Concrete alkali aggregate, what is the alkali aggregate reaction of concrete? What harm does it do t

Concrete alkali aggregate refers to the alkali activity of sand and gravel. It is divided into three types of aggregates (aggregates) with non-alkali activity, low alkali activity and alkali activity. It has nothing to do with raw materials such as cement and admixtures, but cement and admixtures themselves have corresponding alkali content, and they affect the total amount of alkali in concrete.

Alkali-aggregate reaction (AAR) refers to the chemical reaction between alkali (K2O, Na2O) in concrete and active aggregate. There are two main types of alkali aggregate reactions: alkali-silicic acid reaction (ASR) and alkali-carbonate reaction (ACR), among which alkali-silicic acid reaction is more prevalent.

The result of the alkali aggregate reaction is not to raise and improve the structure of the concrete, but to produce expansion stress in the concrete, which causes concrete cracking or concrete structure failure after a certain extent. Alkali aggregate reaction is one of the important durability indicators of concrete, because of the slow reaction process, the influencing factors are very complex, the time to cause concrete cracking is difficult and once the damage is almost impossible to repair, etc., it is known as the "cancer" of concrete.

Measures to prevent and inhibit alkali aggregate reactions include two categories: physical measures and chemical measures, including;

1) Use non-reactive aggregates.

2) Use low-alkali cement.

3) Limit the total alkali content of concrete.

4) Use mineral admixtures. Mineral admixtures commonly used are silica fume, slag, fly ash and zeolite powder.

5) Surface treatment. Coating on the surface of concrete to prevent the penetration of external media, especially water and erosion media, into the concrete can effectively prevent the alkali aggregate reaction of concrete.

6) Use chemical admixtures. Salts containing alkali metal lithium such as lithium nitrate, lithium hydroxide and sodium fluorosilicate, phosphate, and some nitrates have a certain inhibitory effect on the reaction of alkali aggregates.

Concrete alkali aggregate reaction. It refers to the further chemical reaction between the specific internal components in the aggregate and the alkaline substances in the cement, admixtures, admixtures, etc. in the concrete under certain conditions.

The harm to concrete is mainly to cause the concrete structure to expand, crack and even break; It will cause the concrete structure to collapse and is one of the important factors affecting the durability of concrete.

I hope the above content will be helpful to you.

Alkali aggregate reaction refers to the chemical reaction with the silica contained in the aggregate when the alkaline oxide content in the cement is high, and the alkali-silicate gel is formed on the surface of the aggregate, which will produce a large volume expansion after water absorption, resulting in the expansion and cracking of concrete.

The harm caused by the alkali aggregate reaction to the concrete project is quite serious, the concrete expands and cracks from the inside, and finally loses its strength.

The alkali-aggregate reaction (AAR) condition is formed during the preparation of concrete, that is, there is only enough alkali and reactive aggregate in the prepared concrete.

After the concrete is poured, it will gradually react, and when the number of reaction products absorbs water and expands and the internal stress is enough to crack the concrete, cracks will begin to appear in the project. This crack and damage to the project develops with the development of the alkali aggregate reaction, and in severe cases, the project collapses.

The alkali metal-containing lime saturated solution, sodium oxide, potassium oxide and other alkaline solutions in the pores of the concrete react with the reactive silica in the aggregate to form an alkali-silicate gel, and in the presence of enough water, the gel absorbs water and expands to cause cracks in the concrete, which may eventually lead to the complete destruction of the concrete. This phenomenon is called alkali aggregate reaction.

Alkali aggregate reaction, also known as alkali-silicon reaction, refers to the chemical reaction between the alkaline substances in the concrete and the active ingredients in the aggregate, causing the cracking of the concrete due to self-expansion stress. The harm brought by alkali aggregate reaction to concrete engineering is quite serious. Because the reaction time of alkali aggregate is relatively slow, it can be found in a few years or decades.

Alkali active aggregate refers to the aggregate that will chemically react with the alkali substances in the cement, admixtures, admixtures, etc. in the concrete under certain conditions, resulting in the expansion, cracking and even destruction of the concrete structure.

Alkali silicic acid reaction: Li Yan Sun.

The alkali-silicic acid reaction is the reaction of the alkali in the cement and the active silica component in the aggregate to produce the alkali-silicate gel, which has strong water absorption, and the expansion after water absorption causes the expansion stress of concrete.

