Preplaced Aggregate Concrete

Preplaced aggregate concrete (PAC) is a cost effective, long lasting repair solution for both above and below water conditions. This method involves the placement of aggregate and cementitious grout separately. First, steel embedments are installed and formwork is erected in much the same manner as they would be for traditional concrete placement methods. As the name suggests, clean, washed aggregate is then sluiced into the formwork before it is grouted. Once the formwork is full of aggregate, a high strength, non-shrink grout is then injected, starting at ports located in the bottom of the formwork and then progressing upwards.

Preplaced aggregate concrete is an ideal surface repair both below the waterlineand right at the waterline. Because the aggregate and the grout is placed separately, the materials do not separate. When sluicing concrete into place in underwater conditions, one can run the risk of “washing” their aggregates. Because divers start at ports located at the bottom of the formwork, the PAC method forces the water up and out of the top. The result is a dense, long last repair that will resist damage from freeze-thaw cycles.

There are several advantages to PAC over traditional concrete:

• Higher density due to a higher average aggregate content
• Lower shrinkage because of uniformity and the use of non-shrink grouts
• Resistance to freeze-thaw cycles
• Increased compressive strength due to point-to-point contact of aggregates
• Underwater place-ability
• Reduction in the need for heavy equipment
• Better bond-ability to the existing structure
• Grouting technique will also lead to consolidation of the structure if cracks and voids are present