Glossary

Vehicle in which plastic concrete is delivered to site.

Australian Standard for Concrete Structures (mainly focussed on how to design concrete structures and used by design and construction engineers). This is an important standard as it references AS1379 for concrete supply. It is the starting point for the translation of information from buildings and structures to concrete. Many buyers of concrete make reference to this document.

Australian Standard on "The Specification and Supply of Concrete". It forms the basis of contracts/agreements for concrete supply to customers and minimum standards on how concrete should be produced.

A unit to maintain reinforcement in the correct position.

Quantity weighed and loaded in any one truck as per mix design.

The process of the manufacture of concrete involving weighing of materials in weigh bins and loading into agitators.

• see: AS1379 (Australian Standard on the "Specification and Supply of Concrete").

A term sometimes used for coarse aggregate. Generally a crushed hard rock.

Mix water which is released from concrete after placement. Normally forms pools on the concrete surface. Degree of bleeding is controlled by good mix designs.

Mix which appears to lack sand or cement. Is bony in appearance and has a high percentage of voids. Difficult to place and compact.

• see: Formwork.

A surface finish applied to concrete to give a non skid surface. Involves using a broom over the concrete surface (when it is plastic) in one direction to provide a roughened grooved surface.

The main code used by architects/builders/contractors to ensure that their concrete structure or building conforms to relevant standards. This document calls up AS3600 for concrete. Many buyers of concrete reference this document.

Is the compressive strength grade of concrete determined statistically as described in AS1379. Basically, a characteristic compressive strength means that out of 100 test results, 95 or more will be equal to or greater than a specified strength. Typical specified strengths for this are 20 MPa, 25 MPa, 32 MPa, 40 MPa and 50 MPa. Denoted as f'c in Australian Standards AS3600 and AS1379.

Powdery substance manufactured from limestone, clay and gypsum and when combined with water, forms a bonding and hardening agent used in pre-mixed concrete. Main types are as follows:

• Type GP (General Purpose) see: G.P.
• Type HE (High Early) see: H.E.
• Type LH ( Low Heat) see: L.E.
• Type SR (Sulphate Resistant) see: S.R.
• Type GB ( General Blend) see: G.B.

Ability of mix to resist segregation (aggregates separating from the rest of the concrete constituents) during transportation and placement.

Australian Standard measure of concrete strength. Procedures for this can be found in AS1012 (Methods of Testing Concrete). Measured in Megapascals (MPa) which is basically a force applied per unit of area.

This involves taking a standard size concrete cylinder and curing as per Australian Standard AS1012 (Methods of Testing Concrete). Cylinders are normally cast on site, put in a water tank (cured) for 7, 14 or 28 days at which point they are tested for compressive strength by applying an increasing compressive force until failure.

Vehicle on site used for pumping concrete into forms.

A concrete specimen used for testing. Described in AS1012 (Methods of Testing Concrete) the commonly used standard size specimen is 100 mm diameter by 200 mm long.

Mix of high fly ash, low cement and sand 1-8 MPa. Nominal trench fill or mass fill. Often a branded product with specific properties.

see: Characteristic strength.

Is the process of keeping freshly placed concrete moist by reducing surface water loss to maximise the hydration process and reduce the probability of shrinkage cracks. Commonly used methods are wet hessian, plastic or sprayed on chemical curing compound. These products maintain moisture in the concrete to enhance curing (the better the curing treatment on freshly placed concrete, the better the concrete will be).

The term is also commonly used to describe the process of preparing concrete test cylinders prior to testing for compressive strength to ensure hydration and, therefore, strength potential is achieved as described in Australian Standards.

Is the weight per unit volume of concrete i.e., Density = Mass/Unit Volume (kg/m3). The density of most concrete is around 2400 kg per cubic metre which is a default design value in AS3600.

Deep groove in concrete designed to control shrinkage cracks whilst maintaining load transfer (like a moving truck on a concrete slab). Important in all paving concrete. Usually needs to be designed into a structure by a qualified engineer.

