Wpływ wewnętrznych reakcji faz cementowych na trwałość betonu
Influence of the Internal reactIons In cement Phases on the DurabIlIty of concrete
Streszczenie
Klasyczna teoria korozji siarczanowej (the DEF – The Delayed Ettringite Formation) zakłada tworzenie się igieł ekspansywnego etryngitu przy 3-molowym stężeniu jonów siarcza- nowych, jako podstawowego warunku występowania fazy etryngitu. Jednakże, wyniki badań wskazują, że może także występować faza nieekspansywnego, włóknopodobnego etryngitu z niedoborem jonów siarczanowych, który tworzy się przy deficycie jonów siarczanowych oraz z rozkładu w wodzie hydratu monosiarczanu. Taki etryngit włącza jony siarczanowe do struktury i staje się ekspansywny.
Opisano mechanizm powstawania taumazytu w reakcjach faz cementowych prze- prowadzonych w symulowanych czystych układach. W reakcji etryngitu z wodnym roztworem krzemianu sodu o stężeniu molowym 1:1 i pH ~11 przy obecności CO2 i w temperaturze 7oC następuje obniżenie pH do 9,5, co powoduje rozkład etryngitu i wzrost ciśnienia. Powstaje faza przejściowa zidentyfikowana w badaniach w podczer- wieni dla długości fali w zakresie 1027-30 cm-1. Ten przedział jest charakterystyczny dla aragonitu, kalcytu, rozłożonego etryngitu, zkarbonatyzowanego żelu krzemionkowego i najbardziej prawdopodobne krzemu o oktaedrycznej koordynacji. Podniesienie pH do 12,5 przez dodatek wapna w tej samej temperaturze prowadzi do reakcji fazy przejściowej z wapnem i utworzenia taumazytu, przy czym nie jest potrzebna dodatkowa ilość jonów siarczanowych z zewnątrz, aby powstał taumazyt. Szczegółowe wyniki zaprezentowano dla obu przypadków wpływających na trwałość betonu.
Abstract
The classical theory of internal sulfate attack, the DEF, considers the formation of a needle- like, expansive ettringite with 3 moles sulfates as a main requirement for the existence prof. dr. rer. nat. Hanaa Youssef Ghorab – Helwan University and G&W Science and Engineering Company Cairo, Egypt
of ettringite phase. Results, however, indicate the existence of a fiber-like non-expansive sulfate-deficient ettringite which forms in sulfate deficient media, as well as from the decomposition of monosulfate hydrate in water. The sulfate-deficient ettringite accom- modates more sulfate in its structure and becomes expansive.
The mechanism of thaumasite formation in cement systems simulated in pure systems is described as follows: Bubbling an ettringite - sodium silicate- water mix of a mole ratio 1:1 and a pH-value of ~11 with CO2 gas at ~7oC, lowers the pH to ~9.5, decomposes the ettringite and creates localized pressure. An intermediate phase, previously mentioned in the literature without specific definition, forms. Results show that the intermediate phase is identified by infrared band at 1027-30 cm-1. It incorporates aragonite, calcite, the decomposed ettringite, and carbonated silica gel. most probably with octahedrally coordinated silicon. Rerising the pH to 12.5 through an extra supply of lime at the same temperature, leads to the combination of the intermediate phase with lime and the forma- tion of thaumasite. No excess sulfate is needed for the thaumasite to be formed.
Detailed results are presented for both cases affecting the durability of concrete.
1. Modified mechanism of DEF
1.1 Problem description
Late ettringite formation was reported as early as 1965 [1], and the problem of internal sulfate attack (ISA) induced by delayed ettringite (DEF) in heat-treated concrete was explored in the eighties [2, 3]. Several researchers tackled the DEF phenomena to under- stand the reason of the damage occurring in heat treated concrete [4-12]. They agreed on three requirements for the DEF to occur (Figure 1): 1) excess sulfate in concrete to fulfill the need of ettringite to 3 moles sulfates to reform from the monosulfate hydrate 2) high temperature curing 3) water supply at ordinary temperature.
