NPCA PRECAST LEARNING LAB

Precast Show 2019

NPCA 1

precast.org/education

• What is it?• A new library of short, educational

videos

• What can I learn?• Topics cover production best practices and sales and

marketing

• How many videos are available?• Four videos are currently available

• Videos will be added each year

• How do I access it?• NPCA members can access the videos for free at

precast.org/education and click the Precast Learning Lab button.

PRECAST 101Presented by Kayla Hanson

OVERVIEW

• What is precast?

• Raw materials

• Strength development

• Reinforcement

• Types of precast concrete

• Production

• Curing

• Testing and quality control

HISTORY

WHAT IS PRECAST?

• Composite material

• Made of natural ingredients, manufactured materials, and industrial byproducts

• Displays highest strength in compression

• Service life can approach around 100 years

• Structural and architectural

• Infrastructure, residential, commercial, industrial, natural habitats

WHAT IS PRECAST?

• Precast concrete: concrete cast elsewhere than its final location, cured in a controlled environment

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RAW MATERIALS

• Paste

• Aggregates

RAW MATERIALS

• Paste• Cement

• Water

• SCMs

• Admixtures

• Aggregates

PORTLAND CEMENT

• Joseph Apsdin

• 1778-1855

PORTLAND CEMENT

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CEMENT TYPES – ASTM C150• Type I: For general use when the special properties specified for any other

type are not required

• Type IA: Air-entraining cement for the same uses as Type I, where air-entrainment is desired

• Type II: For general use, or when moderate sulfate resistance is desired

• Type IIA: Air-entraining cement for the same uses as Type II, where air-entrainment is desired

• Type II(MH): For the same uses as Type II, and when moderate heat of hydration is desired

• Type II(MH)A: Air-entraining cement for the same uses as Type II(MH), where air-entrainment is desired

• Type III: For use when high early strength is desired

• Type IIIA: Air-entraining cement for the same uses as Type III, where air-entrainment is desired

• Type IV: For use when a low heat of hydration is desired

• Type V: For use when high sulfate resistance is desired

CEMENT TYPES – ASTM C150• Type I: For general use when the special properties specified for any other type

are not required

SUPPLEMENTARY CEMENTITIOUS MATERIALS

• Supplementary cementitious materials (SCMs) are used in conjunction with portland cement

• Pozzolanic vs. hydraulic

• Can arrived pre-blended with hydraulic cement –ASTM C595

• Fly ash

• Slag

• Silica fume

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SUPPLEMENTARY CEMENTITIOUS MATERIALS

• Most SCMs offer increased long-term strength

• SCMs typically increase density, decrease permeability, and improve durability

• Early-age strength gain is often lower in mixes using SCMs compared to mixes using just Portland cement

• The finer particle size can also increase water demand and make finishing tougher

• Fly ash – ASTM C618

• Slag – ASTM C989

• Silica fume – ASTM C1240

CHEMICAL ADMIXTURES

• Air-entraining

• Water-reducing

• Plasticizers

• Accelerators

• Retarders

• Corrosion inhibitors

• Coloring

• Water must be potable

• Well water or city water

• Well water must conform to ASTM C1602

NORMAL WEIGHT AGGREGATES

FINE AGGREGATE

(SAND)

COARSE AGGREGATE

(CRUSHED STONE)

COARSE AGGREGATE

(GRAVEL)

LIGHTWEIGHT AGGREGATES

EXPANDED CLAY

EXPANDEDSHALE

HEAVYWEIGHT AGGREGATES

GEOTHITE MAGNETITE

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AGGREGATE SIZES

• Fine aggregates: less than 5mm (0.2 in.)

• Coarse aggregates: greater than 5mm (0.2 in.)

