Hamlin M. Jennings, adjunct professor in the Department of Civil and Environmental Engineering and principal investigator in the Concrete Sustainability Hub, died on July 8 at his home in Cambridge, Massachusetts, after a battle with cancer. He was 68.
A prominent scientist and engineer, Jennings was widely recognized as a preeminent researcher and leader in the field of cement chemistry. He developed fundamentals of cement sciences that were transformational in concrete engineering applications, including the first fully quantitative model of the nanostructure of calcium silicate hydrate (C-S-H), the major component of hydrated cement.
Jennings joined the MIT Concrete Sustainability Hub in 2010 as the inaugural executive director, leading a multi-disciplinary team of physicists, materials scientists, engineers and architects, and pushing them to new frontiers of science-based engineering.
When Jennings started his career in cement science in the late 1970s, the field was classically divided in two branches: cement chemistry and mechanics. Only a small number of researchers were exploring the intersection of chemistry, materials science, and mechanics. Trained as a physicist and materials scientist, Jennings recognized that a true materials science approach for cementitious materials remained to be developed. For the next 35 years, he led advances in the field, ultimately defining what is now known as the materials science of cement-based materials.
Jennings was born on August 4, 1946, in Massachusetts. His father was a professional accountant. His mother was a professor of chemistry at Wheaton College. He graduated with a BS in physics from Tufts University in 1969, and a PhD in materials science from Brown University in 1975. Following a research fellow position at the University of Cape Town in South Africa, he began studying cementitious materials at Imperial College in London, where he was strongly influenced by Hal F.W. Taylor, considered the father of modern cement chemistry.
Jennings joined the National Institute of Standards and Technology (NIST) of the U.S. Department of Commerce as a physical scientist from 1982 to 1987, where he built a group in computational materials science of concrete aimed, for the first time, at blending physical chemistry of cement with prediction of mechanical behavior. During this time, he developed the first computer model of cement hydration. This groundbreaking work was quickly recognized by his contemporaries and it launched a whole new field of computational cement science, leading ultimately to the development of NIST’s Virtual Cement and Concrete Testing Laboratory.
Jennings joined Northwestern University as an associate professor in 1987, becoming a full professor in 1994 and serving as chair of the Department of Civil and Environmental Engineering from 2002 to 2006. Jennings’ growing scientific reputation was instrumental in the establishment at Northwestern of the Advanced Cement-Based Materials Research Center, a National Science Foundation-sponsored multi-institutional and multi-disciplinary research center aimed at expanding and improving the application of cement and concrete to meet society’s pressing future needs for housing, shelter, hospitals, and infrastructure.
Jennings broke new ground in cement science in the mid-1980s with his proposition that the performance of concrete materials can be captured in terms of quasi-equilibrium phase diagrams of the hydration products. A decade later, this fundamental contribution enabled the development of ultra-high-performance concrete, which attains properties like mild steel, and which revolutionized the concrete world. In research, these phase diagrams became the foundation for the implementation of molecular science approaches of cement hydrates, the binding phase of concrete.
In 2000, Jennings published his most widely cited and influential paper, entitled simply “A model for the microstructure of calcium-silicate-hydrate in cement paste.” This was known for years as the “colloid model” of C-S-H, and more recently and appropriately, as the “Jennings model” of C-S-H. Hamlin continued to refine and extend the model and its associated insights into the nanostructure and behavior of C-S-H, particularly with regard to the role of water in the smallest pores and spaces. He published a major update to his model in 2008 called “CM-II” that described the internal structure of the fundamental C-S-H particles. He led a large group of researchers to publish, just one week before his death, an important paper on the hysteresis behavior of water in C-S-H during drying and rewetting.
The Jennings Colloid Model closed the loop between molecular understanding and manufacturing of cement-based materials so that it is now possible to design cement-based materials with specific strength, fracture and durability properties. These quantitative breakthroughs on the science front resulted in many industrial concrete materials innovations, including seeded cement-based materials, innovative cement-based materials for oil- and gas well applications, and silicate-based protective coatings for metals.
Jennings’ most recent research efforts at MIT were aimed at developing sustainable cement-based materials to meet India’s need for housing and infrastructure. In this research, he returned to the very foundation of his unique thermodynamic framework for cementitious materials, at the intersection of materials science and mechanics as a basis for predicting and fine-tuning long-term durability properties.
Jennings, an entrepreneurial inventor who carried his research findings all the way from the lab to full commercial production, was also a highly sought consultant for the concrete and cement industry, the glass and fiberglass industry, and real-estate development. With his unique blend of science-inspired engineering, he proposed a new vision for cement-based materials in the 21st century — one that capitalizes on the availability of the raw materials and recognizes the social impact of the concrete on our living conditions while minimizing the environmental footprint.
Throughout his distinguished career, Jennings was dedicated educator, an inspiring instructor, and a generous and encouraging mentor. He left a lasting impact on his many students and colleagues; in the classroom, on the drawing tables and whiteboards in his offices at Northwestern University and MIT, and through the more than 200 scholarly papers he authored and co-authored.
Hamlin Jennings is survived by his wife, Glenys Jennings; his mother, Bojan Jennings; and his daughter, Ashley Jennings.