Research and application of composite cement in Vietnam (стр. 1 )

Associate Professor - PhD. Luong Duc Long, PhD. Luu Thi Hong

Vietnam Institute for Building Materials

RESEARCH AND APPLICATION OF COMPOSITE CEMENT IN VIETNAM

Abstract: In recent years, domestic cement demand of Vietnam has increased very fast therefore cement manufactories improved. Up to 2014, Vietnam cement industry has design capacity reached about 70 million tons and it would be more than 80 million tons in 2015. Together with increasing of the manufacturing capacity, quality and type of cement are posite cement is one of new cement type studied by Vietnam Institute for Building Materials (VIBM) and Japanese partners. The content of clinker in the composite cement is from 20% to 60%. The composite cement has high resistibility in aggressive conditions such as sulfate and marine water. Beside creation of new cement product with high sulfate and marine resistance, this kind of cement using of high industry waste content, therefore contributes for decreasing emission of CO2 in cement manufacture.

Key words: Composite cement, GGBFS, FA, sulfate resistant.

1. Overview of Vietnam cement industry

Vietnam is an ASEAN country with area about 330,951 km2 and population about 90 million people. In period from 2000 to 2010, the economic growing rate reached 7% annually. The demand of building materials including cement has been increasing fast. The domestic cement demand is showed in 1 table.

Table.1 The cement consumption in Vietnam from 2000 – 2013.

Year	2000	2002	2004	2006	2008	2010	2012	2013
Cement consumption, (million Ton)	13.9	20.6	26.5	32.9	40.2	51.5	45.5	47.1

The first cement sharp kilns were built in 1899 and the first rotary kiln with wet technology from FL. Smidth was built in 1932. In 1981, Vietnam started operating first rotary kiln with five-stage preheaters without calciner and its capacity of 3300 tons of clinker per day using dry technology provided by FL. Smidth. Nowadays, total cement design capacity of Vietnam has reached more than 70 million tons and it would be more than 80 million tons in 2015 [1]. More than 95% of cement production lines of Vietnam is rotary kiln with five-stage preheaters, calciner and grate cooler. Together with increasing of production, quality and type of cement are increasing. The strength activity of clinker of Vietnam cement factories is average from 45 – 55 MPa, at some of cement factories it reaches 60 MPa. The main cement types in Vietnam are: Portland blended cement PCB 40, PCB 30 (PCB30 is decreasing percentage); ordinary Portland cement (similar Type I in according to ASTM C150); sulfate resistant cement and low heat Portland cement (similar Types V, Type II, Type IV in according to ASTM C150 and BS 4027); sulfate resistance Blended Portland Cement and low heat Blended Portland cements (similar these cements by ASTM C959, ASTM C1157); white Portland cement; masonry cement; oil well cement class G according to API spec.10 A. Beside the standards for common cement products, there are standards for special products such as: Alumina cement, granulated blast furnace slag (GBFS) for cement production, Portland blast furnace slag cement, composite cements,… In general, Vietnam government promulgated national standard system meeting actually demand of manufacturers and users.

2. Research on manufacturing composite cement.

2.1 The goal of the research

Research on manufacturing composite cement was carried out via researching collaboration among VIBM and Japanese partners namely Taiheyo cement corporation, Tetsugen corporation. The goal of the research is: Use of Portland cement clinker and some of other mineral additives such as GBFS, fly ash (FA), lime stone for making composite cement possessing characteristics like general cement but improving in sulfate and marine water resistance.

2.2 Background theory

Category and mechanism of sulfate attack on concrete shown in Table 2.

Table 2. Category and Mechanism of sulfate attack on concrete [2].

Category of sulfate attack	Reaction with SO2-4
Sulfate attack	Chemical sulfate attack	External sulfate attack	(a) Enttringite formation
Ca(OH)2 , H2O, SO2-4 Monosunphat ---> ettingite C-A-H
(b) Gypsum formation H2O, SO2-4 Ca(OH)2 ------> CaSO4.2H2O C-H
(c) Thaumasite formation
CO3, H2O, SO2-4 C-S-H ------> CaSiO3.CaCO3.CaSO4.15H2O
Internal sulfate attack	(d) Delayed ettringite fromation
Ca(OH)2 , H2O, SO2-4 Monosunphat ---> ettingite C-A-H
Physical sulfate attack	(e) Salt crystallization
H2O Na2SO4 <---> Na2SO4 .10H2O

Physical sulfate attack on concrete is not only caused by chemical reaction between SO42- and cement paste components but also by salt crystallization of SO42-- bearing salts in concrete pores.

