Lesson 6: Portland Cement Concrete

1
Lesson 6 Portland Cement Concrete

• CEE 595 Construction Materials
• Winter Quarter 2008

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Lesson 6 Portland Cement Concrete Topics

• Traditional Portland Cement Concrete
• 6.1 Introduction (Chapter 1 and Powers et al)
• 6.2 Hydraulic Cements (Chapter 2 and USGS
  references)
• 6.3 Fly Ash, Silica Fume, Other Pozzolans
  (Chapter 3)
• 6.4 Mixing Water for Concrete (Chapter 4)
• 6.5 Aggregates for Concrete (Chapter 5)
• 6.6 Admixtures for Concrete (Chapter 6)
• 6.7 Proportioning Normal Concrete Mixtures
  (Chapter 9)

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Lesson 6 Portland Cement Concrete Topics
(continued)

• Traditional Portland Cement Concrete
• Lesson 6a PCC Case StudyNew Tacoma Narrows
  Bridge
• Lesson 6b PCC Case StudyUS 395 Test Sections
• Lesson 6c PCC Case StudyWSDOT PCC Intersections
• Lesson 6d PCC Case StudyWSDOT PCC Pontoons for
  Hood Canal Floating Bridge
• Lesson 6e Lafarge Cement PlantSeattle

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Lesson 6 Portland Cement Concrete

• This lesson contains a modest amount of material.
  It is difficult to cover traditional PCC in one
  weekhowever we will do what we can. The primary
  purpose of the lesson is to refresh the knowledge
  you already have about PCC or learn something
  about this important construction material if you
  have limited exposure to it. The basic reference
  is excellentDesign and Control of Concrete
  Mixtures. The version on the CD contains the
  latest information.

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Lesson 6 Portland Cement Concrete

• You are encouraged to pick and choose
  information from the PCA publication. This
  PowerPoint along with the case studies will be
  helpful but, undoubtedly, incomplete. There are
  so many factors that make for a well-designed and
  constructed concrete project. These notes focus
  on basic material issues but job site specific
  conditions are always criticalsuch as the
  weather conditions, transport of the fresh mix,
  placing and finishing, etc.

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Lesson 6.1 IntroductionMajor Topics

• Introduction
• Freshly Mixed Concrete
• Hardened Concrete
• Durability

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6.1 Introduction

• For those that have studied or worked with PCC,
  this portion of Lesson 6 will be a
  straightforward review. For those that have not,
  the basics associated with PCC is important to
  most working in construction and specifically
  heavy construction.

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6.1 Introduction

• Concrete Basically formed by two
  componentsaggregate and paste.
• Paste is a mixture of portland cement and water.
  Paste chemically reacts with water to form
  cementing products (hydration) that bind
  aggregate into a rocklike mass.

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6.1 Introduction

• Paste has two types of air entrapped and
  entrained. Entrapped air occurs in all PCC
  mixturesusually small amounts. Entrained air is
  deliberately designed into the PCC mixture to aid
  the durability of the hardened PCC.
• Volumes
• Paste 25 to 40 of total volume
• Aggregates 60 to 75 of total volume
• Refer to PCA, Chapter 1, Figure 1-2 for
  additional details.

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6.1 Introduction

• Aggregate described by two sizes fine and coarse
  aggregate.
• Fine aggregate 100 passes a 9.5 mm (3/8 inch)
  sieve.
• Coarse aggregate Generally maximum aggregate
  size is about 37.5 mm (1.5 inches) but this can
  be much larger. Ranges down to 9.5 to 2.36 mm to
  (3/8 inch to No. 8).
• Aggregates will be covered in more detail in 6.5
  of these notes (PCA, Chapter 5).

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6.1 Introduction

• The less water in the paste (and hence the total
  PCC mixture)in generalthe better for the
  hardened material.
• Less water in the PCC mixture offers the
  following benefits
• Higher compressive and flexural strength
• Lower permeability and improved water tightness
• Increased resistance to weathering
• Improved bond between PCC and reinforcing steel
• Reduced drying shrinkage and cracking (which can
  also occur due to construction placing and curing
  operations)
• Reduced volume changes due to wetting and drying.

