Aggregates Flashcards
What is aggregate made of?
quarried crushed rock:
> igneous: basalt/granite
> metamorphic: slate, marble, quartzite
> sedimentary: shale, limestone, sandstone
Why are hydrophobic aggregates preferable? (limestone, dolomite)
> if hydrophilic, water will COMPETE with ASPHALT for ADSORPTION on aggregate surface
What is slippage?
> if the aggregate/cement bond breaks down due to water entering the concrete and permeating the interface
What effect does porosity have on strength?
> lower porosity = higher strength
What is the maximum aggregate diameter?
~1/2”
What’s the difference between round and rough aggregate particles?
> round particles can slide over another, rough interlock with another and improve stability
What is the most optimal aggregate for stability?
> a dense graded (broad distribution from find to coarse)
How much of concrete is aggregates?
> 90%
need just enough cement to coat the aggregate particles and fill in voids
What happens if theres too much asphalt content?
> aggregates will float in the asphalt cement, attenuating INTERLOCKING and STABILITY
Why don’t we want soft aggregates?
> they break and wear under load
Why do we use aggregates of different hardnesses?
> so traffic wear polishes surface aggregates, so one aggregate polishes faster than another, leaving rough pavement texture
