Any finely ground material (powdered), after adding an appropriate amount of water, becomes a plastic slurry, which can harden in the air and harden in water, and can firmly cement the sand, stone and other materials together. Material, commonly known as cement.

Classification of cement:

There are many types of cement. According to its use and performance, it can be divided into: general cement, special cement and characteristic cement.

General cement such as Portland cement, ordinary Portland cement, slag Portland cement, pozzolanic Portland cement, fly ash Portland cement, etc.;

Special cements such as oil well cement, masonry cement, etc.;

Characteristic cements such as fast hard Portland cement, low heat slag Portland cement, expanded sulphoaluminate, etc. At present, there are more than 100 kinds of cement varieties.

Chemical composition, characteristics and effects of cement components

Cement clinker

The raw material of the appropriate component is burned to a partial melting, and the product obtained by using calcium silicate as a main component is obtained.

(1) Cement clinker composition

Oxide composition

CaO, SiO2, Al2O3, Fe2O3 ~95%

MgO, SO3, TiO2, P2O5, K2O and Na2O, etc. ~5%

The main oxide content fluctuation range:

CaO 62~67%;

SiO2 20~24%;

Al2O3 4~7%;

Fe2O3 2.5~6.0%.

Mineral composition

After calcination at a high temperature, two or more kinds of oxides are reacted to form a plurality of mineral aggregates, and the crystals are fine (30 to 60 μm).

Four main minerals:

Tricalcium silicate 3CaO·SiO2, which can be abbreviated as C3S;

Dicalcium silicate 2CaO·SiO2, which can be abbreviated as C2S;

Tricalcium aluminate 3CaO·Al2O3, abbreviated as C3A;

The iron phase solid solution 4CaO·Al 2 O 3 ·Fe 2 O 3 is a representative formula and can be abbreviated as C4AF.

In addition, it also contains a small amount of free calcium oxide (f-CaO), periclase (crystalline magnesium oxide), alkali-containing minerals, and glass bodies.

Calculation of mineral composition

Bogue method:

C3S=4.07C-7.60S-6.72A-1.43F-2.86SO3;

C2S=8.60S+5.07A+1.07F+2.15SO3-3.07C=2.87S-0.754C3S;

C3A=2.65A-1.69F;

C4AF=3.04F;

CaSO4=1.70SO3

Wherein C - CaO; S - SiO2; A - Al2O3; F - Fe2O3 percentage.

plaster

Natural or industrial by-product gypsum (CaSO4, CaSO4·2H2O)

Function: adjust the setting time, improve the early strength, reduce the shrinkage deformation, improve the durability, impermeability and other properties, and activate the mixed material.

Dosage: According to the content of C3A and the amount of mixed materials, the SO3 content in cement is too small as the control index of gypsum content. It can not properly adjust the normal setting time of cement. It will form hydrous aluminate with calcium aluminate. Calcium, the volume will increase when crystallizing, resulting in poor cement volume stability.

Active mixed material

The active mixed material means that it does not react with water itself, and after the activator is added, the reaction occurs under the action of the activator and water to produce strength.

Alkaline activator: CaO, Ca(OH)2, NaOH, KOH, etc.

Sulfate activator: CaSO4, etc.

Admixture: water reducing agent, quick-setting agent, expansion agent, etc.

Definition: Mixing materials with cement, lime and gypsum after grinding, and adding water to harden in water and in air is called active mixture.

Granulated blast furnace slag: The molten slag of ironmaking blast furnace is formed by water quenching and quenching. The phase composition is mostly vitreous, which has high chemical potential and is hydraulic under the action of an activator.

Chemical composition: CaO, Al2O3, SiO2 >90%

MgO, MnO, Fe2O3, CaS, FeS, TiO2, etc.

Mass coefficient = (CaO + MgO + Al2O3) / (SiO2 + MnO)

Active slag quality coefficient >1.2, inactive slag quality coefficient <1.2

Activity index of granulated blast furnace slag powder (A)=R/R0×1

Granulated blast furnace slag powder grade (28d A): S105, S95, S75

Volcanic ash mixture

Natural and artificial mineral raw materials with silica and alumina as the main components are not hardened after being ground into fine powder and added with water. However, mixing with lime and adding water can not only harden in the air, but also Those who continue to harden in the water are called volcanic ash mixtures.

Nature: volcanic ash, volcanic tuff, pumice, diatomaceous earth, diatomite, opal, etc.

Artificial: burnt clay, activated siliceous slag, fly ash, burnt shale, etc.

Fly ash

Fine ash collected by electric dust collector of coal-fired power plant

Main chemical composition: SiO2, Al2O3, Fe2O3, CaO

Phase composition: glass body 60~85%; crystalline compound 10~30%; unburned carbon about 5%.

Inactive mixed material

An inactive mixture that is chemically inactive or has little chemical action with the cement component.

Fine quartz sand, limestone, slow cold slag, etc.

Role: increase cement production, reduce hydration heat, reduce cement labeling. No reaction occurs under any circumstances, it can only act as a filler.

Introduction to cement standards

Mandatory standard:

1. National standard (code GB)

2, building materials industry standards (code JC)

Recommended standards:

1. National standard (GB/T)

2. Building materials industry standard (code JC/T)

Enterprise standard: (code: Q)

Cement standard code description

Technical requirements for cement

1. Insoluble matter

Type I Portland cement insolubles do not exceed 0.75%. The insoluble matter in type II Portland cement shall not exceed 1.50%.

2, magnesium oxide

The magnesium oxide content in the cement does not exceed 5.0%. If the cement steam stability test is acceptable, the magnesium oxide content in the cement is allowed to relax to 6.0%.

3. Sulfur trioxide

The SO3 content in cement should not exceed 3.5%.

4, loss on ignition

The loss on ignition in type I Portland cement shall not exceed 3.0%, and the loss on ignition in type II Portland cement shall not exceed 3.5%. The loss of burning in ordinary cement shall not exceed 5.0%.

5, fineness

The specific surface area of Portland cement is more than 300m2/kg, and the remaining 80μm square hole sieve of ordinary cement should not exceed 10.0%.

6, condensation time

The initial setting of Portland cement should not be earlier than 45 minutes, and the final setting should not be later than 390 minutes. The initial setting of ordinary cement shall not be earlier than 45 minutes, and the final setting shall not be later than 10 hours.

7, stability

It is necessary to pass the boiling test.

8, strength

The cement label is divided according to the compressive strength and flexural strength of the specified age. The strength of each grade of cement shall not be lower than the value in Table 1-2-1.

9. Alkali

The alkali content of cement is expressed by the calculated value of Na2O+0.658K2O. If the active aggregate is used, when the user requests low alkali cement, the alkali content of the cement should not exceed 0.60% or agreed by the supplier and the buyer.

Scrap and non-conforming products

1, waste

Any of magnesium oxide, sulfur trioxide, initial setting time, and stability does not meet the requirements of this standard, and is waste.

2, non-conforming products

Any item of fineness, final setting time, insoluble matter and loss on ignition that does not meet the requirements of this standard or when the amount of mixed materials exceeds the limit and the strength is lower than the specifications specified in the product label is called nonconforming product. The cement type, label, factory name and factory number in the cement packaging mark are also inferior.