- Email: [email protected]
Development of building material utilizing a low pozzolanic activity mineral
Construction and Building Materials 121 (2016) 300–309
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Development of building material utilizing a low pozzolanic activity mineral Changming Li, Lijiu Wang, Tingting Zhang ⇑, Jingliang Dong School of Civil Engineering, Dalian University of Technology, Dalian 116024, PR China
h i g h l i g h t s The potential use of a low pozzolanic activity mineral in producing building materials was reported. The mechanical properties and hydration progress of alkali activated Pisha mortar were studied. A maximum compressive strength of 14.4 MPa of mortar was achieved with water glass. The main reaction products are amorphous aluminosilicate gel (C–A–S–H) and CaCO3.
a r t i c l e
i n f o
Article history: Received 4 January 2016 Received in revised form 18 May 2016 Accepted 26 May 2016
Keywords: Low pozzolanic activity Alkali activated mortar Activator type Hydration progress Mechanical properties
a b s t r a c t In this work, the effects of different activators, particle size and curing conditions on the mechanical properties and hydration progress of alkali activated Pisha mortars were studied. Four different activators (NaOH, Na2CO3, Na2SO4 and water glass) based on two different fineness Pisha were used, two kinds of curing temperature, 25 and 80 °C were considerate. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG) and scanning electron microscopy (SEM) were conducted to analyze the reaction products, indentify the phase composition and observe the micromorphology, respectively. It was found that the modulus of water glass and fineness of Pisha have significant influence on the compressive strength and hydration process of alkali activated Pisha mortars. The optimum activators were water glass, the sample (Ms = 1.5, curing at 80 °C) exhibited the highest compressive strength (14.4 MPa) at 28 days. The results of the investigation also show that the amorphous aluminosilicate gels were the main hydration products. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction Compared to Portland cement, alkali activated materials could offer the same mechanical properties, but with lower CO2 product [1–3]. The mechanical properties and economic benefit of the utilization of alkali activated materials in engineering have been well studied [4–6]. The type of activator played an important role for alkali activated material, the optimum dosage differs according to the type of aluminasilicate used and the type of activation solution [7,8]. Pisha (PS) was a special kind of pozzolanic mineral with a low activity [9], it was mainly composed of clay minerals (montmorillonite, illite and mica et.al), sand (quartz) and other minerals (feldspar, calcium, et al.) [10]. PS has a bad bonded mechanism and an ⇑ Corresponding author at: School of Civil Engineering, Dalian University of Technology, The First Comprehensive Experimental Building No. 217, Ling gong Road No. 2, Gaoxinyuan District, Dalian City, Liaoning Province 116024, PR China. E-mail address: [email protected] (T. Zhang). http://dx.doi.org/10.1016/j.conbuildmat.2016.05.161 0950-0618/Ó 2016 Elsevier Ltd. All rights reserved.
unsatisfactory petrographic structure, its cementitious material, free oxide (e.g., iron oxide), is easy to dissolve in water, moreover, the structure also would be destroyed due to the expansion of soggy montmorillonite, therefore, PS is hard when it is dry, but would collapse when is immersed in water. Due to the fractured landscape and the deteriorated ecological environment, soil erosion occurs frequently during and after rainstorm, there are 20,000 tons PS per square kilometer were carried into the local river every year [11], and the PS was considerate as one of the main sources of sediment into the local river. However, there is rarely researchers pay their attention to study the exploitation of PS. In fact, PS could be reused to produce alternative binding materials for dam building and other civil engineering [9]. Therefore, it would be a beneficial exploration to apply PS in the construction industry (e.g., dam building materials or building brick) as a pozzolanic material for the production of alkali activated materials. The aim of this paper is to produce a new alkali activated building materials by using PS, and study the effect of alkaline type and
301
C. Li et al. / Construction and Building Materials 121 (2016) 300–309
the fineness of PS at different curing conditions on the geopolymerisation of PS. It is hoped that the processing of alkali activated Pisha martors (APSM) could be well understood and found the optimal scheme of manufacture APSM by using PS. 2. Materials and methods 2.1. Materials The PS was obtained from Loess Plateau in Inner Mongolia, China. The PS was air-dried and pulverized to give a granular material with particles less than 1.0 mm in diameter, and part of the PS (clay mineral, sand and all the other phases) was dry milled using a porcelain ball mill with alumina milling media for 30 min to increase the specific surface area. The particle size distributions of PS and milled PS shown in Fig. 1 were determined using laser diffraction (Mastersizer 2000, Malvern Instruments). For PS and milled PS, Fig. 1 indicates a mean particle size of approximately 111 and 18.9 lm, respectively. The d90 (90% of volume less than this size) of PS and milled PS was found to be 309.6 and 52.6 lm, and the value of d10 was fund to be 8.52 and 2.68 lm, respectively. The chemical composition of PS showed in Table 1 was determined by X-ray fluorescence (XRF) spectrometry (Germen, Siemens-Bruker, SRS 3400). The activator solution was prepared by dissolving NaOH, NaCO3 and Na2SO4 pellets (99% purity quotient, Tianjin Kemiou Chemical Reagent Co., Ltd. China) in distilled water to a certain concentration, and cooled to room temperature. Water glass with Ms (molar ratio SiO2/Na2O) = 3.0 (Na2O = 8.83 wt%, SiO2 = 26.5 wt%, H2O = 64.67 wt%) was used as alkaline activator, and the others were a mixture of this commercial sodium silicate with NaOH solution to give a combined modulus of Ms = 2.0 (Na2O = 13.25 wt% SiO2 = 26.5 wt%, H2O = 60.25 wt%) and Ms = 1.5 (Na2O = 17.67 wt% SiO2 = 26.5 wt%, H2O = 55.83 wt%), respectively. The pH value of the activator solution was measured using a pH meter (METER TOLEDO, Delta 320, LAB, Switzerland) after the activator solution was prepared. 2.2. Sample preparation
Table 1 Chemical composition of PS determined by X-ray fluorescence. Chemical
Component (wt%)
SiO2 Al2O3 CaO Na2O K2O MgO Fe2O3 SO3 LOI
62.46 20.08 5.10 0.56 2.23 5.02 3.10 0.04 1.41
LOI is loss on ignition at 1000 °C. Att values in wt%.
Table 2 Mix proportion of mixture (wt%). Sample
PS
Activator solution Activators
W1-1 W1-2 W1-3
84
Water glass (Ms = 1.5)
3
Water
pH
13
11.5
W1-4 W2-1 W2-2 W2-3
2.3. Methods The compressive strength was tested by using an electronic universal testing machine with a 100 kN capacity and a constant displacement rate of 0.05 mm/ min. The composition of raw materials and mortars were tested by X-ray diffraction (XRD), XRD was recorded on a Siemens-Bruker D5000 using Cu Ka radiation (k = 1.54 Å) operating at 40 kV and 30 mA. The samples were scanned from 5 to 70° (2h range) at a rate of 2°/min and step size of 0.02°. Fourier transform infrared (FTIR) analysis was performed using the KBr pellet method (1 mg sample per 100 mg KBr) on a Bruker EQUINOX 55 spectrometer, with 32 scans per sample collected from 4000 to 400 cm 1 at 4 cm 1 resolution. A Switzerland Mettler-Toledo simultaneous thermal analyser was used to measure some physical properties of the material as a function of the temperature change. The samples were heated
W3-1 W3-2 W3-3
84
Water glass (Ms = 2.0)
3
13
10.7
84
Water glass (Ms = 3.0)
3
13
9.0
86
Na2CO3
1
13
8.8
80 25 80
80 25 80
80 25 80 25
86
Na2SO4
1
13
7.4
NS4 NH1 NH2 NH3
PS PS Milled PS Milled PS PS PS Milled PS Milled PS PS PS Milled PS Milled PS PS PS Milled PS Milled PS PS PS Milled PS Milled PS PS PS Milled PS Milled PS
25
NC4 NS1 NS2 NS3
80 25 80
25
W3-4 NC1 NC2 NC3
PS type
25
W2-4
The materials used to prepare the mortars were summarized in Table 2. For all samples, the total mass of the mixture was kept at 392.5 g. Add the PS powder into activator solution (e.g., NaOH, NaCO3, Na2SO4, water glass), in order to achieve complete mixing between the solid and solution, the mixture was mixed for 15 min by a magnetic stir bar. To make regularly shaped specimens for mechanical testing, the mixtures were poured into cylindrical steel molds, and mixture was pressed (30 kN) to specimens with an diameter of 5 cm and height of 10 cm (i.e., an aspect ratio of 2.0) bar on a hydraulic testing machine. To ensure repeatability, 3 specimens were prepared for each type of mortar. To investigate the effect of curing temperature on strength of APSM, the specimens were sealed with plastic bags and cured in oven (80 °C) and laboratory at ambient temperature (25 ± 2 °C), respectively.
Curing temperature °C
80 25 80 25
86
NaOH
1
NH4
Fig. 1. Particle size distribution curve of raw materials. (a) PS, (b) milled PS.
