Cert III Concreting key terms

The process of removing trapped air from freshly placed concrete by vibration or tamping so the mix consolidates fully around reinforcement and forms a dense, strong mass.

Mechanical agitation of wet concrete using poker, screed or table vibrators to release air and improve density, applied at controlled duration to avoid over-vibration and segregation.

Separation of coarse aggregate from the mortar or paste in a concrete mix, usually caused by over-vibration, dropping from height, or a mix that is too wet.

Voids and gaps left in concrete where mortar has failed to fill spaces between coarse aggregate, typically from poor compaction, congestion of reinforcement, or a stiff mix.

A field test in which a cone-shaped mould filled with fresh concrete is lifted away and the drop in height measured to indicate workability and consistency of the mix.

The ease with which a concrete mix can be placed, compacted and finished without segregation, influenced by water content, aggregate shape and the use of admixtures.

The mass of water divided by the mass of cementitious material in a mix; a key control on strength, durability and permeability, with lower ratios generally giving stronger concrete.

Keeping concrete moist and at a suitable temperature after placing so cement hydration can continue, protecting strength development and reducing shrinkage cracking.

A material other than cement, aggregate or water added to a concrete mix in small quantities to change properties such as set time, workability or air content.

The temporary moulds, sheeting, frames and supports that hold wet concrete in the required shape and position until it has gained enough strength to stand alone.

The controlled removal of formwork once concrete has reached adequate strength, sequenced to avoid damage to edges, surfaces or the structure itself.

The temporary structural support system of props, beams and bearers that carries formwork and wet concrete loads down to a firm base until the permanent structure can support itself.

A coating applied to formwork faces to stop concrete bonding to the mould, giving a cleaner surface finish and easier, less damaging stripping.

Steel bars, mesh or fibres placed in concrete to resist tensile and shear forces, positioned to the specified cover and lap lengths before concrete is poured.

The depth of concrete between the outer surface of embedded reinforcement and the nearest exposed concrete face, protecting steel from corrosion and fire.

The distance over which two reinforcing bars are overlapped and tied so that force transfers from one bar to the other, specified by the designer for each bar size.

A small support, usually wire or plastic, placed under reinforcement to hold the top or bottom bars at the correct height so the specified concrete cover is maintained.

Striking off excess fresh concrete and levelling it to the required height and fall using a straightedge, screed board or mechanical screed.

Finishing concrete with a hand or power trowel to produce a smooth, dense surface, timed to avoid bringing excess paste or water to the top.

The rise of mixing water to the surface of freshly placed concrete as heavier solids settle, which can weaken the top layer and delay finishing.

A deliberately formed or sawn line of weakness in a concrete slab that forces shrinkage cracking to occur at a chosen, neat location.

A gap or compressible filler between concrete elements that allows them to move with temperature and moisture changes without damaging each other.

The designed slope built into a concrete surface, such as a path or floor, so that water drains to a specified point instead of ponding.

Temporary props installed under a suspended slab after formwork is removed, sharing construction loads between floors until the concrete has fully matured.

A written document that sets out the high-risk construction tasks for a job, the hazards involved, and the controls that will be applied to manage them.

The ranked order in which risk controls are chosen, starting with eliminating the hazard and working down through substitution, engineering controls and administration to protective equipment.

Clothing and gear worn by a worker to reduce exposure to hazards, such as hard hat, safety boots, gloves, eye protection and hearing protection.

A chemical or material that can harm health, such as cement dust or silica, requiring a current safety data sheet, labelling and controls before use.

A standard document supplied with a hazardous chemical that describes its hazards, safe handling, required protective equipment and first-aid measures.

Fine crystalline particles released when cutting, grinding or drilling concrete, stone or masonry, which can cause serious lung disease if inhaled without dust controls.

A machine that moves wet concrete through pipes or a boom to a placement point, allowing pours in locations that are difficult or unsafe for trucks and chutes.

Depositing fresh concrete into its final position in even layers at a controlled rate, close to its final location, to avoid segregation and cold joints.

A weak plane formed where fresh concrete is placed against concrete that has already begun to set, preventing a proper bond between the two layers.

A guide set at the required level and fall, used to strike off and level freshly placed concrete to a consistent surface.

Working out the amount of concrete needed by multiplying length, width and depth in consistent units, then adding an allowance for waste and over-excavation.

A rating assigned to a concrete element describing the severity of its environment, which sets minimum strength, cover and mix requirements for durability.

Concrete elements cast and cured in a controlled off-site location, then transported and lifted into position on the building site.

Temporary covers and barriers used to shield fresh concrete from rain, wind, sun or heat so the surface finish and curing are not spoiled.