1.2 Our findings
Our research on pure systems showed that the reformation of ettringite from the mono- sulfate hydrate does not need 3 moles sulfate. The monosulfate hydrate decomposes in water at room temperature to a sulfate-deficient ettringite. Both phases exist together sharing less than one mole sulfate; their electric neutrality is probably satisfied by car- bonate ions [13-16].
The sulfate-deficient ettringite is non-expansive [17-19]. It incorporates more sulfate ions in its structure and becomes expansive. This occurs in presence of enough water to facilitate the ion- transport.
Figure 1: Occurrence conditions of DEF [5,10]
The requirement of 3 moles sulfate to reform the ettringite from the monosulfate hy- drate in heat-treated concrete is therefore modified to “the decomposition of the monosulfate hydrate to a sulfate-deficient, non-expansive- ettringite which becomes expansive by incorporat- ing more sulfate in its structure”. Figure 2 illustrates the modified presentation of the DEF.
Details of our findings are described below.
Figure 2: Modified occurrence conditions of DEF; MS=Monosulfate hydrate, H=Water, ISA=
Internal Sulfate Attack.
1.3 Experimental
1.3.1 The stability of ettringite and monosulfate hydrate
To study the stability of the calcium sulfoaluminate hydrates, both phases were prepared in the laboratory as follows
• The ettringite was prepared by mixing a stoichiometric ratio of C3A and gypsum with enough water at room temperature [20]. Separate samples of the prepared ettringite, 0.5 g each, were stirred in 100 ml boiled redistilled water for 1 hour and up to 14 days.
At the prescribed times, the solutions were filtered off, the composition of the filtrates were determined, and the solids were analyzed by means of X-ray diffraction (XRD).
• The monosulfate hydrate was prepared according to the method described by Lerch at al [21], by mixing equal amount of saturated lime solution with monocalcium alumi- nate solution then adding saturated calcium sulfate solution. Separate samples of the pure monosulfate hydrate, 0.3 g each, were stirred in 100 ml redistilled water at room temperature from 1 hour to 14 days [13, 22]. The solution composition of the filtrate was determined and the solid was analyzed by means of XRD.
1.3.2 The ettringite solids with different sulfate contents
To understand the effect of sulfate content on the ettringite phase with respect to its morphology and the expansion behavior, the following procedures were carried out at room temperature:
• An ettringite solid with stoichiometric 3 moles sulfate was prepared from aluminum sulfate and lime suspension according to equation below. The lime suspension was added increasingly starting with a mole ratio of CaO/SO3 =1 and ending up with CaO/
SO3 =2, the CaO/Al2O3 was = 6.
6CaO + Al2(SO4)3.8H2O + H2O 6CaO.Al2O3.3SO3.32H2O
• A sulfate-deficient ettringite with 2 and 1 moles sulfate were prepared by adding gibbsite to the aluminum sulfate solution then supplying the lime suspension to the mixes in two separate series. The starting mole ratio was CaO/SO3 =1 and ended up withCaO/SO3 = 3 and 6 in the two series respectively. The end mole ratio of CaO/
Al2O3 was equal to 6.
The mixtures were filtered off after two minutes from mixing. The composition of the filtrates was determined. The solids were dried 1 day at 50oC, analyzed by means of X-ray diffraction analysis and their free lime contents were measured.
Three ettringite samples E3, E2 and E1, which subscripts denote the sulfate content of the respective series, were collected at the first detection of the free lime in the solids and the parallel appearance of XRD patterns of the ettringite in the three series respec- tively. Their morphology was examined on a Hitachi scanning electron microscope Type S-3400N with EDAX attachment.
1.3.3 Expansion behavior of clinker doped with ettringite solids of different sulfate contents
A clinker powder was doped with the E3-, E2- and E1- ettringite solids keeping a final SO3 content of 5%. Three clinker-doped specimens, C3, C2 and C1 were obtained. Pastes were prepared from the three clinker samples as well as from the reference C0, using a water/
solid ratio of 0.3. They were cast in cylindrical shaped plastic molds, 20 mm in diameter and 40 mm height. The molds were covered with plastic bags, left 24 hours to harden
then demolded. The zero readings were measured using a micrometer with a sensitivity of 0.01mm. The cylinders were cured in water, 0.01, 0.1 and 1M sodium sulfate solution at room temperature. Readings were monitored at different time intervals starting from 2 minutes to 60 days.
