Designing Buildings - User contributions [en]

Sustainable aggregates

2016-03-15T15:23:22Z

Mineral Industry Research Organisation:

= Introduction =

UK quarries and marine dredging sites produce approximately £3billion worth of products per annum and employ around 40,000 people. Quarried products represent the cornerstone of our economy. With each person using approximately 4 tonnes of aggregate per annum, that’s around 200 million tonnes. These products are used to create vital infrastructure, homes and services, yet aggregates have a relatively low value. Their low value combined with their high bulk means that, unlike other valuable minerals, they are not traded globally.

This interesting juxtaposition of high worth but low intrinsic value, combined with the ever-increasing pressures on land use, raises issues around what a sustainable aggregate industry looks like for the UK. It’s a bit surprising to note that more than 40% of our permitted land-won aggregate reserves are in areas with an environmental designation, whether National Park, Site of Special Scientific Interest or Green Belt.

Research by --[[User:KLH_Sustainability|KLH Sustainability]] has uncovered a number of interesting facts.

= The recycled and secondary aggregate market =

BREEAM is still the assessment methodology of choice for clients who wish to demonstrate their sustainability credentials. However, BREEAM currently only awards credits for secondary and recycled aggregate use.

Over 80% of recycled and secondary aggregates, approximately 42 million tonnes, is produced from recycling construction and demolition waste (C&D waste). Although data on recycled aggregates is considered variable and inconsistent, national surveys state that most of the evidence indicates that C&D waste is actually being recycled into aggregate rather than landfilled as waste.

But what about secondary aggregates? The annual production of secondary aggregates in England is approximately 13 million tonnes. The China Clay industry in Cornwall represents 8.3 million tonnes of this production, of which 1.2 million tonnes is currently used, mainly in the construction industry. The next most significant sources of secondary material for use as aggregates are colliery spoil and pulverised fuel ash (PFA) in the Humber area at 1.97 million tonnes and 1.07 million tonnes respectively, of which a total of 1.31 million tonnes is used in the construction and other industries. The remaining 2 million tonnes of secondary aggregate produced annually in England is widely distributed and of a marginal scale.

These numbers are relatively small compared to demand. The economic viability of the aggregates industry, and indeed the environmental sustainability of the industry is a function of the distance to market. Recycled aggregates have an advantage over secondary aggregates as they are often produced in locations with a future requirement for extensive aggregate use such as redevelopment and regeneration areas. The distance to market from the secondary aggregate reserves in Cornwall is likely to be a limiting factor to the sustainable use of these materials in the industry.

= Pushing recycled and secondary materials up the value chain =

It seems there is little opportunity for BREEAM to drive increased diversion of C&D waste from landfill as the market already operates at near capacity. But perhaps there is a sustainable benefit in pushing recycled materials up the value chain as BREEAM aims to?

Analysis of the Collation of Results of the Aggregate Minerals Survey for England and Wales and the Mineral Extraction in Great Britain demonstrates that significant quantities of primary materials continue to be used as construction fill and other graded construction uses.

These types of uses generally have fewer technical constraints and are a prime market for recycled aggregates. These lower value end uses also provide a valuable demand for ‘waste’ by-products generated at crushed rock sites whose production profile is driven by demand for concreting and asphalt products. In 2005, the UK quarrying industry produced more than 55 million tonnes of quarry ‘fines’ and 24 million tonnes of ‘quarry waste’ in addition to 216 million tonnes of saleable aggregate, however these quarried by-products still attract the Aggregates Levy and are therefore not defined as a waste product under legislation or within BREEAM.

In theory, both waste products from crushed rock quarries or recycled products could be further processed to drive them up the value chain.

Either option has the potential to reduce unused stockpiles of overburden, scalpings and crushed rock waste and put them to good use:

* If recycled aggregates undergo additional processing to move them up the value chain the quarried by-products will likely replace them in the lower value chain uses such as sub-base and engineered fills.
* Additional processing of these quarried by-products could push them further up the value chain.

As BREEAM does not quantify these quarried waste products as secondary material, the criteria for BREEAM is biased towards recycling industry investment in additional processing to push recycled materials up the value chain, ignoring the opportunity to process quarried by-products for low value fill. Favouring additional processing for recycled aggregates without considering other options is likely to require significant quantities of water and energy. There is no clear evidence base as to why recycled materials specifically should be pushed up the value chain when a demand is then created for low value materials; one that is too often met by primary aggregates, rather than quarried by-products.

= An alternative approach =

KLH Sustainability are developing an alternative approach to the assessment of sustainable sourcing and use of aggregates that responds to the limitations identified within existing methodologies (having looked extensively at the ability of Environmental Product Declarations to help differentiate between sources of aggregates, too).

The assessment methodology is based on key impact factors that have been identified through analysis of existing data and research and include:

* Local availability of aggregates defined by regional Abiotic Depletion Potential.
* Social impact of transportation defined by the Department for Transport freight modal shift methodology.
* Carbon footprint. The focus here is not in establishing an absolute carbon footprint for aggregate sources and respective end uses but to understand the key differentials that should influence decision making.

Economics are not directly included in the analysis as market complexities prevent a robust analysis of the economic viability of using specific aggregates in given products and regions. This is not considered to be a significant limitation of the proposed methodology as the sustainability assessment criteria selected indirectly considers cost in the form of carbon, transportation and abiotic depletion potential.

KLH Sustainability provide more detail in the definition and calculation of regional Abiotic Depletion Potential in Material Flow Analysis: A tool for sustainable aggregate sourcing.

See aggregate for more information.

[[Category:Sustainability]] [[Category:Products_/_components]]

Screed

2016-03-15T15:22:51Z

Mineral Industry Research Organisation:

= Introduction =

Generally, concrete floors, other than those in buildings such as warehouses which may be left exposed, are covered with a screed layer. This is a layer of material, usually a sand and cement mix (sometimes with added fibres and other additives), generally laid to prepare for the installation of a floor covering, such as tiles, carpet or timber. Standards for screeds are set out in BS 8204, Screeds, bases and in-situ floorings.

The specification of screeds will vary depending on the requirement for:

* Load-bearing capacity.
* Durability.
* Creating a level surface.
* Providing a suitable base for flooring.
* Providing a suitable wearing surface.

= Types of screed =

The most common types of screed include:

=== Bonded screed ===

The screed layer is fully bonded to the substrate using a primer or bonding agent. This method is commonly used for thinner screeds where heavy loading is expected and where there is not enough space available to lay an unbonded screed. The optimum thickness of a sand and cement bonded screed is generally in the region of 25-40mm. Care must be taken during the laying process to ensure de-bonding does not occur as this can lead to instability and ultimately, the screed may fail.

