Leaching in concretes containing recycled ceramic aggregate from the sanitary ware industry César Medina a, * , Moisés Frías b , María Isabel Sánchez de Rojas b a Departamento Construcción, Unidad Asociada UEX-CSIC, Avenida de la Universidad, s/n, 10071 Cáceres, Spain b Eduardo Torroja Institute for Construction Science (CSIC), C/Serrano Galvache, 4, 28033 Madrid, Spain article info Article history: Received 2 July 2013 Received in revised form 2 October 2013 Accepted 20 October 2013 Available online 5 November 2013 Keywords: Leaching behaviour Recycled concrete Re-use Ceramic waste Water quality abstract The re-use of construction and demolition, ceramic and similar waste in the construction industry has aroused considerable interest in recent years, as an avenue for furthering the sustainable use of resources and reducing the volume of waste dumped in landfills. Recycling materials as components in the manufacture of cement-based products, however, calls for an understanding of the leachability of the elements present in the new materials that may be harmful to human health or the respective ecosystems. The present study addresses the effect of including recycled ceramic sanitary ware waste as a partial substitute (25%) for natural coarse aggregate in the manufacture of recycled concrete in direct contact with water intended for human consumption. The findings show that the inclusion of ceramic aggregate raises the alkali concentration (Na and K) slightly and lowers the concentration of other elements (B, Si, Cl and Mg) in the water. The levels of all the leached elements were observed to be lower than the limits specified in the legislation in effect on water for human consumption. Consequently, these new concretes are apt for use in such applications, for they ensure water quality. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The need to set aside landfill space to accommodate the growing amounts of waste generated by the construction, ceramics and automobile industries is a serious environmental concern. Heightened public sensitivity to this problem has led to the implementation of new sustainability-based environmental pol- icies that encourage the recycling and re-use of such waste (Delay et al., 2007). The three keys to sustainability of construction materials are reduction, re-use and recycling (Marie and Quiasrawi, 2012). The versatility of the cement and concrete industry affords it huge potential (Medina, 2011) to absorb new materials of varying origin as active additions in cement, as coarse or fine aggregates in mortar, concrete and road base/sub-base manufacture. These recycled materials, such as construction and demolition (C&DW) or ceramic industry waste, are chemically inert (Galvin et al., 2012; Rodrigues et al., 2013). Nonetheless, depending on their origin, they may contain a certain proportion of hazardous elements, including metals (such as Znor Pb), anions (chlorides and sulfates) or organic compounds (polycyclic aromatic hydrocarbons) that may leach out when the materials are in contact with rain, surface or underground water. This constitutes a potential threat to the environment and for human health and safety (Dijkstra et al., 2012). The requirements that must presently be met by all construction materials throughout their service life, in particular in connection with health, hygiene and the environment, are laid down in Directive 89/106/EEC on Construction Products (CPD) (Hjelmar et al., 2012). This directive will be repealed in 2013 by Construc- tion Products Regulation n o. 305/2011 (CPR), which calls for very meticulous assessment of recycled products containing substances that may have an adverse effect on human health. The leaching resistance of granulated cement-based materials at the end of their useful life has been the object of considerable recent research (Delay et al., 2007; Meza et al., 2008; Engelsen et al., 2010, Galvin et al., 2012). The general consensus is that the leach- ability of substances from a given material is related to factors such as their solubility (Mulugeta et al., 2011). That, in turn, depends on other properties, including pH, the formation of inorganic com- plexes, the presence of dissolved organic matter and redox reactivity. The intrinsic properties of materials that play a more or less prominent role in leaching can be divided into two categories: chemical factors such as pH or the chemical composition of the * Corresponding author. Tel.: þ34 927 25 72 03x51539; fax: þ34 927 25 70 00. E-mail address: [email protected](C. Medina). Contents lists available at ScienceDirect Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro 0959-6526/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jclepro.2013.10.029 Journal of Cleaner Production 66 (2014) 85e91
0959-6526/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.jclepro.2013.10.029
a b s t r a c t
The re-use of construction and demolition, ceramic and similar waste in the construction industry hasaroused considerable interest in recent years, as an avenue for furthering the sustainable use of resourcesand reducing the volume of waste dumped in landfills.
