Journal of Environmental Management 133 (2014) 275e283

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New methodology for assessing the environmental burden of cement mortars with partial replacement of coal bottom ash and fly ash E. Menéndez a, *, A.M. Álvaro a, b, M.T. Hernández c, J.L. Parra d a

Eduardo Torroja Institute of Construction Science (IETcc-CSIC), Spain ETSIT e Polytechnic University of Madrid (UPM), Spain c EUITI e Polytechnic University of Madrid (UPM), Spain d ETSIM e Polytechnic University of Madrid (UPM), Spain b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 11 July 2013 Received in revised form 18 October 2013 Accepted 1 December 2013 Available online 7 January 2014

This paper assess the mechanical an environmental behaviour of cement mortars manufactured with addition of fly ash (FA) and bottom ash (BA), as partial cement replacement (10%, 25% and 35%). The environmental behaviour was studied by leaching tests, which were performed under several temperature (23  C and 60  C) and pH (5 and 10) conditions, and ages (1, 2, 4 and 7 days). Then, the accumulated amount of the different constituents leached was analysed. In order to obtain an environmental burden (EB) value of each cement mixture, a new methodology was developed. The EB value obtained is related to the amount leached and the hazardous level of each constituent. Finally, the integral study of compressive strength and EB values of cement mixtures allowed their classification. The results showed that mortars manufactured with ordinary Portland cement (OPC) and with coal BA had similar or even better environmental and mechanical behaviour than mortars with FA. Therefore, the partial replacement of cement by BA might be as suitable or even better as the replacement by FA. Ó 2013 Elsevier Ltd. All rights reserved.

Keywords: Coal bottom ash Fly ash Cement additions Environmental burden Mechanical properties

1. Introduction Concrete and steel are currently the most widely used construction materials. The main component of concrete is cement, which main constituent is clinker. The manufacture of clinker consumes non-renewable resources, both in the fuels and in the raw materials themselves, and releases CO2. The partial replacement of clinker by additions, like coal combustion residues, minimizes these disadvantages. Furthermore, the use of additions in the cement manufacture modifies the microstructure of the hydrated pastes. In general, the use of additions in cements causes denser hydration products and a more closed porous network than that of Ordinary Portland Cement (OCP). This results in more durable construction materials. (Menéndez and de Frutos, 2009, 2011). From the point of view of wastes, construction materials have normally been used for their inertia and stabilization, avoiding CO2 gas emissions or reducing the leaching of dangerous substances (Maeda et al., 2011; Lima et al., 2012). The European standard EN 197e1, 2011 limits both the type and the amount of additions that can replace clinker in cement manufacture. Among these additions, some are industrial by* Corresponding author. E-mail address: [email protected] (E. Menéndez). 0301-4797/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jenvman.2013.12.009

products, that is, wastes recycled in the production of cement. One of the by-products most commonly used in cement and concrete manufacture is fly ash (FA) from coal-pulverized power plants, which are fine particles collected by electrostatic or mechanical precipitation. Coal power plants also produce bottom ash (BA), which are coarse and glassy particles that fall to the bottom of the furnace and conglomerate. FA represents between 70% and 90% of the coal ashes produced in power plants, while coal BA represents between 10% and 30% (Siddique, 2010). The European production of FA and BA in 2008 was 37.5 MT and 4.8 MT, respectively (ECOBA, 2008). Despite the amounts produced coal BAs have not been used yet as cement additions. There are differences between FA and BA, both in chemical and physical composition. The chemical composition of coal BA contains lightly more heavy metals than FA. However, BA radioactivity content (e.g. 226Ra, 232Th, 40K, 238U and 210Pb) is lower than that of the respective FA (Karangelos et al., 2004; Puch et al., 2005; Lu et al., 2006). Regarding their physical properties, BA particles are denser and coarser than FA particles (Siddique, 2010; Bai and Bashaer, 2003). The properties of FA as addition to cement have been widely studied due to they are included as authorized additions to cement in replacement amounts of up to 50% (EN 197e1, 2011 and RC-08, 2008). It can be deduced from these studies that the addition of FA produces properties similar to or even better than Portland

