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108 Cards in this Set
- Front
- Back
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Lime (CaO)
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60-65%, Calcite, limestone, shale
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Silica (SiO2)
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10-25%, Clay, sand, shale
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Alumina (Al2O3)
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5-10%, Aluminum ore refuse, clay, fly ash, shale
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Iron Oxide (Fe2O3)
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2-4%, Iron ore, clay, mill scale
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Point of incipient fusion
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clinkering temperature
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clinker
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raw ingredients are recombined to form basic chemical components of Portland cement
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final grinding
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clinker is ground with 2-3% gypsum
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gypsum
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controls set time of portland cement when added to water
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cement distribution
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rail, barge, truck, bag
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1 barrel = 4 bags =
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376 lbs
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1 bag = 94 lbs
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1 bulk cubic foot of cement
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4 basic compounds produced in kiln
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tricalcium silicate
dicalcium silicate tricalcium aluminate tetracalcium aluminoferrite |
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tricalcium silicate
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hardens rapidly
responsible for early set and initial strength |
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dicalcium silicate
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Hardens slowly
Responsible for strength beyond one week of curing |
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Tricalcium Aluminate
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First compound to hydrate
Strength in first few days of curing High heat generation reactive with soils and sulfates found in seawater |
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Tetracalcium Aluminoferrite
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Assists in manufacturing process by allowing lower clinkering temp.
hydrates rapidly doesn't affect strength |
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Type 1 (normal)
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general construction
not sulfate resistant too much heat generated for mass pours |
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Type II (moderate/modified heat)
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Moderate sulfate resistant
Lower heat of hydration than Type 1 Used in mass pours Warm weather concreting |
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Type III (High early strength)
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heat of hydration not critical
forms need to be stripped quickly cold weather concreting |
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Type IV (Low heat)
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Slow strength gain
large mass pours -thermal gradient needs to be controlled -large thermal gradients cause large thermal stresses and loss of strength |
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Type V (sulfate resistant)
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high sulfate concentration
-seawater and groundwater |
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White cement
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negligible amounts of iron and manganese oxide
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Fineness
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Measured by specific surface (blaine air-permeability test)
300-500 Fine grinding = higher heat of hydration = accelerate strength gain Acceleration occurs more quickly |
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Soundness
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ability to retain volume after setting
Unsoundness caused by excessive amounts of free lime or magnesium |
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Consistency
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ability to flow (workability)
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Paste
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water + cement
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Mortar
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water + cement + sand
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Setting time
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indication of normal hydration
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setting time is regulated by
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gypsum
fineness w/c ratio admixtures |
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False set
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significant loss of plasticity without much evolution of heat shortly after mixing
problem when placing fixed by remixing |
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compressive strength
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2-inch mortar cubes
prescribed curing procedure influenced by cement type does not predict concrete strength |
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Heat of hydration
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controlled by tricalcium aluminate (C3A) and Tricalcium silicate (C3S)
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loss of ignition
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pre-hydration and carbonation
cement heated to 900 to 1000 C |
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Specific Gravity
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3.15
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Impurities - carbonates and bicarbonates
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setting time (accelerate or retard)
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Impurities - calcium chloride
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accelerate (up to 2% by weight of cement
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Impurities - salts of magnesium, tin, zinc, copper, and lead
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variable set times
loss of strength |
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Impurities - sodium iodate, phosphate, arsenate, sulfide
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retarder
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Impurities - Sugar
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.03 to .15% retarder
20-25% accelerant > 25% rapid set and strength loss |
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Impurities - Clay or fines
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Can be tolerated up to 2,000 ppm without affecting strength
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Impurities - Mineral oils
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>2% = strength loss of more than 20%
vegetable and animal oils have greater of an effect |
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Impurities - organics
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strength loss and excessive air entrainment
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flat/elongated aggregate
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less than 15%
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rounded aggregate
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reduce mixing water by 15lb/cy
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Freeze/thaw resistance affected by
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porosity
absorption Pore structure |
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fineness modulus
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sum of cumulative percent retained on sieves divided by 100
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higher FM
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coarser aggregate
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fine aggregate FM
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2.3 < FM < 3.1
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harsh sands
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unworkable mixes
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very fine sands
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uneconomical mixes
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smooth grading curves
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better mixes
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larger aggregates
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less water required
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bulk unit weight
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weight of aggregate per unit volume
-includes volume of aggregate and voids |
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Specific gravity
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SSD: characterizes volume of pores filled with cement and water
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air entrainers
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keep air bubbles suspended, reduce surface tension, prevents connectivity of air bubbles that would allow water to enter deeper into the concrete
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water reducers
