We are bidding a project which calls for gap-graded mixes. What are the advantages and disadvantages?
Gap-graded mixes are often specified for exposed aggregate architectural concrete finishes in order to increase the likelihood of obtaining uniform surface appearance. Gap-graded concretes also show less segregation, tend to be more workable at given slumps, permit lower water-cement ratios and develop required strength with lower cement factors. Creep and shrinkage are also less in gap-graded concrete than in comparable standard mixes. Aside from its cost, which will be higher than the cost of conventional concrete, we are not aware of any disadvantages, but it is important that ready mixed concrete trucks used for transporting gap-graded concrete be capable of discharging the very low slumps usually called for.