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cement (Papadakis, 1999, 2000). One of the main improvements is the lower demand of water and less heat in the hydration process (González et al., 2009). As regards coal BAs, they have only been used in some applications in the construction industry, mainly as an aggregate to concrete in the manufacture of blocks and as filling material, for example, in the foundations of road construction (ECOBA, 2008; Siddique, 2010; Lee et al., 2010). Although BA is not considered an addition to cement (Cheriaf et al., 1999), several authors have tested their pozzolanic properties and the compressive strength of cement mortars with partial replacements of BA and these studies have obtained satisfactory results. Jatuapitakkul and Cheerarot (2003) studied the pozzolanic properties and the mechanical strength of mortars manufactured with coal BA, reporting that the pozzolanic activity appears at 28 days of hydration, improving this property with a suitable grind. This fact was also observed by Jatuapitakkul and Cheerarot (2003) and Sanjuan and Menéndez (2011). Good mechanical properties of mortars were observed by Canpolat et al. (2004) and Argiz et al. (2013) when cement was replace for FA, BA or a mixture of both up to 25%. Suitable strength was also observed when cement with 25% replacement was used in the manufacture of concrete (Jatuapitakkul and Cheerarot, 2003). Canpolat et al. (2004) studied the effects of the addition of zeolite and BA or FA in different proportions in Portland cement, reporting that the majority of the cements studied showed compressive strength greater than the CEM I 42.5 cement, according to the European Standards. However, some suitable pozzolanic and mechanical properties are not enough qualities for reuse these ashes as secondary construction materials (Chatveera and Lertwattanaruk, 2011; Kayhanian et al., 2012). The protection of the environment, especially those aspects related to air, water and soil quality, as well as human health, are essential requirements expressed in the European Construction Products Directive (CPD, 1989). More specifically the CPD focuses on the leaching of dangerous substances from construction materials to the water, which is an especially concern when secondary materials are used (van der Sloot et al., 1997). Therefore, construction materials must be tested with regard to their leaching properties. Leaching process is influenced by both the characteristics of the material and environmental factors. The multiple variables involved in the process have resulted in multiple types of testing methods, originally used to characterised wastes or wastes stabilized in matrix (e.g. cement matrix). From the point of view of the own material, it can be classified as monolithic or granular. The release of constituents from monolithic materials are mainly controlling by diffusion process while the release of constituents from granular materials are due to percolation (van der Sloot et al., 1997; van der Sloot and Dijikstra, 2004; Barna et al., 2005; Tiruta-Barna et al., 2005). Cement based materials often behave as porous monoliths. There are different testing methods for monolithic material and several authors using different methods have studied the leaching of dangerous elements from materials made of FA from Municipal Solid Waste Incineration (MSWI). Aubert et al. (2007) used the French Standard NFX 31e211 regulation as testing method in order to obtain the behaviour of the dangerous elements contained in these materials. Sinyoung et al. (2011) and Chai et al. (2009) used the EA NEN 7375, 2004 “tank test method” in order to evaluate the leaching behaviour of chromium, a heavy metal with negative effects on the environment. This method was also used by Ginés et al. (2009) to study this type of addition compared to BA produced in the same process. Cinquepalmi et al. (2008) developed a method for the leaching behaviour of the chemical elements based on the results obtained from the “sequential leach test on monolithic specimens” developed by Kosson et al. (2002).

Table 1 Chemical composition of cement and ashes (%). Chemical composition

OPC

Fly Ash (FA)

Bottom Ash (BA)

Loss of ignition (LOI) Insoluble Residue (RI) Free lime SiO2 Al2O3 Fe2O3 CaO MgO K2O CO2 TiO2 Na2O P2O5 SO3 SrO Cr2O3 ZnO Mn2O3 Cl

3.60 2.14 0.12 17.74 3.49 3.42 58.92 1.51 0.84 2.11 0.23 0.20 0.09 2.88 0.10 0.00 0.03 0.03 0.01

3.65 1.03 0.11 54.20 27.17 6.23 6.89 1.16 0.67 2.78 1.79 0.17 0.97 0.11 0.21 0.04 0.01 0.05 0.01

1.85 0.31 0.07 49.97 26.95 8.34 8.28 1.12 0.78 0.00 2.25 0.14 0.95 0.11 0.29 0.05 0.01 0.05 0.02