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6.1 Introduction

• Quote The less water used, the better the
  quality of the concreteprovided the mixture can
  be consolidated . The course instructors could
  not agree more.
• Refer to PCA, Chapter 1, Figure 1-4. This figure
  shows the relative proportions of water.
  Designated by water to cement ratios (weight of
  water divided by the weight of portland cement).
  The w/c ratios in the figure range from 0.25
  (very low ratio) to 0.70 (a very high ratio).

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6.1 Freshly Mixed Concrete

• Subtopics include
• Mixing
• Workability
• Bleeding and settlement
• Consolidation
• Hydration, Setting Time, and Hardening

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6.1 Freshly Mixed Concrete

• Mixing
• Ensures that the separate PCC components are
  mixed properly. This will be covered in more
  detail in Lesson 4.9 (which covers PCA, Chapter
  10).
• Workability
• Quote from PCA, Chapter 1 The ease of placing,
  consolidating, and finishing freshly mixed
  concrete and the degree to which it resists
  segregation is called workability.
• Workability is a critical element in concrete
  construction.

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6.1 Freshly Mixed Concrete

• Workability
• Factors that influence the workability of
  concrete
• The method and duration of transport.
• Quantity and characteristics of cementitious
  materials.
• Concrete consistencywhich is defined by the
  measurement of slump.
• Grading, shape, and surface texture of fine and
  coarse aggregates.
• Entrained air
• Water content
• Concrete and ambient air temperatures
• Admixtures

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6.1 Freshly Mixed Concrete

• Workability
• Figure 1-6 (PCA, Chapter 1) illustrates the
  influence of temperature on the slump of two
  mixeseach with a different portland cement.
• Bleeding and Settlement
• Bleeding The development of a layer of water on
  the PCC surface (most often noted on PCC slabs).
• Bleeding cause Settlement of the cement and
  aggregate particles.

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6.1 Freshly Mixed Concrete

• Bleeding and Settlement
• Bleeding results in a higher w/c ratio at the top
  of the PCC which results in lower strength and
  durability.
• Consolidation
• An introduction to the positive features
  associated with vibration of PCC to obtain its
  final shape or form.

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6.1 Freshly Mixed Concrete

• Hydration, Setting Time, and Hardening
• Hydration Chemical reaction between cement and
  water.
• Unhydrated portland cement a combination of many
  compounds. Four compounds make up 90 or more of
  a typical cement
• Tricalcium silicate
• Dicalcium silicate
• Tricalcium aluminate
• Tetracalcium aluminoferrite

75 of portland cement
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6.1 Freshly Mixed Concrete

• Abbreviations
• Tricalcium silicate 3CaOSiO2C3S
• Dicalcium silicate 2CaOSiO2C2S
• Tricalcium aluminate 3CaOAl2O3C3A
• Tetracalcium aluminoferrite 4CaOAl2O3Fe2O3C4AF
  

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6.1 Freshly Mixed Concrete

• Tricalcium silicate (C3S) Hydrates and hardens
  rapidly and is largely responsible for initial
  set and early strength.
• Dicalcium silicate (C2S) Hydrates and hardens
  slowly and contributes largely to strength
  increase at ages beyond one week.

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6.1 Freshly Mixed Concrete

• Tricalcium aluminate (C3A) Liberates a large
  amount of heat during the first few days of
  hydration. Gypsum added to the cement during
  final grinding slows the hydration rate of C3A.
• Tetracalcium aluminoferrite (C4AF) Used to
  assist in manufacturing of cement. Hydrates
  rapidly but contributes little to strength. Most
  PCC color effects due to C4AF and its hydrates.

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6.1 Freshly Mixed Concrete

• Hydration, Setting Time, and Hardening
• All types of portland cement contain the same
  four compoundsjust in different amounts.
• Calcium silicates water form
• Calcium hydroxideabout 25 by weight
• Calcium silicate hydrate (tobermorite gel)about
  50 by weight
• Calcium silicate hydrate most important for PCC
  engineering properties.

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6.1 Freshly Mixed Concrete

• Hydration, Setting Time, and Hardening
• Calcium silicate hydrate forms interlocking
  structure between other crystalline phases,
  remaining unhydrated cement grains, and aggregate
  particles.
• As PCC hardens, the overall volume remains
  essentially unchanged.