AGGREGATES

• Together, coarse aggregate and fine aggregate make up about:

• 60% - 75% of the concrete VOLUME

• 70% - 85% of the concrete MASS

❑ Clean

❑ Hard

❑ Strong

❑ Durable

❑ Free of impurities

AGGREGATE GRADING

MAXIMUM AGGREGATE SIZE

FormDistance Between

Forms (B)

Rebar Spacing (S)

Reinforcing

BarsAggregate

B/5 MSA

3/4S MSA

FormDistance Between

Forms (B)

Rebar Spacing (S)

Reinforcing

BarsAggregate

B/5 MSA

3/4S MSA

Slabs on Grade

Depth (D)

D/3 MSA

Aggregate

Slabs on Grade

Depth (D)

D/3 MSA

Aggregate

CONCRETE STRENGTH

• What does 5,000 psi mean?

• What kind of stresses do we anticipate?

CONCRETE STRENGTH

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CONCRETE STRENGTH

• Stress = load per unit area• Load = 36,000 lb

• Area = 9 in.2

• Stress = 36,000 lb/9 in.2 = 4,000 lb/in.2 = 4,000 psi

Load = 36,000 lb

A = 9 in.2

LOADS AND FORCES

• Self-weight

• Hydrostatic loads

• Handling loads

• Thermal movement

• Concrete shrinkage

• Buoyant forces

• Soil forces

• Wheel loads

• Wind, snow, rain, and seismic loads

CONCRETE STRENGTH

• What kind of loads and stresses do we anticipate?• Point loads

• Distributed loads

CONCRETE STRENGTH

• What kind of loads and stresses do we anticipate?• Point loads

• Distributed loads

CONCRETE STRENGTH

• How do these forces act on the structure?• Compression

• Tension

• Flexure

• Torsion

• Axial

CONCRETE STRENGTH

• Tension

• Flexure

• Torsion

• Axial

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CONCRETE STRENGTH

• Tension

• Flexure

• Torsion

• Axial

CONCRETE STRENGTH

• Tension

• Flexure

• Torsion

• Axial

CONCRETE STRENGTH

• Tension

• Flexure

• Torsion

• Axial

REINFORCEMENT

• Reinforcement supplies strength to withstand tensile and shear forces

CONCRETE STRENGTH

REINFORCEMENT

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MAIN HYDRATION PRODUCTS

• CSH: calcium silicate hydrate• Greatest contributor to concrete strength

• CH: calcium hydroxide• Contributes very little to concrete strength

TRADITIONAL REBAR

• 60,000 ksi minimum tensile yield strength (Gr. 60)

• Elastic vs. plastic deformation

COMMON REBAR TYPES

• ASTM A615: deformed and plain carbon-steel bars

• ASTM A706: low-alloy steel deformed and plain bars

• ASTM A767: zinc-coated (galvanized) steel bars

• ASTM A775: epoxy-coated reinforcing steel bars

• ASTM A955: deformed and plain stainless-steel bars

REBAR MARKINGS

REBAR SIZE CHART

REINFORCEMENT ISSUES

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EPOXY-COATED REINFORCEMENT

GALVANIZED REINFORCEMENT

FIBERGLASS REINFORCEMENT

STEEL FIBER REINFORCEMENT

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STEEL FIBER REINFORCEMENT

SYNTHETIC FIBERS

WELDED WIRE REINFORCEMENT

• ASTM A185, ASTM A1064

PRESTRESSING

• Prestressed: concrete placed in compression prior to supporting applied loads

• Pre-tension

• Post-tension

PRESTRESSING

POSITIONING OF REINFORCEMENT

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CONCRETE COVER

• Concrete cover over reinforcement must always be ½” or greater

• Some ASTM standards have additional requirements

• Example: ASTM C478 (for precast manholes) requires at least ¾” concrete cover

CEMENT AND WATER

HYDRATION

CEMENT

HYDRATION PRODUCTS

CEMENT HYDRATION

Calcium Silicate Hydrate

(Greatest contributor to strength)

Calcium Hydroxide

WATER TO CEMENT RATIO

• Water to cement ratio (w/c): weight of water / weight of cement in the batch

• Water to cementitious materials ratio (w/cm): weight of water / weight of all cementitious materials in the batch

• In the right quantities, water and cement will create a very strong, durable, and impermeable paste

