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The investigation of microstructure and strength properties of lightweight mortar containing mineral admixtures exposed to sulfate attack
Measurement 77 (2016) 143–154
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The investigation of microstructure and strength properties of lightweight mortar containing mineral admixtures exposed to sulfate attack Harun Tanyildizi ⇑ Department of Civil Engineering, Firat University Elazig, Turkey
a r t i c l e
i n f o
Article history: Received 15 January 2015 Received in revised form 3 August 2015 Accepted 1 September 2015 Available online 4 September 2015 Keywords: Lightweight mortar Electron microscopy Energy-dispersive X-ray X-ray diffraction Compressive strength
a b s t r a c t The aim of this study was to evaluate the effect of magnesium sulfate concentration on the microstructure and strength properties of lightweight mortars containing fly ash and silica fume. Lightweight mortar specimens containing 15% fly ash and 10% silica fume were prepared for this study. The specimens were exposed to different sulfate concentrations (0% MgSO4 2 , 2% MgSO4 2 and 4% MgSO4 2 ) for one year after specimens were kept in water at 20 ± 2 °C for 28 days. The microstructure analyses and compressive strength were monitored for cure periods to evaluate the performance of the test specimens exposed to different sulfate attacks. The microstructure analyses were performed using the scanning electron microscopy, the energy-dispersive X-ray, and the X-ray powder diffraction. The microstructure results showed that the deterioration mechanism of lightweight mortars exposed to magnesium sulfate has changed according to magnesium sulfate concentration percentage and mineral admixture type. Furthermore, the compressive test results showed that the performance of lightweight mortars containing silica fume were higher than lightweight mortars without mineral admixture and with fly ash. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Lightweight aggregates are generally classified as natural and artificial types. Lightweight concrete is made using lightweight aggregate [1]. The use of lightweight mortar has been increasing. The lightweight concrete can be produced with densities from 300 to 1200 kg/m3 and compressive strengths from 1 to 100 MPa [2]. Lightweight concrete was used successfully in buildings and bridges [3]. The first examples of lightweight mortar were produced the ships during World War-I [4]. The lightweight
⇑ Tel.: +90 424 2370000-4315; fax: +90 424 2367064. E-mail address: [email protected] http://dx.doi.org/10.1016/j.measurement.2015.09.002 0263-2241/Ó 2015 Elsevier Ltd. All rights reserved.
mortars with higher compressive strengths have been made for many years [5]. The presence of sulfate ion can be caused the deterioration of concrete exposed to marine environments or placed in soils and groundwater contaminated with sulfate salts [6–8]. The feature of some material increased the rate of sulfate attack [9–12]. The permeability of concrete should be decreased for the sulfate resistance of concrete. The sulfate attack can be prevented with ASTM Type I cement, Type II cement or Type V cement. Furthermore, it can also be prevented by using pozzolans in concrete [13–15]. The chloride in waters increases the rate of portlandite. It increases the porosity of concrete. Thus, its strength is decreased. The sulfates are harmful to concrete. They cause by expansion, cracking, spalling and the decrease of strength after their reactions with hydrated cement mortar
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[16,17]. Binici and Aksogan [18] reported that natural pozzolan and ground granulated blast furnace slag blended Portland cements clearly outperformed plain Portland cement in sulfate resistance evaluated by a strength reduction on Rilem prisms. Binici et al. showed [19] that concrete improves the mechanical properties and chemical resistance of concrete by using the marble and granite aggregates. Sahmaran et al. [20] showed that the physical sulfate attack can affect the performance of cements against sulfate attack. Felekoglu et al. showed [21] that the expansions of blended cements changed by the amount of mineral addition. Turkmen et al. [22] showed that the Taguchi method could successfully be applied to the mechanical properties of concrete exposed to sulfate. Binici et al. [23] showed that pumice aggregate for the sulfate resistance was a suitable material for the cement production. In this experimental study, the effects of sulfate attack on the microstructure and the compressive strength of lightweight mortars with fly ash and silica fume were investigated.
2. Experimental 2.1. Materials The materials were provided by different sources in Turkey. The cement used in this study was selected as TS EN 197-1-CEM I 42.5 N in Turkey. Silica fume and Fly ash were obtained from Turkey. Pumice aggregate was used in the lightweight mortars. Pumice aggregate was obtained from natural deposits in Turkey. The specific gravity of lightweight aggregate was 2. The chemical analysis properties of the cement, pumice aggregate, fly ash, silica fume and were presented in Table 1. Furthermore, Fig. 1 showed that the grading curve of aggregate. 2.2. Preparation of specimens Pumice with a maximum size less than 4 mm was used for producing lightweight mortars. The mix proportions were shown in Table 2. The reference group was named as H. The groups with fly ash and silica fume were named
Table 1 The chemical properties of cement, fly ash and silica fume. Bulk oxide
The percentage by weight
SiO2 Al2O3 Fe2O3 CaO MgO LOI Specific surface area (cm2/g) Particle size Specific gravity (g/cm3)
Portland cement
Fly ash
Silica fume
Pumice aggregate
21.12 5.62 3.24 62.94 2.73 1.42 3430 – 3.10
48.53 24.61 7.59 9.48 2.28 0.93 2836 87.5% < 125 lm 2.27
91 0.58 0.24 0.71 0.33 1.84 – 96.5% < 45 lm 2.2
48.19 24.78 7.22 12.26 7.55 – – – 2
Fig. 1. Grading curve for the experimental work.
Table 2 Mixture proportion of concretes. Mix
Cement (kg/m3)
Fly ash (kg/m3)
Silica fume (kg/m3)
W/B
Pumice aggregates (kg/m3)
SP (L/m3)
H U S
400 340 360
– 60 –
– – 40
0.77 0.77 0.77
1038 1024 1028
4.8 4.8 4.8
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as U and S, respectively. The super plasticizer was used for this study. It meets ASTM C 494 requirements for Type A, water-reducing, and Type F, high-range water-reducing, admixtures. The produced mortar was placed in the standard cube (50 50 50 mm). 156 specimens were prepared in each production. They kept in a water tank at 20 ± 2 °C for 28 days. 2.3. Exposure to magnesium sulfate of samples The specimens were separated into two groups after the curing. The first group of specimens was continuously kept under a water tank at 20 ± 2 °C. The other group was kept in three tanks with the following sulfate concentrations:
2% MgSO4 2 (20.000 mg/l), 4% MgSO4 2 (40.000 mg/l). In two relevant standards, both ACI-225R-85 [24] and ACI-201.2R-77 [25], any sulfate water in which the sulfate ion concentration was within: 1500 ppm < SO=4 < 10,000 ppm was defined as ‘‘severe” sulfate environment, and those for which the sulfate ion concentration was greater than 10,000 ppm is defined as ‘‘very severe” sulfate water environment. The sulfate water tanks prepared in this study had two different ranges of SO=4 concentration: 20,000 ppm and 40,000 ppm, which are both in ‘‘very severe” condition according to ACI [24,25]. The samples were taken out of the sulfate solutions at the end of one year
Ettringite
Gypsum
(a) SEM image (150x)
(b) SEM image (1500x)
Ca
Si Ca
Si
Ca
Al Ca
Al
Ca Ca
Ca Ca
Al
0 Cursor= 15.280 keV 0 cnt ID = Bk la1 Vert=81 Window 0.000 - 40.950 = 2230 cnt
10
keV
(d) XRD patterns
(c) EDX analysis Fig. 2. SEM, EDX and XRD analysis of lightweight cement paste exposed to magnesium sulfate 2% for 365 days.