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6.1 Freshly Mixed Concrete

• Hydration, Setting Time, and Hardening
• Hardened paste has pores containing water and
  air. Fewer pores results in higher strength.
• Goal is to use no more water than necessary to
  hydrate the portland cement.

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6.1 Freshly Mixed Concrete

• Hydration, Setting Time, and Hardening
• Powers et al showed in a 1948 publication that
  0.4 grams of water is required to completely
  hydrate 1.0 gram of portland cementhowevercomple
  te hydration of portland cement is rare.

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6.1 Freshly Mixed Concrete

• Hydration, Setting Time, and Hardening
• Initial rate of hydrationgypsum is added to the
  ground cement to control the initial setting of
  PCC.
• Other factors that control initial set time are
• Fineness of portland cement
• Amount of water added
• Admixtures
• Temperature at the time of mixing.

27
6.1 Hardened Concrete

• Subtopics include
• Curing
• Drying Rate of Concrete
• Strength
• Density
• Permeability and Watertightness
• Abrasion Resistance
• Volume Stability and Crack Control

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6.1 Hardened Concrete

• Curing
• Curing Increase in strength with time.
• Curing continues if
• Unhydrated cement is present.
• The concrete remains moist or has a relative
  humidity above 80.
• The concrete temperature remains favorable.
• Space is available for hydration products to
  form.

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6.1 Hardened Concrete

• Curing
• Curing stops if
• Concrete temperature drops below freezing.
• Concrete relative humidity drops below about 80.

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6.1 Hardened Concrete

• Drying Rate of Concrete
• Quote from PCA, Chapter 1 Concrete does not
  harden or cure by drying.
• Freshly mixed concrete has adequate water for
  curing but this quickly changes. Insufficient
  moist curing for a floor slab can result in a
  weak surface which is subject to dusting under
  traffic.
• Drying concrete
• Shrinkage occurs due to drying
• Drying shrinkage a primary cause of PCC cracks

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6.1 Hardened Concrete

• Drying Rate of Concrete
• Moisture content of PCC after several months
  typically 1 to 2 by total mass of PCC.

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6.1 Hardened Concrete

• Strength
• Compressive strength of concrete is an often
  specified requirement. Typically, the compressive
  strength is reported as a function of a 28 day
  cure. However, many different cure periods are
  specified depending on project requirements.
• The basic relationship between w/c ratio and
  strength has been known for about 100 years.

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6.1 Hardened Concrete

• Strength
• Specified compressive strength is designated
• Two types of compressive strength tests
• Mortar 50 mm X 50 mm (2 in. X 2 in.) cubes
• PCC cylinders 150 mm diameter X 300 mm high (6
  in X 12 in). Sometimes smaller cylinders are used
  that are 100 mm diameter X 200 mm high (4 in X 8
  in).
• Specified compressive strength ranges
• General use applications 20 to 40 MPa (3,000 to
  6,000 psi)
• Special bridge and high-rise building
  applications 70 to 140 MPa (10,000 to 20,000
  psi).

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6.1 Hardened Concrete

• Strength
• Flexural strength (or modulus of rupture)
  sometimes used in the design of pavements and
  slabs.
• Approximate correlations with compressive
  strength
• Flexural Strength 0.7 to 0.8 (in MPa)
• Flexural Strength 7.5 to 10 (in psi)
• Direct tensile strength approximately 8 to 12 of
  compressive strength.

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6.1 Hardened Concrete

• Strength
• Splitting tensile strength approximately 8 to 14
  of compressive strength.
• Modulus of elasticity (E) ranges between 14,000
  to 41,000 MPa (or 2 to 6 million psi) for normal
  weight concrete.
• Modulus of elasticity can also be approximated
  from compressive strength
• E 5,000 (in MPa)
• E 57,000 (in psi)

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6.1 Hardened Concrete

• Density
• Typical concrete density 2200 to 2400 kg/m3 (137
  to 150 lb/ft3)
• Density varies as a function of
• Aggregate
• Amount of air entrapped or entrained
• Water and cement contents
• Some mix water does evaporate from the concrete
  when exposed to ambient conditionsthis amounts
  to about 0.5 to 3 of concrete weight.

