Early lime andashA mixture ofLime pozzolanic cement[1]Similarly, the concrete made of cemented macadam has not only high strength after hardening, but also can resist the erosion of fresh water or salt water.For a long time, as an importantCementitious material, widely used in civil construction, water conservancy, national defense and other projects.
In the old days, cement was also called "putty".In April 2023,New negative carbon environmental cement developed in the United States[4]。
2024On June 7, five departments including the National Development and Reform Commission jointly released special action plans for energy conservation and carbon reduction in four industries, including cement, and deployed a series of key tasks.[7]
Chinese name
cement
Foreign name
The word "cement" is developed from the Latin caementum
Cement is named according to different categoriesMixed materials, purpose and main characteristics, and try to be concise and accurate. If the name is too long, the abbreviation is allowed.
General cement is named after the main hydraulic mineral name of cement followed by the name of mixed material or other appropriate names.
Special cement is named for its special purpose and can be labeled with different models.
Characteristic cement is named after the main hydraulic minerals of cement and the main characteristics of cement, and can be named after different models or mixed materials.
The cement with pozzolanic or potential hydraulic materials and other active materials as the main component is named after the name of the main component followed by the name of the active material, or can be followed by the name of the characteristic, such asGypsum slag cement、Lime pozzolanic cementEtc.
Definition of cement type
(1) Cement: mixed with water to form a plastic slurry, which can cement sand, stone and other materials in the form of powder that can harden both in air and in waterHydraulic cementitious material。
(3) Ordinary Portland cement: hydraulic cementing material made of Portland cement clinker, 6%~20% mixed material, and appropriate amount of gypsum, called ordinary Portland cement (hereinafter referred to as ordinary Portland cement)Ordinary cement）, code: PO。
(4) Portland slag cement: hydraulic cementing material made of Portland cement clinker, 20%~70% granulated blast furnace slag and appropriate amount of gypsum, called Portland slag cement, code: PS。
(5) Pozzolanic Portland cement: Portland cement clinker, 20%~40%Pozzolanic mixtureThe hydraulic cementitious material made by grinding with appropriate amount of gypsum is called pozzolanic Portland cement, code: PP。
（6）Fly ash Portland cement: hydraulic cementing material made of Portland cement clinker, 20%~40% fly ash and appropriate amount of gypsum, called fly ash Portland cement, code: PF。
（7）Composite Portland Cement: hydraulic cementing material made of Portland cement clinker, 20% ～ 50% two or more specified mixing materials and appropriate amount of gypsum, called composite Portland cement (composite cement for short), code PC。
（8）Moderate heat Portland cement: Hydraulic cementitious material with medium hydration heat, which is made of Portland cement clinker with appropriate composition and added with appropriate amount of gypsum.
（9）low heat slag portland cement : A hydraulic cementing material with low hydration heat, which is made of Portland cement clinker with appropriate composition and added with appropriate amount of gypsum.
(10) Rapid hardening Portland cement: Portland cement clinker added with appropriate amount of gypsum is ground to produce high early strength cementcompressive strengthexpressgradeCement.
（11）Sulphate resistant Portland cement: Cement with good sulfate corrosion resistance made of Portland cement clinker and appropriate amount of gypsum grinding.
(13) Portland cement for roads: Portland cement for roadsclinker，0%～10%Active mixed materialsHydraulic cementitious material made by grinding with appropriate amount of gypsum is called road Portland cement (Road cement）。
（14）Masonry cement: It is made of active mixed materials, added with appropriate amount of Portland cement clinker and gypsum, and grinded, mainly used forMasonry mortarOflow gradeCement.
(15) Oil well cement:mineral composition It is made of Portland cement clinker, appropriate amount of gypsum and mixed materials, and is suitable for oil and gas wells under certain well temperature conditionscementing engineering Cement used.
(16) Gypsum slag cement: cement made by taking granulated blast furnace slag as the main component material and adding appropriate amount of gypsum, Portland cement clinker or lime grinding.
Production process
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The production process of Portland cement hasRepresentativenessIt is made of limestone and clay as the main raw materials through crushing, batching and grinding, and then fed into the cement kiln to calcine the mature materials, and then the clinker is grinded with appropriate amount of gypsum (sometimes mixed with mixed materials or additives).
Cement production can be divided into dry method (including semi dry method) and wet method (including semi wet method) according to different raw meal preparation methods.
① Dry production.Drying and grinding raw materials at the same time, or drying and grindingRaw meal powderRear feedingDry process kilnwithincalcinationMethod of mature material.But it is also made by adding raw meal powder with proper amount of waterRaw meal ballThe method of calcining clinker into Libor kiln is called semi dry process, which is still one of dry production.
New dry process cement production technologyIt was developed in the 1950s, Japan, Germany, etcdeveloped countryNew dry process cement clinker with suspension preheating and pre decomposition as the coreProduction equipment95%, China's first suspension preheating andPrecalciner kilnIt was put into production in 1976.The advantages of this technology: rapid heat transfer,thermal efficiencyHigh, larger output per unit volume than wet cement, low heat consumption.
② Wet production.Grind raw materials with water powderRaw slurryRear, feedWet kilnMethod of calcining mature material.There is also a method of dehydrating the wet prepared raw material slurry to make raw material blocks and calcine mature materials in the kiln, called semi wet process, which is still a kind of wet production.
The main advantages of dry production areHeat consumptionLow (if withpreheaterThe heat consumption of dry process kiln clinker is 3140~3768 coke/kg), the disadvantage is that the raw meal composition is not easy to be uniformFugitive dustLarge,Power consumptionHigher.Wet production has the advantages of simple operation, easy control of raw meal composition, good product quality, convenient slurry transportation, less dust in the workshop, etc. The disadvantage is high heat consumption (clinker heat consumption is usually 5234~6490 coke/kg).