Recycling materials as components in the manufacture of cement-based products, however, calls for anunderstanding of the leachability of the elements present in the new materials that may be harmful tohuman health or the respective ecosystems. The present study addresses the effect of including recycledceramic sanitary ware waste as a partial substitute (25%) for natural coarse aggregate in the manufactureof recycled concrete in direct contact with water intended for human consumption. The findings showthat the inclusion of ceramic aggregate raises the alkali concentration (Na and K) slightly and lowers theconcentration of other elements (B, Si, Cl and Mg) in the water. The levels of all the leached elementswere observed to be lower than the limits specified in the legislation in effect on water for humanconsumption. Consequently, these new concretes are apt for use in such applications, for they ensurewater quality.
� 2013 Elsevier Ltd. All rights reserved.
1. Introduction
The need to set aside landfill space to accommodate the growingamounts of waste generated by the construction, ceramics andautomobile industries is a serious environmental concern.Heightened public sensitivity to this problem has led to theimplementation of new sustainability-based environmental pol-icies that encourage the recycling and re-use of such waste (Delayet al., 2007).
The three keys to sustainability of construction materials arereduction, re-use and recycling (Marie and Quiasrawi, 2012).
The versatility of the cement and concrete industry affords ithuge potential (Medina, 2011) to absorb new materials of varyingorigin as active additions in cement, as coarse or fine aggregates inmortar, concrete and road base/sub-base manufacture.
These recycled materials, such as construction and demolition(C&DW) or ceramic industry waste, are chemically inert (Galvinet al., 2012; Rodrigues et al., 2013). Nonetheless, depending ontheir origin, they may contain a certain proportion of hazardouselements, including metals (such as Znor Pb), anions (chlorides andsulfates) or organic compounds (polycyclic aromatic hydrocarbons)
539; fax: þ34 927 25 70 00..
All rights reserved.
that may leach out when the materials are in contact with rain,surface or underground water. This constitutes a potential threat tothe environment and for human health and safety (Dijkstra et al.,2012).
The requirements that must presently bemet by all constructionmaterials throughout their service life, in particular in connectionwith health, hygiene and the environment, are laid down inDirective 89/106/EEC on Construction Products (CPD) (Hjelmaret al., 2012). This directive will be repealed in 2013 by Construc-tion Products Regulation no. 305/2011 (CPR), which calls for verymeticulous assessment of recycled products containing substancesthat may have an adverse effect on human health.
The leaching resistance of granulated cement-basedmaterials atthe end of their useful life has been the object of considerablerecent research (Delay et al., 2007;Meza et al., 2008; Engelsen et al.,2010, Galvin et al., 2012). The general consensus is that the leach-ability of substances from a given material is related to factors suchas their solubility (Mulugeta et al., 2011). That, in turn, depends onother properties, including pH, the formation of inorganic com-plexes, the presence of dissolved organic matter and redoxreactivity.
The intrinsic properties of materials that play a more or lessprominent role in leaching can be divided into two categories:chemical factors such as pH or the chemical composition of the
Table 1Physical and mechanical properties of the aggregates studied.
Property Gravel Ceramicaggregate
Specificationfor EN 12620
Real density of dry samples(kg/dm3) e (EN 1097-3)
2.63 2.39 e
Water absorption (wt%) e(EN 1097-3)
0.23 0.55 <4.5
Flakiness index (wt%) e (EN 933-3) 3 23 �35Los Angeles coefficient (wt %) e (EN 1097-2) 33 20 �40Total porosity (vol. %) e (ASTM D 4404-84) 0.23 0.32 e
Table 2Chemical composition of materials obtained by X-ray fluorescence.
