Physics-chemical study of hydration process of three calcium aluminate phase and Metakaolin

This research based on X-Ray Diffraction, SEM and chemical analyses were revealed that decreasing of Ca(OH)2 phase content and increasing of C3AH6 and trisulfate aluminate calcium-3 as the stable phases for the hydration period of first 30 to 60 minutes when comparing K-crent doping to the phase to without any doping. Also results have been proposed in case of doping metakaoline to draw structural analogies as formation of stable hydrated phases and the decrease of new formed unstable crystalline metaphases in the early stage of 3CAO·Al2O3 hydration process. Introduction ricalcium aluminate (C3A), which could compose up to 15% of the Portland cement, reacts very quickly with water to form calcium hydro aluminates that induces the stiffening of cement paste. To avoid this phenomenon, calcium sulphate is usually added which leads to the formation of calcium three sulfoaluminate with a slow hydration [1-2]. In last 5-6 years research for obtaining of a new crystallizing component such as crent from kaoline, basalts and zeolites has been successfully going on at the Centre for Chemistry and Technology of New Materials, National University of Mongolia. Such research also have conducted in high developed countries since ninety years. It was established that cement compressive strength increased by 100-250 kg/cm 2 when doped 5-10% of Crent to the cement weight [3-6]. However, there were a lot of complicated situation with crystal structure formationing and crystal growth mechanisms during the cement hydration processes [8-10, 16]. In recent years many researchers have interested in the study of crystallizing a substance which can serve as crystal nuclei centre and accelerate their crystal growth process [11-15]. Portland cement is a fine-dispersial system consisting of multiple phases, therefore, understanding its hydration process means studying of its each phase hydration processes [17]. Theoretical and practical consequences of this work were considered the possibility to decrease Ca(OH)2 phase formation and increase C3AH6 and trisulfate aluminate calcium as the stable phases of cement hydrated compoundsby using the K-crent doping. These stable phases’ formation would increase of cement paste compressive strenght by 100-250 kg/cm 2 when doping this Crent to the C3A as cement interphases. Experimental Making mineral additives Kaolin from Khongor-Ovoo deposit of Dornogovi province’s was employed in this T


Introduction
ricalcium aluminate (C 3 A), which could compose up to 15% of the Portland cement, reacts very quickly with water to form calcium hydro aluminates that induces the stiffening of cement paste.To avoid this phenomenon, calcium sulphate is usually added which leads to the formation of calcium three sulfoaluminate with a slow hydration [1-2].In last 5-6 years research for obtaining of a new crystallizing component such as crent from kaoline, basalts and zeolites has been successfully going on at the Centre for Chemistry and Technology of New Materials, National University of Mongolia.Such research also have conducted in high developed countries since ninety years.It was established that cement compressive strength increased by 100-250 kg/cm 2 when doped 5-10% of Crent to the cement weight [3-6].However, there were a lot of complicated situation with crystal structure formationing and crystal growth mechanisms during the cement hydration processes [8- 10,16].
In recent years many researchers have interested in the study of crystallizing a substance which can serve as crystal nuclei centre and accelerate their crystal growth process [11][12][13][14][15]. Portland cement is a fine-dispersial system consisting of multiple phases, therefore, understanding its hydration process means studying of its each phase hydration processes [17].Theoretical and practical consequences of this work were considered the possibility to decrease Ca(OH) 2 phase formation and increase C 3 AH 6 and trisulfate aluminate calcium as the stable phases of cement hydrated compoundsby using the K-crent doping.These stable phases' formation would increase of cement paste compressive strenght by 100-250 kg/cm 2 when doping this Crent to the C 3 A as cement interphases.

Sample preparation
C 3 A standard samples and gypsum were sieved through 80m sieves and their mixtures with a stoichiometric ratio homogenized in bal mill for 2 hour.X-Ray diffraction (XRD), Thermal analysis (TG/DTA) and tunnelling electron microscope XRD measurements were carried out with DRON-2, Russia, using Co-filtered K, step size 0.001 o .TG/DTA were undertaken with DERIVATOGRAPH, Hungary, thermo analyzer at a heating rate of 10 o C/min using -Al 2 O 3 as a reference material.