Cement production can generally be divided into three processes: raw meal preparation, clinker burning and cement productionProduction processIt can be summarized as“Two grinding and one burning”。
Raw meal grinding
Cement process flow
There are two methods: dry method and wet method.Dry method is generally adoptedclosed circuitOperating system, i.e. raw materialMillAfter grinding, enterPowder concentratorSorting,Coarse powderReturn to the mill for grinding operation, and most of the materials are dried and ground in the mill at the same time. The equipment used include pipe mill, intermediate discharge mill and roller mill.The wet process usually adopts pipe mill, baseball mill and other open circuit systems that pass through the mill once and no longer return, but there are alsoclassifierorCurved screenOf the closed circuit system.
Clinker burning
The equipment for calcining clinker mainly includes shaft kiln andRotary kilnTwo types: vertical kiln is suitable for factories with small production scale, and rotary kiln is suitable for large and medium-sized factories.
① Shaft kiln:
concrete
kilnCylinderThe vertical kiln is called vertical kiln.It is divided into ordinary shaft kiln and mechanized shaft kiln.Ordinary shaft kiln is fed and unloaded manually or mechanically, and unloaded manually;Mechanical shaft kiln is mechanical feeding and mechanical unloading.Mechanical shaft kiln isContinuous operation, its production, quality andlabour productivityThey are higher than ordinary shaft kilns.Most shaft kilns abroad have been replaced by rotary kilns, but they still play an important role in China's cement industry.According to building materialstechnology policy It is required that small cement plants should use mechanized shaft kilns to gradually replace ordinary shaft kilns.
② Rotary kiln:
The kiln with horizontal kiln shell (slightly inclined, about 3%) and rotary movement is called rotary kiln.Calcined raw mealDry process kilnAnd calcined slurry（water contentUsually about 35%).
a. Dry process kiln
Dry process kiln can be divided into hollow kilnWaste heat boilerKiln, suspension preheater kiln and suspensionCalcinerKiln.Around the 1970s, a calcination process - decomposition technology outside the kiln, which can greatly increase the output of rotary kiln, was developed.It is characterized by the use of a precalciner kiln, which is based on the suspension preheater kiln, and a precalciner furnace is added between the preheater and the kiln.Add 50%~60% of the total fuel consumption into the decomposing furnaceCombustion processPreheating andcarbonateDecomposition process, from inside the kilnHeat transfer efficiencyThe lower zone is moved to the calciner for heat exchange with the hot gas flow in the suspended or boiling state, so as to improve the heat transfer efficiency and make the raw mealcalcium carbonateDecomposition rateMore than 80%, reducing kilnthermal load, ExtensionKiln liningService life and kilnOperating cycle, in keeping the kilnfeverThe purpose of greatly improving the output under the condition of capacity.
b. Wet kiln
The cement kiln used in wet production is called wet kiln. Wet production is to make raw materials into slurry with water content of 32%~40%.Since the slurry with fluidity is prepared, the raw materials are well mixed, and the raw materials have uniform composition, so thatFiringThe main advantage of wet production is the high quality of clinker.
Wet kiln can be divided into wet long kiln andWith materialShort wet kilns of slurry evaporators are widely used, but short kilns are rarely used.In order to reduce the heat consumption of wet long kiln, various types ofheat exchanger, such as chain, slurry filter preheater, metal orCeramic heat exchanger。
Due to the pre homogenization of raw materials, homogenization transportation of raw meal powder andDust collectionNew technologies and new equipment have been adopted, especially the appearance of decomposition technology outside the kiln, and a new dry production process has emerged.With this new process, the quality of clinker produced by dry process is no less than that produced by wet process, and the power consumption is also reduced, which has become the trend of cement industry development in various countries.
After the raw materials and fuels enter the plant, they shall be sampled, analyzed and inspected by the laboratory, homogenized according to the quality, and stored in the raw material storage shed.Clay, coalPyritePowder is dried by dryer to process waterIndicator value, viaHoistUpgrade to the corresponding raw material warehouse.LimestonefluoriteAfter two-stage crushing, gypsum will be sent to their respective warehouses by elevators.
According to limestone, clayanthraciteThe quality of fluorite and pyrite ore powder, the process formulaBatching systemThe whole black raw meal shall be batched and ground by the raw meal mill, and the raw meal shall be sampled and tested once an hourcalcium oxideThe percentage content of Fe2O3 and fineness shall be adjusted in time to make all data meet the requirements of process formula.The ground black raw meal passes throughBucket elevatorThe raw material shall be taken into the raw material warehouse, and the laboratory shall homogenize the raw material by means of multi warehouse matching and mechanical transfer according to the quality of raw material discharged from the mill, and then take twoRaw meal homogenization silo, raw meal is processed by twoHomogenization libraryMatch the materials toBalling discThe silo is composed of pre added water on the shaft kiln surfaceBallingcontrol device Proportioning of raw meal and water, and balling of raw meal through balling disc.The ball formed by shaft kilnAugerThe raw meal balls are distributed at different positions in the kiln for calcination, and the burnt clinker passes through the discharge pipe and scaleTriggerSent to clinkerCrusherCrushing is carried out, and the laboratory takes samples every hour for clinker chemistryPhysical analysis。
According to the clinker quality, the elevator is put into the corresponding clinker silo, andProduction and operationRequirements andbuilding materials marketThe laboratory will mix clinker, gypsum and slag with cement through the clinker microcomputer batching system. The cement mill will grind No. 425 and No. 525 ordinary Portland cement respectively, and samples will be taken every hour for analysis and inspection.The ground cement is lifted into 3 pieces by bucket elevatorCement siloThe laboratory homogenizes the cement according to the quality of grinding cement by means of multi warehouse matching and mechanical transfer.It is sent to two cement homogenization silos by hoist, and then matched by two cement homogenization silos, controlled by microcomputerpackerPack the cement, and store the packaged bagged cement inFinished product warehouseAfter passing the test and sampling inspection, the cement will be issued for deliveryNotice。
Rapid setting of cement refers to an abnormal phenomenon of early solidification or hardening of cement.High temperature makes gypsumCrystal waterDehydrate and become slurry, thus losing regulationsetting time Ability.PseudocoagulationIt is related to many factors and is generally believed to be mainly due toCement grinding When the temperature in the mill is highDihydrate gypsumDehydrationHemihydrate gypsumBecause of.When cement is mixed with water, hemihydrate gypsum reacts with water quickly to form dihydrate gypsum, forming needle like crystalsReticular structure, causingSlurrysolidification.In addition, some cement with high alkali content,potassium sulphateGenerated with dihydrate gypsumPotassium gypsumRapid growth will also cause false coagulation.False setting is different from rapid setting. The former has little heat release, and the slurry can recover its plasticity and achieve normal setting after intense mixing, without adverse impact on strength.
