Prestressed Concrete Blocks
Arridano Tillo
Holcim offers decades of experience in designing, producing and engineering innovative precast concrete and prefabricated elements. Our solutions are suitable for all construction applications, including residential, commercial and infrastructure projects.
Our precast and prefabricated offer ranges from traditional to innovative solutions, all of which greatly improve the efficiency of concrete projects.
Precast concrete is produced in a controlled factory environment. This enables more precise production and curing. It is then transported to the construction site, where it is lifted into place. Projects using precast typically finish faster, since work time onsite is reduced and fewer vehicles are needed to transport construction material.
Holcim offers a broad range of standard and engineered prefabricated and precast products and solutions. Our standard offer includes concrete paving for landscaping, concrete masonry blocks for buildings and concrete pipes and culverts for water management. We also manufacture engineered architectural and structural elements such as columns and wall panels for buildings, tunnel liners, rail products and bridge solutions for infrastructure.
Holcim is a global leader in innovative and sustainable building solutions with net sales of CHF 27.0 billion in 2023. Driven by our purpose to build progress for people and the planet, our 63,448 employees are on a mission to decarbonize building, while improving living standards for all. We empower our customers across all regions to build better with less, with a broad range of low-carbon and circular solutions, from ECOPact and ECOPlanet to our circular technology platform ECOCycle. Through innovative systems, from Elevate roofing to PRB insulation, Holcim makes buildings more sustainable in use, driving energy efficiency and green retrofitting. With sustainability at the core of our strategy, we are on the way to becoming a net-zero company with 1.5C targets validated by SBTi.
There are many technical varieties of modern concrete, but historic buildings and bridges generally used three main types: plain or unreinforced concrete, reinforced concrete, and prestressed concrete.
Concrete, like stone, is very strong in compression and works well when used as a vertical column or supporting post, for example. When used horizontally as a slab or beam, concrete can typically span only short distances before it begins to crack and fail unless it is made thicker. The depth and weight of a plain concrete beam soon become too large and impractical for longer horizontal spans required in buildings and bridges.
Builders learned that the addition of metal reinforcing bars in a concrete beam or slab would allow it span greater distances before cracking. As a result, reinforced-concrete became an important structural material for bridge construction after 1900. Virtually all modern concrete is reinforced with metal.
The post-tensioning system required simple equipment and could be done almost anywhere, including at the bridge site. In fact, the first prestressed-concrete bridge in Minnesota was post-tensioned.
Because post-tensioning was limited to smaller beams and slabs, the alternate method of pretensioning became the industry standard after the early years.
Figure 5- Walnut Lane Bridge, Philadelphia, Historic American Engineering Record (HAER) photo. This documentary photo, taken in 1968, shows the Walnut Lane Bridge span, comprised of a parallel series of prestressed, post-tensioned concrete beams, aligned closely together. Image retrieved from the Library of Congress.
In 1952, brothers Norbert and Leonard Soukup established the Northern States Prestressed Concrete Co. to build the first prestressed-concrete bridge of any kind in Minnesota, using the post-tensioning method. They assembled rows of specially designed concrete blocks, tensioned them together in a long row with cables, and created a series of prestressed-concrete block-beams. The beams created the span for a bridge carrying local traffic from U.S. Highway 61 to a Boy Scout Camp outside Lake City. The bridge has since been replaced.
Figure 6- Constructing the Lake City Bridge in a series of numbered views: (1) The post-tensioned block beams were assembled in the Minneapolis plant of the Northern States Prestressed Concrete Co. and trucked to the bridge construction site near Lake City, just off Hwy. 61. (2) A closeup view of three of the block beams resting on the ground next to the workhouse. The tensioning cable is visible along the side of the nearest beam. (3) A view of one block-beam in place from the center pier to the far abutment, extending away from the camera, with a second beam being lowered by crane. (4) All the block beams are in place. (5) Workmen on the block-beam span, preparing to install the transverse cables that tie the beams together, side by side.
