Performance Criteria for Ready Mixed Concrete: Where Are We Today? (Part 2)-Concrete Slabs-on-Ground and the Practicality of Performance-Based Specifications (PDF)

Concrete Slabs-on-Ground and the Practicality of Performance-Based Specifications (PDF)

Pdf Summary

The document, authored by Patrick Harrison, FACI, Vice President of Structural Services, Inc., discusses the practicality of performance-based specifications for concrete. Performance-based specifications outline functional requirements for concrete depending on its application. These requirements must be clear, achievable, measurable, and enforceable.<br /><br />Key performance indicators include compressive strength (typically a minimum of 3,500 psi at 28 days), flexural strength, low drying shrinkage, timely and uniform setting, placement and finishing characteristics, flatness/levelness, abrasion resistance, and aesthetics. The document provides specific guidelines for mix design, indicating the minimum cement content should be 520 pounds per cubic yard with a maximum water-to-cement ratio of 0.55. It's recommended to use polycarboxylate admixtures at a mid-range dosage while avoiding naphthalene or melamine types.<br /><br />The aggregate size should range from 3/4 to 1 inch for 6-inch thick materials, and larger for thicker slabs. The mix should aim for a combined aggregate gradation distribution, with coarseness factor ranging from 60% to 75%, and balanced fine content from natural or manufactured sand with a maximum air content of 3%. The document illustrates the effect of different accelerators on setting time.<br /><br />Through the examination of compressive strengths across various projects like Amazon, Home Depot, and Walmart, it stresses the importance of a well-documented specification process that enhances material quality and ensures efficiency in concrete applications. The focus is also on minimizing cracking and curling while maintaining good finishability and achieving the required flexural strengths.<br /><br />Ultimately, performance-based specifications offer a structured method to control the quality and performance of concrete, tailored to diverse applications across various job sites.

Keywords

performance-based specifications

concrete

compressive strength

mix design

cement content

aggregate gradation

setting time

flexural strength

polycarboxylate admixtures

material quality