Backfilling is using soil that has been removed during excavation for ground-level or sub-grade structures for projects like utility repairs, structural fill applications, pipe conduit, and more. The problems associated with backfill have always been part of building with cement at or below ground level, and any project that involves excavation.
Backfill supports these and other finished structures like foundations, slabs, utility vaults and trenches. It can use soil just removed from the work site, or a mix of soil from elsewhere, rocks, stone, and other materials depending on the need, location, and project.
However, several common problems can crop up when backfilling this way:
- Some sites due to size or location don’t permit stockpiling backfill material, let alone processing it if needed; and can make it difficult to bring in fill material from elsewhere.
- Depending on the location and application, a utility or construction company may need to have one of several different backfill materials available. Those include byproducts like slag or ash, rock, shale, coarse-grained soils, fine-grained soils, or, worst case, less-than-ideal materials.
- It can be difficult to ensure that backfill material is properly mixed, consistent, and free of debris and contaminants so it fills the void in a consistent manner.
- Waiting for concrete to cure and putting material in place layer by layer and compacting it is time-consuming.
- Getting adequate water to the site to wet down each layer can be difficult.
- When water used in the compaction process evaporates, backfill material volume can change significantly.
- Compaction can be incomplete and lead to settling later.
- Compaction can damage, break, or collapse newly laid pipes, repairs, or structures just completed.
- Some soils, like expansive soil, are not stable backfill material; and, like granular soils, can be hard to compact. Non-ideal materials typically require processing and additives to improve their suitability as fill.
Volumetric Flowable Fill to the Rescue
You can avoid all these issues by using flowable fill (also known as controlled density fill concrete, CDFC, or controlled low-strength material, CLSM) made on-site, on demand by a volumetric concrete mixer truck. That enables making just the right amount of fill at exactly the time it’s needed, with no wait and no waste.
It’s not quite one-size-fits-all, but by mixing fresh flowable fill on site, the operator can adjust the mix at a moment’s notice to produce the ideal flowable fill, anywhere, any time. Even better, a volumetric mixer can easily switch to making high-strength concrete. One machine on a job site can handle both, making it faster, easier, more efficient, and less costly than using barrel mixer trucks hauling each onto the job site.
There is no waiting for a barrel mixer truck, and no need to plan how much barrel load will fill, nor how long each has been sitting, waiting. There’s no overpaying for the wasted balance of a barrel mixer’s load because of the need to always order too much rather than too little. There is no additional expense of paying a premium to open a batch plant during off hours for night work or over weekends.
Projects and PlacementIf placing freshly mixed fill is challenging because of location or site size, a boom truck can set up alongside the volumetric mixer truck and place the fill exactly where it’s needed from a distance. Working alongside a busy highway? Mix fresh flowable fill on a quieter frontage road and use the boom to pump it into place. Laying pipe in a trench or have an excavation that needs to be filled immediately after work on each section is done? A volumetric mixer can create whatever amount is needed at that moment to cover that specific section. Then, using a telebelt, a series of fold up conveyor belts, the proper flowable fill volume can be placed correctly, extending its reach as areas further from the volumetric mixer are completed and ready for fill.
Done properly, using flowable fill on concrete projects increases strength, supports and protects, improves stability and performance, and extends the lifespan of the project. It reduces settling soil and loading on slopes. It can also be significantly less dense than soil, protecting against overloading and collapsing the structure it protects while eliminating the need for compaction. For those in earthquake zones, it is more stable than soil during quakes given it’s not subject to liquefaction. It can also be removed relatively easily when the time comes.
Finally, flowable fill is relatively easy to mix and uses less cement powder than typical concrete mixes, which can make a significant difference when it comes to materials shortages and project costs. You can even have color dye mixed into it to color code and signify the medium being covered.
Interested in avoiding backfilling headaches, and making jobs much easier? Contact us today to schedule a meeting and talk about how a Holcombe volumetric mixer truck making flowable fill can help. You will finish jobs faster, at less cost, with greater flexibility and control while producing a superior finished product.