Consturction Material EGC 1131
(a) A significant tendency for large and fine particles in a concrete mix, separate among each others. Segregation is caused by * Too wet mix, extremely high workability or less cohesive mixture causes the mixture unable to hold heavy aggregate * Dropping from excessive height
* Over compaction of fresh concrete.
Two methods to minimize segregation in fresh concrete:
* Adequate workability is enough.
* Don’t over compact the fresh concrete.
* If over or extremely high workability, it will cause segregation on the final production, as formation of honey-comb. * Workability is an important element that can influence the quality and other properties of final concrete product. ( c )
(i) I would use High-Early-Strength Cement for my project due to it can develop strength in 7 days (equivalent strength at 28 days). Since it has high heat evolution, High-Early-Strength Cement should not be used in large masses.
* After firstly use High-Early-Strength Cement, use Low Heat Portland Cement to overcome the problems due to it is used for mass-concrete applications. * Can add admixtures to overcome or solve the problems.
(ii) Air-entraining Agents and Bonding Admixtures. It would damage the concrete or occur some reduction in compressive strength.
(a) -Different burning temperature
-Different fineness of grinding
-Add the cement powder with other materials, i.e. calcium chloride, flyash or silica fume, to produce special cements.
(b) A reaction generates considerable amount of heat and cause the cement stiffen within a few minutes after mixing with water. * Can be overcome by adding water, but low overall strength and quality of final product.
( c )
A pozzolan is a siliceous or siliceous and aluminous material which, in itself, possesses little or no cementitious value but which will, in finely divided form and...
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