1.4 Results
1.4.1 The decomposition of ettringite to monosulfate hydrate by heating
Figure 3 illustrates the XRD patterns of the ettringite prepared from C3A and gypsum after boiling 1 hour in water [13,14]. The figure shows clearly the decomposition of most of the ettringite to monosulfate hydrate. The solution composition showed the release of 2.5 mole SO4-- and a pH value of ~11.8. After 6 hours the ettringite was completely decomposed to the MS and lasted 9 days long.
1.4.2 The decomposition of monosulfate hydrate to ettringite at room temperature Figure 4 illustrates the XRD patterns of the monosulfate hydrate prepared according to Lerch method, after 6-hours immersion in water at room temperature. Both calcium sulfoaluminate hydrate phases appear beside each other and remained 14 days long [16, 20]. Traces of the monocarboaluminate phase are observed in the diffractogram which indicate the partial carbonation of the hydrate phases. The solution composition of the monosulfate-ettringite mix showed a sulfate ion concentration of around 1/3 mole in equilibrium with both hydrates at a pH of ~11.8.The position of the XRD patterns of the ettringite are at 9.7 and 5.6 A in spite of its sulfate deficiency.
Figure 3: The X-ray diffraction patterns of ettringite after boiling in water for 1 hour. Most of the ettringite has decomposed to monosulfate hydrate. The solid phases are in equilibrium with 2.5 moles sulfate ions in solution
Figure 4: The X-ray diffraction patterns of the monosulfate hydrate after 6 hours immersion in water at room temperature. The MS has decomposed to ettringite. Both phases are in equi- librium with 1/3 mole sulfate ions in solution at a pH- value =~11.8.
1.4.3 The morphology of the ettringite with different sulfate contents
Figure 5 illustrates the morphology of the 3-mole SO3 ettringite, the E3 solid, prepared from lime and aluminum sulfate solution. The traditional needle-like ettringite structure is observed in the micrograph. The crystals identified are 2.5 micron long and 0.5-micron width. The Ca: S: Al ratio of the EDAX shows the usual high sulfur concentration relative to that of aluminum [17,18]. The XRD patterns of ettringite were weak but the main peaks lay in the exact position of the main d-value lines of ettringite at 9.7 and 5.6 A.
The solutions of the reactants indicated very little change in the dissolved calcium sulfate, and aluminum up to the appearance of ettringite peak and the free lime in the solid. This means that the E3 solid formed from the reaction of portlandite, gypsum and aluminum hydroxide gel in the solid.
a b
Figure 5: The scanning electron micrograph and EDAX of the ettringite with 3 moles sulfate, the E3 solid, showing a traditional needle -like morphology.
The morphology of the 2-mole sulfate ettringite, the E2 solid, showed a diffused needle; that of the E1- solid with 1 mole sulfate appeared as fiber-like structure, 1 micron long and 0.05- micron width (Figure 6); the sulfur peaks in the EDAX of the E2 and E1 solids were lower than that of aluminum. Their XRD patterns were weak as in the case of the stoichiometric ettringite with maximum peaks at the same 2 theta positions of the E3. This proves that the different sulfate ettringites cannot be differentiated by means of X-ray. The solution composition of the E1 solid indicated that the dissolved calcium sulfate contributed partially to the reaction.
a b
Figure 6: The scanning electron micrograph and EDAX of the ettringite with 1 mole sulfate, the E1 solid, showing a fiber -like morphology.
