11.4 Cement and Concrete

Cement and concrete are essential materials in construction, combining strength and versatility. They're made from simple ingredients but involve complex chemistry. Understanding their composition, properties, and production is key to creating durable structures.

Cement's hydration process transforms it from powder to solid, while concrete's properties depend on its mix. Both materials face challenges in durability and sustainability, driving innovations in production and use to reduce environmental impact and improve performance.

Cement Composition and Hydration

Chemical Composition of Cement

Top images from around the web for Chemical Composition of Cement

• 

  Synthesis, Properties and Hydration Characteristics of Novel Nano-Size Mineral Trioxide and ... View original

  Is this image relevant?

• 

  Revealing the dependence of the physiochemical and mechanical properties of cement composites on ... View original

  Is this image relevant?

• 

  Influence of the Ca/Si ratio on the compressive strength of cementitious calcium–silicate ... View original

  Is this image relevant?

• 

  Synthesis, Properties and Hydration Characteristics of Novel Nano-Size Mineral Trioxide and ... View original

  Is this image relevant?

• 

  Revealing the dependence of the physiochemical and mechanical properties of cement composites on ... View original

  Is this image relevant?

1 of 3

Top images from around the web for Chemical Composition of Cement

• 

  Synthesis, Properties and Hydration Characteristics of Novel Nano-Size Mineral Trioxide and ... View original

  Is this image relevant?

• 

  Revealing the dependence of the physiochemical and mechanical properties of cement composites on ... View original

  Is this image relevant?

• 

  Influence of the Ca/Si ratio on the compressive strength of cementitious calcium–silicate ... View original

  Is this image relevant?

• 

  Synthesis, Properties and Hydration Characteristics of Novel Nano-Size Mineral Trioxide and ... View original

  Is this image relevant?

• 

  Revealing the dependence of the physiochemical and mechanical properties of cement composites on ... View original

  Is this image relevant?

1 of 3

• Cement is a fine powder composed primarily of calcium silicates, aluminates, and ferrites
• The main components are:
  • Tricalcium silicate (C3S)
  • Dicalcium silicate (C2S)
  • Tricalcium aluminate (C3A)
  • Tetracalcium aluminoferrite (C4AF)

Hydration Process of Cement

• When water is added to cement, a complex hydration process occurs, forming various hydration products that contribute to the strength and durability of the hardened cement paste
  • C3S and C2S react with water to form calcium silicate hydrate (C-S-H) gel, the primary binding phase in cement, and calcium hydroxide (Ca(OH)2)
  • C3A reacts with water and gypsum (calcium sulfate dihydrate) to form ettringite, which helps control the setting time and early strength development
  • C4AF hydration contributes to the formation of C-S-H gel and iron oxide-hydroxide phases
• The hydration process is exothermic and involves:
  • Dissolution of cement particles
  • Nucleation and growth of hydration products
  • Development of a porous microstructure
• The rate of hydration depends on factors such as:
  • Cement composition
  • Fineness
  • Water-to-cement ratio
  • Temperature
  • Presence of admixtures (superplasticizers, retarders)

Concrete Properties and Applications

Properties of Concrete

• Concrete is a composite material consisting of cement, water, aggregates (sand and gravel), and optional admixtures
• The properties of concrete depend on the proportions and characteristics of its constituents
• Key properties of concrete include:
  • Compressive strength: the most important mechanical property, typically ranging from 20 to 100 MPa, depending on the mix design and curing conditions
  • Tensile strength: significantly lower than compressive strength, usually about 10% of the compressive strength
  • Elastic modulus: a measure of the stiffness of concrete, related to its deformation under load
  • Durability: resistance to deterioration caused by environmental factors (freeze-thaw cycles, chemical attack)
  • Workability: ease of mixing, placing, and compacting fresh concrete
  • Thermal properties: heat capacity, thermal conductivity, and coefficient of thermal expansion

