Inorganic cementing materialbuilding materialIn the process of physicsChemical action, or after mixing with other substances (such as water, etc.) through a series of physical and chemical actions, the slurry can become hardsolidAnd can cement granular materials (such as sand, stone, etc.) or block, sheet materials (such as brick, stone, etc.) into a whole, calledCementitious material。
China also has a long history in using inorganic cementitious materials.As early as the Zhou Dynasty, the tombs of emperors were built with lime.From the Zhou Dynasty to the Southern and Northern Dynasties, people used a mixture of lime, loess and fine sandRammed earth wallOr plastering of adobe walls, or making floors of houses and tombs.During the Ming and Qing Dynasties,Triassic soilThe use and development of lime make it more widely used.Lime in ChinaArchitectureIt also occupies a certain position.In addition, in Chinese ancient buildings, lime and some organics are commonly used to prepare composite cementitious materials, which has achieved good results.According to historical records, during the construction of Hezhou City in the sixth year of Qiandao in the Southern Song Dynasty (1170), the mixture of glutinous rice juice and lime was used as the cementing material;An important part of the brick city wall of Nanjing City, built in the Ming Dynasty, is to use lime and glutinous rice juice as groutingMaterial Science。Ming《Tiangong Kaiwu》In the book, there are more detailed records about glutinous rice juice lime.In addition, in ancient buildings, blood - lime andtung oil- Lime, etc., commonly used[1]doputty 。
history
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In the early human construction activities, lime and gypsum were the first cementitious materials used.EgyptOld Kingdom(circa 3000 BC)Great Pyramid, it's plastermortarIt is built with cemented stones and slabs.The Greeks used lime in the 8th century BC.For RomansLime mortarAs wallMasonry materials。The ancient Greeks andAncient RomansutilizeashAdd lime to make mortar, and the structures built with it are solid and durable.This cementing material has been used for a long period of time, until Roman cement andPortland cementIt was gradually replaced when it came out.At the beginning of the 20th century, with the development of modern civil engineering, cementitious materials such as gypsum, lime and Portland cement can no longer meet the needs of special projects, and new cementitious materials must be developed and researched.On the one hand, by adjusting the mineral composition of Portland cement, a large class of special cements with special properties are obtained, such asQuick hardening cement, low and medium heat cementsulphate-resistant cement 、Oil well cement、Expansive cement、White cementColor cement, antibacterial cement, etc.On the other hand, special cements of aluminate, sulphoaluminate and fluoroaluminate systems, such as quick hardening cementMolding sand cement、Refractory cement、Radiation proof cementAnd anti algae cement, etc.In addition, phosphate, sodium silicate, magnesium and sulfurair-hardening binding material Research and success.The emergence of a large number of new inorganic cementitious materials promotes the development of civil engineering[2]。
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1. Cementitious materials can be divided intoOrganic cementing material(such as asphalt, resin, etc.) and inorganic cementing materials (such as lime, cement, etc.).
Pneumatic cementing materials can only be hardened in air, and their strength can only be maintained or developed in air, such as gypsum, lime, etc;Hydraulic cementitious materials can not only harden in air but also in water to maintain and develop their strength[3], such ascement。
development
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In modern civil engineering, cement andconcreteThe application scope ofImpact strengthLow,ImpermeabilityAnd poor corrosion resistance.In order to improve the performance of cement and concrete, polymer cement andPolymer concreteAnd other modern composite materials.Inorganic cementitious materials used in civil engineering are of great importance for their variety, large amount and wide applicationCivil construction materials。According to the needs of the development of modern civil engineering, the development trend of inorganic cementitious materials will be to continuously develop and research new varieties with multi-function, low energy consumption, durability and good quality and low price on the basis of improving the old varieties.Both inorganic cementitious materials andOrganic cementing materialCombination of advantagesGellingMaterials will also be an important development direction[3]。
Quicklime (lump ash) cannot be directly used in the project, and needs to be cured before use.Quicklime (CaO) reacts with water to formcalcium hydroxideCa(OH)two（Hydrated lime, also known asSlaked lime）The process of slaking or digestion (digestion) of lime.During the lime curing process, a lot of heat will be released, and the volume will increase by 1~2.5 times.Lime can be cured intoSlaked lime powderorLime cream。
threeWater resistancePoor.Lime should not be used in humid environment, nor should it be used alone for building foundation.
