With certificates of quality, weight, packing and loading issued by independent inspection agencies, we manufacture
and supply quality clinker conforming to the following standards:
• China’s cement standard GB 175-2007 and clinker standard GB/T 21372-2008;
• American standard ASTM C-150 07;*
• European standard EN 197-1:2000;
• Russian standard GOST 30515-97.
A particular brand, country of origin, etc. are not factors which influence the quality and consistency of the clinkers which is a big misconception on the side of the Buyers – rather, quality depends on the sequence of the clinker formation, specification or standards followed, etc., - sulfate and alcali contents of the clinker much affect the quality of clinker.
Clinkers are of two major colours - white and grey.
Cement clinkers are formed by the heat processing of cement elements in a kiln. Limestone, clay, bauxite, and iron ore sand in specific proportions are heated in a rotating kiln at 2,770° Fahrenheit (1,400° Celsius) until they begin to form cinder lumps, which are also known as cement clinkers. These are usually ground with gypsum to produce the fine powder later mixed with liquid to produce cement, although some manufacturers ship clinkers in their lump form to cut down on dust.
The clinker manufacturing process starts with the extraction of the raw meal from the homogenization silo to insure that the raw meal is stable and homogenized in order to produce consistent clinker quality. The preheating of the material takes place in pre-heater cyclones fitted with a pre-calciner fired with petroleum, natural gas or coal. The calcinations of the material begin during this stage, changing its phase to the oxide phase for each component to be ready for the burning process. The burning phase takes place in a rotary kiln. The clinker temperature in the kiln burning zone has to reach 1,500°C and then it is cooled in a cooler by air which decreases the temperature.
The entire manufacturing process is continuously monitored and controlled from the central control room. The clinker is ground with an amount of gypsum to a fine powder in order to regulate the setting time of cement and to gain the most important property of cement, which is compressive strength. Portland cement clinker is the essential ingredient of Portland cement. Portland cement is obtained by grinding clinker with only minor amounts of a few other minerals, so its composition does not depart far from that of clinker. Other cements (i.e. non-Portland cements, for example pozzolanic cements, blast furnace slag cements, limestone cements and masonry cements) contain larger amounts of other minerals and have a much wider composition range.
Although the other potential ingredients may be cheap natural materials, clinker is made in an energy-intensive chemical process - in a kiln.. Between one and two billion tons a year of clinker are made world-wide, and the details of its formation are therefore of great economic significance, since no viable alternative ingredients for making cement-like materials currently exist. Unlike many other thermal products (e.g. aluminum, pig-iron), clinker is a fairly complex mixture of different minerals, and so its production depends on a multi-dimensional control of raw materials and a multi-staged heat treatment. It has been likened to a “man-made igneous rock”, and an understanding of its structure and chemistry requires the application of many principles of geochemistry.
Portland Cement Clinker consists essentially of four minerals: alite, belite, tricalcium aluminate and tetracalcium aluminoferrite and, there are also many other non-essential minerals that occur in small quantities.
The composition of clinker is examined by two separate approaches:
• by mineralogical analysis, using petrographic microscopy and/or x-ray diffraction analysis.
• by chemical analysis, most accurately by x-ray fluorescence spectrometry.
The early analyses were all based upon classical “wet” methods involving dissolution of the material, then estimating components gravimetrically – i.e. by precipitating and weighing them – or volumetrically by titration with a reagent that reacts with the element in question. Without going into excessive detail, the most important parts of the analysis scheme consisted of:
Dissolving the sample in acid (properly made clinker dissolves in hydrochloric acid very easily and completely).
• Weigh what little fails to dissolve as “insoluble residue”.
• Reduce the pH to precipitate silica: ignite and weigh it.
• Neutralize with ammonia, precipitating “R2O3” - consisting of most of the Al2O3, Fe2O3, TiO2, P2O5 and Mn2O3. This is ignited and weighed.
• Add ammonium oxalate to precipitate calcium oxalate: ignite it to CaO and weigh.
• Concentrate the remaining solution and add ammonium phosphate to precipitate MgNh3PO4: ignite it to Mg2P2O7 and weigh.
• Redissolve the “R2O3” in acid and separately determine Fe2O3 by selective precipitation or by a redox reaction.