• Water demand varies day-to-day

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WATER TO CEMENT RATIO

• Water to cement ratio (w/c): weight of water / weight of cement in the batch

• 240 lbs water / 500 lbs cement = 0.48

• Water to cementitious materials ratio (w/cm): weight of water / weight of all cementitious materials in the batch

• 240 lbs water / (50 lbs fly ash + 450 lbs cement) = 0.48

CEMENT AND WATER

WATER CEMENT CONCRETE

CEMENT AND WATER

WATER CEMENT CONCRETE

PORES AND POROSITY

• Porosity: volume of the voids / total volume

• Pores are the remnants of mixing water

• Pores do not carry load

• More pores means less strength

• Porosity is a volumetric ratio

PERMEABILITY

• Permeability: the ability of a material or substance to pass through another material or substance

• Measured as a speed

• More pores and higher porosity results in higher level of permeability

AGGREGATE MOISTURE CONTENT

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precast.org/education precast.org/education

WATERTIGHTNESS

• Watertightness: constructed to be impervious to water

• More pores and higher porosity results in higher level of permeability

• Higher level of permeability reduces watertightness

LOWW/C

LOW POROSITY

LOW PERMEABILITY

PRODUCTION

AGGREGATE STORAGE

AGGREGATE CROSS CONTAMINATION

HOPPERS

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HOPPERS

CEMENT STORAGE

WEIGH BELTS

AGGREGATE MOISTURE PROBES

MIXERS

Horizontal Shaft - Spiral Blade

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MIXERS

Horizontal Shaft - Paddle Blade

MIXERS

Twin Shaft

MIXERS

Pan - Turbine

MIXERS

Pan – Counter-Current

MIXER PROBES

AUTOMATED BATCH PLANTS

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PLACING

• Concrete should be deposited as near to its final location as possible

• Minimize free-fall heights to less than 6’

CONSOLIDATION

• Helps draw entrapped air to the unformed surface and out of the concrete

• Bugholes are a sign of insufficient consolidation

• Segregation is a sign of over-consolidation

CONSOLIDATION

FINISHING

THREE KEYS TO CURING

Time Temperature Moisture

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HOT AND COLD WEATHER CURING

STEAM CURING

QUALITY CONTROL PROGRAMS• Qualified and educated personnel

• Completeness of work orders and product drawings

• Quality of raw materials

• Quality of forms

• Fabrication and Positioning of Reinforcing Steel

• Concrete Quality

• Placement and consolidation of concrete

• Product dimensions

• Positioning of embedded items

• Curing of concrete

• Handling, storing and transporting products

• Recordkeeping

• Testing

QUALITY CONTROL PROGRAMS

CONCRETE PROPERTIES

• Fresh concrete properties• Unit weight• Air content• Slump• Slump flow, spread, or VSI• Temperature

• Hardened concrete properties• Strength• Durability (resistance to abrasion, freeze/thaw, impact, fire,

etc.)• Volume stability• Density• Watertightness• Thermal and acoustic insulation

CONCRETE TESTING

• Unit Weight – ASTM C138 (at least weekly)

99 100

101 102

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CONCRETE TESTING

• Air content – ASTM C231 and C173 (at least weekly)

CONCRETE TESTING

• Slump – ASTM C43 (daily)

CONCRETE TESTING

• Slump flow, spread, VSI – ASTM C1611 (daily*)

CONCRETE TESTING

• Temperature – ASTM C1064 (daily)

DIFFERENT TYPES OF PRECAST

• Conventional wet-cast

• Dry-cast

• Self consolidating concrete (SCC)

• High-performance concrete (HPC)

• Ultra high-performance concrete (UHPC)

WET CAST CONCRETE

103 104

105 106

107 108

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DRY CAST CONCRETE

SELF-CONSOLIDATING CONCRETE

HIGH PERFORMANCE CONCRETE AND ULTRA-HIGH PERFORMANCE CONCRETE

OVERVIEW

• What is precast?

• Raw materials

• Strength development

• Reinforcement

• Types of precast concrete

• Production

• Curing

• Testing and quality control

PRECAST 101Presented by Kayla Hanson

khanson@precast.org

109 110

111 112

NPCA PRECAST LEARNING LAB

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