• planning for quantities needed
• quarrying limestone from nearby rock outcrops
• transporting to the kiln site
• crushing/sizing raw limestone
• gathering fuel/cutting to size
• constructing the kiln
• loading kiln with limestone and fuel
• burning (calcining) limestone to make lime
• removing and inspecting/sorting of properly burned lime
• laying out the architecture of the building: rectangular and oriented
• transporting lime cement and aggregates to the construction site
• mixing
• placing
• finishing

Bentur (1991) examined 2-inch-thick, two-layer floor samples from a building at Yiftahel and found compressive strengths of 1-inch cubes to be 4900 psi for the base layer and 6500 psi for the combined base plus the finish coat. Chemically, the samples consisted of nearly pure calcium carbonate (carbonated lime) and a small percentage of silica, attributed to sand. The base layer had porosity and crystal sizes suggesting it rough compaction, while the finish layer was dense with very fine crystals, suggesting it had been wet and well troweled.

Some of the floor samples recovered in 2008 clearly show a rough, porous base layer and a dense, bright white, sanded finish coat. One small area was painted red, so some decoration was used but it's unknown to what extent. The floors with white finish coats were probably decorative wearing surfaces, but other areas are rougher and somewhat easily abraded; it is speculated that some areas might have been covered with boards or textiles.

Many large holes were found in the floors and pits, some with intact skeletons or modeled plastered skulls. It's known that Neolithic cultures often buried their dead within the boundaries of a structure; in this case, the floors were excavated, bones interred, and floor patched over with fresh concrete.

This larger section of floor shows one of the various crack patterns for the concrete floors at Yiftahel. Subgrade under the concrete was compacted with smooth surfaces allowing for movement in the concrete as shrinkage occurred. When all these cracks occurred will never be known. They could have developed at any time for the past 10,000 years. PHOTO: HOWARD KANARE

During this past summer, samples were collected from 12 separate floors, along with samples of limestone likely used as the raw material for the cement and local sand that might have been used as fine aggregate. Subbase materials under the floors also were collected as well as calcined limestone from the remains of a kiln (by now, completely carbonated). The quantity and diversity of these samples will help estimate the load-bearing capacity of the floors, and lead to an understanding of the ancient construction means and methods used.

The site investigations raised many intriguing questions, such as: Were the floors constructed by the local inhabitants or by itinerant skilled crafters (the earliest cement masons)? Were the buildings used as homes or stone-tool workshops, and used for storage or animal care? Why were the buildings sited and oriented as found? How long would they have taken to construct? How long were they occupied? What did the people learn about making concrete over time?

Carbonized wood and seeds at the site provide accurate and precise dates for occupancy, but the precise reason for abandonment of the site is unknown. Some scholars suggest that swift climate changes brought about by northern Atlantic Ocean currents reduced the ability to grow crops and caused game animals to migrate south, with humans following. It's possible this event probably occurred 1000 years after the initial occupation of the area.

The archaeologists working at Yiftahel have extensive experience investigating ancient sites from the viewpoints of archaeology, anthropology, sociology, and history, but not as construction experts. The mission now is to examine the samples using “concrete construction eyes” to better understand concrete materials and construction techniques. It is hoped that funding will help the concrete industry learn all it can from these remarkable ancient people and the world's oldest concrete floors.

Howard Kanare (hkanare@ctlgroup.com) is senior principal scientist at CTLGroup, Skokie, Ill. He consults on design-phase, construction, and post-construction troubleshooting of concrete floors. He is chair of ASTM F06.40.05 Task Group on Moisture Measurement in Concrete Floors and author of the PCA book, “Concrete Floors and Moisture.” Ianir Milevski (ianir@israntique.org.il), Hamoudi Khalaily (hamudi@israntique.org.il), and Nimrod Getzov (getzov@israntique.org.il) are research archaeologists at the Israel Antiquities Authority. They have excavated and researched extensively in Israel, focusing on late prehistoric sites. Joe Nasvik (jnasvik@hanleywood.com) is senior editor for CONCRETE CONSTRUCTION magazine.

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