Final answer:
Specific performance admixtures are used in concrete to provide desired characteristics beyond standard ones like workability or setting time, addressing specific requirements like durability or environmental resistance.
Step-by-step explanation:
"Specific performance admixtures" are admixtures used in concrete and cement mixtures that provide desired performance characteristics. These characteristics could include improvements in workability, setting time, and durability, to name a few. The question seems to imply that there are certain standard characteristics that admixtures modify such as workability or cure time, but specific performance admixtures are formulated to address additional, specific requirements that could be anything from reducing the water content without affecting the workability, to enabling the concrete to withstand particular environmental conditions. Therefore, specific performance admixtures enhance the concrete's properties beyond the more common modifications like setting time control or workability enhancement.