Precast Concrete

Source:www.stonediamondtool.com Date:2017/12/28 Read:479

Precast concrete is a construction product produced by casting concrete in a reusable mold or “form” which is then cured in a controlled environment, transported to the construction site and lifted into place. In contrast, standard concrete is poured into site-specific forms and cured on site. Precast concrete is being used more and more in home and building construction because it is more readily available than ever before, and provides quality and uniformity that may be lacking in on-site concrete work. Because the plant specializes in concrete, they can usually offer a variety of shapes, sizes, thicknesses, and finishes for your concrete structure. When you consider the cost of labor for a team of skilled workers pouring concrete on-site, precast concrete may save significant money on the cost of the project. Precast concrete is not a new concept, as Ancient Roman builders made use of concrete and soon poured the material into moulds to build their complex network of aqueducts, culverts, and tunnels.

By producing precast concrete in a controlled environment (typically referred to as a precast plant), the precast concrete is afforded the opportunity to properly cure and be closely monitored by plant employees. Utilizing a Precast Concrete system offers many potential advantages over site casting of concrete. The production process for Precast Concrete is performed on ground level, which helps with safety throughout a project. There is a greater control of the quality of materials and workmanship in a precast plant rather than on a construction site. Financially, the forms used in a precast plant may be reused hundreds to thousands of times before they have to be replaced, which allow cost of formwork per unit to be lower than for site-cast production. 

The strength of precast concrete gradually increases over time. Other materials can deteriorate, experience creep and stress relaxation, lose strength and deflect over time. The load-carrying capacity of precast concrete is derived from its own structural qualities and does not rely on the strength or quality of the surrounding backfill materials.

Studies have shown that precast concrete products can provide a service life in excess of 100 years. For severe service conditions, additional design options are available which can extend the life of the precast concrete product. This is extremely important when calculating life cycle costs for a project. Precast concrete also resists most substances. While no material is completely immune to attack from aggressive chemical agents, precast products can often be designed to resist corrosion in specific applications. Because precast concrete products typically are produced in a controlled environment, they exhibit high quality and uniformity. Variables typically affecting quality on a job site such as temperature, humidity, craftsmanship, are closely controlled in a plant environment.

Because of the joints between the sections, this type of subfloor requires finishing with a concrete topping before resilient flooring is installed.

The topping prevents the finished floor from cracking or loosening from the subfloor due to movement of the concrete. Trowelable underlayments are not satisfactory for smoothing preformed concrete subfloors. Concrete toppings on precast concrete must be tested for moisture as for ordinary concrete floor slabs. Structural Topping thicknesses vary with a minimum of 2″ to 2 1/2″ depending on code requirements. Structural topping must be bonded to the planks, continuous from support to support uninterrupted by walls or expansion joints. 

Precast concrete should be tested for moisture the same as regular concrete. When testing per ASTM F2170, the depth of the probe should be located 20% of the slab thickness (not the overall system thickness) since it is drying from both sides. 

Double Tees

Double tees are an excellent choice for parking decks and can also be used in floor and roof applications where a long, clear span is required such as gyms and pools. Spans up to 70′ can be achieved using Precast Double Tees. Double Tees are plant-fabricated, which provides excellent quality control and speeds up the construction process.