=== Unbonded screed ===

Instead of being bonded directly to the base, unbonded screeds are applied over a damp proof membrane (DPM) laid on top of the concrete base. The minimum thickness of an unbonded screed is usually in the region of 50mm. The advantage of an unbonded screed is that the flooring is not in direct contact with the main structure and so the potential impacts of settlement or shrinkage can be less problematic. The DPM creates a barrier preventing damp rising from the substrate.

However, this type of screed can be more prone to curling if dried quickly. Curling is a vertical distortion of the edges due to temperature differences or moisture content throughout the thickness of the screed. This can be prevented by adhering to minimum specified thicknesses and allowing for slow drying.

=== Floating screed ===

The screed is laid on top of insulation to create a thermally efficient floor. Floating screeds are commonly used where underfloor heating systems are provided or thermal or acoustic insulation is required. Floating screeds generally have a thickness greater than 65 mm for lightly-loaded floors and 75 mm for more heavily-loaded floors.

=== Screed over underfloor heating ===

This is where the floating screed layer is installed over underfloor heating pipes or insulation. The screed serves to conduct the heat evenly across the floor surface, avoiding hot or cold spots, and helps to retain heat for longer. In order that heat propagates only in the required direction of the room to be heated or cooled, the elements are inserted above insulating panels. Sand cement screeds require a minimum thickness of 65 mm, with the ideal being between 65-75 mm.

Where fibres are added or when using anhydrite screeds the minimum thickness may be reduced to 50 mm. Care must be exercised in allowing adequate drying time (usually around 21 days) before incrementally turning on the heating system, otherwise cracking may occur. Additives can be included in the screed mix to allow the drying time to be reduced.

= Composition of screed =

Most screeds are made from a 1:3 to 1:4.5 ratio of cement to sand. Enhanced screeds include additives to improve the properties of the standard screed. This can allow for faster drying times and extra strength if required.

Manufacturers also offer self-leveling screeds that can be pumped through a delivery hose and leveled with a dappling bar. The majority of these screeds are anhydrite compounds based on a calcium sulphite binder. Large areas can be covered more quickly, however, care must be taken to ensure this type of screed dries completely and it can be susceptible to water damage, so is not the most suitable screed for external or permanently wet areas.

All screeds expand and contract to some degree so large areas need to have expansion joints or crack inducer cuts in the screed to allow movement without cracking.

= Find out more =

=== Related articles on Designing Buildings Wiki ===

* Aggregate.
* Basement.
* Cement.
* Concept structural design.
* Concrete.
* Damp proof membrane (DPM).
* Floor definition.
* Flooring.
* Insulation.
* Power float.
* Raised floor.
* Rendering.
* Separating floor.
* Substructure.
* Underfloor heating.

External references

[http://www.warmafloor.co.uk/documents/Floating%20screeds.pdf Warmafloor]

[http://www.concrete.org.uk/ Concrete]

[http://www.floorscreeding.co.uk/considerations-required-in-the-processes-of-floor-screed-construction/ Floorscreeding]

[http://www.cscscreeding.co.uk/screed-systems/fast-drying-floor-screed/ CSC Screeding]

[[Category:Construction_techniques]] [[Category:Design]]

Mortar

2016-03-15T15:22:32Z

Mineral Industry Research Organisation:

To help develop this article, click ‘Edit this article’ above.

-----
Mortar is one of the oldest building materials, enabling large structures to be constructed from small, easy-to-handle components. It was used by the Romans, Greeks and Egyptians, and the oldest example may date back as far as 10,000 years in Israel (ref [http://www.mortar.org.uk/documents/LT01-Introduction-to-Mortar.pdf Mortar Industry Association]).

It is composed from a mixture of a fine aggregate (typically sand), a binder (typically cement, but sometimes lime or a combination of lime and cement) and water. This combination creates a paste that is used in masonry construction as a bedding and adhesive to bind and fill the gaps between adjacent blocks of brick, concrete or stone.

Mortar is applied as a thick paste which sets hard as it cures. It creates a tight seal between bricks and blocks to prevent air and moisture entering into the construction. It can compensate for variations in brick or bock size to produce an aesthetically-pleasing and structurally-sound construction. Generally, it is structurally weaker than the blocks or bricks it bonds, creating a sacrificial layer that is more easily repaired than defects would be in the bricks or blocks themselves.

Mortar is generally very durable and has a typical lifespan of between 20-30 years, after which repairs (or re-pointing) can be necessary to fill cracks or gaps that may begin to appear.

Mortar may be provided in its component parts and mixed on site, or factory-mixed. The two main types of factory-produced mortar are:

* Wet ready-to-use mortar that requires no further mixing.
* Dry ready-to-use mortar which requires the addition of water.

Factory-produced mortar is made under tightly-controlled conditions and provides:

* Consistent quality, colour and strength.
* Reduced mixing and labour costs.
* Reduced wastage.
* Guaranteed specification.
* Improved site health and safety.

The profile of mortar joints (pointing) can be varied depending on exposure or to create a specific visual effect. The most common profiles are; flush (rag joint), bucket handle, weather struck, weather struck and cut, and recessed.

A wide range of colours are available to match or contrast with the surrounding bricks or blocks, or to match existing mortar. Pigments are specified according to BS EN 12878:2014 Pigments for the colouring of building materials based on cement and/or lime. Specifications and methods of test.

A range of admixtures can be included in mortar, such as plasticisers, bonding agents, and waterproofing. These can be specified according to BS EN 934-3:2009+A1:2012 Admixtures for concrete, mortar and grout. Admixtures for masonry mortar. Definitions, requirements, conformity and marking and labelling.

Mortar must have good workability to ensure there are no air pockets which might prevent proper bonding. Plasticisers can improve workability by entraining very small air bubbles in the mix. Alternatively, the addition of lime can improve the workability of mortar.

Where porous bricks or blocks are being laid, the mortar may dry quickly, preventing proper levelling and so preventing a good bond from being formed. This can be countered by laying shorter lengths, or by limited wetting.

= Find out more =

=== Related articles on Designing Buildings Wiki ===

* Aggregate.
* Blockwork.
* Brick
* Cavity tray.
* Cement.
* Ceramics.
* Concrete.
* Damp-proof course.
* Defects in brickwork.
* Defects in stonework.
* Efflorescence.
* High alumina cement.
* Interstitial condensation.
* Rendering.
* Spalling.
* Wall tie failure.

=== External references ===

* [http://www.mortar.org.uk/ Mortar Industry Association] (MIA).

