Three high belite laboratory clinkers were prepared from traditional and alternative raw materials. Reference clinker was obtained from 77% limestone, 11% sandy clays, 11% fatty clays and 1% iron scales. The fatty clays were replaced by red brick powder in the raw meal of the second clinker and were lowered to 2% with the replacement of 10% of the limestone by egg shells in the third clinker. The SEM examination revealed clear presence of crossed striae and twinning in the rounded belite grains of the reference clinker caused by the transformation of the α‘-belite to the β polymorph. Striae were weaker in the second and third clinkers indicating a probable stabilization of the α ‘-belite polymorph.
Compressive strength of the respective cements were attained first after 28 days and the early strength did not improve with increasing fineness. Higher compressive strength values were found for the cement prepared from second clinker.
El estudio realizado por SEM muestra superficies estriadas alrededor de los granos de belita que indican una transformación del polimorfo α′a la forma β-C2S, durante el enfriamiento. Esas estrías son menos marcadas en el segundo y tercer clinker, indicando, una estabilización del polimorfo α′-C2S.
Los valores de resistencias a compresión de los correspondientes cementos, a 28 días de curado, no se ven incrementados por la finura de dichos cementos. Las mayores resistencias se obtuvieron en el cemento preparado a partir del clínker con polvo de ladrillo rojo.
Portland cement is an essential component for the daily life. It is one of the most consumed materials in the world. The global cement consumption was expected to grow from 448 kg/person in 2009, to 539 kg/person in 2012 and to 645 kg/person by 2017 (
On the other hand, the climate change is directly related to the CO2 emission. On the global level, the cement industry produces ∼1.4 Bt CO2/ year, i.e. ∼6% of the total CO2 production and ∼4% of the global warning (
There is therefore an urgent need to reduce the energy consumption and the CO2 emission in the cement sector. Recent data revealed that a good utilization of waste materials might reduce the CO2 emission by up to 9% (
One way to achieve these targets is to limit the consumption of Portland cement clinker by enhancing the production of blended cements within the scope of the international standard specifications such as EN 197-1, EN 14216 and ES 4756 (
Other solutions deal with the partial substitution of the high-lime cement by the lower temperature belite phase with the stabilization of the more active belite polymorph, the α′-phases (
To overcome the lack of early strength, the high belite cements are blended with calcium sulfoaluminate or sulfoferrite (
The activation of a low temperature clinker through the stabilization of the α‘- belite modification adds value to the cement manufacture process and leads to better durability.
Another important aspect related to the reduction of the production costs is the use of alternative raw materials and/or alternative fuels (
The aim of the present paper deals with the use of alternative raw materials to contribute to the reduction of energy, CO2 and production cost. In this work, the effect of replacing parts of the clays and limestone with red brick powder and egg shells on the quality of the clinker and the respective cement is investigated.
The raw materials used were limestone, sandy and fatty clays quarried from the quarries of Tourah cement plant, Suez Cement Group, Cairo, Egypt. Iron scales supplied from Alexandria Steel Company were utilized as a corrective material. Red brick powder was available from the red brick factories located in the surrounding of the cement factory and the egg shells were obtained from the alimentation market.
The oxide composition of the raw materials was determined by means of X-ray fluorescence using a Philips apparatus PW 2404 Type X-CEM. The trace elements of the red brick powder and the egg shells were detected by carrying out the scanning mode of the XRF apparatus on the samples. The alkali contents were estimated with the help of a flame photometer Jenway PFP7.
The mineralogical composition of the raw materials was defined by means of X'PERT MPD Philips X-ray diffractometer and their thermal behavior was measured by differential thermal and thermogravimetric analyses on a 60H Shimadzu equipment.
