With so many options of concrete mixes available today, architects and designers can basically decide exactly what type of concrete they need. And this doesn’t only mean the aesthetic look of the concrete finish, but concrete can actually be designed and proportioned to meet an extremely wide range of specific requirements including consistencies, flows, setting times and hardened properties.
“In fact, the product is flexible enough to produce varying strengths at early or late stages, different types of strengths in general, pre-determined densities, as well as the required levels of abrasion resistance and shrinkage,” explains Bryan Perrie, managing director of The Concrete Institute.
Perrie points out that this versatility of concrete boosts the building material’s sustainable merits and should be a decisive factor when maximum quality and longevity are aimed for in infrastructural projects.
When building with concrete, some of the many flexibility benefits include:
• Concrete can be produced on the building site using a wide variety of transport and placing mechanisms.
• It can be transported from batch plants to the construction site via a myriad of means, ranging from simple wheelbarrows to heavy engineering vehicles and equipment such as dumpers, trucks, conveyors, cranes and pumps.
• Concrete can be placed by cranes, pumps, trunks, spraying equipment and tremies (large metal hoppers and pipes used to place freshly mixed concrete underwater).
• Self-compacting concrete (SCC) offers additional flexibility in the placing of concrete and the achievement of excellent off-shutter finishes.
“Concrete has an advantage over other materials in that concrete elements such as walls, columns, beams, trusses and slabs can be constructed in situ as part of the structure being erected, or precast on site on the ground and lifted into their final position via the tilt-up and stack-casting methods,” Perrie adds.
“As a hybrid of precast and in situ concrete, concrete can also be precast kilometres away in a precast yard and transported to site and placed into position there.
“An additional benefit is that all of the above options can be combined on one project. This may mean that some elements are constructed in situ, while others may be precast on site and still other precast off-site.”
As an example of an economical construction product, precast concrete is derived by casting concrete into a reusable mould or form which is then cured in a controlled environment and transported to the construction site to be lifted into place, as opposed to standard concrete which is poured into site-specific forms and cured on site.
“By producing precast concrete in a controlled environment – the so-called ‘precast yard’ – it is possible to monitor and control all stages of production, including ensuring that adequate curing is carried out to ensure that the final products fully comply with strength requirements,” says Perrie.
Precast yards may be established operational factories or can be created on site. The precast concrete is generally cast at ground level, which helps with safety and productivity throughout a project.
“Since there is greater control of the quality of materials and workmanship in a precast yard than when concrete is cast in situ, precast yard production tends to lead to better durability. When the products and structure last longer, the end-result is cost saving in maintenance, materials and energy – not to mention eliminating inconvenience. The forms used in a precast plant may be reused hundreds to thousands of times before they have to be replaced, which ensures that the cost of formwork per unit is lower than for in situ construction.”
Furthermore, if the structure has been appropriately designed, precast products can be removed and reused after the structure has reached the end of its life.
Forms of precast concrete products include:
• Precast architectural panels used to clad all or part of a building.
• Stormwater drainage, water and sewage reticulation pipes, culverts, manholes, sumps and tunnels.
• Precast building components used architecturally as cladding, trimmings, accessories and curtain walls.
• Precast concrete’s structural applications include bricks, blocks, foundations, beams, floors, walls and other similar components.
• Precast concrete products are also used in the building, safety and site protection of various transportation systems in the form of culverts, bridge beams and segments, railway sleepers, sound walls or barriers, safety barriers and kerbs.
“The increased control of precast concrete in the production phase ensures fewer reject products and consequent saving of raw materials, as well as speeding up construction on site,” adds Perrie, pointing out that examples of this were the precast plants that manufactured the thousands of precast concrete tunnel and bridge segments of the Gautrain infrastructure.
“The social contribution of concrete to civilisation cannot be overestimated. It is the second-most used resource in the world after water and contributes significantly to the human standard of living, including the houses we live in, the schools and universities we attend, the offices we work in, the infrastructure of water reticulation and sewers, the dams that hold our water and the roads that fulfil the needs of mankind globally,” he concludes.
Full thanks and acknowledgement are given to The Concrete Institute (www.theconcreteinstitute.org.za) for the information provided.
Concrete can be precast on site on the ground and lifted into its final position via the tilt-up and stack-casting methods.
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