13
10.9
80 25 80 25
302
C. Li et al. / Construction and Building Materials 121 (2016) 300–309
from 40 to 1000 °C in an atmosphere of nitrogen with a heating rate of 10 °Cmin 1. The microstructure and chemical elemental of mortar was examined using a JEOL JSM 6460 scanning electron microscope (SEM) with an EDAX energy dispersive Xray spectroscope device equipped.
3. Results and discussion 3.1. Mechanical properties 3.1.1. Activator type The activator is a very important factor in the reaction process of alkali activated materials, the properties of alkali activated materials based on different activator are very different [12]. The effects of different types of activator on compressive strength of APSM (curing at 80 °C) is shown in Fig. 2. For the samples which were synthesized by PS and activators solution, it can be seen that the strength of APSM based on different types of activator solution showed the following rank: W1 > NH > NS > W2 > NC > W3. The samples activated by W1 show highest compressive strength (6.26 MPa), and the compressive strength of the samples activated by W2, W3, NC, NS and NH is lower (2.59 3.99 MPa). For the samples which were synthesized by milled PS and activator solution, the resulting strength of samples activated by W1, NH and NC exhibit a higher strength (12.68 14.4 MPa), and the strength of the samples based on W2, W3 and NS was lower (7.52 11.28 MPa), and the strength of the corresponding mortars had the following order: W1 > NH > NS > W2 > W3 > NC. As shown in Fig. 2, the NaOH, Na2SO4 and W1 are the optimum activators required to improve compressive strength of APSM. 3.1.2. Modulus of water glass solution Fig. 3 shows the compressive strengths of APSM prepared using water glass with different SiO2/Na2O molar ratios (Ms = 1.5, 2.0, 3.0), for PS and milled PS samples for cured at 25 and 80 °C, respectively. It was shown that the compressive strength increases as the value of Ms decreased, for the water glass used in this work, the Na2O content would increase as the decreasing modulus when the amount of water glass is kept constant, that means that the lower the values of Ms, the higher the Na2O content, and the higher the alkalinity (pH) of activator solution. During the reaction process, high alkalinity could lead to a higher efficiency in dissolve the amorphous, reactive silicate and alumina, the source material would dissolution faster and more extensive when the PS was activated with a more caustic alkalinity activator solution, so that a higher extent and degree of reaction between the PS and activator takes place, leading to more geopolymer gels produced. Therefore, the final geopolymer gel would be more stiffness and the compressive strength of APSM would be improved with a higher alkalinity activator solution [13,14]. In contrast, a higher values of Ms with a lower Na2O content, and a lower alkalinity results in a lower compressive strength.
3.1.3. Fineness of PS The effect of PS fineness on compressive strength is summarized in Fig. 4. The compressive strength of the mortar increased as the decreasing PS particle size. For the samples produced by PS and activators solution, the compressive strength is about 1.8 6.2 MPa (curing at 25 °C), 2.6 6.3 MPa (curing at 80 °C), and for milled PS samples, it is about 6.75 13.5 MPa (curing at 25 °C), 7.5 14.4 MPa (curing at 80 °C). It shows that increasing the Blaine surface area of PS leads to a significant development in compressive strength. For the samples (milled PS) based on W and NC, the compressive strength would be increased to 212% 511% when compared with the samples produced by PS, and for the samples based on NS and NH samples it would be increased to 326% 557%. It reveals that a smaller particle size would give a larger surface area and reaction area. Larger reaction area would improve the reactivity of source materials and lead a higher reaction efficiency between the solid particles and solution [15,16]. As a result, the milled PS with a larger surface area showed better performance in compressive strength. Moreover, a smaller particles size would increased the density of mortar [17,18], thus, the samples produced by milled PS performance more homogeneous and denser. In contrast, the coarse particles with a smaller specific surface area would have a lower reactivity, Fig. 5 shows the feature of the PS and milled PS samples based on different activators. It clearly that the milled PS samples have a higher reaction degree than the PS samples. For PS samples, the reaction of PS and alkali activator is low and insufficient, the excessive activator leaching out and covered the surface of the sample. Moreover, the excessive alkali would make a negative effect on the mechanical strength [19], due to the excessive free OH were remain in the samples, weakening the structure of mortar [20–22].
3.1.4. Curing temperature The effect of curing temperature on compressive strength is demonstrated in Fig. 6. It can be seen that the compressive strength increased as the increasing curing temperature. For the APSM samples, increasing temperature up to 80 °C yield a increase in compressive strength. This could be explained that the high curing temperature could accelerate the reaction process and enhance the reaction efficiency. For the PS samples curing at 80 °C, the compressive strength would be increased to 115% 165% when compared with the samples curing at 25 °C (except W1), and for the milled PS samples, the compressive strength of the samples curing at 80 °C would be increased to 110% 129% when compared with the samples curing at 25 °C (except W3 and NH). For PS samples activated by W1 and the milled PS samples based on W3 and NH, the increasing curing temperature has no remarkable effect on compressive strength.
Fig. 2. Effect of types of activator on compressive strength of APSM curing at 80 °C. (a) PS samples, (b) milled PS samples.
C. Li et al. / Construction and Building Materials 121 (2016) 300–309
Fig. 3. Effect of Ms of water glass on compressive strength of APSM. (a) PS samples, (b) milled PS samples.
Fig. 4. Effect of fineness of PS on compressive strength of APSM. (a) curing at 25 °C, (b) milled PS samples at 80 °C.
Fig. 5. The feature of APSM samples based on different activators.
Fig. 6. Effect of curing temperature on compressive strength of APSM. (a) PS samples, (b) milled PS samples.
303
304
C. Li et al. / Construction and Building Materials 121 (2016) 300–309
3.2. XRD analysis Fig. 7 shows XRD patterns of the PS and APSM samples. PS sample shows broad humps between 5–7° 2h and 8.5–9° 2h, indicating that the montmorillonite (Ca0.2(Al,Mg)2Si4O10(OH)24H2O, PDF# 01-013-0135) [23] are found, the quartz (SiO2, PDF# 01-0650466) was observed at approximately around 26.6° 2h and the sharp peaks around 27.9° and 28° 2h were attribute to albite (NaAlSi3O8, PDF# 01-009-0466), the peak around 29° 2h was calcite (CaCO3, PDF# 01-047-1743). From the result of Fig. 7, it can be seen that the difference in the XRD spectra of PS and APSM are hardly perceptible. For the APSM samples, the intensity of the peak around 5.9° 2h are very weak, and the distinct peak at 7.1° 2h is observed. Thus, it is clear from the XRD that the peak of sample (2h = 6°) is shifted towards the higher angle region after activated by activator (e.g., water glass, NH, NC, NS), reaching the value 2h = 6.3°, at the same time a new phase begins to develop at 2h = 7.1°. This shift and the presence of new peak was mainly attributed the dehydration of montmorillonite [24]. Moreover, the reaction of the activator activated PS seems to result in the formation of geopolymer gels (C-S-H gel, Ca1.5Si3.5nH2O, PDF# 01033-0306) [25,26]. This point will be revisited in Sections 3.3 and 3.4 in the context of the discussion of FTIR and TG/DTG. The quartz (SiO2, PDF# 01-065-0466), albite (NaAlSi3O8, PDF# 01-009-0466) detected in APSM samples resulting from the unreactive nature of these phase supplied by the PS.
3.3. Fourier transform infrared FTIR analyses for PS and APSM samples are shown in Fig. 8a–d. For PS samples, it shows the main adsorption bands as follows: 468, 522, 584, 645, 713, 778, 875, 1035, 1421, 1635, 3421 and 3620 cm 1. The bands due to free (or weakly hydrogen-bonded water molecules to the surface oxygen of tetrahedral sheet) water molecules, water-water hydrogen bond (Mn+–O–H–O–H–) and water bending modes are observed near 3622, 3421 and 1635 cm 1, respectively [27,28]. The peaks at 1421, 875 and 713 cm 1 are attributed to anti-symmetric stretching and out-ofplane bending modes of CO23 ions [29]. The strong band at 1035, 522 and 468 cm 1 are assigned to Si–O–Si bending vibration bond, whereas the Si–O asymmetric stretching vibration bond can be seen at 1035 cm 1, and these stretching modes are related to quartz (SiO2). The peaks at 778, 645 and 584 cm 1 are attributed to Al–Al–OH, Al–Mg–OH bending vibration [30–32]. For APSM
samples activated by NaOH, it can be seen that the bands at 1635 and 3421 cm 1 were disappeared and the mode at 3622 cm 1 became sharper and had an increase in the intensity. The disappeared of the bands at 1635 and 3421 cm 1 indicated that the free water molecules (or weakly hydrogen-bonded water molecules to the surface oxygen of tetrahedral sheet) decreased or disappeared. And the increased in the intensity of the mode at 3622 cm 1 due to the formation of structure water which was trapped in the geopolymeric products (geopolymer gel). A weak new mode at 2517 cm 1 corresponding to the stretching vibration of O–C–O bonds in the carbonate group (CO23 ) was also observed, the intensity of the bands at 1448, 875 and 713 cm 1 which were assigned to carbonate C–O stretching vibrations increased. These indicated that carbonates were present in the samples due to reaction of older geopolymer gel (C–S–H gel) and CO2 with formation of calcium carbonate (CaCO3) [33]. Fig. 8b–d show the infrared spectra of APSM based Na2CO3, Na2SO4 and water glass, respectively. It can be seen that the infrared spectra of APSM based on different activator are very similar, and there were no significant difference in all bands. It was found that the asymmetric stretching vibration of O–C–O bonds of CO23 groups shifted (1421 cm 1 to 1440 1, 1446 cm 1), and there was a increase in the intensity in the vibration when compared with PS samples. This indicates chemical changes in the reaction products formed by alkaline activation of the PS, in particular the decalcification of the C–S–H gel to form calcium carbonates. The mode at 875 cm 1 became sharper and had an increase in the intensity is associated with the formation of calcite.
