Glossary

Additions meant to improve the properties of concrete, including setting time, porosity, workability, etc. They vary in type from accelerators, retarders, plasticizers, curing agents, anti-freezers, etc.

A material other than aggregate, cement and water that is added to concrete during mixing to modify one or more of its properties in the fresh or hardened state

Granular, insoluble, non-cementitious material such as sand and stone, used with cement and water to make concrete and mortar

• Coarse aggregate (stone) - Particles are usually larger than 4,75 mm

• Fine aggregate (sand) - Particles are usually smaller than 4,75 mm

The volume of air voids in cement paste, mortar or concrete, excluding pore space in aggregate particles; usually expressed as a percentage of total volume of the paste, mortar or concrete

Stone, gravel or crushed rock laid down as the base for a railway line

A tar-like substance obtained from crude oil and used in road surfacing and roofing

The upward movement of water in freshly placed concrete after compaction and before initial set

A substance applied to a suitable substrate to create a bond between it and a succeeding layer

A fine mineral powder that reacts chemically with water causing the mixture to set and harden to form a rigid mass. On this website the following terms are used:

• Cement - Refers to all branded "common" cements, bearing the SABS mark, that comply with SABS EN 197-1/SANS 50197-1 strength class 32,5N and are commonly available from hardware stores and builder’s yards in 50 kg bags
• Masonry cement - Cement which is intended for use in mortars or plasters and complies with SABS ENV 413-1/ SANS 50413-1 strength class MC 22,5X

Having cementing properties

Chunks or nodules of solidified ash made from burning limestone and other products in a kiln at high temperatures.

In the cement industry, this is a greenhouse gas emitted during the physical transformation of raw material at high temperatures as well as from combustion needed to heat the cement furnace

Having the ability to resist segregation

The process of removing entrapped air and consolidating the fresh concrete during placement, usually by vibration, rodding, tamping or some combination of these

A mixture of cement, sand, stone and water that hardens to form a strong composite building material. In the fresh or “green” state, concrete is workable and takes on the shape of the mould into which it is placed and compacted. In the hardened state, concrete properties include compressive strength, abrasion and chemical resistance

A partial fracturing without complete separation of the parts

• Plastic cracking – Occurs in the surface of fresh concrete soon after it is placed and while it is still plastic; due to loss of water from the fresh concrete

• Drying shrinkage cracking – Occurs in a structure or member some time after the concrete has hardened

Fine hairline surface cracking, usually in a network pattern

Material measuring from 5 to 25 mm made from crushing hard rock

Preventing freshly placed concrete from drying out and ensuring a favourable temperature for long enough to allow the ‘green’ concrete to develop strength

A concrete, mortar, or plaster mixture, commonly sold in bags, containing all components except water

The ability of material to stretch or bend without breaking

The ability of concrete to resist weathering action, chemical attack, abrasion and other conditions for its designed service life

Material passing the 75 mm (0,075 mm) sieve

The strength of concrete or mortar usually as developed at various times during the first 72 hours after placement

A finely divided material, which on its own has little or no cementing properties, but produces cementing compounds when used with cement. Includes ground granulated blast furnace slag (GGBS) and fly ash (FA)

• GGBS - Finely ground powder produced from the granulated slag which is a by-product from the manufacture of iron in a blast furnace
• FA – A by-product of the burning of powdered coal in power stations 

A product of the burning of the powdered coal in a power station. It contains some unburnt coal, the proportion of which (as measured by the Loss on Ignition Test) should not exceed 5%

A temporary structure or mould into which newly mixed concrete is placed and compacted to harden

The base of a structure made of poured concrete which is meant to distribute weight of a structure and ensure its stability

A finely ground powder produced from granulated slag which is a by-product from the manufacture of iron in a blast furnace. It is commonly used as a component of some types of cement blends

A pourable mixture of cement and water, with or without sand, normally used to fill voids or act as a bonding layer between subsequent pours

A product used during the construction process made by grinding the gypsum mineral in a kiln