4. Large volume shrinkage during hardening.In addition to mixing into lime milk for painting, it should not be used alone, and sandPaper bar、Hemp knifeAnd other materials to reduce shrinkage and save lime.
fivequick limeHygroscopicityStrong.Quicklime should not only be protected from moisture, but also should not be stored for too long[2]。
Gypsum
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GypsumGellingMaterial is a kind ofcalcium sulfate（CaSO4）It is the main component of pneumatic inorganic cementing material.The main varieties areArchitectural plasterHigh strength gypsumPlastering gypsum、AnhydriteCement, high temperaturecalcinationGypsum, etc.Wherein, semi hydrated gypsum (CaSOfour·1/2HtwoO) Building gypsum andHigh strength gypsumIt is widely used in construction engineering, and the most commonly used is building gypsum.
Architectural plasterIt is based on β - type hemihydrate gypsum β - CaSOfour·1/2HtwoO) As the main component, the powder cement without any admixture is mainly used to make gypsum building products.Building gypsum is white in color, with little impurities and fine particle size. It is also called type gypsum, and is also the main raw material for making decorative products.Because the building gypsum particles are fine,Specific surface areaLarge, so the water demand during mixing is large, so the strength is low[2]。
Technical properties of building gypsum
1. Rapid setting and hardening.Initial setting andFinal setting timeBoth are very short. Generally, the initial setting time is a few minutes to more than ten minutes, and the final setting time is within half an hour, about a week.To meet the construction requirements, it is necessary to addRetarder, such as boraxPotassium sodium tartrate, citric acidPolyvinyl alcoholLime activationBone glueOr leather glue, etc.
2. The volume expands slightly when hardening.When setting and hardening, gypsum paste does not shrink like lime and cement, but expands slightly (the expansion rate is about 1%), making the surface of gypsum hardened body smooth and full, which can produce fine texture relief decoration.
4. Good fireproof performance.In case of fire,Dihydrate gypsumWill come outCrystal waterIt can absorb heat and evaporate, and form steam curtain and dehydrated material insulation layer on the surface of the product, which can effectively reduce the harm of flame to the internal structure.Architectural plasterThe product will be damaged when it is fireproof, and the gypsum product should not be used for a long time near the high temperature of 65 ℃ or above, so as to prevent the dihydrate gypsum from losing its crystal water at this temperature, thus losing its strength.
fiveWater resistanceandFrost resistancePoor.Architectural gypsumHygroscopicityStrong, absorbed moisture will weaken gypsumgrainThe strength is significantly reduced by the binding force between;If it is immersed in water for a long time, the gypsum products will be damaged due to the gradual dissolution of dihydrate gypsum crystals. After being saturated with water, the gypsum products will be frozen, and will be damaged due to the expansion of water crystals in the pores.Therefore, gypsum products have poor water resistance and frost resistance, and should not be used in wet parts.To improve its water resistance, appropriate amount of cementslagIt can also add organic waterproof agent to improve the pore state of gypsum products or make the pore wall[2]haveHydrophobicity。
Fineness refers to the fineness of cement particles.The finer the cement particles are, the larger the surface area that reacts with water is, and the hydration is fast and complete, so the setting and hardening is fast, and the early strength is high, but the early heat release and hardening shrinkage are large, and the cost is high, and the storage period is short.Therefore, the fineness of cement should be moderate.
The setting time of cement is divided into initial setting time andFinal setting time。Initial setting time is from cement mixing with water tocement pasteTime required to start losing plasticity;The final setting time is the time required from the time when the cement is mixed with water until the cement slurry completely loses its plasticity and begins to produce strength.The setting time of cement is of great significance in construction.In order to ensure that there is enough time to complete the concrete mixing, transportation, pouring and tamping, mortar painting, masonry and other construction processes before the initial setting, the initial setting time should not be too short;In order to make the concrete and mortar harden to a certain strength as soon as possible, so as to facilitate the next process as early as possible, and the final setting time should not be too long.According to the national standard, the initial setting time of six common cements shall not be less than 45min,portland cement The final setting time of other five types of common cement shall not be longer than 10h[1]。
