Grindibilty etc
Lime in the clinker gets
Lime in the clinker gets saturated and the grinding will saturated and the grinding will be easier and the quality of be easier and the quality of cement reduces withcement reduces with ageing.
ageing.
Usually storage of clinker in open y
Usually storage of clinker in open yard is normal practice. No doubt ard is normal practice. No doubt Free Cao reduces with reduction inFree Cao reduces with reduction in cement strength made from exposed clinker. It
cement strength made from exposed clinker. It was experienced that Residue of the finish productwas experienced that Residue of the finish product increases with exposed clinker; moreover, cement mill temperature maintenance is another issue face increases with exposed clinker; moreover, cement mill temperature maintenance is another issue face by the process people. In general long
by the process people. In general long exposure OR Open yard clinker storage be avoided.exposure OR Open yard clinker storage be avoided.
Ted Krapkat
Ted Krapkat••Hello Muhammad,Hello Muhammad,
As others have mentioned;- Free CaO is
As others have mentioned;- Free CaO is reduced in clinker stored in the open due to reduced in clinker stored in the open due to reaction withreaction with atmospheric moisture and rain. This water
atmospheric moisture and rain. This water also reacts with the clinker minerals producing additionalalso reacts with the clinker minerals producing additional Ca(OH)2. For example the reaction with C3S
Ca(OH)2. For example the reaction with C3S is;-is;- 2(3CaO.SiO2) +7H2O --> 3CaO.2SiO2.4H2O +
2(3CaO.SiO2) +7H2O --> 3CaO.2SiO2.4H2O + 3Ca(OH)23Ca(OH)2 So, as the
So, as the clinker weathers, its XRD CaO content decreases but clinker weathers, its XRD CaO content decreases but it's Free Lime content, as measured byit's Free Lime content, as measured by Ethanol/Glycol titration, actually increases. LOI also increases, and is often used as
Ethanol/Glycol titration, actually increases. LOI also increases, and is often used as a measure of a measure of weathered clinker prehydration
weathered clinker prehydration
But there is a further reaction;- If the clinker is exposed to high humidity for more than a
But there is a further reaction;- If the clinker is exposed to high humidity for more than a week or two,week or two, the Ca(OH)2 which first forms reacts with atmospheric CO2 to form CaCO3, releasing water in the the Ca(OH)2 which first forms reacts with atmospheric CO2 to form CaCO3, releasing water in the process. ie Ca(OH)2 + CO2 --> CaCO3
process. ie Ca(OH)2 + CO2 --> CaCO3 + H2O+ H2O This water can then
This water can then hydrate more clinker minerals and Free CaO, releasing further Ca(OH)2.... and so hydrate more clinker minerals and Free CaO, releasing further Ca(OH)2.... and so on.on. Once enough water has been absorbed by
Once enough water has been absorbed by the clinker these reactions can continue to occur for the clinker these reactions can continue to occur for somesome time... even if the clinker is later
time... even if the clinker is later covered, or removed from the elements. There will of covered, or removed from the elements. There will of course be a largecourse be a large increase in the LOI of
of the prehydration of the
of the prehydration of the clinker minerals.clinker minerals.
However, if you are adding limestone as a filler in your cement, there is a solution to using partially However, if you are adding limestone as a filler in your cement, there is a solution to using partially weathered clinker, while experiencing little reduction in mortar strengths, provided that
weathered clinker, while experiencing little reduction in mortar strengths, provided that the L.O.I. of thethe L.O.I. of the weathered clinker is not greater t
weathered clinker is not greater than the contribution of the normal limestone filler content.han the contribution of the normal limestone filler content.
For example, if your GP cement normally contains say 5% of pure limestone as mineral filler and 5% For example, if your GP cement normally contains say 5% of pure limestone as mineral filler and 5% gypsum, then your GP cement L
gypsum, then your GP cement L.O.I. will be around 3.3%, using .O.I. will be around 3.3%, using fresh clinker. This LOI includes;-fresh clinker. This LOI includes;- LOI contribution of fresh clinker =
LOI contribution of fresh clinker = ~0.3%~0.3% LOI contribution of 5% gypsum = ~0.8% LOI contribution of 5% gypsum = ~0.8% LOI contribution of 5%
LOI contribution of 5% limestone = ~2.2%limestone = ~2.2%
If you are already adding CaCO3, in the form of limestone, it is a simple matter to reduce the amount of If you are already adding CaCO3, in the form of limestone, it is a simple matter to reduce the amount of limestone mineral filler added to the cement, so as to just compensate for the extra CaCO3 in the
limestone mineral filler added to the cement, so as to just compensate for the extra CaCO3 in the weathered clinker. At the same time,
weathered clinker. At the same time, reducing the amount of limestone filler has reducing the amount of limestone filler has the effect of increasingthe effect of increasing the cement clinker mineral content back to its
the cement clinker mineral content back to its normal level.normal level. But there's a
But there's a limitation;- In the above example (using 5% limestone filler) it limitation;- In the above example (using 5% limestone filler) it would not be possible towould not be possible to compensate for this extra CaCO3 if the LOI of the weathered clinker is greater than 2.2%.
compensate for this extra CaCO3 if the LOI of the weathered clinker is greater than 2.2%.