Three mixes were designed to prepare raw meals of the high belite cement with a lime saturation factor of 77%, silica and alumina modulus of ∼2.2 and ∼1.2 respectively (
Design of the raw mixes (%) and their burning parameters
Limestone | Sandy clay | Fatty clay | Iron scales | Red brick powder | Egg shells | LSF | SM | AM | |
---|---|---|---|---|---|---|---|---|---|
|
77.0 | 11.0 | 11.0 | 1.0% | – | – | 77.10 | 2.22 | 1.26 |
|
77.0 | 12.0 | – | 1.0% | 10.0% | – | 77.06 | 2.28 | 1.31 |
|
66.7 | 20.3 | 2.0 | 1.0% | – | 10.0% | 76.61 | 2.24 | 1.23 |
LSF = Lime saturation factor. SM = Silica modulus AM = Alumina modulus.
The raw materials were separately dried, finely ground and sieved up to a residue of 15–17% on a 90 µm sieve. They were intimately mixed and pressed as pellets 40 mm diameter. The pellets were burned 15 minutes in a platinum crucible at 1350 °C. At the end of the burning period the clinkers obtained were quenched in air at room temperature with an approximate cooling rate of 850 °C/ minute then finely ground to a fineness <90 µm, their free lime content indicating their burnability (
The oxide composition of the clinkers was determined by means of X-ray fluorescence; (XRF, PANalytical; Model Magix Pro PW 2440, PANalytical). Their phase identification was performed with EVA software and Rietveld refinements were performed using TOPAS 3, Bruker-AXS Panatical X'Pert. Supplementary diffractograms were obtained at low scanning modes in the 2 theta region from 25 to 35° then from 35 to 40° on the X'PERT MPD Philips X-ray diffractometer.
The boron concentration in the clinkers was checked by means of atomic absorption apparatus model GBC Avanta.
The clinkers were treated with KOH-sucrose to dissolve C3A and C4AF for 10 minutes (
The morphology of fractured surfaces was examined with the secondary electron mode by means of Quanta 250 FEG scanning electron microscope as well as on the back scattered mode with EDAX on Zeiss EVO 50XVP, analyzer Bruker AXS XFlash Detector 410.
The gypsum content added to each clinker was estimated from the Na equivalent and C3A in the clinker as follows: Naeq = Na% + 0.658 K%, the optimum SO3 = 1.841 + 0.095 C3A + 1.636 Naeq (
The compressive strength results were monitored with of a compression tester Toni Technik Model 2010.010 with an accuracy of 0.04 ± 0.01%.
Oxide composition of the raw materials (%)
Material (%) | Primary raw materials | Secondary raw materials | |||||
---|---|---|---|---|---|---|---|
|
|||||||
Limestone | Sandy clay | Fatty clay | Iron scales | Gypsum | Egg shells | Red brick powder | |
|
41.79 | 6.64 | 11.17 | 0.08 | 9.33 | 42.26 | 1.53 |
|
51.14 | 1.56 | 1.86 | none | 29.23 | 53.82 | 2.93 |
|
3.63 | 63.51 | 53.98 | 0.27 | 2.54 | 0.06 | 58.75 |
|
0.49 | 14.73 | 17.24 | 0.16 | 0.74 | none | 16.83 |
|
0.20 | 7.81 | 10.89 | 99.00 | 0.11 | none | 7.50 |
|
0.86 | 2.00 | 2.70 | 0.07 | 1.50 | 0.75 | 1.77 |
|
0.07 | 1.38 | 1.36 | none | 0.09 | 0.07 | 1.22 |
|
0.10 | 1.36 | 1.27 | none | 0.14 | 0.02 | 1.41 |
|
0.37 | 0.03 | 0.16 | 0.17 | 48.41 | 0.98 | 1.47 |
|
0.13 | 0.05 | 0.05 | none | 0.16 | 0.01 | 0.05 |
|
0.06 | 0.11 | 0.18 | 0.11 | 0.07 | none | 0.11 |
|
0.01 | 0.08 | 0.21 | 0.08 | 0.02 | none | 0.05 |
|
0.04 | 1.52 | 2.05 | none | 0.01 | 0.72 | 0.93 |
LOI = Loss on ignition.
