Concrete gutters are an essential part of pavement construction for discharging water and preventing infiltration beneath the pavement. Installing a concrete gutter eliminates the need for side ditches, and improves the performance of the road by protecting it from water damage. To ensure that the gutter meets the requirements of the project specifications, the best construction techniques and procedures must be applied.
Construction Methods for Concrete Gutter: Two construction methods are commonly used for concrete gutter installation: stationary and slipform. Stationary construction involves the use of wood, plastic, or metal forms, whereas slipform construction employs a slipform machine.
Considerations for Concrete Gutter Construction: When constructing concrete gutters, it is important to consider various factors to ensure that the gutter functions adequately. This includes using the right materials and construction techniques to meet the project’s specifications. Additionally, the construction process must be properly managed to ensure the gutter achieves the desired performance.
Concrete Gutter Construction- Methods and Work Procedure
For building concrete gutters, there are several techniques used. In the past, wooden forms were used to build them by hand. Nowadays, more efficient methods such as using reusable forms and slip form construction are used to speed up the process and improve the quality.
1. Set Layout of Concrete Gutter
The layout of concrete gutter is usually in line with the pavement. Surveyors must consider the profile and curves in accordance with the design drawings.
2. Sub-grade Preparation
Preparing the Sub-Grade for Concrete Gutter: The sub-grade of a concrete gutter needs to be adequately prepared regardless of the construction method used, such as slip form or cast in situ. This includes leveling the sub-grade to the required elevation and compacting it with the suitable tools. Additionally, it is important to moisten the sub-grade prior to the placement of concrete to prevent shrinkage and cracking. If the soil at the project is poor, a granular base may need to be placed to prevent future settlement issues.
Preventing Settlements and Tilts: To prevent the concrete gutter from suffering from settlements, tilts, and cracks, it is essential to practice good construction methods. This helps to ensure the structural integrity of the concrete gutter and ensure that it performs adequately. To prevent settlements and tilts, the sub-grade should be properly prepared and compacted, and a granular base may be necessary if the soil quality is poor. Additionally, proper moistening of the sub-grade prior to the placement of the concrete is also important.
3. Formwork Placement
Types of Formwork for Concrete Gutter Construction
Wood Formwork: Wood formwork is the most economical and adaptable type of formwork for small scale construction projects. It is fixed manually at the construction and is relatively quick and easy to set up. However, it is costly and labour intensive for larger scale projects, as the wood can only be used a few times before needing to be replaced.
Metal Formwork: Metal formwork is a suitable option for larger scale construction projects. It is more durable and can be reused multiple times, making it more cost-effective. Additionally, metal formwork requires less maintenance and can be quickly assembled, making it suitable for projects with tight deadlines.
Plastic Formwork: Plastic formwork is lightweight and easy to install, making it suitable for a variety of construction projects. It is also more cost-effective than wood or metal formwork, as it can be reused multiple times. However, it is not as durable and is more prone to damage than other types of formwork.
The process of fixing formwork begins after the preparation of the subgrade is complete. A surveyor will determine the exact location and trajectory of the gutter. Stakes are then driven into the ground at the designated location and the formwork is raised to the specified elevation. To securely hold the formwork in place, wedges are used to lock it to the stakes.
When the size of the concrete gutter construction project is large, Slip form concrete gutter construction is often employed. This process begins with the specification of the path and elevation of the concrete gutter, which is typically done with a string line. Sensors are then attached to the string line and the slipforming operation can commence. Depending on the project, it may be necessary to prepare the area on which the slipform machine will be moved. Once this is done, the slipforming operation can begin.
4. Reinforcement Placement
Steel Reinforcement Placement in Utility Trenches: The American Concrete Pavement Association (ACPA) requires that steel bars be placed when concrete gutters cross utility trenches. The bars should be extended 3m on each side of the trench to provide reinforcement.
Soft Soil Reinforcement: Softer and weaker soils may require the installation of reinforcement to help control or restrict settlements and crack widths. Usually two No.13 bars are placed longitudinally to provide the necessary reinforcement.
5. Concrete Placement
Slipform Construction: The slipform construction method requires the use of a slipform machine to place the concrete. The machine forces the fresh concrete out and moves along the path of the concrete gutter at a specified rate, as illustrated in Fig. 8.
Stationary Construction: For stationary construction, suitable means must be chosen for the delivery and placement of the concrete. This could include pumping, for example.
6. Contraction and Expansion Joint Construction
Contraction Joint Construction:
To prevent concrete gutters from developing cracks due to shrinkage, contraction joints must be installed at a spacing not exceeding 7.62m. When metal forms are used, division plates should be used to create the contraction joints. If the gutter and the curb are integral, the contraction joints should be extended into the curb. If they are separate, the location of contraction joints in the concrete gutter and the curb should be the same.
Expansion Joint Construction:
To avoid any damage due to expansion, expansion joints must be installed at a spacing not exceeding 30.48m. This will ensure that the structure is able to withstand any changes in temperature or other environmental factors.
7. Finishing of Concrete Gutter
Floating of Cast in Place Concrete Gutter: When the cast in place method is used to construct a concrete gutter, the finishing process requires the surface to be floated. Floating is done by using a tool with a flat edge, such as a trowel, to smooth out and level the concrete surface. This ensures that the concrete surface is even and will not have any imperfections or bumps.
Slip Form Construction of Concrete Gutter: Slip form construction is a method used to construct a concrete gutter without the need for floating. This process involves creating forms for the concrete, which are then filled with concrete and allowed to harden. Once the concrete is dry, the forms are removed, leaving behind a concrete gutter with a smooth, even surface. No additional finishing is required, as the surface of the concrete is already even and smooth.
8. Curing Process for Construction Projects
Finishing Work for Construction Projects
Once the construction work is completed, the finishing work begins. This includes activities such as painting, tiling, installation of windows and doors, and other interior and exterior finishing touches. The finishing team must ensure that all finishing tasks are completed as per the plan and in a timely manner.
After the construction and finishing work is completed, the curing process begins. A suitable curing mechanism must be employed to ensure that all materials used in the project are cured properly. This will help to ensure the longevity of the project and its structure.