Additives improve the properties of concrete: setting time, viscosity, porosity, mechanical resistance, etc. There are 9 families of additives: accelerators, retarders, plasticizers, flow promoters, air-entraining agents, anti-freezers, water-repellents and curing agents.
These materials were laid down during the Quaternary era by glaciers, water courses and shallow sea floors. They are most commonly found in river beds.
Aggregates are small rock fragments (0.08 to 80 mm) of mineral origin. Aggregates come in different types: maritime, fluvial and terrestrial. They may be sand, gravel or crushed gravel. Aggregates, mixed with water and cement, are essential for the production of concrete.
Bituminous concretes are made of gravel, sand, filler and bitumen (a petroleum product), which acts as a binder. They are generally used as the top layer of road surfaces.
The bed of stone, gravel or crushed rock laid down as the base for a railway line is called "ballast". Ballast can be recycled and used as an alternative material.
Concrete is a building material made by mixing water, aggregates and sand with a binding agent (usually cement) and, if necessary, with additions. This mixture is made on building sites and factories.
The characteristics of a concrete can vary greatly depending on the choice of cement and cement-aggregate ratio, the type of aggregate used, the inclusion of additions, etc. The way concretes are used and surface treated can also have an impact on their performance and appearance. So concrete is reconstituted stone and is sometimes referred to as "liquid stone".
Carbon dioxide (CO2) is a greenhouse gas. It is produced by the combustion of organic compounds and the respiratory systems of animals and plants.
The cement industry naturally emits CO2:
- 60% of emissions are due to the physical-chemical transformation of raw materials at high temperatures
- 40% result from the combustion needed to heat the cement furnace to 1500°C.
Concrete plants are industrial sites where all of the raw materials for concrete production are brought together. They are often transported by barge.
In the mixing building, the raw materials and additions are dosed and put in the mixer, where they form a homogenous concrete mixture. The wet concrete is then transported to work sites in cement trucks equipped with revolving drums.
Clinker is the main ingredient in cement. These hardened granules are obtained by firing a mixture of approximately 80% limestone and 20% clay to a high temperature. Cement is obtained by grinding clinker and, in some cases, supplementing it with additives.
Crushed gravel is produced by crushing hard rock. These gravel samples measure from 5 to 25 mm.
Crushed gravel is used as an aggregate during concrete manufacture and as a paving base for road surfaces.
Crushing is one phase in the aggregate production process. After scalping (removal of unwanted clay, etc.), the materials are crushed and ground (broken into smaller pieces).
Cement is a hydraulic bonding agent which is obtained by heating, then grinding, a mixture of limestone and clay. Most cements are made from clinker and additives and are usually used in the form of a powder. Cement sets when mixed with water. Combined with sand and aggregates (sand or gravel), it turns into rock-hard concrete or mortar.
Called "cement additives", these minerals are used in varying proportions during the last phase of the cement production process. The additives make it possible to obtain a range of cements with different properties. They can be:
- of natural origin, for example limestone or volcanic and sedimentary rock,
- of industrial origin, for example by-products of the steel industry (slag from blast furnaces), the microchip industry (silica fume), and coal-fired power plants (pulverised fuel ash).
The use of cementitious additives reduces CO2 emissions:
- firstly, because using additives in cement production automatically reduces the proportion of clinker (the decarbonation phase of clinker production releases a lot of CO2),
- secondly, because it uses industrial waste which would otherwise have been discarded and treated by the local authority.
Ductility refers to a material's capacity to be stretched or bent without breaking. A material which does not have this quality is fragile.
A material is fire retardant if it prevents or slows the inflammation of a naturally combustible object. Fire retardant properties can result either from the addition of chemicals to the mass of a material or from the surface application of a fire retardant product. Gypsum has fire retardant properties.
An inert, finely ground mineral material that is included in paints and hydraulic binders (cement) to reduce costs and, in some cases, modify their physical characteristics. In this respect, they are considered to be a cement additive.
Fibre-reinforced concrete contains an array of different fibres (polypropylene, metal, fibreglass, carbon, etc.) that create a reinforced mesh, improving the concrete's solidity and resistance to cracking. This is a rapidly developing approach to reinforcing concrete.