Trace elements of the alternative raw materials (ppm)
V | Cr | Co | Ni | Cu | Zn | Rb | Sr | Y | Nb | Ba | Pb | Zr | |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
15.7 | 7.6 | 2.7 | 7.4 | 25.3 | 65.8 | 43.3 | 521.8 | 16.6 | 12.4 | 287.1 | 27.2 | 246.3 |
|
93.5 | 12.6 | 1.5 | 4.5 | 4.0 | 105.0 | 65.1 | 357.0 | 33.4 | 71.5 | 388.7 | 15.0 | 375.4 |
The X-ray diffraction patterns of limestone indicate that the calcite phase (Cc) is the main constituent of limestone and quartz (Q) appears as a minor phase in the sample (
The X-ray diffraction patterns of limestone and egg shells (Cc = Calcite, Q = Quartz).
The X-ray diffraction patterns of the clays and red brick powder are presented in
The X-ray diffraction patterns of the sandy clays, fatty clays and red brick powder (M = Montmorillonite- swelling clays, K = kaolinite, Q = Quartz, Ha = Halloysite F = Feldspar He = Hematite, I = Ilite).
The red brick powder is composed of a weak halloysite (Ha) pattern observed at 2 theta value lower than 10° beside traces of feldspar (F) and hematite (He). The weak peak appearing at 3.50 Å is attributed to the anhydrite. A clear hump is seen at a 2 theta range of 20 to 30° indicating the existence of a glassy phase in this sample.
The oxide composition of the raw mixes is given in
Differential thermal analysis of the three raw mixes: a) M1ref, b) M2 and c) M3.
The oxide composition of the raw mixes (%)
XRF | Fl.Photometer | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
|
||||||||||||
L.O.I | CaO | SiO2 | Al2O3 | Fe2O3 | MgO | SO3 | Cl | P2O5 | MnO | TiO2 | Na2O | K2O | |
|
32.96 | 39.43 | 15.74 | 3.96 | 3.14 | 1.39 | 0.30 | 0.27 | 0.43 | 0.06 | 0.10 | 0.35 | 0.31 |
|
32.79 | 39.17 | 16.26 | 3.87 | 2.96 | 1.40 | 0.31 | 0.19 | 0.33 | 0.03 | 0.09 | 0.38 | 0.30 |
|
34.86 | 39.31 | 15.93 | 3.92 | 3. 20 | 1.31 | 0.27 | 0.19 | 0.46 | 0.05 | 0.09 | 0.33 | 0.32 |
Fl. photometer: Flame photometer.
The results obtained from the burnability tests of the mixes are illustrated in
The variation in the free lime content of the raw mixes with temperature a) M1ref b) M2 c) M3.
The oxide composition of the clinkers is given in
The oxide composition of the clinkers (%)
XRD | Fl.photometer | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
|
||||||||||||
FL | L.O.I | CaO | SiO2 | Al2O3 | Fe2O3 | MgO | SO3 | P2O5 | MnO | TiO2 | Na2O | K2O | |
|
0.62 | 0.59 | 59.45 | 24.75 | 6.17 | 4.91 | 1.78 | 0.16 | 0.12 | 0.05 | 0.61 | 0.21 | 0.24 |
|
0.45 | 0.56 | 59.53 | 25.23 | 5.97 | 4.67 | 1.75 | 0.26 | 0.11 | 0.04 | 0.51 | 0.28 | 0.22 |
|
0.52 | 0.65 | 59.07 | 24.6 | 6.11 | 5.17 | 1.63 | 0.13 | 0.17 | 0.05 | 0.63 | 0.23 | 0.28 |
FL = Free lime LOI- = Loss on Ignition.