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exactly, left in the laboratory environment without washing for a couple of days to attain air-dry forms. The measurements were made at 4, 6, 9, and 12 months according to ASTM C 1012 [26]. Due to this, the max exposure time to sulfate attack was selected 12 months. 3. Results 3.1. Microstructure analysis of lightweight mortar Sulfate attack has been investigated in the reaction between the cement hydrates and dissolved compounds in the attacking solution [27]. Furthermore, there have been many works with sulfate deterioration. The ettringite, gypsum, M–S–H and brucite are formed in concrete after sulfate attack [27–30]. Besides, many researchers [31–33]
have studied that the sulfate deterioration in cement system containing significant levels of limestone filler at the certain temperature. In this study, the lightweight mortars were kept in magnesium sulfate for 365 days. The scanning electron microscopy (SEM), the energy-dispersive X-ray (EDX) and the X-ray powder diffraction (XRD) analysis were examined the effect of magnesium sulfate on lightweight mortars containing mineral admixtures. The results were given in Figs. 2–7. It can be seen from Figs. 2a–7a that cracks were observed at the mortar–aggregate interface and in the surrounding mortar after lightweight mortars were kept in magnesium sulfate for 365 days. Networks of cracks are a depth of about 6 mm as a result of sulfate attack [34]. It can be seen from Figs. 2–7 that ettringite and gypsum occurred in samples. The magnesium sulfate attack has
Thaumasite
(a) SEM image (150x)
(b) SEM image (13500x)
(d) XRD patterns
(c) EDX analysis Fig. 3. SEM, EDX and XRD analysis of lightweight cement paste containing fly ash exposed to magnesium sulfate 2% for 365 days.
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caused the ettringite and gypsum formation in mortars [35]. Brucite was wrapped up the cement gel. It was protected further deterioration [36,39,16]. This was in the early stages. At other stages, deterioration processes would become dominant due to brucite [11]. The locations of the energy-dispersive X-ray (EDX) analyses were marked on each the scanning electron microscopy (SEM) image (Figs. 2c–7c). The energydispersive X-ray analysis in Fig. 2c showed only high calcium and silica, and aluminum peaks. The percentages of these materials are 44.24, 7.62 and 5.77, respectively. It was then concluded that the phase was ettringite. The energy-dispersive X-ray (EDX) analysis in Fig. 3c showed
a silica and high calcium, aluminum and smaller (K) potassium peaks. The percentages of these materials were 17.38, 40.02, 5.06 and 2.56, respectively. It was then concluded that the phase was thaumasite. The energy-dispersive X-ray (EDX) analysis in Fig. 4c showed only high calcium and silica, and aluminum peaks. The percentages of these materials were 81.5, 14.3 and 2.17, respectively. It was then concluded that the phase was thaumasite. The energy-dispersive X-ray (EDX) analysis in Fig. 5c showed only high calcium and silica, and sulfur peaks. The percentages of these materials were 53.23, 32.1 and 14.67, respectively. If Figs. 2c and 5c were compared, calcium and silica rate were increased 20.3%, 321.3% in Fig. 5c, respectively. It
Thaumasite
(a)SEM image (150x)
(b)SEM image (3500x)
Ca
Ca
Si
Ca K
Al
K
Al
K
K 0
Cursor= Vert=489
Ca Ca Ca 10
keV
Window 0.000 - 40.950 = 9295 cnt
(c) EDX analysis
(d) XRD patterns
Fig. 4. SEM, EDX and XRD analysis of lightweight cement paste containing silica fume exposed to magnesium sulfate 2% for 365 days.
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was then concluded that the phase was thaumasite. The energy-dispersive X-ray (EDX) analysis in Fig. 6c showed only high calcium and silica, and oxygen peaks. The percentages of these materials were 34.38, 8.26 and 57.36, respectively. If Figs. 3c and 6c were compared, calcium and silica rate were decreased 14.1%, 52.5% in Fig. 6c, respectively. It was then concluded that the phase was ettringite. The energy-dispersive X-ray (EDX) analysis in Fig. 7c showed only high calcium and silica peaks. The percentages of these materials were 34.38 and 12.49, respectively. If Figs. 4c and 7c were compared, calcium and silica rate were increased 7.4%, 475.6% in Fig. 7c,
respectively. It was then concluded that the phase was ettringite and thaumasite. Thaumasite was commonly thought to occur when sulfate, C–S–H and calcium carbonate reacted. Unless the coarse aggregate was serving as the source of carbonate, the thaumasite formation could occur in the absence of carbonate. Since the formation was required a carbonate source, micro-structural damage was caused by ettringite formation [37,38]. Furthermore, thaumasite can be found in pre-existing voids and cracks without necessarily causing deterioration of the mortar [39]. Figs. 2d–7d showed the X-ray powder diffraction (XRD) patterns of lightweight mortars after exposed to
Thaumasite
Gypsum
(b)SEM image (2000x)
(a)SEM image (150x)
Ca
S Ca Si
S Ca Si Ca
S
Ca
Ca Si S
S 0
Ca
Cursor= Vert=23
10 Window 0.000 - 40.950 = 708 cnt
(c)EDX analysis
keV
(d)XRD patterns
Fig. 5. SEM, EDX and XRD analysis of lightweight cement paste exposed to magnesium sulfate 4% for 365 days.