Heat evolved from the chemical reaction between cement and water during the setting and hardening of concrete, mortar or plaster

The voids left in hardened concrete due to failure of the mortar to effectively fill the spaces between stone particles due mainly to incomplete compaction or too much stone

The chemical reaction between cement and water

• Cold joint - A discontinuity in concrete resulting from the failure to knit together two successive layers because of a delay in placing
• Construction joint - The surface where two successive placements of concrete meet
• Contraction joint - A groove formed, sawed or tooled in a concrete structure to create a weakened plane, controlling the location of cracking resulting from dimensional changes of different parts of the structure
• Expansion or isolation joint - A separation provided between adjoining parts of a structure to allow movement where expansion is likely to exceed contraction or allow independent movement between adjoining parts

Specifically calcium hydroxide with the chemical formula Ca(OH)_2.  Builders Lime is a general term for the various chemical and physical forms of quicklime, hydrated lime and hydraulic lime.

A sedimentary rock consisting primarily of calcium carbonate. Milled limestone may also be used as a component of blended cement

Hollow or solid bricks and blocks used with bedding mortar to build walls and structures

The proportions of ingredients that make the most economical use of available materials and the required water: cement ratio to make concrete, plaster or mortar with the desired properties for a specific application

A mixture of cement, sand and water

A colouring agent, usually in the form of an insoluble fine powder, added to concrete during the mixing process. A wide range of colour can be produced by the use of organic or inorganic pigments

A cementitious material or combination of cementitious material and fine aggregate when mixed with a suitable amount of water, forms a plastic mass or paste that when applied to a surface (usually vertical) adheres to it and subsequently hardens

Refers to the volumes of void spaces to total volume in a material

Refers to a method used to overcome concrete’s natural weakness in tension by pouring concrete onto stretched high tensile strands

A blend of raw materials, ground to desired fineness, correctly proportioned and blended, and ready for burning such as that used in the manufacture of cement clinker

This is a method of counteracting concrete’s low tensile strength and ductility by including reinforcement material which has higher tensile strength and ductility properties

A manufactured product applied to the inner faces of formwork to prevent concrete from adhering. Assists in striking without damage to concrete or formwork

The art or method of creating desired finishings on brick, cement, stone or mud brick in an effort to improve appearance by adding a premixed layer of sand

Failure of a concrete or mortar to adequately set and gain strength due to use of an unsuitable release agent, excess or unwanted dosage of admixture, or presence of wood sugars in timber formwork

The unwise process of adding water and remixing concrete or water which has started to harden in order to restore workability

A layer of well-compacted material (cement and course sand) applied to a floor at the appropriate thickness a layer of cement, sand and water applied over a slab

The unwanted separation of the constituents of concrete, usually due to too much water in the mix or incorrect mix proportions

The condition reached by plaster, mortar or concrete when it has lost plasticity

The length of time that packaged materials can be stored under specific conditions and remain unusable

Very fine non-crystalline silica produced in electric arc furnaces as a by-product of the production of elementary silicon or alloys containing silicon

See GGBS

A measure of consistency of freshly mixed concrete determined by carrying out a slump test

A rough-textured coating applied to a surface to improve the adhesion of plaster

Coarse aggregate predominantly retained on the 4.75 mm sieve or that portion retained on the 4.75 mm sieve

The measure of mechanical strength on hardened cement used to determine the load under which cracking will develop

Agitation of fresh concrete with mechanical devices (e.g. poker vibrators) after placing to assist in consolidating the concrete by eliminating voids and entrapped air in the form or mould.

• See also Compaction

The ratio of the mass of water to the mass of cement in a concrete, mortar, plaster or grout

Cement where the method of production has been modified to give it a high degree of whiteness and is mostly used for decorative purposes

The amount of useful internal work that produces full compaction and is influenced by water content, mix proportion and the use of admixtures

Volume (measured as compacted) of freshly mixed concrete, mortar or plaster produced from a known quantity of ingredients