Cement history
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In 1756, when studying the hardening characteristics of some limes in water, British engineer J. Smiton found that:Hydraulic propertyLime must be fired with limestone containing clay;be used forUnderwater buildingThe most ideal composition of the masonry mortar is composed of hydraulic lime and pozzolanic ash.This important discovery laid a theoretical foundation for the development of modern cement.
In 1796, British J. Parker usedMarlA kind of cement is fired, which is brown in appearance, very similar toAncient RomeThe lime and volcanic ash mixture of the era, namedRoman cement。It is also called natural cement because it uses natural marl as raw material and is fired directly without ingredients.It has good hydraulic properties and fast setting characteristics, especially suitable for projects in contact with water.
In 1813,FranceBijia, a civil engineer of, discovered that the cement made by mixing lime and clay in a ratio of three to one has the best performance.
In 1824, British construction workersJoseph Aspodine(Joseph Aspdin) invented cement and obtainedPortland cementOfpatent right。He uses limestone and clay as raw materials, and after mixing them in a certain proportioncalcinationThe mature material is then ground into cement.becauseCement hardeningColor afterEnglandThe stones used for building in Portland on the island are similar and are named Portland Cement.It has excellentBuilding performance, which has epoch-making significance in the history of cement.
In 1871, Japan began to build cement plants.
In 1877, the British clapton inventedRotary furnaceAnd was reformed into a better rotary furnace by Lansam in 1885.
In 1889, Hebei, ChinaTangshanNear Kaiping Coal Mine, Tangshan "Fine Coal Mine" with shaft kilnCotton soil”Factory.It was established on the basis of the plant in 1906Qixin Ash CompanyThe annual output of cement is 40000 tons.
In 1893, Hidehiko Endo and Mizen Inland invented the Portland cement that is not afraid of seawater.
In 1907, French Pierre usedAluminium oreIron ofBauxiteInstead of clay, mixed limestone is burned to make cement.Because this cement contains a large amount ofaluminaTherefore, it is called "bauxite cement".
In the 20th century, while continuously improving the performance of Portland cement, people successfully developed a batch of specialarchitectural engineeringCement, such asHigh alumina cement、Special cementEtc.There are more than 100 kinds of cement in the world. In 2007, cementAnnual outputAbout 2 billion tons.In 1952, China formulated the first national unified standard, which determined that cement production should be diversifiedgradeAccording to the principle ofmineral composition RenamedSilicatesCement, which was later renamed as Portland cement till now.
In April 2023,Scientists from Washington State University in the United States injected environment-friendly biochar into ordinary cement to obtain a new type of negative carbon environment-friendly cement[4]。
Classified production indicators
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Type of decorative cement
Decorative cementIt is often used to decorate the surface of buildings, with simple construction, convenient modeling, easy maintenance and low price.The varieties are as follows:
stayFamily decorationMedium,floor tile, wall brick pasting and masonrycement mortarIt can not only enhance the adsorption capacity of surface material and base layer, but also protect the internal structure, and can be used as a buildingHairinessOfLeveling layerTherefore, cement mortar is an indispensable material in decoration engineering.
Many customers believe that the greater the proportion of cement in the whole mortar, the stronger its adhesion is. Therefore, the cement is often used withdecoration companyDisagreement arises.In fact, it is not so. Take pasting ceramic tiles as an example, ifCement gradeIf it is too large, when the cement mortar is set, the cement will absorb a lot of waterSurface courseIf the water in the ceramic tile is excessively absorbed, it is easy to crack and shorten the service life.Cement mortar shall be generally mixed in the proportion of cement: sand=1:2 (volume ratio).
The foaming agent is added to the slurry made of cement-based cementitious materials, aggregates, admixtures, admixtures and water, and then mixed, stirred and poured to make it react chemically in the moldSlurryIt is a thermal insulation board formed by curing and cutting with closed pores inside.
matters needing attention
Silicate cement raw materials
The ex factory quality certificate of cement shall be stamped by the quality department of the manufacturer;hisTest reportThere should be a test number for verification with the relevant data of the laboratory, and there should be clear conclusions with complete signatures and seals;The manufacturer's cement 28 day strength supplement report cannot be missing;The user must carefully check the validity period of cement, retest the expired cement, and carefully check whether the measured values in the test report meet the standard values specified in the specification;Cement with quality problems can be degraded for use according to the data in the test report, but it must be signed and approved by the relevant technical director, and the name of the project to be used and the position to be used shall be indicated.If it is a continuous construction project, the time of two adjacent cement tests shall not exceed its validity period.
The cement hardened by moisture will reduce or even lose its original strength, so the specification stipulates that the cement that has been delivered for more than 3 months should be rechecked and tested, and used according to the test results.Yes, dampedAgglomerateOr hardened cement, which must be used after sievingLumpIt is generally used for secondary works after being rubbed or groundMasonry mortarorplastering mortar 。For cement agglomerates that are ready to be powdered in one touch or one pinch, the strength grade can be appropriately reduced for use.
(2) Avoid sun exposure and quick drying
If the concrete or plaster is exposed to the sun after operation, its strength will be reduced or even completely lost with the rapid evaporation of water.Therefore, the base course must be strictly cleaned and fully wetted before construction;After construction, it shall be strictly covered and watered for curing according to the specifications.