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the main constituents. The absence of brucite ettringite and thaumasite indicated that the diffusion of sulfates into the sample was very slow. Furthermore, the X-ray powder diffraction (XRD) pattern for the lightweight mortar exposed to a low solution of magnesium sulfate indicated maximum intensity peaks gypsum. The X-ray powder diffraction (XRD) patterns of lightweight mortars containing fly ash exposed to magnesium sulfate 2–4% were presented in Figs. 3d and 6d. Gypsum and calcite were the main constituents, but the gypsum peaks increased with increased of concretion of magnesium sulfate. The X-ray powder diffraction (XRD) patterns of lightweight mortars containing silica fume exposed to magnesium
magnesium sulfate for 365 days. The presence of ettringite (E), thaumasite (T), gypsum (G), calcite (C) and brucite (B) showed in figures. These patterns were produced the reactions between cement hydration and magnesium sulfate attack. Furthermore, the one of the most general causes for deterioration because of the magnesium sulfate attack might be attributed to both thaumasite formation and gypsum formation. Hartshom et al. reported that the gypsum and thaumasite played an important role in cement with limestone filler because of the magnesium sulfate attack [40]. The X-ray powder diffraction (XRD) patterns of lightweight mortars exposed to magnesium sulfate 2–4% were presented in Figs. 2d and 5d. Gypsum and calcite were
Ettringite
Gypsum
(a) SEM image (150x)
(b) SEM image (3500x)
Ca
Ca
O
Ca Si
Ca Ca Ca 0 Cursor= Vert=58
Si Si
Ca Ca 10 keV
Window 0.000 - 40.950 = 1102 cnt
(c) EDX analysis
(d) XRD patterns
Fig. 6. SEM, EDX and XRD analysis of lightweight cement paste containing fly ash exposed to magnesium sulfate 4% for 365 days.
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Ettringite
Brucite
Gypsum
Thaumasite
(b)SEM image (3500x)
(a)SEM image (150x) Ca
Ca
Ca Si Ca
Ca
Si
Ca Si
Ca 0
Cursor= Vert=70
Ca
Window 0.000 - 40.950 = 1381 cnt
keV
(c)EDX analysis
(d)XRD patterns
Fig. 7. SEM, EDX and XRD analysis of lightweight cement paste containing silica fume exposed to magnesium sulfate 4% for 365 days.
sulfate 2–4% were presented in Figs. 4d and 7d. Gypsum and calcite were the main constituents. Moreover, the gypsum and calcite peaks increased with increased of concretion of magnesium sulfate. The gypsum peaks of lightweight mortar samples always gave the highest values followed by lightweight mortar with fly ash and silica fume. Calcium hydroxide could also be consumed throughout the potential of gypsum formation [41]. Thus, the addition of the some minerals could be caused to richer aluminate systems. These have become more resistant to thaumasite form of sulfate attack [42]. The pozzolanic materials reduce concrete permeability. It is blocked the ingress of the deleterious sulfate ions [41].
3.2. Compressive strength results of lightweight cement mortar When the mortars were exposed a sulfate solution, sulfate ions entered into the specimens. It was known that the wetting and drying cycles accelerated the penetration of the sulfate ions in the mortars. After sulfate ions entered the concrete pores, they reacted with hydrated cement. The reactions were complicated. The reactions have been consistent involves numerous mechanisms [43]. Two forms of sulfate attack, which including the ettringite and thaumasite, can be warranted based on concrete exposures. The ettringite form (C3A3CaSO431H2O) can be
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caused by the reaction of calcium, sodium and/or magnesium sulfates with C3A, hydrated aluminates, or monosulfate (C3ACaSO412H2O). On the other hand, thaumasite can be described as calcium–silicate–sulfate–carbonate hydrate (CaSiO3CaCO3CaSO415H2O), which is the result of the reaction between calcium–silicate hydrates and sulfates in the presence of carbonate ions. Eventually, these two types will make expansion and cracking of mortar and concrete [44,45]. In this study, the compressive strength results of lightweight mortars containing fly ash and silica fume exposed to different magnesium sulfate concentration during 365 days could be seen in Figs. 8–10. It could be seen from Figs. 8–10 that compressive strength of lightweight mortars was decreased with the increase of sulfate concentration. The compressive strengths of lightweight mortars without mineral admixtures were decreased 12.29%,
151
9.38%, 12.46%, 16.31%, 17.43%, 10.07%, 4.76%, and 15.51% compared to that compressive strength of lightweight mortars without mineral admixtures exposed to 2% sulfate attack at 28, 60, 90, 120, 150, 180, 210, and 365 days, respectively. The compressive strengths of lightweight mortars without mineral admixtures were decreased 26.24%, 25.51%, 25.66%, 17.45%, 19.63%, 12.93%, 13.52%, and 23.12% when compressive strength of lightweight mortars without mineral admixtures exposed to 4% sulfate attack were compared at 28, 60, 90, 120, 150, 180, 210, and 365 days, respectively. The compressive strengths of lightweight mortars containing fly ash were decreased 6.07%, 7.91%, 7.71%, 7%, 8.13%, 4.55%, 9.20%, and 8.73%, according to that compressive strength of lightweight mortars containing fly ash exposed to 2% sulfate attack at 28, 60, 90, 120, 150, 180, 210, and 365 days, respectively. The compressive strengths of lightweight mortars containing fly
Fig. 8. Compressive results of lightweight cement paste exposed 0% sulfate attack.
Fig. 9. Compressive results of lightweight cement paste exposed 2% sulfate attack.
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ash were decreased 16.73%, 16.56%, 21.04%, 12.63%, 12.89%, 8.24%, 13.83%, and 17.23% compared to that compressive strength of lightweight mortars containing fly ash exposed to 4% sulfate attack at 28, 60, 90, 120, 150, 180, 210, and 365 days, respectively. The compressive strengths of lightweight mortars containing silica fume were decreased 6.75%, 3.97%, 2.77%, 3.75%, 7.27%, 7.07%, 8.19%, and 9.13% when compressive strength of lightweight mortars containing silica fume exposed to 2% sulfate attack were compared at 28, 60, 90, 120, 150, 180, 210, and 365 days, respectively. The compressive strengths of lightweight mortars containing silica fume were decreased 18.74%, 23.40%, 9.32%, 6.78%, 8.56%, 9.60%, 12.4%, and 12.05%, according to that compressive strength of lightweight mortars containing silica fume exposed to 4% sulfate attack at 28, 60, 90, 120, 150, 180, 210, and 365 days, respectively. The effect of chemical composition of mineral admixtures (fly ash, silica fume, etc.) is a significant factor affecting its sulfate resistance performance [45]. Lightweight cement mortars containing silica fume
were given the best results among mineral additives. Wee et al. said that the samples containing 5% and 10% silica fume played a major role in resisting sodium [46]. The mortar samples with the silica fume decrease calcium hydroxide because of the pozzolanic reaction. Furthermore, it allows the magnesium sulfate to more easily attack the C–S–H because the cement bond is destruction. The gypsum would tend to form due to locally reduce pH and the limited local of aluminums [47–49]. The performance of lightweight mortars containing fly ash was given better than lightweight mortars without mineral admixture. The fly ash has the major roles in resistance to sulfate attack. They are given below.
