Mass concrete brings with it many challenges, among them the generation of high heat and problems that can stem from it. While creating these projects can be difficult, careful design of mass concrete can minimize or eliminate issues, and new research points to approaches that will allow us to create bigger projects than ever before.
Defining Mass Concrete
ACI Committee 116 defines mass concrete as “any large volume of cast-in-place concrete with dimensions large enough to require that measures be taken to cope with the generation of heat and attendant volume change to minimize cracking.” This categorization can include structural components with moderate- to high-cement-content concrete, massive structural elements of mat foundations, and to dams and other large structures that use concrete with a low cement content.
In any mass concrete application, temperatures rise through heat of hydration. As the interior concrete rises in temperature, the outer concrete may be cooling and contracting; if the temperature varies too much within the structure, the material can crack. A variety of factors influence temperature changes, including the size of the component, the amount of reinforcement, the ambient temperature, the initial temperature of the concrete at time of placement and curing program.
Engineers use a variety of approaches to tackle the potential for thermal cracking and successfully create mass concrete. These methods include: refining concrete mix proportions, protecting exposed surfaces and formwork from environmental extremes, using aggregate with desirable thermal properties, pre-cooling the concrete constituent materials, using internal pipes to cool the concrete itself, and placing the concrete in several lifts or pours.
Some designs include supplementary cementitious materials in the mix, including slag cement or fly ash. The Slag Cement Association offers some guidance on specifying slag cement for mass concrete here. The American Coal Ash Association offers information here on the benefits and specification of fly ash.
CTLGroup offers a collection of articles on mass concrete here.
ACI publication 207.1R-96: Mass Concrete examines mass concrete in detail.
Design and Control of Concrete Mixtures, 15th Edition, EB001
Every industry has one outstanding reference book, and for concrete it is Design and Control of Concrete Mixtures—the guide to applications, methods, and materials. For more than 85 years, the publication has been the cement and concrete industry’s primary reference on concrete technology. The fully revised 15th edition published in 2011 highlights the many advances that have occurred in the past decade while providing a concise, current reference on the fundamentals of concrete technology and construction. This book is a “must have” for anyone involved with concrete.
ACI Article: Minimizing Temperature Differentials in Mass Concrete
Constructing a Mat Slab - Article from Concrete Construction, February 2005
Professional Development Series—Engineering Mass Concrete Structures, November 2006