CSA Expansive Agent (Cement Additive)

Introduction
General characteristics
 
High-efficiency CSA expansive agent is obtained by blending suitable natural anhydrite with a specially manufactured clinker which consists essentially of calcium sulphoaluminate and CaO. CSA expansive agent is always mixed with ordinary cement. When mixed in the proper proportions with ordinary cement and hydrated, cement mortar or concrete expands during the early stages of hydration. This expansion, when restrained, makes it possible to minimize drying shrinkage. Moreover, when the ratio of shrinkage reducing admixture to ordinary cement is increased its high expansion qualities make it ideal for use in prestressed concrete.
 
High-efficiency shrinkage reducing admixture is being used in all sections of the construction fields and by a wide variety of concrete products manufacturers.
 
High-efficiency CSA expansive agent is manufactured under a strict quality assurance systems GB/T 19001-2000 (i.e. ISO9001:2000) and GB/T 24001-1996 (i.e. ISO 14001:1996) which accommodates the technical requirements of building chemistry formulators.
 
The properties of CSA expansive agent conform to the standards of the manufacturer and to the Chinese relevant standards.
 
Properties
 
Characteristics of High-efficiency CSA Expansive Agent
 
Low alkalinity. High-efficiency CSA Expansive Agent has a very low alkali content (R2O < 0.3%) which is beneficial to avoid AAR in concrete.
 
Short stable stage of expansion. The stable stage of expansion is not more than 14 days, thus the ultimate strength of concrete is not affected.
 
Low dosage and high expansion capacity. The normal dosage of High-efficiency CSA Expansive Agent is 6~8% by the weight of ordinary cement, which is lower compared with other expansive additives such as UEA and CEA (their dosages are about 10~12% by the weight of cement) in the market.
 
Features by using High-efficiency CSA Expansive Agent
 
Prevents cracking due to drying shrinkage and hydration heats.
 
Increases the water tightness of concrete and thus is useful for waterproofing buildings.
 
Enables the manufacture of high strength concrete products through chemical prestressing.
 
 
 
Chemical Analysis
 
Main constituents (%)
 

Item	SiO2	Al2O3	Fe2O3	CaO	MgO	SO3	CaO	R2O	Cl-	Lg-loss
Usual Range	4-7	8-12	＜1.5	50-55	2-4	22-25	10-15	＜0.3	＜0.05	＜5

Mineral Composition: CaO, CaSO4, 3CaO·3Al2O3·CaSO4.
Specific Surface Area: 200~400 m2/kg.
Specific Gravity: 2.8~3.0.
 
Physical Properties
The restrained expansion rate tested under standard condition:
 
 

Dosage in OPC (%)	Restrained-expansion rate (%)
	Curing 7d in water	Curing 7d in water then 21d in air
Type I, 7	0.050-0.080	≥ 0
Type II, 7	0.025-0.045	≥ -0.015
Type II, 10	0.055-0.080	≥ 0

 

 
 
 

Dosage(%)	Compressive Strength (Mpa)
	7 days	28 days
7	> 40.0	> 54.0
0	37.0	56.5

 
Longitudinal change of mortar:
 

 
Application Method
 
1. Dosage
 
High-efficiency csa expansive agent is used as a part of cement, its proportion to ordinary Portland cement depends upon the intended use and the degree of restraint. The proportion of high-efficiency csa expansive agent to ordinary cement generally used in China is about 6~8%.
 
2 .Mixing
 
High-efficiency csa expansive agent and ordinary cement must be thoroughly and uniformly mixed in a mechanical mixer with aggregate and water for a slightly longer time than normal concrete.
 
3. Curing
 
To ensure the proper development of the ettringite needle crystals which are important in preventing shrinkage cracks which occur during drying period, it is recommended that water be sprayed or membrane curing onto the concrete surface for curing at least 14 days after the concrete is cast.
 
Storage
 
High-efficiency csa expansive agent is more sensitive to water and moisture than other cementitious material and is therefore packed in completely waterproof bags and should always be kept and stored in a dry place.