[[Category:Articles_needing_more_work]] [[Category:Products_/_components]]

Material Flow Analysis: A tool for sustainable aggregate sourcing

2016-03-15T15:22:15Z

Mineral Industry Research Organisation:

= Introduction =

In a previous article, ‘Sustainable aggregates’ KLH Sustainability highlighted the need for a broader assessment for aggregate selection beyond “recycled/secondary equals good and primary equals bad.”

It was suggested that an assessment methodology could be based around three criteria:

* Local availability of aggregates – defined by regional abiotic depletion potential.
* Social impact of transportation – adapted from the Department for Transport’s freight modal shift methodology.
* Carbon footprint.

Here, they explore the measurement of aggregate availability in more detail.

= What is abiotic depletion potential? =

Environmental product declarations, as defined by BS EN 15804, measure abiotic depletion potential (ADP). ADP is a function of the natural reserves of a resource combined with their rates of extraction. ADP generally includes both the direct resource depletion and the resource depletion associated with the fossil fuel consumption in extraction, processing and transportation of the resource.

BS EN 15804 defines abiotic depletion potential of non-fossil resources as:

[extraction rate of resource (kg/year) / (ultimate reserve (kg))^2] / [extraction rate of antimony resource (kg/year) / (ultimate antimony reserve (kg))^2]

However the standard also recognises that “the depletion of abiotic resources is subject to further scientific development. The use of this indicator is intended to be reviewed during the revision of this standard”.

When applied to aggregates there are two fundamental issues with this definition of non-fossil ADP.

The definition of ADP utilises antimony, of which China is the largest producer, as a reference resource and therefore measures the availability of a given resource on a global scale. Using this definition of ADP, sand, gravel and rock may be considered infinite, and indeed the global ultimate reserve of aggregates is more or less infinite. However, given the relatively low value and high bulk of aggregates, geographic proximity is paramount to economic utilisation. As sands and gravels are not transported over a long distance, it seems more important to have a territory-based approach to evaluate the availability of aggregate resources.

The estimate of the reserve of aggregate resources is also problematic. The ultimate reserve has historically been defined as the quantity of resource that is ultimately available. It is estimated by multiplying the average natural concentration of the resource in the primary extraction media (e.g. the earth’s crust) by the mass or volume of these media (e.g. the mass of the crust assuming a certain depth of for example 10 km). There are, of course, a range of complex economic, social and environmental factors that dictate whether a given reserve is exploited or not.

= What is the alternative? =

KLH Sustainability have been exploring the concept of material flow analysis (MFA). MFA is an analytical method of quantifying flows and stocks of material or substances in a well-defined system. It is an important tool in assessing the physical consequences of human activities and needs, and aids the sustainable management of material flows.

The methodology used provides an estimate of the time to exhaustion and the reserve in a given region by analysing the historic social metabolism of the area (the manner in which human societies organise their growing exchanges of energy and materials with the environment). Using this reserve estimate and the trend in domestic mineral consumption, along with an understanding of the available capacity of the local recycled and secondary markets, we are able to calculate a figure for the regional ADP.

It is then possible to provide an estimate of the regional reserves and time to exhaustion of quarried stone, land based sand and gravels and marine minerals.

The 2013 Aggregates Mineral Surveys data will provide a further data point for analysis which will allow trends to be observed from 16 years of historic data.

This isn’t without its limitation, but it is believed the data generated will be a valuable tool to inform future scenarios, regional planning and sustainable sourcing of aggregates.

--[[User:KLH_Sustainability|KLH Sustainability]]

= Find out more =

=== Related articles on Designing Buildings Wiki ===

* Aggregate.
* Cement.
* Concrete.
* Concrete vs. steel.
* Concreting plant.
* Efflorescence.
* Formwork.
* High alumina cement.
* Mortar.
* Power float.
* Screed.

[[Category:Sustainability]]

High alumina cement

2016-03-15T15:21:57Z

Mineral Industry Research Organisation:

High Alumina Cement (HAC, sometimes known as calcium aluminate cement (CAC) or aluminous cement) is composed of calcium aluminates, unlike Portland cement which is composed of calcium silicates. It is manufactured from limestone or chalk and bauxite.

High Alumina Cement was first developed by Lafarge, the cement producer, and became available in the UK in 1925. It was used in particular for marine applications where it was considered to be resistant to chemical attack. It became popular in the 1950’s, 60’s and 70’s, as it developed strength rapidly and so was relatively fast to manufacture. It was widely was used in structural concrete such as pre-cast beams.

However, High Alumina Cement was prone to a crystalline re-arrangement (or ‘conversion’), which could result in reduced strength and also vulnerability to chemical attack when exposed to water for long periods (perhaps as a result of poor detailing or poor manufacturing). This resulted in a 5 high-profile structural failures of roof beams (where the presence of water is more likely) during the 1970’s.

In 1975, MP for Sutton and Cheam, Neil Macfarlane, said “Those words—or the abbreviation "HAC"—are rapidly and relentlessly becoming a combination of misery, apprehension, worry and fear for thousands of people in the United Kingdom.”

High Alumina Cement is no longer used in structural concrete in the UK, although it is still prevalent in buildings constructed in the 50’s and 60’s, and continues to be used for non-structural uses under the name Calcium Aluminate Cement (CAC).

In 1975, The Department of the Environment (DOE) Building Regulations Advisory Committee (BRAC) published guidance for design-check procedures for High Alumina Cement. Commonly known as the [http://www.brebookshop.com/details.jsp?id=140304 BRAC rules], this guidance remains the best advice available and continues to be used to assess the structural performance of buildings containing pre-cast HAC concrete beams.

It should be noted that many buildings that contain HAC components are entirely problem free, and the problems that have occurred have been traced back to manufacturing faults. However, If the presence of HAC is suspected, testing should be carried out, and if it is confirmed, HAC components should be assessed for strength and long-term durability. This is likely to require expert advice.

= Find out more =

=== Related articles on Designing Buildings Wiki ===

* Aggregate.
* Asbestos.
* Brick.
* Cement.
* Concrete v steel.
* Defects in brickwork.
* Deleterious materials.
* Demolition
* Pre-construction information.
* Screed.
* Sustainable materials.

=== External references. ===

* [http://www.brebookshop.com/details.jsp?id=140304 Building Regulations Advisory Committee (BRAC) rules].

[[Category:Products_/_components]]

Concrete

2016-03-15T15:21:35Z

Mineral Industry Research Organisation:

To help develop this article, click ‘Edit this article’ above.

= Introduction =

Concrete is the most commonly used man-made material on earth. It is an important construction material used extensively in buildings, bridges, roads and dams. Its uses range from structural applications, to paviours, kerbs, pipes and drains.

