Terminology

• f'c: specified compressive strength at a stated age, usually 28 days
• w/cm: water to cementitious materials ratio; lower gives stronger, more durable concrete (Abrams' law)
• SCM: supplementary cementitious material (fly ash, slag, silica fume) replacing part of the cement
• Normal-weight / lightweight: by aggregate; lightweight uses lightweight coarse aggregate
• Cast-in-place / precast: placed in the final position / cast off site and erected
• Prestressed concrete: concrete with steel tensioned to put it in compression
• GFRC: glass fiber-reinforced concrete
• ICF: insulating concrete forms

History and demand

Invention

• 1824: Joseph Aspdin patented portland cement
• 1849: Joseph Monier invented reinforced concrete
• 1928: Eugène Freyssinet patented prestressed concrete (October 2)

First uses in construction

• About 1400 to 1200 BC: concrete floors at Tiryns, Greece
• About 300 BC to AD 476: Roman use of opus caementicium, roughly 20 MPa (2,900 psi); the Pantheon dome, finished in AD 128, is the largest unreinforced concrete dome
• 1853: François Coignet built the first reinforced concrete house; 1875: Monier built the first reinforced concrete bridge

Sourcing

• Concrete is mixed near the point of use from cement, sand, and gravel or crushed stone; the leading cement producers are China (47.5 percent of world output in 2024) and India

Demand trend

• Rising with cement: 4.4 billion tons of cement were manufactured in 2023 (see Cement); cement is one of the largest sources of global greenhouse gas emissions, about 5 to 10 percent

Composition and production

Raw materials

• Aggregate (gravel, crushed stone, sand) bound by cement paste of portland cement and water
• SCMs such as fly ash, slag, and silica fume can replace part of the cement

Manufacturing process

• Hydration of the cement paste hardens the mix; reinforced with steel bars because concrete is weak in tension

Product forms

• Ready-mixed cast-in-place concrete, precast members, masonry units, shotcrete, and glass fiber-reinforced concrete panels

Grades and types

• Normal-weight: the default structural concrete
• Lightweight: coarse lightweight aggregate
• Shotcrete: sprayed concrete
• GFRC: thin precast panels
• Prestressed: pretensioned or post-tensioned structural members

Properties

Physical

• Density (normal weight): about 145 lb/ft³; unit weights run about 140 to 155 lb/ft³ and rise about 1 lb/ft³ per 1,000 psi of strength

Mechanical

• Compressive strength: typical normal-strength concrete 3,000 to 6,000 psi (20 to 40 MPa)
• Modulus of elasticity: Ec = 33 w^1.5 √f'c (psi, w in lb/ft³); about 3,200 ksi at 3,000 psi and 3,800 to 4,100 ksi at 5,000 psi for 145 lb/ft³ concrete

Thermal and moisture

• Coefficient of thermal expansion: about 5.5 × 10⁻⁶ in./in./°F; FHWA default 6 × 10⁻⁶

Standards

Material specifications

• ACI 318 (318-19): structural concrete design and the materials standards it lists
• ACI 117: tolerances for cast-in-place concrete
• ACI ITG-7: tolerances for precast concrete
• ASTM E2634: insulating concrete form material for flat walls
• PCI 128: glass fiber-reinforced concrete

Uses in buildings

Building elements

• Spread and Continuous Footings, Slab on Grade, Polished Concrete: foundations, slabs, and finished slab surfaces
• Cast-in-Place Concrete Walls, Cast-in-Place Concrete Beams and Columns, Shear Walls, Tilt-Up Concrete Walls: cast structural walls, frames, and tilt panels
• Precast Concrete, CMU Walls: factory-cast members and masonry units
• Retaining Walls: cast and segmental wall units
• Composite Metal Deck Floors: topping slab on steel deck
• Clay and Concrete Tile Roofing: concrete roof tile
• Grease Interceptors, Site and Pole Lighting: precast tanks, and pole foundations

Pros and cons

Pros

• Strong in compression and moldable to any shape
• Compressive strength 3,000 to 6,000 psi in ordinary mixes
• Reinforced and prestressed forms carry tension and long spans
• Cement can be partly replaced by SCMs

Cons

• Weak in tension; needs reinforcement
• About 145 lb/ft³, a heavy dead load
• Cement drives its embodied carbon

Design considerations

Movement

• Expansion about 0.07 in. per 10 ft for a 100°F swing (calculated from 5.5 × 10⁻⁶ in./in./°F); joints per ACI 224.3R

Sustainability

Embodied carbon

• Cement alone is about 0.80 kg CO2 per kg

Recycled content and end of life

• SCMs (fly ash, slag, silica fume) replace part of the cement

Manufacturing and cost

Main manufacturers and suppliers

• Heidelberg Materials
• CEMEX
• GCC

Trade associations: National Ready Mixed Concrete Association; American Concrete Institute.

Sources

• Wikipedia: Concrete, https://en.wikipedia.org/wiki/Concrete
• Wikipedia: Properties of concrete, https://en.wikipedia.org/wiki/Properties_of_concrete
• FHWA: concrete properties, https://www.fhwa.dot.gov/publications/research/infrastructure/bridge/05057/appc.cfm
• UpCodes: 2024 IBC Chapter 19 concrete, https://up.codes/viewer/department-of-defense/ibc-2024/chapter/19/concrete
• Wikimedia Commons: 2023-07-12 10 47 34 60-year old sidewalk along Lochatong Road in the Mountainview section of Ewing Township, Mercer County, New Jersey.jpg, photo by Famartin (CC BY-SA 4.0), https://commons.wikimedia.org/wiki/File:2023-07-12_10_47_34_60-year_old_sidewalk_along_Lochatong_Road_in_the_Mountainview_section_of_Ewing_Township,_Mercer_County,_New_Jersey.jpg