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Palaash Gaunekar Grade: 12
        

Setting of cement involves


a)Absorption of heat                b)Evolution of of heat


c)Expansion                            d)Contraction


Can anyone help me out with proper reasoning

6 years ago

Answers : (1)

AskiitiansExpert Abhinav Batra
25 Points
										

Dear Palaash


the correct options are (b) and (d)


 


When mixed with water, cement sets to a hard mass. It first forms a plastic mass which hardens after some time due to 3-dimensional cross-links between the --Si-O-Si-- and --Si-O-Al-- chains. The first setting occurs within 24 hours whereas the subsequent hardening requires a fortnight, when it is covered by a layer of water. This transition from plastic to solid state is called setting.


Reactions Involved in Setting of Cement



  • On hydration silicates and aluminates of calcium get converted to their respective hydrated colloidal gels.





  • At the same time, hydrolysis precipitates calcium hydroxide and aluminium hydroxide.



This calcium hydroxide binds calcium silicate particles together. On the other hand, aluminium hydroxide fills the interstices (an intervening space) rendering the mass impervious (not affording passage to a fluid).




  • Role of gypsum - Gypsum reacts with tricalcium aluminate.




ALL THE best


AskIITIANsExpert


ABhinav Batra


6 years ago
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