Concrete is a composite material, consisting mainly of Portland cement, water and aggregate (gravel, sand or rock). When these materials are mixed together, they form a workable paste which then gradually hardens over time.

= History =

A material similar to concrete was first developed by the Egyptians, consisting of lime and gypsum. Typically, lime, chalk or oyster shells continued being used as the cement forming agent until the early 1800s.

In 1824, Portland cement, a mixture of limestone and clay was burned and ground, and since then, this has remained the predominant cementing agent used in concrete production.

= Benefits of concrete =

There are numerous positive aspects of concrete:

* It is a relatively cheap material and has a relatively long life with few maintenance requirements.
* It is strong in compression.
* Before it hardens it is a very pliable substance that can easily be shaped.
* It is non-combustible.

= Limitations of concrete =

The limitations of concrete include:

* Relatively low tensile strength when compared to other building materials.
* Low ductability.
* Low strength-to-weight ratio.
* It is susceptible to cracking.

= Characteristics of concrete =

The characteristics of concrete are determined by the aggregate or cement used, or by the method that is used to produce it. The water-to-cement ratio is the determining factor in ordinary structural concrete with a lower water content resulting in a stronger concrete. This however reduces the workability (and pumpability) of the concrete, which can be measured using the slump test. The grading, shape, texture and proportion of aggregate can also have a similar affect. If a particularly strong concrete is required, the amount of aggregate can be reduced in relation to the cement. However, cement is a significant cost factor, and increasing its proportion in the mix will increase the overall price.

= Concrete strength =

Concrete strength is determined by the force required to crush it and is measured in pounds per square inch or kilograms per square centimetre. Strength can be affected by many variables including moisture and temperature.

The tensile strength of concrete can be improved with the addition of metal rods, wires, cables or mesh. Where very high tensile stresses are expected (such as in wide unsupported spans in roofs or bridges) concrete can include pretensioned steel wires. This creates compressive forces in the concrete that help offset the tensile forces that the structure is subject to.

Sacrificial probes can be integrated within concrete to provide strength determination and this is likely to help improve construction methodologies.

= Formwork =

Formwork is a temporary mould into which concrete is poured and formed. Traditional formwork is fabricated using timber, but it can also be constructed from steel, glass fibre reinforced plastics and other materials. Formwork may be; temporary, re-usable, or stay-in-place. There are also a number of proprietary systems such as those used to support vertical formwork while concrete cures, consisting of a series of tubes and ties.

Efficiency within concrete construction is being improved by the adoption of hybrid solutions and innovations in formwork such as self-climbing forms.

See Formwork for more information.

= Sustainability =

Concrete has a relatively high embodied energy, resulting from its extraction, manufacture and transportation. Waste materials can be included within the concrete mix such as RCA (Recycled Crushed Aggregate), GGBS (Ground Granulated Blast-Furnace Slag) and PFA (Pulverised Fuel Ash). In addition, moves are being made to assess the potential of using recycled concrete, however, issues such as moisture content and material variability may make this unviable.

Concrete is a very durable, low maintenance material and can provide thermal mass, helping reduce the energy consumption of buildings in operation.

= Find out more =

=== Related articles on Designing Buildings Wiki. ===

* 3D concrete printer.
* Aggregate.
* Blockwork.
* Brick.
* Carbon fibre.
* Cement.
* Ceramics.
* Concrete vs. steel.
* Concreting plant.
* Efflorescence.
* Formwork.
* Mortar.
* Power float.
* Thermal mass.
* Timber.
* Screed.
* Slip form.
* Spalling.
* Structural systems for offices.
* Sustainability.

[[Category:Products_/_components]]

Cement

2016-03-15T15:21:18Z

Mineral Industry Research Organisation:

= Introduction =

Cement is a substance used for binding and hardening other materials. Water and cement set and harden through a chemical reaction known as ‘hydration’. The process of hardening is described as ‘curing’, which requires particular conditions of temperature and humidity.

[[File:Cement.jpg|link=File:Cement.jpg]]

Cement can be mixed with a fine aggregate and water to produce mortar, used in masonry construction as a bedding and adhesive to bind and fill the gaps between adjacent blocks of brick, concrete or stone. It can be also be mixed with water, aggregates (such as gravel, sand or rock), and sometimes admixtures, to form concrete, and can be used to make renders, screeds and so on. The ratio of water and cement will determine the overall strength and quality of the mix.

The exact properties of the cement paste are very important:

* It must be fluid enough for some time after mixing to allow the mix to be formed into its final shape.
* It must then set and gain strength so that it binds the aggregates together to produce a strong material.

= Types of cement =

== Portland cement ==

Almost all concrete is made with Portland cement. It is also the principal cement used in most masonry mortars and renders. It is manufactured by heating together limestone (or chalk) and clay (or shale) in large rotary kilns. The chemistry of Portland cement largely consists of calcium silicate which reacts with water to form a strong, durable cement paste.

== Low heat blast-furnace Portland cement ==

This is a special blended cement with low heat of hydration characteristics for mass concreting. The advantage of this kind of cement over ordinary Portland cement is that, although it has a slower strength gain, it has a higher ultimate strength, as well as better workability.

== Rapid hardening cement ==

This hardens faster than Portland cement, as it includes more silicates, however, the final strength is only slightly higher. The one-day strength of this cement is equal to the three-day strength of Portland cement with the same water-cement ratio. It is mainly used where formwork has to be removed for reuse.

== Sulphate resisting cement ==

Sulphates exist in rain and sea water and can be harmful to building materials. Sulphate resisting cement is a type of modified Portland cement that can be used in conditions where concrete is exposed to the risk of deterioration due to sulphate attack.

== High alumina cement ==

High alumina cement (HAC, sometimes known as calcium aluminate cement (CAC) or aluminous cement) is composed of calcium aluminates rather than calcium silicates. It is manufactured from limestone or chalk and bauxite. Historically, HAC was used in marine applications where it was considered to be resistant to chemical attack, as well as in structural concrete such as pre-cast beams. However, HAC is no longer used in structural concrete in the UK as it prone to a crystalline re-arrangement (or ‘conversion’), which can result in reduced strength and vulnerability to chemical attack when exposed to water for long periods.

For more information see High alumina cement.

= Storage of cement =

Cement is hydroscopic which means it absorbs water. If it is not protected in air-tight silos or bags on-site, it can hydrate. Water initiates the hydration process which can lead to a 20% reduction in strength over 3 months, and a 50% reduction in strength over 2 years. It is important therefore to ensure hydration does not occur; for example, paper bags of cement incorporate a plastic layer and to inhibit moisture uptake.