XRD study on influence of metakaolin for the early hydration of 3CAO•Al 2 O 3
The sample of C 3 A and the mixture of C 3 A and metakaolin as we've abbreviated it Kcrent were prepared and were hydrated for 30 minutes and for an hour.The X-ray fluorescence analysis of those hydrated samples was done (see Figures 1-4 and Table  2-5).The X-ray diffraction analysis results for C 3 A phase hydrated for 30 min show high intensity diffraction lines of CAH 10 at d=7.16Ǻ, d=2.88Ǻ, and of C 2 AH 8 at d=3.80Ǻ, d=2.78Ǻ and medium size peaks of Ca(OH) 2 at d=2.628Ǻ, d=1.92Ǻ, respectively.Also there were some low intensity peaks of calcium aluminate's phase hydration product such as C 3 AH 6 at d=1.817Ǻ, d=1.574Ǻ and d=2.226Ǻ.Moreover, C 3 A peak shown at d=1.90Ǻ for uncompletely hydrated phases  The X-ray diffraction analysis results for C 3 A phase hydrated for an hour show diffraction lines of CAH 10 at d=7.16Ǻ, d=5.39 Ǻ, d=2.88Ǻ,C 2 AH 8 at d=10.7Ǻ, d=2.39Ǻ, d=4.25Ǻ, d=3.80Ǻ, d=2.86Ǻ, d=2.78Ǻ, d=2.49Ǻ, d=2.45Ǻ and of C 4 AH 13 at d=2.69Ǻ and d=2.04Ǻ, respectively.The presence of diffraction lines of C 3 AH 6 at d=5.14Ǻ, d=3.366Ǻ, d=2.469Ǻ, d=2.30Ǻ, d=1.817Ǻ and that of C 3 A at d=4.08Ǻ shows increase in calcium hydro aluminates compounds content in comparison to the samples hydrated for 30 minutes.But the existence of spectral line of C 3 A phase shows that the reaction wasn't even completed for the given time.The X-ray diffraction analysis results for C 3 A phase with metakaolin as we've abbreviated it as K-crent addition hydrated for 30 min show low intensity spectral lines of CAH 10 at d=14.30Ǻ, d=2.88Ǻ and of C 4 AH 13 at d=8.05Ǻ and its high intensity peaks at d=4.05Ǻ, d=2.17Ǻ etc, respectively Also there were some low intensity peaks of calcium aluminate's phase hydration product formed as C 2 AH 8 at d=4.25Ǻ, d=2.45Ǻ and medium intensity peaks at d=3.80Ǻ, d=2.86Ǻ, d=2.78Ǻ which show hydration was rapid for this system.
But there were C 3 AH 6 hydrated compound's medium intensity d=5.14Ǻ, d=3.366Ǻ, d=2.816Ǻ, d=2.226Ǻ, d=2.043Ǻ peaks and low intensity d=3.149Ǻ and very low intensityC 3 A phase peak at d=3.34Ǻ, respecively.From these C 3 A with K-crent addition XRDA results can be suggested that there were increased the content of calcium hydroaluminate phase if compared them to the XRD patterns of C 3 A phase for 30 min time period.From the TEM analysis results of these hydrated 3CaO•Al 2 O 3 and 3CaO•Al 2 O 3 + Kcrent systems can be concluded that the following reactions take place: From the TEM analysis results of 1 hour hydrated 3CaO•Al 2 O 3 and 3CaO•Al 2 O 3 +Kcrent samples can be suggested that crystal hydrates with more stable structures formed as a result of hydration reactions.This was especially the case in the samples with addition of K-crent.This shows that K-crent intensifies the formation of stable crystal hydrates.

Physics-chemical study on synthesis of three calcium aluminate as С 3 A phase
Russian standard sample of C 3 A was used in this study.One of the main goals of this work was to prepare standard sample in our laboratory.For this, chemically pure CaCO 3 and Al 2 O 3 reagents from China were mixed in stoichometric ratio and were calcined at 1000-1200 0 C for 6 h.Physical and chemical analyses were done in each aluminate phase prepared.The results are shown below in Table 6.First of all, the free calcium oxide content for the samples was determined according to the methodology described in materials and methods section.The results of this analysis are shown in Table 6.The results of compressive strength of Russian standard sample C 3 A, the same standard sample with K-crent addition and the C 3 A prepared sample with K-crent addition are shown in Figure 9 and in Table 7.The results of above mentioned analysis show that the optimal preparation temperature of C3A phase is 1150 0 C.

Conclusions
 X-ray Diffraction analysis results show that the final product of hydration C3AH6 forms dominantly within 30 to 60 minutes after the addition of K-crent to 3CaO•Al 2 O 3 phase.
 TEM analysis results show that compared to 3CaO•Al 2 O 3 without the addition of Kcrent the one with addition crystallizes with forming of stable crystals with right geometric forms.This supports the results of XRDA. X-ray analysis results show that the content of Ca(OH) 2 phase decreases and the formation of trisulfate aluminate calcium phase increases due to the addition of K-crent in "3CaO•Al 2 O 3 +gypsum" system at the beginning of hydration.

Figure 1 .
Figure 1.XRDA results for 30 min hydrated C 3 A phase

Figure 2 .
Figure 2. XRD results for 1 hour hydrated C 3 A phase

Figure 3 .
Figure 3. XRD results for 30 min hydrated C 3 A phase with metakaolin

Figure 4 .
Figure 4. XRD results for 1 hour hydrated C 3 A phase with K-crent

Figure 5 .
Figure 5. TEM results for 30 min hydrated C 3 A phase

Figure 7 .
Figure 7. TEM results for 1 hour hydrated C 3 A phase

Figure 10 .
Figure 10.Study on K-crent influence on compressive strength of C 3 A phase

Table 1 .
Chemical analysis results of kaolin, %

Table 2 .
XRDA results for 30 min hydrated C 3 A phase

Table 3 .
XRDA results for 1 hour hydrated C 3 A phase

Table 4 .
XRD results for 30 min hydrated C 3 A phase with metakaolin

Table 5
. XRD results for 1 hour hydrated C 3 A phase with K-crent

Table 6 .
Content of CaO free for varous temperature burning № Temperature, 0 С

Table 7 .
Study on compressive strength for C 3 A with K-crent