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6.1 Hardened Concrete

• Density
• Specialty concrete density can range from as low
  as 240 kg/m3 (15 lb/ft3) to as high as 6000 kg/m3
  (375 lb/ft3).

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6.1 Hardened Concrete

• Permeability and Watertightness
• Watertightness Ability of concrete to hold back
  water without visible leakage.
• Permeability Amount of water transmitted through
  concrete when water under pressure.

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6.1 Hardened Concrete

• Permeability and Watertightness
• Permeability of concrete a function of
• Permeability of the paste
• Permeability and gradation of the aggregate
• Quality of paste and aggregate transition zone
• Relative proportion of paste to aggregate.

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6.1 Hardened Concrete

• Abrasion Resistance
• Pavements, floors, and hydraulic structures
  should have a high abrasion resistance.
• Concrete abrasion resistance linked to
• Compressive strength hence w/c ratio and
  curing conditions.
• Type of aggregate
• Surface finish or treatment
• Refer to Supplemental Lesson 6b for additional
  insight into a form of abrasion resistance via
  studded tire wear.

41
6.1 Hardened Concrete

• Volume Stability and Crack Control
• Hardened concrete volume changes due to
• Temperature
• Moisture
• Stress
• Thermal volume changes of hardened concrete about
  the same as for steel.

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6.1 Hardened Concrete

• Volume Stability and Crack Control
• Two basic causes of cracks in concrete
• Stress due to applied loads
• Stress due to drying shrinkage or temperature
  changes when concrete is restrained.
• Drying shrinkage is an inherent property of
  concrete but it can be minimized by mix design
  and curing and
• Reinforcing steel to keep cracks closed
• Joints (more information is available via PCA,
  Chapter 11).

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6.1 Hardened Concrete

• Volume Stability and Crack Control
• Thermal stresses induced by ambient temperature
  changes can cause crackingthis can be a major
  issue for early age concrete.
• Thermal stresses a major factor to consider in
  designing PCC jointed pavements.

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Lesson 6.2 Major Topics

• Types of cements
• Production of cements
• Cement supply
• Location of Washington State cement plants

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6.2 Types of Cements

• Type I General purpose cement.
• Type II Protects PCC against moderate sulfate
  attack. Generates less heat than Type I. Some
  cement manufacturers can meet both the Type I and
  II requirements with one cement.
• Type III Provides high strength PCC with a
  shorter cure period. Similar to Type I but the
  clinker is ground finerthus allowing more rapid
  hydration.

46
6.2 Types of Cements

• Type IV Produces less heat during hydration but
  slower strength gain. Sometimes used with mass
  concrete.
• Type V Used for PCC exposed to severe sulfate
  action from soils or groundwater.
• Blended Cements Refer to Chapter 2.
• Special Cements A wide variety of cements are
  available for specific applicationsrefer to
  Table 2-4, Chapter 2.

47
6.2 Hydraulic CementsProduction

• World cement production for 2003top 10 producing
  countries

48
6.2 Hydraulic CementsProduction

• US production in 2003
• 87 million metric tons of portland cement
• 4.5 million tons of masonry cement
• Produced at 118 plants in 37 states and Puerto
  Rico by 39 companies.
• Annual imports of hydraulic cement 21 million
  tons
• Total cement use in US 112 million tons/year
  (imports about 20 of consumption)

49
6.2 Hydraulic CementsProduction

• Import sources
• 19 Canada
• 18 Thailand
• 12 China
• 7 Venezuela
• 44 Others (32 other countries)
• US cement applications
• 75 to ready-mixed concrete producers
• 13 to concrete product manufacturers
• 6 to contractors (mostly road paving)
• 6 others

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6.2 Cement Shortages in the US--2004

• US cement supply is currently short of
  demandwhy?
• Strong construction markets
• Long lead times needed to bring new cement plants
  online (permitting process) and lots of capital.
• Freight
• Limited availability of transport ships for
  importing more cement
• Shipping rates increased significantly during 2004