SiO2 20.16 97.69 67.91Al2O3 4.36 1.73 22.01Fe2O3 2.52 0.13 1.41MgO 2.21 e 0.29CaO 63.41 0.04 2.41Na2O 0.35 e 1.91K2O 0.91 0.16 2.79TiO2 0.21 e 0.45ZnO e e 0.16
Minority element (ppm)P 610.99 e 741.92S 14297.71 8.88 280.35Rb 0.01 e 45.72Sr e e 84.56CrTotal 50.00 e 68.42Pb e e 55.70Cl 0.02 e 0.004B 3.00 e e
Mn e e 542.12
C. Medina et al. / Journal of Cleaner Production 66 (2014) 85e9186
aqueous phase in their pores, and physical factors such as perme-ability, release mechanism (diffusion), and form (monolithic orgranular) (Van Der Sloot, 2000, 2002; Van Der Sloot and Dijkstra,2004).
In recent years, Europe has made great strides in the harmo-nisation of its legislation on the assessment of substance leach-ability from monolithic or granular material to determine theapplications for which materials can be used (Van Der Sloot et al.,2006). The background references for that endeavour includedthe existing European standards (NEN 7341, DEV S4, NFXP 31-211)and studies conducted by a number of researchers (Hohberg et al.,2000; Van Der Sloot, 2000; Sánchez de Rojas et al., 2004; Mezaet al., 2008) to compare the variations in the findings whendifferent methods are used.
As a result, European standard EN 12457 (CEN, 2002) is now thereference to be used to analyse leaching in granular waste andsludge, classified by particle size and liquid/solid ratio (L/S).Stan-dard EN 14944 (CEN, 2007), in turn, is to be used to assess sub-stance leaching from the factory-made cementitious products(concrete tanks and pipes) that carry and store water intended fordirect human consumption, as well as the raw water from whichdrinking water is processed.
Thepresent studyconstitutes anovel approach, given thepaucityof international research (Marion et al., 2005; Hohberg et al., 2000)on the in-service leaching of substances from monolithic concreteand mortar. This question is of special relevance in new concretesthat are in continuous contact with water intended for humanconsumptionand that containdifferent typesof recycledaggregates.
The use of waste from the ceramic sanitary ware industry ascoarse aggregate to manufacture structural concrete has beenwidely studied by the authors of the present paper, who observedthat concretes with 25% recycled aggregate have higher splittingtensile and compressive strength than the conventional material(Medina et al., 2012a,b, 2013).
The present study explores substance leachability in recycledconcrete inwhich 25% of the natural coarse aggregate was replacedwith recycled ceramic materials, based on the concentration of theleached material after various leaching periods. Research in thisarea is essential to determining the feasibility of applying thesenew concretes to uses that call for direct contact with waterintended for human consumption, such as deposits or pipes.
2. Materials
Spain is the world’s leading producer and exporter of ceramicsanitary ware, with a yearly output of seven million items (2008).The percentage of articles rejected for sale and thus discarded de-pends on the type of industry, as well as product requirements andother technical considerations. Rejects nonetheless account for 5e7% of total output according to data provided by manufacturers.
The recycled ceramic aggregate used to prepare the experi-mental concretes, supplied by a sanitary ware manufacturer, con-sisted of ceramic waste crushed with a jaw crusher to a size of 4/12.5 mm.
Table 1 lists the physical andmechanical properties of the coarseaggregates used in the present study. Both types conformed to therequirements laid down in European standard EN 12620 andSpanish code on structural concrete EHE 08 for the (natural orrecycled) aggregates used in concrete manufacture.
The table shows that the ceramic aggregate had a higher porevolume and was consequently less dense than the gravel. With apore volume similar to the value observed for ceramic electricalinsulation, the recycled aggregate was 2.4 times more water-absorbent than the natural material. The flakiness index waseight times higher in the recycled ceramic aggregate than in gravel,
primarily as a result of its outer morphology, in turn due to theoriginal form of the waste and the crushing procedure. Anotherimportant property in aggregates is their Los Angeles coefficient.The recycled sanitary ware aggregate was found to be 39% morefragmentation-resistant than gravel (Medina et al., 2013).