= Aggregates =

Aggregates are mixed with cement and water to provide bulk and to modify the physical and chemical properties of the mix. There are several desirable properties of aggregates:

* Clean: Free from any organic substances such as dust or other fine materials.
* Hard/strong: Most cement in construction is used to resist compressive forces.
* Durable: Must be able to resist forces over a long time period.
* Capable of good adhesion: The cement paste needs to physically bind to other aggregates and grip effectively.
* Good shape: Smooth and round aggregates provide good workability, whereas angular and rough aggregates tend to give better compressive strength.

The two most common sources for aggregates are rivers (smooth) or crushed rock from quarries (rough), both make very good concrete.

* Fine: < 5 mm (sand or crushed rock)
* Coarse: > 5 mm (naturally occurring gravel or crushed rock)

== Grading of aggregates ==

Grading is the distribution of sizes of particles in aggregates, usually expressed in terms of cumulative percentages larger or smaller than each other. It is important in terms of preventing voids.

For grading, a sample of aggregate is placed in a container of sieves of successively reducing sizes. The container is vibrated for a specified period and the aggregate retained on each sieve is measured. This provides a profile of the distribution of different particle sizes in the aggregate.

= Setting and hardening =

For some time, the mix remains plastic and may be moulded into the desired shape. After a period (dependent upon temperature, humidity, etc.), the mixture loses its plasticity and begins to harden and gain strength. The gain in strength is rapid in early stages, but it will continue to gain strength for some months provided there is still water to combine with cement.

= Find out more =

=== Related articles on Designing Buildings Wiki ===

* Aggregate.
* Concrete.
* Concrete vs. steel.
* Concreting plant.
* Efflorescence.
* Formwork.
* High alumina cement.
* Material Flow Analysis: A tool for sustainable aggregate sourcing.
* Mortar.
* Power float.
* Rendering.
* Screed.

[[Category:Products_/_components]]

Brick

2016-03-15T15:20:58Z

Mineral Industry Research Organisation:

[[File:Brick_wall.jpg|link=File:Brick_wall.jpg]]

= Introduction =

Bricks are small rectangular blocks that can be used to form parts of buildings, typically their walls. The use of bricks dates back to before 7,000 BC, when the earliest bricks were formed from hand-moulded mud, dried in the sun. During industrial revolution, mass-produced bricks became a common alternative to stone, which could be more expensive, less predictable and more difficult to handle.

Bricks are still in common use today for the construction of walls and paving and for more complex features such as columns, arches, fireplaces and chimneys. They remain popular because they are relatively small and easy to handle, can be extremely strong in compression, are durable and low maintenance, they can be built up into complex shapes and can be visually attractive. However, more recently, other materials have been developed that can be used as alternatives for building walls or for cladding facades and for some building types, particularly larger buildings, bricks can be seen as time consuming, expensive (although this is disputed by the [http://www.brick.org.uk/about-the-brick-development-association/why-brick/ Brick Development Association]), structurally limiting, and requiring too much on-site labour. Some of these difficulties have been overcome by the introduction of reinforcement systems and by the development of pre-fabricated brick panels.

= Size =

In the UK, standard bricks are 215 mm long × 102.5 mm wide × 65 mm high.

This gives a ratio of 3:2:1:

* With a standard mortar joint of 10 mm, a repeating unit of bricks laid in a stretcher bond will be 225 mm lengthwise and 75 mm in height.
* If bricks are laid cross-wise, two 102.5 mm widths plus two mortar joints gives the same repeating unit as the length of one brick, ie 225 mm.
* If they are laid height wise, three 65 mm heights plus three mortar joints gives the same repeating unit as the length of one brick, ie 225 mm.

= Manufacture =

Bricks are most typically made from clay, although they are also commonly made from calcium-silicate and concrete.

Soft mud or dry-press bricks are formed by pressing the brick mixture into moulds and then firing them in a kiln. Soft-mud bricks are made from a thin mix whereas dry-press bricks are made from a thicker mix that gives crisper definition. Greater strength is achieved by using greater force when pressing the brick and by firing it for longer, but this increases the cost.

Extruded bricks are formed by pushing the brick mixture through a die to create an extrusion that is then wire cut to produce bricks of the required length.

Bricks can be solid, or can have holes perforated through them to reduce the amount of material used. Alternatively they may have an indentation on one surface (or two surfaces) commonly called a ‘frog’. The frog must be filled with mortar when bricks are laid otherwise the structural and acoustic performance of the wall will be affected. For this reason it is best practice to lay bricks with the frog facing upwards so that it is easy to fill. Where there are two frogs, the larger frog should face upwards.

= Special bricks =

Other than the standard rectangular block, a number of special shapes exist for particular circumstances that may be encountered when building with bricks. These include:

* Radial, tapered or arch bricks.
* Angle and cant bricks that form returns and chamfers.
* Bullnose bricks with rounded corners.
* Capping and coping bricks.
* Cill bricks.
* Plinth bricks.
* Slip bricks (thin bricks that can be used for cladding).
* Soldier bricks, that form returns for soldier courses.

Bricks can also be cut to size.

Engineering bricks have particularly high strength, low water absorption and good acid resistance. They are generally used for civil engineering applications.

= Bonds =

Bricks can be laid as soldiers (standing upright), stretchers (laid lengthwise along the wall) or headers (laid width wise along the wall).

Bricks are laid with a mortar joint bonding them together. The profile of the mortar joint (pointing) can be varied depending on exposure or to create a specific visual effect. The most common profiles are; flush (rag joint), bucket handle, weather struck, weather struck and cut, and recessed.

The bonding pattern describes the alignment of the bricks. There are a large number of standard bond patterns, including:

* Stretcher bond. This is the most commonly used bond in the UK. Each stretcher (brick laid length-wise) is offset by half a brick relative to the course above and below.
* English bond. Alternating courses of stretchers and ‘headers’ (bricks laid width-wise) are laid with the alternating courses aligned to one another.
* American common bond. Similar to the English bond but with one course of headers for every six stretcher courses.
* English cross bond. Alternating courses of stretchers and headers, but with the alternating stretcher courses offset by half a brick.
* Flemish bond. Alternating stretchers and headers in each course.
* Header bond. Courses of headers offset by half a brick.
* Stack bond. Bricks laid directly on top of one another with joints aligned. This is a fundamentally weak bond and is likely to require reinforcement.
* Garden wall bond. Three courses of stretchers then one course of headers.
* Sussex bond. Three stretchers and one header in each course.

