Concrete primarily comprises coarse aggregate, fine aggregate (sand), portland cement, water, and admixtures. Aggregates largely establish strength and stability bound together by the hardened cement paste binder. Admixtures are used for workability and performance of the fresh concrete mix including water reducers, accelerators, retarders, superplasticizers, air entrainers, and other high-performance enhancers. Mix designs are specifically formulated depending on how the concrete will be placed and performance requirements.
Fresh concrete can be cast-in-place, precast, or shot in place through a nozzle and pressure, known as shotcrete. Concrete is durable, dense, and strong in compression, but needs reinforcing steel for tensile strength and to limit shrinkage. Shrinkage is a characteristic of the cement paste hydration and moisture loss as the concrete cures. Size, spacing, and placement of the reinforcing steel is critical to the design and durability of the concrete that surrounds it.
Cast-in-place concrete is concrete that’s poured onsite and is found in foundations, slabs, beams, columns, walls, parking lots, and other areas in the construction industry. Forms are constructed to create the desired shape and support the fresh concrete until it’s gained enough strength to remove the formwork. Reinforcing steel, such as bars or welded wire mesh, is placed within the formwork to add tensile strength and help reduce shrinkage, but must have adequate cover of concrete to protect the steel. There are many concrete mix design choices for an array of properties and needs.
Fresh concrete should be placed in a manner that’s well consolidated within the forms and around the reinforcing steel. Rock pockets, segregation of aggregates, and over and under vibration lead to premature deterioration or failure.
Concrete materials by nature shrink, so control joints (partial-depth cuts) are necessary and should be installed in the fresh concrete while it’s still green – timing is critical. Joint spacing and cut depth should be calculated and planned based on the size and thickness of the concrete. Shrinkage cracks form at these notches to control where cracking occurs. These joints can be filled with materials suitable for the application so that edge raveling is not created from areas that are loaded (for example, a warehouse with forklift traffic). Construction joints allow for large portions of concrete to have some movement and are formed full depth. Cold joints, on the other hand, are not considered movement joints but rather are the bonded plane between 2 separate pours of concrete.
Timing and technique for finishing concrete is important so that the top surface is durable. Over finishing can trap bleed water and lead to scaling. Textures, such as broom, float, or trowel can be achieved. Flatness and moisture content should meet the requirements of the applied finish materials, if applicable.
Rubber templates or stamping can be used prior to initial set of the concrete to alter the texture and make the concrete look like brick, stone, wood, or other materials. It should be noted, however, that while concrete can be made to look like other masonry materials, its performance and long-term durability vary greatly from unit masonry systems. Pigments or dyes can also be added to concrete mixes to create a variety of shades and colors; topical stains can be applied when hardened.
Curing procedures commonly include wet methods or a spray applied coating application. Moist curing helps limit the amount of moisture in the fresh concrete from evaporating quickly and creating shrinkage cracks. It also enables the mix to mature at a rate that develops higher long-term strength. This step for concrete work is critical.
Coatings are often applied to concrete as added protection from the environment and traffic. Vertical surface coatings can range from acrylic, polyurethane, mineral silicate, silane/siloxane, to cementitious. Horizontal, often high foot or vehicular traffic areas are coated with traffic bearing membrane systems, which can be polyurethane, polyurea, epoxy, methyl methacrylate, or cementitious. Interior concrete flooring surfaces may also use any of the above listed coating types, however, it’s critical that moisture content and vapor drive be tested in conjunction with interior coating applications. Mockups and pull-off testing are recommended as well as quality assessment during the project.
IMI’s free project support, technical assistance, and education is here to help you at any stage in your building’s lifecycle.
Our multidisciplinary team draws on decades of experience developing solutions for high-performing masonry and tile projects.
Here are some resources and industry standards that focus on concrete construction. For additional guidance, contact IMI.
Small text files that are placed on your machine to help the site provide a better user experience. In general, cookies are used to retain user preferences, store information for things like shopping carts, and provide anonymised tracking data to third party applications like Google Analytics. As a rule, cookies will make your browsing experience better. However, you may prefer to disable cookies on this site and on others. The most effective way to do this is to disable cookies in your browser. We suggest consulting the Help section of your browser or if you decline you will be redirected to the About Cookies website which offers guidance for all modern browsers.