Until there is a problem, retaining walls are not a topic of discussion. A properly designed and constructed retaining wall does what it is supposed to, quietly, for decades, while trapped under the weight of the soil and restrained from shifting, slumping or collapsing by the surrounding ground. Whether it performs this way for the next fifty years or begins to exhibit problems within the first five depends on just one thing: how it was made. Precast Retaining Wall panels are manufactured on our plant in Umm Al Quwain and the manufacturing process that makes every panel is what makes the difference between a wall that will hold up in the extremely challenging UAE weather conditions and one that will not.
What Is a Precast Retaining Wall?
Precast retaining walls are concrete walls that are pre-cast in a factory with controlled conditions and then transported to the site for installation to retain soils and provide control over changes in ground elevations. Precast walls are delivered to the site cured and ready to install, whereas cast-in-place retaining walls are poured and cured at the site. This moves the variables which determine the quality of a concrete – temperature, humidity, consistency and curing time – from the unpredictable site to the controlled environment of the concrete factory where these variables can be precisely controlled.
This is more relevant in the UAE compared with other markets. There are real-world challenges to curing site-poured concrete in the heat of summer and to ensure that the concrete is consistent and of good appearance, whereas a factory-controlled process eliminates weather as a variable. That control difference is what makes precast the preferred material for retaining wall projects all over the region’s infrastructure and development projects.
Why the Manufacturing Process Determines Performance
Three manufacturing decisions are directly linked to the long-term strength and durability of a retaining wall: the concrete mix design, the reinforcement configuration and the curing environment. If you get any one of these items incorrect, the effects will become apparent when it comes time to apply the load capacity of a wall or the failure of a wall (cracking etc.). These problems can be much more costly to repair after the wall is in place and holding soil than if they were avoided at the time of production.
That’s why a well-managed precast operation treats each of these tasks as a managed and monitored process instead of a mundane one that is expedited through. The engineering and quality controls used in the construction process provide a project owner with the assurance that a wall built today will perform properly without being interfered with 30 or 40 years later.
Precast Retaining Wall Manufacturing Process – Step by Step
The process of making precast retaining wall panel starts before concrete is placed. Engineers first determine the soil pressure the wall will have to withhold, the thickness of the wall, the height of the wall, the load conditions of the project and other requirements according to the characteristics of the project site. These calculations are based on the structural concrete codes, such as the provisions in ACI and ASTM International for reinforced concrete design. The design stage establishes the parameters for all subsequent design work, even the strongest of concrete mixes will fail to perform if the engineering does not properly reflect the actual soil and loading conditions of the site.
After the design is completed, the next step is to prepare moulds for production. Each panel is cast in a steel mould, which ensures dimensional accuracy and a smooth surface on all of the panels manufactured in a production run. The moulds are thoroughly cleaned and treated with a release agent before each pour so that the cured panel can be released without surface scratching.
The placement of reinforcement is one of the most critical phases in the process, and it is carried out after the mould preparation stage. The steel reinforcement in the panel adds tensile strength and will help prevent cracking under load, as well as add strength to the overall wall to bear the pressure of the surrounding soil when it is installed. These are reinforcement layouts that are designed based on the calculations made previously in the design phase and if they are not positioned accurately during installation, the strength of the finished panel can be affected, making this an important step that should be carefully performed and checked and not treated as routine assembly.
Once the reinforcement is in place, the concrete is then mixed with cement, aggregates, water, and admixtures that have been chosen and combined to provide the strength and durability needed for the project. The ratios listed here are not near the ratios—actual ratios have been calculated to provide a specific compressive strength and also to maintain the workability necessary for a clean, void free pour. After mixing, the concrete is placed into the prepared moulds and is vibrated during the placement to remove any air pockets and to provide uniform compaction throughout the panel. The air voids that remain in the concrete after compaction impact the eventual load-bearing capacity of the panel, therefore this compaction step is an important factor that directly influences the performance of the load bearing capacity of the panel.
The curing is where the concrete gains the majority of its final strength, and is perhaps the area where site-poured concrete is least competitive with factory production. During this step, the temperature, moisture and curing duration are all regulated, creating a more dense and consistent concrete structure compared to what would normally be achieved when curing in the varying outdoor climate in UAE. Correct curing means increased strength and less cracking potential and service life in the cured wall.
After removal from the panel moulds, panels are carefully examined for aesthetic and surface quality, cracks, and dimensional tolerances before any treatments will be applied. The inspection stage is followed by formal quality control testing, usually compressive strength testing, dimensional testing and visual inspection according to established ASTM International standards. Panels that satisfy these tests are then stored under conditions that will not cause damage prior to transport and are then transported to the project site using equipment and handling procedures that will not cause cracking or edge damage during transport.
What Does This Process Mean for Contractors and Developers?
For contractors and developers in the UAE comparing the various options for retaining walls, this manufacturing process is important to understand and is why precast walls are always the better choice than cast-in-place retaining walls. The consistency found in factory production is achieved, as pouring and curing concrete on an active construction site, add to the variations that are found in each concrete panel. Panels are delivered cured, and installation can be done right away, eliminating the time-consuming on-site curing process and significantly reducing project time on schedule sensitive jobs. The overall lower demand of on-site labour and the fact that more work can be done in a controlled environment than at site, also creates a greater durability than site-cured concrete is likely to achieve in the long term.
The Most Frequent Errors That Reduce the Effectiveness of Retaining Walls
Despite a well-designed manufacturing process, there are decisions that can cause trouble in a retaining wall project that are made outside the factory. One of the most common methods that projects end up with substandard walls is by choosing the cheapest manufacturer without checking the quality control system they have. Another common error is to not include adequate drainage behind the panel installed in a retaining wall, even if the panel itself is made to highest standards. Installation quality is as critical as the manufacturing quality; a high-quality panel installed out of position or not backfilled properly and compacted can not perform as well as its design specification.
Expected Service Life
The long-term durability that is specifically intended by factory production is a reasonable expectation of the longevity of a precast retaining wall that is carefully made and properly installed with consistent and appropriate maintenance. Concrete structures constructed to this level of standard are likely to benefit from lower life cycle costs than less rigorous options which will need remediation work to be carried out sooner than the structure is constructed to this standard.
Why Precast Retaining Walls Suit UAE Conditions
The UAE has its own set of requirements for the installation of retaining walls: the site is usually exposed to high ambient temperatures, sandy soils, and even highly variable soil properties, as well as tight construction schedules with limited tolerance for delay. Precast concrete can directly solve all of these. On-site curing does not offer the strength or finish guaranteed by the factory control, and the mix design and reinforcement are designed based on the soil conditions of a particular site. With a shorter installation time frame, pre-cured panels also work well within the timeframes of infrastructure and development projects in UAE.
Choosing a Precast Retaining Wall Manufacturer
Choosing the right precast retaining wall manufacturer has a long-term impact on the performance of the finished wall as each step in the process above relies on the manufacturer’s engineering discipline and quality control. At our Umm Al Quwain plant, we have implemented the engineering principles and quality control procedures expressed in this process to every wall we make.
Call our team today to discuss your project’s soil conditions, wall height, load requirements and delivery timeline, and receive a competitive quotation for high-quality precast retaining walls manufactured in Umm Al Quwain for projects across the UAE.
