Friday, March 26, 2010

How rocks break under pressure: Conjugate Shearing

Before I get back into undercuts, mold release, and assembly of shapes; first we’ll take a look at conjugate shear fractures. This is an important aspect of this masonry system, since it uses this failure mechanism to its advantage.

It’s important to know how rock (or concrete, or ceramics) breaks. Concrete is strong if it is squeezed together, under compression. A high compressive strength is central to the masonry design I’ve been working on. The idea is to keep the assembled structure under compression, to take advantage of this high compressive strength.

When concrete is squeezed together (compressed) until it breaks, it eventually breaks at angles to the applied force. These fracture angles are at around 60 degrees to the applied force. Sets of fractures occur which allow for displacement. This is known as conjugate shearing, the mode of failure is known as conjugate shear fractures. Conjugate shear fractures are common in geology, and are well documented.

To give an example of conjugate shearing, if you take some chilled butter, and press into it with the flat side of a knife, the butter will shear away from the applied force: conjugate shearing.

Triangular blocks are inherently disposed to conjugate shearing without suffering brittle failure. In other words, a control joint (one that allows for movement) allows blocks to move the way they want to move without breaking. Stress is relieved by strain. Gravity acts as the restoring force, returning a structure to its original position.

It just so happens that every face of the interlocking block system I’ve developed is a conjugate shear plane. The system will remain locked together while allowing some movement (strain) to relieve any applied force (stress) that may occur in extreme loading conditions, such as an earthquake, tornado, hurricane, etc. This masonry system is very tough, meaning that it is resistant to crack propagation.

With this short discussion of conjugate shearing, it should help the reader to more fully grasp the beneficial aspects of the articulated interlocking block, which I’ll begin to describe tomorrow.


  1. This comment has been removed by a blog administrator.

  2. It was a great article! expansive mortar chemical that cracks rocks and concrete. It is a concrete cutting, granite breaking and general demolition solution. Thanks for such a nice blog. Rock & Concret Breaking

  3. Nice post! It is a high-powered Nonexplosive Soundless Cracking Agent called SILENT BLAST. This non-explosive demolition agent is useful, cost effective and a safer option for silently breaking up hard materials like rock or concrete. Simply drill, mix and pour. Thanks
    Rock & Concret Breaking