51
6.2 Cement Shortages in the US--2004
52
6.2 Local Cement Production

• In Seattle, portland cement is produced by
• Ash Grove Cement
• Lafarge Cement (formerly Holnam Cement and before
  that Idea Cement)

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6.2 Local Cement Production--South Seattle
Industrial Area
54
6.2 Location of Ash Grove and Lafarge Plants in
Seattle
West Seattle Bridge
Ash Grove Plant Site
Lafarge Plant Site
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6.2 Lafarge Cement PlantSeattle
Photo source Rob Shogren, Lafarge
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6.2 Lafarge Cement PlantBritish Columbia
Photo source Rob Shogren, Lafarge
57
6.2 Lafarge KilnProduction of Clinker
Photo source Rob Shogren, Lafarge
58
6.2 Lafarge KilnProduction of Clinker
Photo source Rob Shogren, Lafarge
59
6.2 Ash Grove and Lafarge Plants in SeattleUse
of Scrap Tires as Fuel

• Both cement plants in Seattle use scrap tires as
  a portion of the fuel for their kilns.
• National-wide about 290 million scrap tires are
  generated each year with about 233 million being
  consumed (or about 80).
• Cement plants are estimated to consume about 53
  million tires per year (or 18 of total scrap
  tires generated).
• Benefits to cement manufacturers
• Reduces energy costs
• Less nitrogen oxide emissions compared to other
  fuels
• Tire-derived fuel (TDF) is becoming a standard
  practice. Refer to ASTM D6700.

60
6.3 Fly Ash, Silica Fume, Other Pozzolans

• These are broadly classed as supplementary
  cementitious materials and are used in about 60
  of ready mixed PCC produced in the US.
• Definitions
• Pozzolan A siliceous or aluminosiliceous
  material that, in finely divided form and in the
  presence of moisture, chemically reacts with the
  calcium hydroxide released by the hydration of
  portland cement to form calcium silicate hydrate
  and other cementitious compounds.

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6.3 Fly Ash, Silica Fume, Other Pozzolans

• Definitions
• Fly Ash The most widely used supplementary
  cementitious material in concrete, is a byproduct
  of the combustion of pulverized coal in electric
  power generating plants. Conforms to ASTM C618
  Standard Specification for Coal Fly Ash and Raw
  or Calcined Natural Pozzolan for Use in
  Concrete.

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6.3 Fly Ash, Silica Fume, Other Pozzolans

• Definitions
• Silica Fume Silica fume, also referred to as
  microsilica or condensed silica fume, is a
  byproduct material that is used as a pozzolan.
  This byproduct is a result of the reduction of
  high-purity quartz with coal in an electric arc
  furnace in the manufacture of silicon or
  ferrosilicon alloy. Condensed silica fume is
  essentially silicon dioxide (usually more than
  85) in noncrystalline (amorphorous) form. It has
  a spherical shape and is extremely fine with
  particles less than 1 µm in diameter and with an
  average diameter of about 0.1 µm, about 100 times
  smaller than average cement particles.

63
6.3 Fly Ash

• Produced from coal burning power plants
• Three types of fly ash according to ASTM C618
  Standard Specification for Coal Fly Ash and Raw
  or Calcined Natural Pozzolan for Use in Concrete
• Class N Raw or calcined natural pozzolans
• Class F Fly ash normally produced from burning
  anthracite or bituminous coal. This class has
  pozzolanic properties.
• Class C Fly ash normally produced from lignite
  or subbituminous coal. This class has pozzolanic
  properties and some cementitious properties.

64
6.3 Locally Produced Fly Ash

• In Washington State, the only fly ash producing
  power plant is located in Centralia, WA and is
  owned and operated by TransAlta Corp (based in
  Calgary). ISG Resources markets the Class F fly
  ash recovered from electrostatic precipitators.
  The power plant consumes about 5 million tons of
  coal per year with about 4 million tons being
  mined from a 14,000 acre facility near Centralia.
  The coal mined at Centralia is classified as
  bituminous or soft coal.
• Over 50 of the electricity produced in the US is
  via coal fired power plants.

