Halfaya bridge DEC -2008 PHOTOS

General Information

•Concrete: Composite material composed of portland cement, fine aggregate (sand), coarse aggregate (gravel/stone), and water; with or without other additives.

•Hydration: Chemical process in which the cement powder reacts with water and then sets and hardens into a solid mass, bonding the aggregates together

•Heat of Hydration: Heat is released during the hydration process. In large concrete masses heat is dissipated
slowly ---- temperature rises and volume
expansion --------------- later cooling causes contraction.
Use special measures to control cracking
Concrete Mixing and Proportioning

•1. Proportioning: Goal is to achieve mix with
•Adequate strength
•Proper workability for placement
•Low cost
–Low Cost:
•Minimize amount of cement
•Good gradation of aggregates (decreases voids and cement paste required)


–Water-Cement Ratio (W/C)
•Increased W/C: Improves plasticity and fluidity of the mix.
•Increased W/C: Results in decreased strength due to larger volume of voids in cement paste due to free water.

–Water-Cement Ratio (W/C) (cont..)
•Complete hydration of cement requires W/C ~ 0.25.
•Need water to wet aggregate surfaces, provide mobility of water during hydration and to provide workability.
•Typical W/C = 0.40-0.60