Thernardite (Na2SO4) and mirabilite (Na2SO4.10H2O) are known as substance causing physical sulfate attack (BRE, 2005).

This crystallization salt in the pores of harden cement to creates stress to excess ability of withstanding hardened cement beyond concrete cracking. Stress of the salt crystallization can reach values ​​as follows: for Na2SO4 reaches 4.4 MPa; for MgSO4 reaches 36 MPa; of NaCl reaches 2.7 MPa. These salts can be crystallized in the pores of hardened cement if the concentration of dissolved salts, Na2SO4, MgSO4, NaCl reaches over 1% in soil or water containing these salts at higher concentrations and degrees from 3g/L relative humidity of air greater than 30% [3].

When moisture in the environment increases, the water occurs in the cement pores, then Na2SO4 and MgSO4 salts will absorb water and form Na2SO4.10H2O MgSO4.7H2O that may increase volume of salt crystallization from 1.3 to 3 times to give rise tensile stress to MPa dozens to cause deformation and destruction of concrete [3].

2Na+ + SO42- 　　　→ 　　　Na2SO4.10H2O

　　　　　　　　(solution) (evaporation) (crystallization)

This process generates expansive forces that result in a subsequent disruption of the concrete. The disruption may be accelerated by wetting and drying cycles that lead to thernardite - to-mirabilite recrystallization, which causes repeated expansive damage in the pore of concrete:

Na2SO4.10H2O 　　　 Na2SO4

(repeated recrystallization)

In marine water, chloride is dangerous agent for cement concrete. Chloride (Cl–) is a common anion in soil and groundwater, in most cases being associated with sodium (sodium chloride, NaCl, is common salt). However, the levels of chloride found in the ground are generally chemically innocuous; indeed, they may be beneficial since there is considerable evidence, from seawater studies as the reaction mechanism forming binder C3A. CaCl2, that the presence of chloride generally reduces sulfate attack in concrete.

The concrete exposes in dry - moist environment containing sulfate and dissolved chloride originating in the ground can lead to degradation of concrete through a physical mechanism involving crystallization of chloride salts near to the surface of the concrete. The salt crystallization into the pores of the concrete surface to create it as breaking stress of concrete surface due to salt deposition. This process can be increased by repeated cycles moist - dry on the surface of the concrete, leading to the formation of insoluble precipitate salt and cyclical, creating stresses in the concrete. On the other hand the original crystal salt occurs at high temperatures forming anhydrous salt, due to changes in moisture, from anhydrous salt will turned into hydrated salt to increase volume. The risk of corrosion of embedded metals in buried concrete in non-aggressive soil is generally lower than in externally exposed concrete. However, high chloride concentrations in the ground will increase the risk of corrosion since chloride ions may migrate into the concrete and lead to a reduction in passivity at the metal surface.

To decrease of sulfate and marine attack on concrete: Minimize amount of late ettringite, gypsum content, Portlandite; decrease of water cement ratio; improve density of concrete and concrete posite cement is overall solution for durability improvement of concrete in sulfate and marine water environment.

2.3 Materials and Mix proportions.

Materials used in the study including: Clinker and lime stone from Nghison cement factory (Nghison cement factory is Vietnamese – Japanese Joint venture factory); ground granulated blast-furnace slag (GGBFS) from Japan; fly ash (FA) from Phalai thermo-power station; gypsum from Laos.

The chemical compositions of the materials used in study are showed in Table 3.

Table 3. Chemical compositions of the materials

Materials	Content, %
SiO2	Al2O3	Fe2O3	CaO	MgO	SO3	R2O	LOI
Lime stone	0.77	0.39	0.27	53.82	0.80	0.00	0.00	43.08
Fly ash	55.14	26.63	6.86	0.60	0.97	0.05	3.08	0.94
GGBFS	32.05	14.28	0.22	42.98	7.66	1.47	0.45	-
Gypsum	2.00	0.36	0.05	32.16	0.50	42.60	0.03	21.84
Clinker	22.09	5.10	3.51	63.64	1.90	0.19	0.82	1.81

The fineness of the materials are: Lime stone – 4500 cm2/g; ground clinker and gypsum – 3100 cm2/g; GGBFS – 4000 cm2/g.