= Find out more =

=== Related articles on Designing Buildings Wiki ===

* Aggregate.
* Blockwork.
* Cavity tray.
* Cavity wall.
* Cement.
* Ceramics.
* Concrete.
* Damp-proof course.
* Defects in brickwork
* Defects in stonework.
* Dry lining.
* Efflorescence.
* Interstitial condensation.
* Mortar.
* Rendering.
* Spalling.
* Wall tie failure.

=== External references ===

* [http://www.brick.org.uk/ The Brick Development Association].

[[Category:Products_/_components]]

Aggregate

2016-03-15T15:20:09Z

Mineral Industry Research Organisation:

[[File:Aggregate2.jpg|link=File:Aggregate2.jpg]]

= Introduction =

Aggregate is the term given to material frequently used in construction as a means of stabilising and reinforcement. Aggregates are widely used in drainage applications and as base material under foundations and roads. In the 10 years ending in 2010, 2.5 billion tonnes of aggregates were consumed by the UK. These aggregates were supplied from various sources:

=== Land based ===

The largest source is from quarrying of the land for sand and gravel, or for rock suitable for crushing (mainly limestone, sandstone, and igneous rock, but also some unusually hard occurrences of chalk, ironstone, slate, etc.).

=== Marine ===

Sand and gravel is dredged from the seabed and is a regionally significant source.

=== Recycled and by-products ===

A wide variety of construction wastes and industrial by-products make a major contribution to supply. These include construction, demolition and excavation wastes, slags and ashes, and mineral wastes;

=== Specialist ===

Small amounts of certain lightweight and high density aggregates are manufactured for specialist purposes.

=== Imported ===

The balance of supply consists of imported material (mainly as crushed rock or value-added products) principally from elsewhere in the UK and Norway.

The industry takes its environmental impact very seriously and as a result the UK industry has become a world leader in terms of the quality of its land restoration work. More than 700 Sites of Special Scientific Interest have their origins in mineral operations. In 2009 the industry planted 313,000 trees and 14.4 kilometres of hedgerows. By 2009, there were 283 liaison groups in aggregate quarries.

[[File:Aggregate1.jpg|link=File:Aggregate1.jpg]]

= Uses =

As a basic raw material aggregates can be put to many uses, although certain tasks may require a specific type of aggregate. A large proportion of aggregate is used to manufacture concrete, as well as the cement that is used in the concrete.

Aggregates are used in construction to provide drainage, fill voids, protect pipes, and to provide hard surfaces.

Aggregates are not just used for construction. A vast array of other products, many of which are taken for granted, are manufactured using materials derived from quarrying. These include: paper, glass, cosmetics and toothpaste to name but a few. Aggregates are also used in agriculture, food manufacture, and water and sewage purification. Water will percolate through a trench filled with aggregate more quickly than it will through the surrounding soil, thus enabling an area to be drained of surface water. This is frequently used alongside roads in order to disperse water collected from the asphalt surfacing.

Voids created around the foundations of buildings during construction are filled with aggregate because it is easier to compact than the original soil that was removed, resulting in a more solid finish that will support the structure. Aggregates generally are not affected by the weather as much as soils, particularly clay soils, and will not suffer from shrinkage cracking during dry spells.

Pipes laid to convey treated water, or as conduits for cables, need to be protected from sharp objects in the ground and are therefore laid on, and surrounded by, fine aggregate before trenches are backfilled.

Unpaved roads and parking areas are covered in a surface layer of aggregate to provide a more solid surface for vehicles, from bicycles to lorries. This prevents the vehicles from sinking into the soil, particularly during wet weather.

== Concrete ==

Concrete is a mixture of aggregates, cement and water. The purpose of the aggregates within this mixture is to provide a rigid skeletal structure and to reduce the space occupied by the cement paste. Both coarse aggregates (particle sizes of 20 mm to 4 mm) and fine aggregates (particle sizes less than 4 mm) are required but the proportions of different sizes of coarse aggregate will vary depending on the particular mix required for each individual end use.

The smaller the aggregate size the greater its surface area and the more cement will be required to bind it all together, resulting in a higher cost. However, in general terms, the greater the quantity of cement used the stronger the concrete will be. Therefore, a balance needs to be made between the strength requirements of the end use and the price willing to be paid.

== Asphalt and roadstone ==

This category includes not just roads, but also pavements, airport runways, school playgrounds, car parks, most footpaths or cycleways, and other similar structures. Although each type of structure will require some variation in the material, it is useful to look at the basic structure of roads because they represent the bulk of the aggregate use in this category.

The subgrade represents the natural soil, which will be compacted before the road construction starts. The capping layer is an optional layer, used when the local soils require extra strength, and it is not coated with bitumen. The sub-base is the main uncoated roadstone layer and its role is to give strength and act as a solid platform for the layers above.

The binder course (previously two layers known as the base course and roadbase) and surface course (previously known as wearing course) are commonly called 'asphalt' or 'tarmacadam'. They consist of coarse aggregates, with particle sizes typically between 2 mm to 28 mm, and fine aggregates, with particle sizes of less than 2 mm, mixed with a bitumen binder and occasionally some additional filler if required. The exact sizes required for the coarse aggregates will depend on the particular use and the asphalt recipe specified.

== Railway ballast ==

A fully loaded train weighs a considerable amount (> 2 000 tonnes), added to this is the weight of the track itself and the sleepers it rests on. A very tough aggregate is needed to support this weight and distribute the load of a passing train to avoid serious damage to the ground, or other structures, underneath. Similarly the railway track and sleepers must be held in place firmly and not move as a train passes along them.

Railway ballast generally consists of a tough igneous rock, such as granite, with large (40-50 mm size) angular pieces that lock together. Because of the way igneous rock is formed it is highly resistant to pressure and does not break easily.

== Non-aggregate uses of sand, gravel and crushed rock materials ==

=== Cement ===

Cement is a substance manufactured from limestone and shale, with other minor additives, at temperatures in excess of 1,200ºC. It has unique properties - as a powder it is loose and friable, but mixed with water it hydrates into a paste and then as it dries it sets hard and binds all the surrounding particles together.

=== Agriculture ===

Lime is taken up by plants (either crops or grass) and trees but is also naturally lost from soils through leaching by rainwater and the use of fertilisers. This can result in an increase in acidity, loss of fertility in the soil and sometimes an adverse affect on soil structure.

To redress the balance, 'agricultural lime' is applied to fields to maintain the necessary growing conditions for crops or grassland. Lime can be simply ground limestone or dolomite (which also contains magnesium) or burnt limestone, (or burnt dolomite) where the rock is heated in a kiln.

=== Glass ===

Glass is made from melting silica sand at a high temperature, in the presence of sodium as a flux. The molten glass, at approximately 1,000ºC is poured continuously from a furnace onto a shallow bath of molten tin, where it spreads out evenly. It is then cooled quickly before crystallisation can occur.

