Lime (चूना): Classification (Fat lime, Hydraulic lime), slaking process aur purane constructions mein iska mahatva

Classification of Lime

IS: 712 ke mutabiq, lime ko unki properties ke hisaas se classify kiya jata hai, lekin main do types ye hain:

A. Fat Lime (White Lime / Rich Lime)

Ise pure limestone ko jalane se banaya jata hai. Isme calcium oxide ($CaO$) ki maatra bahut zyada (95% tak) hoti hai.

• Properties: Ye bahut dheere set hota hai aur paani ke niche set nahi ho sakta. Iska color ekdam safed hota hai.

• Uses: Iska use mainly White washing (putti) aur plastering ke liye kiya jata hai kyunki iska volume slaking ke baad 2-3 guna badh jata hai.

B. Hydraulic Lime

Isme clay (mitti) aur ferrous iron ki impurities (5% se 30%) hoti hain.

• Properties: Iski sabse badi khoobi ye hai ki ye paani ke andar (underwater) bhi set ho sakta hai. Isme cement jaisi binding properties hoti hain.

• Uses: Iska use structural works jaise foundations, brick masonry, aur thick walls mein kiya jata hai.

Slaking Process (Chuna Bujhana)

Jab "Quick Lime" ($CaO$) mein paani milaya jata hai, toh ek chemical reaction hoti hai jisse wo "Slaked Lime" ($Ca(OH)_2$) mein badal jata hai. Isi process ko Slaking kehte hain.

• Chemical Equation:

  $$CaO + H_2O \rightarrow Ca(OH)_2 + \text{Heat}$$

• Process: Reaction ke dauran bahut zyada garmi (heat) nikalti hai aur ek "hissing sound" (shrrr ki awaaz) aati hai.

• Result: Lime ka dhera (lump) toot kar ek fine powder ya paste ban jata hai. Agar fat lime hai, toh uska volume kaafi badh jata hai.

Importance in Old Constructions (Purane Constructions mein Mahatva)

Aajkal hum cement use karte hain, lekin purani imaraton mein Lime (Chuna-Surkhi) ka mahatva in reasons ki wajah se tha:

• Self-Healing Property: Lime ki sabse hairatangez baat ye hai ki agar diwar mein barik crack aaye, toh lime hawa ki $CO_2$ ke saath react karke fir se limestone ban jata hai aur crack ko khud hi bhar deta hai.

• Breathability: Lime mortar se bani diwaren "saans" le sakti hain (moisture ko andar-bahar aane deti hain), jisse purani imaraton ke andar ka temperature maintain rehta tha.

• Durability: Cement ki life lagbhag 50-100 saal maani jati hai, lekin lime se bani imarate hazaro saalo tak tikti hain (Jaise Roman structures aur Indian temples).

• Workability: Lime mortar kaafi plastic hota hai, jisse mistry (masons) ko kaam karne mein aasani hoti thi.

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