The last stage was often missed out in early analyses. SO3 was measured on a fresh sample by precipitation as BaSO4. This was a typical cement plant analysis: from early times, more scientific investigations performed additional analysis for Na, P, Cl, K, Ti, Mn, Zn, Sr, Ba, etc. No even moderately accurate method of analysis for Al2O3 existed until the arrival of XRF in the 1960s.
Reliable alkali metal analysis remained quite inaccessible until flame photometry was introduced. One glaring omission from early analysis was any estimation of the amount of “free” or “uncombined” CaO in clinker. A method was developed in the USA in 1920s involving non-aqueous dissolution and titration of the free CaO using glycols in an alcohol solvent. A variant finally came into use in Britain after WWII. For many years prior to this it was often claimed that there was no free lime in cement - a claim very wide of the mark. Early manufacturers often “matured” their cement for several months before daring to sell it, to give time for the free lime to hydrate. Accurate analysis only started to develop as “instrumental” techniques became available – and in particular, various spectrometric techniques that provided absolutely element-specific data. Among these, atomic emission and absorption techniques were used, but overwhelmingly the most important is x-ray fluorescence spectrometry. Even with highly automated instrumental techniques, accurate analysis of cement is particularly difficult. The analysis problem is subtly different from that of most other process materials. Other major products for which chemistry is important – for example iron or aluminum – usually consist largely of a single element or compound in which the other constituents are only present in minor or trace quantities. At worst, an alloy may be a simple binary mixture. The minor constituents can be measured in the knowledge.
Chemical parameters based on the oxide composition are very useful in describing clinker characteristics. The following parameters are widely used (chemical formulae represent weight percentages):
The Lime Saturation Factor is a ratio of CaO to the other three main
oxides. Applied to clinker, it is calculated as:
LSF=CaO/(2.8SiO2 + 1.2Al2O3 + 0.65Fe2O3)
Often, this is referred to as a percentage and therefore multiplied by
The LSF controls the ratio of alite to belite in the clinker. A clinker with a higher LSF will have a higher proportion of alite to belite than will a clinker with a low LSF.
Typical LSF values in modern clinkers are 0.92-0.98, or 92%-98%. Values above 1.0 indicate that free lime is likely to be present in the clinker. This is because, in principle, at LSF=1.0 all the free lime should have combined with belite to form alite. If the LSF is higher than 1.0, the surplus free lime has nothing with which to combine and will remain as free lime.
In practice, the mixing of raw materials is never perfect and there are always regions within the clinker where the LSF is locally a little above, or a little below, the target for the clinker as a whole. This means that there is almost always some residual free lime, even where the LSF is considerably below 1.0. It also means that to convert virtually all the belite to alite, an LSF slightly above 1.0 is needed.
The LSF calculation can also be applied to Portland cement containing clinker and gypsum if (0.7 x SO3) is subtracted from the CaO content.
NB: This calculation (0.7 x SO3) is based on the ratio of the molar masses of calcium oxide and sulfur trioxide, ie: 56/80 = 7/10. It therefore assumes that all the sulfate in the clinker is present as anhydrite; it does not account for sulfate present as clinker sulfate in the form of potassium and sodium sulfates, or for water in gypsum, and the calculation will therefore not be exact.
Neither does it account for fine limestone or other material such as slag or fly ash in the cement. If these materials are present, calculation of the original clinker LSF becomes more complex. Limestone can be quantified by measuring the CO2 content and the formula adjusted accordingly, but if slag or fly ash are present, calculation of the original clinker LSF may not be conveniently practicable.
The Silica Ratio (also known as the Silica Modulus) is defined as:
SR = SiO2/(Al2O3 + Fe2O3)
A high silica ratio means that more calcium silicates are present in the clinker and less aluminate and ferrite. SR is typically between 2.0 and 3.0.
Alumina Ratio (AR)
The alumina ratio is defined as:
This determines the potential relative proportions of aluminate and ferrite phases in the clinker.
An increase in clinker AR (also sometimes written as A/F) means there will be proportionally more aluminate and less ferrite in the clinker. In ordinary Portland cement clinker, the AR is usually between 1 and 4.
The above three parameters are those most commonly used. A fourth, the ‘Lime Combination Factor’ (LCF) is the same as the LSF parameter, but with the clinker free lime content subtracted from the total CaO content. With an LCF=1.0, therefore, the maximum amount of silica is present as C3S.