How To Slope Concrete?

Introduction
Sub-grade Preparation
Sloping for Interior Drainage Purposes
Placement of Reinforcement
Rebar Detailing Accommodations
Summary

How to slope concrete? Means & Methods for Concrete Sloping

Sloping of concrete is done for a variety of reasons. Obviously, within the context of residential construction, driveways, ramps, and pathways can be sloped to facilitate changes in elevation. Sloping concrete is also done to provide for adequate drainage for various elements of a building or property including concrete patios, concrete sidewalks, concrete ramps, pathways and more. Sloped concrete within buildings is used for adequate drainage to floor drains, trench drains, and even for building elements such as showers.

Sloping concrete can be done in a couple of ways.

For one, the minimum structural requirements for concrete elements are dictated through things like the overall dimensions of the structural elements (critically thickness for slope) and also the presence of reinforcement. Some of these structural requirements include things like concrete cover or type of steel reinforcement, which need to be kept consistent regardless of the slope of the concrete structure or item.

Photo Above: Concrete ramp structure sloped, with sub-grade structure sloped to coincide with this structure. Slopes like this are important to ensure are kept as close to spec as possible as they are in use for barrier-free requirements.

Sub-grade Preparation

So, on the one hand, sloping can be done by sloping the sub-grade structure of the concrete element. For instance, a sloped driveway will be constructed through the utilization of the subgrade & bases(engineered fill, compacted crushed gravel etc.) to match the slope of the architectural requirements dictated for the structural element at hand.

Additionally, concrete elements are sloped according to percentages, like the pitch of a roof too!

So, slopes for concrete elements like pathways, ramps, and barrier-free paths of travel have critical slope percentages to which they need to match. Sloping of concrete elements in ramp construction has to be done precisely as possible, to avoid issues with the utilization and barrier-free compliance of the concrete ramp.

As an alternative to sloping the subgrade & sub-base structure, and where conditions allow for, sloping can be done through concrete placing and finishing, hand trowel, power trowel etc. 

For minor conditions that require sloping, hand tools commonly used in the concrete finishing process can be utilized.

Sloping for Interior Drainage Purposes

Fine attention to detail facilitates accurate sloping through interior floors in rooms, basements, garages and more to provide proper drainage to things like floor drains (cast-in / embeds).

Slopes on architectural layouts and plans are provided as indicators on a drawing (arrows with percentages).

Concrete with slumps that allow for precise finishing can be sloped accordingly. If the slump is too high, concrete can be difficult to slope. Alternatively, the utilization of certain concrete mix-additives can make concrete more workable, and easier to handle for concrete sloping. This sloping has to be done properly to ensure the adequate travel of drainage.

Placement of Reinforcement

Placement of reinforcement should also be done to ensure that the correct cover requirements are carried through the concrete element at hand. For instance, in some cases, for continuity of rebar, bends will have to be provided by the rebar detailing foresight and subsequent order. Overlaps in rebars from the sloped to horizontal portions of concrete still, require the correct bends (or field bending where permitted). As such, with significant concrete slopes, the actual steel reinforcement is critical to get correct, as it can seriously affect the structural integrity of a concrete element.

Concrete sloping, if too aggressive, and not actually accommodating cover requirements, can cause significant issues with potential exposure of rebar, and corrosion of the rebar quicker than anticipated.

Concrete cover plays a major role in the inhibition of corrosion of rebar as it acts as a physical barrier, that and the passive barrier surrounding the rebar.

Photo Above: Reinforcement within a slab-on grade construction, installed to coincide with base course.

Rebar Detailing Accommodations

Detailing is the process of taking structural/architectural conditions and providing the necessary steel reinforcement with small details, like accommodation in changes in slope, and using that to ensure orders of material coincide with the concrete element at hand. 

Finally, concrete slope for even more critical items, like concrete ramps for parkades and parking structures, can require sub-structural support like grade beams, pile-caps, piles, concrete ramps and more. Make sure to carry through the subsequent structural supports at the correct elevations to coincide with the slope of the concrete elements.

Conclusion

In conclusion, concrete sloping is not a complex task, and in minor inferences is done to facilitate drainage, flooring changes, and minor changes in elevation. However for significant concrete slopes, like ramps, or wheelchair access, necessary adjustments to the subgrade & foundation are required to ensure structural and architectural completeness of your project. The services of a professional concrete contractor come in handy for more detailed concrete work.