The phase composition of the clinkers
C3S | C2S | C3A cubic | C4AF | |
---|---|---|---|---|
|
5.60 | 64.30 | 11.00 | 13.40 |
|
5.39 | 66.91 | 8.05 | 14.94 |
|
7.70 | 67.10 | 7.20 | 14.30 |
|
3.75 | 69.52 | 7.92 | 14.21 |
|
10.10 | 60.50 | 9.90 | 14.90 |
|
5.01 | 66.76 | 7.45 | 15.73 |
The trace elements content of the clinker residues (after dissolution with KOH and sucrose) shows highest strontium and zirconium concentrations of 1272 and 252 ppm in Clik2 followed by 718 and 160 ppm in Clik1ref then 544 and 128 ppm in Clik3.(
Trace elements of the clinker after selective dissolution (ppm)
V | Cr | Co | Ni | Cu | Zn | Rb | Sr | Y | Nb | Ba | Pb | Zr | La | |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
23.3 | 16.8 | 7.0 | 5.6 | <2 | 22.0 | 31.0 | 718.0 | 15.0 | 9.4 | 274.8 | 20.0 | 160 | 15 |
|
25.5 | 20.3 | 6.4 | 5.6 | <2 | 20.1 | 31.9 | 1272.0 | 14.3 | 8.4 | 170.0 | 13.0 | 252 | 16.7 |
|
25.5 | 19.0 | 5.9 | 5.2 | <2 | 19.5 | 31.7 | 544.5 | 13.6 | 8.3 | 321.0 | 12.7 | 128.7 | 15.8 |
The electron micrographs of the reference clinker are illustrated in
Scanning electron micrographs of the reference clinker M1ref obtained from burning limestone with sandy, fatty clays and iron ores (LSF = ∼77%), a and b = Secondary electron mode, c = back scattered mode.
The scanning electron micrographs of the second clinker (Clik2) made with red brick powder indicates lower melt portion compared to Clik1ref and fewer amount of the interstitial phases (
Scanning electron micrographs of Clik2 prepared from the total replacement of fatty clays by red brick powder (LSF = ∼77%), a and b = Secondary electron mode, c = back scattered mode.
The scanning electron micrographs of the third clinker (Clik3) prepared from egg shells and 2% from fatty clays show a lower amount of melt than in Clik1ref and weak parallel striae on the rounded belite crystals (
Scanning electron micrographs of Clik3 prepared from 2% of fatty clays and egg shells (LSF = ∼77%), a and b = Secondary electron mode, c = back scattered mode.
The EDAX analysis on the three clinkers showed only the major elements in the clinkers. Element present below 0.1% could not be detected.
The X-ray diffractograms of the clinkers are illustrated in The main peak of the α‘-belite at 2.753Å (32.49°) is very close to that of the β-belite at 2.749 Å (32.56°) and to that of the main d-value line for alite at 2.77 Å A characteristic belite peak is seen at an angle of 31.04° with a d-value line of 2.81 Å The α′- and β-belite patterns appear in the diffractograms as a splitted peak and are relatively higher than the alite peak in Clik3
The characteristic patterns of C3A identified at 2.70 Å is well recognized in Clik1ref, but appears weakly in Clik3 and is absent in Clik2
The XRD of the clinkers prepared. A = Alite, B = Belite.
No characteristic peaks for belite were identified in the diffractogram run in the 2 theta region of 38°.
