The malleability of concrete’s performance characteristics is one of its inherent strengths. Through adjusting a variety of variables including paste to aggregate ratios, water content, aggregate composition, paste characteristics, and a number of potential admixtures, a variety of physical characteristics can be controlled. Typically concrete used in buildings is divided into two categories: structural and architectural (sometimes called “finish”), with nuanced and exacting mix designs well established through a long development history to create a wide performance spectrum within each category.

However, concrete has an equally long history as a thermal material utilized both as thermal storage and to reduce or enhance thermal movement through building envelopes, the ancient Roman public baths at Ostia and the Anasazi pueblos in present day New Mexico being just two examples. Similarly, long before the advent of the contemporary concept of insulation, concrete and other mass materials have constituted the full volume of the building envelopes of perhaps the vast majority of the world’s buildings, providing whatever resistance to heat flow there was that allowed a different temperature to be maintained indoors than existed outdoors. Yet concrete mix designs focusing on thermal performance in building envelopes are essentially non-existent.

My feeling is that investigating the efficacy of such a mix design strategy is an important component in the search for more energy efficient building envelopes that utilize concrete and in the general movement to lower the embodied energy and consequent carbon footprint of concrete in the built environment. The central rationale is that in a lifecycle analysis the lion’s share of a typical building’s environmental impact is through its operation . Therefore, improving building operational performance will have the most significant effect on its energy and carbon impact. It has been well established that the key to maximizing operational performance is to reduce heating, cooling, lighting and plug loads first before considering improving HVAC applications or employing renewable energy systems. Which load category has the largest effect on building performance is determined by many variables, but the thermal properties of the building envelope consistently play a significant role. Add to this the ubiquity with which concrete is employed as a major component of the built environment in its current incarnation, and it seems clear that there is a compelling rationale for investigating thermal optimization strategies for concrete mix designs in building envelopes.

I have completed an initial study of the thermal characteristics (specific heat capacity and thermal conductivity) of concrete mixes of differing paste to aggregate ratios, comparing OPCC to GCC mixes. The results along with an incipient methodology for optimizing concrete mix designs for thermal characteristics were published in the Journal of Architectural Engineering.