npca precast learning lab
TRANSCRIPT
Precast Show 2019
NPCA 1
precast.org/education
NPCA PRECAST LEARNING LAB
• 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.org/education
PRECAST 101Presented by Kayla Hanson
NPCA
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OVERVIEW
• What is precast?
• Raw materials
• Strength development
• Reinforcement
• Types of precast concrete
• Production
• Curing
• Testing and quality control
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HISTORY
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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
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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
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RAW MATERIALS
• Paste• Cement
• Water
• SCMs
• Admixtures
• Aggregates
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PORTLAND CEMENT
• Joseph Apsdin
• 1778-1855
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PORTLAND CEMENT
+ + =
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PORTLAND CEMENT
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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
precast.org/education
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
precast.org/education
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
precast.org/education
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
precast.org/education
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
precast.org/education
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
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CHEMICAL ADMIXTURES
• Air-entraining
• Water-reducing
• Plasticizers
• Accelerators
• Retarders
• Corrosion inhibitors
• Coloring
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WATER
• Water must be potable
• Well water or city water
• Well water must conform to ASTM C1602
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NORMAL WEIGHT AGGREGATES
FINE AGGREGATE
(SAND)
COARSE AGGREGATE
(CRUSHED STONE)
COARSE AGGREGATE
(GRAVEL)
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LIGHTWEIGHT AGGREGATES
EXPANDED CLAY
EXPANDEDSHALE
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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.)
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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
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AGGREGATE GRADING
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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
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CONCRETE STRENGTH
• What does 5,000 psi mean?
• What kind of stresses do we anticipate?
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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
3 in.
3 in
.
Load = 36,000 lb
A = 9 in.2
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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
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CONCRETE STRENGTH
• What kind of loads and stresses do we anticipate?• Point loads
• Distributed loads
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CONCRETE STRENGTH
• What kind of loads and stresses do we anticipate?• Point loads
• Distributed loads
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CONCRETE STRENGTH
• How do these forces act on the structure?• Compression
• Tension
• Flexure
• Torsion
• Axial
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CONCRETE STRENGTH
• How do these forces act on the structure?• Compression
• Tension
• Flexure
• Torsion
• Axial
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CONCRETE STRENGTH
• How do these forces act on the structure?• Compression
• Tension
• Flexure
• Torsion
• Axial
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CONCRETE STRENGTH
• How do these forces act on the structure?• Compression
• Tension
• Flexure
• Torsion
• Axial
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CONCRETE STRENGTH
• How do these forces act on the structure?• Compression
• Tension
• Flexure
• Torsion
• Axial
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REINFORCEMENT
• Reinforcement supplies strength to withstand tensile and shear forces
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CONCRETE STRENGTH
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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
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TRADITIONAL REBAR
• 60,000 ksi minimum tensile yield strength (Gr. 60)
• Elastic vs. plastic deformation
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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
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REBAR MARKINGS
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REBAR SIZE CHART
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REINFORCEMENT ISSUES
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BOND
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EPOXY-COATED REINFORCEMENT
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EPOXY-COATED REINFORCEMENT
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GALVANIZED REINFORCEMENT
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FIBERGLASS REINFORCEMENT
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STEEL FIBER REINFORCEMENT
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STEEL FIBER REINFORCEMENT
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SYNTHETIC FIBERS
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WELDED WIRE REINFORCEMENT
• ASTM A185, ASTM A1064
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PRESTRESSING
• Prestressed: concrete placed in compression prior to supporting applied loads
• Pre-tension
• Post-tension
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PRESTRESSING
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POSITIONING OF REINFORCEMENT
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CONCRETE COVER
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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
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CEMENT AND WATER
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HYDRATION
WATER
CEMENT
HYDRATION PRODUCTS
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CEMENT HYDRATION
Calcium Silicate Hydrate
(Greatest contributor to strength)
Calcium Hydroxide
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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
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CEMENT AND WATER
WATER CEMENT CONCRETE
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CEMENT AND WATER
WATER CEMENT CONCRETE
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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
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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
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AGGREGATE MOISTURE CONTENT
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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
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PRODUCTION
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AGGREGATE STORAGE
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AGGREGATE CROSS CONTAMINATION
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HOPPERS
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HOPPERS
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HOPPERS
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CEMENT STORAGE
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WEIGH BELTS
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AGGREGATE MOISTURE PROBES
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MIXERS
Horizontal Shaft - Spiral Blade
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MIXERS
Horizontal Shaft - Paddle Blade
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MIXERS
Twin Shaft
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MIXERS
Pan - Turbine
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MIXERS
Pan – Counter-Current
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MIXER PROBES
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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’
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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
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CONSOLIDATION
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FINISHING
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THREE KEYS TO CURING
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THREE KEYS TO CURING
Time Temperature Moisture
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HOT AND COLD WEATHER CURING
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STEAM CURING
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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
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QUALITY CONTROL PROGRAMS
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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
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CONCRETE TESTING
• Unit Weight – ASTM C138 (at least weekly)
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CONCRETE TESTING
• Air content – ASTM C231 and C173 (at least weekly)
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CONCRETE TESTING
• Slump – ASTM C43 (daily)
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CONCRETE TESTING
• Slump flow, spread, VSI – ASTM C1611 (daily*)
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CONCRETE TESTING
• Temperature – ASTM C1064 (daily)
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DIFFERENT TYPES OF PRECAST
• Conventional wet-cast
• Dry-cast
• Self consolidating concrete (SCC)
• High-performance concrete (HPC)
• Ultra high-performance concrete (UHPC)
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WET CAST CONCRETE
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DRY CAST CONCRETE
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SELF-CONSOLIDATING CONCRETE
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HIGH PERFORMANCE CONCRETE AND ULTRA-HIGH PERFORMANCE CONCRETE
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OVERVIEW
• What is precast?
• Raw materials
• Strength development
• Reinforcement
• Types of precast concrete
• Production
• Curing
• Testing and quality control
precast.org/education
PRECAST 101Presented by Kayla Hanson
NPCA
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