65
6.3 Effects on Freshly Mixed PCC
66
6.3 Effects on Freshly Mixed PCC
67
6.3 Effects on Hardened PCC
68
6.4 Mixing Water for PCC
Almost any natural water that is drinkable and
has no pronounced taste or odor can be used as
mixing water for making concrete.
69
6.5 Aggregates for PCC

• Chapter 5 in the PCA publication contains a
  substantial amount of detailed information about
  aggregates for PCC. To a limited extent,
  aggregates were introduced in Lesson 2. Further
  information will be provided on aggregates in the
  HMA Lessons.
• A few of the more significant aspects of PCC
  aggregates will be noted in the following slides.
  No attempt is made to cover all the details
  available in Chapter 5.

70
6.5 Aggregates for PCC

• Table 5.2 Characteristics and Tests of
  Aggregates is an excellent summary and suggests
  that this is a detailed topic!
• Note in Table 5.2 two ASTM standards
• ASTM C125 Standard Terminology Relating to
  Concrete and Concrete Aggregates
• ASTM C294 Standard Descriptive Nomenclature for
  Constituents of Concrete Aggregates
• These two standards should be reviewed since they
  cover basic terms and terminologysort of a
  language primer for concrete. Most of the terms
  will be familiar.

71
6.5 Aggregates for PCC

• Fineness Modulus (FM) This is an index of the
  fineness of an aggregate. The lower the FM, the
  finer the gradation. The FM is used in
  proportioning PCC mixes (PCA, Chapter 9).
• Particle shape and surface texture
• Mostly influences the properties of freshly mixed
  concrete but not hardened concrete (unlike hot
  mix asphalt which requires crushed aggregate to
  achieve good long-term performance).

72
6.5 Aggregates for PCC

• Absorption and surface moisture
• Review the following terms
• Oven dry
• Air dry
• Saturated surface dry
• Damp or wet
• Figure 5-12 is helpful in reviewing the above
  terms.

73
6.5 Aggregates for PCC

• Alkali-Aggregate Reactivity
• Review carefully the content in Chapter 5 on
  alkali-silica reactions (ASR). This is a very
  serious PCC topic since it is generally
  preventable if early measures are taken. ASR can
  cause major damage to PCC structures.
• The extent of ASR problems vary throughout the US
  since the basic problem lies with the aggregate
  used in the PCCand generallymost PCC aggregate
  is locally produced.

74
6.5 Aggregates for PCC

• Recycled concrete aggregate
• This is another topic that requires some
  attention. There are a number of possible uses
  for recycled concrete including use as aggregate
  for new PCChowever there are risks associated
  with that use.
• The use of recycled concrete pavement as
  aggregate has experienced severe performance
  problems on at least one project in Michigan.

75
6.6 Admixtures for Concrete

• Admixtures are those ingredients in concrete
  other than portland cement, water, and aggregates
  that are added to the mixture immediately before
  or during mixing.

• Types of admixtures
• Air-entraining admixtures
• Water-reducing admixtures
• Plasticizers
• Accelerating admixtures
• Retarding admixtures
• Hydration-control admixtures
• Corrosion inhibitors
• Shrinkage reducers
• Alkali-silica reactivity inhibitors
• Coloring admixtures
• Miscellaneous admixtures

76
6.6 Admixtures for PCC

• Table 6-1 provides an excellent overview of
  concrete admixtures by classification
• Some of the most commonly used admixtures include
• Air entraining admixtures
• Water reducers
• Water reducerhigh range
• Superplasticizers

77
6.6 Admixtures for PCC

• Air entrainment became a standard practice for
  most types of concrete in about 1945.
• The work that led up to the wide-spread use of
  air entrainment started much earlier than 1945.

78
6.6 Admixtures for PCC

• ASTM C494 Standard Specification for Chemical
  Admixtures for Concrete lists Types A through G
  (a number of which are covered in PCA, Chapter 6,
  Table 6-1)
• Type A Water reducing admixtures
• Type B Retarding admixtures
• Type C Accelerating admixtures
• Type D Water reducing and retarding admixtures
• Type E Water reducing and accelerating
  admixtures
• Type F Water reducing, high range admixtures
• Type G Water reducing, high range, and retarding
  admixtures

