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Alkali-activated building materials made with recycled construction and demolition wastes
Construction and Building Materials 149 (2017) 130–138
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Alkali-activated building materials made with recycled construction and demolition wastes Rafael Andrés Robayo-Salazar, Jhonathan Fernando Rivera, Ruby Mejía de Gutiérrez ⇑ Composites Materials Group (GMC-CENM), Universidad del Valle, Cali, Colombia
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Alkali-activated cements (AACs)
based on construction wastes (CDW) are obtained. High compressive strengths of up to 102 MPa were obtained for AACs. Blocks, pavers, roof tiles and tiles (building materials) were made from AACs. The recycled of CDW through ‘‘Alkali activation technology” were demonstrate.
a r t i c l e
i n f o
Article history: Received 27 February 2017 Received in revised form 7 May 2017 Accepted 12 May 2017 Available online 19 May 2017 Keywords: Construction and demolition wastes Red clay brick waste Concrete waste Glass waste Alkali-activated cements Geopolymers Recycling materials
a b s t r a c t The goal of this study was to test the viability of using red clay brick waste (RCBW), concrete waste (CW) and glass waste (GW) to produce alkali-activated cements (AACs) that can be used to fabricate blocks, pavers, roof tiles and tiles. The alkaline activators used were solutions of either NaOH or NaOH and waterglass. Ordinary Portland cement (OPC) was mixed with RCBW and CW in proportions of up to 30% to create hybrid cements. The AACs obtained with the RCBW, the CW and the GW exhibited maximum compressive strengths (28 days) of 102, 33 and 57 MPa, respectively. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction The construction industry is considered one of the most influential sectors for improving the socioeconomic conditions of developing countries, and its dynamism is driven by the demand for housing and civil infrastructure. However, one of the consequences ⇑ Corresponding author. E-mail address: [email protected] (R. Mejía de Gutiérrez). http://dx.doi.org/10.1016/j.conbuildmat.2017.05.122 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.
of high demand is the generation of considerable volumes of waste, which have become a significant environmental problem, representing up to 30% of the solid waste generated globally. The search for sustainable solutions that exploit materials from construction industry waste (e.g., brick, glass, ceramics and concrete) is currently an urgent challenge for this sector [1–3]. Generally, construction and demolition waste (CDW) can be divided into three groups, depending on their origin: waste generated during the construction of new buildings, waste originating
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from the renovation and demolition of infrastructure (e.g., buildings, bridges and roads), including natural disasters and military conflicts, and waste originating from the ceramics industry (e.g., white and red clay) [2]. The largest producers of CDW are China, the U.S. and certain European countries, which generate more than 605.5 million tonnes per year [4–6]. It is estimated that approximately 54% of this waste comprises ceramic materials (i.e., bricks, tiles and other forms), and 12% is concrete [7]. Moreover, the ceramics industry discards approximately 3–7% of its production [8] despite the use of automation and monitoring in the production processes. For reference, the global production of brick red clay is approximately 1500 billion units per year [9,10]. In certain EU countries such as Germany, Denmark and the Netherlands, nearly 80% of CDW is reused, whereas in most other countries the rate is closer to 30% [11]. The EU directive 2008/98/CE (article 11.2.b) mandates a minimum reuse rate of 70% (by weight) of CDW before 2020 [12]. In Latin America, countries such as Brazil and Mexico have begun to implement processes for the production of recycled concrete aggregates. CDW consists mainly of siliceous-aluminous materials (SiO2 and Al2O3). Therefore, the alkaline activation process is considered a viable alternative for the increased use of this fraction (>75%) of the CDW. This process has been demonstrated to be highly practical for transforming industrial waste and by-products with suitable characteristics into useful materials. Puertas et al. [13] evaluated the use of residues from ceramic floor tile produced with red and white clays for geopolymeric cements, where the residue was activated with NaOH and waterglass (Na2OnSiO2mH2O). The authors reported that samples cured for 8 days exhibited compressive and flexural strengths of 13 and 4 MPa, respectively. Allahverdi and Kani [14] developed a cement using waste from a brick production plant and activated it with NaOH in proportion of 8% Na2O with respect to the binder. This cement had a compressive strength of 40 MPa after 28 days of curing. In a subsequent study, the same authors reported strengths of up to 50 MPa using a mixture of 60% concrete waste (CW) and 40% red clay brick waste (RCBW) activated with a solution of NaOH and waterglass (in concentrations of 1.4% and 8% Na2O with respect to the binder). The authors stressed the importance of countering efflorescence in the final product [15]. Reig et al. [7] activated RCBW with a 7 M solution of NaOH and a SiO2/Na2O ratio of 1.6 and measured a strength of 30 MPa in mortars after 7 days of curing at 65 °C. In subsequent studies, mixes with 40% calcium aluminate were prepared, and specimens exhibited a compressive strength approaching 50 MPa after 3 days of curing at room temperature [16]. Sun et al. [17] produced a geopolymeric cement from the alkaline activation of ceramic waste using waterglass and potassium hydroxide (KOH) as activators, and after 28 days of curing at 60 °C, the specimens exhibited a compressive strength of 71 MPa. Reig et al. [18] evaluated the influence of the alkaline activator concentration (NaOH and waterglass) and the use of Ca(OH)2 on mortars made with sanitary porcelain waste. Samples exhibited a strength of 36 MPa after 7 days of curing at 65 °C. Komnitsas et al. [19] studied the potential of geopolymeric cements made with various construction residues including bricks, tiles and concrete and observed compressive strengths of up to 49.5 and 57.8 MPa in samples made with RCBW and tile waste, respectively. However, cements made with CW and NaOH (in a 14 M solution) exhibited a strength of only 13 MPa after being cured at 90 °C for 7 days. These values were consistent with those reported recently by Zaharaki et al. [20]. Lampris et al. [21] used alkali-activated ground construction waste (63 mm) from recycling plants and obtained a compressive strength of 18.7 MPa after 7 days of curing at room temperature. Curing at 105 °C for 24 h increased the strength by 112%, and introducing 20% metakaolin as a source of soluble alumina increased the mechanical strength of the
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geopolymer by 63%. Vázquez et al. [22] used NaOH and waterglass solutions with CW and 10% metakaolin, and after 28 days of curing at room temperature (25 °C), the cement made with CW exhibited a strength of 25 MPa, and the cement made with metakaolin exhibited a strength of 46 MPa. A small percentage of CDW is glass waste (GW) from demolition, typically from windowpanes. Although this material is difficult to handle and reuse, several studies, such as those by Puertas et al. [23,24] and Cry et al. [25], have evaluated the possibility of recycling GW using alkaline activation, either as a source of SiO2 for obtaining water glass or as a component of the activated cement. Important results on the microstructure, the mechanical properties and the durability were reported by Novais et al. [26]. This investigation considered the exploitation of RCBW, CW and GW using alkaline activation to obtain binders that can be used in the fabrication of various masonry construction products such as blocks, pavers, roof tiles and tiles. The residues were manually separated from actual CDW samples obtained from demolition activities on the campus of Universidad del Valle in Cali, Colombia. Using these residues to produce building materials would be a sustainable solution to the environmental problems associated with CDW. 2. Materials and experimental methodology 2.1. Materials Table 1 presents the chemical compositions of the primary binders, RCBW, CW, and GW, and ordinary Portland cement (OPC), which was used as a supplementary source of CaO to obtain hybrid cements. RCBW and CW with high molar ratios of SiO2/Al2O3 and GW with greater than 10% CaO and Na2O, i.e., sodic calcic glass, were used. Fig. 1 shows the mineralogical compositions of the primary binders. It can be observed that the RCBW and the CW have a semi-crystalline structure, whereas the GW is amorphous. A hammer crusher and subsequently a ball mill were used to reduce the size of the residue particles. Fig. 2 presents the granulometric distributions for the RCBW, CW and GW particles. The volume mean diameters, i.e., D(4,3), of the RCBW, CW, GW and OPC particles were 24.25, 24.73, 43.12 and 21.65 mm, respectively. The angular morphology of the ground waste particles can be observed in Fig. 3. The presence of particles with reduced porosity and the significant fraction of small impalpable particles (D < 10 mm) are noted in the SEM images (Fig. 2).