1.4.4 The expansion of ettringite with different sulfate contents
The expansion behavior of the clinker doped with the three-sulfate ettringites, the C3, C2 and C1, and the reference C0, in water and 0.01, 0.1 and 1M sodium sulfate solutions is shown in Figure 7. The results show insignificant expansion in water. In sodium sulfate solutions, the length of the three clinkers increase with increasing the sulfate content of ettringite and with the increased concentration of the sodium sulfate solution from 0.01, 0.1 and 1M.
Figure 7: The expansion of the clinker pastes doped with the ettringite solids having three, two and one moles sulfate and exposed to water and sodium sulfate solutions
2. Modified mechanism of the thaumasite formation
2.1 Problem description
The first case of thaumasite attack was detected in 1962 in a grout sample and was pub- lished with three other cases in 1965 [23]. In Europe and UK, the thaumasite attack was first reported by Bensted in 1977 for mortar in Stoke-on-Trent [24].
The classical requirements for the thaumasite formation are the availability of 1) sulfate-, 2) carbonate-, 3) silicate ions, 4) lime, 5) excess water, and 6) low temperature (0–5o C) [25]. The mechanism of its formation is still under debate.
The structure of thaumasite is very similar to that of ettringite with Si(OH)62- replacing Al(OH)63- in the columns and 2SO42- plus 2CO32- replacing 3SO42-.2H2O in the channels [26].
The column structures are similar crystallographically but the difference between them is the fine structural details in the ordered arrangement of the intercolumn materials.
The ettringite expansion and the respective cracking was claimed to be a prior cause for the thaumasite to be formed [27]. The thaumasite was, however, found in no cracked paste. It was also thought that its formation is necessarily dependent on ettringite; it
was, however, found to take place in areas of pure calcium silicate pastes not previously occupied by ettringite [28].
It is confirmed that the ettringite salt catalyzes the thaumasite formation [29], and that the alumina favors its nucleation. Any alumina present will be incorporated into the thaumasite structure [30, 31] but its absence does not prevent its formation [32,33].
Low temperatures are prerequisite for the thaumasite to be formed in cement system.
The thaumasite was also successfully formed at room temperature in pure system rich in sucrose. Low temperatures and sucrose increase the solubility of lime [34-37].
It is evident that the thaumasite formation is strongly dependent on lime [32, 33] and extra lime is always needed for its formation.
Another important requirement is the availability of carbonate. The carbonation process reduces the pH-value and favors the thaumasite formation at a pH-range of 13- 10.5 [38, 39].
Most of thaumasite was identified in sulfate media and was therefore called “the thaumasite form of sulfate attack”.
The core of our finding completes the opinion of Bensted reported in 2003. Bensted stated that a transition intermediate state must exist to permit an octahedral arrange- ment of OH- ions around the highly polarizing Si [25]. This can arise at low temperatures where atomic and molecular vibrations are relatively slow. The[Si(OH)6]2- groups formed is distorted because the carbonate ions delocalize the high charge of the strongly polar- izing Si ions. We could define this intermediate phase as a carbonated hydrated silicate incorporating the decomposed ettringite, identified at an infrared shoulder at ~ 1027-30 cm-1 [40-41]. We also found that the thaumasite formation does not depend on an excess amount of sulfate. It is mainly concerned with the carbonation effect, the lime concentra- tion, and the respective pH-value.
The explanation of our findings is given below.
2.2 Our findings
The intermediate phase suggested in 2003 by Bensted [25] is found to be a carbonated silicate phase encompassing the carbonated ettringite [40-41]. This phase was formed through bubbling a mix of ettringite and alkali silicate of pH=11, with CO2 gas at 7oC and decreasing the pH from 11 to 9.5. The intermediate phase is identified by an IR shoulder at ~1027-30 cm-1. The thaumasite formed through supplying extra lime to the intermediate phase and re-increasing the pH to 12.5 without an excess supply of sulfate.
A localized pressure was created through bubbling the ettringite-silicate mix with CO2 at low temperature. It is supported by the detection of the high-pressure polymorph of the calcium carbonate, the aragonite, beside calcite in the XRD of the intermediate phase.
