The setting and hardening of slag cement is very slow at the low temperature, so insulation measures should be strengthened in the winter construction. But its strength develops very fast under the condition of heat, thus conserved with vapor.
4 Cement 69
4.2.4 Portland Pozzolana Cement
All the hydraulic hardening binding materials generated by grinding Portland cement clinker, pozzolana blended materials and appropriate amount of gypsum are called Portland pozzolana cement (simply called pozzolana cement), code-named POP. The mixing amount of pozzolana blended materials accounts for 20%-50% of the total mass. The technical requirements for pozzolana cement are the same to those of blast-furnace slag cement.
Pozzolana cement and blast-furnace slag cement have many common grounds in performance (see Table 4.6), such slow hydration, setting and hardening process, low early strength, high growth of the later strength, low heat of hydration, high corrosion, poor frost-resistance, and easy carbonization.
The water demand of pozzolana cement is large. The dry shrinkage is more obvious than blast-furnace slag cement in the process of hardening. And under dry and heat conditions, dry shrinkage happens and the cement cracks. Thus, the conservation should be strengthened in use and it should be kept in the moist state for a long time.
The particles of pozzolana cement are very tiny, and the water segregation is low. Thus, its impermeability is good, favorable for the concrete projects.
4.2.5 Portland Fly-ash Cement
All the hydraulic hardening binding materials generated by grinding Portland cement clinker, blast furnace slag and appropriate amount of gypsum is known as Portland fly-ash cement (simply called fly-ash cement), code-named P.F. The mixing amount of fly-ash cement accounts for 20%-40% of the total mass.
The fineness, setting time, soundness and other technical requirements of fly-ash cement are the same to those of ordinary cement.
The hydration and hardening process of fly-ash cement is basically the same to that of pozzolana cement. And their performances have many similarities.
The main character of fly-ash cement is its little shrinkage, even less than Portland cement and ordinary cement. Therefore, its frost resistance is good.
The water demand of fly-ash cement is little and the concrete mixed by it is
70 Building materials in civil engineering
Compressive Strength (MPa)
workable because its particles are mostly spherical and the water absorption is low.
Bending Strength (MPa)
4.2.6 Composite Portland Cement
All the hydraulic hardening binding materials that are generated by grinding Portland cement clinker, two or more blended materials regulated above, and appropriate amount of gypsum is known as composite Portland cement (simply called composite cement), code-named P'C. The total mixing amount of blended materials in cement should be more than 15% but no more than 50%. Kiln dust under 8% is allowed to replace part of the blended materials;
the mixing amount of blended materials should not overlap the Portland blast furnace slag cement when blended by slag.
In the light of Composite Portland Cement (GB12958-1999), the national standard, the content of magnesium oxide in cement clinker should be no more than 5.0%. If the cement is qualified through autoclave method for soundness, the content of magnesium oxide in clinker is allowed to reach 6.0%. The content of sulfur trioxide in cement should not exceed 3.5%.
The strength of composite Portland cement at each age in various strength grades should not be lower than the values in Table 4.5.
Table 4.5 Strength Values of Composite Cement at Various Ages (GB12958-1999)
32.5R
42.5 16.0 42.5
42.51 21.0 42.5 4.0
52.5 22.0 52.5 4.0 7.0
52.5R 26.0 52.5 5.0 7.0
Note: R-pid strengthening type.
The properties of composite cement have different similarities with slag cement, pozzolana cement, and fly-ash cement, referring to Table 4.6. The selection of common cement can be seen in Table 4.7.
4 Cement 71
Priority Propcrties and Surrounding
Conditions of Concrete Engineering
I 1
Table 4.6 Properties of Common Cement
Available Slan Cement.