The mortars containing fly ash have shown that the sulfate-containing hydrate has the long-term stability. The formation of the monosulfate phase occurs the less volume change when compared to the formation of ettringite.
Fig. 10. Compressive results of lightweight cement paste exposed 4% sulfate attack.
Fig. 11. Variation of mass of samples exposed to sulfate attack.
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Fig. 12. Photo of lightweight cement pastes exposed to magnesium sulfate 4% for 365 days.
There is no recrystallisation as the case with ettringite formation [50]. Fig. 11 shows the variations in mass with time under magnesium sulfate environment for a period of 1 year. Fig. 12 shows the photo of lightweight cement pastes exposed to magnesium sulfate 4% for a period of 1 year. The variation in mass in very severe exposure conditions showed different trend. The mass of sample increased with the increase of sulfate ratio. This increase may be explained by the water absorption capacity of the LWA [51], as internal pores of the LWA are very slowly filled with water, it may take several months of immersion to approach saturation [52]. 4. Conclusions In this study, the microstructure and compressive strength of lightweight mortar exposed to different sulfate concentration
(0%
MgSO4 2
(0 mg/l),
2%
MgSO4 2
2
(20.000 mg/l), 4% MgSO4 (40.000 mg/l)) for 365 days was investigated by using the scanning electron microscope (SEM), the energy-dispersive X-ray (EDX), the X-ray powder diffraction (XRD), and compressive strength test. The main results of this research were given in the following conclusions. The scanning electron microscopy (SEM) image showed that the cracks were observed at the mortar–aggregate interface and in the surrounding lightweight mortar after lightweight mortars were immersed in magnesium sulfate for 365 days. The energy-dispersive X-ray analysis (EDX) showed that the lightweight mortar containing silica fume exposed to magnesium sulfate 4% indicated the presence of the calcium 87%, silica 13%, while the lightweight mortar exposed to magnesium sulfate 2% indicated aluminum 2.1%, silica 14.3%, potassium 2.1% and calcium 81.5%. The lightweight mortar containing fly ash exposed to magnesium sulfate 4% indicated the presence of the calcium oxygen 57.3%, silica 8.3% and calcium 34.4% while the lightweight mortar exposed
to magnesium sulfate 2% indicated oxygen 39.1%, sodium 1.6%, magnesium 1.6%, aluminum 7.5%, silica 7.7% and potassium 4.3%. The lightweight mortar exposed to magnesium sulfate 4% indicated the presence of the calcium 53.2%, sulfur 32.1% and silica 14.7% while the lightweight mortar exposed to magnesium sulfate 2% indicated calcium 69.5%, silica 22.5% and aluminum 8%. The X-ray powder diffraction (XRD) analysis showed that the degree of deterioration of the lightweight mortar was different from each other. The maximum formation of gypsum was obtained from the lightweight mortar without mineral admixtures exposed to magnesium sulfate 2%. The minimum formation of gypsum was obtained from the lightweight mortar containing fly ash exposed to magnesium sulfate 2%. The maximum formation of calcite was obtained from the lightweight mortar without mineral admixtures exposed to magnesium sulfate 2%. The minimum formation of calcite was obtained from the lightweight mortar without mineral admixtures exposed to magnesium sulfate 4%. The compressive strength results of lightweight mortars containing silica fume gave the best results among mineral additives. Furthermore, the microstructure of silica fume based mortar confirms the compressive strength. The compressive strength results of lightweight mortars containing fly ash gave higher values than the cement specimens without mineral admixtures.
Acknowledgments The author is grateful for the financial support of the Firat University BAPYB (Project No. 1481).
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[29] O.S.B. Rasheeduzzafar Al-Amoudi, S.N. Abduljauwad, M. Maslehuddin, Magnesium-sodium sulfate attack in plain and blended cements, J. Mater. Civ. Eng. 6 (1994) 201–222. [30] T.L. Seung, R.D. Hooton, H.S. Jung, D.H. Park, C.S. Choi, Effect of limestone filler on the deterioration of mortars and mortars exposed to sulfate solutions at ambient temperature, Cem. Concr. Res. 38 (2008) 68–76. [31] S. Tsivilis, G. Kakali, A. Skaropoulou, J.H. Sharp, R.N. Swamy, Use of mineral admixtures to prevent thaumasite formation in limestone cement mortar, Cement Concr. Compos. 25 (2003) 969–976. [32] E.F. Irassar, V.L. Bonavetti, M.A. Trezza, M.A. Gonzalez, Thaumasite formation in limestone filler cements exposed to sodium sulphate solution at 20 °C, Cement Concr. Compos. 27 (2005) 77–84. [33] E.F. Irassar, V.L. Bonavetti, M. Gonzalez, Microstructural study of sulfate attack on ordinary and limestone Portland cements at ambient temperature, Cem. Concr. Res. 33 (2003) 31–41. [34] P.W. Brown, J.P. Skalny, Microstructural observations of sulfate attack in field concrete, in: L. Jany, A. Nisperos, (Eds.), Proceedings of the 24th International Conference on Cement Microscopy, 2002, pp. 189–203. [35] W.G. Hime, B. Mather, Sulfate attack or is it, Cem. Concr. Res. 29 (1999) 789–791. [36] M.D. Cohen, A. Bentur, Durability of Portland cement-silica fume mortars in magnesium sulfate and sodium sulfate solutions, ACI Mater. J. 85 (1988) 148–157. [37] R.S. Gollop, H.F.W. Taylor, Micro structural and micro analytical studies of sulphate attack, Cem. Concr. Res. 26 (1996) 1029–1044. [38] P. Brown, R.D. Hooton, B. Clark, Microstructural changes in concretes with sulfate exposure, Cement Concr. Compos. 26 (2004) 993–999. [39] A.M. Ramezanianpour, R.D. Hooton, Thaumasite sulfate attack in Portland and Portland-limestone cement mortars exposed to sulfate solution, Constr. Build. Mater. 40 (2013) 162–173. [40] S.A. Hartshorn, J.H. Sharp, R.N. Swamy, The thaumasite form of sulfate attack in Portland-limestone cement mortars stored in magnesium sulfate solution, Cement Concr. Compos. 24 (2002) 351–359. [41] K. Sotiriadis, E. Nikolopoulou, S. Tsivilis, A. Pavlou, E. Chaniotakis, R. N. Swamy, The effect of chlorides on the thaumasite form of sulfate attack of limestone cement concrete containing mineral admixtures at low temperature, Constr. Build. Mater. 