Prescription to Performance (P2P) specifications frequently asked questions.
What is a prescriptive specification?
A prescriptive specification is a how-to specification that defines the recipe for completing a project. These specifications describe the products, the installation procedures, and the workmanship that is required. Work performed in accordance with a prescriptive specification is expected to accomplish the desired end result, although the end result is not always precisely defined. (Ref: Preparation of Construction Specifications for Civil Projects, Committee on Specifications of the Construction Institute, ASCE, 2013, www.asce.org/pubs.)
For concrete, prescriptive specifications impose restrictions on the materials that can be used and include requirements that control the concrete mixture proportions.
What is a performance specification?
A performance specification describes the end product that is desired. It does not describe how to achieve the result. In this case, the contractor is typically allowed to choose products, equipment, and construction techniques. The contractor is allowed to develop methods to accomplish the end result. There should be a reliable testing and inspection program that may need to be more detailed. (Ref: Preparation of Construction Specifications for Civil Projects, Committee on Specifications of the Construction Institute, ASCE, 2013, www.asce.org/publications.)
For concrete, performance specifications should be based on performance indicators measured by standard test methods with defined acceptance criteria stated in contract documents and with no restrictions on the parameters of concrete mixture proportions. Establishing requirements, even though prescriptive, based on durability exposure classes or when reliable test methods do not exist can be considered as performance. (Approved by the P2P Steering Committee)
What is a hybrid specification for concrete?
Combining prescriptive and performance requirements in the same specification for the same product is referred to as a hybrid specification. For example, a specification may have a minimum cement content and a compressive strength requirement for a specific concrete mixture. Care should be taken to avoid conflicting requirements and ensure that prescriptive requirements do not prevent the performance requirements from being attained.
What are the benefits of a performance specification?
A performance specification assures that the desired performance is attained. Concrete mixtures can be better optimized for performance. It incentivizes the concrete supplier with improved quality practices who can now benefit from reducing variability. It provides a clearer assignment of responsibility. All of the above will elevate the competency of the bidders, which will ensure improved project schedules and reduced costs. Performance specifications support the use of innovative concrete mixtures and construction practices and most often result in a reduced carbon footprint.
What are the drawbacks of a performance specification?
The success of a performance specification depends on the design engineer’s ability to specify the appropriate tests and performance criteria that are required for the project application and the concrete producer’s ability to proportion concrete mixtures that meet those performance criteria. There may be some developmental work to prepare bids that may require a longer lead time.
How are performance specifications implemented?
The design engineer should define the durability exposure (if any) for the concrete and specify the appropriate performance tests and acceptance criteria. The design engineer should also specify the producer and contractor qualification requirements. The producer and contractor should ensure that the optimized and economical mixture is designed, delivered, and installed. The producer should ensure that the required pre-qualification test data is documented in the mixture submittal and the concrete supplied meets the specified performance tests and criteria. Referee methods and criteria should be agreed upon if field tests fail to comply.
Are performance specifications always a better alternative?
Regardless of the location or type of the project, the performance of the concrete and service life with minimal cost for maintenance is always important to the project owner. Performance specifications are the right approach as long as the design engineer and the producer have put in the initial effort to understand performance specifications. Materials and construction standards of care vary considerably in different regions and prescriptive specifications may not achieve the desired outcome.
What are the goals of the P2P initiative?
The primary goal of the P2P Initiative is to promote performance specifications as an alternative to current prescriptive specifications through education and communication. This goal is achieved by assisting architects and engineers to address concrete specifications by minimizing prescriptive requirements and establishing applicable performance requirements. Additionally, it involves assisting concrete producers through educational tools to proportion concrete mixtures that meet the performance criteria. There is no intent to eliminate prescriptive specifications that work well in some market areas and some established relationships.
How do responsibilities change with specifications?
The basic premise for construction is that responsibility should go to the entity with the freedom to effect the change. The general premise in a prescriptive specification is that a contractor cannot be faulted if construction complies with the specification and the desired result is not achieved. The general premise in a performance specification is that a contractor is responsible for the desired result. The specifying entities are responsible for establishing the performance requirements to meet the owner’s needs. In a hybrid specification responsibility for the desired result is less clear.