Pouring concrete on a sloped surface is a task that demands skill, experience, and careful planning. Whether working on sloped concrete members, driveways, or wheelchair ramps, the use of low slump concrete is common to ensure the concrete stays in place and maintains its strength and durability. This article explains the step-by-step procedure and important considerations for pouring concrete on slopes successfully.
Preparation Before Pouring Concrete
Before any concrete is poured, thorough preparation is essential. The formwork must be constructed accurately and checked for proper leveling to hold the concrete in the desired shape. Reinforcements, embedment objects, and the formwork itself need to be inspected to confirm they are firmly in place and free from dirt or debris. For concrete driveways and wheelchair ramps, special attention should be given to making sure the surface area is level and the forms are secure and clean.
The Role of Low Slump Concrete
Low slump concrete is typically used for sloped surfaces because it has a lower water content, making it less prone to flow or slump downhill along the slope after placement. This type of concrete has excellent structural properties and is more likely to remain stable at its position once placed, allowing for proper compaction. However, due to its drier consistency, it requires more energy and skill to place and compact effectively.
Understanding Concrete Slump and Workability
The slump test is a standard method to measure the consistency and workability of concrete. A lower slump value indicates a drier mix, while a higher slump value means a wetter, more fluid mix. For sloped surfaces, the appropriate slump depends on the angle of the slope:
- For slopes less than 30 degrees, a slump between 5 cm and 10 cm is suitable.
- For slopes between 30 degrees and less than 45 degrees, a lower slump range of 2.5 cm to 7.5 cm is recommended.
- For slopes greater than 45 degrees, special measures such as double forming for thicknesses of 15 cm or more or the use of shotcrete are advised.
It is important to test the concrete slump on-site before placement to ensure the mix is suitable for the specific slope and structural requirements.
Lightweight Concrete Considerations
Lightweight concrete behaves differently from normal-weight concrete in terms of slump. A 5 cm slump of lightweight concrete can flow almost as easily as a 10 cm slump of normal-weight concrete. Therefore, when a very low slump is required, especially for steep slopes, lightweight concrete can be an effective option to maintain workability without compromising stability.
Concrete Placement on Slopes
When placing concrete on a sloped surface, begin at the lowest point and gradually work upward. This technique prevents the concrete from moving downhill and helps maintain the desired shape and thickness. Proper vibration is critical during placement to compact the concrete and eliminate voids that could weaken the structure. After vibration, remove any excess concrete from the top and finish the surface according to project specifications.
Conclusion
Pouring concrete on sloped surfaces requires meticulous preparation, the right choice of concrete mix, and careful placement procedures. Using low slump concrete tailored to the slope angle, ensuring proper formwork and reinforcement checks, and applying vibration for compaction all contribute to a durable and well-formed concrete slope. With the right approach and experience, concrete can be successfully poured on slopes for various structural and accessibility applications.