B-Presenter: Properties Of Concrete

Showing posts with label Properties Of Concrete. Show all posts

Tuesday, February 21, 2017

-Change in Volume after setting

-Once set it should not undergo a large change in volume

-Expansion may happen due to the delayed or slow hydration

-Done By Vicat Apparatus

-Minimum time of 60 mins is prescribed by ENV 197-1:1992 for cements up to 42.5MPa

-45 mins for cements with higher strengths

-ASTM C 150-94 minimum time for initial set is 45 mins

-final setting time <45mins

-Components such as tricalcium silicate, dicalcium silicate, and tricalcium aluminate

-Fineness of Cement

-Cement content, water-cement ratio, curing temperature, and chemical admixtures

-Quantity of Heat (J/g) of unhydrated cement evolved upon complete hydration at a given temperature

-Exothermic Reaction (up to 500J/g) between cement & water

-In normal construction heat is dissipated into the soil or air

-For Massive Structures like dams or mat foundations the heat cannot be readily released and thus attains high internal temperatures

-Total Surface Area of Cement that represents the material available for Hydration

-Rate of Hydration depends on the fineness of the cement particles

-High Fineness is necessary for rapid strength and development

-The gain of strength of a set cement paste

-Change from fluid to rigid stage

-During setting, the paste acquires some strength

-Setting time decreases with the rise in Temperature

-Portland Cement Becomes a bonding agent

-Silicates & Aluminates form products of hydration which produce a firm & hard mass