The calcium hydroxide (CH) produced by the cement hydration reaction and the gypsum in the cement will serve as an activator to stimulate volcanic ash materials (such as fly ash) or mineral admixtures with potential hydraulic activity (such as ground slag powder) to participate in the hydration reaction, forming hydraulic hydration products that gradually compact the microstructure of the concrete with age and improve the later strength growth rate.

Chemical erosion and physical erosion of environmental medium on concrete structure are related to cement hydration products
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The hydration products of cement, especially hydrated calcium silicate (C-S-H), endow the cement slurry with cementitious properties.

Compared to the particle size of coarse and fine aggregates, cement (including mineral admixtures) has the smallest particle size, so the cement slurry (or cementitious material slurry) also has a filling gap effect, which further compacts the concrete.

Concrete Technology Exchange Group 2.

Firstly, analyze the positive and negative effects of Portland cement in concrete: 1.

Therefore, the volume stability of concrete materials determines the durability of their structure.

The smaller the amount of cement used, the lower the early strength of cement mixed with slag powder.

During its setting and hardening process, the aggregate is cemented into a whole, giving strength to the hardened concrete.

However, the addition of fly ash increases the water cement ratio (the ratio of water to cement content), which can promote the hydration rate of cement and improve its hydration degree.

The self shrinkage generated by cement hydration will make concrete structures prone to cracking when the water cement ratio is small, especially in high-strength concrete.

Compared to cement, the early hydration rate is lower.

However, the rate of mineral admixtures participating in the reaction is very slow, such as fly ash, which hardly participates in the reaction at room temperature.

Negative Effects: Cement hydration releases heat, causing temperature rise and temperature gradient in concrete.

Positive effect: cement and water, and if necessary, chemical admixtures are added to form a cement slurry, which endows the fresh concrete with fluidity and cohesiveness, making it constructable.

The volume of aggregates in concrete is stable, while the volume of cement slurry is unstable and varies with changes in environmental temperature, humidity, and time.

Early temperature rise and temperature gradient in concrete increase the risk of cracking of concrete structures under constraint conditions when the early creep and tensile strength of concrete are small.

Slag is a material with potential hydraulic hardness, and the finer it is ground, the greater its chemical activity; For the current commercially available slag powder (with a specific surface area of 400m2/kg to 450m2/kg), it participates in hydration earlier than fly ash, but also requires cement to stimulate it.

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