introduCtion What is Honeycombing? Perhaps the most misunderstood and misused term in descibing concrete, and in particular drycast concrete, is that of “honeycombing”. Visually, honeycombing can be described as an area of concrete that has an exposed cluster of aggregates with an absence of mortar and an abundance of air pockets. The concrete in an area subject to honeycombing is generally weaker than the surrounding concrete and, if structural in function, will require repair. Some common causes of honeycombing include: Poor Consolidation • Improper vibration; A lack of vibration will cause poor consolidation, where as, over vibration may cause segregation. Placement of concrete • Placing concrete into tight areas or over horizontal distances can separate the aggregates from the mortar. Formwork • Formwork that does not properly seal during consolidation may allow a sufficient amount of mortar to escape leaving only aggregates behind. Mix Design • A mix design that does not provide sufficient mortar to fully cover all of the aggregate. • Or, a mix design that is not stable and results in segregation of the concrete. Mix time • Insufficient mix time may result in unmixed cement powder which will cause a decrease in mortar quantity. • Too much mix time may result in setting up of concrete before it can be properly consolidated. Segregation • Segregation that is significant enough may cause a majority of the aggregates to all settle into an isolated area. box seCtions manhole and CatCh basin material stormwater treatment teChnologies ConCrete pipe LAFARGE PIPE eMANUAL PAGE 65