The use of aggregate is common across a wide range of construction, engineering, and renovation projects. You might wonder if it's possible to make substitutions between different types, though. For example, maybe you can't find your desired aggregate for sale. Here are some reasons you may or may not do this.
Unless you've had the chance to discuss the substitution options with an engineer, it's almost always a bad idea to swap out aggregate materials. The reason is that seemingly similar aggregates can have very different characteristics.
This is especially the case when the materials have to support a load. If you're planning to use aggregate to amend the soil and provide a base for a heavy structure, for example, the materials could compress more or less than needed. That may throw all of your measurements off. Worse, if you level the area to make up the difference, you might get a greater amount of compression down the road.
Presuming a feature is 100% decorative, you might be able to get away with purchasing whatever a supplier has for aggregate for sale. If you're mixing it into decorative concrete, though, be aware that it may change the appearance of the feature. For example, a coarser aggregate might not provide as smooth and refined of a look as a sandy one would. Similarly, there could be chipping and cracking issues if the selected aggregate isn't able to hold the entire structure together.
It's unwise to use any materials that aren't approved for a historical project. First, you might end up with issues matching the original appearance. Second, there are may be structural problems when you try to apply something like concrete to a surface. Finally, local, state, or federal regulations governing the historical nature of the building might prohibit anything unapproved.
Why Are There Potential Problems?
Aggregates are designed to be mixed with other materials to produce a particular result. These range from the fairly simple, such as cement, to the highly complex, such as engineered soils for supporting heavy and large buildings.
Under the worst circumstances, the risks associated with getting the mixture wrong are potentially dramatic. Even under the best circumstances, a different aggregate might shorten the life of a structure or surface. Unless an engineer has thoroughly reviewed and approved the decision to make a substitution, it's usually best to not do it on the fly. Get the right aggregate for the job, even if it means paying more.