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reduce required amount of mixing water to produce certain slump
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reduce w/c ratio
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minimize drying shrinkage cracking
less water = less volume change |
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standard water reduction
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5-7%
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moderate water reduction
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7-12%
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High water reduction
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12-30%
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lignosulfates
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water reducer, byproduct of wood pulping processes
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retarders
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offset accelerating effect of hot weather
control initial set for difficult work (pumping, large piers) Delay set for special finish processes |
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side-effects of retarders
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act as water reducers and entrain air in concrete
some reduction in compressive strength |
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accelerants
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high early strength
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can accomplish high early strength by
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adding accelerant
using type III cement reducing w/c ratio by adding 100-200 lbs of additional cement/cy curing at higher temperatures |
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most common accelerant
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calcium chloride
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calcium chloride
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added in solution form in the mix water
no more than 2% by weight of cement too much - drying shrinkage problems |
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conditions accelerants shouldn't be used
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reinforcing steel (corrosion)
steel, aluminum in humid environments alkali-aggregate reaction is a potential problem placing in hot weather mass pours |
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Pozzolan's
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silicieous or siliceous and aluminous material, which in itself possesses little or no cementitious property, but which will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperature to form compounds possessing cementing properties
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The three e's
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Engineering
Economics Ecological |
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Pozzolans (engineering)
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improves workability
reduces permeability improves durability resistance to thermal cracking |
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Pozzolans (economics)
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can be used to lower amount of cement required
cheap - industrial byproduct |
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Pozzoloans (ecological)
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pozzolans are by-products generated by thermal power plants and metallurgical furnaces
-exceed 500 million tons/year contain toxic elements can be safely incorporated into the hydration products of cement |
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Natural pozzolans
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diatomaceious earth, opaline cherts, clays, shales, volcanic tuffs, and pumicites
require grinding and calcification |
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metallurgical slag (pozzolans)
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limited use as only a small portion is granulated
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rice-husk ash
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20 million tons/year available
furnace needs to be tightly controlled so as not to produce crystalline silica microporosity and high surface area = very high pozzolanic reactivity |
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coal ash
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by-product of coal-fired plants
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Silica Fume
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metal industry byproduct, high cost and handling difficulty
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Types of pozzolans
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Natural
Metallurgical slags Rice-husk ash Coal Ash Silica Fume |
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sub angular aggregate
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reduce water content by 20 lb
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gravel with some crushed particles
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reduce water content by 35 lbs
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rounded particles
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reduce water content by 45 lbs
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severe freeze/thaw
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minimum cement = 564 lb/yd3
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underwater applications
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minimum cement = 650 lb/yd3
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unit weight
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lb per cubic foot of freshly mixed concrete
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yield
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volume of fresh concrete poured in a batch
total weight of mixture/unight weight of mixture |
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Absolute volume
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weight of material/(specific gravity of material*unit weight of water)
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water demand- increase temperature
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increase water demand
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water demand- increase cement content
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increase water demand
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water demand- increase slump requirement
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increase water demand
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water demand- increasew/c ratio
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increase water demand
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water demand- increase aggregate angularity
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increase water demand
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water demand - decreased proportion of coarse aggregate to fine aggregate
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increase water demand
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water demand - increase air content
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reduce water demand
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water demand - increased aggregate size
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reduced water demand
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water demand - rounded aggregates
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reduced water demand
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water demand - fly ash (water-reducing admixture)
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reduced water demand
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splitting tensile strength (ft')
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tends to overestimate true tensile strength by 15%
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empirical tool
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based on testing one parameter and relating it to the desired property
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flexural strength
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tends to overestimate true tensile stress by about 50%
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rebound hammer
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empirical tool
affected by: surface smoothness coarse aggregate type moisture content age of concrete |
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high strength concrete
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very fine cement with high percent of c3s (tricalcium silicate)
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HSC - Fine aggregate properties
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FM of 2.7 to 3.2
Gradation: 1.max 2% passing no. 100 2. 0-10% passing No. 50 3. 35-45% passing No. 30 |
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HSC admixture: superplasticizers
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reduces water by 15% to 40%
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HSC admixture: water-reducing retarder
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extend time of set and allow for difficult to place material
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HSC mineral admixtures: Pozzolans
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fly ash, silica fume, round granulated blast furnace slag
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silica fume
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improves cohesiveness, viscosity, and water demand
need more air entrainment to get desired voids |
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HSC - air entrainment
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difficult and not necessary
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