Therefore, it is always best to keep your "outside" clinker covered. But if you are then forced to use it, Therefore, it is always best to keep your "outside" clinker covered. But if you are then forced to use it, and you already add limestone as
and you already add limestone as a mineral filler, it is a mineral filler, it is possible to use partially weathered clinker withoutpossible to use partially weathered clinker without significant effect on mortar or concrete strengths. But in extreme cases you may have to grind the
significant effect on mortar or concrete strengths. But in extreme cases you may have to grind the cement made from weathered clinker slightly finer to expose
cement made from weathered clinker slightly finer to expose enough fresh clinker mineral surfaces.enough fresh clinker mineral surfaces. You will need to continually test the LOI of the clinker being fed to the cement mill (after first drying it You will need to continually test the LOI of the clinker being fed to the cement mill (after first drying it fully) and adjust the limestone feed according to the
fully) and adjust the limestone feed according to the LOI result obtained.LOI result obtained. Of course there is a
Of course there is a cost penalty since every 1% less limestone added to cost penalty since every 1% less limestone added to cement means 1% more clinkercement means 1% more clinker consumption for the same amount of
consumption for the same amount of cement. Maintainincement. Maintaining cement performance when using weatheredg cement performance when using weathered clinker ALWAYS comes at a price.
clinker ALWAYS comes at a price.
Nohman Mahmud
Nohman Mahmud••Agreed with Mr Ted that whenever clinker is stored in open yard ,its free lime asAgreed with Mr Ted that whenever clinker is stored in open yard ,its free lime as tested by wet /
tested by wet / chemical analysis increases from the free lime content at which clinker was chemical analysis increases from the free lime content at which clinker was dumped indumped in open yard due to hydration reactions as the method do not distinguish before free CaO and free open yard due to hydration reactions as the method do not distinguish before free CaO and free Ca(OH)2----Refer ASTM C114 , 27
Ca(OH)2----Refer ASTM C114 , 27 Mohammed Abdo
Mohammed Abdo••yes the setting time will influence due to C3A reaction with water is great andyes the setting time will influence due to C3A reaction with water is great and rapidly more than other m
that causing to partial attrition of C3A thus the setting time will increase as result of that,
that causing to partial attrition of C3A thus the setting time will increase as result of that, there for it willthere for it will causing to use less amount of gypsum than normal addition .
causing to use less amount of gypsum than normal addition . Maréchal Philippe
Maréchal Philippe••Dear Muhammad,Dear Muhammad, It is always
It is always possible to store clinker outside but the quality will possible to store clinker outside but the quality will decrease with the rainfall level.decrease with the rainfall level. Below 6 months, you will have minor problems. A little bit increase of LOI (up to 2% on weight
Below 6 months, you will have minor problems. A little bit increase of LOI (up to 2% on weight basis) andbasis) and an easier grindability that gives fineness in the
an easier grindability that gives fineness in the cement but no compressive strenght according tho thecement but no compressive strenght according tho the increase of fineness.
increase of fineness.
Usually, to recover an old clinker pile, one can mix old clinker and fresh clinker (20 % fresh and 80% old Usually, to recover an old clinker pile, one can mix old clinker and fresh clinker (20 % fresh and 80% old one) and finally reuse all the
one) and finally reuse all the stock.stock. We have no experience of wasting old
We have no experience of wasting old clinker stored outside.clinker stored outside. Let me know if you need support to solve your problem. Let me know if you need support to solve your problem. Regards
Regards Philippe Philippe
Mohammed Abdo
Mohammed Abdo••but how could yard clinker be easier but how could yard clinker be easier grind ability although the clinker mineral'sgrind ability although the clinker mineral's partially solidify due to react with rain water ???
partially solidify due to react with rain water ??? can you explain further
can you explain further
The hydrated clinker is easier to
The hydrated clinker is easier to grind because of micro cracks inside the alite crystals grind because of micro cracks inside the alite crystals partlypartly deteriorated by weathering effect water and CO2.
deteriorated by weathering effect water and CO2. Note the free lime in
Note the free lime in clinker (around 1%) is usually recarbonated.clinker (around 1%) is usually recarbonated. Jagat Singh Rathee
Jagat Singh Rathee••Prolonged storage of clinker in the open has both the advantages andProlonged storage of clinker in the open has both the advantages and disadvantages
disadvantages Advantages : Advantages :
Clinker becomes easier to grind, Clinker becomes easier to grind,
cement mill output improves though slightly , cement mill output improves though slightly , which consequently reduces specific power consu
which consequently reduces specific power consumption of cement / finish mill circuit, frmption of cement / finish mill circuit, free lime inee lime in clinker gets hydrated,
clinker gets hydrated,
easy to handle this clinker etc. easy to handle this clinker etc. Disadvantages :
Disadvantages :
Reduction in cement strength , Reduction in cement strength , degree or quantum of
degree or quantum of decrease ,shall depend upon the duration of outside storing and tdecrease ,shall depend upon the duration of outside storing and t he condition of he condition of storing,
storing, if you are m
if you are making blended cements like PPC or PSC , aking blended cements like PPC or PSC , the additives consumption at the finish grindingthe additives consumption at the finish grinding stage shall reduce
and consequently ,the manufacturing cost shall increase ,that is detrimental for
and consequently ,the manufacturing cost shall increase ,that is detrimental for the company.the company. Material handling cost is an added disadvantage
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