=== Industrial and other uses ===

Limestone is used as a flux in the extraction of iron from iron ore. Iron is extracted from ore by heating in a furnace. Limestone is added so that the silicon in the ore forms a calcium silicate (with the calcium carbonate that is limestone) otherwise it would form an iron silicate and thus reduce the quantity of metallic iron produced. The calcium silicate, together with other impurities, forms the 'slag' and this substance can be used as a lightweight secondary aggregate.

Sand, usually silica sand, is used to make moulds in a foundry. These are the hollow containers into which molten metal is poured to produce a casting of a particular shape. The exact type of sand used depends on the particular metal or alloy that is to be cast, but it usually contains clay and/or some other material to bind it together.

The burning of coal at power stations produces sulphur dioxide, one of the main gases that causes acid rain. Rather than simply emit this gas along with their other flue gases, most coal fired power stations today use limestone in a process known as 'flue-gas desulphurisation'.

Limestone is finely crushed and mixed with water to form a slurry. It is then sprayed into the absorber tower of the power station where a chemical process converts the limestone and sulphur into gypsum. This 'artificial' gypsum is then recovered and sold for the manufacture of plasterboard.

Limestone, or calcium carbonate, also has many other uses. Ground to a fine powder it is used as a whitening agent or filler in paper, adhesives, paint, plastics, PVC, toothpaste, medical tablets and cleaning products. It is also used to provide additional calcium in vitamin and mineral supplements, flour and animal feed.

= Specialist aggregates =

Specialist aggregates are required for use in certain demanding applications; notably where lightweight members are required in constructions or where heavy, high density materials are required.

=== Light weight aggregate ===

Light weight aggregates (LWA) are required for situations where concrete is required that imposes low loads on structural elements of constructions. The aggregates therefore need to have low density and weight, achieved by using porous materials, but adequate strength.

A variety of materials can be pelletised (formed into pellets) and heated causing them to harden and expand. These include clay, shale and slate, sludge (e.g. from sewerage works), fine grained sediments dredged from the sea or rivers, and pulverised fuel ash.

Other materials that can be used are natural volcanic materials that are full of gas cavities including pumice and scoriae ('natural cinders'). The volcanic materials do not occur in the UK but can be imported, particularly from Italy.

=== High density aggregate ===

High density aggregates are required for manufacture of concrete that is capable of, for instance, attenuating radiation and thus be suitable for shielding nuclear installations and medical facilities such as radio-therapy treatment rooms.

Aggregates are a most critical and important component of high density concrete and are principally crushed minerals containing relatively heavy elements, in combination with various additives but can also include scrap steel or certain ceramics.

The relevant minerals include crushed hematite and magnetite (both iron oxides), limonite (iron hydroxide) ilmenite (iron titanium oxide) and barite (barytes - barium sulphate). Other additives can include serpentinite (hydrous calcium magnesium silicate) and borax (sodium borate).

-----
This article was authored by the [http://www.sustainableaggregates.com/index.html Mineral Industry Research Organisation].

--[[User:Mineral_Industry_Research_Organisation|Mineral Industry Research Organisation]]

= Find out more =

=== Related articles on Designing Buildings Wiki ===

* Brick.
* Cement.
* Concrete.
* High alumina cement.
* Material Flow Analysis: A tool for sustainable aggregate sourcing.
* Mortar.
* Screed.
* Sustainable aggregates.
* Sustainable materials.

[[Category:Products_/_components]]

Aggregate

2016-03-15T15:18:57Z

Mineral Industry Research Organisation:

[[File:Aggregate2.jpg|link=File:Aggregate2.jpg]]

= Introduction =

Aggregate is the term given to material frequently used in construction as a means of stabilising and reinforcement. Aggregates are widely used in drainage applications and as base material under foundations and roads. In the 10 years ending in 2010, 2.5 billion tonnes of aggregates were consumed by the UK. These aggregates were supplied from various sources:

=== Land based ===

The largest source is from quarrying of the land for sand and gravel, or for rock suitable for crushing (mainly limestone, sandstone, and igneous rock, but also some unusually hard occurrences of chalk, ironstone, slate, etc.).

=== Marine ===

Sand and gravel is dredged from the seabed and is a regionally significant source.

=== Recycled and by-products ===

A wide variety of construction wastes and industrial by-products make a major contribution to supply. These include construction, demolition and excavation wastes, slags and ashes, and mineral wastes;

Specialist

Small amounts of certain lightweight and high density aggregates are manufactured for specialist purposes.

=== Imported ===

The balance of supply consists of imported material (mainly as crushed rock or value-added products) principally from elsewhere in the UK and Norway.

The industry takes its environmental impact very seriously and as a result the UK industry has become a world leader in terms of the quality of its land restoration work. More than 700 Sites of Special Scientific Interest have their origins in mineral operations. In 2009 the industry planted 313,000 trees and 14.4 kilometres of hedgerows. By 2009, there were 283 liaison groups in aggregate quarries.

[[File:Aggregate1.jpg|link=File:Aggregate1.jpg]]

= Uses =

As a basic raw material aggregates can be put to many uses, although certain tasks may require a specific type of aggregate. A large proportion of aggregate is used to manufacture concrete, as well as the cement that is used in the concrete.

Aggregates are used in construction to provide drainage, fill voids, protect pipes, and to provide hard surfaces.

Aggregates are not just used for construction. A vast array of other products, many of which are taken for granted, are manufactured using materials derived from quarrying. These include: paper, glass, cosmetics and toothpaste to name but a few. Aggregates are also used in agriculture, food manufacture, and water and sewage purification. Water will percolate through a trench filled with aggregate more quickly than it will through the surrounding soil, thus enabling an area to be drained of surface water. This is frequently used alongside roads in order to disperse water collected from the asphalt surfacing.

Voids created around the foundations of buildings during construction are filled with aggregate because it is easier to compact than the original soil that was removed, resulting in a more solid finish that will support the structure. Aggregates generally are not affected by the weather as much as soils, particularly clay soils, and will not suffer from shrinkage cracking during dry spells.

Pipes laid to convey treated water, or as conduits for cables, need to be protected from sharp objects in the ground and are therefore laid on, and surrounded by, fine aggregate before trenches are backfilled.

Unpaved roads and parking areas are covered in a surface layer of aggregate to provide a more solid surface for vehicles, from bicycles to lorries. This prevents the vehicles from sinking into the soil, particularly during wet weather.

