Using ASTM E1155 to determine finished floor quality: minimum sampling requirements used to establish compliant floor flatness and levelness

A commonly accepted standard to quantify finished quality of elevated and slab-on-ground slabs is the ASTM Standard, ASTM E1155. The procedure outlines the method of profiling finished concrete to determine the flatness (FF) and levelness (FL) of the concrete finish; this method is thought of as an improvement to the “straight-edge” method and has been adopted by the American Concrete Institute (ACI, 2004) as the default measurement system for concrete finish quality. Data gathered from this standard is often used in the forensics arena to determine the root cause of finish quality issues, such as using the profiles to determine the lack of initial camber of steel beams. Although the standard is very thorough and has been used successfully for many years by owners, general contractors, and concrete subcontractors, problems arise when the standard is interpreted incorrectly and the owner is left with no guidance on the quality of the sampled data or the quality of the finished surface. This paper will explore one of the major issues in the current standard: What to do when the number of samples does not meet the required minimum number of samples. The intent and meaning of the number of sample points is not clearly defined in the standard and has been commonly misinterpreted for years, without any changes to the standard. This leaves the owner questioning the validity of the data. In a statistical conceptualization, flatness can be regarded as a characteristic (parameter) of the constructed floor, defined as the FF value one would obtain with complete measurement of the floor (infinite sampling). For any calculated FF value, regardless of sample size, hypothesis tests—or, equivalently, confidence intervals— can be constructed to determine whether the constructed floor possesses the specified flatness with a high degree of confidence. Results from simulated floor profiles adapted from a case studies show that sampling at levels below the minimum requirements established in the ASTM standard may nonetheless provide sufficient information to reliably judge the flatness of constructed floors. BACKGROUND