79
6.7 Proportioning Normal Concrete Mixtures

• Mix design The process of determining required
  and specifiable characteristics of a concrete
  mixture.
• Mixture proportioning Refers to the process of
  determining the quantities of concrete
  ingredients, using local materials, to achieve
  the specified characteristics of the concrete. A
  properly proportioned concrete mix should possess
  these qualities
• Acceptable workability of the freshly mixed
  concrete
• Durability, strength, and uniform appearance of
  the hardened concrete
• Economy

80
6.7 Proportioning Normal Concrete Mixtures

• So how do you decide what concrete durability or
  strength is needed?
• Determine the minimum strength needed via
• Building code
• Durability requirements
• Other design requirements
• An example of building code requirements is the
  International Building Code (IBC)typical
  requirements from the IBC follow. As you likely
  know, building code requirements tend to be
  detailedthus the criteria shown are only a small
  sample.

81
6.7 PCC Code Requirements

• IBC, Chapter 19
• The IBC makes extensive use of ACI 318.
• Let us take a look at typical code requirements
• Section 1904 Durability Requirementsthese are
  based on three separate criteria which are
• Water-cementitious ratio
• Freezing and thawing exposures
• Sulfate exposures
• Criteria for each of the three criteria will be
  shown in the following images.

82
6.7 PCC Code Requirements

• IBC, Chapter 19
• Section 1904 Durability Requirementsthese are
  based on three separate criteria which are
• Water-cementitious ratio
• Minimum specified compressive strengths (fc) can
  be as low as 2,500 psi for negligible exposure to
  3,500 psi for severe exposure (exposures
  determined by project location and type of
  construction).
• Maximum water-cementitious ratios and minimum fc
  for concrete exposed to sulfate containing
  solutions
• Maximum w/c ratios range from 0.50 to 0.45
• Minimum fc ranges from 4,000 to 4,500 psi (28
  day cure)
• Freezing and thawing exposures
• Sulfate exposures

83
6.7 PCC Code Requirements

• IBC, Chapter 19
• The IBC makes extensive use of ACI 318.
• Let us take a look at typical code requirements
• Section 1904 Durability Requirementsthese are
  based on three separate criteria which are
• Water-cementitious ratio
• Freezing and thawing exposures
• Air entrainment requirements
• Maximum water-cementitious ratios and minimum fc
  for concrete conditions
• Maximum w/c ratios range from 0.50 to 0.40
• Minimum fc ranges from 4,000 to 5,000 psi (28
  day cure)
• Sulfate exposures

84
6.7 PCC Code Requirements

• IBC, Chapter 19
• The IBC makes extensive use of ACI 318.
• Let us take a look at typical code requirements
• Section 1904 Durability Requirementsthese are
  based on three separate criteria which are
• Water-cementitious ratio
• Freezing and thawing exposures
• Sulfate exposures
• Similar to w/c ratio criteria

85
6.7 Proportioning Steps

• Select required strength
• Tables 9-1 and 9-2 show minimum strength
  requirements for various exposure conditions.
• Table 9-3 shows typical compressive strengths for
  various water-cementitious ratios. Example
  Compressive strength 7,000 psi _at_ 28 day cure
  for a w/c ratio 0.33 (non-air entrained).

86
6.7 Proportioning Steps

• Select aggregates
• Maximum aggregate sizeexamples include
• Max aggregate size should not exceed 1/5 the
  narrowest dimension between sides of forms nor ¾
  the clear space between reinforcing barsetc.
• Slab (unreinforced) Max size should not exceed
  1/3 stab thickness.
• High strength PCC (greater than 10,000 psi) Max
  aggregate should be no more than ¾ inch.
• Bulk volume of coarse aggregate Refer to Table
  9-4.

87
6.7 Proportioning Steps

• Select air content and initial water content
• Depends on exposure conditions for the concrete.
  Refer to Figure 9-4 and Table 9-5. Table 9-5 is a
  function of slump, max aggregate size, and
  whether there is a need for air entrainment. The
  table provides an important mix proportion
  ingredientthe approximate amount of mix water.
• The water contents shown in Table 9-5 are for
  crushed aggregate. If rounded gravel is being
  used (often the case), then it is recommended
  that water reductions be made in the estimate.