Figure 7- This is an advertisement for Northern States Prestressed Concrete Co., with an illustration of their block beams as used for the Lake City Bridge spans. Compare this view with the photo of the beams in Figure 6 (see view 2 upper right), showing the side of the block-beam with the post-tensioning strand on the outside of the beam. Ad from the "Construction Bulletin," August 6, 1953.
Created by the Federal Aid Highway Act of 1956, the new Interstate Highway System demanded thousands of new bridges across the nation. Designed as freeways, the new highways would have no traffic intersections anywhere. All highways and railroads would go over or under the new Interstates. Because the design of the new Interstate was so uniform and consistent with an original four-lane system, most of the bridges were similar in shape and length. The requirements created a perfect match for the new prestressed-concrete system, which readily turned out quantities of uniform beams, cast in off-site plants, under controlled factory conditions, independent of the weather and site conditions. Also, the new prestressed-concrete beams proved competitive with steel beams in size and cost, especially when steel was scarce and expensive in the 1950s.
The Interstate System helped create a major prestressed-concrete industry virtually overnight. The same plants often fabricated beams, slabs, and planks for roofs and floors to build the many new shopping centers, schools, stadiums, offices, and other structures for the suburbs accessed by the Interstate Highways.
Figure 10 - These sketches of an Interstate highway show the consistent design and dimensions of the bridge to cross four lanes as seen in various situations. The spans lengths remain the same for bridge after bridge.
With a dedicated design team and mould manufacturing facilities on-site, we are able to produce a wide range of precast concrete components that are completely bespoke to your construction project.
Our standard Betaloc unit is 800 x 800 x 1,600 mm long, made of solid precast concrete and weighs approximately 2.4 tonnes. With 2 lifting points the units are quick and easy to install, thanks to the stacking design of the units provided by an interlocking system. We also produce a half unit allowing for a flush finish to your walling, if required, which is 800mm in length.
Our Betaloc interlocking concrete blocks are popular with farmers looking for a flexible crop storage system. As requirements change, the concrete blocks can be easily moved to a different configuration to create smaller and larger bays depending on your requirements.
In addition to our extensive product range we are able to offer a full installation service and can manage the whole process for you, from the initial design plan through to installation and aftercare. This means you can have one point of contact to manage your whole project for you from start to finish. We manage all the logistics and deliver you a completed project, on time and within budget.
Many of our customers prefer the installation to be carried out by our teams but ultimately the choice is yours. We can offer our products on a supply only basis, or supply and install, depending on your requirements.
Whether you have a grain store that needs a breath of new life, a state of the art recycling facility or plans to build a new anaerobic digester or silage clamp, Poundfield Precast are able to work with you every step of the way to supply, deliver and fit, a tailored solution designed specifically around you.
These concrete blocks feature an interlocking design, with projections and depressions that allow them to fit neatly into the adjacent block, creating a secure and stable structure. The interlocking system ensures easy alignment both horizontally and vertically, making them simple to install without requiring specialised skills or equipment. They are specifically designed to lock together without the need for cement mortar or adhesives to bond them.
The interlocking blocks each weigh 2.4 tonnes and are simply laid on top of each other and are held in position by the interlocking lugs. With two cast-in lifting points, the units are quick to install and once in place the wall is immediately ready for use. The only real requirement prior to installation is to have a sound and level base.
As a major precast concrete manufacturer, we recognise the contribution we can make to help our customers lower their carbon footprint and since January 2022 every product currently manufactured by Poundfield Precast is available in an ultra-low carbon concrete option which can save up to 76% in embodied CO2 compared to a conventional concrete.
Twice a year, each plant undergoes two thorough, unannounced audits. They are conducted by third-party engineers who audit the plant according to requirements specifically targeted to the products being manufactured at that location. PCI Certified plants are audited in accordance with standards published in three PCI quality-control manuals:
Since the various precast concrete product lines require different levels of expertise and production techniques to produce, PCI Certification provides a system of categories. This system ensures that producers are qualified to produce the products that you are specifying. Precast concrete plants can be certified in as many as four product groups:
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