The chemical composition of the materials used to manufacturethe concrete tested in the present study is given in Table 2. Note thesubstantial differences between the two types of coarse aggregate.The natural aggregate consisted primarily of silica (97.69%) withtraces of other elements (Al, Fe, Ca, K and S), while the majorityelements in the new recycled aggregate were silica (67.91%) andalumina (22.01%), with P, Pb, Cr and others as trace elements.
If these concretes are in contact with drinking water, the metals(Al, Fe, Mn, Cr and Pb), alkalis (Na) and halogens (Cl) present in therecycled ceramic aggregate might leach out, to the detriment ofwater quality (European Directive 98/83/EC and Spanish RoyalDecree RD 140/2003).
Finally, the ceramic aggregate contained no organic materialthat would alter concrete setting or hardening rates nor did itexhibit alkali-aggregate reactivity, according to the petrographicstudy conducted.
3. Methods
3.1. Leaching test
The four-stage method described in European standard EN14944-3 was used to assess substance leaching from cement-basedproducts into the test water after exposure.
1) Four cubic specimens (150 � 150 � 150 mm3) were preparedwith the two types of concrete: reference concrete (RC) andrecycled concrete containing 25% recycled ceramic aggregate
C. Medina et al. / Journal of Cleaner Production 66 (2014) 85e91 87
(CC-25). The concretes were prepared and cured as specified inEuropean standard EN 12390, except that release agents werenot used to remove the material from the moulds, to avoid allmanner of contamination. Concrete batching is listed in Table 3.
2) Secondly, an 83 mm high glass cylinder with an internal diam-eter of 140 mm was placed on top of the concrete specimen(Fig. 1) to attain a surface/volume (S/V) ratio of 1.3� 0.1 dm�1, asspecified in standard EN 14944.
3) The samples were pre-conditioned by exposure, in fivesequential periods, to the pre-conditioning water (one 72-hourpreceded by four 24-hour periods). The aim was to ensure thatafter the fifth period, the pH of the pre-conditioning water waslower than 9.5. The pre-conditioning water consisted of a so-lution of demineralised water containing anhydrous calciumchloride (CaCl2) and sodium hydrogen carbonate (NaHCO3)(Table 4).
4) To conduct the leaching test, the concrete samples were set inthe test water for three leaching periods, after which theleachate was analysed. Each leaching period lasted 72 h.
The test water (Table 4) contained anhydrous calcium chloride(CaCl2), sodium hydrogen carbonate (NaHCO3) and sodium silicate(Na2SiO3 * 9H2O) dissolved in demineralised water in the pro-portions specified in Table 4. The pH was 7.0 and the electricalconductivity 426 mS/cm.
A control test was conducted on a glass specimen exposed to thesame conditions as the concrete specimens (S/V, pre-conditioning,test water composition).
3.2. Chemical analysis of migration water
The majority and minority elements present in the leachatewere determined with inductively coupled plasma e opticalemission spectrometry (ICP-OES). The instrumental conditionswere: Varian 725-ES spectrometer fitted with a sample changerand diluter; argon plasma ionisation.
The concentration of the leached elements, as well as the elec-trical conductivity and pH, were compared to the limits establishedin European Directive 98/83/EC and Spanish Royal Decree RD 140/2003 (see Table 5).
Fig. 1. Test layout: a) conventional concrete
3.3. Data treatment
Eq. (1) was used to calculate elemental concentration (cnT), inwhich an
T is the concentration of the element in the leachate (mg/L)and bn
T its concentration in the control water (mg/L).
cTn ¼ aTn � bTn (1)
The migration rate for each element (MnT) (mg/dm2*day), was found
with Eq. (2):
MTn ¼ cTn=ðS=V$tÞ (2)
where S/V is the surface/volume ratio (1.3 dm�1) and t is theleaching time in days (3 days).
Lastly, the mean migration rate was calculated as the arithmeticmean of the rate found for the three leaching periods.
(RC) and b) recycled concrete (CC-25).
Fig. 2. Leachate pH by type of concrete vs leaching period.
Fig. 3. Leachate electrical conductivity by type of concrete vs leaching period.
C. Medina et al. / Journal of Cleaner Production 66 (2014) 85e9188
4. Results
Figs. 2 and 3 show the means and standard deviations observedfor leachate pH and electrical conductivity, respectively, after thethree leaching periods (M1med, M2med and M3med).
According to the graph in Fig. 2, the pH in the leachates incontact with the concrete containing ceramic aggregate (CC-25)was no higher than the pH observed in the leachates in contact withconventional concrete (RC). The minor differences observed weredue to the variations in the alkali content in the two types ofleachate (see Table 5). These pH values lie within the range (9.5e6.5) specified in the existing legislation for this parameter (Euro-pean Directive 98/83/EC and Spanish Royal Decree RD 140/2003).
Table 6Mean concentration (mg/L) of leached elements after several leaching periods.
Note: Mean concentrations calculated using Eq. (1).a � Standard deviation.
That legislation also lays down other requirements for waterintended for human consumption, such as electrical conductivity,which constitutes a measure of dissolved salts and of the concen-tration of certain cations and anions. To be apt for human con-sumption, water must conform to both requisites.
Fig. 3, in turn, shows that the leachate in contact with concreteRC had higher electrical conductivity than the water in whichconcrete CC-25 was immersed, due to the higher Naþ and Cl�
concentration in the former. Here also, the values after all threeleaching periods were comfortably below the limit (2500 mS/cm)stipulated in the legislation in effect on water for human con-sumption. The values lay within the 400e800-mS/cm range previ-ously reported by Sani et al. (2005) for concretes containingrecycled C&DW.
The mean and standard deviation values for the elementsleached in the water after the various leaching periods are given inTable 6. As the table shows, the presence of metalloids (B and Si),alkaline-earths (Mg), alkalis (K and Na) and halogens (Cl) wasdetected. Their concentration was below the upper limits estab-lished for drinking water (see Table 5).
Leaching is directly related to solubility in these elements,which depends in turn on pH (Van Der Sloot, 2000), availability andconcrete pore system characteristics (pore size distribution).
The calcium concentration in the leachate found after applyingEq. (1) was less than zero (<0) due to precipitation (Commission,2000). That process was due primarily to two developments: a)the presence of aqueous carbon dioxide and bicarbonate ions inthe test water induced calcium penetration in the pore solution; b)Ca2þ solubility gradually declined at pH > 7. The reaction betweenthe hydroxide ions in the pore solution and the dissolved aqueouscarbon dioxide and bicarbonate ions yields carbonate ions. Thatmay have given rise to conditions suitable for spontaneous cal-cium carbonate precipitation in the pores near the exposed sur-face (carbonation), which would explain why the finalconcentration of this element was greater in the test water than inthe leachate.
The concentrations of the elements not listed in Table 6 were toolow to be ICP-OES-detectable. The most prominent of these ele-ments were metals with an adverse effect on human health such asPb, Fe, Crtotal, Al and Mn, found in recycled ceramic aggregate (seeTable 2). Their maximum allowable concentration in water inten-ded for human consumption is strictly regulated (see Table 4).
Corroborating earlier reports, these metals did not leach out ofthe concrete (see Fig. 2) because they are scantly soluble at neutralor basic pH. Engelsen et al., for instance, found solubility to be lowfor aluminium at pH of 6e10 (Engelsen et al., 2009), for lead at 6e13(Engelsen et al., 2010) and for iron at over 6 (Engelsen et al., 2009),while Burriel Martí (1994) reported low manganese solubility atpH > 8.
Chromium was not observed to leach at all, since this elementcan replace Al or the SO4
Fig. 4. Migration rates for the leached elements (B) by type of concrete vs leachingperiod. Fig. 6. Migration rates for the leached elements (Cl) by type of concrete vs leaching
period.
C. Medina et al. / Journal of Cleaner Production 66 (2014) 85e91 89
monosulfoaluminate hydrate, where it is immobilised (Sercleratet al., 2000; Laforest and Duchesne, 2005; Giergiczny and Krol,2008).
The migration rates observed for the leached elements in eachperiod are shown in Figs. 4e9.
