Concrete Flashcards
What is concrete made of?
mortar and aggregate
How is concrete compared to cement
stronger and cheaper
How much of concrete is aggregate
75%
What is the aggregate in concrete made of?
gravels, granite, sandstone, limestone, dolomite, blast furnace slag, broken bricks
What does a concrete need to be workable?
It needs fine particulates like sand and cement (>300um) in excess of that required to fill the voids of coarse aggregate, acts as a lubricant
What is the theoretical water/cement ratio? What is it in practice?
> 0.25 for complete hydration
~0.38 is used because of 1. losses from water going to the surface and 2. water trapped in CSH fibrils
What happens if the water/cement ratio is too high?
CSH fibrils can’t grow to fill in all the pore space, resulting in open porosity
What are accelerators?
> CaCl2, NaCl
used in cold weather to REDUCE SETTLING TIME
What are retarders?
> sugar
adsorbed onto the surface of CEMENT, keeps concrete from hardening
What is air entrainment?
> bubbles function as lubricant to improve workability
agents are ORGANIC SALTS/FATTY ACIDS that have polar and nonpolar groups. They attach to bubbles to keep them from coalescing
Give an example of air entrainment.
> Isolated ~50um bubbles separated by ~200um show increased durability against freeze-thaw cycles
freezing water expands 9%, bubbles act as a reservoir for remaining water to allieviate pressure that would induce cracking
