Ready Mixed Concrete - Further Information
Readymix concrete can be manufactured in many specifications to take account of the site conditions, aesthetic and structural requirements.
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Specifying visual concrete
Many architects, bridge engineers and designers aspire to high quality, well-finished site cast concrete. However, many of those who would like to experiment with visual concrete fear that they might not achieve the required standard of finish. To specify visual concrete the specifier must first have confidence in the ability and experience of the contractor and in turn the contractor must receive proper guidelines and specifications from the designer as to how to achieve the required quality and colour of the fair-faced concrete. To properly specify fair-faced concrete the designer must understand the material, how it breathes, takes in moisture, attracts dirt and pollution and weathers like stone. They must also understand the various additives and surface treatments that can be utilised to minimise the effects of the above.
The book ‘Exploring Concrete Architecture’ by David Bennet, which gives detailed examples of projects featuring fair-faced concrete, is an excellent introduction to the subject. Further information on how to acquire this book is available from Irish Cement.
Further Information
The introduction to David Bennet’s book ‘Exploring Concrete Architecture’ gives a useful guide to specifying visual concrete. Click here to download the full text
Self-Compacting Concrete
Self-compacting concrete (SCC) is an innovative concrete that does not require vibration for placing and compaction. It is able to flow under its own weight, completely filling formwork and achieving full compaction, even in the presence of congested reinforcement. The hardened concrete is dense, homogeneous and has the same engineering properties and durability as traditional vibrated concrete.
Self-compacting concrete offers a rapid rate of concrete placement, with faster construction times and flow around congested reinforcement. The fluidity and segregation resistance of SCC ensures a high level of gomogeneity, minimal concrete voids and uniform concrete strength, providing the potential for a superior level of finish and durability to the structure. SCC is often produce with low water-cement ratio providing the potential for high early strength, earlier de-moulding and faster use of elements and structures.
Further Information
- Self Compacting Concrete / Particle bonded board formwork – Roebuck Hall student residence / Concrete Today, Dec 2006 Click here
- New European guidelines on self-compacting concrete / Concrete Today, Nov 2005 Click here
- Self Compacting Concrete – Dr. Roger West TCD / Concrete Today, Dec 2003 Click here
Cellular Concrete
Cellular concrete is a lightweight material that solves many heavy-duty construction problems. Used beneath roadways, bridges and ramps, buildings and other structures, it reduces soil loading while adding compressive and shear strength. In America and Japan in particular, contractors and engineers frequently use cellular lightweight concrete as backfill for tunnels, waterlines and sewers, to provide shock absorption in earthquake zones, to fill voids in silos and abandoned mines, to reduce hydrostatic pressure on walls and a myriad of other uses.
Further Information
- Cellular Concrete for Road Construction / Concrete Today, Jan 2003 Click here
Shotcrete
Shotcrete is an all-inclusive term to describe the spraying of concrete or mortar that may be accomplished through either a dry or wet-mix process. Wet-mix shotcrete is requires less skill to apply and involves pumping of a previously prepared mixture, typically ready mixed concrete, to the nozzle. Compressed air is introduced at the nozzle to impel the mixture onto the receiving surface. The mixture usually contains = 12mm aggregate, although larger-size aggregate has also been used. Shotcrete is often applied to vertical surfaces which require temporary or permanent stabilisation such as open cut tunnelling.
Further Information
- Shotcrete – Dublin Port Tunnel award winning solution / Concrete Today, June 2004 Click here
Self-cleaning Concrete
Scientists at the Italcementi Group in Bergamo, Italy, have developed a self-cleaning concrete that keeps buildings from turning black from pollutants in the atmosphere. The concrete is made by adding particles of white pigment titanium dioxide to the cement component.
When titanium dioxide absorbs ultraviolet light, it becomes highly reactive and breaks down pollutants that come into contact with the concrete's surface. The reactive material can kill bacteria and fungi and also break down pollutants such as nitric oxide, sulphur dioxide, and many volatile organic compounds that contribute to concrete's darkening.
Self-cleaning concrete has already been used in several new buildings, including a the modern ‘Dives in Misericordia’ church in Rome. The brilliant white concrete of the new Jubilee Church in Rome is expected to stay clean for the ages thanks to a photocatalytic additive to the concrete.
Photocatalysts are additives that allow concrete to keep itself clean. They decompose organic material on the concrete’s surface. What’s more, they reduce air pollution by scouring nitrous oxide from the air.
Strong sunlight or ultraviolet light decomposes many organic materials in a slow, natural process. Photocatalysts speed up this process and, like other types of catalysts, stimulate a chemical transformation without being consumed or worn-out by the reaction. When used on or in a concrete structure, photocatalysts decompose organic materials that foul the surface. The organic compounds affected by photocatalysts include dirt (soot, grime, oil and particulates) biological organisms (mold, algae, bacteria and allergens), air-borne pollutants (VOCs including formaldehyde and benzene; tobacco smoke; and the nitrous oxides (NOx) and sulphuric oxides (SOx) that are significant factors in smog), and even the chemicals that cause odors. The catalyzed compounds break down into oxygen, carbon dioxide, water, sulphate, nitrate and other molecules that are either beneficial to or have a relatively benign impact on the environment. Most inorganic pollutants and stains, including rust, are not catalyzed.
Further Information
- Self-cleaning concrete – new weapon in fight against smog / Concrete Today, Nov 2005 Click here Click here
Translucent Concrete
Hungarian architect Áron Losonczi who experiments with construction materials, invented the translucent concrete. LiTraCon, based in Aachen, Germany, has developed a concrete that contains glass optical fibers the thickness of a hair. They transmit light from one side of the material to the other.
To ensure that the ends of each fiber make contact with the surfaces on both sides of the material, blocks of concrete are built in stages. First, a thin layer of concrete is poured into a long, narrow mould. Then, a layer of optical fibres is laid along the length of the mould. After several repetitions, the resulting long beam can be cut into short, rectangular building blocks riddled with the thin light pipes.
The fiber diameters range from 2 microns to 2 millimeters. By using fibers of different diameters, LiTraCon designers can achieve different illumination effects. Varying the size of the blocks, however, doesn't change the effect. So far, LiTraCon has made continuous concrete beams up to 20 meters long, and the fibres transmit light the entire length.
With these blocks, architects can design and build a large variety of structures, ranging from translucent concrete walls to floors lit from below.
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