Despite multiple existing test methods, they are not able to assess the complete impact of the material considering proportionally the different hazards of each leached substance. While methods like that used in the French Standard NFX 31e211 regulation are focuses on not to exceed a limited value of several substances, other are occupied on study the complex leaching process calculating leaching parameters like diffusion coefficients (EA NEN 7375, 2004). In this paper, a methodology was developed to assess the environmental burden of several cement materials by establishing a single value for each one starting from a usual leaching test. This value, denominated Environmental Burden (EB), is related to the relative amount and the hazard level of each substance leached. The methodology was applied to several cement mortars with different proportions of partial replacement of FA and BA from coal fired power plants in order to study the usability of BA as addition to cement from the point of view of environmental impact. Then, the EB values obtained were faced to the compressive strength results to classifying the cement mixtures taking into account both the mechanical and environmental behaviour. 2. Experimental In this work, mechanical and leaching behaviour of different cement mixtures with FA and BA were studied. First, the compressive strength of cement mortars were tested according to established limits. Then, the leaching test of cement mortars were studied in different test conditions. Finally, a new methodology was developed and applied to the cement mortars studied in order to evaluate and classify them according to their mechanical and environmental behaviour. 2.1. Raw materials and sample preparation The cement used was an OPC classified as CEM I 42.5 type. FA and BA were collected from the ENDESA e Carboneras power plant (Almería-Spain) because of the satisfactory chemical and physical properties of that FA. This power plant has a power production of 1,158,900 kW and uses coal from South Africa (90%) and Colombia (10%). The main components of these raw materials was determined by X-ray fluorescence using a Bruker, S8 The Insoluble Residue (RI) was analysed through the sodium carbonate method and the

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content of Lost on Ignition (LOI) was determined burning the ashes during 1 h (950  C); both methods are described in the standard EN e 196e2:2006, EN 196e2, 2006. Each determination is the average of three values. The results, expressed as oxides, are listed in Table 1. A similar chemical composition between FA and BA was observed. However, BA had a somewhat greater proportion of heavy metals than FA, specifically as regards to iron, titanium, strontium and zinc. The total amount of alkalis (sodium and potassium) was virtually the same, but the distribution was different: BA had a greater amount of potassium than FA. With regard to compliance requirements, the chemical composition of this coal BA is in accordance with the limits established in European Standard EN 197e1, 2011 for FA. FA was used in its original size, while BA was grinded before used it due to the greater size of BA particles compared to FA particles. Furthermore, grinding process improves the pozzolanic activity of ashes (Cheriaf et al., 1999; Jatuapitakkul and Cheerarot, 2003). The particle distribution was determined through granulometry laser by using the Malvern Instrument MasteSizer 2000 equipment. The cumulate particle size distribution of the cement components is detailed in Fig. 1. Seven cement mixtures were studied both mechanically and environmentally. Cement mixtures with 10%, 25% and 35% of cement replacement by FA or BA were used. These percentages would correspond to those for cement types II/A, II/B and IV, respectively, in accordance with the standard EN 197e1, 2011. A reference cement mortar without additions was also tested. A summary of the seven cement mixtures tested is shown in Table 2. For each cement mixture, six prismatic specimens of 40 mm  40 mm  160 mm were prepared. Mortars were manufactured with siliceous sand (with 95% quartz content) and water according to the specifications described in the standard EN 196e1, 2005. The relations sand/cement ratio of 3:1 and water/cement ratio of 0.5 were used. The specimens were manufactured according to the standard mentioned and curing in moisture chamber (20,0  1.0  C y 90% HR) during 24 h according to the standard EN 196e1, 2005. After unmolding, three specimens were cut in three parts obtaining twelve cubes of 40 mm  40 mm  40 mm. Then, all the specimens were covered with water until the tests. The three specimens of 160 mm length were used in the mechanical test while the twelve cubic specimens of 40 mm length were used in the leaching test.

277

Table 2 Cement mixtures proportions for testing. Cement mixture

FA

BA

OCP

EN 197e1[3]

OPC 90Ce10FA 90Ce10BA 75Ce25FA 75Ce25BA 65Ce35 FA 65Ce35BA

0% 10% 0% 25% 0% 35% 0%

0% 0 10% 0% 25% 0% 35%

100% 90% 90% 75% 75% 65% 65%

CEM CEM CEM CEM CEM CEM CEM

I II/A II/A II/B II/B IV/A IV/A

Table 3 Temperature and pH conditions for leaching test Designation TC TC TC TC

e e e e

RA RB HA HB

Test condition

Temperature ( C)

pH

Room temperature e acid pH Room temperature e base pH High temperature e acid pH High temperature e base pH