These conditions would favor the formation of octahedral silicon with the residual OH ions in the mix
This sequence simulates what occurs in a carbonated cement system at low tem- perature which leads to the formation of the intermediate phase. The re-supply of lime from the hydration of the calcium silicate phase to the intermediate phase leads to the formation of thaumasite.
2.3 Experimental
Chemically pure liquid sodium silicate (Na2Si2O5) of pH 13 was mixed with an ettringite prepared with the stoichiometric amount of sulfate, at a mole ratio of 1:1, in 50 ml distilled water [40]. The pH of the mix was 11. The mix was stored 12 months in plastic bottles at 7oC. After 7 months, the pH was lowered to 9.5 by bubbling CO2 gas at 7oC, and at the 9th month the pH was raised again to 12.5 by adding 20 ml of lime water at 7oC. The mix was allowed to stand for another 3 months. At these time intervals, the solids were filtered off, washed with isopropyl alcohol, dried in a desiccator, and analyzed by means of X-ray diffraction analysis, infrared spectroscopy and scanning electron microscope.
2.4 Results
Figure 8 illustrates the infrared spectra of the ettringite (Figure 8-a) and the liquid sodium silicate (Figure 8- b) used as reactant in the study and indicate the following:
• The ettringite spectra: The vibrational frequency of OH/portlandite appears at 3633 cm-1. The stretching and bending modes of water are identified at 3433 cm-1 and 1675 cm-1. A weak carbonate band is observed at 1427 cm-1. The stretching vibration of sul- fate (S-O) is observed at 1115 cm-1, its bending vibration at 614 cm-1. The pronounced bands seen at 850 cm-1 and 548 cm-1 are attributed to the Al-O stretching and bending vibrations
a b
Figure 8: The infrared spectra of a) the ettringite b) sodium silicate [40]
• The sodium silicate spectra: The broad OH stretching mode of water appears at a fre- quency of 3460 cm-1. The weak band at 2344 cm-1 is due to hydrogen bonding. The OH bending mode at 1654 cm-1. The strong band observed at 1008 cm-1 is attributed to the Si-O stretching vibration of [SiO(OH)3]-. The shoulder of 894 cm-1 is assigned to a partial dissociation of [SiO2(OH)2] 2-.The weak bands observed at 615 and 455 cm-1 are due to the rocking modes of Si-O-Si.
Figure 9 illustrates the X-ray patterns and infrared spectra of the solids obtained after 7 months storage of the ettringite- silicate mix at pH 11. The phase identification can be described as follows:
a b
Figure 9: a) The X-ray diffraction patterns b) the infrared spectra of the ettringite-silicate mix, after 7 months storage in pH 11 at 7oC [40, 41]
• All ettringite patterns are clearly seen in the diffractogram of Figure 9-a beside weak d-value line of calcite at 3.03. A small hump is detected in the 2θ range of ~20-40o at- tributed to the amorphous hydrated silicate.
• Figure 9-b indicates the appearance of calcite bands at 1431-1384 and 869 cm-1; those of sulfate at 1113 and 615 cm-1. A small shoulder is observed at 1030 cm-1. The bands located in the frequency region ~500-400 cm-1 broaden and reflects the occurrence of a certain reaction not be recognized in the X-ray diffractogram. No indication for the formation of calcium silicate hydrate as the CSH band usually appearing at 980 cm-1 is absent.
Figure 10 illustrates the X-ray patterns and the infrared spectra of the solids obtained after bubbling the ettringite-silicate mix with CO2 at 7oC to decrease the pH to 9.5 then further storing the mix 2 months. The phase identification can be described as follows:
• Figure 10-a shows no more characteristic peaks of the ettringite in the carbonated mix.
Instead an amorphous phase forms with clear hump appears in the range of 2θ 20 to 40o . The aragonite phase is detected 3.4, 3.27 and 1.98 A and the calcite phase at 3.03, 2.49 and 1.87A.