The oxide composition of the cements
(%) | L.O.I | CaO | SiO2 | Al2O3 | Fe2O3 | MgO | Na2O | K2O | SO3 | Cl | P2O5 | MnO | TiO2 | IR | Naeq |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
1.37 | 59.67 | 23.26 | 6.08 | 4.81 | 1.85 | 0.26 | 0.24 | 3.32 | 0.035 | 0.63 | 0.10 | 0.16 | 0.92 | 0.42 |
|
1.14 | 59.93 | 23.30 | 6.11 | 4.62 | 1.82 | 0.32 | 0.22 | 3.22 | 0.038 | 0.45 | 0.06 | 0.15 | 0.94 | 0.46 |
|
1.20 | 59.84 | 23.37 | 6.02 | 5.03 | 1.72 | 0.23 | 0.28 | 3.28 | 0.037 | 0.67 | 0.07 | 0.13 | 0.90 | 0.41 |
|
≤5 | ≤3.5 | ≤0.1 | ≤5 | ≤0.6 |
The phase composition and physical properties of the cements
Phase composition (%) | Physical properties | |||||||
---|---|---|---|---|---|---|---|---|
|
|
|||||||
C3S | C2S | C3A | C4AF | Stand. Consis. (%) | I.S. (min.) | F.S. (min.) | Soundness (mm) | |
|
8.88 | 60.06 | 7.98 | 14.64 | 21.5 | 180 | 205 | 0 |
|
9.99 | 59.34 | 8.38 | 14.06 | 22.0 | 175 | 195 | 0 |
|
8.94 | 60.33 | 7.45 | 15.31 | 22.0 | 180 | 200 | 0 |
|
≥75 | ≤10 |
The compressive strength of the high belite cement prepared from primary and alternative raw materials
Age (d) | Compressive strength (N/mm2) | |||||
---|---|---|---|---|---|---|
|
||||||
Blaine 3500 cm2/g | Blaine 4500 cm2/g | EN 197-1 | ES 4756 | |||
|
|
|||||
Cem1ref | Cem2 | Cem3 | Cem1ref | |||
|
5.3 | 5.6 | 5.3 | 6.1 | ||
|
6.9 | 7.3 | 7.0 | 7.6 | ||
|
9.9 | 10.2 | 9.7 | 10.7 | ≥16 | ≥16 |
|
37.2 | 38.8 | 37.5 | 38.0 | 32.5–52.5 | 32.5–52.5 |
|
55.4 | 57.1 | 55.0 | 55.8 |
The manufacture of low lime cement aims to reduce the energy consumption, the green house effect as well as the production cost. It is realized through the decrease of the LSF of the clinker. Lowering the LSF from 100 to 75 leads to a 12% reduction in the theoretical heat requirement and 6% in CO2 emission (
The LSF of the clinkers produced in this work is ∼77%. It was successfully used for the formation of high belite clinker with 60–67% C2S, and 5–10%.C3S. The formation of the high belite clinkers is supported by the morphology of the phases in the SEM micrographs.
The differentiation between the various belite polymorphs is difficult but recent work was indicative with the use of synchrotron analysis (
The present study indicates a probable stabilization of the α′
According to the literature, the α′-belite phase is stabilized by P2O5
(
However, the significantly high concentrations of strontium (1272 ppm) in the residue of Clik2 made of red brick powder could be a strong indication for a role played by this element in the stabilization of the α′
The strontium concentration detected in Clik3 made of egg shell (544.5 ppm) is lower than those of Clik2 and Clik1ref. The morphology of the clinker grains attributed to the possible stabilization of the active belite phase could be due to the barium content (321 ppm) as previously reported in the literature (
The higher 28 days strength values of the second cement prepared from Clik2 is attributed to a higher alite content but the contribution of the more reactive α′-belite modification to the strength values is not excluded.
The following conclusions can be drawn for the present work: Red brick powder and egg shells can be successfully used in the cement manufacture process The use of these secondary raw materials to replace the clays obtained from the quarry of Tourah Cement Company leads to a probable stabilization of the more reactive α The stabilization of the α A strontium concentration of 1272 ppm in the residue of red brick powder clinker and a barium content of 321 ppm in that of egg shells are expected to stabilize the active belite polymorph The cement made of the red brick powder clinker showed higher strength values than the other clinker
The authors would like to thank, Customer Support team, Suez Cement Group of Companies, Egypt, Italcementi Group: Mr. Stefano Gallini, Eng. M. Yildirim Manager, Eng A. Arafa and Eng. A. Abdel Moaty.
Special thanks for Eng. Xavier Guillot, R&D cement and hydraulic binders Sector Head, France, CTG, Italcementi Group. They offered us continuous support and help to achieve important analyses needed in this work.