Variety
The Concrete i n Dry Conditions Major
Properties
Ordinary Cement Slag Cement
~
Portland Cement
D Very rast Setting md Hardening Bvery High Early Strength 3 v c r y High lleat of I lydration a v c r y Good Frost Resistance 3Very Small Shrinkage o v c r y Pool Corrosion Resistance Dvery Pool I leal Resistance
Ordinary Cement
@ Fast Setting and Hardening
@I ligh Early Strength Heat of Hydration
@Good Frost Resistance
@Little Shrinkage
@Poor Corrosion Resistance
@)Poor Heat Resistance
@I iigh
Slag Cement
3 Slow Setting and Hardening
LOW Early Strcngth, High Later Strength
@Low I Icat of Hydration
@Poor Frost Resistance
@Big Shrinkage
@Good Frosl Rcsistance OGood lleat Resistance
@High Water Segregation
Pozzolana Cement
3 Slow Setting ind Hardening BLOW Early Strength, :ast-growing Later Strength 3 L o w I Icat of I lydration 3Poor Frost Resistance BBig Shrinkage DGood Frost Resistance 3Good Heat Resistance BGood lmpermeahility
Fly-ash Cement
0 Slow Setting and Hardening
@Low Early Strength, Fast-growing L a m Strength
@Low Heat of Hydration
@Poor Frost Resistance
@Small Shrinkage, Good Crack Resistance
@Good Frost Resistance
@)Good I leal Resistance
Ordinary Cement
The Concrete in General Climate
Pozzolana Cement, Fly-ash Cement.
Ordinary Cement
. Com osite Cement
The Concrete in High Ilumidity or in Water for a
+- lleavy Volume The Concrete in
I Slag Cement,
Pozzolana Cement, Fly-ash Cemcnt, Composite Cement Slag Cement, Pozzolana Cement, Fly-ash Cemcnt, Composite Cement
Ordinary Cement
Composite Cement
They are related to varieties and mixing amounts of the two or more blended materials.
And its Properties are basically the same to those of slag cement.
pozzolana cement, and fly-ash cement.
Inadvisable
Pozzolana C e m e n t , Fly-ash Cement
Portland Cement
72 Building materials in civil engineering
Priority
Portland Cement
Properties and Surrounding Available
Ordinary Cement Conditions
The Concrete with Special Requirem- ents
I
4
5
Concrctc Engineering The Concrete Requiring Fast Hardening Rate and High Strength (X60) The Concrete in Cold and Open-air Area, or in the Changing Water lleight in Cold Area The Concrete in the Changing Water lleight in Cold Area The Concrete Requiring Good Frost Resistance The Concrete Requiring Wear Resistance
Ordinary Cement
Ordinary Cement (Strength Grade>42.5)
Slag Cement (Strength Grade>32.5)
Portland Cement, Ordinary Cemeqt Ordinary Cement, Po7zolana Cement
Slag Cement (Strength Grade>32.5)
6 Pozzolana Cement,
Fly-ash Cement, The Concrete
Affccted by Corrosive Media
:ontinued Inadvisable
~
Slag Cemcnt, Pozzolana Cemcnt, Fly-ash Cement, Composite Cement Pozzolana Cement, Fly-ash Cemcnt Slag Ccment, Pozzolana Ccment, Fly-ash Cement, Composite Cement Slag Cement Pozzolana Cemcnt, Fly-ash Cemcnt Portland Cement
4.3 Other Varieties of Cement
4.3.1 Numinous Cement
Alumina bauxite and lime stone-the main raw materials-and the clinker whose main component is calcium aluminate after calcination are ground into hydraulic hardening material, belonging to aluminate cement, of which the code name is CA. A limited amount of a- A1203 powder can be added when the cement whose A1203 content is over 68% is ground based on the specific needs.
Aluminate cement can be divided into four categories by its A1203 content:
CA-60 60% d A1203 <68%;
CA-50 50% d A1203 <60%;
4 Cement 73 CA-70 68% d A1203 €77%;
CA-80 77% d A1203.
According to Aluminate Cement (GB20 1 -2000), the national standard, the aluminate cement requirements are as follows:
1. Chemical Composition
The chemical composition of aluminate cement should be consistent with the requirements in Table 4.8, calculated by the mass percentage.
Table 4.8 The Chemical Composition ofAluminate Cement (“41)
G0.40 GO.1
CA-RO
1) Producers should provide the results and test methods when users need.
CI!’
G0.l