Using rebar in aquatic design

By Barry Justus

Builders of swimming pools, spas and water features are required to work under a variety of conditions and in diverse locations. Earthquake zones, expansive clays, hillsides, ascending slopes, rooftops, freeze/thaw, solar cycles and a wide array of increasingly sophisticated and complex aquatic designs can challenge one’s construction abilities.

Reinforced concrete, which comprises reinforcement bar (rebar), cement, aggregates, air, additives and water for hydration, is a versatile building material suitable for a variety of applications. It is one of the main components used by builders when working in the conditions or locations described above.

Concrete is strong in compression and weak in tension, but when combined with rebar, which is strong in tension, these materials provide swimming pool and hot tub builders with a powerful building tool.

Aquatic concrete construction

In the aquatic industry, concrete is applied via pressure hose over a rebar grid by means of shotcrete, both wet and dry, as well as by pump into prepared forms for cast-in-place methods.

A growing industry trend has seen pool contractors become more involved throughout the entire backyard project. In addition to the actual swimming pool, this has resulted in the use of steel mesh for decks, and various grades and sizes of rebar for columns, walkways, bridges over pools, double curtains of steel in vanishing edge dam walls, cast retaining walls and catch basins.

Most projects benefit from the use of structural engineering plans that detail the grade, size, placement and spacing of rebar, along with the concrete coverage, strength and characteristics such as slump and additives. Typically, 10M (11.3 mm), 15M (16 mm) or 20M (19.5 mm) rebar is used in residential swimming pools, spas and water features.

Rebar spacing is determined by the structural engineer—generally a larger diameter bar can be spaced farther apart than a smaller diameter bar under the same load conditions. Structural engineering plans take the guesswork out of a project and also limit the contractor’s liability. In Canada, the placement of concrete reinforcing steel must conform to Canadian Standards Association (CSA) A23.1, Concrete Materials and Methods of Concrete Construction, while design requirements must be in accordance with CSA A23.3, Design of Concrete Structures.

Hatching rebar

Rebar is manufactured by pouring molten steel into casters, then running the strands through a mill, resulting in the final shape, size, strength and hatchings. Hatchings are the deformations or ridges typically found on most rebar. These ridges help bond the concrete to the steel and contribute greatly to the overall strength of reinforced concrete.
In Canada, rebar is produced in accordance with CSA G30.18-09, Carbon Steel Bars for Concrete Reinforcement, while in the United States, hatching characteristics are designated by the American Society for Testing and Materials (ASTM) A615/A615M – 09b, Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement.

Rebar manufactured from steel is ideal for use in reinforced concrete, as its expansion co-efficiency is nearly identical to concrete. This is critical for the large temperature variations concrete is exposed to on site. Rebar is also manufactured with a number of individual markings, which include the location it was cast, bar size, material type (carbon or alloy steel) and its grade. It is available in various material strengths and is measured in metric and imperial bar sizes, as well as hard and soft metric sizes.

Bar sizes can be confusing; hard metric sizes are the actual size of the bar in millimetres, while soft metric sizes are the closest even metric number to the imperial equivalent. For example, a 1-in. imperial size eight rebar is 25.4 mm hard metric and 25 mm soft metric. Manufacturers and distributors can decrease the number of rebar sizes they stock and produce.