43 (2013) 156–164. [42] I. Juel, D. Herfort, R. Gollop, J. Konnerup-Madsen, H.J. Jakobsen, J. Skibsted, A thermodynamic model for predicting the stability of thaumasite, Cem. Concr. Compos. 25 (2003) 867–872. [43] Z. Minghua, C. Jiankang, L. Yunfeng, W. Dongjie, Y. Jian, Study on the expansion of concrete under attack of sulfate and sulfate–chloride ions, Constr. Build. Mater. 39 (2013) 26–32. [44] R.D. Hooton, M. Thomas, The use of limestone in Portland cements: effect on thaumasite form of sulfate attack, PCA R&D 2658 (2002) 1–9. [45] A.A.H. Assem, A.A. Abouhussien, J. Mayo, The use of silica-breccia as a supplementary cementing material in mortar and concrete, Constr. Build. Mater. 51 (2014) 321–328. [46] T.H. Wee, A.K. Suryavanshi, S.F. Wong, K.M. Anisur, Rahmani Sulfate resistance of concrete containing mineral admixturei, ACI Mater. J. 97 (2000) 536–549. [47] O.S.B. Rasheeduzzafar Al-Amoudi, S.N. Abduljauwad, M. Maslehuddin, Magnesium-sodium sulfate attack in plain and blended cements, ASCE J. Mater. Civil Eng. 6 (1994) 201–222. [48] O.S.B. Al-Amoudi, Sulfate attack and reinforcement corrosion in plain and blended cements exposed to sulfate environments, Build. Environ. 33 (1998) 53–61. [49] S.T. Lee, H.Y. Moon, Sulfate attack and role of silica fume in resisting strength loss, Cement Concr. Compos. 27 (2005) 65–76. [50] C. Plowman, J.G. Cabrera, The use of fly ash to improve the sulphate resistance of concrete, Waste Manage. 16 (1966) 145. [51] P. Nielsen, S. Nicolai, A. Darimont, X. Kestemont, Influence of cement and aggregate type on thaumasite formation in concrete, Cement Concr. Compos. 53 (2014) 115–126. [52] A. Bogas, A. Mauricio, M.F.C. Pereira, Microstructural analysis of Iberian expanded clay aggregates, Microsc. Microanal. 18 (2012) 1190–1208.
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The investigation of microstructure and strength properties of lightweight mortar containing mineral admixtures exposed to sulfate attack Harun Tanyildizi ⇑ Department of Civil Engineering, Firat University Elazig, Turkey
a r t i c l e
i n f o
Article history: Received 15 January 2015 Received in revised form 3 August 2015 Accepted 1 September 2015 Available online 4 September 2015 Keywords: Lightweight mortar Electron microscopy Energy-dispersive X-ray X-ray diffraction Compressive strength
a b s t r a c t The aim of this study was to evaluate the effect of magnesium sulfate concentration on the microstructure and strength properties of lightweight mortars containing fly ash and silica fume. Lightweight mortar specimens containing 15% fly ash and 10% silica fume were prepared for this study. The specimens were exposed to different sulfate concentrations (0% MgSO4 2 , 2% MgSO4 2 and 4% MgSO4 2 ) for one year after specimens were kept in water at 20 ± 2 °C for 28 days. The microstructure analyses and compressive strength were monitored for cure periods to evaluate the performance of the test specimens exposed to different sulfate attacks. The microstructure analyses were performed using the scanning electron microscopy, the energy-dispersive X-ray, and the X-ray powder diffraction. The microstructure results showed that the deterioration mechanism of lightweight mortars exposed to magnesium sulfate has changed according to magnesium sulfate concentration percentage and mineral admixture type. Furthermore, the compressive test results showed that the performance of lightweight mortars containing silica fume were higher than lightweight mortars without mineral admixture and with fly ash. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Lightweight aggregates are generally classified as natural and artificial types. Lightweight concrete is made using lightweight aggregate [1]. The use of lightweight mortar has been increasing. The lightweight concrete can be produced with densities from 300 to 1200 kg/m3 and compressive strengths from 1 to 100 MPa [2]. Lightweight concrete was used successfully in buildings and bridges [3]. The first examples of lightweight mortar were produced the ships during World War-I [4]. The lightweight
⇑ Tel.: +90 424 2370000-4315; fax: +90 424 2367064. E-mail address: [email protected] http://dx.doi.org/10.1016/j.measurement.2015.09.002 0263-2241/Ó 2015 Elsevier Ltd. All rights reserved.
mortars with higher compressive strengths have been made for many years [5]. The presence of sulfate ion can be caused the deterioration of concrete exposed to marine environments or placed in soils and groundwater contaminated with sulfate salts [6–8]. The feature of some material increased the rate of sulfate attack [9–12]. The permeability of concrete should be decreased for the sulfate resistance of concrete. The sulfate attack can be prevented with ASTM Type I cement, Type II cement or Type V cement. Furthermore, it can also be prevented by using pozzolans in concrete [13–15]. The chloride in waters increases the rate of portlandite. It increases the porosity of concrete. Thus, its strength is decreased. The sulfates are harmful to concrete. They cause by expansion, cracking, spalling and the decrease of strength after their reactions with hydrated cement mortar
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[16,17]. Binici and Aksogan [18] reported that natural pozzolan and ground granulated blast furnace slag blended Portland cements clearly outperformed plain Portland cement in sulfate resistance evaluated by a strength reduction on Rilem prisms. Binici et al. showed [19] that concrete improves the mechanical properties and chemical resistance of concrete by using the marble and granite aggregates. Sahmaran et al. [20] showed that the physical sulfate attack can affect the performance of cements against sulfate attack. Felekoglu et al. showed [21] that the expansions of blended cements changed by the amount of mineral addition. Turkmen et al. [22] showed that the Taguchi method could successfully be applied to the mechanical properties of concrete exposed to sulfate. Binici et al. [23] showed that pumice aggregate for the sulfate resistance was a suitable material for the cement production. In this experimental study, the effects of sulfate attack on the microstructure and the compressive strength of lightweight mortars with fly ash and silica fume were investigated.
