1. Air Hardening Inorganic Binding Materials Binding Materials Chapter 2

2. Brief Introductions of Gypsum Production Setting and Hardening of Gypsum Technical Requirements and Properties of Gypsum Applications of building Gypsum §2.2Gypsum §2.2 Gypsum Chapter 2

3. Building gypsum is a kind of powdery binding material without any admixture and its main component is β- hemi-hydrate gypsum. Brief Introduction of Production Fig.2.2.1 Micro picture of Gypsum mineral building Gypsum

4. 1 It is the process of making di-hydrate gypsum by reacting with water of Hemi-hydrate. Setting and Hardening of Gypsum 2 It is the process of beginning to produce strength when the fictile paste loses plasticity.

5. Water making di-hydrate gypsum Adsorbent water Vaporizable water free water in solution Paste becomes thicker Frictional force bond force Losing plasticity Setting process Setting and Hardening of Gypsum

6. 3 It is the process of increasing strength of paste with the loss of plasticity. Setting and Hardening of Gypsum

7. Hardening Process Forming gypsum crystallite Crystallite developed Forming crystallite net Developing strength Setting and Hardening of Gypsum Fig.2.2.2 Micro picture of gypsum crystallite

8. 1 Fineness Strength Setting time Technical Requirements and Properties of Gypsum

9. 2 1.Setting and hardening quickly 2.The strength develops quickly in the early time but is not high enough in the later time. 3.Micro-dilatability: Gypsum brings approximately one percent expansion during the hardening. 4.High porosity 5.Strong fireproofing ability 6.Gypsum and gypsum products can only be used in the dry condition. Technical Requirements and Properties of Gypsum

10. Tab.2.1 Technical requirements of building gypsum （ GB9776-88 ） Technical requirements Top-rate materials First-rate materials Qualified materials Bending strength MPa ≥2.5≥2.1≥1.8 Compressive strength MPa ≥4.9≥3.9≥2.9 Fineness, sieve residue (0.2mm), 0.2mm ≥5.0≥10.0≥15.0 Setting time Initial setting time is no earlier than 6min; final setting time is no later than 30min

11. Applications of building gypsum 1 Plastering and rendering in the room Gypsum products Gypsum board Small gypsum block Medium gypsum block Decorative board Soundproof board 2