2.1. Concrete

Lime

• One of the oldest building materials used as a mortar and plaster
• Quicklime (calcium oxide): Reacts with water; used in masonry mortar.
• Slaking/Hydration: Mixing quicklime with water, releases heat.
• Hydrated Lime (Calcium Hydroxide): Used for mortar, base coat plaster, and concrete
  • Mason's hydrated lime: Made from quicklime, used in mortars, base coat plaster
  • Finishing hydrated lime: White and plastic; used in finishing plaster coats
  • Special finishing hydrated lime: Becomes more plastic after 30 minutes

Gypsum

• Used as plaster by Egyptians, Greeks, and Romans
• Gypsum rock: Heated to remove water, turning it into plaster products.
• Products:
  • Plaster of Paris: Pure gypsum product
  • Hard wall plaster: Contains impurities (39.5%)
• Hard finishing plaster: All water removed with heating; hardens slowly
  • Example: Keene's cement
• Plasticity: Can be made more plastic by adding hydrated lime
• Fibers: Hemp, sisal, jute fibers/hair added for cohesiveness

Cement

• Romans developed cement by mixing slaked lime with pozzolana
• Cement knowledge lost after the Roman Empire
• Rediscovered by Smeaton in 1756
• Portland cement invented by Joseph Aspdin in 1824
• Today, "cement" generally refers to Portland cement

Cementitious Materials

• Quick-Setting Alumina Cement (Bauxite): Quick-setting cement made from bauxite
• High Alumina Cement: Also known as Aluminous Cement and Calcium Aluminate Cement; resistant to hydroxylic compounds; can be used as an accelerator for Portland Cement
• Masonry Cements: Portland cement mixed with Hydrated Lime, slag, silica, etc.
• Natural Cements: Made from natural materials; sets faster than Portland cement but develops strength more slowly
• Pozzolanic Cement: Lime mortar mixed with pozzolanic material (high silica content) like volcanic ash, slag, or pumice
  • Slag cement: A type of pozzolanic cement made from slag
  • Flyash: Another pozzolanic cement, aluminous and siliceous material reacting with water
• Natural and Slag Cements: Used in structures where mass and weight are important

Types of Portland Cement

• Portland Cement: Finely pulverized clinker mixed with argillaceous and calcareous materials; gypsum regulates settling time
• Portland Cement Components:
  • Tricalcium Silicate (C3S): Responsible for early hardening and strength gain
  • Dicalcium Silicate (C2S): Responsible for long-term strength gain
  • Tricalcium Aluminate (CA): Contributes to initial setting
  • Tetracalcium Aluminoferrite (C4AF): Contributes to cement manufacturing, allows lower clinkering temperatures
• Types of Portland Cement:
  • Slow-setting cement: Used for situations requiring a slower setting time
  • Quick-setting high early strength cement: Used when early strength is essential
  • Sulphate-resisting cement: Used where the cement needs to resist alkaline water or similar soils
  • White Portland Cement: Used for its light color, widely applied today; free of iron; common in marble, granite, and limestone applications
• Types conforming to ASTM C-150:
  • Type I (Ordinary Portland): General use; used in concrete, pavements, floors, reinforced concrete buildings
  • Type IA (Air-entrained): Type I cement with air-entraining additives to create air-entrained concrete

Other Cementitious Materials

• Magnesium-OxySulphate Cement: Good binding properties but weaker than oxychloride cement
• Phosphate Cement (Quick-Setting): Used for patching, sprayable foamed insulation, and coatings
• Waterproof Cement: Used in cementitious waterproofing membranes

Cement Types

Portland Cement Types

• Type I: Ordinary Portland Cement

Blended Cement

• Portland cement blended with by-product materials (slag, fly ash, silica fume, pozzolans)
• Five classes recognized by ASTM C 596, including Portland pozzolan cement (Type IP and Type P)

Special Cements

• Masonry Cements: Portland cement, air-entraining additives, and plasticizers; used in mortar for masonry
• Expansive Cements: Increase in volume during setting; used for shrinkage control in concrete
• Special Cements:
  • Oil Well Cement: Slow setting, resistant to high temperatures and pressure, used for sealing oil wells
  • Waterproofed Portland Cement: Reduces capillary water transmission
  • Plastic Cement: Portland cement and plasticizing agents; for mortar, plaster, and stucco
  • Gun Plastic Cement: Similar to plastic cement; applied by compressed air guns
  • Block Cement: Similar to Type III, but with controlled color
  • Pipe Cement: Specially made for centrifugally spun pipe
  • White/Colored Portland Cement: Made from selected raw materials; white or another color instead of gray; used for architectural purposes

Concrete

Definition

• A proportioned mixture of cement, aggregate, and water.
• Concrete hardens and becomes stone-like with proper proportions.