(3) Avoid freezing at negative temperature
After the concrete or mortar is mixed, if it is frozen, its cement cannot be hydrated, and the water freezes and expands, the concrete or mortar will be damaged by the crispness gradually deepening from the outside to the inside, so it should be strictly observed《Specification for winter construction of building engineering》（JGJ104-97).
(4) Avoid high temperature
The solidified mortar layer or concrete component, if often in high temperature and extreme heat, will have strength loss, which is due to the high temperature,cement stoneIncalcium hydroxideDecomposable;In addition, some aggregates will also decompose orVolumetric expansion。
It can be used for occasions with high temperature for a long timerefractory bricksyesOrdinary mortarOr concrete for isolation protection.In case of higher temperature, specialHeat resistant concreteFor pouring, a certain amount of ground heat resistant materials can also be added into the concrete.
(5) Avoid dirty and soft base
The cement can be firmly bonded or wrapped with the hard and clean base course, but its bonding strength is similar to that of the base course faceDegree of finishofWhen constructing on the smooth base course, it is necessary to chisel, smash and brush the cement in advance to make the cement bond firmly with the base course.
The dirt, grease, acid and alkali on the base layer will act as isolation, so it must be carefully cleaned and cleaned before brushingPlain cement slurryAnd then apply mortar or pour concrete.
Cement inSolidification processShrinkage will occur in the process of dry, wet, cold and hot changes, and its volume changes extremely with loose and weak base coursenot suited to, inevitablehollowing Or cracks appear, which makes it difficult to bond firmly.Therefore, woodSlag cushionandLime soil cushionIt shall not be firmly bonded with mortar or concrete.
(6) Avoid impure aggregate
As aggregate for concrete or cement mortarsand, if there is dust, clay or otherOrganic impuritiesWill affect the bonding strength between cement, sand and stone, thus eventually reducingcompressive strength。Therefore, if the impurity content exceeds the standard, it must be cleaned before use.
(7) Avoid too much water, too gray and thick
People often ignorewater consumptionFor the influence on concrete strength, in order to facilitate pouring and vibrating, sometimes the mix proportion is not carefully implemented, and the concrete is mixed very thin.Since the water required for hydration is only about 20% of the weight of cement, the excess water will leave many pores in the concrete after evaporation, which will reduce the strength of concrete.Therefore, on the premise of ensuring the compactness of pouring, the mixing water shall be minimized.
Many people believe that the more cement is used for plasteringPlastering layerThe stronger.In fact, the more cement is used, the thicker the mortar is, the greater the shrinkage of the plastering layer volume will be, and the more cracks will be generated.Generally, when plastering, the leveling layer shall be plastered with 1: (3-5) coarse mortar, and then 1: (1.5-2.5)cement mortarWhen plastering thin surface layer, do not use too much cement.
(8) Avoid acid corrosion
AcidsAnd calcium hydroxide in cementNeutralization reaction，ProductLoose volume, expansion, water contactPosterior poleIt is easy to hydrolyze and pulverize.As a result, the concrete or plastering layer is gradually corroded and disintegrated, so the cement is not subject to acid corrosion.
The cement output in July 2015 was 212 million tons, a year-on-year decrease of 4.7%, and the growth rate was 1.1% higher than that in June and 8.21% lower than that in the same period of 2014. The cement output from January to July totaled 1.291 billion tons, a year-on-year decrease of 5% and a slowdown of the growth rate. The growth rate was 0.3% higher than that in June and 8.69% lower than that in the same period of 2014.Accumulated from January to July 2015Investment in fixed assets28.85 trillion yuan, up 11.2% year on year, 0.2% lower than that in June, and 5.8% lower than that in the same period of 2014;From January to July 2015, the investment in fixed assets of railway transportation was 336.6 billion yuan,Year on year growth10.9%, 15.1% lower than that in June and 8.7% higher than that in the same period of 2014.Accumulated from January to JulyReal estate investment5256.2 billion yuan, up 4.3% year on year, 0.3% lower than that in June, and 9.4% lower than that in the same period of 2014;Accumulated from January to JulyNewly started area of the house817 million square meters, down 16.8% year on year, 1% lower than that in June, and 4% lower than that in the same period of 2014;Accumulated from January to JuneSales area of commercial housing599 million square meters, up 6.1% year on year, 2.2% higher than that in May, and 13.7% higher than that in the same period of 2014.
China's cement industryCompetition patternWith leading enterprisesanalysis reportdata displayFrom January to July, the cement output maintained a negative growth and a decreaseRing ratioNarrow slightly.Real estate data indicators remain depressed. On the one hand, the month on month decline of investment and new construction data has expanded. In addition, the investment growth rate is less than 5%, and it is possible to continue to explore the bottom. The future trend is not optimistic.In July, the railway transportation dropped by 15.1% month on month, the biggest drop in the same period since 2003Decline, capital construction, etcThe project startedIt is still lower than expected.[1]
According to the website of the National Bureau of Statistics on July 17, 2023, in the first half of the year, the cement output was 953 million tons, an increase of 1.3%.[5]
Space cement
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According to a paper published in the Astronomical Journal in 2019, ISS astronauts successfully mixed cement in microgravity environment for the first time.The results are unexpected: compared with the cement processed on the earth, the microstructure of the cement samples processed on the space station has changed greatly.The cement on the earth has a layered structure due to gravity, while ISS lacks gravity, so the density of mixed cement is very uniform, which means that space cement is more solid.At the same time, there are more voids in space cement, and porosity will also significantly affect the performance of cement materials.This result marks an important step towards the goal of "building houses on the moon".[6]
Production index standard
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1. Main technical indicators of cement
(1) Specific gravity and unit weight: the specific gravity of standard cement is 3.1, and the unit weight is usually 1300 kg/m3.
(2) Fineness: refers to the fineness of cement particles.The finer the particles, the faster the hardening,early strength The higher.