After alkali silica gel absorbs water, it promotes the development of alkali aggregate reaction, which leads to concrete cracking, and serious development will cause the collapse of concrete structure.

Alkali carbonate reaction.

The mechanism of alkali carbonate reaction is completely different from that of alkali carbonic acid reaction, when alkali reacts with this calcium carbonate magnesium, the dolomite is converted into brucite, and the brucite crystal is discharged into Xiangling column pressure and the clay absorbs water to expand, causing internal stress in the concrete, which leads to concrete cracking.

The cement alkali-active aggregate swelling reaction is referred to as the "alkali-aggregate reaction".It is a phenomenon in which the alkali in the cement reacts with the silicon oxide in the active aggregate to form sodium silicate and absorbs water from the surrounding medium and expands. It is necessary to have three types of soak conditions at the same time before the alkali-aggregate reaction phenomenon can occur

1. The alkali content in cement (Na2O exceeds a certain value, and the current relevant regulations of various countries are mostly stipulated;

2. The content of active aggregates (opal, chalcedony, lemosmosis and cristobalite quartz, etc., which has been determined so far) exceeds a certain value, and the current relevant specifications of various countries are mostly stipulated to be 1%;

3. Sufficient water, such as for leaky hydraulic engineering or port concrete.

However, if all three conditions are met, expansion will not necessarily occur, and a mortar or concrete test must be performed to determine whether there is expansion cracking.

The process of alkali-aggregate reaction is: after the concrete is mixed with water, the alkali in the cement is continuously dissolved, and the calcium aluminate and calcium silicate in the cement slurry absorb water, so that the concentration of alkali increases, and the silica in the active aggregate acts with the silicon dioxide in the active aggregate to generate sodium silicate during the curing period after coagulation. The reaction formula is as follows:

h2o2naoh＋sio2→na2sio3＋h2o

For example, the 2 in h2o should be a subscript, but I know that I can't get it, so I am suspicious! If you need to know the characteristics, they can also tell you. Because of handwriting! Troublesome!

The alkali aggregate reaction of concrete mainly refers to the chemical reaction between the active ingredient in the aggregate and the cement, which causes the volume expansion of the concrete and the destruction due to self-stress. The main apparent phenomenon is the slow occurrence of map-like cracking of the concrete as a whole, until it fails. There are six test methods to determine the alkali activity of aggregate parent rock, including petrographic method, chemical method, mortar rod rapid method, and mortar length method.

Concrete light aggregates include: foam concrete aggregates, algae aggregates, etc.

1. Foam concrete aggregate Zhengjialan: It is made of foam agent mixed with cement, sand and other aggregates, and has the characteristics of light weight, high strength and good thermal insulation.

2. Algal aggregate: It is made of heat treatment and grinding of algae of water boring plants, which has the characteristics of low density, large volume, good water absorption and high heat insulation.

Concrete light aggregate has different characteristics and scope of application, and the selection of light aggregate of Xiangshout Huying variety can meet different engineering or product needs.

Alkali-aggregate reaction (AAR) refers to the further chemical reaction between specific internal components in aggregate and alkaline substances in cement, admixtures, admixtures, etc. in concrete under certain conditions, resulting in expansion, cracking and even destruction of concrete structures, which will seriously collapse the concrete structure and is one of the important factors affecting the durability of concrete; Concrete alkali aggregate reaction can be divided into alkali silicate reaction and alkali carbonate reaction according to the reaction mechanism

Definition of alkali aggregate reaction refers to the chemical reaction with the silica contained in the aggregate when the alkaline oxide content in the cement is high, and the alkali-silicate gel is generated on the surface of the aggregate, which will produce a large volume expansion after water absorption, resulting in the expansion and cracking of concrete.

The alkali metal-containing lime saturated solution, sodium oxide, potassium oxide and other alkaline solutions in the pores of the concrete react with the reactive silica in the aggregate to form an alkali-silicate gel, and in the presence of enough water, the gel absorbs water and expands to cause cracks in the concrete, which may eventually lead to the complete destruction of the concrete. This phenomenon is called alkali aggregate reaction.

The alkali metal-containing lime saturated solution, sodium oxide, potassium oxide and other alkaline solutions in the pores of the concrete react with the reactive silica in the aggregate to form an alkali-silicate gel, and in the presence of enough water, the gel absorbs water and expands to cause cracks in the concrete, which may eventually lead to the complete destruction of the concrete. This phenomenon is called alkali aggregate reaction.