Pre-placed aggregate concrete (PAC) is a type of concrete which is made by forcing cement grout into the voids of a clean, graded coarse aggregate which is densely pre-packed in formwork. Pre-placed aggregate concrete is used where placing conventional concrete is extremely difficult, such as where massive reinforcing steel and embedded items are present, in underwater repairs, concrete and masonry repair, or where shrinkage of concrete must be kept to a minimum.

The grout typically consists of sand, cement, pozzolana, plasticiser/ super-plasticiser and an air entraining agent. The pozzolana and the plasticiser/super plasticiser are used to impart flowability to the grout to fill the voids. The coarse aggregate is washed to remove all fines and screened just prior to placement. Grout is then injected through forms to provide the cementing matrix. Grouting is begun at the bottom of the pre-placed aggregate.

Characteristics of the grout are affected by the water content, sand grading, cement, pozzolana and the types & amount of admixtures. For each design of grout mixture, there are optimum amounts of fillers and admixtures to produce the best pumpability or consistency. Proper proportioning for the structural grout mix components is necessary to get the required strength and durability of the finished pre-placed aggregate concrete. Trial mix design is necessary for each job.