（3）setting time : The time required for cement mixing with water to start setting is called initial setting time.The time required from mixing with water to completion of condensation is called final setting time.The initial setting time of Portland cement and ordinary Portland cement shall not be earlier than 45 minutes, and the final setting time shall not be later than 6.5 hours;The final setting time of pozzolanic cement, fly ash cement and composite Portland cement shall not be later than 10 hours.In fact, the initial setting time is 1-3 hours, while the final setting time is 4-6 hours.The cement setting time is measured by a special setting time tester.
(4) Strength:Cement strengthIt shall comply with national standards.
（5）Volume stability: refers to the uniform performance of cement volume change during hardening.There are many impurities in the cement, which will produceNon-uniform deformation。
(7) Standard consistency: refers toCement pasteConsistency when there is a certain resistance to the sinking of the standard test rod.
2. Revision of cement standards
There are mainly two changes in the new Chinese cement standard compared with the old one: one is the adoption of GB/T 17671-1999《Test method for strength of cement mortar (ISO method)》Replace the current GB177-85 Test Method for Strength of Cement Mortar;Second, six general cement standards in China have been revised based on ISO strength.
(1) GB/T 17671-1999 Test Method for Strength of Cement Mortar (ISO Method)Standard formulation
GB/T 17671-1999 and GB177-85 belong to the "soft training method" for testing the strength of cement mortar, that is, plastic sand, 40X40X160mmprismFor the test body, the bending strength test shall be carried out first, and then the compression test shall be carried out for the two half sections of the test body after fracturestrength test 。The core difference between the two is that the composition of mortar is differentWater cement ratioModerate,Lime sand ratioModerate, especially the use of graded standard sand, so the strength value obtained by ISO method is closer to the use effect of cement in concrete than that of GB177 method.
a. Test method for strength of cement mortar is changed to GB/T 17671-1999
Six major cementsProduct standardGB/T 17671-1999 method is cited as the strength test method of cement mortar, instead of GB 177-85 method.Therefore, GB/T 17671-1999 method has been upgraded to mandatory method, while GB 177-85 method has been downgraded to recommended method.
Six old cement standards adopt cement grades expressed in Kgf/cm2, such as 325, 425, 425R, 525, 525R, etc.
The six new cement standards implement the strength grade expressed in Mpa, such as 32.5, 32.5R, 42.5, 42.5R, 52.5, 52.5R, etc., so that the value of the strength grade is the same as the lowest value of the 28 day compressive strength index of cement.
The new standard also uniformly plans the strength grade of Chinese cement. Portland cement is divided into three grades and six types, 42.5, 42.5R, 52.5, 52.5R, 62.5, 62.5R, ordinary Portland cement is divided into two grades and four types, 42.5, 42.5R, 52.5, 52.5R, slag Portland cementashPortland cement and fly ash Portland cement are divided into three grades and six types, namely 32.5, 32.5R, 42.5, 42.5R, 52.5 and 52.5R, while the strength grade of ordinary Portland cement does not include 32.5 grade, and other grades are the same as slag Portland cement.
c. Strength Age and Strength Indicator Settings of Each Age
The cement strength ages specified in the six new cement standards are 3 days and 28 days, and each age has requirements for flexural and compressive strength indicators.
3. Cement pollution prevention standard
cement industry Carbon emissionsSecond only to the power industry, resource consumption andecological damageThe cement industry with prominent problems is about to usher in a new wave of elimination.
countryMinistry of Environmental ProtectionCementIndustrial pollution preventiontechnology policy 》（Draft for Comments）And the Guide to the Best Feasible Technology for Pollution Prevention and Control in the Cement Industry (Draft for Comments).The message conveyed by these two documents is that the state will prevent and control pollution in the cement industrytechnical standardAnd comprehensively reduce the pollutant emissions of the cement industry, and at the same time defuse the cement industryexcess production capacityThe problem of;Both technical policies and technical guidelines should be mandatory.
The cement industry is the third largest user of coal in China after electricity and steelCement clinkerAverage firingHeat consumption115 kgStandard coal/Tons, more than 10% higher than the international advanced level.There are about 4000 cement production enterprises above designated size in China, and the new dry processCement production lineMore than 1500.Cement industrycarbon dioxideIts emissions are second only to the power industry, ranking second in the country.Mine resource consumption and ecological destruction of cement enterprises are also prominent problems.
Chinese Society of Environmental Sciences、Hefei Cement Research and Design InstituteThe Guide to the Best Feasible Technology for Pollution Prevention and Control in the Cement Industry (Draft for Comments) prepared by the preparation team introduced that the preparation team investigated 158 cement enterprises in 2010, and for each 5000t/d clinker new dry process cement production line, the enterprise needs to paySewage chargesAbout 900000~1000000 yuan.
If the technical transformation and supervision are in place, the particulate matter emissions will be reduced by 50%,nitrogen oxide The reduction of 25% will reduce the sewage charges by about 300000 yuan every year, which is equivalent to an annual cement underpayment of 1500 yuan. If the national cement volume is 1.86 billion tons, the sewage charges can be reduced by 1.395 billion yuan in the next five years.At the same time, dust, sulfur dioxideNitrogen dioxidePollution, environment andsocial resultsHuge.
If the cement industry can reach 30% of raw materials/fuels in the next five yearsSubstitution rate, carbon dioxide emissions can be reduced by 280 million tons per yearfossil fuelThe use ofCost savings372 billion yuan, generating huge environmental protection andeconomic performance。
Secretary General of China Cement AssociationKong XiangzhongIt indicates that the cement industryTechnological innovation processChina is always accompanied by overcapacity.The red token of the state's control of cement overcapacity has been continuous, but major technological innovation, improvement and development at each stage have made a decisive contribution to resolving the industry's overcapacity.
According to the China Cement Association, in the first three years, 463 new dry process cement production lines were invested and the new clinker production capacity reached 547 million tons, which means that at least about 200 million tons of backward technical capacity has been run out and become excess capacity.But "it is the overcapacity in the cement industry that has strengthened the pursuit of cement enterprisestechnical progressAnd improve managementmarket competition Optimized resource allocation. "Kong Xiangzhong said.