2. Experimental 2.1. Materials The materials were provided by different sources in Turkey. The cement used in this study was selected as TS EN 197-1-CEM I 42.5 N in Turkey. Silica fume and Fly ash were obtained from Turkey. Pumice aggregate was used in the lightweight mortars. Pumice aggregate was obtained from natural deposits in Turkey. The specific gravity of lightweight aggregate was 2. The chemical analysis properties of the cement, pumice aggregate, fly ash, silica fume and were presented in Table 1. Furthermore, Fig. 1 showed that the grading curve of aggregate. 2.2. Preparation of specimens Pumice with a maximum size less than 4 mm was used for producing lightweight mortars. The mix proportions were shown in Table 2. The reference group was named as H. The groups with fly ash and silica fume were named
Table 1 The chemical properties of cement, fly ash and silica fume. Bulk oxide
The percentage by weight
SiO2 Al2O3 Fe2O3 CaO MgO LOI Specific surface area (cm2/g) Particle size Specific gravity (g/cm3)
Portland cement
Fly ash
Silica fume
Pumice aggregate
21.12 5.62 3.24 62.94 2.73 1.42 3430 – 3.10
48.53 24.61 7.59 9.48 2.28 0.93 2836 87.5% < 125 lm 2.27
91 0.58 0.24 0.71 0.33 1.84 – 96.5% < 45 lm 2.2
48.19 24.78 7.22 12.26 7.55 – – – 2
Fig. 1. Grading curve for the experimental work.
Table 2 Mixture proportion of concretes. Mix
Cement (kg/m3)
Fly ash (kg/m3)
Silica fume (kg/m3)
W/B
Pumice aggregates (kg/m3)
SP (L/m3)
H U S
400 340 360
– 60 –
– – 40
0.77 0.77 0.77
1038 1024 1028
4.8 4.8 4.8
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as U and S, respectively. The super plasticizer was used for this study. It meets ASTM C 494 requirements for Type A, water-reducing, and Type F, high-range water-reducing, admixtures. The produced mortar was placed in the standard cube (50 50 50 mm). 156 specimens were prepared in each production. They kept in a water tank at 20 ± 2 °C for 28 days. 2.3. Exposure to magnesium sulfate of samples The specimens were separated into two groups after the curing. The first group of specimens was continuously kept under a water tank at 20 ± 2 °C. The other group was kept in three tanks with the following sulfate concentrations:
2% MgSO4 2 (20.000 mg/l), 4% MgSO4 2 (40.000 mg/l). In two relevant standards, both ACI-225R-85 [24] and ACI-201.2R-77 [25], any sulfate water in which the sulfate ion concentration was within: 1500 ppm < SO=4 < 10,000 ppm was defined as ‘‘severe” sulfate environment, and those for which the sulfate ion concentration was greater than 10,000 ppm is defined as ‘‘very severe” sulfate water environment. The sulfate water tanks prepared in this study had two different ranges of SO=4 concentration: 20,000 ppm and 40,000 ppm, which are both in ‘‘very severe” condition according to ACI [24,25]. The samples were taken out of the sulfate solutions at the end of one year
Ettringite
Gypsum
(a) SEM image (150x)
(b) SEM image (1500x)
Ca
Si Ca
Si
Ca
Al Ca
Al
Ca Ca
Ca Ca
Al
0 Cursor= 15.280 keV 0 cnt ID = Bk la1 Vert=81 Window 0.000 - 40.950 = 2230 cnt
10
keV
(d) XRD patterns
(c) EDX analysis Fig. 2. SEM, EDX and XRD analysis of lightweight cement paste exposed to magnesium sulfate 2% for 365 days.
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exactly, left in the laboratory environment without washing for a couple of days to attain air-dry forms. The measurements were made at 4, 6, 9, and 12 months according to ASTM C 1012 [26]. Due to this, the max exposure time to sulfate attack was selected 12 months. 3. Results 3.1. Microstructure analysis of lightweight mortar Sulfate attack has been investigated in the reaction between the cement hydrates and dissolved compounds in the attacking solution [27]. Furthermore, there have been many works with sulfate deterioration. The ettringite, gypsum, M–S–H and brucite are formed in concrete after sulfate attack [27–30]. Besides, many researchers [31–33]
have studied that the sulfate deterioration in cement system containing significant levels of limestone filler at the certain temperature. In this study, the lightweight mortars were kept in magnesium sulfate for 365 days. The scanning electron microscopy (SEM), the energy-dispersive X-ray (EDX) and the X-ray powder diffraction (XRD) analysis were examined the effect of magnesium sulfate on lightweight mortars containing mineral admixtures. The results were given in Figs. 2–7. It can be seen from Figs. 2a–7a that cracks were observed at the mortar–aggregate interface and in the surrounding mortar after lightweight mortars were kept in magnesium sulfate for 365 days. Networks of cracks are a depth of about 6 mm as a result of sulfate attack [34]. It can be seen from Figs. 2–7 that ettringite and gypsum occurred in samples. The magnesium sulfate attack has
Thaumasite
(a) SEM image (150x)
(b) SEM image (13500x)
(d) XRD patterns
(c) EDX analysis Fig. 3. SEM, EDX and XRD analysis of lightweight cement paste containing fly ash exposed to magnesium sulfate 2% for 365 days.
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caused the ettringite and gypsum formation in mortars [35]. Brucite was wrapped up the cement gel. It was protected further deterioration [36,39,16]. This was in the early stages. At other stages, deterioration processes would become dominant due to brucite [11]. The locations of the energy-dispersive X-ray (EDX) analyses were marked on each the scanning electron microscopy (SEM) image (Figs. 2c–7c). The energydispersive X-ray analysis in Fig. 2c showed only high calcium and silica, and aluminum peaks. The percentages of these materials are 44.24, 7.62 and 5.77, respectively. It was then concluded that the phase was ettringite. The energy-dispersive X-ray (EDX) analysis in Fig. 3c showed
a silica and high calcium, aluminum and smaller (K) potassium peaks. The percentages of these materials were 17.38, 40.02, 5.06 and 2.56, respectively. It was then concluded that the phase was thaumasite. The energy-dispersive X-ray (EDX) analysis in Fig. 4c showed only high calcium and silica, and aluminum peaks. The percentages of these materials were 81.5, 14.3 and 2.17, respectively. It was then concluded that the phase was thaumasite. The energy-dispersive X-ray (EDX) analysis in Fig. 5c showed only high calcium and silica, and sulfur peaks. The percentages of these materials were 53.23, 32.1 and 14.67, respectively. If Figs. 2c and 5c were compared, calcium and silica rate were increased 20.3%, 321.3% in Fig. 5c, respectively. It
Thaumasite
(a)SEM image (150x)
(b)SEM image (3500x)
Ca
Ca
Si
Ca K
Al
K
Al
K
K 0
Cursor= Vert=489
Ca Ca Ca 10
keV
Window 0.000 - 40.950 = 9295 cnt
(c) EDX analysis
(d) XRD patterns
Fig. 4. SEM, EDX and XRD analysis of lightweight cement paste containing silica fume exposed to magnesium sulfate 2% for 365 days.
