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Study on utilization of red brick waste powder in the production of cement-based red decorative plaster for walls
Accepted Manuscript Study on Utilization of Red Brick Waste Powder in the Production of Cement-based Red Decorative Plaster for Walls Haoxin Li, Liuliu Dong, Zhengwu Jiang, Xiaojie Yang, Zhenghong Yang PII:
S0959-6526(16)30628-X
DOI:
10.1016/j.jclepro.2016.05.149
Reference:
JCLP 7331
To appear in:
Journal of Cleaner Production
Received Date: 26 May 2015 Revised Date:
20 May 2016
Accepted Date: 23 May 2016
Please cite this article as: Li H, Dong L, Jiang Z, Yang X, Yang Z, Study on Utilization of Red Brick Waste Powder in the Production of Cement-based Red Decorative Plaster for Walls, Journal of Cleaner Production (2016), doi: 10.1016/j.jclepro.2016.05.149. 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.
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Study on Utilization of Red Brick Waste Powder in the Production of Cement-based Red Decorative Plaster for Walls Haoxin Li
Liuliu Dong
Zhengwu Jiang*
Xiaojie Yang
Zhenghong Yang
Key Laboratory of Advanced Civil Engineering Materials Ministry of Education, Tongji University, Shanghai, 201804, PR. China
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First author Tel./Fax: +86 21 69584723. E-mail addresses: [email protected] (H. Li)
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Corresponding author Tel./Fax: +86 21 69584723. E-mail addresses: [email protected] (Z. Jiang)
Abstract: Current management for red brick waste is insufficient, and a new method is needed. We sought to develop a
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new approach for effective management. Red cement-based decorative plasters were prepared with red brick waste powder (RBWP), white Portland cement, quartz sand, redispersible emulsion powder, hydroxypropyl-methyl cellulose ethers and silicone hydrophobic agent. The colors, water absorptions and strengths of different plasters were investigated, and the mechanisms responsible for their performance variations were explored by high-resolution transmission electron microscopy, X-ray powder diffractometry and scanning electron microscopy. The relative economic and environmental benefits were also analyzed. The feasibility of recycling RBWP in the production of cement-based red decorative plaster for walls was evaluated. The resulting plaster provided appropriate color adjustment, and the water resistance of the plaster was not greatly affected. The compressive and flexural strengths of plaster were improved. However, the improvement decreased as the sand replacement ratio increased. The tensile bond strength of the plaster is related to the RBWP content. More RBWP negatively affects the tensile bond strength of the plaster. Calcium hydroxide in the hardened paste varies with RBWP content. This variation correlates with the appearance and level of pozzolanic reaction in the plaster with RBWP. Plaster with RBWP has a denser microstructure than the control. In addition to the pozzolanic reaction, this denser microstructure also contributes to performance improvements such as compressive and flexural strengths. To improve the economic and environmental efficiencies, it is also feasible to recycle RBWP in the production of cement-based red decorative plaster for walls. These results demonstrate the effective use of red brick waste. They also provide a reference strategy for the management of red brick waste in other developing countries that are carrying out or will carry out urbanization activities.
Key words: Red Cement-based Decorative Plaster; Waste Red Brick; Strength; Water Absorption; Microstructure
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1 Introduction
In the past three decades, unprecedented urbanization has occurred in developing countries. The intense urbanization of recent decades has generated huge volumes of construction and demolition waste and has led to the excessive consumption of natural resources (Song et al., 2014). Demolition waste is responsible for approximately 30-40% of the total waste generated in the municipality (Villoria Saez et al., 2015; Ravindra et al., 2015). It has become a major environmental issue and has created pressure for authorities to manage waste in a more sustainable manner (Song et al., 2014; Coelho and de Brito, 2013; Coelho and de Brito, 2013a). In 2014, Chinese construction and demolition waste reached several billion tons. Chinese brick-making has a 2000-year history, and an incalculable number of red and gray bricks have been used in rural construction and building since 1900 (Wu et al., 2011). In recent years, rural reconstruction has accelerated, and many old brick-concrete houses were purposefully demolished in China. A great deal of brick waste has been generated, and approximately 0.4 billion tons of this waste is produced every year. In other developing countries such as India, Russia, and Brazil, great quantities of brick waste are also produced due to recent urbanization (Villoria Saez et al., 2015). The waste 1
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must be transported to appropriate disposal areas, which are often landfills. The disposal cost is greatly increased because of transport and because of the land requirements for ecological management of the waste. Additionally, dust is easily generated during the transport of the waste, which causes pollution of the surrounding environment. There is an urgent need to responsibly manage it. It has been suggested that the waste could be recycled to replace the natural aggregates in concrete production (Jankovic et al., 2012; Cachim, 2009; Yang et al., 2011) and self-compacting cement paste (Heikal et al., 2013). However, more brick waste leads to low workability, which makes it difficult to compact and finish the fresh concrete. In addition, the waste increases the permeability and physical shrinkage of the concrete, and it decreases the elastic modulus. As a result, such waste has not been widely used as a recycled aggregate. Other problems also prevent its use, such as impurities in the material, lack of knowledge about the behavior of concrete, and the limited available standards for the use of recycled aggregates. Studies have demonstrated that waste brick could be used as a pozzolanic material to prepare pozzolanic cement (Turanli et al., 2003), mortar (Naceri and Hamina, 2009) and concrete (Heikal et al., 2013; Ge et al., 2012). It improves the grinding efficiency of the clinker when it is recycled to produce the cement (Kaminskas et al., 2006). There are additional benefits such as cost reductions, energy savings, and improved ecological balance and conservation of natural resources. However, it delays the setting times. It reduces the alkali–silica reactions when used in the production of the cement-based mortar, self-compacting cement paste and concrete. Moreover, concrete with this material has a higher compressive strength than control concrete made with the optimum mixture ratio. However, it negatively affects the clinker mechanical properties. To provide the same strength as the control, the concrete has to be kept with a lower water cement ratio and more super-plasticizer has to be used in the mixing process. This incurs higher costs. The material has to be ground to a particle size of less than 0.06 mm, and the replacement ratio should not be more than 25%. These variables (particle size and replacement ratio) need to be highly controlled. This makes it challenging to prepare concrete with brick waste as the pozzolanic material. Asphalt mastic can also be prepared with brick powder as a mineral filler. This powder can have positive effects on asphalt mastic high-temperature properties, but it negatively affects the low temperature properties of asphalt mastic (Wu et al., 2011). In general, it is good to find other recycling methods for brick waste. The potential environmental liabilities of the brick waste will be alleviated, and the product will be diversified. Cement-based decorative plaster is an important building material. It has many advantages, such as natural quality, low cost, strong competitiveness and a desirable texture, in contrast with other ornamental materials such as paint and ceramic tile (Doroudiani and Omidian, 2010; Bartza and Filar, 2010). Thus, it is widely used in many developed countries to decorate walls in buildings. In its production, inorganic pigments, such as various colors of iron oxides, are commonly used to alter the plaster color. These pigments have low cost, better durability and alkali resistance (Lee et al., 2005; Marmol et al., 2010; Diamanti et al., 2013). Additionally, the mechanical properties of plasters are not affected by these inorganic pigments. However, their prices are high, generally about 1.5-6.5 USD per kg. Moreover, they are prepared from non-renewable resources. Most importantly, the construction industry is one of the best targets of solid waste reconversion due to the large amounts of raw materials it consumes and the large volume of final products in construction. Resources can be conserved by reusing the waste, which diversifies the production and reduces the final cost and also provides alternative raw materials for a number of building sectors (Lopez et al., 2009; Xuan et al., 2015; Li et al., 2012). For example, granite sludge waste can be recycled as a colored aggregate to produce cement-based colored decorative plaster (Marmol et al., 2010). Brick waste is typically red or gray because it contains many ferrum elements, and the ions of these ferrum elements are commonly red or gray. Red brick waste is red because it contains ions such as Fe3+. To maintain the required color and properties, silicon dioxide (SiO2), ferric oxide (Fe2O3) and calcium oxide (CaO) are used in brick, although the chemical components of brick vary in color, origin, variety, raw materials and properties (Demir and Orhan, 2003). Therefore, red brick waste can theoretically be used as an alternative source of red pigments or colored aggregates to produce cement-based red decorative plaster. The variations in chemical components do not prevent this. However, there are no reports describing the preparation of cement-based red decorative plaster with red brick waste. In addition, although there are reports in the literature, none of them properly evaluate the feasibility of recycling the red brick waste in the production of cement-based red decorative plaster. The main reason is that cement-based red decorative plaster pertains to the other system. The organic 2
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constituents such as redispersible emulsion powder (REP), hydroxypropyl-methyl cellulose ethers (HMCE) and silicone hydrophobic agent (SHA) have to be used along with cement in this system. In addition to compressive strength, the different properties are required, such as water absorption and tensile bond strength. There are important points that remain to be systematically studied because they play important roles in the effective use of red brick waste in colored plaster production. Therefore, cement-based red decorative plaster was prepared with red brick waste powder (RBWP) in the laboratory, and properties such as color, water absorption and strength were investigated based on the Chinese building material industry standard JC/T 1024-2007. The RBWP characteristics were discussed. The mineral components and microstructures of hardened plaster were observed, and the mechanisms of these property variations were explored. Heavy metal leaching from the hardened paste was also evaluated because of the appearance of heavy metals in the brick waste. Economic and environmental analyses were also carried out because brick waste had to be ground into powder for the study. The feasibility of using red brick waste powder in the production of cement-based red decorative plaster for walls was studied in this work.
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2 Experimental methods 2.1 Materials
Na2O 1.31 0.55
MgO 1.52 1.12
Al2O3 17.25 3.73
SiO2 67.95 21.34
SO3 0.17 3.48
K2 O 2.33 2.02
CaO 1.35 67.30
TiO2 1.03 0.20
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Oxides RBWP Cement
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Red brick waste was obtained from a demolition field. It was separated from the concrete and other building materials and ground in a centrifugal ball mill into 200 ASTM mesh size, which corresponds to common inorganic pigment. White Portland cement P.W 52.5 was also used to provide the background for the red cement-based decorative plaster. The chemical components of RBWP and white Portland cement are listed in Table 1. The mineralogical composition of white Portland cement is also given in Table 2. Quartz sand, REP (VINAPAS 5010N), HMCE (30000 Pa.s) and SHA (SEAL 80) are all commercial products. The main chemical component of quartz sand is SiO2, and its mass content is above 99.5%. The size of quartz sand is 100 ASTM mesh. Table 1 Chemical components of RBWP and white Portland cement (wt%) MnO 0.10 0.04
Fe2O3 6.93 0.15
SrO 0.02 0.07
CuO -
ZnO 0.01 -
PbO -
NiO -
Cr2O3 0.02 -
Table 2 Mineralogical composition of white Portland cement (wt%) Dicalcium silicate
Tricalcium aluminate
Tetracalcium aluminoferrite
(C3S)
(C2S)
(C3A)
(C4AF)
69.48
18.67
8.56
0.43
2.2 Mix designs
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Tricalcium silicate
Others 2.86
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To simplify the experiments and to easily analyze the effect of RBWP on the plaster properties, all plasters had the same cement content, REP, HMCE and SHA. They differed only in that different concentrations of RBWP were used to replace the quartz sand. RBWP1, RBWP2, RBWP3, RBWP4 and RBWP5, respectively, were plaster samples in which 20, 40, 60, 80 and 100% quartz sand were replaced by RBWP. Different amounts of mixing water were added to maintain a similar level of workability. All plasters received a similar slump flow of approximately 160±10 mm. The fresh plaster was put in a 5-L measuring cylinder and was spread and smoothed with a scraper to make the plaster level with the top of the measuring cylinder. Then, the total weight was measured. The measuring cylinder weight was subtracted from the total weight to determine the plaster weight. This was divided by the measuring cylinder volume (5 L), and the fresh plaster density was determined. RBWP has a lower density than quartz sand, the plaster density decreases with increasing RBWP. The detailed mix designs, water/cement ratios, slump flows and densities of all plasters are given in Table 3. Table 3 Detailed mix designs of all plasters Plasters Cement REP HMCE SHA Sand RBWP Water/cement Slump flow Density (mm) (kg/m3) (wt%) RBWP0 30.0 5.0 0.2 0.9 63.9 0.0 162 1963 0.625 3
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30.0 30.0 30.0 30.0 30.0
5.0 5.0 5.0 5.0 5.0
0.2 0.2 0.2 0.2 0.2
0.9 0.9 0.9 0.9 0.9
51.1 38.3 25.6 12.8 0.0
12.8 25.6 38.3 51.1 63.9
159 160 158 162 159
0.653 0.681 0.722 0.806 0.903
1916 1869 1828 1807 1792
2.3 Methods
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Particle size distributions of RBWP and white cement were analyzed on an LS230 Laser particle size analyzer (LPSA). Ethyl alcohol was used as the medium to disperse the RBWP and white cement particles used in this work. The slump flow of the plaster was also tested to maintain similar levels of workability. The tests were carried out according to Chinese national standard GB/T 2419-2005 (test method for fluidity of cement plaster). The fresh plaster was used to fill the cone mold, and it was spread and smoothed with the scraper to make it level with the top of the mold. Then, this mold was placed on the apparatus for fluidity testing, and the plaster took on a disc shape after being vibrated for 25 s. The diameter was measured in three different directions, and the plaster slump flow was determined. The plaster color was also determined in this work. A silicone rubber mold with 6 holes was used in this procedure, and the holes had dimensions of 70 mm × 150 mm × 5 mm. These holes were filled with plaster. The plaster samples were demolded after being cured for 1 d, and they were continuously cured at 20 ± 2 °C and a relative humidity exceeding 90% for up to 28 d. Then, the lights from the plasters were probed with a sensor for color measurement, and their colors were evaluated with the tristimulus values L*, a* and b*, which are represented in the chromatic space (Fig. 1). Two factors were considered, and L* and C* represent lightness and saturation, respectively. L* shows the variation between white (top), gray (center of the sphere) and black (bottom). The parameter C* is related to the color purity and is represented by a vector from the center to a point in the plane a*–b*. It can be determined with the following equation:
C* = a *2 + b *2
(1)
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In this equation, a* and b* are the tristimulus parameters. a* represents the color change from green to red; b* represents the color transformation from yellow to blue.
Fig. 1 Chromatic space and color system The water penetration of the plaster was also evaluated by the water absorption method. Water absorption was measured according to Chinese Building Material Industry Standard JC/T 1024-2007. The plasters were prepared in molds with dimensions 40 mm × 40 mm × 160 mm. The molded plasters were kept at 20 ± 2 °C and a relative humidity exceeding 90% for 5 d, and then they were removed from the molds. The four exposed surfaces were sealed with epoxy resin after these demolded plasters were continuously cured for 16 d. The sealed plasters were put in the same conditions and cured for 7 d. Then, their water absorption was tested for 30 min and 240 min. Three water absorption values for each plaster sample were recorded, and the average values were calculated. The water absorption values of the plasters were accepted if the three water absorption values did not exceed 90-110% of the average values. The mechanical strengths of different plasters were measured in this study. The plasters were cast in accordance with Chinese National Standard GB/T 17671-1999. Then, these 40 mm × 40 mm × 160 mm molded plasters were cured at 20 ± 2 °C and a relative humidity exceeding 90% for 5 d. Finally, their compressive and flexural strengths were determined after 4
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(2)
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the demolded plasters were continuously cured in the same conditions for 23 d. Three prismatic specimens were tested at every age, and six compressive strength values and three flexural strength values were acquired. Their average values were calculated, and the compressive and flexural strengths of the plasters were determined if the six compressive strength values and three flexural strength values did not exceed 90-110% of the average values. According to Chinese Building Material Industry Standard JC/T 1024-2007, steel plates were used in the testing of tensile bond strength. The plates had a thickness of 5 mm, and there were 10 holes with dimensions of 50 mm × 50 mm. Before casting, a plate was placed on a clean concrete board with the same dimensions as the plate. Plaster was then poured into these 10 holes and was spread and smoothed with a scraper to create a plaster thickness of 5 mm. These plasters were cured for 1 d and demolded and continuously cured for 26 d at 20 ± 2 °C and a relative humidity exceeding 90%. They were then bonded with to the steel plates with epoxy resin. The plates had dimensions of 50 mm × 50 mm × 2 mm. The plasters with steel plates were cured for 24 h, the maximum loads were tested, and the tensile bond strengths were determined by using equation (2). Ten tensile bond strength values were recorded for each plaster sample, and the average values were calculated. Tensile bond strength values were accepted if the ten tensile bond strengths did not exceed 90-110% of the average values.
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In this equation, P is the tensile bond strength; F is the maximum load; and S is the area of the stress-bearing surface of the plaster. S is a constant with a value of 2500 mm2. A D/max 2550 X-ray powder diffractometer (XRD) was used to identify the mineral phases of the RBWP and plaster that was cured for 28 d. The 2θ range was 10°~70°, in 0.02° steps, counting by 4 s per step. The radiation was CuKa at a wavelength of 0.1541 nm (40 kV). In these tests, the plaster samples were placed in ethyl alcohol to stop the hydration after they were hydrated for 28 d. The RBWP was a powder produced by grinding in a ball mill. A JEM-2100F high resolution transmission electron microscope (HRTEM) was used to identify the RBWP phase. The accelerating voltage was 200 kV. The plasters were placed in ethyl alcohol after they were hydrated for 28 d. Hydration was stopped, and the microstructures of the samples were studied. A Quanta 200 FEG field emission environmental scanning electron microscope (SEM) was used, and the accelerating voltage was 20 kV. The magnification was adjusted as needed. According to the toxicity characteristic leaching procedure (TCLP) stipulated in the synthetic precipitation leaching procedure (EPA method 1312, 1994) and Chinese National Standard GB 5085.3-2007, the leachabilities of heavy metals in the specimens were studied. The specimens (<5 mm) were agitated with glacial acetic acid buffer solution (pH = 2.88 ± 0.05) for 18 h at 25 °C, and the sample-to-fluid ratio was maintained at 1:20. The agitation frequency was kept at 130 r/min. After agitation, leachates were collected by using 0.8-mm glass fiber filters, and they were acidified with HNO3 to pH < 2.00 to preserve the samples. Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to determine the concentrations of the filtrates.
3. Results and discussion
3.1 Characteristics of Red Brick Waste Powder Table 1 shows the chemical components of RBWP. It has high proportions of SiO2 (64.2%) and Al2O3 (16.3%). Other components are present, such as Fe2O3 (6.55%) and CaO (1.28%). Its particle diameters are mainly distributed from 10-50 µm; the particles this range account for 85% of the material (as shown in Fig. 2). Fig. 3 illustrates the XRD pattern of RBWP. Quartz and hematite are the main mineral phases. The HRTEM was used to further investigate the RBWP phase characteristics. The morphology, selected area diffraction pattern and high-resolution lattice image of RBWP grains A and B are presented in Fig. 4A and B. The energy spectrum results of the selected areas are given in Table 4. Table 4 Energy spectrum results of the selected areas in grains A and B 5
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“1” region
“4” region
Elements Weight (%) Atomic (%) Elements Weight (%)
O 42.60 57.30 O 42.60
Mg 1.20 1.00 Mg -
Al 14.60 11.60 Al -
Si 36.70 28.10 Si 36.70
Fe 4.90 1.90 Fe -
Atomic (%)
57.30
-
-
28.10
-
5 a
b
4
RBWP Cement 3
2
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Quartz
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a
Hematite
a
1
0 0.1
1
10 100 Particel diameter (µm)
b
a
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a a
a
a
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a
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a
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Fig. 3 XRD pattern of RBWP
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Fig. 2 Particle size distributions of RBWP and cement
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Fig. 4 HRTEM morphology of RBWP powder The energy spectrum results for region “1” in grain A indicate that there are several elements, such as O, Mg, Al, Si and Fe. As shown in regions “2” and “3” of the high-resolution lattice image, the selected area diffraction patterns of the crystalline and amorphous phases were observed. The results show that in addition to the crystalline phase, there are some amorphous phases in RBWP. The energy spectrum results show that Si and O are the main elements of region “4,” and the atomic ratio of these two elements is 57.30:28.10. This atomic ratio is close to that of SiO2, which demonstrates that SiO2 is the main component of region “4.” In addition, region “4” has a typical selected area diffraction pattern for the amorphous phase (as shown in Fig 4B). Therefore, amorphous SiO2 also appears in RBWP, except for the crystalline phase.
3.2 Color The plasters were prepared with RBWP. Their colors were evaluated, and the color parameters are shown in Fig. 5. All color parameters changed with RBWP content. L* values gradually decreased with increasing RBWP content. The decorative plaster color gradually darkened as RBWP content increased. The parameters C*, a* and b* showed similar changes. Their values increased as more RBWP was included in the mix. The plaster color became more pure. RBWP adjusts 6
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L* a* b* C*
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RBWP1
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the plaster color much like the red pigments that are typically used for cement-based decorative plaster (Marmol et al., 2010). This is related to the presence of Fe2O3 in the RBWP. Although the RBWP can vary depending on the color, origin, raw material, type and properties of the red brick, Fe2O3 is always one of the main components, along with SiO2 and CaO (Demir and Orhan, 2003). Moreover, the requirements for plaster color vary and are usually not specified in detail (Marmol et al., 2010). This means that the colors of RBWP1, RBWP2, RBWP3, RBWP4 and RBWP5 all meet the engineering requirements. Therefore, it is feasible to prepare red cement-based decorative plaster with RBWP added as fine colored aggregates for staining.
RBWP2
RBWP3
RBWP4
RBWP5
Mortar
Fig. 5 Color parameters of mortar with RBWP
3.3 Water absorption
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The water absorption characteristics of plasters are given in Fig. 6. Pacheco-Torgal and Castro-Gomes (2006) reported that the water permeability of concrete also depends on aggregate physical properties. RBWP usually show a porous structure, and it is well known that it has noteworthy absorption water characteristics. Concrete prepared with RBWP as an aggregate shows very high water absorption (Jankovic et al., 2012). However, plaster with RBWP also shows a very slight increase in water absorption, which leads to the formation of a denser microstructure. RBWP does not remarkably affect the water resistance of plaster. The 30 min values did not exceed 1 g, and they were far lower than the limit specified by Chinese building industry standard JC/T 1024-2007. The plaster with 100% RBWP still provided good water resistance for the 30 min testing period. The plaster water absorption at 240 min also increased slightly. Plaster with 100% RBWP absorbs 1.07 g water in 240 min. This value is quite satisfactory, and it exceeds the corresponding value required for decorative plaster for walls. The plaster with RBWP still had good water resistance at 240 min. Large amounts of water cannot penetrate the plaster pores by capillary force to cause deterioration by chemical dissolution and transportation of soluble compounds.
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RBWP0
RBWP1 RBWP2 RBWP3 RBPW4 Mortar
Compressive strength Standard value for compressive strength Flexural strength Standard value for flexural strength
20
15
10
5
0
RBWP5
Fig. 6 Water absorption
RBWP0
RBWP1
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6
Compressive and flexural strength (MPa)
Water absorption at different time (g)
30 min Standard water absorption for 30 min 240 min Standard water absorption for 240 min
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RBWP3 RBWP4
Mortar
RBWP5
Fig. 7 Compressive and flexural strengths at 28 d
3.4 Compressive and flexural strengths
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Fig. 7 shows the compressive and flexural strengths of the plasters. As the figure shows, RBWP has a strong influence on the compressive and flexural strengths at 28 d. REP, HMCE and SHA were incorporated in all plasters. These have the effect of postponing cement hydration. Thus, RBWP0 had very low strength (Wang and Wang, 2013; Wang and Wang, 2011). However, sharp increases in compressive and flexural strengths were observed when more quartz sand was replaced with RBWP. The compressive and flexural strengths of plaster with 40% RBWP were up to 22.0 and 5.4 MPa. These values were far higher than the compressive and flexural strengths of the control samples. Even when 100% of the quartz sand was replaced with RBWP, the plaster still had higher compressive and flexural strengths than the control. The higher strengths are relevant to the RBWP filler and pozzolanic effects. Fig. 2 shows that the RBWP and cement have different particle size distributions. The larger RBWP particles fill the voids and pores and make the plaster microstructure denser. In addition, there are some amorphous phases in RBWP. These amorphous phases and active SiO2 are activated by the cement hydration product Ca(OH)2 (CH), which they then react with. The RBWP pozzolanic effect also comes into play. When more RBWP is blended, there are more amorphous phases and active SiO2 available. Thus, the pozzolanic reaction occurs to a greater extent, and more new hydration phases are formed. The plasters with RBWP display better compressive and flexural strengths than the control. However, in the end, each paste produces almost the same amount of CH for similar cement proportions, and more RBWP lowers the CH/SiO2 ratio (here, SiO2 refers to the reactive SiO2). The plaster strength is also related to the amount of water. RBWP3, RBWP4 and RBWP5 were mixed with more water, as shown in Table 3. Their water/cement ratios reach up to 0.722, 0.806 and 0.903. Therefore, although RBWP improves the compressive and flexural strengths, this improvement is weakened when more quartz sand is replaced by RBWP for the higher water/cement ratios. As a result, the compressive and flexural strengths of plasters with more RBWP, such as RBWP3, RBWP4 and RBWP5 are reduced (Naceri and Hamina, 2009; OFarrell et al., 2001; Jiang et al., 2015).
3.5 Tensile bond strength
Tensile bond strength is also one of the most important measures of mechanical performance for decorative plaster. Fig. 8 shows the tensile bond strengths of plasters cured for 28 d. The tensile bond strength of the control is compared with other samples. The results show that the tensile bond strength of the plaster varies with RBWP content. The plaster with 40% RBWP has the highest tensile bond strength. The plaster with 100% RBWP has the lowest tensile bond strength. Thus, the RBWP can be adjusted to maintain an appropriate tensile bond strength. However, excessive RBWP has adverse effects and reduces tensile bond strength. This reduction occurs because of the water absorption characteristics of RBWP. It is well known that the tensile bond strength of plaster is mainly related to the contributions of REP and the binding materials (Wang and Wang, 2013; Wang and Wang, 2011). However, RBWP absorbs water, and REP is absorbed along with water. This 8
ACCEPTED MANUSCRIPT bonding role is actually reduced. Thus, the tensile bond strength of the plaster is lowered to 0.57 MPa when 100% RBWP is used. Despite this case, the tensile bond strength of plaster with 100% RBWP still meets the requirements for decorative plaster for walls. The integrity and durability of the decorative region are maintained, and the long-term decorative effect of red plaster is also maintained.
Tensile bond strength Standard value for tensile bond strength
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0.8
0.4
0.0
RBWP2 RBWP3 RBWP4 RBWP5 Mortar Fig. 8 Tensile bond strengths of plasters cured for 28 d
RBWP0
RBWP1
3.6 X-ray diffractometry analysis A
a Ca(OH)2 b SiO2
RBWP5
d c
c C3S d C2S
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b
Intensity
a b
Intensity
b ab b b
b
RBWP3
RBWP2
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RBWP5 a RBWP4 RBWP3 RBWP2 RBWP1 RBWP0
RBWP1
dd cc
RBWP0
30
40 2Theta
50
60
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Intensity
RBWP4
70 10
15
d c
2028 30 32 34 36 38 40 17.0 2Theta
17.2
17.4
17.6 17.8 18.0 2 Theta (degree)
18.2
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Fig. 9 XRD patterns of hydrated plasters at 28 d The crystalline phase compositions of hardened plasters cured for 28 d were determined by XRD, and the XRD patterns are presented in Fig. 9. As shown in Fig. 9A, in addition to the characteristic peaks of SiO2, which is the main mineral composition of the quartz sand used in this study, the characteristic peaks of the cement hydration product CH are also found in all hardened plasters. As shown in Fig. 9B, the un-hydrated cement phases also appeared, such as C2S and C3S. Although the CH diffraction peak intensity at 18.007° is not directly proportional to the content of the crystalline phase, some important information can be obtained from comparisons of the relative intensities and the variations in intensity. Fig. 9C (XRD at this region was collected by step-scanning method with back pressing) shows that all hardened plasters have different peak intensities at 18.007°. RBWP0 has the strongest peak intensity. However, this peak intensity gradually decreases as the RBWP replacement ratio increases. This result implies that RBWP has a strong influence on CH content. This influence is associated with the RBWP pozzolanic effect. More amorphous phases and active SiO2 are introduced as 9
ACCEPTED MANUSCRIPT more RBWP is blended, and thus more CH is consumed for the pozzolanic reaction. Therefore, a decrease in peak intensity is observed, and different quantities of CH are consumed when different amounts of RBWP are added. RBWP0 has the highest CH content and strongest peak intensity because there were no pozzolanic components in RBWP0. The pozzolanic reactions in different pastes proceeded to different extents, and plasters with different RBWP content had different strengths. In addition, the efflorescence incurred by CH also was also limited for this reaction.
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3.7 SEM images
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3.8 Leachability
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Fig. 10 SEM images of plasters prepared with different concentrations of RBWP SEM images of hardened pastes prepared with different concentrations of RBWP are shown in Fig. 10. The quartz sand and cement hydration products, such as CH and calcium–silicate–hydrate (C-S-H) gel, are loosely gathered together, and all can be observed in the fracture surface micrograph of plaster without RBWP (shown in RBWP0-0). As shown in RBWP0-1, all of these substances can easily be found even at 400x magnification. The paste envelops the quartz, the structure becomes denser and it is difficult to find some loose regions at 1000x magnification (shown in RBWP1-0). The quartz sand and CH grow together with C-S-H gel when region A is magnified 4000 times (shown in RBWP1-1). The sheet-shaped CH is also found to be overlaid with the C-S-H gel (shown in RBWP2-0 and RBWP2-1). The same shapes for CH and C-S-H also appear in region C (shown in RBWP3-0). The quartz sand is closely surrounded by the C-S-H gel and other substances in the hydrated paste D (shown in RBWP3-1, magnifying morphology of region D). Quartz sand and CH are not found, as they are buried by the paste (shown in RBWP4-0). The C-S-H gel and RBWP are clumped together with other substances in the hydrated paste, and this morphology is shown in the RBWP4-1(magnifying the morphology of region E). The microstructure of RBWP5 is looser than that of others with RBWP (shown in RBWP5-0). The RBWP can be observed, and it crowds together with other substances (shown in RBWP5-1, the magnified region of F). However, its structure is obviously denser than that of the plaster without RBWP. RBWP can compact the plaster paste, and the plasters with RBWP have better compressive and flexural strengths. They show satisfactory water resistance.
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There are several easily leachable heavy metals in RBWP, such as Cr, Cd, Zn, Ni, Cu and Pb. These heavy metals may leak from the matrices and cause a potential threat to the surroundings. To prepare the red decorative plaster with RBWP in a safe way, the leachabilities of matrices are used as an important index to evaluate the adsorption behavior and immobilizing effect. TCLP tests were carried out for the crushed hardened plaster at 28 d, and the results are shown in Table 5. The results show that heavy metal leaching concentrations of the decorative plaster prepared with RBWP are far lower than the standard values stipulated in Chinese national standard GB5085.3-2007. The heavy metals are mainly immobilized or stabilized in the matrices by the hydration products C-S-H and ettringite (Li et al., 2012). C-S-H is the hydrated product of C3S and C2S. C3S and C2S are the main phases of White Portland cement and account for more than 90% of the total cement mass. Ettringite is the hydrated product of C3A and C4AF. However, these substances account for only 10% of the White Portland cement composition. Thus the heavy metals are mainly immobilized in matrices by the hydration product C-S-H. The heavy metal leaching concentrations are within the safe range, even though the hardened pastes were ground to particle sizes smaller than 5 mm, as in this TCLP test. Heavy metal leaching, in reality, is a slow and gradual process. Additionally, the hardened plaster usually cannot be ground into grains smaller than 5 mm. As a result, the heavy metals immobilized in the decorative plasters with RBWP are more reliable in the practical environment. The plaster does not threaten people's health or the environment 11
ACCEPTED MANUSCRIPT when RBWP is used. Table 5 Heavy metal leachability of plasters (mg/L) Cr Cd Zn Ni Cu 0.0105 0.0037 0.0048 0.0070 0.0400 0.0154 0.0041 0.0049 0.0081 0.0532 0.0160 0.0043 0.0052 0.0082 0.0564 0.0173 0.0047 0.0071 0.0081 0.0647 0.0201 0.0049 0.0083 0.0082 0.0724 0.0211 0.0051 0.0082 0.0079 0.0910 15 1 100 5 100
Pb 0.0021 0.0032 0.0037 0.0075 0.0085 0.0091 5
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Samples RBWP0 RBWP1 RBWP2 RBWP3 RBWP4 RBWP5 Standard value
3.9 Economic and Environmental analyses
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4. Conclusions
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In this work, all properties of the red decorative plasters, even the one prepared with 100% RBWP, satisfy the requirements of Chinese building material industry standard JC/T 1024-2007. Generally, approximately 1-3% red pigment is needed to produce red decorative plaster. RBWP adjusts the plaster color and saves red pigment, reducing costs by approximately 15 USD/m3. In China, the price of quartz sand, which is used to prepare the color plaster, is high, up to 0.1 USD per kg. The red brick waste has to be ground into powder with 200 ASTM mesh size, and the energy consumed in the grinding process contributes to the final cost. However, this cost is low compared with the cement clinker, quartz sand, fly ash and granulated blasted furnace slag because the brick waste has better grindability; the maximum cost is approximately 0.02 USD per kg (Bensted and Barnes, 2002). This cost is far lower than that of the quartz sand. 20, 40, 60, 80 and 100% quartz sand were replaced with RBWP in the production of red decorative plaster. Approximately 10, 20, 30, 40 and 50 USD /m3 cost were saved. Moreover, the plasters with 20, 40 and 60% RBWP had much better properties, such as compressive, flexural and tensile bond strength, compared to the control. The amount of cement needed was also reduced. In China, the cost of White cement is 0.8 USD per kg, which is higher than the cost of RBWP. These corresponding expenses can also be saved. Therefore, the production cost of decorative plaster will be greatly reduced by using RBWP. It is self-evident that RBWP utilization will also eliminate a potential threat to the environment and contribute to sustainable construction. In addition to this environmental benefit, the environmental burden resulting from pigment use will also be alleviated. Additionally, although RBWP grinding consumes energy, the energy used is far lower than that used to grind quartz sand and cement (Bensted and Barnes, 2002). The extraction of natural sand from rivers and sea beds also has a strong environmental impact (Rodrigues et al., 2013). This extraction causes changes to the beds. These changes may lead to the loss of balance between the coastal sand and sea bed sand, which could have dire consequences for the coast. Therefore, other environmental advantages are also obtained by reducing the use of quartz sand and cement. In several ways, it is environmentally friendly to use RBWP in the production of cement-based red decorative plaster for walls.
The use of RBWP in the production of cement-based red decorative plaster for walls was evaluated in this study. The important conclusions are summarized as follows: (1) RBWP can be used to adjust the cement-based decorative plaster color. This effect is related to the presence of Fe3+ in RBWP. (2) Plasters made with RBWP have satisfactory water resistance and denser microstructure. (3) The filler and pozzolanic effects contribute to the properties of the plaster, and the compressive and flexural strengths of plasters made with RBWP are improved. However, excessive RBWP leads to a decrease in the CH/SiO2 ratio in the paste and creates high requirements for water in the mixing of the paste. Thus, the compressive and flexural strengths of the plaster decrease as more RBWP is used in the production. (4) The addition of RBWP helps to maintain the tensile bond strength, but excessive RBWP has adverse effects on the tensile bond strength for RBWP absorption to REP. Nevertheless, plaster with 100% RBWP has satisfactory tensile 12
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bond strength. (5) The hydration and un-hydration phases of cement are found in the hardened paste. The CH content varies in different plasters, showing that the pozzolanic reaction proceeds to different extents. (6) RBWP increases the density of the plaster microstructure. The plaster with RBWP exhibits better performance. (7) As far as the economic and environmental benefits are concerned, it is feasible to use RBWP in the production of red cement-based decorative plaster. These facts show that red cement-based decorative plaster can be produced with RBWP. The economic and environmental analyses also show that the production costs of cement-based plaster will be reduced and that RBWP environmental impacts will be minimized. Moreover, plaster made with RBWP has better resistance to efflorescence for CH consumption. These results are important for the effective management and use of red brick waste in China and other developing countries.
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Acknowledgements
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The authors gratefully acknowledge the financial support provided by the National Basic Research Program of China (973 Program: 2011CB013805), the National Natural Science Foundation of China (No.51302189, 51578412 and 51308406), the National Key Project of Scientific and Technical Supporting Programs of China (No. 2014BAL03B02), the Fundamental Research Funds for the Central Universities, and the Key Laboratory of Advanced Civil Engineering Materials (Tongji University), Ministry of Education.
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Abbreviations
RBWP: red brick waste powder
REP: redispersible emulsion powder HMCE: hydroxypropyl-methyl cellulose ethers SHA: silicone hydrophobic agent LPSA: laser particle size analyzer XRD: X-ray powder diffractometer HRTEM: high resolution transmission electron microscope SEM: scanning electron microscope 14
ACCEPTED MANUSCRIPT TCLP: toxicity characteristic leaching procedure ICP-AES: inductively coupled plasma atomic emission spectrometer Na2O: sodium oxide MgO: magnesium oxide Al2O3: aluminum oxide SO3: sulfur trioxide
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K2O: potassium oxide CaO: calcium oxide SiO2: silicon dioxide Fe2O3: ferric oxide TiO2: titanium oxide MnO: manganese oxide
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SrO: strontium oxide CuO: copper oxide ZnO: zinc oxide NiO: nickel oxide Cr2O3: chromic oxide C-S-H: calcium–silicate– hydrate CH: calcium hydroxide, Ca(OH)2 ASTM: American Society for Testing Material C2S: dicalcium silicate C3S: tricalcium silicate
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C4AF: tetracalcium aluminoferrite USD: US dollar
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C3A: tricalcium aluminate
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PbO: lead oxide
15
ACCEPTED MANUSCRIPT Highlights ► Plaster color is well adjusted by red waste brick powder (RWBP) ► RWBP does not pose remarkable impact on the water resistance of plaster ► RWBP favorably improves the compressive and flexural strengths of plaster ► The tensile bond strength of plaster is related to the content of RWBP ► Calcium oxide content in hardened
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paste is various with the content of RWBP
S0959-6526(16)30628-X
DOI:
10.1016/j.jclepro.2016.05.149
Reference:
JCLP 7331
To appear in:
Journal of Cleaner Production
Received Date: 26 May 2015 Revised Date:
20 May 2016
Accepted Date: 23 May 2016
Please cite this article as: Li H, Dong L, Jiang Z, Yang X, Yang Z, Study on Utilization of Red Brick Waste Powder in the Production of Cement-based Red Decorative Plaster for Walls, Journal of Cleaner Production (2016), doi: 10.1016/j.jclepro.2016.05.149. 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.
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Study on Utilization of Red Brick Waste Powder in the Production of Cement-based Red Decorative Plaster for Walls Haoxin Li
Liuliu Dong
Zhengwu Jiang*
Xiaojie Yang
Zhenghong Yang
Key Laboratory of Advanced Civil Engineering Materials Ministry of Education, Tongji University, Shanghai, 201804, PR. China
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First author Tel./Fax: +86 21 69584723. E-mail addresses: [email protected] (H. Li)
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Corresponding author Tel./Fax: +86 21 69584723. E-mail addresses: [email protected] (Z. Jiang)
Abstract: Current management for red brick waste is insufficient, and a new method is needed. We sought to develop a
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new approach for effective management. Red cement-based decorative plasters were prepared with red brick waste powder (RBWP), white Portland cement, quartz sand, redispersible emulsion powder, hydroxypropyl-methyl cellulose ethers and silicone hydrophobic agent. The colors, water absorptions and strengths of different plasters were investigated, and the mechanisms responsible for their performance variations were explored by high-resolution transmission electron microscopy, X-ray powder diffractometry and scanning electron microscopy. The relative economic and environmental benefits were also analyzed. The feasibility of recycling RBWP in the production of cement-based red decorative plaster for walls was evaluated. The resulting plaster provided appropriate color adjustment, and the water resistance of the plaster was not greatly affected. The compressive and flexural strengths of plaster were improved. However, the improvement decreased as the sand replacement ratio increased. The tensile bond strength of the plaster is related to the RBWP content. More RBWP negatively affects the tensile bond strength of the plaster. Calcium hydroxide in the hardened paste varies with RBWP content. This variation correlates with the appearance and level of pozzolanic reaction in the plaster with RBWP. Plaster with RBWP has a denser microstructure than the control. In addition to the pozzolanic reaction, this denser microstructure also contributes to performance improvements such as compressive and flexural strengths. To improve the economic and environmental efficiencies, it is also feasible to recycle RBWP in the production of cement-based red decorative plaster for walls. These results demonstrate the effective use of red brick waste. They also provide a reference strategy for the management of red brick waste in other developing countries that are carrying out or will carry out urbanization activities.
Key words: Red Cement-based Decorative Plaster; Waste Red Brick; Strength; Water Absorption; Microstructure
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1 Introduction
In the past three decades, unprecedented urbanization has occurred in developing countries. The intense urbanization of recent decades has generated huge volumes of construction and demolition waste and has led to the excessive consumption of natural resources (Song et al., 2014). Demolition waste is responsible for approximately 30-40% of the total waste generated in the municipality (Villoria Saez et al., 2015; Ravindra et al., 2015). It has become a major environmental issue and has created pressure for authorities to manage waste in a more sustainable manner (Song et al., 2014; Coelho and de Brito, 2013; Coelho and de Brito, 2013a). In 2014, Chinese construction and demolition waste reached several billion tons. Chinese brick-making has a 2000-year history, and an incalculable number of red and gray bricks have been used in rural construction and building since 1900 (Wu et al., 2011). In recent years, rural reconstruction has accelerated, and many old brick-concrete houses were purposefully demolished in China. A great deal of brick waste has been generated, and approximately 0.4 billion tons of this waste is produced every year. In other developing countries such as India, Russia, and Brazil, great quantities of brick waste are also produced due to recent urbanization (Villoria Saez et al., 2015). The waste 1
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must be transported to appropriate disposal areas, which are often landfills. The disposal cost is greatly increased because of transport and because of the land requirements for ecological management of the waste. Additionally, dust is easily generated during the transport of the waste, which causes pollution of the surrounding environment. There is an urgent need to responsibly manage it. It has been suggested that the waste could be recycled to replace the natural aggregates in concrete production (Jankovic et al., 2012; Cachim, 2009; Yang et al., 2011) and self-compacting cement paste (Heikal et al., 2013). However, more brick waste leads to low workability, which makes it difficult to compact and finish the fresh concrete. In addition, the waste increases the permeability and physical shrinkage of the concrete, and it decreases the elastic modulus. As a result, such waste has not been widely used as a recycled aggregate. Other problems also prevent its use, such as impurities in the material, lack of knowledge about the behavior of concrete, and the limited available standards for the use of recycled aggregates. Studies have demonstrated that waste brick could be used as a pozzolanic material to prepare pozzolanic cement (Turanli et al., 2003), mortar (Naceri and Hamina, 2009) and concrete (Heikal et al., 2013; Ge et al., 2012). It improves the grinding efficiency of the clinker when it is recycled to produce the cement (Kaminskas et al., 2006). There are additional benefits such as cost reductions, energy savings, and improved ecological balance and conservation of natural resources. However, it delays the setting times. It reduces the alkali–silica reactions when used in the production of the cement-based mortar, self-compacting cement paste and concrete. Moreover, concrete with this material has a higher compressive strength than control concrete made with the optimum mixture ratio. However, it negatively affects the clinker mechanical properties. To provide the same strength as the control, the concrete has to be kept with a lower water cement ratio and more super-plasticizer has to be used in the mixing process. This incurs higher costs. The material has to be ground to a particle size of less than 0.06 mm, and the replacement ratio should not be more than 25%. These variables (particle size and replacement ratio) need to be highly controlled. This makes it challenging to prepare concrete with brick waste as the pozzolanic material. Asphalt mastic can also be prepared with brick powder as a mineral filler. This powder can have positive effects on asphalt mastic high-temperature properties, but it negatively affects the low temperature properties of asphalt mastic (Wu et al., 2011). In general, it is good to find other recycling methods for brick waste. The potential environmental liabilities of the brick waste will be alleviated, and the product will be diversified. Cement-based decorative plaster is an important building material. It has many advantages, such as natural quality, low cost, strong competitiveness and a desirable texture, in contrast with other ornamental materials such as paint and ceramic tile (Doroudiani and Omidian, 2010; Bartza and Filar, 2010). Thus, it is widely used in many developed countries to decorate walls in buildings. In its production, inorganic pigments, such as various colors of iron oxides, are commonly used to alter the plaster color. These pigments have low cost, better durability and alkali resistance (Lee et al., 2005; Marmol et al., 2010; Diamanti et al., 2013). Additionally, the mechanical properties of plasters are not affected by these inorganic pigments. However, their prices are high, generally about 1.5-6.5 USD per kg. Moreover, they are prepared from non-renewable resources. Most importantly, the construction industry is one of the best targets of solid waste reconversion due to the large amounts of raw materials it consumes and the large volume of final products in construction. Resources can be conserved by reusing the waste, which diversifies the production and reduces the final cost and also provides alternative raw materials for a number of building sectors (Lopez et al., 2009; Xuan et al., 2015; Li et al., 2012). For example, granite sludge waste can be recycled as a colored aggregate to produce cement-based colored decorative plaster (Marmol et al., 2010). Brick waste is typically red or gray because it contains many ferrum elements, and the ions of these ferrum elements are commonly red or gray. Red brick waste is red because it contains ions such as Fe3+. To maintain the required color and properties, silicon dioxide (SiO2), ferric oxide (Fe2O3) and calcium oxide (CaO) are used in brick, although the chemical components of brick vary in color, origin, variety, raw materials and properties (Demir and Orhan, 2003). Therefore, red brick waste can theoretically be used as an alternative source of red pigments or colored aggregates to produce cement-based red decorative plaster. The variations in chemical components do not prevent this. However, there are no reports describing the preparation of cement-based red decorative plaster with red brick waste. In addition, although there are reports in the literature, none of them properly evaluate the feasibility of recycling the red brick waste in the production of cement-based red decorative plaster. The main reason is that cement-based red decorative plaster pertains to the other system. The organic 2
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constituents such as redispersible emulsion powder (REP), hydroxypropyl-methyl cellulose ethers (HMCE) and silicone hydrophobic agent (SHA) have to be used along with cement in this system. In addition to compressive strength, the different properties are required, such as water absorption and tensile bond strength. There are important points that remain to be systematically studied because they play important roles in the effective use of red brick waste in colored plaster production. Therefore, cement-based red decorative plaster was prepared with red brick waste powder (RBWP) in the laboratory, and properties such as color, water absorption and strength were investigated based on the Chinese building material industry standard JC/T 1024-2007. The RBWP characteristics were discussed. The mineral components and microstructures of hardened plaster were observed, and the mechanisms of these property variations were explored. Heavy metal leaching from the hardened paste was also evaluated because of the appearance of heavy metals in the brick waste. Economic and environmental analyses were also carried out because brick waste had to be ground into powder for the study. The feasibility of using red brick waste powder in the production of cement-based red decorative plaster for walls was studied in this work.
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2 Experimental methods 2.1 Materials
Na2O 1.31 0.55
MgO 1.52 1.12
Al2O3 17.25 3.73
SiO2 67.95 21.34
SO3 0.17 3.48
K2 O 2.33 2.02
CaO 1.35 67.30
TiO2 1.03 0.20
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Oxides RBWP Cement
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Red brick waste was obtained from a demolition field. It was separated from the concrete and other building materials and ground in a centrifugal ball mill into 200 ASTM mesh size, which corresponds to common inorganic pigment. White Portland cement P.W 52.5 was also used to provide the background for the red cement-based decorative plaster. The chemical components of RBWP and white Portland cement are listed in Table 1. The mineralogical composition of white Portland cement is also given in Table 2. Quartz sand, REP (VINAPAS 5010N), HMCE (30000 Pa.s) and SHA (SEAL 80) are all commercial products. The main chemical component of quartz sand is SiO2, and its mass content is above 99.5%. The size of quartz sand is 100 ASTM mesh. Table 1 Chemical components of RBWP and white Portland cement (wt%) MnO 0.10 0.04
Fe2O3 6.93 0.15
SrO 0.02 0.07
CuO -
ZnO 0.01 -
PbO -
NiO -
Cr2O3 0.02 -
Table 2 Mineralogical composition of white Portland cement (wt%) Dicalcium silicate
Tricalcium aluminate
Tetracalcium aluminoferrite
(C3S)
(C2S)
(C3A)
(C4AF)
69.48
18.67
8.56
0.43
2.2 Mix designs
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Tricalcium silicate
Others 2.86
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To simplify the experiments and to easily analyze the effect of RBWP on the plaster properties, all plasters had the same cement content, REP, HMCE and SHA. They differed only in that different concentrations of RBWP were used to replace the quartz sand. RBWP1, RBWP2, RBWP3, RBWP4 and RBWP5, respectively, were plaster samples in which 20, 40, 60, 80 and 100% quartz sand were replaced by RBWP. Different amounts of mixing water were added to maintain a similar level of workability. All plasters received a similar slump flow of approximately 160±10 mm. The fresh plaster was put in a 5-L measuring cylinder and was spread and smoothed with a scraper to make the plaster level with the top of the measuring cylinder. Then, the total weight was measured. The measuring cylinder weight was subtracted from the total weight to determine the plaster weight. This was divided by the measuring cylinder volume (5 L), and the fresh plaster density was determined. RBWP has a lower density than quartz sand, the plaster density decreases with increasing RBWP. The detailed mix designs, water/cement ratios, slump flows and densities of all plasters are given in Table 3. Table 3 Detailed mix designs of all plasters Plasters Cement REP HMCE SHA Sand RBWP Water/cement Slump flow Density (mm) (kg/m3) (wt%) RBWP0 30.0 5.0 0.2 0.9 63.9 0.0 162 1963 0.625 3
ACCEPTED MANUSCRIPT RBWP1 RBWP2 RBWP3 RBWP4 RBWP5
30.0 30.0 30.0 30.0 30.0
5.0 5.0 5.0 5.0 5.0
0.2 0.2 0.2 0.2 0.2
0.9 0.9 0.9 0.9 0.9
51.1 38.3 25.6 12.8 0.0
12.8 25.6 38.3 51.1 63.9
159 160 158 162 159
0.653 0.681 0.722 0.806 0.903
1916 1869 1828 1807 1792
2.3 Methods
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Particle size distributions of RBWP and white cement were analyzed on an LS230 Laser particle size analyzer (LPSA). Ethyl alcohol was used as the medium to disperse the RBWP and white cement particles used in this work. The slump flow of the plaster was also tested to maintain similar levels of workability. The tests were carried out according to Chinese national standard GB/T 2419-2005 (test method for fluidity of cement plaster). The fresh plaster was used to fill the cone mold, and it was spread and smoothed with the scraper to make it level with the top of the mold. Then, this mold was placed on the apparatus for fluidity testing, and the plaster took on a disc shape after being vibrated for 25 s. The diameter was measured in three different directions, and the plaster slump flow was determined. The plaster color was also determined in this work. A silicone rubber mold with 6 holes was used in this procedure, and the holes had dimensions of 70 mm × 150 mm × 5 mm. These holes were filled with plaster. The plaster samples were demolded after being cured for 1 d, and they were continuously cured at 20 ± 2 °C and a relative humidity exceeding 90% for up to 28 d. Then, the lights from the plasters were probed with a sensor for color measurement, and their colors were evaluated with the tristimulus values L*, a* and b*, which are represented in the chromatic space (Fig. 1). Two factors were considered, and L* and C* represent lightness and saturation, respectively. L* shows the variation between white (top), gray (center of the sphere) and black (bottom). The parameter C* is related to the color purity and is represented by a vector from the center to a point in the plane a*–b*. It can be determined with the following equation:
C* = a *2 + b *2
(1)
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In this equation, a* and b* are the tristimulus parameters. a* represents the color change from green to red; b* represents the color transformation from yellow to blue.
Fig. 1 Chromatic space and color system The water penetration of the plaster was also evaluated by the water absorption method. Water absorption was measured according to Chinese Building Material Industry Standard JC/T 1024-2007. The plasters were prepared in molds with dimensions 40 mm × 40 mm × 160 mm. The molded plasters were kept at 20 ± 2 °C and a relative humidity exceeding 90% for 5 d, and then they were removed from the molds. The four exposed surfaces were sealed with epoxy resin after these demolded plasters were continuously cured for 16 d. The sealed plasters were put in the same conditions and cured for 7 d. Then, their water absorption was tested for 30 min and 240 min. Three water absorption values for each plaster sample were recorded, and the average values were calculated. The water absorption values of the plasters were accepted if the three water absorption values did not exceed 90-110% of the average values. The mechanical strengths of different plasters were measured in this study. The plasters were cast in accordance with Chinese National Standard GB/T 17671-1999. Then, these 40 mm × 40 mm × 160 mm molded plasters were cured at 20 ± 2 °C and a relative humidity exceeding 90% for 5 d. Finally, their compressive and flexural strengths were determined after 4
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the demolded plasters were continuously cured in the same conditions for 23 d. Three prismatic specimens were tested at every age, and six compressive strength values and three flexural strength values were acquired. Their average values were calculated, and the compressive and flexural strengths of the plasters were determined if the six compressive strength values and three flexural strength values did not exceed 90-110% of the average values. According to Chinese Building Material Industry Standard JC/T 1024-2007, steel plates were used in the testing of tensile bond strength. The plates had a thickness of 5 mm, and there were 10 holes with dimensions of 50 mm × 50 mm. Before casting, a plate was placed on a clean concrete board with the same dimensions as the plate. Plaster was then poured into these 10 holes and was spread and smoothed with a scraper to create a plaster thickness of 5 mm. These plasters were cured for 1 d and demolded and continuously cured for 26 d at 20 ± 2 °C and a relative humidity exceeding 90%. They were then bonded with to the steel plates with epoxy resin. The plates had dimensions of 50 mm × 50 mm × 2 mm. The plasters with steel plates were cured for 24 h, the maximum loads were tested, and the tensile bond strengths were determined by using equation (2). Ten tensile bond strength values were recorded for each plaster sample, and the average values were calculated. Tensile bond strength values were accepted if the ten tensile bond strengths did not exceed 90-110% of the average values.
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In this equation, P is the tensile bond strength; F is the maximum load; and S is the area of the stress-bearing surface of the plaster. S is a constant with a value of 2500 mm2. A D/max 2550 X-ray powder diffractometer (XRD) was used to identify the mineral phases of the RBWP and plaster that was cured for 28 d. The 2θ range was 10°~70°, in 0.02° steps, counting by 4 s per step. The radiation was CuKa at a wavelength of 0.1541 nm (40 kV). In these tests, the plaster samples were placed in ethyl alcohol to stop the hydration after they were hydrated for 28 d. The RBWP was a powder produced by grinding in a ball mill. A JEM-2100F high resolution transmission electron microscope (HRTEM) was used to identify the RBWP phase. The accelerating voltage was 200 kV. The plasters were placed in ethyl alcohol after they were hydrated for 28 d. Hydration was stopped, and the microstructures of the samples were studied. A Quanta 200 FEG field emission environmental scanning electron microscope (SEM) was used, and the accelerating voltage was 20 kV. The magnification was adjusted as needed. According to the toxicity characteristic leaching procedure (TCLP) stipulated in the synthetic precipitation leaching procedure (EPA method 1312, 1994) and Chinese National Standard GB 5085.3-2007, the leachabilities of heavy metals in the specimens were studied. The specimens (<5 mm) were agitated with glacial acetic acid buffer solution (pH = 2.88 ± 0.05) for 18 h at 25 °C, and the sample-to-fluid ratio was maintained at 1:20. The agitation frequency was kept at 130 r/min. After agitation, leachates were collected by using 0.8-mm glass fiber filters, and they were acidified with HNO3 to pH < 2.00 to preserve the samples. Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to determine the concentrations of the filtrates.
3. Results and discussion
3.1 Characteristics of Red Brick Waste Powder Table 1 shows the chemical components of RBWP. It has high proportions of SiO2 (64.2%) and Al2O3 (16.3%). Other components are present, such as Fe2O3 (6.55%) and CaO (1.28%). Its particle diameters are mainly distributed from 10-50 µm; the particles this range account for 85% of the material (as shown in Fig. 2). Fig. 3 illustrates the XRD pattern of RBWP. Quartz and hematite are the main mineral phases. The HRTEM was used to further investigate the RBWP phase characteristics. The morphology, selected area diffraction pattern and high-resolution lattice image of RBWP grains A and B are presented in Fig. 4A and B. The energy spectrum results of the selected areas are given in Table 4. Table 4 Energy spectrum results of the selected areas in grains A and B 5
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“1” region
“4” region
Elements Weight (%) Atomic (%) Elements Weight (%)
O 42.60 57.30 O 42.60
Mg 1.20 1.00 Mg -
Al 14.60 11.60 Al -
Si 36.70 28.10 Si 36.70
Fe 4.90 1.90 Fe -
Atomic (%)
57.30
-
-
28.10
-
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b
4
RBWP Cement 3
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a
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Fig. 3 XRD pattern of RBWP
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Fig. 2 Particle size distributions of RBWP and cement
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Fig. 4 HRTEM morphology of RBWP powder The energy spectrum results for region “1” in grain A indicate that there are several elements, such as O, Mg, Al, Si and Fe. As shown in regions “2” and “3” of the high-resolution lattice image, the selected area diffraction patterns of the crystalline and amorphous phases were observed. The results show that in addition to the crystalline phase, there are some amorphous phases in RBWP. The energy spectrum results show that Si and O are the main elements of region “4,” and the atomic ratio of these two elements is 57.30:28.10. This atomic ratio is close to that of SiO2, which demonstrates that SiO2 is the main component of region “4.” In addition, region “4” has a typical selected area diffraction pattern for the amorphous phase (as shown in Fig 4B). Therefore, amorphous SiO2 also appears in RBWP, except for the crystalline phase.
3.2 Color The plasters were prepared with RBWP. Their colors were evaluated, and the color parameters are shown in Fig. 5. All color parameters changed with RBWP content. L* values gradually decreased with increasing RBWP content. The decorative plaster color gradually darkened as RBWP content increased. The parameters C*, a* and b* showed similar changes. Their values increased as more RBWP was included in the mix. The plaster color became more pure. RBWP adjusts 6
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the plaster color much like the red pigments that are typically used for cement-based decorative plaster (Marmol et al., 2010). This is related to the presence of Fe2O3 in the RBWP. Although the RBWP can vary depending on the color, origin, raw material, type and properties of the red brick, Fe2O3 is always one of the main components, along with SiO2 and CaO (Demir and Orhan, 2003). Moreover, the requirements for plaster color vary and are usually not specified in detail (Marmol et al., 2010). This means that the colors of RBWP1, RBWP2, RBWP3, RBWP4 and RBWP5 all meet the engineering requirements. Therefore, it is feasible to prepare red cement-based decorative plaster with RBWP added as fine colored aggregates for staining.
RBWP2
RBWP3
RBWP4
RBWP5
Mortar
Fig. 5 Color parameters of mortar with RBWP
3.3 Water absorption
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The water absorption characteristics of plasters are given in Fig. 6. Pacheco-Torgal and Castro-Gomes (2006) reported that the water permeability of concrete also depends on aggregate physical properties. RBWP usually show a porous structure, and it is well known that it has noteworthy absorption water characteristics. Concrete prepared with RBWP as an aggregate shows very high water absorption (Jankovic et al., 2012). However, plaster with RBWP also shows a very slight increase in water absorption, which leads to the formation of a denser microstructure. RBWP does not remarkably affect the water resistance of plaster. The 30 min values did not exceed 1 g, and they were far lower than the limit specified by Chinese building industry standard JC/T 1024-2007. The plaster with 100% RBWP still provided good water resistance for the 30 min testing period. The plaster water absorption at 240 min also increased slightly. Plaster with 100% RBWP absorbs 1.07 g water in 240 min. This value is quite satisfactory, and it exceeds the corresponding value required for decorative plaster for walls. The plaster with RBWP still had good water resistance at 240 min. Large amounts of water cannot penetrate the plaster pores by capillary force to cause deterioration by chemical dissolution and transportation of soluble compounds.
7
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5 4 3 2 1 0
RBWP0
RBWP1 RBWP2 RBWP3 RBPW4 Mortar
Compressive strength Standard value for compressive strength Flexural strength Standard value for flexural strength
20
15
10
5
0
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Fig. 6 Water absorption
RBWP0
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6
Compressive and flexural strength (MPa)
Water absorption at different time (g)
30 min Standard water absorption for 30 min 240 min Standard water absorption for 240 min
RBWP2
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RBWP3 RBWP4
Mortar
RBWP5
Fig. 7 Compressive and flexural strengths at 28 d
3.4 Compressive and flexural strengths
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Fig. 7 shows the compressive and flexural strengths of the plasters. As the figure shows, RBWP has a strong influence on the compressive and flexural strengths at 28 d. REP, HMCE and SHA were incorporated in all plasters. These have the effect of postponing cement hydration. Thus, RBWP0 had very low strength (Wang and Wang, 2013; Wang and Wang, 2011). However, sharp increases in compressive and flexural strengths were observed when more quartz sand was replaced with RBWP. The compressive and flexural strengths of plaster with 40% RBWP were up to 22.0 and 5.4 MPa. These values were far higher than the compressive and flexural strengths of the control samples. Even when 100% of the quartz sand was replaced with RBWP, the plaster still had higher compressive and flexural strengths than the control. The higher strengths are relevant to the RBWP filler and pozzolanic effects. Fig. 2 shows that the RBWP and cement have different particle size distributions. The larger RBWP particles fill the voids and pores and make the plaster microstructure denser. In addition, there are some amorphous phases in RBWP. These amorphous phases and active SiO2 are activated by the cement hydration product Ca(OH)2 (CH), which they then react with. The RBWP pozzolanic effect also comes into play. When more RBWP is blended, there are more amorphous phases and active SiO2 available. Thus, the pozzolanic reaction occurs to a greater extent, and more new hydration phases are formed. The plasters with RBWP display better compressive and flexural strengths than the control. However, in the end, each paste produces almost the same amount of CH for similar cement proportions, and more RBWP lowers the CH/SiO2 ratio (here, SiO2 refers to the reactive SiO2). The plaster strength is also related to the amount of water. RBWP3, RBWP4 and RBWP5 were mixed with more water, as shown in Table 3. Their water/cement ratios reach up to 0.722, 0.806 and 0.903. Therefore, although RBWP improves the compressive and flexural strengths, this improvement is weakened when more quartz sand is replaced by RBWP for the higher water/cement ratios. As a result, the compressive and flexural strengths of plasters with more RBWP, such as RBWP3, RBWP4 and RBWP5 are reduced (Naceri and Hamina, 2009; OFarrell et al., 2001; Jiang et al., 2015).
3.5 Tensile bond strength
Tensile bond strength is also one of the most important measures of mechanical performance for decorative plaster. Fig. 8 shows the tensile bond strengths of plasters cured for 28 d. The tensile bond strength of the control is compared with other samples. The results show that the tensile bond strength of the plaster varies with RBWP content. The plaster with 40% RBWP has the highest tensile bond strength. The plaster with 100% RBWP has the lowest tensile bond strength. Thus, the RBWP can be adjusted to maintain an appropriate tensile bond strength. However, excessive RBWP has adverse effects and reduces tensile bond strength. This reduction occurs because of the water absorption characteristics of RBWP. It is well known that the tensile bond strength of plaster is mainly related to the contributions of REP and the binding materials (Wang and Wang, 2013; Wang and Wang, 2011). However, RBWP absorbs water, and REP is absorbed along with water. This 8
ACCEPTED MANUSCRIPT bonding role is actually reduced. Thus, the tensile bond strength of the plaster is lowered to 0.57 MPa when 100% RBWP is used. Despite this case, the tensile bond strength of plaster with 100% RBWP still meets the requirements for decorative plaster for walls. The integrity and durability of the decorative region are maintained, and the long-term decorative effect of red plaster is also maintained.
Tensile bond strength Standard value for tensile bond strength
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1.2
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0.8
0.4
0.0
RBWP2 RBWP3 RBWP4 RBWP5 Mortar Fig. 8 Tensile bond strengths of plasters cured for 28 d
RBWP0
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3.6 X-ray diffractometry analysis A
a Ca(OH)2 b SiO2
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d c
c C3S d C2S
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b
b
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a b
Intensity
b ab b b
b
RBWP3
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dd cc
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40 2Theta
50
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70 10
15
d c
2028 30 32 34 36 38 40 17.0 2Theta
17.2
17.4
17.6 17.8 18.0 2 Theta (degree)
18.2
18.4
Fig. 9 XRD patterns of hydrated plasters at 28 d The crystalline phase compositions of hardened plasters cured for 28 d were determined by XRD, and the XRD patterns are presented in Fig. 9. As shown in Fig. 9A, in addition to the characteristic peaks of SiO2, which is the main mineral composition of the quartz sand used in this study, the characteristic peaks of the cement hydration product CH are also found in all hardened plasters. As shown in Fig. 9B, the un-hydrated cement phases also appeared, such as C2S and C3S. Although the CH diffraction peak intensity at 18.007° is not directly proportional to the content of the crystalline phase, some important information can be obtained from comparisons of the relative intensities and the variations in intensity. Fig. 9C (XRD at this region was collected by step-scanning method with back pressing) shows that all hardened plasters have different peak intensities at 18.007°. RBWP0 has the strongest peak intensity. However, this peak intensity gradually decreases as the RBWP replacement ratio increases. This result implies that RBWP has a strong influence on CH content. This influence is associated with the RBWP pozzolanic effect. More amorphous phases and active SiO2 are introduced as 9
ACCEPTED MANUSCRIPT more RBWP is blended, and thus more CH is consumed for the pozzolanic reaction. Therefore, a decrease in peak intensity is observed, and different quantities of CH are consumed when different amounts of RBWP are added. RBWP0 has the highest CH content and strongest peak intensity because there were no pozzolanic components in RBWP0. The pozzolanic reactions in different pastes proceeded to different extents, and plasters with different RBWP content had different strengths. In addition, the efflorescence incurred by CH also was also limited for this reaction.
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3.7 SEM images
(RBWP0-1)
(RBWP1-0)
(RBWP2-0)
(RBWP2-1)
(RBWP3-1)
(RBWP4-0)
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3.8 Leachability
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Fig. 10 SEM images of plasters prepared with different concentrations of RBWP SEM images of hardened pastes prepared with different concentrations of RBWP are shown in Fig. 10. The quartz sand and cement hydration products, such as CH and calcium–silicate–hydrate (C-S-H) gel, are loosely gathered together, and all can be observed in the fracture surface micrograph of plaster without RBWP (shown in RBWP0-0). As shown in RBWP0-1, all of these substances can easily be found even at 400x magnification. The paste envelops the quartz, the structure becomes denser and it is difficult to find some loose regions at 1000x magnification (shown in RBWP1-0). The quartz sand and CH grow together with C-S-H gel when region A is magnified 4000 times (shown in RBWP1-1). The sheet-shaped CH is also found to be overlaid with the C-S-H gel (shown in RBWP2-0 and RBWP2-1). The same shapes for CH and C-S-H also appear in region C (shown in RBWP3-0). The quartz sand is closely surrounded by the C-S-H gel and other substances in the hydrated paste D (shown in RBWP3-1, magnifying morphology of region D). Quartz sand and CH are not found, as they are buried by the paste (shown in RBWP4-0). The C-S-H gel and RBWP are clumped together with other substances in the hydrated paste, and this morphology is shown in the RBWP4-1(magnifying the morphology of region E). The microstructure of RBWP5 is looser than that of others with RBWP (shown in RBWP5-0). The RBWP can be observed, and it crowds together with other substances (shown in RBWP5-1, the magnified region of F). However, its structure is obviously denser than that of the plaster without RBWP. RBWP can compact the plaster paste, and the plasters with RBWP have better compressive and flexural strengths. They show satisfactory water resistance.
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There are several easily leachable heavy metals in RBWP, such as Cr, Cd, Zn, Ni, Cu and Pb. These heavy metals may leak from the matrices and cause a potential threat to the surroundings. To prepare the red decorative plaster with RBWP in a safe way, the leachabilities of matrices are used as an important index to evaluate the adsorption behavior and immobilizing effect. TCLP tests were carried out for the crushed hardened plaster at 28 d, and the results are shown in Table 5. The results show that heavy metal leaching concentrations of the decorative plaster prepared with RBWP are far lower than the standard values stipulated in Chinese national standard GB5085.3-2007. The heavy metals are mainly immobilized or stabilized in the matrices by the hydration products C-S-H and ettringite (Li et al., 2012). C-S-H is the hydrated product of C3S and C2S. C3S and C2S are the main phases of White Portland cement and account for more than 90% of the total cement mass. Ettringite is the hydrated product of C3A and C4AF. However, these substances account for only 10% of the White Portland cement composition. Thus the heavy metals are mainly immobilized in matrices by the hydration product C-S-H. The heavy metal leaching concentrations are within the safe range, even though the hardened pastes were ground to particle sizes smaller than 5 mm, as in this TCLP test. Heavy metal leaching, in reality, is a slow and gradual process. Additionally, the hardened plaster usually cannot be ground into grains smaller than 5 mm. As a result, the heavy metals immobilized in the decorative plasters with RBWP are more reliable in the practical environment. The plaster does not threaten people's health or the environment 11
ACCEPTED MANUSCRIPT when RBWP is used. Table 5 Heavy metal leachability of plasters (mg/L) Cr Cd Zn Ni Cu 0.0105 0.0037 0.0048 0.0070 0.0400 0.0154 0.0041 0.0049 0.0081 0.0532 0.0160 0.0043 0.0052 0.0082 0.0564 0.0173 0.0047 0.0071 0.0081 0.0647 0.0201 0.0049 0.0083 0.0082 0.0724 0.0211 0.0051 0.0082 0.0079 0.0910 15 1 100 5 100
Pb 0.0021 0.0032 0.0037 0.0075 0.0085 0.0091 5
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Samples RBWP0 RBWP1 RBWP2 RBWP3 RBWP4 RBWP5 Standard value
3.9 Economic and Environmental analyses
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4. Conclusions
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In this work, all properties of the red decorative plasters, even the one prepared with 100% RBWP, satisfy the requirements of Chinese building material industry standard JC/T 1024-2007. Generally, approximately 1-3% red pigment is needed to produce red decorative plaster. RBWP adjusts the plaster color and saves red pigment, reducing costs by approximately 15 USD/m3. In China, the price of quartz sand, which is used to prepare the color plaster, is high, up to 0.1 USD per kg. The red brick waste has to be ground into powder with 200 ASTM mesh size, and the energy consumed in the grinding process contributes to the final cost. However, this cost is low compared with the cement clinker, quartz sand, fly ash and granulated blasted furnace slag because the brick waste has better grindability; the maximum cost is approximately 0.02 USD per kg (Bensted and Barnes, 2002). This cost is far lower than that of the quartz sand. 20, 40, 60, 80 and 100% quartz sand were replaced with RBWP in the production of red decorative plaster. Approximately 10, 20, 30, 40 and 50 USD /m3 cost were saved. Moreover, the plasters with 20, 40 and 60% RBWP had much better properties, such as compressive, flexural and tensile bond strength, compared to the control. The amount of cement needed was also reduced. In China, the cost of White cement is 0.8 USD per kg, which is higher than the cost of RBWP. These corresponding expenses can also be saved. Therefore, the production cost of decorative plaster will be greatly reduced by using RBWP. It is self-evident that RBWP utilization will also eliminate a potential threat to the environment and contribute to sustainable construction. In addition to this environmental benefit, the environmental burden resulting from pigment use will also be alleviated. Additionally, although RBWP grinding consumes energy, the energy used is far lower than that used to grind quartz sand and cement (Bensted and Barnes, 2002). The extraction of natural sand from rivers and sea beds also has a strong environmental impact (Rodrigues et al., 2013). This extraction causes changes to the beds. These changes may lead to the loss of balance between the coastal sand and sea bed sand, which could have dire consequences for the coast. Therefore, other environmental advantages are also obtained by reducing the use of quartz sand and cement. In several ways, it is environmentally friendly to use RBWP in the production of cement-based red decorative plaster for walls.
The use of RBWP in the production of cement-based red decorative plaster for walls was evaluated in this study. The important conclusions are summarized as follows: (1) RBWP can be used to adjust the cement-based decorative plaster color. This effect is related to the presence of Fe3+ in RBWP. (2) Plasters made with RBWP have satisfactory water resistance and denser microstructure. (3) The filler and pozzolanic effects contribute to the properties of the plaster, and the compressive and flexural strengths of plasters made with RBWP are improved. However, excessive RBWP leads to a decrease in the CH/SiO2 ratio in the paste and creates high requirements for water in the mixing of the paste. Thus, the compressive and flexural strengths of the plaster decrease as more RBWP is used in the production. (4) The addition of RBWP helps to maintain the tensile bond strength, but excessive RBWP has adverse effects on the tensile bond strength for RBWP absorption to REP. Nevertheless, plaster with 100% RBWP has satisfactory tensile 12
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bond strength. (5) The hydration and un-hydration phases of cement are found in the hardened paste. The CH content varies in different plasters, showing that the pozzolanic reaction proceeds to different extents. (6) RBWP increases the density of the plaster microstructure. The plaster with RBWP exhibits better performance. (7) As far as the economic and environmental benefits are concerned, it is feasible to use RBWP in the production of red cement-based decorative plaster. These facts show that red cement-based decorative plaster can be produced with RBWP. The economic and environmental analyses also show that the production costs of cement-based plaster will be reduced and that RBWP environmental impacts will be minimized. Moreover, plaster made with RBWP has better resistance to efflorescence for CH consumption. These results are important for the effective management and use of red brick waste in China and other developing countries.
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Acknowledgements
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The authors gratefully acknowledge the financial support provided by the National Basic Research Program of China (973 Program: 2011CB013805), the National Natural Science Foundation of China (No.51302189, 51578412 and 51308406), the National Key Project of Scientific and Technical Supporting Programs of China (No. 2014BAL03B02), the Fundamental Research Funds for the Central Universities, and the Key Laboratory of Advanced Civil Engineering Materials (Tongji University), Ministry of Education.
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Abbreviations
RBWP: red brick waste powder
REP: redispersible emulsion powder HMCE: hydroxypropyl-methyl cellulose ethers SHA: silicone hydrophobic agent LPSA: laser particle size analyzer XRD: X-ray powder diffractometer HRTEM: high resolution transmission electron microscope SEM: scanning electron microscope 14
ACCEPTED MANUSCRIPT TCLP: toxicity characteristic leaching procedure ICP-AES: inductively coupled plasma atomic emission spectrometer Na2O: sodium oxide MgO: magnesium oxide Al2O3: aluminum oxide SO3: sulfur trioxide
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K2O: potassium oxide CaO: calcium oxide SiO2: silicon dioxide Fe2O3: ferric oxide TiO2: titanium oxide MnO: manganese oxide
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SrO: strontium oxide CuO: copper oxide ZnO: zinc oxide NiO: nickel oxide Cr2O3: chromic oxide C-S-H: calcium–silicate– hydrate CH: calcium hydroxide, Ca(OH)2 ASTM: American Society for Testing Material C2S: dicalcium silicate C3S: tricalcium silicate
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C4AF: tetracalcium aluminoferrite USD: US dollar
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C3A: tricalcium aluminate
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PbO: lead oxide
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ACCEPTED MANUSCRIPT Highlights ► Plaster color is well adjusted by red waste brick powder (RWBP) ► RWBP does not pose remarkable impact on the water resistance of plaster ► RWBP favorably improves the compressive and flexural strengths of plaster ► The tensile bond strength of plaster is related to the content of RWBP ► Calcium oxide content in hardened
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paste is various with the content of RWBP