The compilation team of the Best Available Technical Guide for Pollution Prevention and Control in the Cement Industry (Draft for Comments) specially pointed out that the technical guide should be consistent with variousemission standard(includingLocal standards）EstablishmentAssociationAnd must be mandatory.
national standard
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The latest standard of cement products is《General purpose Portland cement》（GB175-2007), the following is the main content of the standard.
1 Scope
This standard specifiesGeneral purpose Portland cementDefinition and classification, composition and material, strength gradetechnical requirementTest methods, inspection rules, packaging, marking, transportation and storage, etc.
This standard is applicable to general Portland cement.
The clauses in the following documents become clauses of this standard through reference in this standard.For dated references, all subsequent amendments (excluding corrections) orRevisionNone of them is applicable to this standard. However, parties to agreements based on this standard are encouraged to study whether the latest versions of these documents can be used.For undated references, the latest version is applicable to this standard.
GB/T176 Methods for Chemical Analysis of Cement (GB/T176-1996,eqvISO680:1990）
Composite Portland cement P · C ≥ 50 and<80>20 and ≤ 50e
A This component material is in accordance with 5.2.3 of this standardActive mixed materialsAmong them, it is allowed to use non active mixed materials that do not exceed 8% of the cement mass and meet 5.2.4 of this standard, or those that do not exceed 5% of the cement mass and meet 5.2.5 of this standardKiln ashReplace.
B This component material is an active mixed material conforming to GB/T203 or GB/T18046, in which it is allowed to use an active mixed material not exceeding 8% of the cement mass and conforming to Article 5.2.3 of this standard, or an inactive mixed material conforming to Article 5.2.4 of this standard, or a kiln ash conforming to Article 5.2.5 of this standard.
C This component material is an active mixed material conforming to GB/T2847.
D This component material is an active mixed material conforming to GB/T1596.
E This component material is composed of more than two (including) kinds of active mixed materials conforming to Article 5.2.3 of this standard or/and non active mixed materials conforming to Article 5.2.4 of this standard, in which it is allowed to use kiln ash which does not exceed 8% of the cement mass and conforms to Article 5.2.5 of this standard instead.When adding slag, the mixing amount of mixed materials shall not be the same as that of portland slag cement.
5.2.1.1 Natural gypsum: gypsum or mixed gypsum conforming to Class G or Class M Grade II or above specified in GB/T 5483.
5.2.1.2 Industrial by-product gypsum:calcium sulfateIt is the industrial by-product of the main component.It shall be proved harmless to the cement performance by test before use.
Granulated blast furnace slag, granulated blast furnace slag powder, fly ash and pozzolanic mixture with activity index lower than GB/T203, GB/T18046, GB/T1596 and GB/T2847 respectively;Limestone andSandstone, of whichAluminium trioxideThe content shall not be more than 2.5%.
Cement grinding It is allowed to add grinding aids, the amount of which shall not be greater than 0.5% of the cement mass, and the grinding aids shall comply with the provisions of JC/T667.
6 Strength grade
6.1 The strength grade of Portland cement is divided into six grades: 42.5, 42.5R, 52.5, 52.5R, 62.5 and 62.5R. R represents early strength cement.
6.2 The strength grade of ordinary Portland cement is divided into four grades: 42.5, 42.5R, 52.5 and 52.5R.
6.3 Portland slag cementPortland pozzolanic cementThe strength grades of fly ash Portland cement and composite Portland cement are divided into six grades: 32.5, 32.5R, 42.5, 42.5R, 52.5 and 52.5R.
Note: R-early strength type is mainly characterized by higher 3d strength than cement of the same strength grade
A If the cement autoclave test is qualified, the content (mass fraction) of magnesium oxide in cement is allowed to be relaxed to 6.0%.
B If the content (mass fraction) of magnesium oxide in the cement is greater than 6.0%, the cement autoclave stability test shall be carried out and qualified.
C When there are lower requirements, the indicator shall be determined by both parties through negotiation.
In cementAlkali contentPressNa2O+0.658K2O calculated value.If usedActive aggregate, required by the userLow alkali cementThe alkali content in cement shall not be greater than 0.60% or shall be determined by both parties through negotiation.
7.3 Physical indicators
7.3.1 Setting time
The initial setting of Portland cement is not less than 45min, and the final setting is not more than 390min;
Ordinary Portland cement, slag Portland cementPortland pozzolanic cementThe initial setting of fly ash Portland cement and composite Portland cement shall not be less than 45min, and the final setting shall not be more than 600min.
7.3.2 Stability
Boiling method is qualified.
7.3.3 Strength
Different varieties and strength gradesGeneral purpose Portland cement, differentAgeThe strength of shall comply with the provisions in Table 3.
Portland cement and ordinary Portland cement are expressed in specific surface area, not less than 300m2/kg;Portland slag cement, Portland pozzolanic cement, Portland fly ash cement and composite Portland cementSieve residueIt means that the sieve residue of 80 μ m square hole sieve is not more than 10% or that of 45 μ m square hole sieve is not more than 30%.
8 Test method
8.1 Components
It is selected by the manufacturer according to GB/T12960 orAccuracyHigher method.Under normal production conditions, the producer shall check the cement composition at least monthly,Annual averageIt shall comply with Article 5.1 of this standard, and the single inspection value shall not exceed 2% of the maximum limit specified in this standard.
To ensure the determination results of componentsaccuracyThe producer shall adopt appropriate production procedures and methods to verify the reliability of the selected methods, and form the verified methods into documents.
8.2 InsolublesLoss on ignition, magnesium oxide, sulfur trioxide and alkali content
Test according to GB/T176.
8.3 Autoclave stability
The test shall be conducted according to GB/T750.
8.4 Chloride ion
Test as per JC/T420.
8.5 StandardsConsistencyWater consumption, setting time and stability
Test according to GB/T 1346.
