Cement Admixtures : Building Construction

Strength- and Durability-Enhancing Concrete Admixtures for Building Construction

Every building has different technical specifications. Even when building identical office buildings in a commercial complex and residential tract housing, construction managers and contractors may be forced to contend with varying environmental and weather conditions. As such, they cannot rely on a single set of off-the-shelf building materials for each project. In fact, it’s rare that certain building materials do not require some form of enhancement to meet the required technical specifications. Concrete can be bolstered by cement additives during the cement manufacturing process and concrete admixtures during the mixing process.

Concrete for Building Construction

Concrete is essential for multiple elements of building construction projects. There are structural components, including load-bearing, foundation, and skeletal elements, as well as non-structural ones, like facades, drainage, and exteriors. Usually, these components require concrete of varying thickness, compressive and flexural strength, durability, and workability. During cement manufacturing, core ingredients may be proportioned in specific ways to enhance specific properties. Additionally, natural pozzolans (supplementary cementitious materials), such as volcanic ash, shale, diatomaceous earth, or clay, or artificial pozzolans, such as surkhi, blast furnace slag, fly ash, or silica fume, may be added for the same purpose.

Concrete Admixtures for Strength

Once the cement is manufactured, construction managers and contractors often rely on chemical admixtures to further enhance specific properties during the concrete mixing process. Accelerating admixtures increase the rate at which the concrete sets and helps to develop high strength early on. Water reducers help lower the water-to-cement ratio and increase concrete’s strength. Superplasticizers (or high-range water reducers) perform the same function to a greater extent. Lower water-to-cement ratios result in higher strength, but the resulting concrete is harder to work with. Using water reducers and/or superplasticizers allows for the high strength that comes with low water-to-cement ratio, while maintaining the workability required to effectively place the concrete. Construction managers and contractors must carefully consider job-site conditions when using these admixtures not to impair the workability of the finished concrete. However, these three chemical admixtures can help them create concrete with high compressive and flexural strength.

There are also mineral and fiber admixture options available. Mixing fly ash, blast furnace slag, silica fume, rice husk ash, and metakaolin with concrete during the mixing process can also affect strength gains. In some circumstances, it may also be helpful to reinforce concrete with fiber to strengthen it.

Concrete Admixtures for Durability

Strength-enhancing chemical admixtures usually enhance concrete durability to some extent. Air-entraining chemical admixtures are often used to protect concrete against damage due to freeze-thaw cycling, particularly in cooler climates. These admixtures create a system of microscopic bubbles that absorb the pressure created when moisture in concrete expands when it freezes. This helps mitigates the risk of cracking. Some chemical admixtures are also helpful at enhancing concrete density and reducing permeability, allowing it to weather moisture and weather-related conditions.

Treating concrete with these admixtures helps reduce the risk of common issues that develop with concrete over time, such as delaminating and scaling. When using concrete reinforced with steel, using corrosion-inhibiting admixtures is critical to prevent the damage and repair that comes with rusty rebar. This is particularly important in marine environments or when heavy deicing salt use is anticipated. Additionally, water reducers can help reduce the risk of unsightly efflorescence and cracking.

Concrete Admixtures for Job Site Conditions

Admixtures are also essential for handling job site conditions, which may vary greatly from site to site or even throughout the duration of a building project. For example, there may be some distance between a job site and the concrete plant supplying the concrete, necessitating the use of set retarders. These chemical admixtures delay the setting time of concrete, making it workable for longer periods. However, in cold weather conditions, speeding up the setting time with accelerators may be useful to keep construction on schedule. Construction managers and contractors should evaluate which admixtures will help them complete the job to specification, while considering environmental conditions, technical requirements, weather, and other pertinent factors.