23 23 60 60

5 10 5 10

2.2. Mechanical test of mortars The compressive strength of the mortars manufactured was tested according to the standard EN 197e1, 2011 in order to check their mechanical properties. First, three specimens (40 mm  40 mm  160 mm) of each type of cement mixture were tested to determine their flexural strength and then, the compressive strength of the six samples resulted were tested. The measures were realized at different times (1, 7, 14 and 28 days). 2.3. Leaching test of mortars The amount of constituents released from cement mortars specimens when are exposed to a potentially aggressive solution was tested by leaching tests. The tests were based on the method described in the standard NSF/ANSI 61-2009 for barrier materials (NSF/ANSI Standard 61, 1988). This method is based on exposing the material to a test solution which was renewed after 1, 2, 4 and 7 days. At the end of each test period, the solution was collected from the test recipient for its analysis. It was determined the ions presented in the solution and its pH and conductivity. The test procedure was repeated for each of the consecutive periods, using a new test solution each time. The method allows testing specimens under different temperature and pH conditions. Four test conditions were selected in order to cover a wide range of common applications of cements. These test conditions, detailed in Table 3, room or high temperature with a base or acid medium were mixed. The initial acid pH of the solution was obtained using a solution of HNO3 and the initial basic pH using a solution of NaOH. For each test condition, three specimens of 40 mm  40 mm  40 mm were tested. 2.4. Environmental assessment of mortars

Fig. 1. Accumulated particle size distribution of OPC, FA and BA.

After testing, test solutions were analysed by means of inductively coupled plasma (ICP) with ICP Optical Emission Spectrometer Varian 725 e ES equipment. The silicon, aluminium, iron, calcium, magnesium, potassium, titanium, sodium, phosphorous, strontium, magnesium, chromium, sulphur and zinc amounts were determined, expressing them as parts per million (ppm). The pH and conductivity were also analysed in each case. A comparative analysis of the leaching behaviour of the mortars was carried out. First, the cumulative concentration of leached elements was quantified up to 7 days. Then, a new methodology to

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assess the environmental burden and classify the cement mixtures was developed. 3. Results and discussion 3.1. Mechanical test The compressive strength of the cement mortars increased over time because of the hydration process development (Menéndez and de Frutos, 2009, 2011) (Fig. 2). At any time of hydration, an inverse correlation between compressive strength of cement mortars and cement replacement percentage was observed: as the cement replacement percentage increased, the compressive strength decreased. However, the compressive strength of cement mortar up to 25% of BA was slightly higher than 42.5 MPa, the minimum value required to OPCs (EN 197e1, 2011). Actually, the compressive strength of cement mortars with 10% of FA or BA was noticeable higher than that of OPC’s specimen tested. The compressive strength results showed are the average of six measures. At 28 days of hydration, the maximum standard deviation of all the results was lower than 2.5 MPa. Cement mortar mixtures had a standard deviation lower than OPC mortar. For each amount of cement replacement, cements with BA tended to have a higher than those with FA. 3.2. Leaching test The concentration of ions present in the test solutions was determined in the seven different mortars exposed to the different test conditions, and for the different time periods (1, 2, 4 and 7 days). The accumulated concentration results (ppm) of aluminium, calcium, potassium, magnesium, sodium, sulphur, silicon and strontium are detailed in Table 4 (TC-RA and TC-HA) and Table 5 (TC-RB and TCHB. The concentration of chromium, iron, manganese, titanium and phosphorous were below the detection limit of the technique in all cases (12 ppb, 6.35 ppb, 2 ppb, 1.23 ppb and 73.37 ppb, respectively). Therefore, they are not included in the analysis of the results. The pH values of the final solution was also measured and it was observed an increased of pH around 11-12 due to the basicity nature of cement matrix (van der Sloot and Dijikstra, 2004). It is observed that the greatest leaching concentrations were produced with calcium, potassium and silicon, with values of up to 220 ppm, 27 ppm and 13 ppm, respectively. The sodium, aluminium and sulphur released in amounts of between 3.7 ppm