• The IR spectra of the carbonated mix shows a broad CO frequency at 1446 cm-1 (Figure 10-b). This band is attributed to a mixture of calcite and aragonite; the v3 vibrations of pure calcite lies usually at 1430 cm-1, that of the pure aragonite appears at ~1470 cm-1. The band observed at 709 cm-1 lays between that of the pure calcite (at 713 cm-1) and the duplicate of aragonite reported to be at 713/ 700 cm-1 [42].
In this sample, the shoulder detected at 1030 cm-1 in the spectrogram of Figure 9, b, is shifted to a strong broad band at 1027 cm-1 lying beside the sulfate frequencies of sul- fate at 1129 cm-1. This band indicates the formation of the intermediate phase composed of the carbonated silicate encompassing the carbonated ettringite, aragonite and calcite.
a b
Figure 10: a) The X-ray diffraction patterns, b) the infrared spectra of the ettringite-silicate mix, after bubbling with CO2 at 7oC to decrease the pH to 9.5 then further storing for another 3 months [40, 41]
Figure 11 illustrates the X-ray patterns and the infrared spectra of the solids obtained upon increasing the pH value of the intermediate phase (the carbonated silicate-ettringite mix) to a pH 12.5 and storing the alkaline mix for another 3 months at 7oC without an excess of sulfate supply. The phase identification can be described as follows:
• Figure 11-a shows all the XRD patterns of the thaumasite salt formed under these conditions. Significant amount of calcite (Cc) is found in the sample.
• Figure 11-b illustrates the infrared spectra of thaumasite formed which are in accord- ance with those reported in the literature [43]. The functional groups detected are:
the carbonate (CO) bands of the calcite phase at 1419, 879, and 710 cm-1, the sulfate (SO-) bands at 1104 and 638 cm-1, and the two bands characteristic for the octahedral coordinated silicon at 750 and 500 cm-1.
a b
Figure 11: a) The X-ray diffraction patterns, b) the infrared spectra of the thaumasite formed after supplying the carbonated mix with lime, increasing the pH to 12.5, then storing the mix for another 2 months at 7oC [40, 41]
3. Summary and conclusions
3.1 The reformation of ettringite from the monosulfate hydrate at a delayed stage of hydra- tion does not need 3 moles sulfates. Instead, a sulfate-deficient ettringite forms with non-expansive properties. It incorporates more sulfate in its structure and becomes expansive.
3.2 The X-ray diffraction patterns of the ettringite cannot differentiate between the ettringite phases with different sulfate contents.
3.3 The thaumasite formation simulated in pure systems takes place as follows:
• The pH of the starting ettringite- silicate-water mix was 11 at 7oC
• Bubbling CO2 to the mix decreases the pH to 9.5 and decomposes the ettringite
• A carbonated-hydrated silicate phase incorporating the decomposed ettringite forms.
This is the intermediate phase reported by Bensted in 2003. It is identified at an infrared frequency range of 1027-30 cm-1.
• The carbonation effect at low temperature creates a localized pressure and causes the formation of aragonite, the high-pressure form of calcium carbonate
• These conditions favor the formation of hexacoordinated silicon.
• Thaumasite forms through resupplying lime to the intermediate carbonated phase and rerising the pH to 12.5. At this stage lime combines with the hexacoordinated silicon probably formed as a result of the localized pressure.
• The amount of sulfate originally present in ettringite is enough for the thaumasite formation. No excess of sulfate is needed for the thaumasite to form
This mechanism simulates the reactions taking place in the thaumasite form of sulfate attack in cement systems at low temperature:
Bibliography
[1] R. A., Kemerley: Ettringite formation in dam gallery, Journ. Amer. Concr. Inst,, Proc. V 62, No. 5, pp.
559-574, 1965
[2] H.Y. Ghorab, D. Heinz, U Ludwig, T. Meskendahl, A. Wolter: On the stability of calciumaluminate sulphate hydrates in pure systems and in cements, 7th International Congress Chemistry of Cement.
Vol IV, pp. 496-503,1980.
[3] D. Heinz, U. Ludwig: Mechanism of secondary ettringite formation in mortars and concretes subjected to heat treatment. American Concrete Institute. SP 100-105, Detroit, pp. 2059-2071, 1987.