3.4. Thermogravimetry analysis Fig. 9 shows the TG and DTG curves for PS and APSM samples with different type activators. The total mass loss in these samples, in the temperature range of 40–1000 °C, varied from 6.80% to 8.84%. The TG/DTG curves of PS samples are presented in Fig. 9a. On the TG curve for PS, the two steps of weight loss, together with corresponding endothermic DTG peaks, are observed. The relatively weight loss at 40–200 °C was due to the loss of free water and loosely bound water, and the weight loss in the region of 500–800 °C are the decarbonation of the calcite into CaO [29,34]. The DTG curves of PS shows a well-defined strong symmetric double peak near 96 and 163 °C, characteristic for montmorillonites [27,35]. It reflects the release if water adsorbed on the particle surfaces and of water molecules coordinating Ca2+ or Na+ cations,
Fig. 7. X-ray diffraction patterns of 28 days cured specimens. Q-quartz (SiO2, PDF# 01-065-0466), Mo-montmorillonite (Ca0.2(Al,Mg)2Si4O10(OH)24H2O, PDF# 01-013-0135), A-albite (NaAlSi3O8, PDF# 01-009-0466), C-calcite (CaCO3, PDF# 01-047-1743), Cs–C–S–H gel (Ca1.5Si3.5nH2O, PDF# 01-033-0306).
C. Li et al. / Construction and Building Materials 121 (2016) 300–309
305
Fig. 8. Fourier transform infrared spectra of APSM based on different activator types.
respectively. The distinct and symmetrical peak at 538 °C is associated with dehydroxylation of montmorillonites. A sharp and strong peak at 756 °C is observed, and it relative to the decarbonation of the CaCO3 into CaO. Fig. 9b-f, and g show the TG/DTG curves of NH, NS, NC, W1, W2 and W3 samples, respectively. The TG curves are similar for all samples, there are two distinct steps of weight loss at 90–200 °C and 700–800 °C for all the samples were detected. The DTG curve exhibits an endothermic peak at 90– 200 °C for all samples. A mass loss of 1.65%, 1.27%, 1.12%, 1.70%, 1.25% and 1.24% was observed in this temperature range for the NH, NS, NC, W1, W2 and W3 samples, respectively. The mass loss peak between 90 and 200 °C was characteristic of the presence of geopolymer gel (C–S–H gel), and the weight loss refers to the loss of structural water that is present in the form of –OH sites in geopolymer gel [34]. There was a major weight loss peak related to the decarbonation of the CaCO3 at the temperature range 500– 800 °C, and the mass loss in the temperature range 500–800 °C was 5.19%, 5.06%, 4.72%, 4.76%, 4.77% and 4.63% for the NH, NS, NC, W1, W2 and W3 samples, respectively. The DTG data showed the weight loss speed of APSM samples. It can be seen that the peak at temperature about 96 °C (PS) became sharper and stronger and had shifted to high temperature, it means the samples of APSM had a quicker weight loss speed than the PS samples. The peak at temperature around 756 °C (PS) showed a same trend, the peak of APSM became sharper and stronger when compared with PS sample, and the weight loss speed of APSM was connected to the amount of CaCO3, it seems that the amount of CaCO3 of APSM is more than the PS sample, and it indicated that the increased CaCO3 was formed by the carbonation of C–S–H gel [29].
3.5. Microstructural analysis The microstructure and hydration products of APSM samples based on different activators were studied by using the scanning electron microscopy analyser. The EDS micrograph of APSM was examined to analyses the morphology of reaction products, and the elemental concentration is list in Table 3, each given value represents the average of ten readings taken adjacent to each other. The analysis of the morphology of APSM samples revealed that, in general, the reaction products of APSM samples mainly were amorphous aluminosilicate phases, geopolymer gels and calcium carbonate after their contact with activators. Fig. 10 compares the microstructure of the samples of produced by PS and four activators. Fig. 10a–c showed the micromorphology and hydration products of PS samples activated by water glass, NaOH and Na2SO4, respectively. As shown in Fig. 10a–c, the degree of hydration between PS and activators is low and showed a loosely structure, the flocculation-like geopolymer gels coexist with unreacted matrix, the unreacted feldspar block was wrapped by geopolymer gels. The micro-morphology of the PS sample activated by Na2CO3 was shown in Fig. 10d, it display a porous structure formation and the layered monotmorillonite and geopolymer gels were observed. The results of chemical analysis of PS samples which listed in Table 3 showed that the ratio of Ca/Si fluctuated between 0.32 and 0.62 (except Fig. 10d), this indicated that the main composition of geopolymer gels was C–(A)–S–H [34,35]. Fig. 11 showed the micromorphology and hydration products of milled PS samples. It shows that the SEM of samples showed a great amount of dense and
306
C. Li et al. / Construction and Building Materials 121 (2016) 300–309
Fig. 9. DTG and TG of APSM samples. (a) PS, (b) specimens based on NaOH, (c) specimens based on Na2SO4, (d) specimens based on Na2CO3, (e) specimens based on water glass (Ms = 1.5), (f) specimens based on water glass (Ms = 2.0), (g) specimens based on water glass (Ms = 3.0).
4. Conclusions
inexpensive and ecologically alkali activated materials which aiming to apply in the construction industry (e.g., dam building materials or building brick). And the effects of activator type, curing temperature and particle size on mechanical properties and phase composition of APSM were also investigated. Based on the experimental results, the following conclusions can be summarized:
This work studied the possibility of using a low pozzolanic activity mineral as the binder material to produce a new
1. It is possible to produced a new alkali activated materials reusing PS as a binder material. The significant factors affecting the
homogeneity geopolymer gels (Fig. 10a, b and d) and block-like crystal products (Fig. 10c). The ratio of Ca/Si fluctuated between 0.46 and 1.05 (except Fig. 11c), the EDS results of Fig. 11 showed that the dense geopolymer gels and block-like crystal products were C-(A)-S-H and calcite carbon, respectively [34,35].
307
C. Li et al. / Construction and Building Materials 121 (2016) 300–309 Table 3 Composition of APSM by SEM-EDS. Points
Fig. 10
Fig. 11
Elemental composition (at.%)
1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8
Ca/Si
C
O
Ca
Si
Al
Na
Mg
Others
31.91 33.54 26.00 30.45 24.41 26.47 22.94 38.34 34.01 31.82 36.91 38.07 25.99 21.66 22.85 22.56
51.38 50.22 48.06 49.47 49.67 53.66 55.66 43.20 48.57 47.18 51.94 49.72 53.41 53.90 57.98 57.09
2.88 3.29 3.88 3.21 5.82 4.66 0.42 3.52 4.62 6.83 4.60 3.88 2.09 20.37 3.53 4.00
6.65 6.71 12.14 9.41 10.53 7.52 11.67 9.28 6.47 7.83 4.38 5.01 7.97 1.92 7.61 8.54
2.78 2.74 4.41 3.28 4.01 3.09 4.46 3.48 2.53 2.63 1.19 1.99 2.99 0.82 3.13 3.56
2.54 2.18 1.87 1.31 2.95 2.85 3.24 0.41 2.14 1.02 0.29 0.28 1.32 0.77 1.39 1.28
1.30 1.05 1.74 1.06 1.70 1.45 1.49 1.52 1.23 0.93 0.61 0.86 2.53 0.44 2.29 1.60
0.56 0.27 1.90 1.81 0.91 0.30 0.12 0.25 0.43 1.76 0.08 0.19 3.70 0.12 1.22 1.37
0.43 0.49 0.32 0.34 0.55 0.62 0.04 0.38 0.71 0.87 1.05 0.77 0.26 10.61 0.46 0.47
Fig. 10. SEM micrographs of samples based on PS. (a) specimens based on NaOH, (b) specimens based on Na2CO3, (c) specimens based on Na2SO4, (d) specimens based on water glass (Ms = 1.5).
compressive strength of APSM are activator type and PS fineness. The strength of hardened APSM based on water glass (Ms = 1.5) reached the highest compressive strength (14.4 MPa), the effect of activator on strength of APSM showed the following rank: water glass (Ms = 1.5) > NaOH > Na2SO4 > Na2CO3. The Ms of water glass has notable influence on the strength of APSM, the optimum water glass modulus (SiO2/Na2O ratio) is 1.5. Increasing the Blaine surface area of PS (reducing the particle size) greatly increase the mechanical strength of APSM. The fineness of PS had a significant effect on the mechanical strength. With all the other parameters remain constant, the compressive strength of the samples
produced by milled PS based on different activator solution will be increased to 212% 557% compared to which synthesized by PS and activator solution. The effect of the curing conditions on strength is not remarkable, an increase in the curing temperature (from 25 to 80 °C) can improve the 28-day strength of APSM by up to 1% 65% (based on PS) and 4% 29% (based on milled PS), respectively. 2. XRD patterns show change in amorphous phases, the structure of montmorillonite changed due to its interlayer water molecules was slowly expelled after alkali activated. The XRD and FTIR results also indicated that the reaction products of APSM mainly show an alkali aluminosilicate gels.