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was then concluded that the phase was thaumasite. The energy-dispersive X-ray (EDX) analysis in Fig. 6c showed only high calcium and silica, and oxygen peaks. The percentages of these materials were 34.38, 8.26 and 57.36, respectively. If Figs. 3c and 6c were compared, calcium and silica rate were decreased 14.1%, 52.5% in Fig. 6c, respectively. It was then concluded that the phase was ettringite. The energy-dispersive X-ray (EDX) analysis in Fig. 7c showed only high calcium and silica peaks. The percentages of these materials were 34.38 and 12.49, respectively. If Figs. 4c and 7c were compared, calcium and silica rate were increased 7.4%, 475.6% in Fig. 7c,
respectively. It was then concluded that the phase was ettringite and thaumasite. Thaumasite was commonly thought to occur when sulfate, C–S–H and calcium carbonate reacted. Unless the coarse aggregate was serving as the source of carbonate, the thaumasite formation could occur in the absence of carbonate. Since the formation was required a carbonate source, micro-structural damage was caused by ettringite formation [37,38]. Furthermore, thaumasite can be found in pre-existing voids and cracks without necessarily causing deterioration of the mortar [39]. Figs. 2d–7d showed the X-ray powder diffraction (XRD) patterns of lightweight mortars after exposed to
Thaumasite
Gypsum
(b)SEM image (2000x)
(a)SEM image (150x)
Ca
S Ca Si
S Ca Si Ca
S
Ca
Ca Si S
S 0
Ca
Cursor= Vert=23
10 Window 0.000 - 40.950 = 708 cnt
(c)EDX analysis
keV
(d)XRD patterns
Fig. 5. SEM, EDX and XRD analysis of lightweight cement paste exposed to magnesium sulfate 4% for 365 days.
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the main constituents. The absence of brucite ettringite and thaumasite indicated that the diffusion of sulfates into the sample was very slow. Furthermore, the X-ray powder diffraction (XRD) pattern for the lightweight mortar exposed to a low solution of magnesium sulfate indicated maximum intensity peaks gypsum. The X-ray powder diffraction (XRD) patterns of lightweight mortars containing fly ash exposed to magnesium sulfate 2–4% were presented in Figs. 3d and 6d. Gypsum and calcite were the main constituents, but the gypsum peaks increased with increased of concretion of magnesium sulfate. The X-ray powder diffraction (XRD) patterns of lightweight mortars containing silica fume exposed to magnesium
magnesium sulfate for 365 days. The presence of ettringite (E), thaumasite (T), gypsum (G), calcite (C) and brucite (B) showed in figures. These patterns were produced the reactions between cement hydration and magnesium sulfate attack. Furthermore, the one of the most general causes for deterioration because of the magnesium sulfate attack might be attributed to both thaumasite formation and gypsum formation. Hartshom et al. reported that the gypsum and thaumasite played an important role in cement with limestone filler because of the magnesium sulfate attack [40]. The X-ray powder diffraction (XRD) patterns of lightweight mortars exposed to magnesium sulfate 2–4% were presented in Figs. 2d and 5d. Gypsum and calcite were
Ettringite
Gypsum
(a) SEM image (150x)
(b) SEM image (3500x)
Ca
Ca
O
Ca Si
Ca Ca Ca 0 Cursor= Vert=58
Si Si
Ca Ca 10 keV
Window 0.000 - 40.950 = 1102 cnt
(c) EDX analysis
(d) XRD patterns
Fig. 6. SEM, EDX and XRD analysis of lightweight cement paste containing fly ash exposed to magnesium sulfate 4% for 365 days.
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Ettringite
Brucite
Gypsum
Thaumasite
(b)SEM image (3500x)
(a)SEM image (150x) Ca
Ca
Ca Si Ca
Ca
Si
Ca Si
Ca 0
Cursor= Vert=70
Ca
Window 0.000 - 40.950 = 1381 cnt
keV
(c)EDX analysis
(d)XRD patterns
Fig. 7. SEM, EDX and XRD analysis of lightweight cement paste containing silica fume exposed to magnesium sulfate 4% for 365 days.
sulfate 2–4% were presented in Figs. 4d and 7d. Gypsum and calcite were the main constituents. Moreover, the gypsum and calcite peaks increased with increased of concretion of magnesium sulfate. The gypsum peaks of lightweight mortar samples always gave the highest values followed by lightweight mortar with fly ash and silica fume. Calcium hydroxide could also be consumed throughout the potential of gypsum formation [41]. Thus, the addition of the some minerals could be caused to richer aluminate systems. These have become more resistant to thaumasite form of sulfate attack [42]. The pozzolanic materials reduce concrete permeability. It is blocked the ingress of the deleterious sulfate ions [41].
3.2. Compressive strength results of lightweight cement mortar When the mortars were exposed a sulfate solution, sulfate ions entered into the specimens. It was known that the wetting and drying cycles accelerated the penetration of the sulfate ions in the mortars. After sulfate ions entered the concrete pores, they reacted with hydrated cement. The reactions were complicated. The reactions have been consistent involves numerous mechanisms [43]. Two forms of sulfate attack, which including the ettringite and thaumasite, can be warranted based on concrete exposures. The ettringite form (C3A3CaSO431H2O) can be
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caused by the reaction of calcium, sodium and/or magnesium sulfates with C3A, hydrated aluminates, or monosulfate (C3ACaSO412H2O). On the other hand, thaumasite can be described as calcium–silicate–sulfate–carbonate hydrate (CaSiO3CaCO3CaSO415H2O), which is the result of the reaction between calcium–silicate hydrates and sulfates in the presence of carbonate ions. Eventually, these two types will make expansion and cracking of mortar and concrete [44,45]. In this study, the compressive strength results of lightweight mortars containing fly ash and silica fume exposed to different magnesium sulfate concentration during 365 days could be seen in Figs. 8–10. It could be seen from Figs. 8–10 that compressive strength of lightweight mortars was decreased with the increase of sulfate concentration. The compressive strengths of lightweight mortars without mineral admixtures were decreased 12.29%,
151
9.38%, 12.46%, 16.31%, 17.43%, 10.07%, 4.76%, and 15.51% compared to that compressive strength of lightweight mortars without mineral admixtures exposed to 2% sulfate attack at 28, 60, 90, 120, 150, 180, 210, and 365 days, respectively. The compressive strengths of lightweight mortars without mineral admixtures were decreased 26.24%, 25.51%, 25.66%, 17.45%, 19.63%, 12.93%, 13.52%, and 23.12% when compressive strength of lightweight mortars without mineral admixtures exposed to 4% sulfate attack were compared at 28, 60, 90, 120, 150, 180, 210, and 365 days, respectively. The compressive strengths of lightweight mortars containing fly ash were decreased 6.07%, 7.91%, 7.71%, 7%, 8.13%, 4.55%, 9.20%, and 8.73%, according to that compressive strength of lightweight mortars containing fly ash exposed to 2% sulfate attack at 28, 60, 90, 120, 150, 180, 210, and 365 days, respectively. The compressive strengths of lightweight mortars containing fly
Fig. 8. Compressive results of lightweight cement paste exposed 0% sulfate attack.