2.2. Experimental methodology Fig. 4 shows a diagram of the methodology followed in this investigation. The RCBW, the CW and the GW were obtained from a sample of actual CDW (Fig. 5) originating from demolition activities on the campus of Universidad del Valle (Cali, Colombia). The waste materials were separated, ground and characterized using laser granulometry, X-ray fluorescence (XRF), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Based on the chemical compositions, the waste binders were activated using solutions of Na2SiO3, i.e., waterglass (with the composition: 32.09% SiO2, 11.92% Na2O, 55.99% H2O), and/or industrial grade NaOH. OPC was used as a source of CaO in mixtures of less than 30% by weight with the RCBW and the CW to obtain hybrid cements. The AACs were prepared in a Hobart mixer with a mixing time of 5 min. The liquid/solid ratio (L/S) used in all the mixtures was 0.23. The fresh pastes were molded into 20-mm cubes and subjected to vibration for 30 s in an electric vibrating table to remove trapped air. Then, the moulds were covered with a polyethylene film to control the evaporation of the free water, and the specimens were initially cured at temperatures of either 25 °C or 70 °C for 24 h. Subsequently, the specimens were removed from the moulds and placed in a curing chamber that maintained the relative humidity at approximately 90%, where the samples were remained for 27 days. The compressive strengths of the AAC specimens were measured in an INSTRON 3369 universal testing machine, which has a capacity of 50 kN force, at a speed of 1 mm/min. For each mix, a minimum of three specimens were tested. The following instruments and methods were used to analyse the specimens: Laser granulometry was performed using a Malvern Instruments Mastersizer 2000 particle size analyser and a Hydro 2000MU dispersion unit with distilled water as the dispersing medium. X-ray fluorescence (XRF) was performed using a Phillips-PANalytical MagiX Pro PW 2440 spectrometer with a maximum power of 4 kW and equipped with a rhodium tube.
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Table 1 Chemical compositions of the primary binders (RCBW, CW and GW) and supplementary OPC. Material
RCBW CW GW OPC
Percentage SiO2
Al2O3
Fe2O3
CaO
Na2O
MgO
K2O
TiO2
65.92 56.21 72.27 21.23
20.08 10.68 1.49 4.92
9.10 10.39 0.62 4.88
0.73 15.37 11.15 64.27
0.44 2.08 13.37 0.26
0.86 3.35 0.26 1.61
0.97 0.36 0.51 0.25
1.09 0.24 0.08 0.24
Molar ratio SiO2/Al2O3 5.58 8.95 – –
Scanning electron microscopy (SEM) was performed using a JEOL JSM-6490LV microscope with an acceleration voltage of 20 kV. The specimens were evaluated in the low-vacuum mode. An Oxford Instruments Link-Isis X-ray spectrometer was coupled to the microscope. Prototypes of construction elements including blocks, pavers, roof tiles and tiles were cast using the optimum ACC. These pre-fabricated materials were evaluated according to the relevant building codes (Colombian technical standards NTC 4026-4076, 2017, 1085, and 2086). The prototypes were fabricated manually to represent production in less developed communities.
3. Results and analysis 3.1. Performance of AACs
Fig. 1. X-ray diffractograms (XRDs) of the binders (RCBW, CW, and GW) (M; muscovite, Q; quartz, A; albite, An; anorthite, H; haematite, C; calcite and P; portlandite).
Fig. 2. Granulometric distributions of the binder (RCBW, CW and GW) particles.
X-ray diffraction (XRD) was performed using a PANalytical X’Pert MRD X-ray diffractometer with Cu k-a radiation, where the diffraction angle 2h was measured between 5 deg and 60 deg in increments of 0.020.
The effects of the NaOH concentration (expressed in% of Na2O) and the initial curing temperature (25 or 70 °C) on the compressive strength of AAC specimens made with 100% RCBW, CW and GW can be observed in Fig. 6A, C and E, respectively. In general, the higher curing temperature led to better mechanical properties. The highest compressive strength for the RCBW was 11.24 MPa and was achieved with 8% Na2O and curing at 70 °C for the first 24 h (Fig. 6A). For the CW, it can be observed that the optimal amount of Na2O was 6%, for which a compressive strength of 11.64 MPa was obtained for the mixture cured at 70 °C for the first 24 h (Fig. 6C). This represents a 76% increase with respect to the strength obtained with curing at 25 °C. This benefit of hightemperature curing was observed by Komnitsas et al. [19]. Applying heat increases the mechanical strength of these types of binders because of their predominantly crystalline nature, as can be observed in Fig. 1. For the case of the AAC made with 100% GW, activated with NaOH and initially cured at 70 °C for 24 h, it can be observed (Fig. 6E) that the greatest strength was obtained with a concentration of 4.6% Na2O, for which the strength of the specimens was 57.22 MPa. These results are consistent with those obtained by Cyr et al. [25] and demonstrate that this level of performance can be obtained without the use of waterglass. The pH levels of the alkaline solutions promote the solubility of the amorphous silica in the GW and result in the formation of soluble silicate species. This effect has been widely studied by various authors, most notably Puertas and Torres-Carrasco [23,24]. The dissolution of the GW, which is vitreous, is enhanced by the higher initial curing
Fig. 3. Morphology (SEM) of the RCBW (left), CW (centre) and GW (right) particles.
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Fig. 4. Experimental methodology (*; Wood, ceramics, metal, plastic, cardboard, organic matter, etc.)
Fig. 5. Actual CDW sample.
temperature (70 °C for 24 h). Puertas et al. [27] asserted that the alkaline activation at an elevated temperature contributes to the dissolution of a greater amount of GW, particularly for average particle sizes less than 45 mm.
However, the anhydrous GW particles can form alkali-silica gels at the surface as if they were a reactive aggregate, although they are not expansive. This behaviour promotes greater cohesion at the particle-matrix interfaces, as can be observed in the SEM images in Fig. 7. The SEM images do not indicate a clear difference between the alkali-activated phase and the C-S-H hydrates, but the formation of a dense and homogeneous structure would be consistent with the higher mechanical performance. It is probable that the mechanical performance of the AACs made with GW is the result of the precipitation of C-S-H-type hydrates due to the chemical composition of the glass (soda-lime glass) [25]. These hydrates can be formed by the joint presence of the silica species dissolved following the alkaline activation and the calcium in the residue (11.15%); see Table 1. It has been noted that binders obtained from GW cannot be classified as geopolymers because of the low levels of Al (<2%) and thus, the absence of N-A-S-H-type gels (hydrated alkali-aluminosilicates) [28,29]. However, the GW-based binders are composed of alkalisilica gels with greater concentrations of Ca and Al in coexistence with the C-S-H-type hydrates. Therefore, the binder can be considered another type of AAC, an ‘‘alkali-activated glass”, because these compounds are products of the preliminary chemical interaction between the GW and the strongly alkaline solution containing NaOH. In general, there is an optimal NaOH concentration above which the compressive strength of the cement decreases. The optimal concentrations for the RCBW (Fig. 6A), CW (Fig. 6C) and GW (Fig. 6E) cements were 8%, 6% and 4.6% Na2O, respectively. This effect can be attributed to the fact that an excess of NaOH causes the de-polymerization and/or dissociation of the reaction products [27,30]. In addition, a NaOH content greater than that sufficient for
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Fig. 6. Compressive strengths of the AAC specimens: A) RCBW activated with NaOH; B) RCBW activated with NaOH and water glass; C) CW activated with NaOH; D) CW activated with NaOH and water glass; E) GW activated with NaOH.
balancing the charges of the Si and Al tetrahedrons promotes the formation of carbonate salts and subsequently efflorescence [7,21], jointly resulting in a decrease in the mechanical strength. The effect of the waterglass concentration (expressed in the molar ratio SiO2/Al2O3) and the initial curing temperature (25 or
70 °C) on the compressive strength of the AAC specimens made with 100% RCBW and CW can be observed in Fig. 6B and D, respectively. From the results, it can be deduced that the presence of sodium silicate leads to a significant increase in the compressive strengths of the AACs. According to Duxson et al. [31] and
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Fig. 7. Scanning electron microscopy (SEM) images of the AAC specimens.
Pacheco-Torgal et al. [32], this behaviour is due to the presence of soluble silica species (Si-O-) donated by the activator, which promotes the formation of the geopolymeric structure. In addition, the sodium silicate contributes to a stronger interface between the non-reacting particles (anhydrous) and the gel matrix and thus, contributes to the greater mechanical strength of the aluminosilicate gel [15]. Nonetheless, it should be noted that for each type of binder, there are optimal amounts of soluble silicate (SiO2/ Al2O3) and sodium hydroxide (Na2O/SiO2), and higher amounts may significantly affect the final material properties [7]. The maximum compressive strength of the 100% RCBW specimens activated with NaOH and waterglass with SiO2/Al2O3 and Na2O/SiO2 ratios of 7.10 and 0.12, respectively, was 66.56 MPa for an initial curing temperature of 70 °C (Fig. 6B). Note that the maximum strength (54.38 MPa) of the 100% RCBW specimens cured at room temperature (Fig. 6B) was 7.3 times higher than the maximum value (7.49 MPa) obtained for the mixtures activated with NaOH (Fig. 6A). For the case of 100% CW cured at 25 °C, it can be observed that the introduction of waterglass resulted in compressive strengths of up to 25.57 MPa (SiO2/ Al2O3 = 10.0 and Na2O/SiO3 = 0.09) (Fig. 6D), a value 3.39 times greater than the maximum value of 7.55 MPa obtained with NaOH (Fig. 6C). The influence of adding OPC on the compressive strengths (cured at 25 °C) of the optimal mixtures made from RCBW can be observed in Fig. 6A and B; similarly, the effects on the mixtures
made from CW can be observed in Fig. 6C and D. In general, it can be observed that adding OPC increases the compressive strength for the same cure temperature (25 °C) regardless of the type of alkaline activator used or the activator concentration. It can also be observed that the specimens with OPC do not require thermal curing to develop increased strength. For the case of RCBW activated with NaOH (8% Na2O), Fig. 6A shows that the maximum strength (41.39 MPa) was achieved with 10% OPC, and this value was 555% higher than the value obtained for the 100% RCBW mixture activated with NaOH (initial cure temperature of 25 °C). Similarly, for the hybrid RCBW mixtures activated with NaOH and waterglass, the highest strength was obtained by adding 20% OPC (SiO2/Al2O3 = 6.78 and Na2O/SiO3 = 0.13), for which values of up to 102.59 MPa were obtained (Fig. 6B). For the case of CW, the maximum strengths were obtained with 30% OPC. For activation with NaOH (6% Na2O), strengths of up to 10.31 MPa were achieved (Fig. 6C), whereas the maximum value obtained for the mixture activated with NaOH and waterglass (SiO2/Al2O3 = 10.5 and Na2O/SiO3 = 0.09) was 33.69 MPa (Fig. 6D). The positive effect of incorporating OPC can be attributed to the donation of CaO and the resulting coexistence of the C-S-H and N-A-S-H gels, which are products of the hydration of Portland cement and the alkaline activation of the aluminosilicates, respectively [33–35]. Fig. 7 shows that mixing OPC with RCBW or CW creates a denser and more homogeneous matrix than those obtained with 100% RCBW or CW.
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3.2. Potential applications for the AACs based on recycling of CDW To demonstrate the potential applications of the AACs, prototypes of common building elements, i.e., blocks, pavers, roof tiles and tiles, were manually fabricated (Fig. 8). Table 2 presents the parameters for the building elements; the parameters include the type and concentration of the alkaline activator, the curing temperature and the percentage of OPC added to the RCBW and the CW. It should be noted that for the fabrication of the elements, the mortars were formulated based on the results obtained for the cements presented in Section 3.1. The binder:sand ratio and the type of sand used for each case are shown in Table 2. In the production of the tiles, the GW was used both as the primary binder and as a fine aggregate. The blocks, pavers, roof tiles and tiles were evaluated against the specifications for each type of product according to the Colombian standards NTC 4026-4076, 2017, 1085 and 2086, respectively. Table 3 presents the properties of the various building elements required in the Colombian technical standards (NTC) and measured in the samples. The RCBW block satisfied the requirements for high-strength structural blocks given in the standard NTC 4026
with a compressive strength of 17.09 MPa (cured 28 days – 25 °C). The RCBW pavers exhibited a flexural strength of 4.42 MPa (cured 28 days – 25 °C) and satisfied the requirements in the standard NTC 2017 for a type 2 I-shaped pavers suitable for pavements, roads, and platforms. The RCBW roof tile did not meet the required failure load under flexion (1100 N) stated in the standard NTC 2086; however, it did exhibit high impact resistance and low permeability. We anticipate that using an automated and controlled production process (not manual) would produce an item that satisfies the specifications established by the standard. The example CW block satisfied the requirements for a non-structural block stated in the standard NTC 4076 with a compressive strength of 6.06 MPa (cured 28 days – 25 °C). However, it is anticipated that an adjustment in the binder:sand ratio would improve this performance. Finally, it can be observed that the GW tile satisfied the minimum requirements of the standard NTC 1085 for type B tiles. The properties of the prototypes demonstrate the potential applications of these products in the construction industry, and it should be emphasized that these results were obtained with manual fabrication processes and not automated processes. These
Fig. 8. Prototype building elements (blocks, pavers, roof tiles and tiles) fabricated.
Table 2 Parameters and optimal compositions of the AACs used in the applications. Recycled material
Binder:sand ratio
Initial curing temperature °C
Composition Binder
Activator and concentration Na2SiO3 (SiO2/Al2O3 = 6.78) NaOH (Na2O/SiO2 = 0.13) Na2SiO3 (SiO2/Al2O3 = 10.5) NaOH (Na2O/SiO2 = 0.09) NaOH (3% Na2O)
RCBW
1:1 (river sand)
25
90% RCBW/10% OPC
CW
1:2.75 (river sand)
25
70% CW/30% OPC
GW
1:2.25 (GW sand)
70
100% GW
Table 3 Properties of the building elements made with recycled CDW (AACs). Primary binder
Application
Standard*
RCBW
Structural block (high-strength) Pavers
NTC 4026
Roof tile
NTC 2086
CW
Non-structural block
NTC 4076
GW
Tile
NTC 1085
NTC 2017
Mechanical properties Required
Measured
= 13 MPa Abs. = 9% max. MR = 4.2–5 MPa = N.A Abs. = 7% max. Cf = 1100 N Imp. = 500 mm Abs. = 10% max. = 5–6 MPa Abs. = 12% max. Cf = 900–1100 N Imp. = 170 mm Abs. = 7% max.
= 17.09 MPa Abs. = 7.3% MR = 4.42 MPa = 24.60 MPa Abs. = 6.58% Cf = 995 N Imp. = 2500 mm Abs. = 8.7% = 6,06 MPa Abs. = 6.82% Cf = 1006 N Imp. = 312 mm Abs. = 13.85%
: compressive strength, MR: modulus of rupture, Abs.: water absorption percentage, Cf: flexural load; Imp.: impact resistance (height); N.A: not applicable. * NTC = Colombian technical standard.
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results indicate the viability of using these materials in both manual and industrial production processes. 4. Conclusions RCBW and CW, which are two of the main components of CDW, and GW, which is a minor residue that is difficult to handle and reuse, were used to produce alkali-activated cements (AACs) with satisfactory mechanical properties. The best mechanical performance (102 MPa) among the specimens cured at room temperature was obtained for RCBW mixed with 20% OPC and activated with a solution containing NaOH and waterglass (molar ratios SiO2/Al2O3 and Na2O/SiO2 of 6.78 and 0.13, respectively). The second best performance (33 MPa) was obtained for CW mixed with 30% OPC and activated with NaOH and waterglass (molar ratios SiO2/Al2O3 and Na2O/SiO2 of 10.5 and 0.09, respectively). For GW (100%), a maximum compressive strength of 57 MPa was achieved for activation with NaOH with a concentration of 4.6% Na2O and an initial thermal curing at 70 °C for 24 h. For the AACs made from 100% RCBW or CW, that is without OPC, it was possible to achieve adequate mechanical performance when cured at room temperature with appropriated adjustments of the synthesis conditions, particularly the type and proportion of the activator. For the case of 100% RCBW activated with NaOH and waterglass strengths of up to 54.38 MPa were achieved. For the 100% CW binder strengths of up to 25.57 MPa were attained. The results obtained in this investigation demonstrate the viability of reusing RCBW, CW and GW to create useful building materials for the construction industry (cements, masonry mortars and pre-fabricated elements). High-strength structural blocks, type 2 I-shaped pavers, and roof tiles were fabricated using an AAC made with RCBW, and these items exhibited high impact resistance and low permeability. Similarly, type B floor tiles were fabricated using an AAC made with GW. Non-structural blocks were produced using an AAC made with CW. These results demonstrate the advantages of the alkaline activation technique for the exploitation of CDW and the possibility of a sustainable solution to the environmental problems associated with the tremendous volumes of CDW being generated globally. In addition, building materials that satisfy construction codes were manually produced, thus demonstrating the feasibility of production in less developed communities. This type of production can be considered appropriate technology for constructing higher-quality housing in developing countries. Acknowledgments The authors, members of the Composite Materials Group (CMG) of the Centro de Excelencia en Nuevos Materiales (CENM), would like to thank the Universidad del Valle (Cali, Colombia) and the Departamento Administrativo de Ciencia, Tecnología e Innovación (Colciencias) of Colombia, for their support within the framework of the project ‘‘Construcción de prototipo a escala de vivienda rural utilizando materiales innovadores de baja huella de carbono”, contract No. 0696-2016 under which this research was conducted. References [1] R. Robayo, P. Mattey, D. Burgos, Y. Silva, S. Delvasto, Los residuos de la construcción y demolición en la ciudad de Cali: un análisis hacia su gestión, manejo y aprovechamiento, Revista Tecnura 19 (44) (2015) 157–170, http:// dx.doi.org/10.14483/udistrital.jour.tecnura.2015.2.a12. [2] Z. Wu, T.W.Y. Ann, L. Shen, L. Guiwen, Quantifying construction and demolition waste: an analytical review, Waste Manage. 34 (2014) 16–83, http://dx.doi. org/10.1016/j.wasman.2014.05.010. [3] G. Rodríguez, C. Medina, F.J. Alegre, E. Asensio, M.I. Sánchez de Rojas, Assessment of construction and demolition waste plant management in Spain: in pursuit of sustainability and eco-efficiency, J. Cleaner Prod. 90 (2015) 16–24, http://dx.doi.org/10.1016/j.jclepro.2014.11.067.
137
[4] J. Xiao, W. Li, Y. Fan, X. Huang, An overview of study on recycled aggregate concrete in China (1996–2011), Constr. Build. Mater. 31 (2012) 364–383, http://dx.doi.org/10.1016/j.conbuildmat.2011.12.074. [5] H. Yuan, A.R. Choni, Y. Lu, L. Shen, A dynamic model for assessing the effects of management strategies on the reduction of construction and demolition waste, Waste Manage. 32 (2012) 521–531, http://dx.doi.org/10.1016/j. wasman.2011.11.006. [6] European Commission, Resource Efficient Use of Mixed Wastes; Environment, Waste, Studies, 2015. Available from:, Accessed on September 08, 2015. [7] L. Reig, M. Tashima, M. Borrachero, J. Monzó, C. Cheeseman, J. Payá, Properties and microstructure of alkali-activated red clay brick waste, Constr. Build. Mater. 43 (2013) 98–106, http://dx.doi.org/10.1016/j.conbuildmat.2013. 01.031. [8] F. Pacheco-Torgal, S. Jalali, Reusing ceramics waste in concrete, Constr. Build. Mater. 24 (5) (2010) 832–838, http://dx.doi.org/10.1016/j.conbuildmat.2009. 10.023. [9] Habla Zig-Zag Kilns, Brick Market, 2015. Available from: , Accessed on January 28, 2017. [10] F. Pacheco-Torgal, Introduction to eco-efficient masonry bricks and blocks, Woodhead Publishing Series in Civil and Structural Engineering, 2015, pp. 1– 10, http://dx.doi.org/10.1016/B978-1-78242-305-8.00001-2. Chapter 1. [11] M. Bravo, J. de Brito, J. Pontes, L. Evangelista, Mechanical performance of concrete made with aggregates from construction and demolition waste recycling plants, J. Cleaner Prod. 99 (2015) 59–74, http://dx.doi.org/10.1016/j. jclepro.2015.03.012. [12] European Commission, Construction and Demolition Waste (CDW), 2016. Available from: Accessed on August 01, 2016. [13] F. Puertas, A. Barba, M. Gazulla, M. Gómez, M. Palacios, S. Martínez, Residuos cerámicos para su posible uso como materia prima en la fabricación de Clinker de cemento Portland: Caracterización y activación alcalina, Mater. Constr. 56 (281) (2006) 73–84, http://dx.doi.org/10.3989/mc.2006.v56.i281.94. [14] A. Allahverdi, E.N. Kani, Construction waste as raw materials for geopolymer binders, Int. J. Civil Eng. 7 (3) (2009) 154–160. [15] A. Allahverdi, E.N. Kani, Use of construction and demolition waste (CDW) for alkali-activated or geopolymer cements, Handbook of Recycled Concrete and Demolition waste, vol. 18, Woodhead Publishing Series in Civil and Structural Engineering. Capítulo, 2013, pp. 439–475, http://dx.doi.org/10.1533/ 9780857096906.3.439. Capítulo 18. [16] L. Reig, L. Soriano, M. Borrachero, J. Monzó, J. Payá, Influence of calcium aluminate cement (CAC) on alkaline activation of red clay brick waste (RCBW), Cem. Concr. Compos. 65 (2016) 177–185, http://dx.doi.org/10.1016/j. cemconcomp.2015.10.021. [17] Z. Sun, H. Cui, H. An, D. Tao, Y. Xu, J. Zhai, Q. Li, Synthesis and thermal behavior of geopolymer-type material from waste ceramic, Constr. Build. Mater. 49 (2013) 281–287, http://dx.doi.org/10.1016/j.conbuildmat.2013.08.063. [18] L. Reig, L. Soriano, M. Borrachero, J. Monzó, J. Payá, Influence of the activator concentration and calcium hydroxide addition on the properties of alkaliactivated porcelain stoneware, Constr. Build. Mater. 63 (2014) 214–222, http://dx.doi.org/10.1016/j.conbuildmat.2014.04.023. [19] K. Komnitsas, D. Zaharaki, A. Vlachou, G. Bartzas, M. Galetakis, Effect of synthesis parameters on the quality of construction and demolition wastes (CDW) geopolymers, Adv. Powder Technol. 26 (2015) 368–376, http://dx.doi. org/10.1016/j.apt.2014.11.012. [20] D. Zaharaki, M. Galetakis, K. Komnitsas, Valorization of construction and demolition (C&D) and industrial wastes through alkali activation, Constr. Build. Mater. 121 (2016) 686–693, http://dx.doi.org/10.1016/j.conbuildmat. 2016.06.051. [21] C. Lampris, C.R. Lupo, C.R. Cheeseman, Geopolymerisation of silt generated from and demolition waste washing plants, Waste Manage. 29 (2009) 368– 373, http://dx.doi.org/10.1016/j.wasman.2008.04.007. [22] A. Vázquez, V. Cárdenas, R.A. Robayo, R. Mejía de Gutiérrez, Geopolymer based on concrete demolition waste, Adv. Powder Technol. 27 (4) (2016) 1173–1179, http://dx.doi.org/10.1016/j.apt.2016.03.029. [23] F. Puertas, M. Torres-Carrasco, Use of glass waste as an activator in the preparation of alkali-activated slag. Mechanical strength and paste characterization, Cem. Concr. Res. 57 (2014) 95–104, http://dx.doi.org/ 10.1016/j.bsecv.2015.03.004. [24] M. Torres-Carrasco, F. Puertas, Waste glass in the geopolymer preparation. Mechanical and microestructural characterization, J. Cleaner Prod. 90 (2015) 397–408, http://dx.doi.org/10.1016/j.jclepro.2014.11.074. [25] M. Cyr, R. Idir, T. Poinot, Properties of geopolymer mortars made of glass cullet, J. Mater. Sci. 47 (2012) 2782–2797, http://dx.doi.org/10.1007/s10853-0116107-2. [26] R.M. Novais, G. Ascensão, M.P. Seabra, J.A. Labrincha, Waste glass from end-oflife fluorescent lamps as raw material in geopolymers, Waste Manage. 52 (2016) 245–255, http://dx.doi.org/10.1016/j.wasman.2016.04.003. [27] F. Puertas, M. Torres-Carrasco, M.M. Alonso, Reuse of urban and industrial waste glass as a novel activator for alkali-activated slag cement pastes: a case study, Handbook of Alkali-activated Cements, Mortars and Concretes, 2015, pp. 75–109, http://dx.doi.org/10.1533/9781782422884.1.75. Woodhead Publishing Series in Civil and Structural Engineering 54. Capitulo 4. [28] R.A. Fletcher, K.J.D. MacKenzie, C.L. Nicholson, S. Shimada, The composition range of aluminosilicate geopolymers, J. Eur. Ceram. Soc. 25 (2005) 1471– 1477, http://dx.doi.org/10.1016/j.jeurceramsoc.2004.06.001.
138
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[29] K.J.D. MacKenzie, What are these things called geopolymers? A physicochemical perspective, Ceram. Trans. 153 (2003) 175–186, http://dx.doi.org/ 10.1002/9781118406892.ch12. [30] A. Alonso, A. Palomo, Alkaline activation of metakaolin and calcium hydroxide mixtures: influence of temperature, activator concentration and solids ratio, Mater. Lett. 47 (2001) 55–62, http://dx.doi.org/10.1016/S0167-577X (00)00212-3. [31] P. Duxson, J. Provis, G. Luckey, S. Mallicoat, W. Kriven, J. Van Deventer, Understanding the relationship between geopolymer composition, microstructure and mechanical properties, Colloids Surf. A 269 (2005) 47– 58, http://dx.doi.org/10.1016/j.colsurfa.2005.06.060. [32] F. Pacheco-Torgal, J. Castro-Gomes, S. Jalali, Alkali-activated binders: a review. Part 1. Historical background, terminology, reaction mechanisms and
hydration products, Constr. Build. Mater. 22 (2008) 1305–1314, http://dx. doi.org/10.1016/j.conbuildmat.2007.10.015. [33] I. Garcia-Lodeiro, A. Fernandez-Jimenez, A. Palomo, Hydration kinetics in hybrid binders: early reaction stages, Cem. Concr. Compos. 39 (2013) 82–92, http://dx.doi.org/10.1016/j.cemconcomp.2013.03.025. [34] P. Nath, P. Sarker, Use of OPC to improve setting and early strength properties of low calcium fly ash geopolymer concrete cured at room temperature, Cem. Concr. Compos. 55 (2015) 205–214, http://dx.doi.org/10.1016/j. cemconcomp.2014.08.008. [35] T. Suwan, M. Fan, Influence of OPC replacement and manufacturing procedures on the properties of self-cured geopolymer, Constr. Build. Mater. 73 (2015) 551–561, http://dx.doi.org/10.1016/j.conbuildmat.2014.09.065.
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Alkali-activated building materials made with recycled construction and demolition wastes Rafael Andrés Robayo-Salazar, Jhonathan Fernando Rivera, Ruby Mejía de Gutiérrez ⇑ Composites Materials Group (GMC-CENM), Universidad del Valle, Cali, Colombia
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Alkali-activated cements (AACs)
based on construction wastes (CDW) are obtained. High compressive strengths of up to 102 MPa were obtained for AACs. Blocks, pavers, roof tiles and tiles (building materials) were made from AACs. The recycled of CDW through ‘‘Alkali activation technology” were demonstrate.
a r t i c l e
i n f o
Article history: Received 27 February 2017 Received in revised form 7 May 2017 Accepted 12 May 2017 Available online 19 May 2017 Keywords: Construction and demolition wastes Red clay brick waste Concrete waste Glass waste Alkali-activated cements Geopolymers Recycling materials
a b s t r a c t The goal of this study was to test the viability of using red clay brick waste (RCBW), concrete waste (CW) and glass waste (GW) to produce alkali-activated cements (AACs) that can be used to fabricate blocks, pavers, roof tiles and tiles. The alkaline activators used were solutions of either NaOH or NaOH and waterglass. Ordinary Portland cement (OPC) was mixed with RCBW and CW in proportions of up to 30% to create hybrid cements. The AACs obtained with the RCBW, the CW and the GW exhibited maximum compressive strengths (28 days) of 102, 33 and 57 MPa, respectively. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction The construction industry is considered one of the most influential sectors for improving the socioeconomic conditions of developing countries, and its dynamism is driven by the demand for housing and civil infrastructure. However, one of the consequences ⇑ Corresponding author. E-mail address: [email protected] (R. Mejía de Gutiérrez). http://dx.doi.org/10.1016/j.conbuildmat.2017.05.122 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.
of high demand is the generation of considerable volumes of waste, which have become a significant environmental problem, representing up to 30% of the solid waste generated globally. The search for sustainable solutions that exploit materials from construction industry waste (e.g., brick, glass, ceramics and concrete) is currently an urgent challenge for this sector [1–3]. Generally, construction and demolition waste (CDW) can be divided into three groups, depending on their origin: waste generated during the construction of new buildings, waste originating
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from the renovation and demolition of infrastructure (e.g., buildings, bridges and roads), including natural disasters and military conflicts, and waste originating from the ceramics industry (e.g., white and red clay) [2]. The largest producers of CDW are China, the U.S. and certain European countries, which generate more than 605.5 million tonnes per year [4–6]. It is estimated that approximately 54% of this waste comprises ceramic materials (i.e., bricks, tiles and other forms), and 12% is concrete [7]. Moreover, the ceramics industry discards approximately 3–7% of its production [8] despite the use of automation and monitoring in the production processes. For reference, the global production of brick red clay is approximately 1500 billion units per year [9,10]. In certain EU countries such as Germany, Denmark and the Netherlands, nearly 80% of CDW is reused, whereas in most other countries the rate is closer to 30% [11]. The EU directive 2008/98/CE (article 11.2.b) mandates a minimum reuse rate of 70% (by weight) of CDW before 2020 [12]. In Latin America, countries such as Brazil and Mexico have begun to implement processes for the production of recycled concrete aggregates. CDW consists mainly of siliceous-aluminous materials (SiO2 and Al2O3). Therefore, the alkaline activation process is considered a viable alternative for the increased use of this fraction (>75%) of the CDW. This process has been demonstrated to be highly practical for transforming industrial waste and by-products with suitable characteristics into useful materials. Puertas et al. [13] evaluated the use of residues from ceramic floor tile produced with red and white clays for geopolymeric cements, where the residue was activated with NaOH and waterglass (Na2OnSiO2mH2O). The authors reported that samples cured for 8 days exhibited compressive and flexural strengths of 13 and 4 MPa, respectively. Allahverdi and Kani [14] developed a cement using waste from a brick production plant and activated it with NaOH in proportion of 8% Na2O with respect to the binder. This cement had a compressive strength of 40 MPa after 28 days of curing. In a subsequent study, the same authors reported strengths of up to 50 MPa using a mixture of 60% concrete waste (CW) and 40% red clay brick waste (RCBW) activated with a solution of NaOH and waterglass (in concentrations of 1.4% and 8% Na2O with respect to the binder). The authors stressed the importance of countering efflorescence in the final product [15]. Reig et al. [7] activated RCBW with a 7 M solution of NaOH and a SiO2/Na2O ratio of 1.6 and measured a strength of 30 MPa in mortars after 7 days of curing at 65 °C. In subsequent studies, mixes with 40% calcium aluminate were prepared, and specimens exhibited a compressive strength approaching 50 MPa after 3 days of curing at room temperature [16]. Sun et al. [17] produced a geopolymeric cement from the alkaline activation of ceramic waste using waterglass and potassium hydroxide (KOH) as activators, and after 28 days of curing at 60 °C, the specimens exhibited a compressive strength of 71 MPa. Reig et al. [18] evaluated the influence of the alkaline activator concentration (NaOH and waterglass) and the use of Ca(OH)2 on mortars made with sanitary porcelain waste. Samples exhibited a strength of 36 MPa after 7 days of curing at 65 °C. Komnitsas et al. [19] studied the potential of geopolymeric cements made with various construction residues including bricks, tiles and concrete and observed compressive strengths of up to 49.5 and 57.8 MPa in samples made with RCBW and tile waste, respectively. However, cements made with CW and NaOH (in a 14 M solution) exhibited a strength of only 13 MPa after being cured at 90 °C for 7 days. These values were consistent with those reported recently by Zaharaki et al. [20]. Lampris et al. [21] used alkali-activated ground construction waste (63 mm) from recycling plants and obtained a compressive strength of 18.7 MPa after 7 days of curing at room temperature. Curing at 105 °C for 24 h increased the strength by 112%, and introducing 20% metakaolin as a source of soluble alumina increased the mechanical strength of the
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geopolymer by 63%. Vázquez et al. [22] used NaOH and waterglass solutions with CW and 10% metakaolin, and after 28 days of curing at room temperature (25 °C), the cement made with CW exhibited a strength of 25 MPa, and the cement made with metakaolin exhibited a strength of 46 MPa. A small percentage of CDW is glass waste (GW) from demolition, typically from windowpanes. Although this material is difficult to handle and reuse, several studies, such as those by Puertas et al. [23,24] and Cry et al. [25], have evaluated the possibility of recycling GW using alkaline activation, either as a source of SiO2 for obtaining water glass or as a component of the activated cement. Important results on the microstructure, the mechanical properties and the durability were reported by Novais et al. [26]. This investigation considered the exploitation of RCBW, CW and GW using alkaline activation to obtain binders that can be used in the fabrication of various masonry construction products such as blocks, pavers, roof tiles and tiles. The residues were manually separated from actual CDW samples obtained from demolition activities on the campus of Universidad del Valle in Cali, Colombia. Using these residues to produce building materials would be a sustainable solution to the environmental problems associated with CDW. 2. Materials and experimental methodology 2.1. Materials Table 1 presents the chemical compositions of the primary binders, RCBW, CW, and GW, and ordinary Portland cement (OPC), which was used as a supplementary source of CaO to obtain hybrid cements. RCBW and CW with high molar ratios of SiO2/Al2O3 and GW with greater than 10% CaO and Na2O, i.e., sodic calcic glass, were used. Fig. 1 shows the mineralogical compositions of the primary binders. It can be observed that the RCBW and the CW have a semi-crystalline structure, whereas the GW is amorphous. A hammer crusher and subsequently a ball mill were used to reduce the size of the residue particles. Fig. 2 presents the granulometric distributions for the RCBW, CW and GW particles. The volume mean diameters, i.e., D(4,3), of the RCBW, CW, GW and OPC particles were 24.25, 24.73, 43.12 and 21.65 mm, respectively. The angular morphology of the ground waste particles can be observed in Fig. 3. The presence of particles with reduced porosity and the significant fraction of small impalpable particles (D < 10 mm) are noted in the SEM images (Fig. 2).
2.2. Experimental methodology Fig. 4 shows a diagram of the methodology followed in this investigation. The RCBW, the CW and the GW were obtained from a sample of actual CDW (Fig. 5) originating from demolition activities on the campus of Universidad del Valle (Cali, Colombia). The waste materials were separated, ground and characterized using laser granulometry, X-ray fluorescence (XRF), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Based on the chemical compositions, the waste binders were activated using solutions of Na2SiO3, i.e., waterglass (with the composition: 32.09% SiO2, 11.92% Na2O, 55.99% H2O), and/or industrial grade NaOH. OPC was used as a source of CaO in mixtures of less than 30% by weight with the RCBW and the CW to obtain hybrid cements. The AACs were prepared in a Hobart mixer with a mixing time of 5 min. The liquid/solid ratio (L/S) used in all the mixtures was 0.23. The fresh pastes were molded into 20-mm cubes and subjected to vibration for 30 s in an electric vibrating table to remove trapped air. Then, the moulds were covered with a polyethylene film to control the evaporation of the free water, and the specimens were initially cured at temperatures of either 25 °C or 70 °C for 24 h. Subsequently, the specimens were removed from the moulds and placed in a curing chamber that maintained the relative humidity at approximately 90%, where the samples were remained for 27 days. The compressive strengths of the AAC specimens were measured in an INSTRON 3369 universal testing machine, which has a capacity of 50 kN force, at a speed of 1 mm/min. For each mix, a minimum of three specimens were tested. The following instruments and methods were used to analyse the specimens: Laser granulometry was performed using a Malvern Instruments Mastersizer 2000 particle size analyser and a Hydro 2000MU dispersion unit with distilled water as the dispersing medium. X-ray fluorescence (XRF) was performed using a Phillips-PANalytical MagiX Pro PW 2440 spectrometer with a maximum power of 4 kW and equipped with a rhodium tube.
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Table 1 Chemical compositions of the primary binders (RCBW, CW and GW) and supplementary OPC. Material
RCBW CW GW OPC
Percentage SiO2
Al2O3
Fe2O3
CaO
Na2O
MgO
K2O
TiO2
65.92 56.21 72.27 21.23
20.08 10.68 1.49 4.92
9.10 10.39 0.62 4.88
0.73 15.37 11.15 64.27
0.44 2.08 13.37 0.26
0.86 3.35 0.26 1.61
0.97 0.36 0.51 0.25
1.09 0.24 0.08 0.24
Molar ratio SiO2/Al2O3 5.58 8.95 – –
Scanning electron microscopy (SEM) was performed using a JEOL JSM-6490LV microscope with an acceleration voltage of 20 kV. The specimens were evaluated in the low-vacuum mode. An Oxford Instruments Link-Isis X-ray spectrometer was coupled to the microscope. Prototypes of construction elements including blocks, pavers, roof tiles and tiles were cast using the optimum ACC. These pre-fabricated materials were evaluated according to the relevant building codes (Colombian technical standards NTC 4026-4076, 2017, 1085, and 2086). The prototypes were fabricated manually to represent production in less developed communities.
3. Results and analysis 3.1. Performance of AACs
Fig. 1. X-ray diffractograms (XRDs) of the binders (RCBW, CW, and GW) (M; muscovite, Q; quartz, A; albite, An; anorthite, H; haematite, C; calcite and P; portlandite).
Fig. 2. Granulometric distributions of the binder (RCBW, CW and GW) particles.
X-ray diffraction (XRD) was performed using a PANalytical X’Pert MRD X-ray diffractometer with Cu k-a radiation, where the diffraction angle 2h was measured between 5 deg and 60 deg in increments of 0.020.
The effects of the NaOH concentration (expressed in% of Na2O) and the initial curing temperature (25 or 70 °C) on the compressive strength of AAC specimens made with 100% RCBW, CW and GW can be observed in Fig. 6A, C and E, respectively. In general, the higher curing temperature led to better mechanical properties. The highest compressive strength for the RCBW was 11.24 MPa and was achieved with 8% Na2O and curing at 70 °C for the first 24 h (Fig. 6A). For the CW, it can be observed that the optimal amount of Na2O was 6%, for which a compressive strength of 11.64 MPa was obtained for the mixture cured at 70 °C for the first 24 h (Fig. 6C). This represents a 76% increase with respect to the strength obtained with curing at 25 °C. This benefit of hightemperature curing was observed by Komnitsas et al. [19]. Applying heat increases the mechanical strength of these types of binders because of their predominantly crystalline nature, as can be observed in Fig. 1. For the case of the AAC made with 100% GW, activated with NaOH and initially cured at 70 °C for 24 h, it can be observed (Fig. 6E) that the greatest strength was obtained with a concentration of 4.6% Na2O, for which the strength of the specimens was 57.22 MPa. These results are consistent with those obtained by Cyr et al. [25] and demonstrate that this level of performance can be obtained without the use of waterglass. The pH levels of the alkaline solutions promote the solubility of the amorphous silica in the GW and result in the formation of soluble silicate species. This effect has been widely studied by various authors, most notably Puertas and Torres-Carrasco [23,24]. The dissolution of the GW, which is vitreous, is enhanced by the higher initial curing
Fig. 3. Morphology (SEM) of the RCBW (left), CW (centre) and GW (right) particles.
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Fig. 4. Experimental methodology (*; Wood, ceramics, metal, plastic, cardboard, organic matter, etc.)
Fig. 5. Actual CDW sample.
temperature (70 °C for 24 h). Puertas et al. [27] asserted that the alkaline activation at an elevated temperature contributes to the dissolution of a greater amount of GW, particularly for average particle sizes less than 45 mm.
However, the anhydrous GW particles can form alkali-silica gels at the surface as if they were a reactive aggregate, although they are not expansive. This behaviour promotes greater cohesion at the particle-matrix interfaces, as can be observed in the SEM images in Fig. 7. The SEM images do not indicate a clear difference between the alkali-activated phase and the C-S-H hydrates, but the formation of a dense and homogeneous structure would be consistent with the higher mechanical performance. It is probable that the mechanical performance of the AACs made with GW is the result of the precipitation of C-S-H-type hydrates due to the chemical composition of the glass (soda-lime glass) [25]. These hydrates can be formed by the joint presence of the silica species dissolved following the alkaline activation and the calcium in the residue (11.15%); see Table 1. It has been noted that binders obtained from GW cannot be classified as geopolymers because of the low levels of Al (<2%) and thus, the absence of N-A-S-H-type gels (hydrated alkali-aluminosilicates) [28,29]. However, the GW-based binders are composed of alkalisilica gels with greater concentrations of Ca and Al in coexistence with the C-S-H-type hydrates. Therefore, the binder can be considered another type of AAC, an ‘‘alkali-activated glass”, because these compounds are products of the preliminary chemical interaction between the GW and the strongly alkaline solution containing NaOH. In general, there is an optimal NaOH concentration above which the compressive strength of the cement decreases. The optimal concentrations for the RCBW (Fig. 6A), CW (Fig. 6C) and GW (Fig. 6E) cements were 8%, 6% and 4.6% Na2O, respectively. This effect can be attributed to the fact that an excess of NaOH causes the de-polymerization and/or dissociation of the reaction products [27,30]. In addition, a NaOH content greater than that sufficient for
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Fig. 6. Compressive strengths of the AAC specimens: A) RCBW activated with NaOH; B) RCBW activated with NaOH and water glass; C) CW activated with NaOH; D) CW activated with NaOH and water glass; E) GW activated with NaOH.
balancing the charges of the Si and Al tetrahedrons promotes the formation of carbonate salts and subsequently efflorescence [7,21], jointly resulting in a decrease in the mechanical strength. The effect of the waterglass concentration (expressed in the molar ratio SiO2/Al2O3) and the initial curing temperature (25 or
70 °C) on the compressive strength of the AAC specimens made with 100% RCBW and CW can be observed in Fig. 6B and D, respectively. From the results, it can be deduced that the presence of sodium silicate leads to a significant increase in the compressive strengths of the AACs. According to Duxson et al. [31] and
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Fig. 7. Scanning electron microscopy (SEM) images of the AAC specimens.
Pacheco-Torgal et al. [32], this behaviour is due to the presence of soluble silica species (Si-O-) donated by the activator, which promotes the formation of the geopolymeric structure. In addition, the sodium silicate contributes to a stronger interface between the non-reacting particles (anhydrous) and the gel matrix and thus, contributes to the greater mechanical strength of the aluminosilicate gel [15]. Nonetheless, it should be noted that for each type of binder, there are optimal amounts of soluble silicate (SiO2/ Al2O3) and sodium hydroxide (Na2O/SiO2), and higher amounts may significantly affect the final material properties [7]. The maximum compressive strength of the 100% RCBW specimens activated with NaOH and waterglass with SiO2/Al2O3 and Na2O/SiO2 ratios of 7.10 and 0.12, respectively, was 66.56 MPa for an initial curing temperature of 70 °C (Fig. 6B). Note that the maximum strength (54.38 MPa) of the 100% RCBW specimens cured at room temperature (Fig. 6B) was 7.3 times higher than the maximum value (7.49 MPa) obtained for the mixtures activated with NaOH (Fig. 6A). For the case of 100% CW cured at 25 °C, it can be observed that the introduction of waterglass resulted in compressive strengths of up to 25.57 MPa (SiO2/ Al2O3 = 10.0 and Na2O/SiO3 = 0.09) (Fig. 6D), a value 3.39 times greater than the maximum value of 7.55 MPa obtained with NaOH (Fig. 6C). The influence of adding OPC on the compressive strengths (cured at 25 °C) of the optimal mixtures made from RCBW can be observed in Fig. 6A and B; similarly, the effects on the mixtures
made from CW can be observed in Fig. 6C and D. In general, it can be observed that adding OPC increases the compressive strength for the same cure temperature (25 °C) regardless of the type of alkaline activator used or the activator concentration. It can also be observed that the specimens with OPC do not require thermal curing to develop increased strength. For the case of RCBW activated with NaOH (8% Na2O), Fig. 6A shows that the maximum strength (41.39 MPa) was achieved with 10% OPC, and this value was 555% higher than the value obtained for the 100% RCBW mixture activated with NaOH (initial cure temperature of 25 °C). Similarly, for the hybrid RCBW mixtures activated with NaOH and waterglass, the highest strength was obtained by adding 20% OPC (SiO2/Al2O3 = 6.78 and Na2O/SiO3 = 0.13), for which values of up to 102.59 MPa were obtained (Fig. 6B). For the case of CW, the maximum strengths were obtained with 30% OPC. For activation with NaOH (6% Na2O), strengths of up to 10.31 MPa were achieved (Fig. 6C), whereas the maximum value obtained for the mixture activated with NaOH and waterglass (SiO2/Al2O3 = 10.5 and Na2O/SiO3 = 0.09) was 33.69 MPa (Fig. 6D). The positive effect of incorporating OPC can be attributed to the donation of CaO and the resulting coexistence of the C-S-H and N-A-S-H gels, which are products of the hydration of Portland cement and the alkaline activation of the aluminosilicates, respectively [33–35]. Fig. 7 shows that mixing OPC with RCBW or CW creates a denser and more homogeneous matrix than those obtained with 100% RCBW or CW.
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3.2. Potential applications for the AACs based on recycling of CDW To demonstrate the potential applications of the AACs, prototypes of common building elements, i.e., blocks, pavers, roof tiles and tiles, were manually fabricated (Fig. 8). Table 2 presents the parameters for the building elements; the parameters include the type and concentration of the alkaline activator, the curing temperature and the percentage of OPC added to the RCBW and the CW. It should be noted that for the fabrication of the elements, the mortars were formulated based on the results obtained for the cements presented in Section 3.1. The binder:sand ratio and the type of sand used for each case are shown in Table 2. In the production of the tiles, the GW was used both as the primary binder and as a fine aggregate. The blocks, pavers, roof tiles and tiles were evaluated against the specifications for each type of product according to the Colombian standards NTC 4026-4076, 2017, 1085 and 2086, respectively. Table 3 presents the properties of the various building elements required in the Colombian technical standards (NTC) and measured in the samples. The RCBW block satisfied the requirements for high-strength structural blocks given in the standard NTC 4026
with a compressive strength of 17.09 MPa (cured 28 days – 25 °C). The RCBW pavers exhibited a flexural strength of 4.42 MPa (cured 28 days – 25 °C) and satisfied the requirements in the standard NTC 2017 for a type 2 I-shaped pavers suitable for pavements, roads, and platforms. The RCBW roof tile did not meet the required failure load under flexion (1100 N) stated in the standard NTC 2086; however, it did exhibit high impact resistance and low permeability. We anticipate that using an automated and controlled production process (not manual) would produce an item that satisfies the specifications established by the standard. The example CW block satisfied the requirements for a non-structural block stated in the standard NTC 4076 with a compressive strength of 6.06 MPa (cured 28 days – 25 °C). However, it is anticipated that an adjustment in the binder:sand ratio would improve this performance. Finally, it can be observed that the GW tile satisfied the minimum requirements of the standard NTC 1085 for type B tiles. The properties of the prototypes demonstrate the potential applications of these products in the construction industry, and it should be emphasized that these results were obtained with manual fabrication processes and not automated processes. These
Fig. 8. Prototype building elements (blocks, pavers, roof tiles and tiles) fabricated.
Table 2 Parameters and optimal compositions of the AACs used in the applications. Recycled material
Binder:sand ratio
Initial curing temperature °C
Composition Binder
Activator and concentration Na2SiO3 (SiO2/Al2O3 = 6.78) NaOH (Na2O/SiO2 = 0.13) Na2SiO3 (SiO2/Al2O3 = 10.5) NaOH (Na2O/SiO2 = 0.09) NaOH (3% Na2O)
RCBW
1:1 (river sand)
25
90% RCBW/10% OPC
CW
1:2.75 (river sand)
25
70% CW/30% OPC
GW
1:2.25 (GW sand)
70
100% GW
Table 3 Properties of the building elements made with recycled CDW (AACs). Primary binder
Application
Standard*
RCBW
Structural block (high-strength) Pavers
NTC 4026
Roof tile
NTC 2086
CW
Non-structural block
NTC 4076
GW
Tile
NTC 1085
NTC 2017
Mechanical properties Required
Measured
= 13 MPa Abs. = 9% max. MR = 4.2–5 MPa = N.A Abs. = 7% max. Cf = 1100 N Imp. = 500 mm Abs. = 10% max. = 5–6 MPa Abs. = 12% max. Cf = 900–1100 N Imp. = 170 mm Abs. = 7% max.
= 17.09 MPa Abs. = 7.3% MR = 4.42 MPa = 24.60 MPa Abs. = 6.58% Cf = 995 N Imp. = 2500 mm Abs. = 8.7% = 6,06 MPa Abs. = 6.82% Cf = 1006 N Imp. = 312 mm Abs. = 13.85%
: compressive strength, MR: modulus of rupture, Abs.: water absorption percentage, Cf: flexural load; Imp.: impact resistance (height); N.A: not applicable. * NTC = Colombian technical standard.
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results indicate the viability of using these materials in both manual and industrial production processes. 4. Conclusions RCBW and CW, which are two of the main components of CDW, and GW, which is a minor residue that is difficult to handle and reuse, were used to produce alkali-activated cements (AACs) with satisfactory mechanical properties. The best mechanical performance (102 MPa) among the specimens cured at room temperature was obtained for RCBW mixed with 20% OPC and activated with a solution containing NaOH and waterglass (molar ratios SiO2/Al2O3 and Na2O/SiO2 of 6.78 and 0.13, respectively). The second best performance (33 MPa) was obtained for CW mixed with 30% OPC and activated with NaOH and waterglass (molar ratios SiO2/Al2O3 and Na2O/SiO2 of 10.5 and 0.09, respectively). For GW (100%), a maximum compressive strength of 57 MPa was achieved for activation with NaOH with a concentration of 4.6% Na2O and an initial thermal curing at 70 °C for 24 h. For the AACs made from 100% RCBW or CW, that is without OPC, it was possible to achieve adequate mechanical performance when cured at room temperature with appropriated adjustments of the synthesis conditions, particularly the type and proportion of the activator. For the case of 100% RCBW activated with NaOH and waterglass strengths of up to 54.38 MPa were achieved. For the 100% CW binder strengths of up to 25.57 MPa were attained. The results obtained in this investigation demonstrate the viability of reusing RCBW, CW and GW to create useful building materials for the construction industry (cements, masonry mortars and pre-fabricated elements). High-strength structural blocks, type 2 I-shaped pavers, and roof tiles were fabricated using an AAC made with RCBW, and these items exhibited high impact resistance and low permeability. Similarly, type B floor tiles were fabricated using an AAC made with GW. Non-structural blocks were produced using an AAC made with CW. These results demonstrate the advantages of the alkaline activation technique for the exploitation of CDW and the possibility of a sustainable solution to the environmental problems associated with the tremendous volumes of CDW being generated globally. In addition, building materials that satisfy construction codes were manually produced, thus demonstrating the feasibility of production in less developed communities. This type of production can be considered appropriate technology for constructing higher-quality housing in developing countries. Acknowledgments The authors, members of the Composite Materials Group (CMG) of the Centro de Excelencia en Nuevos Materiales (CENM), would like to thank the Universidad del Valle (Cali, Colombia) and the Departamento Administrativo de Ciencia, Tecnología e Innovación (Colciencias) of Colombia, for their support within the framework of the project ‘‘Construcción de prototipo a escala de vivienda rural utilizando materiales innovadores de baja huella de carbono”, contract No. 0696-2016 under which this research was conducted. References [1] R. Robayo, P. Mattey, D. Burgos, Y. Silva, S. Delvasto, Los residuos de la construcción y demolición en la ciudad de Cali: un análisis hacia su gestión, manejo y aprovechamiento, Revista Tecnura 19 (44) (2015) 157–170, http:// dx.doi.org/10.14483/udistrital.jour.tecnura.2015.2.a12. [2] Z. Wu, T.W.Y. Ann, L. Shen, L. Guiwen, Quantifying construction and demolition waste: an analytical review, Waste Manage. 34 (2014) 16–83, http://dx.doi. org/10.1016/j.wasman.2014.05.010. [3] G. Rodríguez, C. Medina, F.J. Alegre, E. Asensio, M.I. Sánchez de Rojas, Assessment of construction and demolition waste plant management in Spain: in pursuit of sustainability and eco-efficiency, J. Cleaner Prod. 90 (2015) 16–24, http://dx.doi.org/10.1016/j.jclepro.2014.11.067.
137
[4] J. Xiao, W. Li, Y. Fan, X. Huang, An overview of study on recycled aggregate concrete in China (1996–2011), Constr. Build. Mater. 31 (2012) 364–383, http://dx.doi.org/10.1016/j.conbuildmat.2011.12.074. [5] H. Yuan, A.R. Choni, Y. Lu, L. Shen, A dynamic model for assessing the effects of management strategies on the reduction of construction and demolition waste, Waste Manage. 32 (2012) 521–531, http://dx.doi.org/10.1016/j. wasman.2011.11.006. [6] European Commission, Resource Efficient Use of Mixed Wastes; Environment, Waste, Studies, 2015. Available from:
138
R.A. Robayo-Salazar et al. / Construction and Building Materials 149 (2017) 130–138
[29] K.J.D. MacKenzie, What are these things called geopolymers? A physicochemical perspective, Ceram. Trans. 153 (2003) 175–186, http://dx.doi.org/ 10.1002/9781118406892.ch12. [30] A. Alonso, A. Palomo, Alkaline activation of metakaolin and calcium hydroxide mixtures: influence of temperature, activator concentration and solids ratio, Mater. Lett. 47 (2001) 55–62, http://dx.doi.org/10.1016/S0167-577X (00)00212-3. [31] P. Duxson, J. Provis, G. Luckey, S. Mallicoat, W. Kriven, J. Van Deventer, Understanding the relationship between geopolymer composition, microstructure and mechanical properties, Colloids Surf. A 269 (2005) 47– 58, http://dx.doi.org/10.1016/j.colsurfa.2005.06.060. [32] F. Pacheco-Torgal, J. Castro-Gomes, S. Jalali, Alkali-activated binders: a review. Part 1. Historical background, terminology, reaction mechanisms and
hydration products, Constr. Build. Mater. 22 (2008) 1305–1314, http://dx. doi.org/10.1016/j.conbuildmat.2007.10.015. [33] I. Garcia-Lodeiro, A. Fernandez-Jimenez, A. Palomo, Hydration kinetics in hybrid binders: early reaction stages, Cem. Concr. Compos. 39 (2013) 82–92, http://dx.doi.org/10.1016/j.cemconcomp.2013.03.025. [34] P. Nath, P. Sarker, Use of OPC to improve setting and early strength properties of low calcium fly ash geopolymer concrete cured at room temperature, Cem. Concr. Compos. 55 (2015) 205–214, http://dx.doi.org/10.1016/j. cemconcomp.2014.08.008. [35] T. Suwan, M. Fan, Influence of OPC replacement and manufacturing procedures on the properties of self-cured geopolymer, Constr. Build. Mater. 73 (2015) 551–561, http://dx.doi.org/10.1016/j.conbuildmat.2014.09.065.