308
C. Li et al. / Construction and Building Materials 121 (2016) 300–309
Fig. 11. SEM micrographs of samples based on milled PS. (a) specimens based on NaOH, (b) specimens based on Na2CO3, (c) specimens based on Na2SO4, (d) specimens based on water glass (Ms = 1.5).
3. TG/DTG results indicated that there were two steps of weight loss, together with corresponding endothermic DTG peaks, responds to aluminosilicate gels and CaCO3 were observed, respectively. The results of TG also showed that there was a positive correlativity between the amount of reaction products (weight loss) and compressive strength. Aluminosilicate gels are the main contributor of mechanical strength, the mechanical strength increased with the increasing amount of reaction products (aluminosilicate gels and CaCO3). 4. SEM results indicate that the reaction products of the samples based on PS were mainly shown a homogeneity geopolymer gels and some unreacted block matrix, the dense and homogeneity amorphous aluminosilicate gels and block-like crystal products were the main reaction products of the samples based on milled PS. The EDS results show that the geopolymer gels and crystals were mainly ascribed to amorphous hydrated calcium aluminosilicate (C–A–S–H) gel and CaCO3, respectively.
Acknowledgments The authors would like to express gratitude for the financial support by the National Key Science & Technology Pillar Program of China (No. 2013BAC05B03), the National Natural Science Foundation of China (Grant No. 51408096), the Fundamental Research Funds for the Central Universities (DUT15RC(4)22), and Liaoning BaiQianWan Talents Program (2015.20). References [1] John.L. Provis, Susan.A. Bernal, Geopolymers and related alkali-activated materials, Annu. Rev. Mater. Res. 44 (2014) 299–327.
[2] N. Amin, Use of clay as a cement replacement in mortar and its chemical activation to reduce the cost and emission of greenhouse gases, Constr. Build. Mater. 34 (2012) 381–384. [3] G. Habert, J.B. d’Espinose de Lacaillerie, N. Roussel, An environmental evaluationof geopolymer based concrete production: reviewing current research trends, J. Clean Prod. 19 (2011) 1229–1238. [4] A. Chakchouk, B. Samet, T. Mnif, Study on the potential use of Tunisian clay as pozzolanic material, Appl. Clay Sci. 33 (2006) 79–88. [5] B. Sabir, S. Wild, J. Baj, Metakaolin and calcined clays as pozzolans for concrete: a review, Cem. Concr. Compos. 23 (2001) 441–454. [6] F. Curcio, B. DeAngelis, S. Pagliolico, Metakaolin as a pozzolanic microfiller for high performance mortars, Cem. Concr. Res. 28 (6) (1998) 803–811. [7] Dali Bondar, C.J. Lynsdale, Neil B. Milestone, N. Hassani, A.A. Ramezanianpour, Effect of type, form, and dosage of activators on strength of alkali-activated natural pozzolans, Cem. Concr. Compos. 33 (2011) 251–260. [8] Behzad. Nematollahi, Jay. Sanjayan, Effect of different superplasticizers and activator combinations on workability and strength of fly ash based geopolymer, Mater. Des. 57 (2014) 667–672. [9] Changming. Li, Tingting. Zhang, Lijiu. Wang, Pozzolanic activaty of Pisha sandstone and mechanical properties of alkali-activated Pisha sandstone materials, J. Chin. Ceram. Soc. 43 (8) (2015) 1090–1098 (in Chinese with English summary). [10] C.M. Li, T.T. Zhang, L.J. Wang, Mechanical properties and microstructure of alkali activated Pisha sandstone geopolymer composites, Constr. Build. Mater. 68 (2014) 233–239. [11] X.M. Zheng, Research on management of concentrated coarse sediment source area of the Loess Plateau, Soil Water Conserv. China 12 (2005) 5–6 (in Chinese with English summary). [12] A. Fernández-Jiménez, Ã. Palomo, Composition and microstructure of alkali activated fly ash binder: effect of the activator, Cem. Concr. Res. 35 (10) (2005) 1984–1992. [13] S.D. Wang, Karen L. Scrivener, P.L. Pratt, Factors affecting the strength of alkaliactivated slag, Cem. Concr. Res. 24 (6) (1994) 1033–1043. [14] D. Hardjito, S.E. Wallah, D.M.J. Sumajouw, B.V. Rangan, On the development of fly ash-based geopolymer concrete, ACI Mater. J. 101 (6) (2004) 467–472. [15] J. Davidovits, Geopolymers–inorganic polymeric new materials, J. Therm. Anal. 37 (8) (1991) 1633–1656. [16] H. Xu, J.S.J. Deventer, Effect of source materials on geopolymerization, Ind. Eng. Chem. Res. 42 (8) (2003) 1698–1706. [17] M.K. Gopalan, Nucleation and pozzolanic factors in strength development of class F fly ash concrete, ACI Mater. J. 90 (M12) (1993) 117–121.
C. Li et al. / Construction and Building Materials 121 (2016) 300–309 [18] G.C. Isaia, A.L.G. Gastaldini, R. Moraes, Physical and pozzolanic action of mineral additions on the mechanical strength of highperformance concrete, Cem. Concr. Compos. 25 (2003) 69–76. [19] J. Temuujin, A. van Riessen, Effect of fly ash preliminary calcinations on the properties of geopolymer, J. Hazard. Mater. 164 (2009) 634–639. [20] T. Bakharev, J.G. Sanjayan, Y.B. Cheng, Effect of admixtures on properties of alkali-actived slag concrete, Cem. Concr. Res. 30 (2001) 1367–1374. [21] M.Y. Hu, X.M. Zhu, F.M. Long, Alkali activated fly ash-based geopolymers with zeolite or bentonite as additives, Cem. Concr. Compos. 31 (10) (2009) 762–768. [22] K. Komnitsas, D. Zaharaki, V. Perdikatsis, Effect of synthesis parameters on the compressive strength of low-calcium ferronickel slag inorganic polymers, J. Hazard. Mater. 161 (2009) 760–768. [23] Raúl Fernández, Lorena González, Ana Isabel Ruiz, Jaime Cuevas, Nature of C– (A)–S–H phases formed in the reaction bentonite/portlandite, J. Geochem. 12 (2014) 1–8. [24] A.F. Koster van Groos, S. Guggenheim, Dehydroxylation of Ca and Mgexchanged montmorillonite, Am. Mineral. 74 (1989) 565–572. [25] K.K. Aligizaki, Pore Structure of Cement-Based Materials: Testing, Interpretation and Requirements, Taylor and Francis, New York, 2006. [26] A. Guettala, A. Abibsi, H. Houari, Durability study of stabilized earth concrete under both laboratory and climatic conditions exposure, Constr. Build. Mater. 20 (2006) 119–127. [27] Jana Hrachová, Peter Komadel, Vladimír Štefan Fajnor, The effect of mechanical treatment on the structure of montmorillonite, Mater. Lett. 61 (2007) 3361– 3365.
309
[28] Farmer V C (ed.). The infrared spectra of minerals, London: Mineralogical Society, 1974, Ch, 15. [29] Taylor H.F.W. Cement Chemistry, in: A.S.o.C. Engineers (Ed), Second Edition. Thomas Telford. England; 1997, 113–4. [30] H.A. Patel, R.S. Somani, H.C. Bajai, R.V. Jasra, Preparation and characterization of phosphonium montmorillonite with enhanced thermal stability, Appl. Clay Sci. 35 (2007) 194–200. [31] W. Xie, R. Xie, W.P. Pan, D. Hunter, B. Koene, L.S. Tan, R. Vaia, Thermal stability of quaternary phosphonium modified montmorillonites, Chem. Mater. 14 (2002) 4837–4845. [32] C.B. Hedley, G. Yuan, B.K.G. Theng, Thermal analysis of montmorillonites modified with quaternary phosphonium and ammonium surfactants, Appl. Clay Sci. 35 (2007) 180–188. [33] L.Y. Yang, Z.J. Zhang, J.G. Dai, Effects of nano-TiO2 on strength, shrinkage and microstructure of alkali activated slag pastes, Cem. Concr. Compos. 57 (2015) 1–7. [34] M. Ben Haha, G. Le Saout, F. Winnefeld, B. Lothenbach, Influence of activator type on hydration kinetics, hydrate assemblage and microstructural development of alkali activated blast-furnace slags, Cem. Concr. Res. 41 (2011) 301–310. [35] Simone Semenzato, Alessandra Lorenzetti, Michele Modesti, Elisabetta Ugel, et al., A novel phosphorus polyurethane FOAM/montmorillonite nanocomposite: preparation, characterization and thermal behaviour, Appl. Clay Sci. 44 (2009) 35–42.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Development of building material utilizing a low pozzolanic activity mineral Changming Li, Lijiu Wang, Tingting Zhang ⇑, Jingliang Dong School of Civil Engineering, Dalian University of Technology, Dalian 116024, PR China
h i g h l i g h t s The potential use of a low pozzolanic activity mineral in producing building materials was reported. The mechanical properties and hydration progress of alkali activated Pisha mortar were studied. A maximum compressive strength of 14.4 MPa of mortar was achieved with water glass. The main reaction products are amorphous aluminosilicate gel (C–A–S–H) and CaCO3.
a r t i c l e
i n f o
Article history: Received 4 January 2016 Received in revised form 18 May 2016 Accepted 26 May 2016
Keywords: Low pozzolanic activity Alkali activated mortar Activator type Hydration progress Mechanical properties
a b s t r a c t In this work, the effects of different activators, particle size and curing conditions on the mechanical properties and hydration progress of alkali activated Pisha mortars were studied. Four different activators (NaOH, Na2CO3, Na2SO4 and water glass) based on two different fineness Pisha were used, two kinds of curing temperature, 25 and 80 °C were considerate. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG) and scanning electron microscopy (SEM) were conducted to analyze the reaction products, indentify the phase composition and observe the micromorphology, respectively. It was found that the modulus of water glass and fineness of Pisha have significant influence on the compressive strength and hydration process of alkali activated Pisha mortars. The optimum activators were water glass, the sample (Ms = 1.5, curing at 80 °C) exhibited the highest compressive strength (14.4 MPa) at 28 days. The results of the investigation also show that the amorphous aluminosilicate gels were the main hydration products. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction Compared to Portland cement, alkali activated materials could offer the same mechanical properties, but with lower CO2 product [1–3]. The mechanical properties and economic benefit of the utilization of alkali activated materials in engineering have been well studied [4–6]. The type of activator played an important role for alkali activated material, the optimum dosage differs according to the type of aluminasilicate used and the type of activation solution [7,8]. Pisha (PS) was a special kind of pozzolanic mineral with a low activity [9], it was mainly composed of clay minerals (montmorillonite, illite and mica et.al), sand (quartz) and other minerals (feldspar, calcium, et al.) [10]. PS has a bad bonded mechanism and an ⇑ Corresponding author at: School of Civil Engineering, Dalian University of Technology, The First Comprehensive Experimental Building No. 217, Ling gong Road No. 2, Gaoxinyuan District, Dalian City, Liaoning Province 116024, PR China. E-mail address: [email protected] (T. Zhang). http://dx.doi.org/10.1016/j.conbuildmat.2016.05.161 0950-0618/Ó 2016 Elsevier Ltd. All rights reserved.
unsatisfactory petrographic structure, its cementitious material, free oxide (e.g., iron oxide), is easy to dissolve in water, moreover, the structure also would be destroyed due to the expansion of soggy montmorillonite, therefore, PS is hard when it is dry, but would collapse when is immersed in water. Due to the fractured landscape and the deteriorated ecological environment, soil erosion occurs frequently during and after rainstorm, there are 20,000 tons PS per square kilometer were carried into the local river every year [11], and the PS was considerate as one of the main sources of sediment into the local river. However, there is rarely researchers pay their attention to study the exploitation of PS. In fact, PS could be reused to produce alternative binding materials for dam building and other civil engineering [9]. Therefore, it would be a beneficial exploration to apply PS in the construction industry (e.g., dam building materials or building brick) as a pozzolanic material for the production of alkali activated materials. The aim of this paper is to produce a new alkali activated building materials by using PS, and study the effect of alkaline type and
301
C. Li et al. / Construction and Building Materials 121 (2016) 300–309
the fineness of PS at different curing conditions on the geopolymerisation of PS. It is hoped that the processing of alkali activated Pisha martors (APSM) could be well understood and found the optimal scheme of manufacture APSM by using PS. 2. Materials and methods 2.1. Materials The PS was obtained from Loess Plateau in Inner Mongolia, China. The PS was air-dried and pulverized to give a granular material with particles less than 1.0 mm in diameter, and part of the PS (clay mineral, sand and all the other phases) was dry milled using a porcelain ball mill with alumina milling media for 30 min to increase the specific surface area. The particle size distributions of PS and milled PS shown in Fig. 1 were determined using laser diffraction (Mastersizer 2000, Malvern Instruments). For PS and milled PS, Fig. 1 indicates a mean particle size of approximately 111 and 18.9 lm, respectively. The d90 (90% of volume less than this size) of PS and milled PS was found to be 309.6 and 52.6 lm, and the value of d10 was fund to be 8.52 and 2.68 lm, respectively. The chemical composition of PS showed in Table 1 was determined by X-ray fluorescence (XRF) spectrometry (Germen, Siemens-Bruker, SRS 3400). The activator solution was prepared by dissolving NaOH, NaCO3 and Na2SO4 pellets (99% purity quotient, Tianjin Kemiou Chemical Reagent Co., Ltd. China) in distilled water to a certain concentration, and cooled to room temperature. Water glass with Ms (molar ratio SiO2/Na2O) = 3.0 (Na2O = 8.83 wt%, SiO2 = 26.5 wt%, H2O = 64.67 wt%) was used as alkaline activator, and the others were a mixture of this commercial sodium silicate with NaOH solution to give a combined modulus of Ms = 2.0 (Na2O = 13.25 wt% SiO2 = 26.5 wt%, H2O = 60.25 wt%) and Ms = 1.5 (Na2O = 17.67 wt% SiO2 = 26.5 wt%, H2O = 55.83 wt%), respectively. The pH value of the activator solution was measured using a pH meter (METER TOLEDO, Delta 320, LAB, Switzerland) after the activator solution was prepared. 2.2. Sample preparation
Table 1 Chemical composition of PS determined by X-ray fluorescence. Chemical
Component (wt%)
SiO2 Al2O3 CaO Na2O K2O MgO Fe2O3 SO3 LOI
62.46 20.08 5.10 0.56 2.23 5.02 3.10 0.04 1.41
LOI is loss on ignition at 1000 °C. Att values in wt%.
Table 2 Mix proportion of mixture (wt%). Sample
PS
Activator solution Activators
W1-1 W1-2 W1-3
84
Water glass (Ms = 1.5)
3
Water
pH
13
11.5
W1-4 W2-1 W2-2 W2-3
2.3. Methods The compressive strength was tested by using an electronic universal testing machine with a 100 kN capacity and a constant displacement rate of 0.05 mm/ min. The composition of raw materials and mortars were tested by X-ray diffraction (XRD), XRD was recorded on a Siemens-Bruker D5000 using Cu Ka radiation (k = 1.54 Å) operating at 40 kV and 30 mA. The samples were scanned from 5 to 70° (2h range) at a rate of 2°/min and step size of 0.02°. Fourier transform infrared (FTIR) analysis was performed using the KBr pellet method (1 mg sample per 100 mg KBr) on a Bruker EQUINOX 55 spectrometer, with 32 scans per sample collected from 4000 to 400 cm 1 at 4 cm 1 resolution. A Switzerland Mettler-Toledo simultaneous thermal analyser was used to measure some physical properties of the material as a function of the temperature change. The samples were heated
W3-1 W3-2 W3-3
84
Water glass (Ms = 2.0)
3
13
10.7
84
Water glass (Ms = 3.0)
3
13
9.0
86
Na2CO3
1
13
8.8
80 25 80
80 25 80
80 25 80 25
86
Na2SO4
1
13
7.4
NS4 NH1 NH2 NH3
PS PS Milled PS Milled PS PS PS Milled PS Milled PS PS PS Milled PS Milled PS PS PS Milled PS Milled PS PS PS Milled PS Milled PS PS PS Milled PS Milled PS
25
NC4 NS1 NS2 NS3
80 25 80
25
W3-4 NC1 NC2 NC3
PS type
25
W2-4
The materials used to prepare the mortars were summarized in Table 2. For all samples, the total mass of the mixture was kept at 392.5 g. Add the PS powder into activator solution (e.g., NaOH, NaCO3, Na2SO4, water glass), in order to achieve complete mixing between the solid and solution, the mixture was mixed for 15 min by a magnetic stir bar. To make regularly shaped specimens for mechanical testing, the mixtures were poured into cylindrical steel molds, and mixture was pressed (30 kN) to specimens with an diameter of 5 cm and height of 10 cm (i.e., an aspect ratio of 2.0) bar on a hydraulic testing machine. To ensure repeatability, 3 specimens were prepared for each type of mortar. To investigate the effect of curing temperature on strength of APSM, the specimens were sealed with plastic bags and cured in oven (80 °C) and laboratory at ambient temperature (25 ± 2 °C), respectively.
Curing temperature °C
80 25 80 25
86
NaOH
1
NH4
Fig. 1. Particle size distribution curve of raw materials. (a) PS, (b) milled PS.
13
10.9
80 25 80 25
302
C. Li et al. / Construction and Building Materials 121 (2016) 300–309
from 40 to 1000 °C in an atmosphere of nitrogen with a heating rate of 10 °Cmin 1. The microstructure and chemical elemental of mortar was examined using a JEOL JSM 6460 scanning electron microscope (SEM) with an EDAX energy dispersive Xray spectroscope device equipped.
3. Results and discussion 3.1. Mechanical properties 3.1.1. Activator type The activator is a very important factor in the reaction process of alkali activated materials, the properties of alkali activated materials based on different activator are very different [12]. The effects of different types of activator on compressive strength of APSM (curing at 80 °C) is shown in Fig. 2. For the samples which were synthesized by PS and activators solution, it can be seen that the strength of APSM based on different types of activator solution showed the following rank: W1 > NH > NS > W2 > NC > W3. The samples activated by W1 show highest compressive strength (6.26 MPa), and the compressive strength of the samples activated by W2, W3, NC, NS and NH is lower (2.59 3.99 MPa). For the samples which were synthesized by milled PS and activator solution, the resulting strength of samples activated by W1, NH and NC exhibit a higher strength (12.68 14.4 MPa), and the strength of the samples based on W2, W3 and NS was lower (7.52 11.28 MPa), and the strength of the corresponding mortars had the following order: W1 > NH > NS > W2 > W3 > NC. As shown in Fig. 2, the NaOH, Na2SO4 and W1 are the optimum activators required to improve compressive strength of APSM. 3.1.2. Modulus of water glass solution Fig. 3 shows the compressive strengths of APSM prepared using water glass with different SiO2/Na2O molar ratios (Ms = 1.5, 2.0, 3.0), for PS and milled PS samples for cured at 25 and 80 °C, respectively. It was shown that the compressive strength increases as the value of Ms decreased, for the water glass used in this work, the Na2O content would increase as the decreasing modulus when the amount of water glass is kept constant, that means that the lower the values of Ms, the higher the Na2O content, and the higher the alkalinity (pH) of activator solution. During the reaction process, high alkalinity could lead to a higher efficiency in dissolve the amorphous, reactive silicate and alumina, the source material would dissolution faster and more extensive when the PS was activated with a more caustic alkalinity activator solution, so that a higher extent and degree of reaction between the PS and activator takes place, leading to more geopolymer gels produced. Therefore, the final geopolymer gel would be more stiffness and the compressive strength of APSM would be improved with a higher alkalinity activator solution [13,14]. In contrast, a higher values of Ms with a lower Na2O content, and a lower alkalinity results in a lower compressive strength.
3.1.3. Fineness of PS The effect of PS fineness on compressive strength is summarized in Fig. 4. The compressive strength of the mortar increased as the decreasing PS particle size. For the samples produced by PS and activators solution, the compressive strength is about 1.8 6.2 MPa (curing at 25 °C), 2.6 6.3 MPa (curing at 80 °C), and for milled PS samples, it is about 6.75 13.5 MPa (curing at 25 °C), 7.5 14.4 MPa (curing at 80 °C). It shows that increasing the Blaine surface area of PS leads to a significant development in compressive strength. For the samples (milled PS) based on W and NC, the compressive strength would be increased to 212% 511% when compared with the samples produced by PS, and for the samples based on NS and NH samples it would be increased to 326% 557%. It reveals that a smaller particle size would give a larger surface area and reaction area. Larger reaction area would improve the reactivity of source materials and lead a higher reaction efficiency between the solid particles and solution [15,16]. As a result, the milled PS with a larger surface area showed better performance in compressive strength. Moreover, a smaller particles size would increased the density of mortar [17,18], thus, the samples produced by milled PS performance more homogeneous and denser. In contrast, the coarse particles with a smaller specific surface area would have a lower reactivity, Fig. 5 shows the feature of the PS and milled PS samples based on different activators. It clearly that the milled PS samples have a higher reaction degree than the PS samples. For PS samples, the reaction of PS and alkali activator is low and insufficient, the excessive activator leaching out and covered the surface of the sample. Moreover, the excessive alkali would make a negative effect on the mechanical strength [19], due to the excessive free OH were remain in the samples, weakening the structure of mortar [20–22].
3.1.4. Curing temperature The effect of curing temperature on compressive strength is demonstrated in Fig. 6. It can be seen that the compressive strength increased as the increasing curing temperature. For the APSM samples, increasing temperature up to 80 °C yield a increase in compressive strength. This could be explained that the high curing temperature could accelerate the reaction process and enhance the reaction efficiency. For the PS samples curing at 80 °C, the compressive strength would be increased to 115% 165% when compared with the samples curing at 25 °C (except W1), and for the milled PS samples, the compressive strength of the samples curing at 80 °C would be increased to 110% 129% when compared with the samples curing at 25 °C (except W3 and NH). For PS samples activated by W1 and the milled PS samples based on W3 and NH, the increasing curing temperature has no remarkable effect on compressive strength.
Fig. 2. Effect of types of activator on compressive strength of APSM curing at 80 °C. (a) PS samples, (b) milled PS samples.
C. Li et al. / Construction and Building Materials 121 (2016) 300–309
Fig. 3. Effect of Ms of water glass on compressive strength of APSM. (a) PS samples, (b) milled PS samples.
Fig. 4. Effect of fineness of PS on compressive strength of APSM. (a) curing at 25 °C, (b) milled PS samples at 80 °C.
Fig. 5. The feature of APSM samples based on different activators.
Fig. 6. Effect of curing temperature on compressive strength of APSM. (a) PS samples, (b) milled PS samples.
303
304
C. Li et al. / Construction and Building Materials 121 (2016) 300–309
3.2. XRD analysis Fig. 7 shows XRD patterns of the PS and APSM samples. PS sample shows broad humps between 5–7° 2h and 8.5–9° 2h, indicating that the montmorillonite (Ca0.2(Al,Mg)2Si4O10(OH)24H2O, PDF# 01-013-0135) [23] are found, the quartz (SiO2, PDF# 01-0650466) was observed at approximately around 26.6° 2h and the sharp peaks around 27.9° and 28° 2h were attribute to albite (NaAlSi3O8, PDF# 01-009-0466), the peak around 29° 2h was calcite (CaCO3, PDF# 01-047-1743). From the result of Fig. 7, it can be seen that the difference in the XRD spectra of PS and APSM are hardly perceptible. For the APSM samples, the intensity of the peak around 5.9° 2h are very weak, and the distinct peak at 7.1° 2h is observed. Thus, it is clear from the XRD that the peak of sample (2h = 6°) is shifted towards the higher angle region after activated by activator (e.g., water glass, NH, NC, NS), reaching the value 2h = 6.3°, at the same time a new phase begins to develop at 2h = 7.1°. This shift and the presence of new peak was mainly attributed the dehydration of montmorillonite [24]. Moreover, the reaction of the activator activated PS seems to result in the formation of geopolymer gels (C-S-H gel, Ca1.5Si3.5nH2O, PDF# 01033-0306) [25,26]. This point will be revisited in Sections 3.3 and 3.4 in the context of the discussion of FTIR and TG/DTG. The quartz (SiO2, PDF# 01-065-0466), albite (NaAlSi3O8, PDF# 01-009-0466) detected in APSM samples resulting from the unreactive nature of these phase supplied by the PS.
3.3. Fourier transform infrared FTIR analyses for PS and APSM samples are shown in Fig. 8a–d. For PS samples, it shows the main adsorption bands as follows: 468, 522, 584, 645, 713, 778, 875, 1035, 1421, 1635, 3421 and 3620 cm 1. The bands due to free (or weakly hydrogen-bonded water molecules to the surface oxygen of tetrahedral sheet) water molecules, water-water hydrogen bond (Mn+–O–H–O–H–) and water bending modes are observed near 3622, 3421 and 1635 cm 1, respectively [27,28]. The peaks at 1421, 875 and 713 cm 1 are attributed to anti-symmetric stretching and out-ofplane bending modes of CO23 ions [29]. The strong band at 1035, 522 and 468 cm 1 are assigned to Si–O–Si bending vibration bond, whereas the Si–O asymmetric stretching vibration bond can be seen at 1035 cm 1, and these stretching modes are related to quartz (SiO2). The peaks at 778, 645 and 584 cm 1 are attributed to Al–Al–OH, Al–Mg–OH bending vibration [30–32]. For APSM
samples activated by NaOH, it can be seen that the bands at 1635 and 3421 cm 1 were disappeared and the mode at 3622 cm 1 became sharper and had an increase in the intensity. The disappeared of the bands at 1635 and 3421 cm 1 indicated that the free water molecules (or weakly hydrogen-bonded water molecules to the surface oxygen of tetrahedral sheet) decreased or disappeared. And the increased in the intensity of the mode at 3622 cm 1 due to the formation of structure water which was trapped in the geopolymeric products (geopolymer gel). A weak new mode at 2517 cm 1 corresponding to the stretching vibration of O–C–O bonds in the carbonate group (CO23 ) was also observed, the intensity of the bands at 1448, 875 and 713 cm 1 which were assigned to carbonate C–O stretching vibrations increased. These indicated that carbonates were present in the samples due to reaction of older geopolymer gel (C–S–H gel) and CO2 with formation of calcium carbonate (CaCO3) [33]. Fig. 8b–d show the infrared spectra of APSM based Na2CO3, Na2SO4 and water glass, respectively. It can be seen that the infrared spectra of APSM based on different activator are very similar, and there were no significant difference in all bands. It was found that the asymmetric stretching vibration of O–C–O bonds of CO23 groups shifted (1421 cm 1 to 1440 1, 1446 cm 1), and there was a increase in the intensity in the vibration when compared with PS samples. This indicates chemical changes in the reaction products formed by alkaline activation of the PS, in particular the decalcification of the C–S–H gel to form calcium carbonates. The mode at 875 cm 1 became sharper and had an increase in the intensity is associated with the formation of calcite.
3.4. Thermogravimetry analysis Fig. 9 shows the TG and DTG curves for PS and APSM samples with different type activators. The total mass loss in these samples, in the temperature range of 40–1000 °C, varied from 6.80% to 8.84%. The TG/DTG curves of PS samples are presented in Fig. 9a. On the TG curve for PS, the two steps of weight loss, together with corresponding endothermic DTG peaks, are observed. The relatively weight loss at 40–200 °C was due to the loss of free water and loosely bound water, and the weight loss in the region of 500–800 °C are the decarbonation of the calcite into CaO [29,34]. The DTG curves of PS shows a well-defined strong symmetric double peak near 96 and 163 °C, characteristic for montmorillonites [27,35]. It reflects the release if water adsorbed on the particle surfaces and of water molecules coordinating Ca2+ or Na+ cations,
Fig. 7. X-ray diffraction patterns of 28 days cured specimens. Q-quartz (SiO2, PDF# 01-065-0466), Mo-montmorillonite (Ca0.2(Al,Mg)2Si4O10(OH)24H2O, PDF# 01-013-0135), A-albite (NaAlSi3O8, PDF# 01-009-0466), C-calcite (CaCO3, PDF# 01-047-1743), Cs–C–S–H gel (Ca1.5Si3.5nH2O, PDF# 01-033-0306).
C. Li et al. / Construction and Building Materials 121 (2016) 300–309
305
Fig. 8. Fourier transform infrared spectra of APSM based on different activator types.
respectively. The distinct and symmetrical peak at 538 °C is associated with dehydroxylation of montmorillonites. A sharp and strong peak at 756 °C is observed, and it relative to the decarbonation of the CaCO3 into CaO. Fig. 9b-f, and g show the TG/DTG curves of NH, NS, NC, W1, W2 and W3 samples, respectively. The TG curves are similar for all samples, there are two distinct steps of weight loss at 90–200 °C and 700–800 °C for all the samples were detected. The DTG curve exhibits an endothermic peak at 90– 200 °C for all samples. A mass loss of 1.65%, 1.27%, 1.12%, 1.70%, 1.25% and 1.24% was observed in this temperature range for the NH, NS, NC, W1, W2 and W3 samples, respectively. The mass loss peak between 90 and 200 °C was characteristic of the presence of geopolymer gel (C–S–H gel), and the weight loss refers to the loss of structural water that is present in the form of –OH sites in geopolymer gel [34]. There was a major weight loss peak related to the decarbonation of the CaCO3 at the temperature range 500– 800 °C, and the mass loss in the temperature range 500–800 °C was 5.19%, 5.06%, 4.72%, 4.76%, 4.77% and 4.63% for the NH, NS, NC, W1, W2 and W3 samples, respectively. The DTG data showed the weight loss speed of APSM samples. It can be seen that the peak at temperature about 96 °C (PS) became sharper and stronger and had shifted to high temperature, it means the samples of APSM had a quicker weight loss speed than the PS samples. The peak at temperature around 756 °C (PS) showed a same trend, the peak of APSM became sharper and stronger when compared with PS sample, and the weight loss speed of APSM was connected to the amount of CaCO3, it seems that the amount of CaCO3 of APSM is more than the PS sample, and it indicated that the increased CaCO3 was formed by the carbonation of C–S–H gel [29].
3.5. Microstructural analysis The microstructure and hydration products of APSM samples based on different activators were studied by using the scanning electron microscopy analyser. The EDS micrograph of APSM was examined to analyses the morphology of reaction products, and the elemental concentration is list in Table 3, each given value represents the average of ten readings taken adjacent to each other. The analysis of the morphology of APSM samples revealed that, in general, the reaction products of APSM samples mainly were amorphous aluminosilicate phases, geopolymer gels and calcium carbonate after their contact with activators. Fig. 10 compares the microstructure of the samples of produced by PS and four activators. Fig. 10a–c showed the micromorphology and hydration products of PS samples activated by water glass, NaOH and Na2SO4, respectively. As shown in Fig. 10a–c, the degree of hydration between PS and activators is low and showed a loosely structure, the flocculation-like geopolymer gels coexist with unreacted matrix, the unreacted feldspar block was wrapped by geopolymer gels. The micro-morphology of the PS sample activated by Na2CO3 was shown in Fig. 10d, it display a porous structure formation and the layered monotmorillonite and geopolymer gels were observed. The results of chemical analysis of PS samples which listed in Table 3 showed that the ratio of Ca/Si fluctuated between 0.32 and 0.62 (except Fig. 10d), this indicated that the main composition of geopolymer gels was C–(A)–S–H [34,35]. Fig. 11 showed the micromorphology and hydration products of milled PS samples. It shows that the SEM of samples showed a great amount of dense and
306
C. Li et al. / Construction and Building Materials 121 (2016) 300–309
Fig. 9. DTG and TG of APSM samples. (a) PS, (b) specimens based on NaOH, (c) specimens based on Na2SO4, (d) specimens based on Na2CO3, (e) specimens based on water glass (Ms = 1.5), (f) specimens based on water glass (Ms = 2.0), (g) specimens based on water glass (Ms = 3.0).
4. Conclusions
inexpensive and ecologically alkali activated materials which aiming to apply in the construction industry (e.g., dam building materials or building brick). And the effects of activator type, curing temperature and particle size on mechanical properties and phase composition of APSM were also investigated. Based on the experimental results, the following conclusions can be summarized:
This work studied the possibility of using a low pozzolanic activity mineral as the binder material to produce a new
1. It is possible to produced a new alkali activated materials reusing PS as a binder material. The significant factors affecting the
homogeneity geopolymer gels (Fig. 10a, b and d) and block-like crystal products (Fig. 10c). The ratio of Ca/Si fluctuated between 0.46 and 1.05 (except Fig. 11c), the EDS results of Fig. 11 showed that the dense geopolymer gels and block-like crystal products were C-(A)-S-H and calcite carbon, respectively [34,35].
307
C. Li et al. / Construction and Building Materials 121 (2016) 300–309 Table 3 Composition of APSM by SEM-EDS. Points
Fig. 10
Fig. 11
Elemental composition (at.%)
1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8
Ca/Si
C
O
Ca
Si
Al
Na
Mg
Others
31.91 33.54 26.00 30.45 24.41 26.47 22.94 38.34 34.01 31.82 36.91 38.07 25.99 21.66 22.85 22.56
51.38 50.22 48.06 49.47 49.67 53.66 55.66 43.20 48.57 47.18 51.94 49.72 53.41 53.90 57.98 57.09
2.88 3.29 3.88 3.21 5.82 4.66 0.42 3.52 4.62 6.83 4.60 3.88 2.09 20.37 3.53 4.00
6.65 6.71 12.14 9.41 10.53 7.52 11.67 9.28 6.47 7.83 4.38 5.01 7.97 1.92 7.61 8.54
2.78 2.74 4.41 3.28 4.01 3.09 4.46 3.48 2.53 2.63 1.19 1.99 2.99 0.82 3.13 3.56
2.54 2.18 1.87 1.31 2.95 2.85 3.24 0.41 2.14 1.02 0.29 0.28 1.32 0.77 1.39 1.28
1.30 1.05 1.74 1.06 1.70 1.45 1.49 1.52 1.23 0.93 0.61 0.86 2.53 0.44 2.29 1.60
0.56 0.27 1.90 1.81 0.91 0.30 0.12 0.25 0.43 1.76 0.08 0.19 3.70 0.12 1.22 1.37
0.43 0.49 0.32 0.34 0.55 0.62 0.04 0.38 0.71 0.87 1.05 0.77 0.26 10.61 0.46 0.47
Fig. 10. SEM micrographs of samples based on PS. (a) specimens based on NaOH, (b) specimens based on Na2CO3, (c) specimens based on Na2SO4, (d) specimens based on water glass (Ms = 1.5).
compressive strength of APSM are activator type and PS fineness. The strength of hardened APSM based on water glass (Ms = 1.5) reached the highest compressive strength (14.4 MPa), the effect of activator on strength of APSM showed the following rank: water glass (Ms = 1.5) > NaOH > Na2SO4 > Na2CO3. The Ms of water glass has notable influence on the strength of APSM, the optimum water glass modulus (SiO2/Na2O ratio) is 1.5. Increasing the Blaine surface area of PS (reducing the particle size) greatly increase the mechanical strength of APSM. The fineness of PS had a significant effect on the mechanical strength. With all the other parameters remain constant, the compressive strength of the samples
produced by milled PS based on different activator solution will be increased to 212% 557% compared to which synthesized by PS and activator solution. The effect of the curing conditions on strength is not remarkable, an increase in the curing temperature (from 25 to 80 °C) can improve the 28-day strength of APSM by up to 1% 65% (based on PS) and 4% 29% (based on milled PS), respectively. 2. XRD patterns show change in amorphous phases, the structure of montmorillonite changed due to its interlayer water molecules was slowly expelled after alkali activated. The XRD and FTIR results also indicated that the reaction products of APSM mainly show an alkali aluminosilicate gels.