Fig. 9. Compressive results of lightweight cement paste exposed 2% sulfate attack.
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ash were decreased 16.73%, 16.56%, 21.04%, 12.63%, 12.89%, 8.24%, 13.83%, and 17.23% compared to that compressive strength of lightweight mortars containing fly ash exposed to 4% sulfate attack at 28, 60, 90, 120, 150, 180, 210, and 365 days, respectively. The compressive strengths of lightweight mortars containing silica fume were decreased 6.75%, 3.97%, 2.77%, 3.75%, 7.27%, 7.07%, 8.19%, and 9.13% when compressive strength of lightweight mortars containing silica fume exposed to 2% sulfate attack were compared at 28, 60, 90, 120, 150, 180, 210, and 365 days, respectively. The compressive strengths of lightweight mortars containing silica fume were decreased 18.74%, 23.40%, 9.32%, 6.78%, 8.56%, 9.60%, 12.4%, and 12.05%, according to that compressive strength of lightweight mortars containing silica fume exposed to 4% sulfate attack at 28, 60, 90, 120, 150, 180, 210, and 365 days, respectively. The effect of chemical composition of mineral admixtures (fly ash, silica fume, etc.) is a significant factor affecting its sulfate resistance performance [45]. Lightweight cement mortars containing silica fume
were given the best results among mineral additives. Wee et al. said that the samples containing 5% and 10% silica fume played a major role in resisting sodium [46]. The mortar samples with the silica fume decrease calcium hydroxide because of the pozzolanic reaction. Furthermore, it allows the magnesium sulfate to more easily attack the C–S–H because the cement bond is destruction. The gypsum would tend to form due to locally reduce pH and the limited local of aluminums [47–49]. The performance of lightweight mortars containing fly ash was given better than lightweight mortars without mineral admixture. The fly ash has the major roles in resistance to sulfate attack. They are given below.
The mortars containing fly ash have shown that the sulfate-containing hydrate has the long-term stability. The formation of the monosulfate phase occurs the less volume change when compared to the formation of ettringite.
Fig. 10. Compressive results of lightweight cement paste exposed 4% sulfate attack.
Fig. 11. Variation of mass of samples exposed to sulfate attack.
H. Tanyildizi / Measurement 77 (2016) 143–154
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Fig. 12. Photo of lightweight cement pastes exposed to magnesium sulfate 4% for 365 days.
There is no recrystallisation as the case with ettringite formation [50]. Fig. 11 shows the variations in mass with time under magnesium sulfate environment for a period of 1 year. Fig. 12 shows the photo of lightweight cement pastes exposed to magnesium sulfate 4% for a period of 1 year. The variation in mass in very severe exposure conditions showed different trend. The mass of sample increased with the increase of sulfate ratio. This increase may be explained by the water absorption capacity of the LWA [51], as internal pores of the LWA are very slowly filled with water, it may take several months of immersion to approach saturation [52]. 4. Conclusions In this study, the microstructure and compressive strength of lightweight mortar exposed to different sulfate concentration
(0%
MgSO4 2
(0 mg/l),
2%
MgSO4 2
2
(20.000 mg/l), 4% MgSO4 (40.000 mg/l)) for 365 days was investigated by using the scanning electron microscope (SEM), the energy-dispersive X-ray (EDX), the X-ray powder diffraction (XRD), and compressive strength test. The main results of this research were given in the following conclusions. The scanning electron microscopy (SEM) image showed that the cracks were observed at the mortar–aggregate interface and in the surrounding lightweight mortar after lightweight mortars were immersed in magnesium sulfate for 365 days. The energy-dispersive X-ray analysis (EDX) showed that the lightweight mortar containing silica fume exposed to magnesium sulfate 4% indicated the presence of the calcium 87%, silica 13%, while the lightweight mortar exposed to magnesium sulfate 2% indicated aluminum 2.1%, silica 14.3%, potassium 2.1% and calcium 81.5%. The lightweight mortar containing fly ash exposed to magnesium sulfate 4% indicated the presence of the calcium oxygen 57.3%, silica 8.3% and calcium 34.4% while the lightweight mortar exposed
to magnesium sulfate 2% indicated oxygen 39.1%, sodium 1.6%, magnesium 1.6%, aluminum 7.5%, silica 7.7% and potassium 4.3%. The lightweight mortar exposed to magnesium sulfate 4% indicated the presence of the calcium 53.2%, sulfur 32.1% and silica 14.7% while the lightweight mortar exposed to magnesium sulfate 2% indicated calcium 69.5%, silica 22.5% and aluminum 8%. The X-ray powder diffraction (XRD) analysis showed that the degree of deterioration of the lightweight mortar was different from each other. The maximum formation of gypsum was obtained from the lightweight mortar without mineral admixtures exposed to magnesium sulfate 2%. The minimum formation of gypsum was obtained from the lightweight mortar containing fly ash exposed to magnesium sulfate 2%. The maximum formation of calcite was obtained from the lightweight mortar without mineral admixtures exposed to magnesium sulfate 2%. The minimum formation of calcite was obtained from the lightweight mortar without mineral admixtures exposed to magnesium sulfate 4%. The compressive strength results of lightweight mortars containing silica fume gave the best results among mineral additives. Furthermore, the microstructure of silica fume based mortar confirms the compressive strength. The compressive strength results of lightweight mortars containing fly ash gave higher values than the cement specimens without mineral admixtures.
Acknowledgments The author is grateful for the financial support of the Firat University BAPYB (Project No. 1481).
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