Cementitious mixtures

• Fine aggregate (less than 6mm): Mortar, stucco, or cement plaster
• Large aggregate (more than 6mm): Concrete
• Steel embedded: Reinforced concrete
• No steel: Plain or mass concrete

Regulated Set Cement

• Sets in a few hours to one hour

Packaging and Storage of Cement

• Packed and sold in bags (1 cubic foot, 94 pounds)
• Quantities also expressed in barrels (4 bags, 376 pounds)
• Protect from injury and dampness.
• Store in a shed with a raised wooden floor
• Avoid storing in high piles to prevent moisture absorption

Water-Cement Reaction

Hydration

• Chemical reaction between Portland cement and water

Setting

• Cement and water form a paste, eventually becoming stiff and hard
• Hardening process is called setting
• False Set: Stiffening of the mixture with little heat generation

Heat of Hydration

• Heat generated during the water-cement reaction

Types of Concrete

Normal Weight Concrete

• 135–165 lbs/ft³, compressive strength between 2,000 and over 8,000 psi
• Used for structural framing, pavements, and floors

Lightweight-Structural Concrete

• 85-115 lbs/ft³, resistance to heat flow
• Used for load-bearing and exterior walls, and prestressed concrete

Lightweight-Insulating Concrete

• 15-90 lbs/ft³, aggregates like perlite, vermiculite, expanded polystyrene, wood chips, or fibers.
• Used to fill over metal roof decks, partitions, and panel walls

Concrete Types

Heavyweight Concrete

• Density: 130-290 lbs/ft³
• Use: Walls of spaces containing radioactive materials; counterweights

Cellular Concrete

• Use: High insulating properties are required (e.g., foundations)
• Properties: Air or bubble gas suspended in mortar

Gap-graded concrete

• Use: Where aggregate is exposed (e.g., foundations)
• Properties: Inexpensive concrete

Shotcrete or Gunite

• Use: Where formwork is not desirable
• Properties: Pneumatic equipment using dry/wet method

Pre-placed concrete

• Use: Special forms/surfaces
• Properties: Coarse aggregate placed dry; mortar pumped into it

Pumped Concrete

• Use: Concrete placed high above grade or complex shapes

Ferrocement

• Use: Containers, bins, boat hulls, etc.
• Properties: Mortar with reinforcing wire

Fiber-reinforced Concrete

• Use: Slabs on grade, pavements, pneumatically placed concrete, precast, overlays
• Properties: Short fibers added to control shrinkage and increase strength.

Other Concrete Types

• Nailing: Roof decks; high nail holding strength
• No slump concrete: Placed in a consistency of 6mm (1/4"); high strength, low shrinkage
• Porous concrete (Pervious concrete): Drainage pipes, walls; allows water to pass through
• Permeable pavement: Pavements; high porosity for rainwater runoff
• Tremie Concrete: Placing concrete underwater; gravity feed from hopper through vertical pipe
• Polymer-impregnated concrete: Surface impregnation of bridge decks; repair; underwater/marine applications; irrigation structures
• Polymer-Portland Cement Concrete (PPCC) or Polymer Cement Concrete (PCC) or Polymer Modified Concrete (PMC) or Latex-Modified Concrete (LMC): Bridge deck coverings, floor construction, precast construction, patching compound
• Polymer Concrete (PC): Curtain and wall facing panels; polymers replace lime-type cements
• Sulphur concrete: Industrial floors, bridge decks, leach tanks, sewer pipes; rapid solidification; strength similar to Portland cement
• Reinforced concrete: Various; primary reinforcing may be bar or rods
• Prestressed concrete: Various, pretensioned: section is placed in compression using pretensioned steel wires
• Posttensioned concrete: Various: section is placed in compression using posttensioned cables after casting

Factors Affecting Strength and Durability of Concrete

• Water-Cement Ratio
• Cement-Aggregate Ratio
• Size of Coarse Aggregates
• Ratio of Fine Aggregates to Coarse Aggregates
• Type of Cement