A form is a temporary mold into which liquid concrete is poured. The form is stripped away after the concrete has set. The form must be strong enough to bear the weight and/or pressure of the wet concrete without any change to its initial shape.
The foundations of structure distribute its weight and ensure its stability. They are made of poured concrete. The design of foundations must allow them to bear the weight of the construction and prevent any vertical or lateral shifting.
A geothermal heat pump takes advantage of the natural warmth of the ground below the frost line to heat spaces above ground, even though thermodynamic principles should result in this warmth being diffused when it comes into contact with cooler elements.
Grout is a mix of gypsum or cement mortar which is liquid enough to be poured or pumped to fill joints and fissures.
Gypsum is a construction material made by firing the gypsum mineral in a kiln and then grinding it. It can be used as a paste or as pre-fabricated boards. Mixed with water, it forms a gel that sets within a few minutes and then hardens. It is widely used for interiors: coatings, dry partitions, ceilings and wall linings. It has several important properties: acoustic and thermal insulation, fire resistance, etc.
Granular stacking is a technique which improves the compactness and resistance of concrete and reduces porosity. Granular stacking is achieved by replacing part of the water with fine and ultra-fine grains that fill in the spaces between larger grains. The result is more consistent, more fluid concrete which becomes more compact upon setting.
Hydraulicity is the extent to which a material hardens in the presence of water.
A joint is the filling or sealing of a gap between two construction elements or a continuous rectilinear separation in a construction, designed to absorb differences in the movement or behavior of 2 adjacent elements.
The Kyoto Protocol aims to counter climate change by reducing carbon dioxide emissions. In effect since February 2005, it has been ratified by over 150 countries but has not been ratified by the United States for example.
Under the Protocol, industrialized countries have until 2012 to reduce their CO2 emissions by 5.2% compared to 1990 levels.
Lime is a binding agent obtained from the calcination of limestone. Limes are divided into 2 categories depending on whether they are set by exposure to carbon dioxide (slaked lime) or to water (hydraulic lime).
Slaked lime is mainly used in traditional finishing plasters, pointing mortars and whitewashes. Hydraulic lime contains clay, giving it similar properties to cement and making it suitable for use as an undercoat or render.
Mortar is a mixture of cement, sand (an inert component which provides body) and water, which may be complemented with additions, supplements and colored pigments. Unlike concrete, mortar does not include aggregates. It may be prepared on site or delivered from a mixing plant. Mortars are used for bonding (to join cut or molded elements), for cladding (waterproofing and dressing of walls and coverings, finishing of floors), and for a number of other purposes including jointing, rendering, insulating, sealing and plugging.
Natural gypsum is a mineral extracted from quarries in the form of small white crystals, clumped together in blocks. It comes from a sedimentary rock made of calcium sulfate dehydrate.
Plasterboard panels are industrial building components. They are made in factories by locking a thin layer of gypsum and additives between two cardboard sheets to create thin panels. Plasterboard is put in place with screws or adhesive mortar. The panels can also be nailed or screwed to wooden or metal frames to dress interior walls and partitions.
An inconvenience of conventional concrete is its drying time, which slows construction on the building site and increases costs. Prefabricated or pre-cast concrete helps to speed up construction work. Concrete pieces (columns, beams or slabs) are formed and prepared in a workshop onsite or close to the site and then transported to the right location. This has the advantage of reducing the length of the construction phase and limiting the impact on local populations.
Pulverised Fuel Ash is hydrophilic and can be used as a cementitious additive. The ash, which is collected from chimney filters in coal-fired power plants, is composed of vitreous silica, alumina, iron oxide and lime.
They can be used as a partial substitute for clinker and thus help to reduce CO2 emissions.
A partition is a lightweight wall that divides an interior space. Plasterboard is frequently used for this purpose.
The difference between walls and partitions is that walls are part of the weight bearing structure (they hold up roofs, ceilings, upper floors, etc.) while partitions do not bear weight.
