What kind of cement should be used for special concrete subjected to aggressive media

Magnesia oxycement Slag cement, pozzolana and fly ash cement, which are mixed with minerals, have good resistance to dissolution corrosion and sulfate corrosion. This is because with the addition of minerals, there is less cement clinker, less calcium hydroxide and calcium aluminate hydrate obtained by hydration, and there is better resistance to erosion.

But it does not include carbonization resistance and acidic water attack resistance, because there is less calcium hydroxide, alkalinity is reduced, so acidic substances are more likely to invade, and these abilities are reduced!

Aluminate cement sets and hardens quickly. The strength of 1D can reach more than 80% of the maximum strength, and it is mainly used for projects with urgent construction periods, such as national defense, roads and special emergency repair projects. Aluminate cement has a large heat of hydration and concentrated heat release.

The heat of hydration released within 1 day is 70% to 80% of the total amount, so that the internal temperature of the concrete rises high, and even if the construction is under 10, the aluminate cement can quickly set and harden, which can be used for winter construction projects. Under ordinary hardening conditions, Portland cement has a strong resistance to sulfate corrosion because the cement stone does not contain tricalcium aluminate and calcium hydroxide, and the compactness is large.

However, the long-term strength and other properties of aluminate cement have a tendency to decrease, and the long-term strength is reduced by about 40% 50%, so aluminate cement is not suitable for long-term load-bearing structures and projects in high temperature and high humidity environments, it is only suitable for emergency military engineering (road construction, bridge), emergency repair engineering (leak plugging, etc.), temporary engineering, and the preparation of heat-resistant concrete.

It still depends on the aggressive medium.

This depends on the type of aggressive medium. For example, offshore concrete.

Usually the admixture of cement is selected.

Spraying diagenetic anti-corrosion and impermeable mortar on the outside of concrete can solve the erosion phenomenon.

Answer]: C The test point involved in this question is the selection of commonly used cement. In the concrete bent concrete affected by the erosion medium, it is not suitable to use biky Portland molded cement.

Answer]: b pozzolane cement is suitable for large-volume projects in underground and water; There are projects with anti-Zen seepage requirements; The construction of the steam Yanghe brother's grip; Corrosion-resistant concrete works requiring high dust silver.

Concrete material is a durable material, but it is essentially a non-uniform porous material, under the erosion of carbon dioxide, water, chloride ions, sulfate and other media, it is inevitable to be affected by external factors and corroded, concrete will accelerate the damage, and the service life is greatly shortened.

Crystallization corrosion of salts.

When the concrete comes into contact with water containing a large number of soluble salt compounds, these salt compounds will penetrate into the concrete Concrete porous bricks, after the evaporation of water, the salts continue to concentrate in the concrete, and finally form crystals, and the crystallization process is often accompanied by an increase in volume. As a result, cracking and damage of concrete materials are caused. Typical is sulfate corrosion.

In the use of concrete materials, the most widespread and common form of chemical corrosion is sulfate corrosion. The sulfate reacts with the calcium vanadium stone in the cement to form sulfoaluminate, which is accompanied by an increase in volume, resulting in cracking of the concrete material. This cracking further accelerates the corrosion of the concrete matrix by the sulfate.

Diafiltration and salt frost corrosion.

When moisture can seep out of the concrete surface, salt frost will always appear on the concrete surface. These salts are crystallized by evaporation of concrete, or by interaction with atmospheric carbon dioxide. It shows that obvious percolation occurs inside the concrete, and severe percolation leads to an increase in porosity, which reduces the strength of the concrete layer and increases the effect of corrosive compounds.

Acid and alkali corrosion concrete material is an alkaline material and generally does not suffer from corrosion by alkaline substances. However, in chemical companies, prolonged exposure to high concentrations of alkaline substances can also cause damage to concrete materials. Concrete materials are less resistant to acids.

For example, carbonic acid reacts with calcium hydroxide to form soluble calcium bicarbonate. Therefore, carbon dioxide is more corrosive to concrete, that is, the cause of carbon dioxide in the air to corrode concrete materials.

Rotten answer]: a, c, d

2021 textbook p173

This question examines mixed Zen concrete. When the environment in which the concrete is located contains aggressive media, the concrete will be eroded, usually soft water erosion, sulfate erosion, magnesium salt erosion, carbonic acid erosion, general acid erosion and strong alkali erosion.

Answer]: a, c, d, answer this e

This Qingxiao Xun question examines concrete. When the environment in which the concrete is located contains aggressive media, the concrete will be eroded, usually soft water erosion, sulfate erosion, magnesium salt erosion, carbonic acid erosion, general acid erosion and strong alkali erosion.

Answer]: B Tips: General acids can cause the corrosion of cement mortar and mixed Dongchang concrete, but a few types of acid buckets such as grass trembling acid, tannic acid, tartaric acid, hydrofluoric acid, phosphoric acid can react with Ca(OH)2 to generate insoluble and non-expansive calcium salt, which has no corrosive effect on mortar and concrete.

When there is a sulfate corrosive medium in the environment, () a. should be preferred for concrete negotiation projectsPortland cement.

b.Portland cement.

c.Slag Portland cement.

d.Fast hard silicate water disturbs the residual mud.

Correct answer: c

Answer] :d according to the content of Section 5 of the third chapter of the "Civil Engineering Textbook", item D should be selected.

Analysis] Distinguish the factors that affect the frost resistance, impermeability, and erosion resistance of concrete.