Interlocking Bricks

I've gotten very interested in interlocking bricks as they seem like a quick and easy way to build, however I don't see anything about fired interlocking bricks. Is there a specific reason that these bricks can't be fired, or is there just no demand for them because bricks are out of style for structural use? Does anyone know if there are any problems with firing interlocking bricks such as warpage? I don't find using bricks made with 10% Portland to be sustainable as many concrete mixes containing 15% cement are much stronger than the soil cement bricks. Fired bricks are also much stronger.