Joe Vaughn wrote:Scoria is insulative. It is thermally valuable in climates where you want your interior temperatures moderated from exterior temperatures. Thermally it makes the most sense to have insulative exterior walls and mass interior walls, with the exception of those areas which are hot during the day and cool off considerably at night, and have decent cold season solar gain--those areas comfortably allow straight mass exterior walls.
Nonetheless, thick mass walls work wonders in hot climates especially if shaded with deep roof eaves (which are also good for natural foundations/walls in rainy environments). EB walls are substantial.
Yes pure Scoria bags are lighter and quicker. Offset that with costs--material and labor. If only a few workers or have other jobs then Scoriabag may make more sense. If this is a big group effort, then maybe show them pure earthbags.
As for mixing Scoria aggregate and clay/sand: don't think you Get the best of both worlds, insulation and mass simultaneously. That's the WRONG REASON to combine. Thermally, It'll just perform as mass. It will lighten the load a bit though and labor should increase as a result.
Also I disagree with the previous comment about it not binding. It'll bind with appropriate clay content as well as the larger aggregates mechanically locking in together. So maybe determine your clay content. If it is high, either cut with sand or Scoria or gravel. Start your tests from 3 aggregate : 2 sand : 1 clay. Which for a high clay content dirt could mean 1 Scoria: 1 high clay content clay-sand dirt. Why did I say gravel? Because we are not talking about some tensile strength here, bag fill is not the tensile stuff of ferrocement or fibers or steel cable. We are talking about compressive strength mass wall construction. It is not monolithic, it is a bunch of tamped bags. The importance here just as much plaster work, I believe good distribution of aggregate size makes sense. All different sized aggregates tamped and locked into place by both clay binder and aggregate distribution. Yes its overkill to state this and to even apply over a regular screened earthen fill but you asked if "there was any practical value to combine Scoria (lightweight larger than sand aggregates) to clay and sand even though you don't receive pure Scoria insulation values". My tests showed that bags with larger and more diverse aggregate performed better--less water usage, quicker dry/hardening time, higher compressive strength, more stable without the bag (and all sands and clays and gravels and scoria have different properties and respond differently--so test each soil). A few times I have seen this combined for the WRONG REASON (thermal performance) in my cold climate, so I must spell this out here for future googlers.
I believe larger aggregates in earthbag fill makes better earthbags; better Scoria aggregate size distribution makes better scoriabags; and logistically (labor or cutting down clay content) the inclusion of Scoria could make the jobsite more efficient. Depends upon mixing methods, material and labor cost, clay content. Doubtful you'd notice any difference in thermal performance from earthbag and earth-Scoria bag mixed at previously stated ratios although it does lighten the bag somewhat.