CIVE 2700 Lecture Notes - Lecture 8: Calcination, Fly Ash, Metakaolin
4 Apr 2016
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Document Summary
Added in extremely small, precise quantities in addition to aggregates, cement and water. Typically <= 1-2% cement mass; 5ml/100kg concrete. Types of admixtures: air-entrainers, water reducers, accelerators, retarders\mineral admixtures, others. Liquid admixtures i. e. shrinkage reducer, water reducer, foaming agent, Solid admixtures (powder) i. e. fly ash, silica fume, blast furnace slag, Added to improve durability during cycles of freeze and thaw. Introduces tiny uniformly dispersed air bubbles (0. 01-1mm) in concrete. Typically 4-6% of air entrained (50ml/100kg cement) in concrete is sufficient in protecting against freeze-thaw damage. But increased air reduces strength by 20% To re-increase compressive strength, must lower w/c ratio. Less water makes cement paste less workable, but more air bubbles increases workability. Different from entrapped air -- harmful larger bubbles. Check for honeycombs - unwanted, spoiled concrete. Never put water in all at once - you never know how saturated the aggregates are -- may have to add more if dry (always measure what you add extra)
