That is properly called “flowable backfill”. It is a mainly sand, gravel, water mixture with only 1 bag of cement. It is used primarily when it is a high traffic road or when mechanical compaction is not an option. That looked like ductile iron pipe (DIP) and it looked a little sketch. This was probably the best option for backfill. No need to worry about voids and it’ll be stiff enough for blacktop in a day or so. If they ever need to excavate around that valve again, that fill will break apart pretty easily. In some localities, the cement mixture is called two sack. It does not encase the valve like regular concrete and can be easily broken apart if necessary. Typically, this mixture is used in electrical work were conduit is laid under a parking lot or driveway with vehicular traffic. It provides good support to keep the conduit from being crushed and the ditch where conduit is set from sinking since the ground will never be compacted to 100% like what nature does.