Concrete is currently the most widely used building material in the world. Over 95% of cement produced and used today is portland cement. However, the production of portland cement consumes large amounts of resources and energy and emits considerable amounts of dust and waste gasses (such as CO₂ and SO₂), adding to environmental pressures. Furthermore, portland cement has certain limitations when used in high-performance concrete. Therefore, people have started exploring the use of mineral admixtures to produce a new kind of binding material to replace portland cement.

Compared to ordinary cement, geopolymers show superior mechanical properties and durability. Furthermore, geopolymers have numerous advantages in raw material sources, energy consumption, performance, and durability. They can be regarded as a “green, environmentally friendly” cement, expected to become a key ecological building material in the 21st-century.

Using a planetary countercurrent concrete mixer, the raw materials can be uniformly blended under high shear conditions, which helps activate their reactive components more effectively.

1.Definition

 (1) A geopolymer is a material made from aluminosilicate compounds of natural or artificial origin under alkaline conditions through geopolymerization, yielding a cement-like material with high strength, stability, and durability.
 (2) A geopolymer is a new alkali-activated binding material different from ordinary portland cement. Compared to portland cement, it utilizes abundant raw materials, has lower energy consumption, emits nearly no waste, and avoids consuming limestone resources, making it a green building material.
 (3) From a production perspective, geopolymers are made by chemically reacting aluminosilicate raw materials (such as metakaolin or fly ash) with an alkaline activator; this reaction produces a material chemically analogous to some volcanic ashes.
 (4) From a structural standpoint, geopolymers form a new class of materials with a 3D aluminosilicate network.
 (5) From a bond perspective, geopolymers consist of a network of covalent bonds predominantly formed by silicon and aluminum.

2.Structure

The main structure of a geopolymer is an amorphous to semi-crystalline 3D aluminosilicate framework. It consists of silicon-oxygen tetrahedrons and aluminum-oxygen tetrahedrons.

Using a planetary countercurrent concrete mixer during production helps uniformly disperse and activate these components, yielding a more homogenous 3D network structure.

Schematic Diagram of Geopolymer Structure

1.Main raw materials

(1) Metakaolin, produced by proper thermal treatment of kaolin clay.
(2) Industrial by-products rich in aluminosilicate, such as blast furnace slag, fly ash, phosphogypsum, and clay waste.
(3) Feldspar-tailings, chemically analogous to metakaolin but with a small amount of calcium.

(4) Alkaline activator, typically sodium or potassium hydroxide, water glass, or potassium silicate.
(5) Setting modifiers, weak calcium silicate, silica fume, and admixtures (such as retarders).

2.Preparation process

(1) If metakaolin is the raw material, first activate it by thermal treatment at about 850°C. The high-temperature shock converts it into a reactive form.
(2) The raw material is then blended in a planetary countercurrent concrete mixer with an alkaline activator and water. Water glass is frequently used; its modulus, concentration, and curing conditions affect final properties.
(3) After adding water and the alkaline solution, the mixture is vigorously blended, poured into molds, compacted by vibration, and then demolded and cured.
(4) If fly ash is the raw material, the procedure is analogous.

Summary: The main procedure comprises (1) raw material preprocessing, (2) alkaline solution preparation and dosing, (3) mixing in a planetary countercurrent concrete mixer, (4) casting and vibration compaction, and (5) demolding and curing.

3.Polymerization Mechanism

The geopolymerization process comprises:
(1) dissolution of aluminosilicate materials under alkaline conditions;
(2) diffusion of dissolved species into pores;

(3) formation of a gel-phase through poly-condensation;
(4) gradual hardening into a monolithic material.
Using a planetary countercurrent concrete mixer during this process guarantees a uniform mixture and more complete reaction.

1.Physical properties

(1) Low shrinkage and expansion coefficients;
(2) Excellent high-temperature resistance;
(3) Higher compressive, bending, and shear strength than ordinary portland cement;
(4) Durable and chemically stable in aggressive conditions.
Using a planetary countercurrent concrete mixer assists in developing a dense and homogenous structure, which directly contributes to these desirable properties.

2.Chemical properties

(1) Ability to encapsulate heavy metal ions;
(2) Fast setting and hardening;
(3) Exceptionally strong acid resistance;
(4) Higher degree of polymerization and oxidation resistance.

3.Advantages

(1) Lower energy consumption during production;
(2) Availability of abundant and cheaper raw materials;
(3) Durable, chemically inert, and environmentally friendly;
(4) Less shrinkage, greater dimensional stability.

1.Infrastructure and Construction:
Geopolymer is used to repair and reinforce buildings and bridges, adding resistance to earthquakes and hurricanes. Continuous-fiber geopolymer composite materials are currently used in many regions for structural strengthening.

2. Aviation Applications:
Geopolymer materials, with their lightweight and thermal resistance, have been used for aircraft components, such as cabin panels and seats.
Using a planetary countercurrent concrete mixer during production guarantees uniform material properties desirable for this application.

3. Automotive Applications:
In 1994-95, the Benetton F1 team successfully applied geopolymer composite materials to their F1 car's components — a breakthrough in lightweight, high-temperature resistance, and mechanical stability.

4. Non-ferrous Casting and Metallurgy:
Because geopolymers can retain their structural stability at temperatures of 1000°C–1200°C, they find applications in non-ferrous casting and metallurgy.

5. Civil Construction:
Geopolymers harden quickly and develop strength rapidly — typically within 4 hours — making them ideal for repairs and fast track projects in highway, airport, and railway industries.

6. Traffic and Repair Applications:
For highway or airport repairs, a planetary countercurrent concrete mixer can produce a fast-setting mixture. Within 1 hour the material can be walked upon; after 6 hours, it can carry aircraft.

7. Nuclear and Hazardous Waste Disposal:
Geopolymers form a cage-like structure that safely encapsulates heavy metal ions and nuclear waste, preventing their release into the environment.

8. Artistic and Decorative Applications:
Geopolymer materials can be processed to resemble natural stone, making them desirable for architectural and ornamental components.

9. Storage Facilities:
Using geopolymer materials to construct grain storage silos provides natural temperature and humidity control and resistance to pests.