concrete

• concrete

  in construction, structural material consisting of a hard, chemically inert particulate substance, known as aggregate, that is bonded together by cement and water
• water

  used in making concrete should be clear and free of sulfates, acids, alakalies, and humus.
• admixtures

  are ingredients added to concrete, other than portland cement, aggregates, and water.
• air entraining admixtures

  used to entrain microscopic air bubbles in concrete
• retarders

  used to slow the setting time of cement paste in concrete
• water reducers

  lower the amount of water needed to produce concrete of a given consistency. also used to increase the amount of slump without requiring additional water
• accelerator

  speeds up the strength development of concrete.
• calcium chloride

  is a frequently used accelerator
• pozzolan

  siliceous and aluminous material that, when finely ground in the presence of moisture, chemically reacts with calcium hydroxide at ordinary temperatures to form compounds processing cementitious prperties
• superplasticizers

  admixtures that coat the cement particles, causing them to break away from the lumps and disperse in water;'
• bonding agents

  increase bond strengh
• two parts of concrete

  • aggregates
  • paste
• slump

  is a measure of the consistency of concrete, defining the ability of fresh concrete flow
• concrete design

  concrete mixes are specially designed to povide the needed characteristics for a particular application
• nondestructive tests

  used to evaluate the strength and durability of hardened concrete.
• rebound tests

  are made with schmidt rebound hammer. it measures the distance a spring-loaded plunger rebounds after striking the concrete surface
• penetration tests

  uses a windsor probe, which is a power-activated gun that drives a hardened alloy probe into the concrete
• pull out tests

  requires that a steel rod with an enlarged end be cast in the concrete
• dynamic or vibration tests

  uses the principle that the velocity of sound in a solid can be measured either by recording the time it takes short impulses of vibrations to pass through a sample
• truck agitators / non agitating trucks

  commonly used to deliver the fresh concrete.
• consolidation

  the process of compacting freshly placed concrete in forms around reinforcing steel to remove air and aggregate pockets