Well, we finally did it! We busted a random sample of blocks and all refused to fail until the pressure exceeded 1200 psi. Some went all the way to 1450 psi, which is nearly 12 tons on our block face. (The Dake press has a cylinder dia. of 2” and at 10 tons yields 20,000 pounds. 3.14 x r=1 x 20,000 = 62,800 lbs. of pressure on a block face of 52 sq. inches. That comes to 1200 psi) The blocks were not completely dry yet, but the criteria for most codes require a compression test after 14 days. While these revised numbers are more modest than I posted at first, they are still entirely safe to build with.
We are thrilled that 10% added cement and about 20% added sharp sand with our low-clay high silt soil makes a very strong, compact and heavy block. We also ran a water erosion (called spalling in the industry) test to see what a hurricane might do while we are under construction. You can see that there is some spalling but no structural damage to the block after 3 minutes of spray at 55psi from 5 ft away. Nothing happened after 3 minutes, so we stopped. (The test is supposed to go to 5 minutes.) The rough edges and indentions are actually useful as they will form adhesion points (called keys) for the future stucco plaster. We don’t expect this kind of damage to the blocks during construction since they will be covered after each day’s course work. The test blocks did not turn to mush as previous ones had because of their high silt content and insufficient cement. I am glad to discover that even high silt content soils can be amended with cement to make a strong block.
We can now safely build our house and actually sleep in peace!
We’ll make 2000 more blocks by our final formula, and then build a model building (16’ x12’) which will house the alternative energy equipment. This structure will test our ability at our age to get it built in good time without accident or injury before we attempt the much bigger house. I’ll use it to document the vital steps of CEB building in moderate seismic zones including the concrete reinforced ring beam and integrated, reinforced window and door openings. We’ll include forming and tying steel to code. We’ll add properly reinforced and placed piers and then the slab and stem wall.
We will not use mud slurry to cement the blocks together. Rather we will use lime cement mortar which is easy to mix, does not require immediate use and creates no stress on the cement stabilized blocks like cement mortar might. It lays up nicely as a temporary coating against rain and knocks off easily when its time to apply the final cement stucco on the outside over code approved wire backing. Lime mortar gives the blocks a bed and eliminates any concern for a point loading and resultant cracking from either small stones or uneven blocks.