High Performance Concrete Overview

High Performance Concrete

• Concrete made with a carefully designed mix, mixed, transported, placed, consolidated and cured properly
• It can be used in structures requiring long service lives, such as oil drilling platforms, long-span bridges and parking structures
• Delivers high performance with good curing and construction practices

Characteristics of High Performance Concrete

• High early strength
• High strength
• High modulus of elasticity
• High abrasion resistance
• High durability and long life in severe environments
• Low permeability and diffusion
• Resistance to chemical attack
• High resistance to frost and deicer scaling damage
• Toughness and impact resistance
• Volume stability
• Ease of placement
• Compaction without segregation
• Inhibition of bacterial and mold growth

Stamped Concrete

• Concrete is patterned or textured to resemble brick, slate, flagstone, stone, tile, wood
• Common applications include patios, sidewalks, driveways, pool decks and interior flooring
• Less expensive alternative to materials such as stone, slate or brick

Factors Affecting Workability

• Mix Proportion:
  • The ratio of fine and coarse aggregates in relation to cement quantity
  • More cement results in a richer concrete, facilitating mobility and flow of aggregates
  • A lower cement quantity makes less paste available for aggregates, hindering mobility
• Size of Aggregates:
  • Workability decreases with an increase in the surface area of aggregates
  • As the maximum size of coarse aggregate is increased, the surface area is decreased, improving workability
• Shape of Aggregates:
  • Rounder particles have a decreased surface area, leading to improved workability
• Surface Texture of Aggregates:
  • Rough textured aggregates have a larger surface area compared to smooth textured aggregates of the same volume
  • Concrete with smooth surfaces is more workable than concrete with rough textured aggregates
• Grading of Aggregates:
  • Increasing the fineness modulus of fine aggregates requires a decrease in the amount of coarse aggregate to maintain workability
  • Increasing coarse aggregate proportion generally benefits workability
• Use of Admixtures:
  • Admixtures such as water-reducing admixtures, superplasticizers and air-entraining admixtures can improve workability
  • They enhance workability even when using a low water/cement ratio

Segregation

• The separation of cement paste and aggregates of concrete during handling and placement
• High-workability mixes should not be over-vibrated, as this can cause segregation
• Vibration can be used to mold concrete around embedment, such as reinforcement, and to eliminate air pockets

Compacting

• Vibrators:
  • Internal vibrators compact concrete through direct contact
  • Form vibrators are attached to the formwork and transfer vibrations to the concrete
  • Surface vibrators are placed on top of the concrete, suitable for thin concrete layers

Finishing

• Compacting or hand tamping may leave an uneven surface
• Surfaces are finished smoothly or according to desired pattern using floats, trowels and screeds
• Floating followed by steel troweling is used for a smooth, hard, dense surface
• Embedding aggregate particles just beneath the surface removes imperfections, humps and voids, compacting the mortar for further finishing operations
• A slip-resistant surface is achieved by brooming before concrete hardens, but only after it has hardened enough to retain the scoring impression

Curing

• Maintaining moisture and temperature to promote hydration and strength gain
• Concrete should be cured in a suitable environment
• Drying in air during the early stages of hardening generally reduces strength
• Curing keeps the concrete saturated to prevent the loss of water from the water-filled capillaries
• Hydration can only occur when the vapor pressure in the capillaries is sufficiently high

Curing Methods

• Maintain the presence of water in concrete
• Seal the surface to prevent water from escaping
• Apply heat and additional moisture
• Consider the size and shape of the structure when choosing a method