Concrete, mortar, and grout mixtures can be enhanced or modified with the addition of admixtures, either individually or in combination, to attain specific properties in either their fresh or hardened state. Admixtures are chosen based on the roles they perform in the mixture.
Functions of admixtures include retarding or accelerating the setting time of concrete, minimizing segregation and the water to cement ratio, enhancing pumpability, and hastening the rate of strength development. These admixtures serve crucial functions in modifying the properties of the mixture to suit the intended application.
Functions of Admixtures to Modify Fresh Concrete, Mortar, or Grout Properties
Concrete and mortar can be modified in various ways to achieve specific performance characteristics. For example, the workability of concrete can be increased without adding more water or by decreasing the water content while maintaining the same workability. This can be done using water-reducing and retarding admixtures. These admixtures can also be used to retard or accelerate both initial and final setting times.
Settlement can be a concern for concrete, but it can be reduced or prevented through the use of appropriate admixtures. Similarly, slight expansion in concrete and mortar can be created using the right admixture.
The rate or capacity for bleeding in concrete and mortar can be modified, as can the segregation of concrete, mortars, and grouts. This can be achieved using air entrainment admixtures. In addition, penetration and pumpability of concrete, mortars, and grouts can be improved through the use of suitable admixtures.
The slump or slump-flow of concrete can be increased without increasing the water content. This can be achieved using water-reducing and retarding admixtures, which can also improve finishability. Rheology/viscosity-modifying admixtures can also be used to modify the rheological properties of concrete and mortar.
Finally, the rate of slump loss can be reduced using water-reducing and retarding admixtures, as well as high range water-reducing admixtures. The placement rate can be increased using high range water-reducing admixtures as well. With the right admixtures, concrete and mortar can be tailored to meet specific requirements and perform optimally.
Functions of Admixtures to Modify Hardened Concrete Properties
Concrete is a versatile building material with a range of properties that can be modified to suit different needs. One common goal is to retard or reduce heat generation during the early stages of hardening. Additionally, it’s often desired to accelerate the rate of strength development or increase the strength of the concrete or mortar. This can be achieved through the use of water-reducing and retarding admixtures or high range water reducing admixtures.
Another concern is reducing scaling caused by deicing salts and increasing resistance to freezing and thawing. Air entrainment admixtures can help with this. It’s also important to decrease the capillary flow of water and the permeability to liquids. High range water reducing admixtures can address these issues.
Control of expansion caused by the reaction of alkalis with certain aggregate constituents can be achieved with the use of lithium admixtures. Additionally, cellular concrete can be produced, and the bond between concrete and steel reinforcement can be increased with high range water reducing and bonding admixtures.
To increase the bond between old and new concrete, bonding admixtures are commonly used. Concrete can also be modified to improve impact resistance and abrasion resistance. Corrosion-inhibiting admixtures can inhibit the corrosion of embedded metal, and colored concrete or mortar can be produced.
However, it’s essential to ensure that modifying any particular property of concrete does not negatively impact other properties. Careful consideration should be taken to achieve the desired result without causing any adverse effects. In this way, concrete can be tailored to meet specific needs in construction and infrastructure projects.