Microscopical study and interprtation of a sample of clinker


Sample Description : A sample of clinker produced under reduction atmospher in brown color


INTRODUCTION


One of the cases that should be avoided is overcoming reduction state in kiln’s atmosphere . The sources of this problem could be listed as : Air deficiency inside the kiln , Raising level in oxygen to fuel ratio in kiln torch and Existence high carbon or sulfide in raw material . These cases could produce a clinker with undesired properties such as cement rapid hardening , the concrete hardening would be shorter than it should be , reducing in twenty eight days resistance , low workability , the problems concern with concrete flowability and cement blockage in its silo


The negative effects of reduction situation would be intensify when the burnt clinker is still in 1250 C and also with reduction atmosphere then further cooling is taking place in free atmosphere and fresh air , in these circumstances we would see clinker with brown color . But if clinker leave kiln , with reduction atmosphere but with temperatures higher than 1250 C then the color of clinker would be gray and the alite would be rather big and euhedral and cooling process would be came through without alite conversion to C2S and free lime . Otherwise in

. final product , we would seen lower percentages of alite instead of the calculated amount of alite but with free lime


: But other cases that would be seen in reduction status are

Ferrite would be in lower reflectivity coefficient

Calcium and iron sulfide would be seen

Alite decomposition to belite , free lime , ferrite and iron sulfide that probably would be seen in all spots of alite crystals as substitution and as a result of it , the wormy textures would be seen . Also the decomposed alites with dark spots would be seen in thin sections . Essentially when existing iron due to reduction is converted to iron II it influences to alite’s lattice and that results to alite instability and decomposition that its result is a crystal shape like a perfect alite but with inclusions and marginal ferrite , belite and free lime . But with further reduction ,

. this Fe (II) itself is converted to metallic iron that is recognizable under microscope with its metallic luster

In status reduction , increasing in the number of triclinic alites and increasing in the number of gama belites with coarse faces are seen . These belites consist of distinctive layering with finger like formation with segmental appearance . These belite grains consist of distinctive layers that show their appearance segmental . Three directions inside the belites is in perfect agreement with the crystal formation of host

. alite

The big crystals of ferrite and aluminate surrounded by matrix are seen and the prismatic C3A existence and zonation in the holes are seen . Even with fewer reduction , the calcium sulfide in clinker yet might be seen . The existence of dendrites and bushes of calcium sulfide isn’t

unlikely and it is possible that exists Fe-K sulfides . Also it is possible that alkali sulfates or Ca-alkali are seen . And finally it is to be told that the concrete firmness of the clinkers that have above mentioned properties that are a result of reduction status are not good and the resulted

. concrete has not needed quality


: Observed cases on studied clinker

. Existence very abnormal big alites with medium length of 82 microns

. Existence very abnormal big belites with medium length of 85 microns

In many cases , existence abnormal shapes of belites as dendrite , tree like and with very branches formed by delicate prisms that in some

. points

. have an inclined layering

. Existence the ferrites with lower reflective coefficient in comparison with normal clinkers

. Existence trivial amounts of metallic iron

. Existence trivial amounts of iron sulfide

. Existence trivial amounts of calcium sulfide or alkali sulfides


picture picture picture picture

PERCENTAGES & SPECIFICATIONS OF CLINKER PHASES


PHASES PERCENTAGE OF PHASES EXCEPT HOLES DIMENSIONS IN MICRONS APPARENT SHAPE COLOR & BIREFRINGENCE
ALITE 43 82 SOMETIMES IN REGULAR SHAPE 0.0075
BELITE 44 85 FRAGMENTED & DENDRITIC ALMOST AMBER
ALUMINATE VERY LOW THICK PRISM
FERRITE 10 LOW REFLECTIVITY
PERICLASE 1
FREE LIME SELDOM
METALLIC RARELY ALMOST 3 VERY SHINY METALLIC & SILVERY SILVERY
IRON SULFIDE RARELY ALMOST 3 SHINY YELLOW YELLOW
CALCIUM or ALKALI SULFIDE RARELY ALMOST 3 IN METALLIC LUSTRE
HOLES(POROSITY) 11

ABCD