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Understanding the properties and characteristics of concrete

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Concrete is one of the most common materials used in the pool-building and construction industry.

By John Petrocelli

Structures surround the modern world. Buildings, bridges, roads, and tunnels are everywhere. By definition, a structure is something made up of parts that are held or put together in a particular way. In construction, structures are designed by architects and engineers, and built by contractors or builders using many different materials. The most common, however, are concrete, steel, timber, plastic, and glass.

Although a variety of materials can be used to create a structure, this article will focus on two primary materials used in the pool industry—concrete and steel. It will also discuss the characteristics and properties of these materials as well as look at how ‘hybrid’ materials incorporate the best of both to create a ‘super’ structural material.

Concrete facts

concrete fine aggregate
Together, sand (left) and stone are referred to as ‘aggregates.’

In general, concrete is one of the most common materials used in the pool-building and construction industry in general. It comprises a heterogeneous mixture of the following main constituents:

  • Cement (Portland);
  • Water;
  • Sand (minerals);
  • Stone (rocks); and
  • Air.

Together, sand and stone are referred to as ‘aggregates.’ Although there are many other ingredients used in modern day concrete mix (e.g. chemical admixtures), the elements above represent the most common. There are also many types of cement, including:

  • Type 10: normal Portland cement;
  • Type 20: moderate Portland cement;
  • Type 30: high-early-strength Portland cement;
  • Type 40: low-heat-of-hydration Portland cement; and
  • Type 50: sulphate-resistant Portland cement.

Normal Portland cement (i.e. Type 10) is general-purpose cement and is the most popular cement powder used to create regular density concrete. This type of concrete is used in pavements, sidewalks, reinforced-concrete structures, bridges, and swimming pools.concrete coarse aggregate

typical concrete batch plant
Normal Portland cement (i.e. Type 10) is manufactured in a batch plant and comprises various raw materials, including lime, iron, silica, alumina, gypsum, and magnesia.

The other cement varieties are used in special applications where specific properties are required. For instance, the use of low-heat-of-hydration cement (i.e. Type 40) in concrete mixes is often used to construct massive structures such as hydro-electric dams, where a tremendous amount of concrete is required.

If normal Portland concrete was used in such an application, the heat generated by the concrete as the cement hydrated would be so extreme it would actually destroy the structure.

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