and 5 ppm. Finally, the magnesium and strontium released in amounts less than 1 ppm, with maximum cumulative values of 0.19 ppm and 0.9 ppm, respectively. However, the integral ambient value is more complex, taking into account the dangerous nature of the element released as well as their concentration. Regarding to the test conditions, the temperature has a higher influence than the pH value on the amount of elements leached: the higher the temperature, the higher the amount of element leached. When samples are tested at high temperature, ph has a little effect on the results. However, when samples are tested at ambient temperature, pH plays a more important role: lower pHs enhance leaching rates. As regard as variability results, for each element and time period, major elements as calcium, silicon and aluminium had a variability lower than 10%, while other elements as sodium, potassium, magnesium, sulphur and strontium had a variability up to 18%. The higher variability might be caused by the lower availability of the element in the cement matrix. No significant difference was noticed between cement mixtures or test conditions. From the point of view of the hazardous nature of the metals, such as aluminium, strontium, iron, titanium, chromium and zinc, a danger to health is assumed if they are ingested in significant quantities. While manganese is dangerous for aquatic organisms, potassium hydroxide and sodium are corrosive. Silicon, calcium, magnesia, phosphorous and sulphur have no significant effect on either health or the environment (INCHEM, 1998). Sometimes, the cements were used to stabilize waste having certain characteristics, or as partial substitutes, due to their reactions with it. The use of waste in cement can induce a higher release of contaminants in the water or in the environment in contact with the construction materials, and it is necessary to evaluate this potential leaching. It is necessary to establish limits for certain types of dangerous elements, such as heavy metals (Yang et al., 2011), and with the increase in leaching knowledge, the limits can be readjusted. The stabilization of waste in cement needs an analysis of the potential leaching of heavy metals to the environment (Yang et al., 2011; Duong and Lee, 2011; Ucaroglu and Talinli, 2012). This ensures that highly dangerous elements, like arsenic, are properly stabilized in the matrix with OPC and mixes of OPC with FA, observing leaching of less than 5% in the most unfavourable conditions (Coussya et al., 2012). When cement base materials with meal and bone meal bottom ash (MAM-BA) waste are analysed the main elements found are calcium, sodium, potassium and aluminium and also heavy metals. However, the composition of the waste and the extracted products is variable. In particular, there is a very important dispersion in the composition of the elements Pb, Ti, Cd, Cr, Fe, Ni, Zn y Cu, although the chemical composition of BA is more homogeneous and can be controlled in accordance with the limits established for coal BA in the European Standard EN 197e1, 2011 (Coutand et al., 2011; Dermol and Konti, 2011). With respect to the percentage of substitution of cement by waste, it is observed that for a good behaviour the limit is around 20%. For example, good solidification/stabilization is observed in automotive phosphate coating sludge containing heavy metals in mortars of OPC (Ucaroglu and Talinli, 2012). 3.3. Environmental assessment

Fig. 2. Compressive strength development of mortars.

In order to obtain a global environmental assessment of cement mortar mixtures, a new methodology has been developed. It consists on establish a single value for each cement mortar mixture starting from the results obtained in the leaching test realised. This value, denominated Environmental Burden (EB), is related to the relative amount and the hazard level of each substance leached.

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279

Table 4 Accumulated leaching of chemicals elements in mortars tested at pH ¼ 5 conditions (p.p.m.). Element

Aluminium

Calcium

Potassium

Magnesium

Sulfur

Silicon

Strontium

Sample

OPC 90Ce10FA 90Ce10BA 75Ce25FA 75Ce25BA 65Ce35FA 65Ce35BA OPC 90Ce10FA 90Ce10BA 75Ce25FA 75Ce25BA 65Ce35FA 65Ce35BA OPC 90Ce10FA 90Ce10BA 75Ce25FA 75Ce25BA 65Ce35FA 65Ce35BA OPC 90Ce10FA 90Ce10BA 75Ce25FA 75Ce25BA 65Ce35FA 65Ce35BA OPC 90Ce10FA 90Ce10BA 75Ce25FA 75Ce25BA 65Ce35FA 65Ce35BA OPC 90Ce10FA 90Ce10BA 75Ce25FA 75Ce25BA 65Ce35FA 65Ce35BA OPC 90Ce10FA 90Ce10BA 75Ce25FA 75Ce25BA 65Ce35FA 65Ce35BA

23  C

60  C

Day 1

Day 2

Day 4

Day 7

Day 1

Day 2

Day 4

Day 7

0.179 0.184 0.190 0.225 0.172 0.208 0.236 32.647 53.682 36.256 55.587 28.957 43.959 35.293 7.240 7.772 6.931 7.798 7.114 7.744 7.288 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.265 0.273 0.240 0.371 0.164 0.260 0.269 0.884 0.702 0.679 0.673 0.669 0.686 0.751 0.151 0.271 0.190 0.297 0.182 0.287 0.216

0.318 0.352 0.325 0.423 0.302 0.587 0.436 55.144 84.642 61.220 84.593 50.151 69.147 58.748 8.307 9.338 8.197 9.312 8.296 9.771 8.513 0.009 0.009 0.010 0.000 0.000 0.015 0.013 0.265 0.449 0.240 0.623 0.164 0.410 0.433 1.799 1.442 1.467 1.592 2.165 1.648 1.607 0.218 0.367 0.278 0.404 0.267 0.403 0.311

0.528 0.600 0.535 0.761 0.522 0.887 0.691 85.844 122.813 93.942 123.332 79.849 98.760 86.285 9.799 11.347 9.870 11.299 9.874 11.633 9.901 0.032 0.028 0.038 0.028 0.017 0.037 0.035 0.496 0.745 0.481 1.012 0.402 0.682 0.659 3.217 2.579 2.775 2.963 3.268 2.739 2.710 0.303 0.483 0.388 0.548 0.380 0.545 0.421

0.809 0.945 0.792 1.197 0.772 1.352 1.109 126.570 173.130 135.814 170.586 113.489 142.164 131.096 12.444 14.771 12.736 14.436 12.204 15.006 12.937 0.058 0.047 0.059 0.053 0.034 0.061 0.067 0.757 1.184 0.788 1.453 0.638 1.089 1.035 5.692 4.799 5.068 5.276 4.983 4.898 4.873 0.396 0.608 0.507 0.702 0.486 0.708 0.566

0.396 0.623 0.512 0.948 0.668 0.901 0.951 48.828 75.208 62.732 73.718 57.068 55.733 61.072 8974 9787 11.504 12.794 11.511 10.610 11.318 0.011 0.000 0.000 0.000 0.000 0.000 0.000 0.903 1.358 0.769 1.593 1.006 1.355 1.328 1516 0.966 1.034 1.191 1.184 1.327 1.404 0.212 0.385 0.336 0.459 0.351 0.419 0.391

0.835 1.160 0.970 1.527 0.995 1.342 1.543 79.101 119.120 101.636 107.552 85.203 81.469 89.716 11.208 13.064 15.415 15.519 13.585 12.316 13.297 0.034 0.013 0.022 0.015 0.020 0.017 0.016 1.128 2.172 1.301 2.148 1.251 1.693 1.843 3.155 2.450 2.462 2.802 2.202 2.626 3.134 0.305 0.540 0.492 0.605 0.465 0.550 0.534

1.388 1.970 1.739 2.317 1.850 2.474 2.494 121.356 166.775 142.760 141.597 122.660 114.203 118.567 15.257 17.127 20.816 17.650 16.252 14.265 14.422 0.054 0.042 0.073 0.047 0.047 0.047 0.050 1.459 2.854 1.818 2.712 1.934 2.653 2.402 6.453 5.450 3.904 5.250 4.972 5.762 6.068 0.444 0.714 0.628 0.757 0.639 0.729 0.677

2.005 2.837 2.550 3.555 2.738 3.876 3.669 173.996 216.330 193.722 182.068 158.190 147.703 150.157 21.616 22.869 27.078 21.032 19.300 16.583 16.559 0.065 0.061 0.088 0.071 0.069 0.080 0.118 1.728 3.237 2.207 3.349 2.362 3.665 3.103 10.633 10.209 8026 10.680 8830 10.485 11.458 0.601 0.870 0.814 0.902 0.781 0.875 0.796

The methodology was applied to the cement mortars mixtures tested to classify them according to their potential environmental impact. First, for each test condition and element released, the accumulated amount has been rating in the seven cement mixtures. Taking into account the maximum amount leached as a 100% of leaching and the minimum amount as a 0% of leaching, a rate of 5 has been assigned when cements leached between 0% and 33%, a rate of 10 when cements leached 34e66% and a rate of 100 when cements leached 67e100% (Table 6). Second, three categories of hazard have been established to weight the dangerous nature of the chemical elements released to the test solution from the mortars, according to the following considerations: (i) Chemical elements dangerous to people’s health, like aluminium, iron, magnesium, chromium and strontium. Only aluminium and strontium appeared in the test solutions.

