Annular Space Grouting
Cellular concrete is an excellent material for annular space grouting. Whether an annulus is just an inch or a few feet, and regardless of host pipe size, cellular concrete is an economical, reliable annular space grouting material. CJGeo has grouted dozens of annular spaces on welded HDPE, corrugated HDPE, mechanically-joined HDPE, concrete, spiral wound, corrugated metal and DI pipes throughout the Eastern United States.
Mix Design for Annular Space Grouting
The typical cellular concrete mix design is 30PCF wet cast density. This yields an average compressive strength of 125psi at 28 days. Each cubic yard in place contains 512 pounds of Portland cement, 256 pounds of water, and 20.3 cubic feet of preformed Aerlite foam. In situations where higher compressive strengths are required, higher density cellular concrete may be used. If exceptionally high strengths are needed, sanded mixes can be used, however sanded cellular concrete mixes don’t flow as well as neat mixes, which can require additional placement steps.
Placement Method for Annular Space Grouting
CJGeo performs all pipe grouting by pumping. While some contractors use gravity placement, pumping ensures uniform material and a complete fill of the annulus. Our continuous generation equipment has integrated pumps so there’s no need for additional equipment. Cellular concrete requires far fewer injection points than traditional grouts.
Cellular concrete is economical for this type of grouting because the majority of the mix is atmospheric air (which is free). Because cellular concrete can be easily pumped long distances, it is easy to install in hard to access locations, very tight annuli and over long stretches.
The lightweight mixes used for pipe grouting generally have expansion ratios of greater than 5 times. The high expansion ratio greatly reduces the number of ready mix truck delivery trips. This reduces job site congestion and allows other trades to work uninterrupted. For applications adjacent to roadways, it can significantly reduce traffic control expenses.
Low Installation Pressure
Installation pressures, even in tight annuluses with long runs are typically below 10psi. As mechanical joint flexible relining pipes become more popular, the need for low pressure grouting has grown. Cellular concrete easily meets the challenge. Using cellular concrete greatly reduces the risk of collapsing or damaging carrier pipes compared to using flowable fill.
Carrier pipe buoyancy during grouting is an often over-looked, but very important concern. Using low density cellular concrete significantly reduces buoyancy of carrier pipes. To completely mitigate buoyancy, some pipes require partial filling with water to compensation for buoyancy. Grouting in lifts adds time to a job, but is sometimes required for reducing buoyancy.
Buoyancy is also controllable using block, spiders or centralizers. Enterable pipes usually facilitate installing blocking prior to sliplining or carrier placement. Non-enterable pipes require spiders or centralizers to counteract buoyancy if water filling isn’t possible.