8.6 Strength
Test according to GB/T17671.However, the water consumption of pozzolanic portland cement, fly ash portland cement, composite portland cement and ordinary portland cement mixed with pozzolanic mixed materials is 0.50 when conducting mortar strength testWater cement ratioAnd mortar fluidity shall not be less than 180mm.When the fluidity is less than 180mm, the water cement ratio must be adjusted to a mortar fluidity of not less than 180mm by an integral multiple of 0.01.
MasticFluidity testIt shall be carried out according to GB/T2419, and the mortar shall be prepared according to GB/T17671.
8.7 Specific surface area
Test according to GB/T8074.
8.8 80 μ m and 45 μ m sieve residue
Test according to GB/T1345.
9 Inspection rules
9.1 Numbering and sampling
Cement shall be numbered and sampled according to the same type and strength grade before delivery.Cement in bags andBulk cementNumbering and sampling shall be carried out respectively.Each number is a sampling unit.Cement factory number by yearthroughputIt is specified that:
Above 200 × 104t, no more than 4000t is a number;
120 × 104t~200 × 104t, no more than 2400t is a number;
60 × 104t~120 × 104t, no more than 1000t is a number;
30 × 104t~60 × 104t, no more than 600t is a number;
10 × 104t~30 × 104t, no more than 400t is a number;
Below 10 × 104t, no more than 200t is a number.
The sampling method shall be in accordance with GB12573.The sample can be taken consecutively or equally from more than 20 different parts, with a total amount of at least 12kg.When bulk cementMeans of transportIf the capacity exceeds the tonnage of the factory number specified by the factory, the tonnage of the number is allowed to exceed the tonnage specified for sampling.
The inspection report shall include the ex factory inspection items, fineness, mixed material type and dosage, gypsum and grinding aid type and dosageRotary kilnorShaft kilnProduction and other technical requirements agreed in the contract.When required by the user, the producer shall send all inspection results except for the 28d strength within 7d from the date of sending the cement, and report the 28d strength inspection results within 32d.
9.6 Delivery and acceptance
9.6.1 The quality acceptance of cement at the time of delivery can be based on the inspection results of physical samples, or the inspection report of the manufacturer of cement with the same number.The method of acceptance shall be determined by the Buyer and the Seller and specified in the contract or agreement.The Seller is responsible for informing the Buyer of the acceptance method.When noneWritten contractOr agreement, or the acceptance method is not specified in the contract and agreement, the Seller shallinvoiceThe words "based on the inspection report of the cement with the same number of our factory" shall be marked on it.
9.6.2 When the inspection results of physical samples are taken as the basis for acceptance, the Buyer and the Seller shall jointly take samples and seal them before shipment or at the place of delivery.The sampling method is in accordance with GB12573, the sampling quantity is 20kg, which is divided into two equal parts.One copy shall be kept by the Seller for 40d, and the other copy shall be inspected by the Buyer according to the items and methods specified in this standard.
Within 40d, if the buyer believes that the product quality does not meet the requirements of this standard, and the seller has objection, then both partiesTheAnother sample kept by the Seller shall be sent to provincial level or aboveNational recognitionCementQuality supervisionInspection agencyConduct arbitration inspection.Cement soundnessThe arbitration inspection shall be completed within 10 days from the date of sampling.
9.6.3 When the inspection report of the manufacturer's cement with the same number is taken as the basis for acceptance, the Buyer shall take samples from the cement with the same number before shipment or at the time of delivery. After both parties jointly sign and seal, the Seller shall keep 90d sealed samples of the cement with the same number, or the Seller shall be recognized to take samples, sign and save 90d sealed samples of the cement with the same number.
Within 90 days, if the Buyer has any doubt about the cement quality, the Buyer and the Seller shall send the jointly approved sample to the cement quality supervision and inspection institution recognized by the provincial or above countries for arbitration inspection.
10. Packaging, marking, transportation and storage
10.1 Packaging
Cement can be packed in bulk or in bags. Each bag of bagged cementNet contentIt is 50kg and shall not be less than 99% of the mark mass;20 bags randomly selectedTotal mass(including packaging bag) shall not be less than 1000kg.Other packaging forms shall be determined by both parties through negotiation, but relevant packaging forms shall be packaged in bagsquality requirement, shall comply with the above provisions.Cement bags shall comply with GB9774.
10.2 Marks
The cement bag shall be clearly marked with:Executive standardsCement type, code, strength grade, producer nameProduction licenseSign（QS）And number, factory number, packing date, net content.The cement name and strength grade shall be printed in different colors on both sides of the packing bag according to the type of cement,portland cement andOrdinary Portland CementIn red,Portland slag cementAdopt green;Portland pozzolanic cement, Portland fly ash cement andComposite Portland CementUse black or blue.
When shipping in bulk, the card with the same content as the bag mark shall be submitted.
10.3 Transportation and storage
Cement shall not be damped or mixed with sundries during transportation and storage, and cement of different varieties and strength grades shall not be mixed during storage and transportation.
concrete
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Concrete, referred to as "concrete (t ó ng)":Cementitious materialThe general term for engineering composite materials that cement aggregate into a whole.Generally speaking, the term "concrete" refers to the use of cement as cementitious material and sand and stone as aggregate;With water (with or without additives andAdmixture）It is prepared by mixing, shaping and curing in a certain proportioncement concrete, also known asordinary concrete , which is widely used in civil engineering.
Cement setting time
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Cement and water will become plasticSemifluid, after a period of time,cement pasteIt gradually loses its plasticity and keeps its original shape. This phenomenon is called condensation (divided into initial setting and final setting).Then it enters the hardening period, and the strength of cement gradually increases.
Cement required in constructionsetting time There is a certain range.If the setting is too fast, the concrete will lose its fluidity soon, which will affect the vibration;On the contrary, if the condensation is too slow, the construction speed will be affected.Therefore, the standard stipulates thatInitial setting timeandFinal setting timeIt should be within a certain range.
