{"id":207713,"date":"2024-01-05T18:53:34","date_gmt":"2024-01-05T23:53:34","guid":{"rendered":"https:\/\/www.constructionspecifier.com\/?p=207713"},"modified":"2025-04-14T15:30:02","modified_gmt":"2025-04-14T19:30:02","slug":"back-to-basics-the-four-steps-to-creating-effective-concrete","status":"publish","type":"post","link":"https:\/\/www.constructionspecifier.com\/back-to-basics-the-four-steps-to-creating-effective-concrete\/","title":{"rendered":"Back to basics: The four steps to creating effective concrete"},"content":{"rendered":"
\"Rendering<\/a>
Rendering by O\u2019Connell Robertson Architects\/courtesy Waco Independent School District. <\/em><\/span><\/figcaption><\/figure>\n

By Chris Bennett, iSCS, CDT and Keith Robinson, FCSC, FCSI, RSW, LEED AP<\/strong><\/p>\n

Just as successful specifications enjoy the four attributes of being clear, concise, correct, and complete, concrete also has four steps that are crucial to its success. Those steps are: mix design, consolidation, finishing, and curing. If the four steps work together in concert, the outcome is low porosity, strong, sustainable concrete. However, make changes to one step and not judicious adjustments to the others, and one will find themselves out of step, over budget, and in trouble.<\/p>\n

CSA A23.1 states it is the general contractor or construction management team’s responsibility to prepare a \u201cConcrete Plan\u201d that defines the expected roles and responsibilities of all parties contributing to the quality of concrete, including mix design, consolidating, finishing and curing. However, it is up to the entire team to understand and execute this process together, employing performance-driven methods, to successfully arrive at the design intent.<\/p>\n

Mix design<\/strong><\/p>\n

The first step, mix design, is the process of determining the ideal proportions of cement, water, aggregates, and additives to produce concrete that meets a project\u2019s specific requirements.\u00a0 ASTM C 125, Standard Definition of Terms Relating to Concrete and Concrete Aggregates<\/em>, explains concrete is a composite of cement and embedded fragments of aggregate (rock and sand). When combined with water, the cement binds the materials together, creating concrete. The quality and properties of raw materials, including supplementary cementitious materials (SCMs), can vary significantly, affecting the consistency and strength of the concrete mix. The mix design is critical for targeting desired strength, workability, and other properties.<\/p>\n

Then the mix design must be carefully adjusted to meet site-specific conditions, such as temperature, humidity, and wind. ASTM C94\/C94M, Standard Specification for Ready-Mixed Concrete<\/em>, provides basic guidance on mixing concrete thoroughly to ensure uniformity and workability. A well-designed mix is essential to ensure the longevity and strength of the structure. It is important to bear in mind that new types of concrete mixes, such as those intended to reduce carbon dioxide emissions, may fundamentally change the behavior of concrete (i.e.<\/em> water demands, workability, set times, etc.) and must be handled differently than traditional approaches to avoid dry-shrinkage, deflection, and other potential problems.<\/p>\n

\"The<\/a>
The American Concrete Institute (ACI) describes consolidation as necessary to freshly placed concrete to reduce air voids. If voids are not mitigated and the concrete is allowed to harden, the resulting concrete will suffer from high porosity, non-uniformity, weakness, and poor ability to bond to reinforcement. <\/span>Photo courtesy Husqvarna Construction Products.<\/em><\/span><\/figcaption><\/figure>\n

Consolidation<\/strong><\/p>\n

Consolidation (also called compaction) is the process of packing and molding the concrete within the forms and other structural elements, removing any trapped air pockets that can weaken the concrete\u2019s overall strength. Consolidation is critical because elimination of any gaps or voids in the concrete leads to more uniform strength and higher density. Improper consolidation results in a weaker concrete structure that can fail. ASTM C138\/C138M, Standard Test Method for Density (Unit Weight), Yield, and Air Content (Gravimetric) of Concrete<\/em>, provides instructions for the consolidation needed to produce concrete that can withstand loads and stresses and limit cracks, defects, and avoid shorter lifecycles.<\/p>\n

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\"When<\/a>
When the four steps of concrete work harmoniously, the result is robust and sustainable concrete. However, should only one step be altered without corresponding adjustments to the others, one will find themselves out of step, over budget, and in trouble.<\/span>Illustration courtesy Bennett Build. <\/em><\/span><\/figcaption><\/figure>\n

Concrete, especially high-consistency mixes, can be over-consolidated, usually from over-vibration. In these instances, a thick film of water will form on the surface. This water can negatively impact the concrete with reduced surface strength, lower permeability, and poor aesthetics. Seth Mailman, a project manager at Baker Concrete, says, \u201cConcrete placed without proper consolidation will not perform as expected. Understanding the relationship between design and construction with respect to concrete is necessary to ensure the final product performs as expected.\u201d<\/p>\n

Finishing<\/strong><\/p>\n

The third phase, finishing, is the process of smoothing out the surface of the concrete to achieve a desired performance texture and appearance. The American Concrete Institute (ACI) 301-20: Specifications for Concrete Construction<\/em> is a solid starting point for information on finishing to make attractive, durable concrete surfaces capable of resisting abrasion, weathering, and other physical stresses. Finishing helps with setting, prevents chipping, and is climacteric to both decorative and industrial polished concrete surfaces.<\/p>\n

Types of finishes<\/strong><\/p>\n