Editor's Note: Modern portland cement is made by heating a mixture of limestone and clay to a high temperature, with additions of aluminates and iron as needed to provide the uniform product that we use today. The concrete that was manufactured by the early culture featured in this article was made from calcined limestone combined with sand and stone aggregate to make floor slabs.

There is much talk about green and sustainability these days. For concrete, the key word is sustainability, which has to do with constructing slabs and structures with low carbon footprints. There are many ways to do this, but the best way is to use the inherent qualities of the material to provide longer life cycles—replacement being the most energy intensive. So how long can the service life of concrete be? How about 9800 years.

The concrete industry is more fascinated with concrete than other trades are about the materials with which they work. Those in the industry push the limits of what it can do, learn about the technical developments that can make it even better, and keep up with the ever-changing upgrading of tools to form, place, and finish it. Concrete professionals point with pride to projects that use concrete to push the limits of what's possible.

Recent discoveries add another dimension to humans' experience with concrete. As a building material, it actually predates the invention of pottery made from clay and the discovery of metal for making tools and implements. Along with wood and rock, it's the oldest building material.

Shown here are six concrete floors that were cast over time in one of the buildings by a “Pre-Pottery Neolithic Part B” culture 9800 years ago. It's hoped that an examination of the concrete in each floor will reveal how their concrete technology developed over time. PHOTO: HOWARD KANARE

In the summer of 2008, Howard Kanare was invited by Hamoudi Khalaily, Ph.D., Israel's Antiquities Authority (IAA), to participate in an archaeological excavation in northern Israel known as Yiftahel. The site was discovered in 1982 when a bulldozer struck unearthed ancient buildings while excavating for a new highway. IAA archaeologists walked several acres of the highway construction path and found artifacts, including flint tools, on the ground's surface, leading them to believe there was an ancient buried settlement. What they found is historically significant, especially for the concrete industry.

Yiftahel is located in Northern Israel about 15 miles east of Haifa and 5 miles west of Nazareth. The archaeological remains are embedded within the eastern bank of Yiftahel Valley and are estimated to cover at least 7.4 acres. This particular site is likely the oldest permanent village ever found, and it has a number of concrete floors.

After years of debates about the site and the road system in the area, the Israel government decided that Yiftahel will be covered by the new construction of a high-speed interchange to alleviate congestion at the intersection of Highways 77 and 79. From September 2007 until August 2008, excavations were conducted for the IAA by Khalaily and his colleagues Ianir Milevski and Nimrod Getzov to document the remains of the several occupation layers. The goal is to record and learn as much about the site's remains before the highway is constructed. The discovery of extensive concrete floors gives an unprecedented opportunity to explore the earliest known concrete.

This aerial photo shows the archaeological site at Yifthel. The square excavations are each 16x16 ft., and the 18x40-ft. building footprint with parts of its floor shown is oriented in the direction of the North Star. Mixing and placing concrete to cover the 720 sq. ft. of floor is a major undertaking. PHOTO: IANIR MILEVSKI

The Pre-Pottery Neolithic Part B (PPNB) culture used rock and mud to construct walls and concrete for the floors. The buildings were rectangular, and aligned to true north, indicating that the inhabitants developed some knowledge of how to do layout work. Archeologists found as many as six layers of floors, one on top of the next, providing the opportunity to find out how their technology developed. The floor finishes vary, indicating differences in ability. They may even have used large stones to polish floor surfaces. However, no evidence of the tools they used exists. Careful laboratory examination of samples may explain how the floors were placed and finished.

Investigations by several scholars for the past 25 years revealed some information about the concretes, but there is still much to learn. Archaeologists usually refer to these materials as plasters, but they are more correctly designated lime-concrete and lime-mortars. Wood-fired kiln temperatures achieved at this point in human history were between 850º to 900° C, sufficient to calcine limestone to make lime, but not enough to fire clay pottery or to produce hydraulic cements.

Garfinkel (1987) studied an 1 1180-square-foot area referred to as “Structure 700”. The floor was 1 3/16 to 2 3/8 inches thick, and required 7 tons of calcined limestone. This early work revealed a highly organized, technological society that developed an industry to produce the lime cement and to construct the concrete floors. The following steps must have been developed: