Macro- and nanomaterials for improvement of mechanical and physical properties of cement kiln dust-based composite materials

Accepted Manuscript Macro- and Nanomaterials for Improvement of Mechanical and Physical Properties of Cement Kiln Dust-Based Composite Materials

Hosam M. Saleh, Fathy A. El-Saied, Taher A. Salaheldin, Aya A. Hezo PII:

S0959-6526(18)32664-7

DOI:

10.1016/j.jclepro.2018.08.303

Reference:

JCLP 14087

To appear in:

Journal of Cleaner Production

Received Date:

03 July 2018

Accepted Date:

29 August 2018

Please cite this article as: Hosam M. Saleh, Fathy A. El-Saied, Taher A. Salaheldin, Aya A. Hezo, Macro- and Nanomaterials for Improvement of Mechanical and Physical Properties of Cement Kiln Dust-Based Composite Materials, Journal of Cleaner Production (2018), doi: 10.1016/j.jclepro. 2018.08.303

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

Macro- and Nanomaterials for Improvement of Mechanical and Physical Properties of Cement Kiln Dust-Based Composite Materials Hosam M. Saleh (Corresponding author) Radioisotope Department, Nuclear Research Center, Atomic Energy Authority, Dokki 12311, Giza, Egypt Tel.: +20 1005191018 Fax: +202 37493042 E-mail: [email protected], [email protected] Fathy A. El-Saied Chemistry Department, Faculty of Science, Menoufia University, Shebin El-Kom, Egypt Tel: +20482222170; E-mail: [email protected] Taher A. Salaheldin Nanotechnology Research Center- British University in Egypt (BUE) Nanotechnology & Advanced Materials Central Lab, Agriculture Research Center E-mail: [email protected], [email protected] Aya A. Hezo Chemistry Department, Faculty of Science, Menoufia University, Shebin El-Kom, Egypt E-mail: [email protected] Abstract In parallel with the progressing technological improvements witnessed in cement industry, nuclear industry also faces the need to address the prevailing issue of handling radioactive waste. Waste management is among the major environmental concerns all around the world, which need optimization in order to preserve our planet. The objective of the present study is getting rid of the hazardous waste cement kiln dust in an advanced fashion; in parallel, this material is upgraded by blending it with proper additives to produce a modified paste suitable for stabilization of radioactive waste in the future. This study presents an in-depth investigation covering incorporation of different additive materials individually or as mix of two constituents with cement kiln dust as the matrix material. Mechanical properties like compressive strength and porosity of the hardened cement kiln dust and modified composites were assessed. Moreover, the physical appearance of the produced blocks including Portland cement or some by-products such as slag and silica fume, as well as nano-materials (nano-sized alumina, silica, titanium dioxide, calcium oxide, zinc oxide) was evaluated. We demonstrate that adding merely 0.1 % of nanomaterials to 20% slag increases the mechanical integrity of the solidified cement kiln dust samples fourfold (more than 12 MPa). Based on the experimental results, a new composite of cement kiln dust and nano-silica are proficient materials with significant ecological and economical advantages for constructions applications, and should be suitable for safe stabilization of radioactive waste in forthcoming studies. Key words: cement kiln dust, nanomaterials, by-products, waste management, hazardous wastes 1

ACCEPTED MANUSCRIPT

1. Introduction Proper disposal of waste from various industries is a serious problem in many countries. The production of industrial waste and non-recyclable byproducts is increasing due to increasing global industrialization and the need for larger quantities of raw materials and fuels to cope with the rapidly growing world population (Taha, et al. 2007). Hence, the elimination of hazardous byproducts generated by various industrial sectors causes current concerns regarding the problem of energy supply and environmental pollution. Cement factories as one of these sectors generate air polluted by solid waste during their operation (Heikal et al. 2002). In this context, high consumption of energy and large amounts of carbon dioxide released by these processes are major problematic issues to be addressed, therefore, it is mandatory to minimize byproducts of the cement production, or to handle them in a sustainable manner (Aly et al. 2012). In this regard, a major current goal is producing durable cementitious materials, which, on the one hand, contain less cement, and, on the other hand, are technologically improved by blending with ecologically benign additives. One of the environmental problems related to the production of cement is the huge emission of bypass dusts of approximately 30 million annual tons worldwide, which has to be remediated and disposed (Konsta-Gdoutos and Shah 2003). Bypass dust (cement kiln dust) is a fine-grained particulate material composed mainly of oxidized, anhydrous and micrometric particles. This byproduct could be considered as hazardous waste according to its harmful effects as reported in previous literatures (Sultan 2004; Abou Taleb et al. 1995; Short and Petsonk 1996; Rafnsson et al. 1997). The most common beneficial uses of bypass dust are waste treatment, soil stabilization, or asphalt pavement. Although bypass dust can also be reused in a number of different ways, the most advanced strategy of its application is to use it instead of cement in some industrial applications; e.g., it could be used in safely treating hazardous sideproducts of nuclear power industry by stabilizing/consolidating radioactive waste (Siddique 2006). In addition to cement, nuclear science is a technology well established in many areas of the world, but still emerging, which makes it still attractive for research activities. Particularly nuclear waste streams are among the most important global environmental problems; in order to protect the environment and human health, smart treatment techniques and safe disposal of radioactive waste is urgently needed. Radioactive waste generated in nuclear power plants needs to be properly stabilized and isolated by a suitable containment systems (Bayoumi et al. 2012; 2

ACCEPTED MANUSCRIPT

Saleh and Eskander 2012a). It is well known that stabilization of radioactive waste is an important request to keep the environment safe and to minimize the risks of such waste during handling, transportation and disposal stages (Saleh et al. 2011). The principal mechanisms involved in stabilization of nuclear waste by cement minerals, cement, or mortar are exhaustively described in literature (Eskander et al., 2013; Eskander and Saleh, 2012). Utilization and improving of new more efficient and/or more economic materials for this purpose is unavoidable and imperatively required to overcome the drawbacks of traditional materials, such as energy consumption. In addition, in recent years, nanotechnology and particularly the use of nano-sized particles (“nanoparticles”) have attracted attention for many types of applications, such as manufacturing materials with new, advanced features. In order to improve cementitious materials, ultrafine particles of different characteristics rather than conventional materials were already incorporated in cement, mortar or concrete to obtain cement composites of fine-tuned characteristics (Li et al. 2004). The use of cement kiln dust as a stabilizing agent for hazardous wastes, where its porosity and absorption capacity can reduce compressive strength and chemical stability, and the improvement by other constituents such as nanoparticles to form durable solid waste will be of great interest to keep the solidified waste stable during long-term disposal (Siddique 2006). The present article aims firstly at improving cement kiln dust generated through the widely spread industry of cement production with proper additives such as cement, other bypass materials and nano-materials to produce more efficient materials, which, in future, might be suitable for safe incorporation of radioactive waste either in a solid or liquid state. Secondly, evaluation of the strength and porosity of the bypass dust composites including different additives is performed in order to determine the optimum mixture of additives and the optimum conditions required to achieve benchmark values for integrity, which make the composites suitable for different construction applications that need to be investigated in follow-up studies. 2. Materials and methods 2.1. Materials Aside from cement kiln dust, different additives such as waste materials including blast furnace slag and Portland cement or nano-materials including silica fume were selected for the production of more efficient materials appropriate for solidification purposes. Bypass dust is a

3

ACCEPTED MANUSCRIPT

fine powdery material similar to Portland cement in appearance, but different in color. Cement kiln dust used in this study was supplied by Tourah Portland Cement Co., Egypt. Portland cement is a local cement manufactured according to the Egyptian Standard Specifications ES 4756-1/2005 and EN 197-1/2004 (Egyptian Standard Specifications 2005). The chemical composition of these two cementitious materials are presented in Table 1. Table 1 Properties and chemical compositions of cement kiln dust and Portland cement Compound, % (wt./wt.) Cement kiln dust Portland cement SiO2 11.41 19.84 Al2O3 3.45 4.74 Fe2O3 2.25 4.0 CaO 55.24 61.01 MgO 1.12 2.5 K2O 4.21 0.6 SO3 6.25 2.4 Na2O n.d. 0.5 Cl 4.21 n.d Others 11.86 4.41 Loss on ignition (LOI) 32.5 3.96 3 Specific gravity (g/cm ) 2.7 3.2 n.d.: not determined Phytoremediation is a promising technology used for remediation of wastewater contaminated with metals or radionuclides. In the present study, different species of local terrestrial plants thriving in Egyptian environment were collected and processed in a blinder after drying, hence, they were used as a type of “phytoremediated solid waste” to be stabilized with the cement kiln dust. This “phytoremediated solid waste” acted as substitute material for radioactive waste, which will be tested in follow-up studies. Table 2 shows the analysis results of dried plants used in this research. The plants used in this experiment were collected, dried, ground, and blended Table 2 Elemental composition of dried plants used as additive Major elements present in dried plants, % (wt./wt.) H N C 2.86 2.98 20.44 Granulated blast furnace slag, a by-product material from iron manufacturing, was used in this study as waste material in form of a fine aggregate to evaluate the integrity and physical property of the cementitious waste material; results of its elementary analysis are presented in Table 3. Table 3 Elemental analysis of blast furnace slag used in this study. Chemical composition of slag powder used in this work, wt./wt. 4

ACCEPTED MANUSCRIPT

Al 16.4

Ca 42.9

Fe 4.99

Mg 12.1

Mn 3.55

Si 28.0

S 0.875

Ti 2.0

Silica fume and other nano-materials consist of ultra-fine particles of different nano-size range are presented by SEM micrographs in Fig.1.

Fig. 1 SEM of different nano-particles used in improvement of cement kiln dust. 2.2. Methods 2.2.1. Sample preparation Cement kiln dust is an important ingredient used in this study and was used as the matrix material to be blended with different additives as presented in several groups of samples. Each group consists of six specimens, three of them were subjected towards compressive strength testing, while the other three were subjected towards permeability tests. Hydration of cement kiln dust solely or with additives was accomplished using tap water. The paste produced according to the specification of each group was mixed thoroughly and poured in polymeric cylindrical tubes, compacted tightly, closed and cured for setting and solidification for 28 days at room temperature in the laboratory (25 ± 5 °C under humid conditions) (ASTM C31, 2000). After the curing duration, the solidified cylindrical specimens were removed and subjected to mechanical

5

ACCEPTED MANUSCRIPT

testing and spectroscopic analyses. A description of these groups of specimens is listed as follows: Group A: Cement kiln dust + different ratios of water This group of test specimens was prepared to evaluate the optimum amount of water required for hydration of cement kiln dust to produce product of higher compressive strength as a control sample. Preparation was carried out as follows: -

300 g of cement kiln dust was used as it has a larger specific volume than cement itself; five series of cement kiln dust were prepared with three different water/cement kiln dust (w/ckd) ratios: 60%, 70%, 80%

-

Water and cement kiln dust were rigorously shaken and blended to obtain a homogeneous paste.

-

Three series of different water/cement kiln dust ratios were made, each one including six similar blocks.

-

After 28 days, it turned out that the samples still contain water, so the covers were opened and the samples were stored open at room temperature for two weeks to ensure complete dryness, as confirmed by mass constancy.

Group B: Cement kiln dust + different ratios of dry grated plants In this group, five series of samples of different ratios of plants used as type of solid waste to be stabilized by cement kiln dust without additives have been prepared as follows: 1%, 2%, 3%, 4% and 5% plant/cement kiln dust (wt./wt.). i- Cement kiln dust were rigorously shaken and blended with the additive with 70% water relative to the bypass added to obtain homogeneous paste. ii- Five series of different additive/cement kiln dust ratios were made, each one including six similar blocks. iii-

After 28 days, the samples were released at room temperature for two weeks to ensure complete dryness.

Group C: Cement kiln dust + different fractions of Portland cement This group contains Portland cement in ascending ratios of cement kiln dust up to 25% to produce appropriate strength with only low cement addition. i-

Starting with 5% (15 g) of Portland cement with 95% (285 g) cement kiln dust + 70% water, (w/ckd = 70%); this ratio was applied as the optimum for hydration based on the results of group A). 6

ACCEPTED MANUSCRIPT

ii-

Five series with w/ckd = 5% , 10%, 15%, 20% and 25% have been prepared.

iii-

After 28 days, the samples were released at room temperature for two weeks to ensure complete dryness.

Group D: Cement kiln dust + different portions of silica fume This group started with 5% (15 g) of silica fume relative to 95% (285 g) cement kiln dust + 70% water. i-

Five series of samples of different ratios of silica fume to cement kiln dust have been prepared at ratios 5%, 10%, 15%, 20% and 25% (wt./wt.) to maintain a proper ratio for higher integrity.

ii-

After 28 days, the samples were released at room temperature for two weeks to ensure complete dryness.

Group E: Cement kiln dust + different ratios of slag This group started with 5% (15 g) of slag relative to 95% (285 g) cement kiln dust + 70% water. i-

Five series of samples of different ratios of slag with cement kiln dust have been prepared at ratios 5%, 10%, 15%, 20% and 25% (wt./wt.) to determine the optimum ratio achieving good mechanical properties.

ii-

After 28 days, the samples were released at room temperature for two weeks to ensure complete dryness.

Group F: Cement kiln dust + different ratios of silica fume and slag i-

Four series of samples of different fractions of slag and silica fume with cement kiln dust have been prepared at ratios: 10% slag+10% fume, 10% slag+5% fume, 15% slag+10% fume, 20% slag+5% fume relative to cement kiln dust with constant value of 70% water (w/ckd =70%).

ii-

After 28 days, the samples were released at room temperature for two weeks to ensure complete dryness.

Group G: Cement kiln dust + 0.1% of different types of nano-materials i-

Five series of samples of different nano-materials with cement kiln dust have been prepared at the ratios 300 g cement kiln dust + 0.1% of (nano-alumina, nano-silica, nano-titanium dioxide, nano-calcium oxide or nano-zinc oxide) with a constant water content of 70% water (w/ckd = 70%).

ii-

After 28 days, the samples were released at room temperature for two weeks to ensure complete dryness. 7

ACCEPTED MANUSCRIPT

Group H: Cement kiln dust + 0.1% of different types of nano-materials + 20% slag i-

Five series of samples similar to that in group H with addition of 20% slag for each series, (the ratio of 20% slag was applied as optimum ratio based on the results of group E).

ii-

After 28 days, the samples were released at room temperature for two weeks to ensure complete dryness.

2.2.2. Test for the mechanical integrity and permeability of specimens Three samples of each series in all the groups were subjected towards compression resistance measurements in a hydraulic press using a Ma-Test measuring machine E-159 SP, Italy. According to Archimedes’s immersion technique (ASTM C20-00, 2015), the apparent porosity was determined by using the equations: V, cm3 = W-S

(1)

P, % = [(W-D)/V] x 100

(2)

V: exterior volume of the specimen, W: saturated weight of the specimen, S: suspended weight of the specimen, D: dry weight of the specimen, P: apparent porosity For this technique, specimens were subjected to a temperature of 105-110oC for constant weight to determine the dry weight (D). The saturated weight, W, was determined by immersing dry specimens in water; immersed specimens were boiled for 2 h keeping the samples totally covered with water without contact with the heated side of the boiling container. The suspended weight (S) was evaluated by weighting the boiled samples after cooling as suspended blocks in water. 2.2.3. Spectroscopic analyses for test specimens Some blocks fractured during compressive strength testing; they were collected and milled for investigation by IR and XRD techniques in order to characterize the physical features of the nominated material before and after the optimization processes. A Fourier Transform Infrared spectrophotometer, (FTIR - 8201PC, Shimadzu) and an X-ray diffractometer (PANalytical's X'Pert PRO, The Netherlands), respectively, were used for this manner. 3. Results and discussions 3.1. Mechanical characterization of the hydrated cement kiln dust after a curing period 3.1.1. Effect of water/cement kiln dust ratio on the compressive strength and porosity

8

ACCEPTED MANUSCRIPT

The solidified waste monoliths have to attain sufficient integrity for handling, transportation and disposal, therefore, mechanical integrity is a crucial parameter that plays an important role to evaluate and improve the material used for solidification. According to recent publications, the degree of hydration increases significantly by increasing the water/cement ratio and the hardening time of the cement paste, varying between 46% - 80% and 7 - 365 days respectively (Atahan et al., 2009). In this study, compressive strength at different water/cement kiln dust (w/ckd) ratios was reported for samples cured for 28 days and opened for 14 days to enable drying. Fig. 2 illustrates the compressive strength and porosity values of cement kiln dust blocks at various ratios of w/ckd (60%, 70%, 80%). Conditions resulting in higher compressive strength and lower porosity are clearly identified in this illustration for setups with a ratio of 70% w/ckd. Further increase in ratio of w/ckd (80%) results in significant reduction of the mechanical integrity of the cementitious sample due to the excess of water, which results in generation of voids and capillaries after drying; consequently, it increases the porosity of the sample (Gani 1997). However, at a lower proportion of w/ckd (60%), the compressive strength was lower than that of the optimum ratio with higher porosity. This can be explained by the presence of unreacted cementitious constituents, i.e., incomplete reaction of cement kiln dust due to deficiency of water needed for hydration (Saleh et al. 2014). Based on these results, specimens

Porosity, %

for all forthcoming experiments as control sample.

100 90 80 70 60 50 40 30 20 10 0

Porosity, % Compressive strength, MPa

97.3

75.0 64.2

2.8

60

Water/bypass 3.7 dust, % Water/bypass dust, %

1.2

70

80

10 9 8 7 6 5 4 3 2 1 0

Compressive strength, MPa

with a compressive strength of about 3.7 MPa as obtained at a ratio of w/ckd (70%) were applied

Fig. 2 Mechanical testing of the cement kiln dust blocks hydrated with different water ratios 9

ACCEPTED MANUSCRIPT

3.1.2. Stabilization of milled plants as a type of solid waste by the cement kiln dust The plants used in this experiment were collected, dried, ground, and blended with cement kiln dust to simulate the immobilization of hazardous biological waste obtained by phytoremediation, which is utilized for treatment and accumulation of heavy metals and radionuclides (Saleh et al. 2017; Saleh 2012; Saleh and Eskander 2012b). Excessive amounts of the dried plants up to 3% were incorporated into the cement kiln dust before casting and curing for 28 days. As expected, the compressive strength of cement kiln dust blocks harboring milled plants decreases with increasing fractions of plant biomass. On the contrary, the porosity increased with increasing plant fractions, which is in accordance to previously published articles (Bayoumi and Saleh 2018; Saleh 2014). This finding makes it indispensable to evaluate and improve the mechanical, physical and chemical characteristics of the cement kiln dust material to make it better suitable for efficient immobilization of hazardous waste. Consequently, various materials were tested in the following

Porosity, %

minimum cost. 100 90 80 70 60 50 40 30 20 10 0

Porosity, % Compressive strength, MPa 82.3 71.7 64.2

90.0

10 8 6

Compressive strength, MPa

experiments as strengthening additives for the cement kiln dust to attain maximum integrity at

4 3.7

Plant/bypass dust, % 2.7 2.4

2.6

Plant/bypass dust, % 0%

1%

2%

2 0

3%

Fig. 3 Compressive strength and porosity of the cement kiln dust incorporated different amounts of plants 3.1.3. Addition of Portland cement at different ratios related to the cement kiln dust Portland cement as a proper binder significantly enhances the compressive strength when replaced by cement kiln dust, as manifested for all prepared samples of different ratios. 10

ACCEPTED MANUSCRIPT

Results presented in Fig. 4 show the progressive trend of compressive strength with increasing amounts of cement kiln dust (5% to 25%) being replaced by Portland cement. In case of 5% replacement by Portland cement, it could be stated that the increase in compressive strength is negligible, while a significant decrease in porosity by more than 60% was obtained. This result may be due to the settling of cement within the voids placed between the granules of cement kiln dust. Unexpectedly, ascending values of porosity with raising compressive strength were recorded at increasing ratios of replacement of cement kiln dust by Portland cement up to 25%. In this study, based on the outcomes of the experiment performed to evaluate the optimum proportion of water with cement kiln dust, the proper ratio was 70% w/ckd. Consequently, this ratio was applied for all test samples under various conditions. However, Portland cement has a maximum compressive strength and proper porosity at water/cement ratio of 35% according to the previous literature (Saleh and Eskander 2009). Accordingly, by increasing the fraction of Portland cement instead of cement kiln dust, the compressive strength was increased to the desired level. Nevertheless, with increasing the Portland cement/cement kiln dust (pc/cd) ratio, the constant volume of water (w/c = 70%) is more than (w/c = 35%), the proper ratio for Portland cement;

Porosity, %

pores (Jensen and Hansen 2001).

70

64.2

Porosity, % Compressive strength, MPa

30

60

25

50

41.6

40 30

0

3.7 0

Cement/bypass dust, %8.5 6.0 5.6 3.5 Cement/bypass dust, % 5

10

15

20

20 15

19.8

20 10

30.9

27.4

34.2

10.4

Compressive strength, MPa

consequently, the hydrated cement paste contains an excess of unbound water present in large

10 5 0

25

Fig. 4 Mechanical properties of cement kiln dust blended with different amounts of Portland cement 11

ACCEPTED MANUSCRIPT

3.1.4. Mechanical improvement of cement kiln dust in presence of silica fume Fig. 5 indicates that addition of silica fume to the cement kiln dust paste had positive effects when increasing the added ratio from 5% to 20%, while a slight decrease was reported for a ratio of 25%. Incorporation of 20% silica fume instead of cement kiln dust at the same ratio resulted in about three times the compressive strength value observed when analyzing the control sample. This behavior is in agreement with the high-performance of Portland cement/ silica fume (10% wt./wt.) mixtures, as previously reported in the literature (Yazıcı 2008). Porosity was decreased when increasing the amount of silica fume as replacement of cement kiln dust. Since silica fume consists of extremely small particles, it potentially fills the voids in the paste (Dehwah 2012). In spite of the gradual decrease in porosity at higher replacement ratios of cement kiln dust by silica fume, porosity was higher than observed for the control sample; this is due to the excess of water used for hydration. As a disadvantage, cracking occurred after drying of the specimens after a curing period. Therefore, another material instead of silica had to be added in order to minimize or even eliminate the cracking. Portland cement displays desirable mechanical properties in presence of

Porosity, %

cycles and massive chloride penetration (Yazıcı 2008).

100 90 80 70 60 50 40 30 20 10 0

Porosity, % Compressive strength, MPa 88.9 88.7 83.8

81.7

30 75.8

64.2

25 20 15

3.7 0

Silica fumes/bypass dust,10.4 % 7.4 5.8 Silica fumes/bypass dust, % 2.8 5

10

15

20

Compressive strength, MPa

fly ash as a valuable mineral admixture together with silica fume even after freezing–thawing

10 9.5

5 0

25 .

Fig. 5 Compressive strength and porosity of the cement kiln dust reinforced by silica fume 3.1.5. Properties of hardened specimens based on bypass dust and different nanomaterials

12

ACCEPTED MANUSCRIPT

Nanomaterials have proper effects due to their small size that positively affects the properties of cementitious materials. With hydration of cementitious grains, simultaneous chemical reactions take place, producing a rigid paste of porous multi-phase matrix containing calcium hydroxide (causing the cement alkalinity) with traces of aluminates embedded into a C–S–H gel. In this alkaline media, interaction of nanoparticles takes place with the different compounds present in cement, mostly calcium ions and traces of magnesium, aluminum, iron, potassium, sodium and sulfur ions; these interactions consequently improve the mechanical property due to acceleration of the hydration process (Chuah et al. 2014). In this manner, incorporation of nanoparticles resulted in a significant improvement in mechanical properties from predictable grain-size materials of the same chemical composition (Amin et al. 2013). In the present study, the economic issue and cost savings were taken in consideration, therefore, only small amounts of nanoparticles were examined not exceeding 0.1% of nano-ZnO, nano-TiO2, nano-Al2O3, nano-SiO2, and nano-CaO. It is shown in Fig. 6 that the low amounts of different nanoparticles incorporated into cement kiln dust have resulted in only

100 90 80 70 60 50 40 30 20 10 0

Porosity, % Compressive strength, MPa 93.7 92.8 89.1

90.5

92.1

10 8

64.2

6 4 3.7

3.2

3.8

3.6

3.3

3.4

2

Compressive strength, MPa

Porosity, %

insignificant increase of compressive strength or porosity.

0 Control

0.1% ZnO 0.1%TiO2 0.1% Al2O3 0.1% SiO2 0.1% CaO

Fig. 6 Mechanical property and porosity of cement kiln dust mixed with different nanomaterials In previous studies, compressive strength of blended cement mortars was improved by adding more than 0.5% nano- TiO2 (Nazari et al. 2010), concrete was reinforced when being partly replacement by more than 2% nano-SiO2 (Jalal et al. 2012) ), more than 2% silica fume (Jalal et al. 2015) and more than 0.5% nano-Al2O3 (Nazari and Riahi 2011). 13

ACCEPTED MANUSCRIPT

Due to the unfavorable results obtained by incorporation of small amounts of different nanoparticles to keep the cost issue in consideration, it was necessary to find another cheap material, most preferably a waste material such as slag to improve the efficiency of small amounts of nanoparticles for more valuable mechanical and physical properties of cement kiln dust. 3.1.6. Mechanical activation of cement kiln dust in presence of blast furnace slag Different amounts of slag (5% to 25%) were added to blend cement kiln dust paste. Fig. 7 shows the variation in compressive strength and porosity with different amounts of slag added to the cement kiln dust samples. A gradual increase in the compressive strength was recorded when increasing the amount of added slag up to 20%, this indicating mechanical improvement. By raising the amount of added slag to 25%, the improvement in compressive strength became less pronounced. A similar trend was observed for Portland slag cement when compressive strength increases by increasing the slag content up to 70% and then decreases (Sobolev 2005; Kumar et al. 2008). Due to the improvement of mechanical properties resulting from incorporation of slag in cement kiln dust blends, as demonstrated experimentally in this study, it is suggested to use

Porosity, %

kiln dust blends; this way blends with enhanced properties can be designed.

100 90 80 70 60 50 40 30 20 10 0

Porosity, % Compressive strength, MPa 85.6 80.6 79.4

10 76.1

64.2

71.8

8 6

6.0

Compressive strength, MPa

20% blast slag furnace together with other additive materials as a binary admixture with cement

4 3.7 2.4

3.8

3.5 Slag/bypass dust, 3.1 % Slag/bypass dust, %

0

5

10

15

2 0

20

25

Fig. 7 Strength development due to slag mixing with cement kiln dust solidified samples

14

ACCEPTED MANUSCRIPT

3.1.7. The performance of silica fume mixed with cement kiln dust in presence of slag Previous experiments described in literature or in this study (vide supra) confirmed the significant improvement gained by mixing silica fume with cement kiln dust accompanied by more cracks within the sample surface, mediocre improvement by mixing blast furnace slag with cement kiln dust, or extra improvement of reactive powder concrete containing high volumes of ground granulated blast furnace slag as previously reported (Yazıcı et al. 2010). In this test series, as illustrated in Fig. 8, a binary mixture of different ratios of silica fume and blast furnace slag was incorporated into cement kiln dust to attain better mechanical properties by adding silica fume and a more compact and reinforced surface by the presence of slag. The ratio of 15% blast furnace slag and 10% silica fume with cement kiln dust hydrated by 70% water turned out as the optimum conditions according to the results for compressive strength of approximately 10 MPa and lower porosity. This value of compressive strength is sufficient for stabilization of hazardous and radioactive waste as well as for preparing other cementitious products, but unfortunately, after drying of the samples, the blocks cracked. Hence, using silica fume with slag as additive binary mixture for improving the mechanical property of cement kiln dust paste is not preferred because of these

Porosity, %

100 90 80 70 60 50 40 30 20 10 0

Porosity, % Compressive strength, MPa 80.3

81.4

20 76.2

78.4

15

64.2

10.0 8.0

6.7

10 8.4

3.7 Control

Compressive strength, MPa

reasons.

5 0

10% slag+10% 10% slag+5% 15% slag+10% 20% slag+5% silica fume silica fume silica fume silica fume

Fig. 8 Mechanical improvement due to mixing of cement kiln dust with silica fume in presence of slag 3.1.8. The role of slag with different nanomaterials mixed with cement kiln dust

15

ACCEPTED MANUSCRIPT

Under the presented conditions, the optimum ratio of slag (20%) relative to cement kiln dust was mixed with 0.1% of five nanoparticles individually before incorporation and hydration of cement kiln dust as presented in Fig. 9. Blast furnace slag has improved the mechanical properties of blended cement kiln dust, resulting in a maximum value of 10 MPa at 20% replacement by an equal amount of cement kiln dust. On the other hand, five types of nano-particles, added at an amount of only 0.1%, have resulted in non-distinguishable improvement of the blended cement kiln dust. Consequently, the predetermined optimized blends of examined nanoparticles and slag were mixed with cement kiln dust to prepare new complexes of three constituents. In presence of slag, the hydration of cement kiln dust with each type of nanoparticles was enhanced and, accordingly, the mechanical properties of the blended cement kiln dust were increased to more than 12 MPa; moreover, reasonable porosity was observed. Experimental results indicated that significant modification of the mechanical strength of the blends of cement kiln dust and nano-ZnO, nano-TiO2, nano-Al2O3, nano-SiO2, or nano-CaO, and blast furnace slag powder were obtained even when adding only a small amount of the nanoparticles. These results are in excellent agreement with results reported by Meng et al. (2012), indicating the improvement of cement mortar with nano-TiO2 in presence of slag powder. With this improvement, composites of cement kiln dust and slag with any of the examined nanoparticles are considered promising materials to be applied for several applications including the stabilization of hazardous and radioactive wastes. Subsequent studies to evaluate the new composites under drastic parameters are needed to cover all scenarios that could occur at the disposal site.

16

Porosity, %

100 90 80 70 60 50 40 30 20 10 0

Porosity, % Compressive strength, MPa 64.2

70.6

Compressive strength, MPa

ACCEPTED MANUSCRIPT

30

68.7

65.6

66.5

68.6

25 20 15

12.8

12.1

12.0

13.2

12.5

5

3.7 Control

10

0 slag+ZnO slag+Al2O3 slag+CaO slag+SiO2 slag+TiO2

Fig. 9 Mechanical enhancement due to mixing of cement kiln dust with nanomaterials in presence of slag 3.2. Crystalline phases in cement kiln dust modified by slag and nanoparticles XRD and FTIR analyses were performed to investigate the improvement of compressive strength produced by mixing slag and different nanoparticles with cement kiln dust during hydration process. The negligible improvement of the porosity, as previously stated, could be attributed to the distance between the constituents not decreasing at a small content of the added nanoparticles. Generally, addition of 0.1% nanoparticles improves the compressive strength with an insignificant enhancement of pores within the cement kiln dust even in presence of 20% slag due to the improvement of hydration (Chuah et al. 2014). After addition of 0.01% nanoparticles to cement kiln dust and slag, the XRD diffractograms obtained after 28 day of hydration display nearly the same hydrated phases as in case of the neat cement kiln dust paste; some peaks characteristic for the nanoparticles added in different experiments, such as nano-Al2O3, are visible in the diffractograms. The peaks characteristic for calcite, dicalcium silicate, dolomite, quartz and calcium sulphate (Heikal et al. 2002) are well visible in presence of reinforcing additives as presented in Fig. 10.

17

ACCEPTED MANUSCRIPT

Fig. 10. XRD patterns of the cement kiln dust improved with slag and different nanoparticles On the other side, FTIR spectra showed the major peaks corresponding to the different functional groups of cement kiln dust as previously reported in the literature (Salem et al. 2015). Three groups of bands as presented in Fig. 11 represent the functional groups of cement kiln dust, such 18

ACCEPTED MANUSCRIPT

as the absorption bands at 3642, 3432, 1637, 1118 cm-1, a strong band at position of 1415 cm-1, and the last group at 2327, 964, 873 cm-1. The peak observed at around 3750 cm-1 in cement dust is typical for vibration of O-H in portlandite (Eskander et al 2012). The strong peak at 3432 cm-1 and the other two peaks at 3642 and 1415 cm-1 illustrate the presence of hydroxyl groups of calcium hydroxide (Al-Ghouti et al. 2003) while the peak at 873 cm-1 corresponds to carbonate and vibration of Si-O group in silicate (Bayoumi et al. 2013). The peaks observed at 2327, 964, 873 cm-1 indicate the presence of silicate (Saleh 2014). It could be stated that the presence of nanoparticles at the reported ratio has no obvious impact on the characteristic FT-IR spectrum of cement kiln dust paste.

Fig. 11. FT-IR spectra of cement kiln dust improved with nanoparticles Based on recent studies, it is known that proper workability, processability, and durability can be attained by mixing concrete with copper slag as partial aggregate with nano-silica (Chithra et al., 19

ACCEPTED MANUSCRIPT

2016) or concrete in presence of silica fume (Ardalan et al., 2017). These findings are in agreement with the results obtained in the present study for the composites of cement kiln dust and blast furnace slag hydrated with nano-silica suspended in water. Therefore, the new developed composite materials could be a potential choice for many applications including the stabilization of hazardous and radioactive wastes in the future. Conclusion This article describes some aspects of extensive validation of cement kiln dust as one of the most hazardous by products released by cement industry. The main objective is to reuse this waste to (partly) replace cement, a material widely used in numerous fields, i.e., using a component environmentally benign when released instead of an environmentally questionable component. The nominated byproduct, cement kiln dust, could not effectively replace the original material, cement, without improvement and reinforcing by introduction of other materials. Based on this perspective, some of traditional materials and nano-materials such as Portland cement, slag, silica fume, nano-alumina, nano-silica, nano-titanium dioxide, nano-calcium oxide and nano-zinc oxide were added with or without addition of cement kiln dust at different ratios. The results obtained in this study show that the best compressive strength of cement kiln dust without any additions was at a water/cement kiln dust ratio of 70%. The noticeable increase in compressive strength by replacing cement kiln dust by Portland cement is no surprise; nevertheless, the central information obtained is “replacement of 15% cement kiln dust by Portland cement duplicated the value of compressive strength”. The presence of 20% slag or 20% silica fume enhances the mechanical and physical properties of cement kiln dust, while the maximum value was obtained when mixing 15% slag and 10% silica fume with the cement kiln dust hydrated at the ratio 70% w/ckd. Moreover, the use of low concentration of different nanomaterials (0.1%) causes only negligible changes in the mechanical integrity of the solidified cement kiln dust samples, while blending with 20% slag generated an economically attractive and environmentally benign product of a compressive strength of more than 12 MPa. It is very likely that the proposed novel composite material composed of cement kiln dust as a waste product blended with slag and small amounts of different nanomaterials is suitable for stabilization of radioactive wastes due to its mechanical property and for construction applications due to its economically and environmentally advantages. In this context, further studies have to be carried out to evaluate the nominated composite and its consistency for waste 20

ACCEPTED MANUSCRIPT

stabilization under different drastic conditions such as freeze/thaw cycles, leaching tests and flooding in various media. Moreover, assessment of construction applications using this composite material would be one of the attractive trends for future research. References Abou Taleb ANM, Musaniger AO, Abdel-Moneim RB, (1995). Health status of cement workers in the United Arab Emirates. Journal of the Royal Society of Health 2: 378-383. Al-Ghouti MA, Khraisheh MAM, Allen SJ, Ahmad MN. (2003).The removal of dyes from textile wastewater: a study of the physical characteristics and adsorption mechanisms of diatomaceous earth. Journal of Environmental Management 69: 229–238. Aly M., Hashmi M.S.J., Olabi A.G., Messeiry M., Abadir E.F., Hussain A.I. (2012) Effect of colloidal nano-silica on the mechanical and physical behavior of waste-glass cement mortar. Materials and Design 33: 127–135. Amin M.S., El-Gamal S.M.A., Hashem F.S. (2013). Effect of addition of nano-magnetite on the hydration characteristics of hardened Portland cement and high slag cement pastes. J Therm Anal Calorim 112: 1253–1259. Ardalan R.B., Joshaghani A, Hooton R.D. (2017). Workability retention and compressive strength of self-compacting concrete incorporating pumice powder and silica fume. Construction and Building Materials 134: 116–122. ASTM C20-00, (2015). Standard Test Methods for Apparent Porosity, Water Absorption, Apparent Specific Gravity, and Bulk Density of Burned Refractory Brick and Shapes by Boiling Water. ASTM International, West Conshohocken, PA. ASTM C31, (2000). Annual Book of ASTM Standards. Philadelphia. 04.02:5–10.6. Atahan H.N., Oktar O.N., Taşdemir M.A. (2009). Effects of water–cement ratio and curing time on the critical pore width of hardened cement paste. Construction and Building Materials 23: 1196–1200. Bayoumi T.A., Reda S.M. and Saleh H.M. (2012). Assessment study for multi-barrier system used in radioactive borate waste isolation based on Monte Carlo simulations, Applied Radiation and Isotopes, 70(1), 99-102. Bayoumi TA, Saleh HM, Eskander SB. (2013). Solidification of hot real radioactive liquid scintillator waste using cement–clay composite. Monatsh Chem 144: 1751–1758

21

ACCEPTED MANUSCRIPT

Bayoumi, T.A., Saleh, H.M., (2018). Characterization of biological waste stabilized by cement during immersion in aqueous media to develop disposal strategies for phytomediated radioactive waste. Progress in Nuclear Energy 107: 83–89. Chithra S., Senthil Kumar S.R.R., Chinnaraju K. (2016). The effect of Colloidal Nano-silica on workability, mechanical and durability properties of High Performance Concrete with Copper slag as partial fine aggregate. Construction and Building Materials 113: 794–804. Chuah S., Pan Z., Sanjayan J.G., Wang C.M., Duan W.H. (2014). Nano reinforced cement and concrete composites and new perspective from graphene oxide. Construction and Building Materials 73: 113–124. Dehwah H.A.F. (2012). Mechanical properties of self-compacting concrete incorporating quarry dust powder, silica fume or fly ash. Construction and Building Materials 26: 547–551. Egyptian Standard Specifications ES 4756-1/2005, (2005). Ordinary Portland Cement (OPC) CEM1 (42.5N). (Egypt) Eskander, S.B., Bayoumi, T.A., Saleh, H.M., (2012). Performance of aged cement-polymer composite immobilizing borate waste simulates during flooding scenarios. J. Nucl. Mater. 420 (1–3), 175–181. Eskander, S.B., Bayoumi, T.A., Saleh, H.M., (2013). Leaching behavior of cement-natural clay composite incorporating real spent radioactive liquid scintillator. Prog. Nucl. Energy 67, 1–6. Eskander, S.B., Saleh, H.M., (2012). Cement mortar-degraded spinney waste composite as a matrix for immobilizing some low and intermediate level radioactive wastes: consistency under frost attack. J. Nucl. Mater. 420 (1–3), 491–496. Gani, M.S.J. (1997) Cement and Concrete. Chapman & Hall, London, 1st edn. pp 62-70. Heikal M., Aiad I., Helmy I.M. (2002). Portland cement clinker, granulated slag and bypass cement kiln dust composites. Cement and Concrete Research 32: 1805–1812. Jalal M., Mansouri E., Sharifipour M., Pouladkhan A.R. (2012).

Mechanical, rheological,

durability and microstructural properties of high performance self-compacting concrete containing SiO2 micro and nanoparticles. Materials and Design 34: 389–400. Jalal M., Pouladkhan A., Harandi O.F., Jafari D. (2015). Comparative study on effects of Class F fly ash, nano silica and silica fume on properties of high performance self compacting concrete. Construction and Building Materials 94: 90–104. Jensen O.M., Hansen P.F. (2001). Water-entrained cement-based materials I. Principles and theoretical background. Cement and Concrete Research 31: 647-654. 22

ACCEPTED MANUSCRIPT

Konsta-Gdoutos M.S., Shah S.P. (2003). Hydration and properties of novel blended cements based on cement kiln dust and blast furnace slag. Cement and Concrete Research 33(8): 1269–1276. Kumar S., Kumar R., Bandopadhyay A., Alex, T.C., Ravi Kumar B., Das S.K., Mehrotra S.P. (2008). Mechanical activation of granulated blast furnace slag and its effect on the properties and structure of portland slag cement. Cement and Concrete Composites 30: 679–685. Li, H., Xiao, H.G., Yuan, J., Ou, J.P. (2004). Microstructure of cement mortar with nano particles. Composites Part B: Engineering, 35, 185–189. Meng T., Yu Y., Qian X., Zhan S., Qian K. (2012). Effect of nano-TiO2 on the mechanical properties of cement mortar. Construction and Building Materials 29: 241–245. Nazari A., Riahi S., (2011). Al2O3 nanoparticles in concrete and different curing media. Energy and Buildings 43: 1480–1488. Nazari A., Riahi S., Riahi S., Shamekhi S.F. and Khademno A. (2010). Assessment of the effects of the cement paste composite in presence TiO2 nanoparticles. Journal of American Science 6(4): 43-46. Rafnsson V, Gunnarsdottir H, Kiilunen M. (1997). Risk of lung cancer among masons in Iceland. Occupational and Environmental Medicine 54: 184-188. Saleh, H.M., (2012). Water hyacinth for phytoremediation of radioactive wastes simulate contaminated with cesium and cobalt radionuclides. Nucl. Eng. Des. 242, 425–432. Saleh, H.M., (2014). Stability of cemented dried water hyacinth used for biosorption of radionuclides under various circumstances. Journal of Nuclear Materials 446, 124-133 Saleh, H.M., Bayoumi, T.A., Mahmoud, H.H., Aglan, R.F., (2017). Uptake of cesium and cobalt radionuclides from simulated radioactive wastewater by Ludwigia stolonifera aquatic plant. Nucl. Eng. Des. 315, 194–199. Saleh, H.M., Eskander, S.B. (2012b). Using Portland cement for encapsulation of Epipremnum aureum generated from phytoremediation process of liquid radioactive wastes. Int. J. Chem. Environ. Eng. Syst. 3 (2), 1–8. Saleh, H.M., Eskander, S.B., (2009). Long-term effect on the solidified degraded cellulose based waste slurry in cement matrix. Acta Montan. Slovaca 14 (4), 291–297. Saleh, H.M., Eskander, S.B., (2012a). Characterizations of mortar-degraded spinney waste composite nominated as solidifying agent for radwastes due to immersion processes. Journal of Nuclear Materials 430 (1-3), 106-113. 23

ACCEPTED MANUSCRIPT

Saleh, H.M., Eskander, S.B., Fahmy, H.M., (2014). Mortar composite based on wet oxidative degraded cellulosic spinney waste fibers. Int. J. Environ. Sci. Technol. 11 (5), 1297–1304. Saleh, H.M., Tawfik, M.E., Bayoumi, T.A., (2011). Chemical stability of seven years aged cement–PET composite waste form containing radioactive borate waste simulates. Journal of Nuclear Materials 411, 185-192. Salem W.M., Sayed W.F., Halawy S.A., Elamary R.B. (2015). Physicochemical and microbiological characterization of cement kiln dust for potential reuse in wastewater treatment. Ecotoxicology and Environmental Safety 119: 155–161. Short S, Petsonk EL. (1996). Non-fibrous inorganic dusts. In: Harber P, Schenker MB, Balmes JR, editors. Occupational and environmental respiratory disease. London (UK): Mosby p. 356. Siddique R. (2006). Utilization of cement kiln dust (CKD) in cement mortar and concrete-an overview. Resources, Conservation and Recycling 48(4):315–338. Sobolev K. (2005). Mechano-chemical modification of cement with high volumes of blast furnace slag. Cement and Concrete Composites 27: 848–53. Sultan A. Meo, (2004). Health hazards of cement dust. Saudi Medical Journal 25(9): 1153-1159. Taha R.A., Alnuaimi A.S., Al-Jabri K.S., Al-Harthy A.S. (2007). Evaluation of controlled low strength materials containing industrial by-products. Building and Environment 42: 3366– 3372. Yazıcı H, (2008). The effect of silica fume and high-volume Class C fly ash on mechanical properties, chloride penetration and freeze–thaw resistance of self-compacting concrete. Construction and Building Materials 22: 456–462. Yazıcı H., Yardımcı M.Y., Yiğiter H., Aydın S., Türkel S. (2010). Mechanical properties of reactive powder concrete containing high volumes of ground granulated blast furnace slag. Cement and Concrete Composites 32: 639–648.

24