[4] R. L. Day: The effect of secondary ettringite formation on the durability of concrete, a literature analysis.
Department of Civil Engineering, Research Report No CE 92-2. The University of Calgary, 112, 1992.
[5] M. Collepardi: A State-of-the-Art Review on Delayed Ettringite Attack on Concrete Cement and Concrete Composites 25, 4-5, pp. 401-407,·2003.
[6] K. L., Scrivener, H. F. W Taylor: Delayed ettringite formation: A microstructural and microanalytical study. Advances in Cement Research 5, 20, pp. 139-146, 1993.
[7] Y. Fu: Delayed ettringite formation in Portland cements products. Thesis (Ph.D.). Department of Civil Engineering, University of Ottawa, 1996.
[8] Y. Fu, J. J. Beaudoin: Microcracking as a precursor to delayed ettringite formation in cement systems.
Cement and Concrete research, 26,10, pp. 1493 – 1498, 1996.
[9] S. Diamond: Delayed ettringite formation - processes and problems. Cement and Concrete Composites, Vol. 18, pp. 205-215, 1996.
[10] S. Hanehara & T. Oyamada: Reproduction of delayed ettringite formation (DEF) in concrete and relationship between DEF and alkali silica reaction. Proceedings of FraMCoS-7, pp.1024-29, 2010.
[11] J. Stark, and K. Bollmann. Delayed Ettringite Formation in Concrete. Proceedings of the Nordic Con- crete Research Meeting, pp. 4–28, 1999.
[12] H. F. W. Taylor, C. Famy, K. L. Scrivener, Delayed ettringite formation, Cement and Concrete Research, 31, pp. 683-693, 2001.
[13] E. A. Kishar: Studies on the stabilities of hydration products of Portland cement, Ph.D. Thesis, Ain Shams University, 1991.
[14] H. Y. Ghorab and E. A. Kishar; The stability of the calcium sulfoaluminate hydrates in aqueous solu- tion, 8th International Congress on the Chemistry of Cement, Rio De Janeiro, Brazil, Vol.5, pp.104-109, 1986.
[15] H. Y. Ghorab: Causes of the delayed ettringite formation. International Symposium Non- Traditional Cement & Concrete (NTCC), Brno, Czech Republic, pp. 472-480, 2002.
[16] H. Y. Ghorab; On the chemistry of the delayed ettringite formation, RILEM TC 186-ISA, Lausanne Switzerland, pp. 65-71, 2002.
[17] A. S. Mohamed: Studies on the expansion behavior of the ettringite in pure systems and its application in cement mortars and concrete, M.Sc. Thesis, Helwan University, 2006.
[18] H. Y. Ghorab, A. M. Zayed, A. S. Mohamed, Y. Abdel Tawab, M.R.Mabrouk and H.E.H. Ahmed: Fac- tors affecting the sulfate expansion in cement systems. 12th International Congress on the Chemistry of Cement (ICCC). Montreal, Canada, TH4-12.4, 2007.
[19] H. Y. Ghorab, A. M. Zayed, A. S. Mohamed, M. R. Mabrouk. The Formation of the ettringite from sulfate solutions. 12th International Congress on the Chemistry of Cement (ICCC). Montreal, Canada, W4-09.3, 2007.
[20] E. A. Kishar: Kinetic Studies on the stability of some calcium aluminate hydrate, M.Sc. Thesis, Ain Shams University, 1986.
[21] W. Lerch, F.W. Ashton, R.H. Bogue: Journal Res. Natn Bur. Stand. 2, 715, 1929.
[22] H.Y. Ghorab, E. A. Kishar and S. H. Abou El Fetouh: Studies on the stability of the calcium sulfoalu- minate hydrates, Part 3: The monophases. Cement and Concrete Research, 28, 5, p.763-771,1998.
[23] R. Brueckner,: Accelerating the thaumasite form of sulfate attack and an investigation of its effects on skin friction, PhD thesis submitted to the university of Birmingham, pp. 2, 2007
[24] J. Bensted,: Some problems with ettringite and thaumasite in the gypsum plaster/cement contact area.