Steel reinforcements give concrete a higher tensile strength. This is the principle of reinforced concrete. However, the elasticity of steel is sometimes not enough to ensure the safety of a structure. In this case, specific reinforcing techniques are used. These consist of stressing the reinforcement (like a spring) to compress the unloaded concrete before it enters service. The stretching takes place before the concrete is poured into the forms (pre-tensioning) or after pouring (post-tensioning). Once the structure is in place and comes under stress, the reinforcing stretches out and the concrete tends to decompress. It is able to do so without bending because it was previously partially compressed.
The name ‘Portland' comes from a peninsula in Great Britain.
The gray stone of this area has a composition and appearance similar to that of cement. Portland cement is the generic name of basic, highly-efficient hydraulic cements. They are obtained by grinding clinker, which is made from firing a carefully-composed mixture of limestone, silica, alumina and, in some cases, other products.
These materials are obtained during the demolition of buildings and roads or as a by-product of industrial processes. Their use reduces the consumption of non renewable, natural materials.
Cement concrete is very resistant to compression but it is less resistant to tensile stress and bending. Steel, on the other hand, is very flexible thanks to its high tensile strength.
Reinforced concrete takes advantage of their different properties by combining steel and concrete to produce a material with high compressive and tensile resistance.
To roll means to reduce a mass into leaves, sheets or thin bars by passing it through compressive rollers.
Raw mix is made of finely ground rock and minerals. It is known also as raw meal, which is preheated and then sent to the kiln to make cement.
Render is a layer of paste or mortar which is applied to a wall to improve its appearance. It protects the wall from the elements and gives an attractive, uniform finish. It also helps to insulate. It consists of a binder (lime, gypsum, cement or earth), aggregates and, sometimes, pigments to obtain a specific colour.
Self-placing concretes are special, highly-fluid concretes which settle into place by gravity alone and do not, therefore, require vibration. They are designed to be poured into watertight formwork. Even without vibration they cover reinforcements perfectly and provide extremely smooth facing.
Screening is the phase following crushing and grinding. Gravel is sieved through a screen of a given size to produce a clean, homogenous mix of a particular size of granule.
Sealing is the masonry operation by which the end of a piece of wood or metal is inserted into a masonry wall, ceiling or floor. In general, a cavity is made into which the beam or post is placed. The area is then filled with quick setting mortar, plaster, lead or sulfur mortar.
This by-product of the silicon industry results when quartz is heated to high temperatures. Silica fume – dust particles which measure only 0.2 micrometers – is collected by electro-filters for use as a cement admixture.
A variant of self-placing concretes, self-leveling concretes have a specially formulated and graded composition to ensure a fluid spread. They form smooth-surfaced slabs with no need for vibration or float finishing (used to make a surface flat).
Natural gypsum resources are limited. Synthetic or chemical gypsum is a useful alternative to this nonrenewable natural resource.
The main sources are:
- phosphoric acid,
- other mineral acids (citric acid, etc.),
- the desulfuration of gases,
- the neutralization of acidic water (sulfuric acid) from the titanium dioxide industry.
Of the 60 million tons of gypsum produced worldwide, nearly half is made from synthetic gypsum (also called chemical gypsum).
This rock comes from thick deposits of hard rock. Massive rocks are mainly old limestone formations or rocks of volcanic origin, called eruptive rock. This rock can be extracted to make aggregates. The extracted minerals are scalped before being crushed.
A superplasticiser is an additive that is mixed with concrete, mortar or grout just before the concrete is used. Its main purpose is to improve the workability of the mix. Its secondary role is to modify the setting or hardening time. Superplasticisers are sometimes called "fluidifiers".
A screed is a thin layer of mortar (15 to 50 mm) that is spread over a base layer of slabs. It gives a flat surface and is generally covered by another material, such as floor tiling.
This mixture of lime, alumina and silica is produced when iron is smelted with coke in blast furnaces. Slag accumulates on top of the molten cast iron. If cooled quickly, its hydraulic properties are close to those of clinker. Slag takes longer to hydrate but it offers greater stability in corrosive conditions. It is, therefore, a suitable additive for cement and concrete so as to reduce CO2 emissions.
Ultra-high-performance fibre-reinforced concrete is an innovative construction material. The addition of metal fibres increases its resistance 6-fold compared to standard concrete and also increases its durability.
Unconsolidated rocks are alluvial deposits in river beds. They can be recovered to make aggregates.