The setting time is measured according to the standardConsistencyOfCement paste, under certain temperature and humidity conditions.From the time of adding water to the time when the test needle sinks into the pasteMidrangeWhen the bottom plate is 0.5~1.0mm, the required time is the initial setting time. At this time, the paste begins to lose its plasticity;The required time is the final setting time until the test needle sinks no more than 1.0mm into the paste. At this time, the paste completely loses its plasticity and begins to harden.
Stability
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During the hardening process of cement, if there is no uneven volume deformation, cracks, bending and other phenomena, it is calledVolume stabilityQualified;If the cement hardens and the volume changes unevenly, causing harmful expansion, which will crack or even collapse the building, it is called soundness unqualified.This kind of cement cannot be used in the project.
If the cement contains too muchFree calcium oxideOr magnesium oxide, especially the coarser particles and the shorter storage time in the factory, will produce the phenomenon of unqualified stability.Because this over heated (above 1000 ℃) calcium oxide and magnesium oxide have not been fully matured, and their hydration is very slowCement settingLater, hydration will start under the constraint of cement paste, and cracking will occur after volume expansion.In addition, if the content of sulfur trioxide in cement is too highCalcium sulphoaluminate, volume expansion will also cause poor stability.
The soundness of cement shall be tested according to GB/T 750-1992.The inspection process is carried out with cement paste of standard consistency, which is made into a test cake with a certain shape (70~80mm in diameter, about 10mm thick in the center, and gradually thinner at the edge), and then putBoiling boxBoil internally for 4h, if the boiled test cake is observed by naked eyesNot foundCrack, usingrulerIf there is no bending phenomenon in the inspection, the soundness is qualified;Otherwise, it is unqualified.
In addition to the above test methods for soundnessCake test methodBesides, there areRayleigh clamp methodAnd length measurement.Although the latter two methods have quantitative numerical limits, they are complex and have poor repeatability;The cake test method has a series of advantages such as simple equipment, convenient operation, sensitive reaction, intuitive observation and good reproducibility, so it is still listed as the national standard method.
Boiling method can only detect the destructive effect of free calcium oxide.Due to the over fire magnesium oxide is more than the over fire calcium oxiderate of hydrationIt is slower. Therefore, the instability caused by magnesium oxide cannot be found by boiling method. This phenomenon can only be judged by high temperature and high pressure autoclave test.However, the instability caused by sulfur trioxide can only be tested by cold cake method and water immersion method, that is, the test cake is placed in 20 ℃± 3 ℃ water for curing for 28 days, and then check whether there is instability.Because when the temperature exceeds 60~70 ℃, it will not be able to formCalcium sulphoaluminate。
As the national standard has stipulated the limit of magnesium oxide and sulfur trioxide contentSteaming methodAnd water immersion method can be omitted.
Quality identification
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The first kind: "look at" mud to know the advantages and disadvantages
First, from the appearancePackaging quality。Check whether the moisture-proof material is usedCompound membraneWoven bagCheck whether the signs are clear and complete.Generally, cement produced by regular manufacturers should be marked with the following contents:Registered trademark, place of originProduction licenseNoExecutive standardsPacking date and baggingNet weightFactory number, cement type, etc.Poor quality cement is often unclear about this phrase.Secondly, carefully observe the color of cement.Generally speaking, the normal color of cement should be grayish white. If the color is too deep or has changes, it may be that there are too many other impurities.
The second kind: "Smell" mud precipitation quality
The "smell" here is not smell. After all, it is unsafe for consumers to smell cement. The "smell" here is "listen". Listen to the merchants' introduction about the ingredients of cement to infer the quality of cement.Some small cement plants in ChinaLow price sales, excessive use in violation of cement standardscement blending material, did not strictly follownational standardPerform raw material proportioningProduct performanceas one can imagine.However, regular manufacturers are very strict in the selection of raw materials for cement. The cement produced has moderate setting time, high bonding strengthDurabilityGood features.
The third kind: the source of "asking" mud
Mainly ask the cement manufacturer andProduction processIt depends on whether their "origin" is regular and whether their production technology is advanced.Currently, illegalBuilding materials decorationThe cement products on the market are mostly produced by small shaft kiln technology, not onlyproduct qualityVery unstable, and also the enemy of environmental protection;However, some professional large factories adopt new dry processRotary kilnProduction, using advancedcomputer technologyControl management, which can ensure stable quality of cement products.
Fourth type: "cutting" mud to know life
This step mainly uses fingers to give cement“Palpation pulse”And identify the length of its delivery time.Cement also hasquality guarantee period, generally speaking, 30 days after the ex factory dateCement strengthThere will be a decrease.The strength of cement stored for three months will decrease by 10%~20%, and 25%~40% after one year.Cement that can be used normally shall be free from moisture and caking. High quality cement can feel fine particles by twisting cement powder with fingers.If the cement is poorly packaged, it will be damped and caked during opening inspection;The poor quality cement is twisted by fingers with cement powder, which has a rough feeling, indicating thatCement finenessCoarse, abnormal, low strength and poor viscosity when used.
2024On June 7, the National Development and Reform Commission and other five departments jointly released the special action plan for energy conservation and carbon reduction in four industries of steel, oil refining, synthetic ammonia and cement, and deployed a series of key tasks.About 16% of the cement industry's production capacity and energy efficiency cannot reach the benchmark level, and there is a huge potential for energy conservation and carbon reduction.From 2024 to 2025, the steel, oil refining, synthetic ammonia and cement industries will save about 32 million tons of standard coal and reduce about 84 million tons of carbon dioxide by implementing energy-saving and carbon reduction transformation and upgrading of energy consumption equipment.By the end of 2025, the production capacity above the benchmark level of energy efficiency in the steel, oil refining, synthetic ammonia and cement industries will all account for 30%, and the production capacity below the benchmark level of energy efficiency will have completed technical transformation or eliminated.Based on the energy efficiency level and environmental protection performance, fine management is implemented for steel, oil refining, synthetic ammonia, cement and other industries.[7]