Concrete that has the surface cement mortar removed to expose the aggregate in the concrete. Used where aesthetic finish is desired or to provide a non-skid surface.

A strength test measuring the ability of concrete to resist failure in bending (beam test). Described in Australian Standards AS3600 (Concrete Structures) and AS1012 (Methods of Testing Concrete).

The process of obtaining the final surface of a concrete element (usually a major process in concrete slab construction).

A powdery material collected from the exhaust gasses produced at coal fired power stations during electricity generation. The material has similar fineness to cement and when mixed into concrete, has cementitious properties. Described in Australian Standard AS3528 and is referred to as a pozzolanic material or a supplementary cementitious material.

Material used to contain concrete in the plastic state. Formwork can be metal, fibreglass or timber.

A type of cement produced by combining Portland cement with supplementary cementitious materials such as fly ash, ground slag and/or silica fume in varying proportions (typically ranging between 5% and 60%) to produce a blended cement. Described in Australian Standard AS3972. The three most common supplementary cementitious materials used are:

• Ground Granulated Iron Blast Furnace Slag (Slag), a by-product of the steel industry. see: Ground slag
• Fly ash, a by-product of coal-fired power stations producing electricity. see: Fly ash
• Silica fume, a fine powder collected from the process of silicon metal manufacturing.

A general purpose cement which is described in Australian Standard AS3972. Produced from grinding cement clinker (silica, alumina and iron based components fused at high temperatures around 1500°C that produces a rock type material called clinker).

Normal concrete with 7 mm maximum size aggregate. Used mainly for surfacing floors, concrete repairs, infills and cavity walls.

High early strength cement as defined under AS3972. A cement that develops strength more rapidly (not to be confused with setting time) than General Purpose (GP) cements. Cement compressive strengths are determined by casting cubes of mortar (cement mixed with water and a specified sand).

Performs similar function to N.C.A (Non-chloride Accelerator). Can be used in lieu of, or in addition to, as a setting aid.

The chemical reaction which takes place as a result of combining cement and water. Maximum hydration equals maximum potential strength of concrete.

Is concrete when placed in its final position.

A strength test that measures a concrete's resistance to being pulled apart (called an indirect tensile test and described in AS1012). Tested by applying a compressive force to a concrete cylinder specimen placed on its side.

Mix with a high sand content with a very low slump (0-30mm) which is placed by a machine. Normally forms the edge of a pavement to direct drainage. Normally maximum size aggregate is 14mm.

A bucket for holding and transferring concrete from the agitator truck discharge point to placement point. Commonly lifted by a crane (crane & kibble).

Low strength concrete (low cement content) used for non-structural applications such as fill, or as a sub base for concrete pavements. Also called lean mix concrete.

Low density concrete using light weight aggregate (scoria) or BST (Polystyrene Beads). Density is usually less than 2100 kg/m3.

As its name implies, generates less heat during hydration or hardening. Used mainly in mass concrete pours such as raft slabs and dams to prevent thermal cracking. Can also be used in high strength concrete where early strength gain is not important. Often has supplementary cementitious materials included in the blend.

Refers to a concrete element that has a substantial cross section (typically greater than 600mm thick). The greater the thickness of the element, the greater the rise in temperature of the concrete after placement (concrete gets hot as the cement and binder materials hydrate and gain strength). Usually, special design and construction methods are needed and this often results in the development of special mix designs.

Metric unit of measuring compressive strength of concrete. Described in Australian Standards AS3600 and AS1012 (example 20 MPa or 32 MPa).

• see: Polythene

Reinforcement which consists of bars (technically referred to as wires) of steel spot welded together to form a mesh. The sizes given to the mesh refer to the wire diameter and wire spacing e.g. F62 is a wire diameter of 6mm spaced at 200mm centres.

