4.2.4.1 Chemical Admixture

1. 4.2.4 Concrete Admixture 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 4.2.4.2 Mineral Admixture

2. Water-Reducing Admixture • Definition • Classification • Water-reducing admixture in common use • Lignin sulfonate water-reducing admixture • Naphthalene sulfonate water-reducing admixture • Resinous water-reducing admixtures • Mechanism • Technical and economic effects

3. Water-Reducing Admixture Definition • Water-reducing admixture permits less amount of water at the same of workability or the increase of the mobility at the same amount of water. • Water-reducing admixtures increase workability and quality by use of water more efficiently in a concrete mixture. By reducing the water, these admixtures densify the concrete and decrease capillary voids and permeability.

4. Classification by effect Water-Reducing Admixture • It can be classified into two types by effect: • Ordinary water-reducing admixture • Super plasticizer • The water-reducing rate of Ordinary water-reducing admixture is less than 10%. • The water-reducing rate of Super plasticizer ,also called super plasticizer or fluid concrete is more than 10%.

5. Water-Reducing Admixture Classification by the effect on setting time • Three types • Standard type • Set retarder type • Coagulant type

6. Water-Reducing Admixture Classification by the effect on air content • Two types by the effect on air content • Air entraining type • Non air entraining type

7. Mechanism • Water-reducing admixture (surfactant) is composed of • hydrophilic group-polar group • hydrophobic group -nonpolar group • When mixed with water • hydrophobic group attaches to cement particle • hydrophilic group attaches to water

8. hydrophobic group hydrophilic group Fig4.2.4 Sketch map of the structure of Water-reducing admixture Mechanism

10. Mechanism • Mechanism of water-reducing admixture is reflected in the apparent active reaction. • Cement paste flocculation structure is wrapped to reduce the mobility of the admixture. • But water-reducing admixtures make flocculation structure dissolve so as to improve the mobility and strength.

11. Mechanism • The flocculation structure dissolves in the following three ways: • Disassemble cement flocculation by electron repelling from the surface of cement particle • Improve the fluidity of paste by forming a solvate membrane on the particle surface • Extend the hydrating area by improving the dispersity of the cement particles • Mobility is improved.

12. Technical and economic effects Technical and economic effects of water-reducing admixture are listed in Tab4.2.10 Tab4.2.10 Technical and economic effects of water-reducing admixture

13. Water-reducing admixture in common use • Lignin sulfonate water-reducing admixture • Naphthalene sulfonate water-reducing admixture • Resinous water-reducing admixture

14. Lignin sulfonate water-reducing admixture • Lignin sulfonate(M) is the most common in use. • It is made by wood pulp through sulfonation and dryness. Definition Definition

15. Lignin sulfonate water-reducing admixture • The amount and its effects • If 0.2-0.3% lignin sulfonate is added • The water-reducing rate will be 10% • Or increasing the slump by 10cm • The strength increased by 10-20% Performance Performance

16. Lignin sulfonate water-reducing admixture • Set retarder activity • Delay the setting time 1-3hours, and add 0.25% Minto lignin sulfonate water-reducing admixture. • Thus, it must be used with the mixture of hardening accelerator in winter. Performance Performance

17. Lignin sulfonate water-reducing admixture • Air entraining activity • To increase the air content from 2% to 3.6% • So that the strength is reduced, while the durability is improved. Performance Performance

18. Lignin sulfonate water-reducing admixture • According to the performances, it applies to • large moulding • sliding formwork • mass concrete • concrete pumping • summer construction Application Application

19. Naphthalene sulfonate water-reducing admixture At present, there are varieties of naphthalene sulfonate water-reducing admixtures in China. The types in common use include NF,NNO,FDN,UNF,MF,AF, and so on. Brief Introduction Brief introduction

20. Performance Adding 0.2-1.0% It has advantages over lignin sulfonate water-reducing admixture for its violent dispersion • water-reducing rate >15% • reinforcing rate >20% • saving cement 10-20% Minor set retarder activity doesn’t affect the strength Most of them are non air entraining.

21. Naphthalene sulfonate water-reducing admixture • Naphthalene sulfonate water-reducing admixture can be used in • High strength concrete • High performance concrete • Liquid concrete • Concrete pumping • Winter construction concrete Application Application

22. Resinous water-reducing admixtures • Resinous water-reducing admixtures are one of superplasticizer. • In China, as the main type of resinous water-reducing admixtures, SM has the perfect water-reducing effect. Introduction

23. Resinous water-reducing admixtures Advantages • It is better than naphthalene sulfonate in dispersion, water reducing, and reinforcing. • The 7d strength is the same with 28d strength of ordinary ones. • The 28d strength can increase by 30-60%. Disadvantages The cost is high