In: Proceedings of the International RILEM Symposium on Calcium Sulfates and Derived Materials, France, pp.479- 487, 1977.
[25] Bensted: Thaumasite––direct, woodfordite and other possible formation routes Cement and Concrete Composites, 25, pp. 873–877, 2003.
[26] R. A. Edge and H. F W. Taylor, Acta Cryst. B27 , 594, 1971.
[27] E.F. Irassar,: Sulfate attack on cementious materials containing limestone filler – A review. Cement and Concrete Research, pp. 39, 241-254, 2009.
[28] N. J. Crammond: The thaumasite form of sulfate attack in the UK. Cement and Concrete Composites, 25, pp. 809–818, 2003.
[29]. R. Lachaud: Thaumasite and ettringite in building materials. Ann ITBTP, 3, pp. 370, 1979.
[30] M. A. Halliwell, N.J. Crammond. Deterioration of brick work retaining walls as a result of thaumasite formation. In: Durability of Building Materials and Components 7. Sweden 1: pp. 235–44, 1996.
[31] N. J. Crammond, M. A. Halliwell. The thaumasite form of sulfate attack in concretes containing a source of carbonate ions. 2nd Symposium Advances in Concrete Technology, AC. 154-19, pp. 357–80, 1995.
[32] F. Bellmann, J. Stark, The role of calcium hydroxide in the formation of thaumasite. Cement and Concrete Research, 389, pp. 1154-1161, 2008.
[33] J. Stark, K. Bollmann, K. Seyfarth, Ettringite - cause of damage, damage intensifier or uninvolved third party?” ZKG International, 51, 5, pp. 280-292, 1998.
[34] Y. A. T. Osman: Studies on the Chemical and Thermal Stability of the Thaumasite Salt and its Expan- sion Behavior. Ph.D. Thesis, Helwan University, 2015.
[35] H.Y. Ghorab, M.R. Mabrouk, K.I. Ismail, Y. A. Osman, S. F. Abd Elnaby, K.M.Yousri, H. H. Ahmed, D. Herfort; The Suitability of Portland Limestone Cement for Use in Construction Applications in Egypt; Cement International 6, pp. 70-77, 2014. 5th International Conference. Non-Traditional Cement
& Concrete (NTCC). Brno, Czech Republic, pp. 63-66, 2014.
[36] H. Y. Ghorab, M. R. Mabrouk, D. Herfort, Y. A. Osman; Infrared investigation on systems related to the thaumasite formation at room temperature and 7oC:.Cement.Wapno. beton , Vol. 4, pp.252-261, 2014.
[37] S. Martinez-Ramirez, M.T. Blanco-Varela, J. Rapazote: Thaumasite formation in sugary solutions: Effect of temperature and sucrose concentration. Construction and Building Materials, 25, pp. 21-29, 2011.
[38] M. E. Gaze, N. J. Crammond: The formation of thaumasite in a cement lime sand mortar exposed to cold magnesium and potassium sulfate solutions. Cement and Concrete Composite. 22: 209–22, 2000.
[39] C. Yangi, B. Liui, X. Xiangi, J. Zhang: The influence of pH on the formation and stability of thaumasite.
Applied Mechanics and Materials, 174-177 pp. 268-274, 2012.
[40] M. K. M. Mohamed Investigations on the formation of thaumasite formation in cement systems. M.Sc.
Thesis, Helwan University, 2017.
[41] H. Y. Ghorab, A. S. Meawad, M. Kamal; On the durability of Portland limestone cement: Effect of pH on the thaumasite formation. Housing and Building Research Journal http://dx.doi.org/10.1016/j.
hbrcj.2017.04.002
[42] A. Andersen, Flemning, L. Brecevic: Infrared spectra of amorphous and crystalline calcium carbonate.
Acta Chemica Scandinavica. 45: 1018-1024, 1991.
[43] M. Rospondek, A. Lewandowska, Mineralogical Society of Poland-Special papers. 20: 187-190, 2002.