Boron (see Table 6), leached because of its high solubility atneutral and basic pH values (Van Der Sloot, 2002). The concentra-tion found in the leachate was similar for the two types of concrete(RC and CC-25) at all leaching times, and consistently below thelimits defined in the legislation in effect (see Table 5). Moreover, themigration rate declined (Fig. 4) at longer leaching periods, droppingto nil in the third (M3med). In fact, these rates were consistentlylower in the water in contact with the CC-25 thanwith the RC. Thiswas due to the fact that boron was present in the chemicalcomposition of the cement only (see Table 2) and that the inclusionof recycled ceramic aggregate (Medina et al., 2012a) essentiallyinduced variations in the pore size distribution with respect toconventional concrete (RC): the (medium and small) capillary porevolume was 40% higher and the macropore volume 17% lower thanin the RC. These findings corroborated the importance of pore sizedistribution in material leachability (Sani et al., 2005; Van Der Slootand Dijkstra, 2004).
The other metalloid detected in the leachate, silicon, leached atpH values of under 11, exhibiting constant solubility at values of 6e9 (Engelsen et al., 2009). Table 6 shows that it leached out of
Fig. 5. Migration rates for the leached elements (Si) by type of concrete vs leachingperiod.
recycled concrete CC-25 less intensely than out of concrete RC,because natural siliceous aggregates, like siliceous rock in naturalenvironments, decay over time. Furthermore, the migration raterose with leaching time, as Fig. 5 shows. The rates observed wereunder 30 mg/L, the standard value in bottled water (Dinelli et al.,2010).
Another element that leached out of the concretes tested (RCand CC-25) after exposure was chlorine, whose concentration washigher in the RC than in the CC-25 leachate. In both cases, itsconcentration and migration rate declined with longer leachingtimes (Fig. 6). The difference in concentration can be explained bythe fact that chlorine is highly soluble (Van Der Sloot and Dijkstra,2004) across the entire range of pH values (2e14) and by theaggregate-induced variation in the concrete pore structure, whichwas less interconnected in the new than in the conventionalconcretes.
The inclusion of recycled aggregate in the concrete loweredmagnesium leachability, as it did in the case of boron and chlorine.Fig. 7 shows that this element was not leached during the firstleaching period, and its concentration (migration rate) in theleachate in the following periods was much lower than observedfor the other two elements. The behaviour of this element, whosecontent was higher in both the cement and the recycled aggregatethan recorded for B or Cl, can be attributed to the steep decline in its
Fig. 7. Migration rates for the leached elements (Mg) by type of concrete vs leachingperiod.
Fig. 8. Migration rates for the leached elements (Na) by type of concrete vs leachingperiod.
C. Medina et al. / Journal of Cleaner Production 66 (2014) 85e9190
solubility at pH values of over 8 (Van Der Sloot et al., 2012; Engelsenet al., 2009), as corroborated in the present study (see Fig. 2).
The concentration of the alkalis sodium and potassium (Figs. 8and 9), in turn, was higher in the concrete containing recycledceramic aggregate than in the conventional material. This was dueprimarily to the higher content of these elements in the recycledthan in the natural aggregate (see Table 2) and to their constantsolubility irrespective of pH (steady at values of 2e14) (Van DerSloot and Dijkstra, 2004).
5. Conclusions
The following conclusions may be drawn from the presentstudy:
- The inclusion of recycled ceramic aggregate in concrete manu-facture has no adverse effect on the pH or electrical conductivityof water intended for human consumption.
- The concentration of leached elements, similar in the concretestested, was consistently lower than the limits stipulated in thelegislation in effect.
- The inclusion of ceramic aggregate induces a rise in the con-centration of alkalis and a decline in all other elements (B, Si, Cland Mg) in water.
Fig. 9. Migration rates for the leached elements (K) by type of concrete vs leachingperiod.
- Recycled concrete made with ceramic sanitary ware waste canbe used in drinking water deposits and pipes, for it has notadverse effect on water quality.
Acknowledgements
The present study was funded by the Spanish Ministry of Sci-ence and Innovation under coordinated research Project (BIA2010-21194-C03-01).
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