88
6.7 Proportioning Steps

• Select slump
• Refer to Table 9-6 for recommended slumps for
  various types of construction.
• Select cementing materials content and type
• The amount of cement should be minimized for
  economy but must be enough to ensure quality
  (hence performance) of the concrete.
• To minimize water and cement requirements include
  (1) the stiffest practical mixture, (2) the
  largest practical maximum size of aggregate, and
  (3) the optimum ratio of fine-to-coarse
  aggregate.
• Water/cementitious ratio is a primary factor that
  is used to determine cement (cementitious)
  content.

89
6.7 Proportioning Steps

• Select cementing materials content and type
  (cont.)
• Minimum cement contents are often specified for
  durability requirements. As examples
• Severe freeze-thaw conditions 564 lb/cu. yd.
• Placement of concrete underwater 650 lb/cu. yd.
• Flatwork Refer to Table 9-7.
• Limits on cementitious materials other than
  portland cement. For concrete exposed to deicers,
  typical limits are shown in Table 9-8. For
  example
• Fly ash and natural pozzolans limit 25 (by
  mass)
• Silica fume limit 10

90
6.7 Proportioning Steps

• Proportioning approaches
• Proportioning based on field data
• Proportioning based on trial mixes
• The absolute volume method (illustrated by
  Example 2 (US units), PCA, Chapter 9) is commonly
  used by laboratories.
• Elements of the absolute volume method include
• Conditions and specifications
• Cementrequired information must include (1)
  cement type, and (2) relative density of the
  cement
• Coarse aggregaterequired information must
  include (1) max aggregate size, (2) specific
  gravity, (3) absorption, (4) dry rodded bulk
  weight, and (5) and lab moisture content.

91
6.7 Proportioning Steps

• Proportioning approaches
• Elements of the absolute volume method include
• Conditions and specifications (cont.)
• Fine aggregaterequired information includes (1)
  specific gravity, (2) absorption, (3) actual
  (lab) moisture content, (4) Fineness Modulus
  (FM).
• Determine required strength
• Determine water-cement ratio
• Check clearances for coarse aggregate
• Select needed air content
• Select target slump

92
6.7 Proportioning Steps

• Proportioning approaches
• Elements of the absolute volume method include
  (cont.)
• Select initial water content
• Calculate cement content
• Determine coarse aggregate content
• Determine dosages for admixtures
• Determine fine aggregate content
• Make moisture corrections
• Prepare trial batch
• Make adjustments based on results from trial
  batch

93
6.7 Proportioning Steps

• Proportioning approaches
• Proportioning by trial batches (cont.)
• Example 5, PCA, Chapter 9 provides an overview
  for proportioning a concrete mix via the absolute
  volume method using multiple cementing materials
  and admixtures. This example may be of interest
  to some of you.
• Concrete mixes for small jobs Advice is
  contained in Chapter 9 for this situationagain
  this may be of interest.

94
Discussion Forum

• Discuss the pros and cons associated with
  concrete mixes with low water-cement ratios (say
  w/c ratios of 0.40 or less). For the cons stated,
  how might they be mitigated.
• So we are all discussing the same application,
  make the concrete application a pavement project
  using fixed forms (not slip forming).

95
Lesson 6 References

• Powers, T. and Brownyard, T. (1948), Studies of
  the Physical Properties of Hardened Portland
  Cement Paste, Bulletin 22, Portland Cement
  Association, reprint from the Journal of the
  American Concrete Institute, Detroit, Michigan,
  March 1948.
• Hosmatka, S., Kerkoff, B., and Panarese, W.
  (2003), Design and Control of Concrete
  Mixtures, 14th Edition, Portland Cement
  Association, Skokie, Illinois.
• USGS (2004), Mineral Commodity Summaries, US
  Geological Survey, January 2004.

96
Lesson 6 References

• RMA (2003), US Scrap Tire Markets, 2003
  Edition, Rubber Manufacturers Association,
  Washington, DC, July 2004.
• ICC (2000), International Building Code,
  International Code Council, Falls Church,
  Virginia, March 2000.
• ACI (2003), Mass Concrete, ACI 207.1R-96, ACI
  Manual of Concrete PracticePart 12003, American
  Concrete Institute, Farmington Hills, MI.