Applications of Concrete

• Concrete is widely used in construction due to its versatility, durability, and cost-effectiveness
• Applications include:
  • Buildings (residential, commercial, industrial)
  • Bridges
  • Dams
  • Pavements (roads, airports, parking lots)
  • Foundations
  • Precast elements (pipes, barriers, panels)
• Specialty concretes are designed to meet specific performance requirements:
  • High-performance concrete: enhanced strength, durability, and workability
  • Self-compacting concrete: flows under its own weight, eliminating the need for vibration
  • Fiber-reinforced concrete: incorporates fibers (steel, glass, synthetic) to improve tensile strength and crack resistance
• Reinforced concrete combines concrete with steel reinforcement (bars, mesh) to improve the tensile strength and ductility of structural elements

Cement and Concrete Production

Cement Manufacturing Process

• Cement manufacturing involves:
  • Extraction of raw materials (limestone and clay)
  • Raw meal preparation: raw materials are crushed, milled, and homogenized to form a raw meal
  • Clinker production: raw meal is preheated and calcined in a rotary kiln at temperatures around 1450°C to form clinker
  • Grinding of clinker with gypsum to produce cement
• Quality control in cement manufacturing involves monitoring and controlling:
  • Chemical composition
  • Fineness
  • Setting time
  • Strength development of cement

Concrete Production and Quality Control

• Concrete production involves:
  • Mixing of cement, water, aggregates, and admixtures in the correct proportions
  • Placing, compacting, and curing of the concrete
• Quality control in concrete production includes:
  • Selection and testing of raw materials (cement, aggregates, water, admixtures)
  • Mix design optimization to achieve desired properties and performance
  • Monitoring of fresh concrete properties:
    • Slump: a measure of the consistency and workability of fresh concrete
    • Air content: important for freeze-thaw resistance
    • Setting time: the time required for concrete to harden and gain strength
  • Assessment of hardened concrete properties through laboratory tests on concrete specimens:
    • Compressive strength
    • Durability (permeability, resistance to chemical attack)
    • Dimensional stability (shrinkage, creep)

Concrete Durability and Sustainability

Factors Affecting Concrete Durability

• Durability of concrete refers to its ability to resist deterioration caused by environmental factors
  • Freeze-thaw cycles
  • Chemical attack (sulfates, acids, chlorides)
  • Reinforcement corrosion
• Factors affecting concrete durability include:
  • Quality of raw materials
  • Mix design parameters (water-to-cement ratio, cement content, use of supplementary cementitious materials)
  • Construction practices (compaction, curing, cover thickness)
  • Exposure conditions (temperature, humidity, aggressive agents)
• Strategies for improving concrete durability:
  • Optimizing mix design: low water-to-cement ratio, adequate cement content, use of supplementary cementitious materials (fly ash, slag)
  • Proper compaction to minimize voids and achieve a dense microstructure
  • Adequate curing to promote hydration and strength development
  • Sufficient cover thickness to protect reinforcement from corrosion

Environmental Sustainability of Cement and Concrete

• Environmental sustainability involves assessing the life-cycle environmental impact of cement and concrete structures
  • Raw material extraction
  • Manufacturing
  • Construction
  • Operation
  • End-of-life management
• The cement industry is a significant contributor to global CO2 emissions
  • Calcination of limestone releases CO2
  • Burning of fossil fuels in the manufacturing process
• Strategies for improving the environmental sustainability of cement and concrete:
  • Use of alternative fuels (waste-derived fuels, biomass)
  • Energy efficiency measures in cement production
  • Incorporation of waste materials as supplementary cementitious materials (fly ash, blast furnace slag, silica fume)
  • Design of durable, long-lasting concrete structures to reduce maintenance and replacement needs
  • Adoption of circular economy principles:
    • Reuse of concrete elements
    • Recycling of concrete as aggregate for new concrete or road base
• Sustainable construction practices and the use of green building rating systems (LEED, BREEAM) promote the environmental sustainability of the built environment