308
C. Li et al. / Construction and Building Materials 121 (2016) 300–309
Fig. 11. SEM micrographs of samples based on milled PS. (a) specimens based on NaOH, (b) specimens based on Na2CO3, (c) specimens based on Na2SO4, (d) specimens based on water glass (Ms = 1.5).
3. TG/DTG results indicated that there were two steps of weight loss, together with corresponding endothermic DTG peaks, responds to aluminosilicate gels and CaCO3 were observed, respectively. The results of TG also showed that there was a positive correlativity between the amount of reaction products (weight loss) and compressive strength. Aluminosilicate gels are the main contributor of mechanical strength, the mechanical strength increased with the increasing amount of reaction products (aluminosilicate gels and CaCO3). 4. SEM results indicate that the reaction products of the samples based on PS were mainly shown a homogeneity geopolymer gels and some unreacted block matrix, the dense and homogeneity amorphous aluminosilicate gels and block-like crystal products were the main reaction products of the samples based on milled PS. The EDS results show that the geopolymer gels and crystals were mainly ascribed to amorphous hydrated calcium aluminosilicate (C–A–S–H) gel and CaCO3, respectively.
Acknowledgments The authors would like to express gratitude for the financial support by the National Key Science & Technology Pillar Program of China (No. 2013BAC05B03), the National Natural Science Foundation of China (Grant No. 51408096), the Fundamental Research Funds for the Central Universities (DUT15RC(4)22), and Liaoning BaiQianWan Talents Program (2015.20). References [1] John.L. Provis, Susan.A. Bernal, Geopolymers and related alkali-activated materials, Annu. Rev. Mater. Res. 44 (2014) 299–327.
[2] N. Amin, Use of clay as a cement replacement in mortar and its chemical activation to reduce the cost and emission of greenhouse gases, Constr. Build. Mater. 34 (2012) 381–384. [3] G. Habert, J.B. d’Espinose de Lacaillerie, N. Roussel, An environmental evaluationof geopolymer based concrete production: reviewing current research trends, J. Clean Prod. 19 (2011) 1229–1238. [4] A. Chakchouk, B. Samet, T. Mnif, Study on the potential use of Tunisian clay as pozzolanic material, Appl. Clay Sci. 33 (2006) 79–88. [5] B. Sabir, S. Wild, J. Baj, Metakaolin and calcined clays as pozzolans for concrete: a review, Cem. Concr. Compos. 23 (2001) 441–454. [6] F. Curcio, B. DeAngelis, S. Pagliolico, Metakaolin as a pozzolanic microfiller for high performance mortars, Cem. Concr. Res. 28 (6) (1998) 803–811. [7] Dali Bondar, C.J. Lynsdale, Neil B. Milestone, N. Hassani, A.A. Ramezanianpour, Effect of type, form, and dosage of activators on strength of alkali-activated natural pozzolans, Cem. Concr. Compos. 33 (2011) 251–260. [8] Behzad. Nematollahi, Jay. Sanjayan, Effect of different superplasticizers and activator combinations on workability and strength of fly ash based geopolymer, Mater. Des. 57 (2014) 667–672. [9] Changming. Li, Tingting. Zhang, Lijiu. Wang, Pozzolanic activaty of Pisha sandstone and mechanical properties of alkali-activated Pisha sandstone materials, J. Chin. Ceram. Soc. 43 (8) (2015) 1090–1098 (in Chinese with English summary). [10] C.M. Li, T.T. Zhang, L.J. Wang, Mechanical properties and microstructure of alkali activated Pisha sandstone geopolymer composites, Constr. Build. Mater. 68 (2014) 233–239. [11] X.M. Zheng, Research on management of concentrated coarse sediment source area of the Loess Plateau, Soil Water Conserv. China 12 (2005) 5–6 (in Chinese with English summary). [12] A. Fernández-Jiménez, Ã. Palomo, Composition and microstructure of alkali activated fly ash binder: effect of the activator, Cem. Concr. Res. 35 (10) (2005) 1984–1992. [13] S.D. Wang, Karen L. Scrivener, P.L. Pratt, Factors affecting the strength of alkaliactivated slag, Cem. Concr. Res. 24 (6) (1994) 1033–1043. [14] D. Hardjito, S.E. Wallah, D.M.J. Sumajouw, B.V. Rangan, On the development of fly ash-based geopolymer concrete, ACI Mater. J. 101 (6) (2004) 467–472. [15] J. Davidovits, Geopolymers–inorganic polymeric new materials, J. Therm. Anal. 37 (8) (1991) 1633–1656. [16] H. Xu, J.S.J. Deventer, Effect of source materials on geopolymerization, Ind. Eng. Chem. Res. 42 (8) (2003) 1698–1706. [17] M.K. Gopalan, Nucleation and pozzolanic factors in strength development of class F fly ash concrete, ACI Mater. J. 90 (M12) (1993) 117–121.
C. Li et al. / Construction and Building Materials 121 (2016) 300–309 [18] G.C. Isaia, A.L.G. Gastaldini, R. Moraes, Physical and pozzolanic action of mineral additions on the mechanical strength of highperformance concrete, Cem. Concr. Compos. 25 (2003) 69–76. [19] J. Temuujin, A. van Riessen, Effect of fly ash preliminary calcinations on the properties of geopolymer, J. Hazard. Mater. 164 (2009) 634–639. [20] T. Bakharev, J.G. Sanjayan, Y.B. Cheng, Effect of admixtures on properties of alkali-actived slag concrete, Cem. Concr. Res. 30 (2001) 1367–1374. [21] M.Y. Hu, X.M. Zhu, F.M. Long, Alkali activated fly ash-based geopolymers with zeolite or bentonite as additives, Cem. Concr. Compos. 31 (10) (2009) 762–768. [22] K. Komnitsas, D. Zaharaki, V. Perdikatsis, Effect of synthesis parameters on the compressive strength of low-calcium ferronickel slag inorganic polymers, J. Hazard. Mater. 161 (2009) 760–768. [23] Raúl Fernández, Lorena González, Ana Isabel Ruiz, Jaime Cuevas, Nature of C– (A)–S–H phases formed in the reaction bentonite/portlandite, J. Geochem. 12 (2014) 1–8. [24] A.F. Koster van Groos, S. Guggenheim, Dehydroxylation of Ca and Mgexchanged montmorillonite, Am. Mineral. 74 (1989) 565–572. [25] K.K. Aligizaki, Pore Structure of Cement-Based Materials: Testing, Interpretation and Requirements, Taylor and Francis, New York, 2006. [26] A. Guettala, A. Abibsi, H. Houari, Durability study of stabilized earth concrete under both laboratory and climatic conditions exposure, Constr. Build. Mater. 20 (2006) 119–127. [27] Jana Hrachová, Peter Komadel, Vladimír Štefan Fajnor, The effect of mechanical treatment on the structure of montmorillonite, Mater. Lett. 61 (2007) 3361– 3365.
309
[28] Farmer V C (ed.). The infrared spectra of minerals, London: Mineralogical Society, 1974, Ch, 15. [29] Taylor H.F.W. Cement Chemistry, in: A.S.o.C. Engineers (Ed), Second Edition. Thomas Telford. England; 1997, 113–4. [30] H.A. Patel, R.S. Somani, H.C. Bajai, R.V. Jasra, Preparation and characterization of phosphonium montmorillonite with enhanced thermal stability, Appl. Clay Sci. 35 (2007) 194–200. [31] W. Xie, R. Xie, W.P. Pan, D. Hunter, B. Koene, L.S. Tan, R. Vaia, Thermal stability of quaternary phosphonium modified montmorillonites, Chem. Mater. 14 (2002) 4837–4845. [32] C.B. Hedley, G. Yuan, B.K.G. Theng, Thermal analysis of montmorillonites modified with quaternary phosphonium and ammonium surfactants, Appl. Clay Sci. 35 (2007) 180–188. [33] L.Y. Yang, Z.J. Zhang, J.G. Dai, Effects of nano-TiO2 on strength, shrinkage and microstructure of alkali activated slag pastes, Cem. Concr. Compos. 57 (2015) 1–7. [34] M. Ben Haha, G. Le Saout, F. Winnefeld, B. Lothenbach, Influence of activator type on hydration kinetics, hydrate assemblage and microstructural development of alkali activated blast-furnace slags, Cem. Concr. Res. 41 (2011) 301–310. [35] Simone Semenzato, Alessandra Lorenzetti, Michele Modesti, Elisabetta Ugel, et al., A novel phosphorus polyurethane FOAM/montmorillonite nanocomposite: preparation, characterization and thermal behaviour, Appl. Clay Sci. 44 (2009) 35–42.