These chemical elements are restricted in water consumption laws according to the European Directive on the Quality of Water Intended for Human Consumption (1998). (ii) Other dangerous chemical elements that might increase the pH of the water and be harmful, and even corrosive, not included in ED on the Quality of Water Intended for Human European Directive on the Quality of Water Intended for Human Consumption (1998), like sodium and potassium (Internationals Safety Data Sheets, 1994e2006). (iii) Other chemical elements in the test solutions, like calcium, silicon, sulphur and phosphorous. In accordance with this classification, a relative weight is established for the three categories in relation to the dangerous nature and the legal aspects of the chemical elements released. A relative value of 84% has been assigned to the category with the greatest potential danger (aluminium and strontium), 10% for the category of medium danger (sodium and potassium) and finally 6%

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Table 5 Accumulated leaching of chemicals elements in mortars tested at pH ¼ 10 conditions (p.p.m.). Element

Sample

Aluminium

Calcium

Potassium

Magnesium

Sulfur

Silicon

Strontium

OPC 90Ce10FA 90Ce10BA 75Ce25FA 75Ce25BA 65Ce35FA 65Ce35BA OPC 90Ce10FA 90Ce10BA 75Ce25FA 75Ce25BA 65Ce35FA 65Ce35BA OPC 90Ce10FA 90Ce10BA 75Ce25FA 75Ce25BA 65Ce35FA 65Ce35BA OPC 90Ce10FA 90Ce10BA 75Ce25FA 75Ce25BA 65Ce35FA 65Ce35BA OPC 90Ce10FA 90Ce10BA 75Ce25FA 75Ce25BA 65Ce35FA 65Ce35BA OPC 90Ce10FA 90Ce10BA 75Ce25FA 75Ce25BA 65Ce35FA 65Ce35BA OPC 90Ce10FA 90Ce10BA 75Ce25FA 75Ce25BA 65Ce35FA 65Ce35BA

23  C

60  C

Day 1

Day 2

Day 4

Day 7

Day 1

Day 2

Day 4

Day 7

0.225 0.251 0.195 0.301 0.221 0.243 0.262 41.022 55.257 50.374 50.014 41.964 42.766 46.040 7.400 7.538 8.260 7.532 8.200 8.287 8.309 0.036 0.015 0.000 0.000 0.000 0.000 0.010 0.299 0.433 0.269 0.463 0.207 0.297 0.313 0.841 1.555 1.497 1.624 1.590 1.648 1.638 0.217 0.299 0.263 0.320 0.269 0.307 0.285

0.454 0.567 0.432 0.568 0.443 0.451 0.593 63.959 86.256 77.320 75.731 68.212 68.176 72.195 8.257 10.194 13.259 8.924 9.279 9.560 9.764 0.096 0.078 0.032 0.022 0.017 0.012 0.025 0.375 0.718 0.427 0.718 0.457 0.297 0.313 1.686 2.589 2.248 2.387 2.381 2.439 2.451 0.379 0.432 0.371 0.429 0.377 0.429 0.390

0.706 0.870 0.692 0.910 0.873 0.799 0.920 96.687 126.640 112.985 110.725 119.904 100.770 104.856 9.456 11.776 14.911 10.366 12.525 11.109 11.064 0.130 0.104 0.051 0.045 0.037 0.035 0.043 0.662 1.139 0.780 1.121 0.930 0.656 0.627 3.209 4.148 3.502 3.709 3.723 3.588 3.565 0.477 0.554 0.489 0.565 0.582 0.582 0.516

1.009 1.266 1.008 1.343 1.228 1.225 1.336 138.302 179.794 156.703 155.087 162.407 138.958 146.807 11.927 14.821 17.845 12.938 15.015 13.620 13.294 0.183 0.144 0.081 0.076 0.056 0.064 0.065 0.947 1.599 1.121 1.590 1388 1031 0.962 5.673 6.898 5.676 5.928 5.491 5.436 5.467 0.602 0.699 0.617 0.713 0.715 0.735 0.652

0.547 0.696 0.592 0.719 0.412 0.623 0.607 56.787 78.091 53.201 66.372 44.368 50.693 48.513 8.790 11.607 10.209 11.009 9.544 10.095 9.157 0.013 0.011 0.013 0.000 0.000 0.012 0.000 1201 1.267 0.929 1.167 0.579 0.820 1.027 2.659 2.027 1.975 1.877 1.595 1.920 2.147 0.242 0.397 0.296 0.411 0.324 0.383 0.299