== Concrete ==

Concrete is a mixture of aggregates, cement and water. The purpose of the aggregates within this mixture is to provide a rigid skeletal structure and to reduce the space occupied by the cement paste. Both coarse aggregates (particle sizes of 20 mm to 4 mm) and fine aggregates (particle sizes less than 4 mm) are required but the proportions of different sizes of coarse aggregate will vary depending on the particular mix required for each individual end use.

The smaller the aggregate size the greater its surface area and the more cement will be required to bind it all together, resulting in a higher cost. However, in general terms, the greater the quantity of cement used the stronger the concrete will be. Therefore, a balance needs to be made between the strength requirements of the end use and the price willing to be paid.

== Asphalt and roadstone ==

This category includes not just roads, but also pavements, airport runways, school playgrounds, car parks, most footpaths or cycleways, and other similar structures. Although each type of structure will require some variation in the material, it is useful to look at the basic structure of roads because they represent the bulk of the aggregate use in this category.<br />

The subgrade represents the natural soil, which will be compacted before the road construction starts. The capping layer is an optional layer, used when the local soils require extra strength, and it is not coated with bitumen. The sub-base is the main uncoated roadstone layer and its role is to give strength and act as a solid platform for the layers above.

The binder course (previously two layers known as the base course and roadbase) and surface course (previously known as wearing course) are commonly called 'asphalt' or 'tarmacadam'. They consist of coarse aggregates, with particle sizes typically between 2 mm to 28 mm, and fine aggregates, with particle sizes of less than 2 mm, mixed with a bitumen binder and occasionally some additional filler if required. The exact sizes required for the coarse aggregates will depend on the particular use and the asphalt recipe specified.

== Railway ballast ==

A fully loaded train weighs a considerable amount (> 2 000 tonnes), added to this is the weight of the track itself and the sleepers it rests on. A very tough aggregate is needed to support this weight and distribute the load of a passing train to avoid serious damage to the ground, or other structures, underneath. Similarly the railway track and sleepers must be held in place firmly and not move as a train passes along them.

Railway ballast generally consists of a tough igneous rock, such as granite, with large (40-50 mm size) angular pieces that lock together. Because of the way igneous rock is formed it is highly resistant to pressure and does not break easily.

== Non-aggregate uses of sand, gravel and crushed rock materials ==

=== Cement ===

Cement is a substance manufactured from limestone and shale, with other minor additives, at temperatures in excess of 1,200ºC. It has unique properties - as a powder it is loose and friable, but mixed with water it hydrates into a paste and then as it dries it sets hard and binds all the surrounding particles together.

=== Agriculture ===

Lime is taken up by plants (either crops or grass) and trees but is also naturally lost from soils through leaching by rainwater and the use of fertilisers. This can result in an increase in acidity, loss of fertility in the soil and sometimes an adverse affect on soil structure.

To redress the balance, 'agricultural lime' is applied to fields to maintain the necessary growing conditions for crops or grassland. Lime can be simply ground limestone or dolomite (which also contains magnesium) or burnt limestone, (or burnt dolomite) where the rock is heated in a kiln.

=== Glass ===

Glass is made from melting silica sand at a high temperature, in the presence of sodium as a flux. The molten glass, at approximately 1,000ºC is poured continuously from a furnace onto a shallow bath of molten tin, where it spreads out evenly. It is then cooled quickly before crystallisation can occur.

=== Industrial and other uses ===

Limestone is used as a flux in the extraction of iron from iron ore. Iron is extracted from ore by heating in a furnace. Limestone is added so that the silicon in the ore forms a calcium silicate (with the calcium carbonate that is limestone) otherwise it would form an iron silicate and thus reduce the quantity of metallic iron produced. The calcium silicate, together with other impurities, forms the 'slag' and this substance can be used as a lightweight secondary aggregate.

Sand, usually silica sand, is used to make moulds in a foundry. These are the hollow containers into which molten metal is poured to produce a casting of a particular shape. The exact type of sand used depends on the particular metal or alloy that is to be cast, but it usually contains clay and/or some other material to bind it together.

The burning of coal at power stations produces sulphur dioxide, one of the main gases that causes acid rain. Rather than simply emit this gas along with their other flue gases, most coal fired power stations today use limestone in a process known as 'flue-gas desulphurisation'.

Limestone is finely crushed and mixed with water to form a slurry. It is then sprayed into the absorber tower of the power station where a chemical process converts the limestone and sulphur into gypsum. This 'artificial' gypsum is then recovered and sold for the manufacture of plasterboard.

Limestone, or calcium carbonate, also has many other uses. Ground to a fine powder it is used as a whitening agent or filler in paper, adhesives, paint, plastics, PVC, toothpaste, medical tablets and cleaning products. It is also used to provide additional calcium in vitamin and mineral supplements, flour and animal feed.

= Specialist aggregates =

Specialist aggregates are required for use in certain demanding applications; notably where lightweight members are required in constructions or where heavy, high density materials are required.

==

Light weight aggregate ==

Light weight aggregates (LWA) are required for situations where concrete is required that imposes low loads on structural elements of constructions. The aggregates therefore need to have low density and weight, achieved by using porous materials, but adequate strength.

A variety of materials can be pelletised (formed into pellets) and heated causing them to harden and expand. These include clay, shale and slate, sludge (e.g. from sewerage works), fine grained sediments dredged from the sea or rivers, and pulverised fuel ash.

Other materials that can be used are natural volcanic materials that are full of gas cavities including pumice and scoriae ('natural cinders'). The volcanic materials do not occur in the UK but can be imported, particularly from Italy.

==

High density aggregate ==

High density aggregates are required for manufacture of concrete that is capable of, for instance, attenuating radiation and thus be suitable for shielding nuclear installations and medical facilities such as radio-therapy treatment rooms.

Aggregates are a most critical and important component of high density concrete and are principally crushed minerals containing relatively heavy elements, in combination with various additives but can also include scrap steel or certain ceramics.

The relevant minerals include crushed hematite and magnetite (both iron oxides), limonite (iron hydroxide) ilmenite (iron titanium oxide) and barite (barytes - barium sulphate). Other additives can include serpentinite (hydrous calcium magnesium silicate) and borax (sodium borate).

This article was authored by the [http://www.sustainableaggregates.com/index.html Mineral Industry Research Organisation].

--[[User:Mineral_Industry_Research_Organisation|Mineral Industry Research Organisation]]

= Find out more =

=== Related articles on Designing Buildings Wiki ===

* Brick.
* Cement.
* Concrete.
* High alumina cement.
* Material Flow Analysis: A tool for sustainable aggregate sourcing.
* Mortar.
* Screed.
* Sustainable aggregates.
* Sustainable materials.

[[Category:Products_/_components]]