Herod Engineering in Israel is using basalt rebar in archeological sites in conformance with requirements of the Israel Antiquities Authority and Israel Nature and Parks Authority preservation architects and engineers.

We did several tests with rebars in order to verify their suitability as reinforcement for ancient buildings. Preservation requires the use of Natural Hydraulic Lime (NHL) as the bond between rebar and stone.

  • STEEL – Steel rebar was corroded by the NHL
  • FIBERGLASS – It didn’t take more than a few dozen pounds to pull the fiberglass rebars out.
  • BASALT – 12 mm basalt rebar was pulled out by 230 kg (2300 Newton) of force in one test and 500 kg (5,000 N) in another test done in better conditions. Failure was gradual.  At 230 kg the basalt rebar started coming out of the stone, but continued to carry a 100 kg load. In the second test, at 500 kg, the rebar started coming out of the stone, but continued to carry 350 kg load.

The rebars were inserted into a typical second temple building stone. A 35 cm deep, 16 mm diameter bore was drilled, filled with NHL-3.5 and then the rebar inserted.

Failures were in the stone or NHL. Use of higher grade, stronger NHL is not advisable, preserving the ancient stone is the important task.

Yossie Laor, Herod Engineering