0.815 1.020 1.030 1.218 0.720 1.206 1.035 85.935 115.039 87.115 101.346 72.617 84.309 78.398 10.438 13.772 12.456 13.528 11.218 12.336 10.730 0.026 0.021 0.030 0.010 0.017 0.032 0.018 1201 1.668 1.267 1.725 1.551 1.302 1.531 4.211 3.304 3.460 3.428 2.548 3.820 3.569 0.320 0.516 0.424 0.558 0.444 0.544 0.425

1.304 1.686 1.550 2.081 1.406 2.496 2.047 128.209 165.080 126.789 137.915 112.519 121.489 116.202 13.240 17.827 15.546 16.545 13.749 15.056 12.707 0.048 0.043 0.057 0.035 0.046 0.076 0.051 1598 2.461 1.698 2.389 2.342 2.056 2.436 6.801 5.449 5.661 5.810 4.505 7.781 6.789 0.445 0.695 0.582 0.731 0.627 0.740 0.605

1.875 2.536 2.273 3.108 2.349 3.773 3.520 179.207 217.015 174.704 174.368 155.578 155.883 155.120 18.756 23.246 20.218 19.101 16.660 16.995 14.514 0.065 0.065 0.081 0.055 0.074 0.106 0.088 1863 2.923 2.056 2.842 2.992 2.887 3.277 12.287 9.718 9.662 10.650 8.242 12.489 12.653 0.585 0.861 0.751 0.870 0.795 0.900 0.769

Table 6 Rating of the relative accumulative concentration of each element migrated against the concentration of the same element from the rest of mortars under the same test conditions. Rating (R)

Relative concentration

100 50 10

42.5

50 EB 51e75 EB 76e100 EB Any value

Optimum Good Medium Low

MPa MPa MPa MPa

allowing the optimal selection of them depending of the objective parameters. In general, the integral assessment realized of the mechanical and environmental behaviour of the cement mortars mixtures shows a better behaviour of the mortars manufactured with BA than those with FA. Specifically, the cement mortar without additions and the cement mortar mixtures with partial replacement of 10% and 25% of BA and 10% of FA had the best integral behaviour. Acknowledgements

Table 9 Qualification of mortars under different test conditions. Test conditions

Group A

Group B

Group C

Group D

pH 10e23  C

OCP 90C-10BA

75C-25BA

90C-A0FA

pH 10e60  C

OPC 90C-10BA 75C-25BA OPC 90C-10BA 75C-25BA OPC 75C-25BA

90C-10FA

75C-25FA 65C-35FA 65C-25BA 75C-25FA 65C-35FA 65C-25BA 75C-25FA 65C-35FA 65C-25BA 75C-25FA 65C-35FA 65C-25BA

pH 5e23  C

PH 5e60  C

90C-10FA

90C-10FA 90C-10BA

improved by grinding the clinker or the BA more finely (Cheriaf et al., 1999; Jatuapitakkul and Cheerarot, 2003). As has been shown, the use of FA is admitted as an additive to cements. The results show that BA has better mechanical and environmental behaviour than FA. This would mean that the use of BA is suitable from the mechanical point of view and the potential leaching of compounds into water. The mechanical and environmental analysis allows the ideal use of a certain actions, such as partial replacements in the cement to be evaluated, evaluating not only the mechanical aspect but also the leaching of compounds into the environment. In order to do this, the strength of the mortars and the value of the EB, defined in this work, are used as analysis parameters. 4. Conclusions The environmental evaluation of mortars made with cements with partial FA or BA replacements allows testing their potential behaviour in water environments with different pH values and ambient or higher temperatures to be tested. The temperature is a determinant parameter as regards the leaching of compounds into the environment. In all cases, independent of the chemical compound analysed, greater leaching is produced when the test temperature is higher. As a test parameter, pH shows more random behaviour than temperature. However, in general, greater leaching is produced when the test is carried out with an acid pH, except in the case of strontium which experiences greater leaching with a higher pH. A new methodology was developed to evaluate the environmental impact of a group of cement mortar mixture through a single value denominated EB, which takes into account both the relative amount of each element leached and their potential danger to human’s health and environment. The bases of this methodology are the results obtained in a common leaching tank test and can be used using different test condition (pH and temperature), allowing the comparison between them. The integral assessment of the EB value and the mechanical behaviour classify cement mortars mixtures in four groups,

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New methodology for assessing the environmental burden of cement mortars with partial replacement of coal bottom ash and fly ash.

This paper assess the mechanical an environmental behaviour of cement mortars manufactured with addition of fly ash (FA) and bottom ash (BA), as parti...
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