ACI Concrete Strength Testing Technician Practice Test

What is the main function of admixtures in concrete?

1. To modify the properties of the concrete

2. To change the color of concrete

3. To increase the weight of the mix

4. To reduce the curing time

The correct answer is: To modify the properties of the concrete

The main function of admixtures in concrete is to modify the properties of the concrete. Admixtures are chemical agents that are added to the concrete mix in small quantities to enhance specific characteristics such as workability, curing time, strength, durability, and resistance to environmental factors. For example, water-reducing admixtures can improve the workability of the concrete without increasing the water content, while superplasticizers can enhance fluidity. Other types of admixtures, such as air-entraining agents, help create tiny air bubbles in the concrete, which can improve freeze-thaw resistance. Modifying properties encompasses a wide range of effects beyond just strength or workability; it also includes factors like setting time, shrinkage, and even resistance to chemical attack. This flexibility in enhancing concrete's performance is what makes admixtures a critical component in concrete technology and construction applications. Other options, while they may represent specific effects or uses of certain admixtures, do not capture the broad and primary purpose that admixtures serve in concrete formulation.