{"id":201969,"date":"2022-10-10T11:52:00","date_gmt":"2022-10-10T15:52:00","guid":{"rendered":"https:\/\/www.constructionspecifier.com\/?p=201969"},"modified":"2022-10-07T12:01:49","modified_gmt":"2022-10-07T16:01:49","slug":"concrete-why-effective-curing-practices-are-important","status":"publish","type":"post","link":"https:\/\/www.constructionspecifier.com\/concrete-why-effective-curing-practices-are-important\/","title":{"rendered":"Concrete tips: why effective curing practices are important"},"content":{"rendered":"
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Photos courtesy Shutterstock <\/span><\/figcaption><\/figure>\n

By Dean E. Craft, DBA, CSI, CDT, CCCA, ASTM, ACI, LtCol USMCR (ret.)<\/strong><\/p>\n

Proper concrete curing methods are critical for achieving the overall strength, durability, performance, and aesthetics of concrete. It is directly related to reducing maintenance costs, extending service life, and enhancing the sustainable attributes of concrete. Unfortunately, despite the relatively low cost of effective curing practices, this step is often overlooked or minimized. Failing to give curing the required level of attention can lead to failed expectations, expensive repairs, and delayed project timelines.<\/p>\n

One might wonder, if the importance of proper curing is so well-documented, why is the process marginalized or even skipped? Part of the reason is confusion around the definition of \u201ccuring.\u201d Few terms associated with concrete have been so misused, misinterpreted, or misquoted as the term \u201ccuring.\u201d Many associate this term with the overall strength gain of concrete and believe the process takes 28 days. Others believe 28 days is the amount of time needed before a moisture-sensitive flooring, roofing material, or coating can be applied to a concrete substrate surface. Unfortunately, neither of these are completely accurate and this misconception routinely leads to confusion and frustration on projects. To accurately understand what curing means, it is necessary to turn to published literature. A quick review gives two different descriptions.<\/p>\n

According to the American Society for Testing and Materials (ASTM) international, ASTM C125, Standard Terminology Relating to Concrete and Concrete Aggregates<\/em> and the American Concrete Institute (ACI), CT-13: ACI Concrete Terminology<\/em>, curing is defined as an \u201caction taken to maintain moisture and temperature conditions in a freshly placed cementitious mixture to allow hydraulic cement hydration and (if applicable) pozzolanic reactions to occur so that the potential properties of the mixture may develop.\u201d<\/p>\n

ACI 308R-16: Guide to External Curing of Concrete<\/em> incorporates the above definition and states, \u201ca mixture is properly proportioned and adequately cured when the properties of the in-place concrete equal or exceed the design properties of the concrete.\u201d Further, the document points out the term \u201ccuring\u201d has been \u201cused in a more general sense to describe the process by which hydraulic cementitious concrete matures and develops hardened properties over time as a result of the continued hydration of the cementitious materials in the presence of sufficient water and heat.\u201d<\/p>\n

Though seemingly similar, there are some key differences between the two. The definition of curing says \u201ccuring\u201d is an \u201caction taken,\u201d meaning curing can, and should, be specified, scheduled, planned for, observed, and evaluated. Also, it uses the term \u201cfreshly placed cementitious mixture,\u201d shifting focus to when curing should take place, which is from the time of placement until the desired concrete properties develop.<\/p>\n

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Wet cure: the process of using a wet burlap to cure concrete. <\/span><\/figcaption><\/figure>\n

In contrast, the second description of curing can be interpreted as the long-term development of concrete, often expressed as \u201cconcrete never stops curing,\u201d and nowhere in this description is there a call to proactive action.<\/p>\n

Based on the evolution of the literature, the first definition above aligns best with the perspective of the concrete industry, which is, curing is something to be specified and done.<\/p>\n

Specifying proper curing<\/strong><\/p>\n

When done right, curing reduces cracking, improves durability, and increases strength. Conversely, when concrete is improperly cured, it can lead to inadequate strength gain, surface dusting, surface crazing, plastic shrinkage cracks, excessive slab curl, reduced resistance to freeze-thaw, scaling, etc.<\/p>\n

Curing requires two conditions: suitable moisture and temperature. Water is a chemical necessity for hydration and pozzolanic reactions to occur, and these reactions turn wet cementitious material and aggregate mix into a hardened mass. As soon as the wet concrete leaves the mixer, ambient conditions immediately begin to reduce the water available for hydration through evaporation. Elevated ambient air temperature, low ambient relative humidity, high concrete mix temperature (from heat of hydration, hot aggregate which has been in the sun, and high temperature for extended periods), wind, and any combination of these, rapidly remove necessary water from the mix. The need to protect freshly placed concrete from excess evaporation is not solely related to warm weather conditions as it can potentially occur at any ambient temperature.<\/p>\n

Recall the second necessity for proper curing is suitable temperature. Curing is not just about keeping sufficient moisture in the freshly placed concrete; it is also about maintaining suitable temperature in and for it. Ambient temperature, mix temperature, and the temperature of the base on which the concrete will be placed on needs to be discussed, monitored, planned for, and addressed.<\/p>\n

It may seem daunting to consider all the variables, but there are many resources to aid in properly specifying \u201ccuring\u201d in project documents. Some ACI standards to follow are:<\/p>\n