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Explain the new ACI polished concrete slab finish specification. But first, why do we need a specification?
Polished concrete slabs are becoming more and more popular, so contractors must have methods to produce them with the highest consistent quality. According to data from Grand View Research, the early polished concrete floors began in the 1990s, but by 2019, in terms of revenue, polished concrete floors accounted for approximately 53.5% of the US concrete floor coating market share. Today, polished concrete slabs can be found in grocery stores, offices, retail stores, big boxes, and homes. The characteristics provided by polished concrete floors are driving the increase in usage, such as high durability, long life, easy maintenance, cost-effectiveness, high light reflectivity and aesthetics. As expected, the sector is expected to increase in the next few years.
The gloss (reflectance) measurement of a polished concrete slab shows how much gloss the surface has. The polished concrete slabs here reflect the overhead lighting of the Sprouts Farmer’s Market. Photo courtesy Patrick Harrison meets this need, and the now available polished concrete slab finish specification (ACI 310.1) determines the minimum standards that polished concrete slabs should meet. Since there is a path to define the expected methods and results, it is easier to meet the architect/engineer’s expectations. Sometimes, basic procedures such as cleaning floor slabs may mean different methods for architects/engineers and contractors. Using the new ACI 310.1 specification, a consensus can be reached and the contractor can now prove that the content outlined in the contract has been met. Both parties now have guidelines for normal industry practices. As with all ACI standards, the specifications will be reviewed and updated as needed in the next few years to reflect the requirements of the industry.
The information in the new ACI 310.1 specification is easy to find because it follows the standard three-part format, namely General, Product, and Execution. There are detailed requirements for the testing and inspection, quality control, quality assurance, evaluation, acceptance and protection of polished concrete slab finishes. In the implementation part, it includes surface finish requirements, coloring, grinding and polishing, and maintenance.
The new specification recognizes that every project has many variables that must be determined. The architect/engineer’s document needs to clarify the specific requirements of the project, such as overall exposure and aesthetic expectations. The included mandatory requirements list and optional requirements list guide architects/engineers to customize specifications according to individual project requirements, whether it is to define the mirror gloss of the polished plate finish, add color or require additional testing.
The new specification proposes to require aesthetic measurements and define how data should be collected. This includes the uniqueness of the image (DOI), which includes the sharpness and the fineness of the surface of the slab in the sequence of polishing steps, so there is a way to measure its quality. Gloss (reflectance) is a measurement showing how shiny the surface is. Measurement provides a more objective definition of surface aesthetics. Haze is also defined in the document, which usually indicates that partial products are included to create aesthetics.
Currently, tests on polished concrete slabs are not consistent. Many contractors did not collect enough readings and assumed that they achieved some measurable level of performance in terms of aesthetics. Contractors usually only test a small model area and then assume that they use the same materials and techniques to reproduce the polishing results without actually testing the final board. The newly released ACI 310.1 specification provides a framework for consistent testing throughout the day and how to report results. Consistent testing of work also provides contractors with a measurable history of results that can be used in future bids.
The new polished concrete slab finish specification (ACI 310.1) provides a minimum standard applicable to any polished concrete slab finish. Cabela’s is one of the retail establishments known for using polished concrete slabs. Courtesy of Patrick Harrison. The new ACI 310.1 specification also determines the tests that must be performed and the location of each test.
The newly available document outlines when to perform various types of tests. For example, at least two weeks before the owner has it, the test must include specular gloss in accordance with ASTM D523, image clarity (DOI) in accordance with ASTM 5767, and haze in accordance with ASTM D4039. The new ACI 310.1 specification also specifies the test location for each type of test, but the record designer needs to determine the minimum requirements for DOI, gloss and haze. By providing guidance on which tests to perform and when, the document provides a roadmap to ensure that the slab meets the requirements outlined in the contract.
Testing and report communication is important to ensure that all parties—owners, architects/engineers, and contractors—know that the slab meets the agreed quality. This is a win-win situation: to ensure that the owner provides high-quality products, and the contractor has measurable numbers to prove success.
ACI 310.1 is now available on ACI’s website, and it was designed through a joint effort between ACI and the American Association of Concrete Contractors (ASCC). To help contractors comply with the minimum standards outlined, ASCC is currently developing guidelines for contractors that reflect the standards in this code. Following the format of the new ACI 310.1 specification, the guide will provide comments and explanations in any areas where the contractor may require additional guidance. ASCC’s ACI 310.1 guidance is expected to be released in mid-2021.
The first polished concrete slab specification from the American Concrete Institute (ACI) is now available on the ACI website. The new polished concrete slab finish specification (ACI 310.1) developed by the ACI-ASCC Joint Committee 310 is a reference specification designed to provide the minimum standard that architects or engineers can apply to any polished concrete slab. The ACI 310.1 specification applies to ground floor slabs and suspended floor slabs. When quoted in contract documents, it provides the finished board standard agreed upon between the contractor and the architect or engineer.
Architects/engineers can now refer to the new ACI 310.1 specification in contract documents and indicate that polished concrete floors must comply with the specification, or they can specify more stringent requirements. This is why this document is called a reference specification because it provides the lowest starting point for polished concrete slabs. When quoted, this new specification is regarded as part of the contract document between the owner and the contractor, and it is important for each polishing contractor to read the specification through to understand it.