A length change measurement usually of drying shrinkage of concrete using a specified concrete prism size described in AS1012. Concrete may have a specified maximum drying shrinkage criteria described as a unit of microstrain. Basically calculated by measuring a final specimen length referenced to an original specimen length.

The process of combining materials in to specified proportions used in producing concrete. Considerations include specified properties such as strength, plastic properties such as bleeding, setting times, customer satisfaction and materials available and costs.

The time taken to satisfactorily mix a load as per agitator manufacturer's specifications.

Water added to concrete at time of batching to enable hydration of cement and provide a workable mix.

A chloride free aid to accelerate setting time of concrete. Dosage rates can vary from 0.5 litres to 6.0 litres per metre depending on circumstances and specifications.

Concrete made with coarse aggregate and cement (up to 10%).

Concrete described in AS1379 specified by standard strength, standard slump and standard maximum size aggregate. Standard strength grades are N20, N25, N32, N40, N50 and standard slumps are between 40mm and 120mm.

Mix with high sand content normally 10mm aggregate. Concrete mix enables patterns of various designs to be created on the concrete surface. Colour usually added.

Concrete that is still capable of being worked and has not reached initial set (see set time).

Thin plastic sheet placed on ground below a slab prior to placement of concrete to prevent seepage of ground water up through the concrete and to prevent moisture loss from the concrete being absorbed by the sub-base (selected fill material placed immediately below a concrete slab). High moisture loss can cause cracking and reduction of strength of concrete.

A material like fly ash or silica fume that reacts chemically with lime produced from cement hydration resulting in concrete strength gain. These materials are used to supplement cement and are termed supplementary cementitious materials. When combined with Type GP cement they form Type GB cement (blended cement). Materials described in AS3582.

Concrete that is cast and cured in moulds and shifted into the final position. Generally enables better quality control and surface finish.

Specially designed concrete elements like slabs and beams that have compressive forces applied by the tensioning of prestressing cables (strands - used as part of the reinforcement). The strands may be pre-tensioned (tension before casting) or post-tensioned (after casting).

Prestressed concrete enables larger spans between columns, greater loads, minimal cracking and fast construction cycles. It can be a more economical construction solution on a project depending on the application.

Concrete is strong in compression but weak in tension. Therefore most concrete is reinforced with steel to improve the tensile strength of the finished concrete element. Reinforcement in concrete is also used to limit cracking by other forces such as shrinkage effects.

Welded wire steel fabric or steel bars used in concrete to control cracking and to meet structural loading requirements.

Test performed by completely drying out a small sample of sand to ascertain the percentage of water it contains. Mixes can then be adjusted accordingly for water content.
see: water:cement ratio

Refers to the condition of aggregates (coarse and fine) that have been soaked in water and the excess water (surface water) removed. SSD figures are used in designing mixes. It is the state of the aggregate where maximum absorption of water has occurred and there is no free water present. SSD density is higher than the density of the aggregate.

Process of levelling freshly placed concrete ready for surface finishing (the process for establishing the final surface of a concrete element).

The separation of fine and course aggregates and other finer fractions in a concrete mix. This is not desirable in supply of concrete. It can typically result from poor mix designs, aggregate shape, excessive slump, over-vibration, poor compaction and/or placement methods.

Concrete that specifically designed and is modified with specialty admixtures to provide a free flowing concrete that requires little or no compaction. SCC is normally specified where the use of vibrators is difficult due to congestion of steel reinforcement or where restricted by formwork.

Time taken for concrete to lose its plasticity and workability and stiffening (initial set). Defined in AS1012 (Methods of Testing Concrete). Setting times can be increased (by retardation) or reduced (by acceleration) in various ways, e.g., by use of chemical admixtures, hot water, using different types of cements and other binders and increasing cement content.

A concrete product designed to be pumped and sprayed using compressed air through a nozzle. Normally has a slump of 60mm and is used for the construction of concrete swimming pools, walls, bank stabilisation etc. Sometimes referred to as Gunite which was an old outdated reference to manufacture and supply of this material at a construction site.

