admixtures for concrete

used to improve properties of fresh and hardened concrete

water reducers

increase mobility of cement, but still have high compressive strength

Slump

measure between top of cone mold and resulting top of concrete when cone is removed

Retarders

delay initial set (increase set time) good for long commutes

stabilizer

stops hydration for up to 72 hours