1. 4.2.4.1 Chemical Admixture Introduction Water-Reducing Admixture Hardening Accelerator Air Entraining Admixture Set Retarding Admixture Flash Setting Admixture Expanding Admixture Frost-resistance Admixture 4.2.4 Concrete Admixture 4.2.4.2 Mineral Admixture

2. Hardening Accelerator  Definition  Application  Common Hardening Accelerator Chloride hardening accelerator Sulfate hardening accelerator Organic amine hardening accelerator

3. It refers to those that improve the strength in early period without affecting that of the later period obviously. Hardening Accelerator Definition

4. Hardening Accelerator It applies to the construction –constructed in winter –in emergency engineering –in time-limited ones The use of hardening accelerator can make –C20 reach mould removal strength within 16 hours –The strength allowing floor slab installment on it within 36 hours to speed up the construction. Application

5. Chloride hardening accelerator  CaCl 2 type is most widely used for  excellent effect  low cost  convenience  Add 0.5-1% chloride hardening accelerator  Strength of 2-3d can improve 50-100%  Strength of 7d 20-40%  Strength of 7d 20-40% Performance-early strength Typical type

6.  CaCl 2, reacted with C 3 A and CH, gives new hydrate-calcium oxychloride. Hydrate-calcium oxychloride is separated in the early period, and formed into the framework. It speeds up the formation of structure of hardened paste  Meanwhile, the CH concentration reduces  These two factors quicken the C 3 S hydration. Thus the strength is improved in the early period. Mechanism of Early Strength

7. separated out in the early period CH concentration is reduced calcium oxychloride formed into the framework speed up the formation of structure of paste speed of hydrate Improvement of strength in the early period

8. Mechanism of Early Strength Speed of hydrate Form new hydration Intensify solubility of cement Improve early strength

9. Sal mirabile are most widely used.  When it is 1-1.5%, sulfate is added.  The concrete strength goes up 70% of design strength in only half of the time. Sulfate hardening accelerator Typical type Performance-early strength

10. Sulfate hardening accelerator Mechanisms Improvement of strength in the early period Na 2 SO 4 +Ca(OH) 2 +H 2 O NaOH+CaSO 4 ·2H 2 O CH Aft formed into the framework speed up the formation of structure of paste speed of hydrate

11.  TEA is the main type of organic amine water- reducing admixtures  It is pale buttery liquid  The quantity is 0.02 － 0.05% Organic amine hardening accelerator Typical type  The early strength improves about 50%.  The 28d strength remains the same.  It plays the to slow setting. Performance-early strength

12. Organic amine hardening accelerator  Complexant in the form of complexion  aqueous alkali produces complex salt of small solubility  framework with cement hydrate Mechanisms