A very misunderstood term in our industry. Occurs in all concrete whilst fresh (plastic shrinkage) and in its hardened state (drying shrinkage). It relates to concrete volume change resulting from water loss whilst the concrete is fresh and to concrete volume change resulting from the hydration process and from drying of concrete once the concrete is hard (in its hardened state).

Shrinkage can be marginally reduced by using the maximum amount of course aggregate permitted in a mix and keeping the concrete moist (curing) as long as possible during setting. Construction site practices have a major influence on shrinkage.

A product produced simultaneously with iron in a blast furnace that is quenched (cooled rapidly with water) and ground to produce a supplementary cementitious material that is used in concrete. Termed ground granulated iron blast furnace slag and described in AS3582, it can be incorporated into concrete directly or as a blended cement. It can provide concrete with many beneficial properties.

A product produced simultaneously with iron in a blast furnace that is cooled naturally (not quenched). The material forms a rock like structure that is crushed to result in an aggregate material that can be incorporated into a concrete mix. Slag aggregates can impart beneficial properties to concrete.

A measure of the consistency of workability of concrete and is a simple means of ensuring uniformity (of a given mix) of concrete on site. The test procedure is described in AS1012 (Methods of Testing Concrete).

A test where a standard size steel slump cone is filled with plastic concrete, procedures for which are described in AS1012. The cone is them removed from the concrete to allow it to "slump". The difference between the height of the cone and the collapsed concrete is measured in millimetres and is termed as the concrete slump. A typical concrete slump is 80mm. Normal Class concretes have slumps in the range between 40mm and 120mm.

Mix of sand and cement at varying ratios 1:2 > 1:10. Slump depends on application. Used for trench fill or block core fill.

Concrete which is specified to have certain properties or characteristics different from or additional to those of Normal Class concrete.

A statistical measurement which indicates the amount of variation. Commonly used for 28 day concrete compressive strength result analysis. A good result is a SD of less than 2 MPa.

Is the numerical value of the characteristic strength of concrete tested at 28 days. Designated by N20, N25, N30, N40 or N50 in the case of Normal Class concretes. Refer characteristic strength and normal class concrete.

Sulphate resistant cement which provides additional protection where the concrete is subject to an aggressive environment rich in sulphate (sulphate attack is a chemical attack detrimental to concrete).

An additive used in concrete to aid placement in difficult applications, eg: where structure has large quantity of reinforcement, or where reinforcement is very close together or where structure has narrow opening. Increases workability (slump) of concrete without negatively affecting strengths.

The average strength the concrete is designed to achieve. For Normal Class concrete mixes, target strength is the characteristics strength plus 1.65 times the standard deviation i.e., TS = f'c + 1.65 x SD. Parameter used by concrete technical managers to manage concrete quality in terms of strength performance.

Is the process of laying concrete over existing concrete. Toppings can be bonded (to the surface) or non-bonded. Special construction considerations are essential for all topping applications.

The relationship (ratio) between the amount of water and cement in concrete. Often also referred to as water:cementitious or water:binder ratio as most concretes now contain some amount of supplementary cementitious materials. The lower the water:binder ratio, the greater the durability and higher the strength of the concrete.

Chemical admixture which reduces the amount of water required to achieve a nominated slump. As the ultimate strength of concrete depends on the quantity of water in the mix (i.e., water:binder ratio). It is possible to achieve target strengths using less cement. Also enables control of setting times to what is desired for construction.

These are chemical additives that are added to concrete to impart properties to limit water ingress, many of which are unsubstantiated. The terms "waterproof" and "impervious" cannot be applied to a material like concrete.

A more correct term for this application is "watertight". In saying that, there is still a lot of confusion as to what "watertight" actually means. Usually, an engineer, contractor and concrete supplier are needed to produce effective solutions on projects even where speciality "watertight" concrete admixtures are used.

The determination of the actual volume of concrete used versus the theoretically determined volume to confirm or establish theoretical mix design volumes.