demolition waste

Construction and Building Materials 40 (2013) 822–831

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Rheological and calorimetric behaviour of cements blended with containing ceramic sanitary ware and construction/demolition waste C. Medina a, P.F.G. Banfill b,⇑, M.I. Sánchez de Rojas a, M. Frías a a b

Eduardo Torroja Institute for Construction Sciences (CSIC), C/Serrano Galvache 4, 28033 Madrid, Spain School of the Built Environment, Heriot – Watt University, Edinburgh EH14 4AS, United Kingdom

h i g h l i g h t s " Two waste materials have been used to supplement cement in an investigation of rheology and hydration. " Ceramic sanitary ware waste reduces yield stress, while construction/demolition waste increases it. " Ceramic sanitary ware waste accelerates hydration, while construction/demolition waste retards it. " Low concentrations of both wastes can be regarded as feasible new supplementary cementitious materials for concrete.

a r t i c l e

i n f o

Article history: Received 13 June 2012 Received in revised form 12 November 2012 Accepted 22 November 2012 Available online 28 December 2012 Keywords: Ceramic sanitary waste Construction and demolition waste Rheology Calorimetry Cement paste

a b s t r a c t This research paper analyses the behaviour of new blended cements containing 10% and 20% ceramic sanitary ware (SW) and construction and demolition waste (C&DW) to determine their suitability as future supplementary cementitious materials for commercial cement manufacture. The effects of these recycled materials on cement rheology and heat conductivity were studied and an analysis of covariance was run to quantify the impact of each factor and co-variable involved on rheological properties. The addition of ceramic waste reduced shear yield stress and retarded the hydration reactions, whereas construction and demolition waste (C&DW) had the opposite effect, raising yield stress and accelerating hydration kinetics. These behavioural differences between the two types of industrial waste would have a direct effect on the final applications of the resulting blended cement. Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction The cement industry is known for being energy – and raw material – intensive, and for emitting not only 6% of the world-wide total of CO2 (672 kg per tonne of cement) [1], but other greenhouse gases such as N2 and O2 as well [2]. The use of supplementary cementitious materials in cement manufacture (fly ash, silica fume, natural pozzolans, etc.) is endorsed by European standard EN 197-1 [3] which provides for their inclusion at replacement ratios of 6–55 wt.%, depending on the nature of the addition and type of cement. The use of blended cements has grown rapidly due primarily to the lower emissions involved [4] as well as to the improved physical and mechanical properties and durability [5,6] of the end product. Over the last 10 years, research has pursued alternatives to the traditional materials used in commercial cement manufacture, with studies focusing on rice husks [7,8], sugar cane [9–11], glass ⇑ Corresponding author. Tel.: +44 131 451 4648. E-mail address: P.F.G.Banfi[email protected] (P.F.G. Banfill). 0950-0618/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2012.11.112

[12,13], ferroaluminous [14] and manganese-siliceous [15] slag, paper sludge [16,17], coal tailings [18,19], and concrete [20] and ceramic waste, in particular in this last category, roof tile [13,21–26] and ceramic block waste [27–30]. The rheology of fresh blended cement [5,31] is highly complex because of the mutual interactions (surface forces [32], Brownian forces, hydrodynamic forces and various contact forces) between the cement particles and new supplementary materials and the involvement of physical factors such as the water/cement ratio and cement grain shape and size, not to mention chemical and mineralogical factors, mixing conditions, measurement conditions and the presence of admixtures [33]. The inclusion of new materials as supplementary cementitious materials in cements generally has an adverse effect on the workability of cement-based materials. Hence the importance of understanding the effect of their inclusion on material handling and on-site placement [31,33]. The aim of the present study was to investigate the effect of the partial replacement (10 or 20 wt.%) of ceramic sanitary ware (SW) and construction and demolition waste (C&DW) on the rheological

C. Medina et al. / Construction and Building Materials 40 (2013) 822–831 Table 1 Chemical and physical properties of the materials. Element (wt.%)

Cement 52.5 R

Sanitary ware

C&DW

SiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O SO3 K2O TiO2 P2O5 ZnO Cl (ppm) ZrO2 (ppm) Loss on ignition

20.16 4.36 2.52 – 2.21 63.41 0.35 3.57 0.91 0.21 0.14 – 200 – 1.99

67.91 22.01 1.41 0.07 0.29 2.41 1.91 0.07 2.79 0.45 0.17 0.16 38 1303 0.23

48.75 9.83 2.49 0.04 1.85 17.98 0.86 2.64 3.17 0.27 0.12 189 – 12.00

Specific surface area (BET) m2/g

1.66

1.36

6.58

823

properties and hydration kinetics of new blended cements. Analysis of covariance (ANCOVA) was also conducted to study the impact of the factors and co-variables on the rheological results. 2. Materials and methods 2.1. Materials The SW used in this research was provided by the Spanish ceramic sanitary ware industry, which manufactures over seven million units yearly. The final products are subjected to strict quality control, whereby 7–8% of total output is rejected for sale and subsequently crushed and deposited in rubbish tips. While the present authors [34–36] have conducted earlier studies on the use of this waste as a coarse aggregate in structural concrete, no research on its application as supplementary cementitious materials can be found in the international literature. The second waste used was a recycled fine aggregate supplied by a Spanish C&DW management plant. At this time, despite the decline in construction business, 23 million tonnes of C&DW are generated yearly in Spain, 17% of which is re-used. No studies have yet been published on the feasibility of using this type of waste as a cement addition, despite the obvious economic and environmental advantages of the possibility.

Fig. 1. Mineralogical composition of wastes.

Fig. 2. Particle size distribution of the materials.

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Fig. 3. Variation of shear rate with time. Table 2 Programme of experimental mixes with ceramic waste from sanitary ware industry (SW). Superplasticizer Water/binder ratio

0.35 0.375 0.40 0.45 0.50

0 SW (%) 0 p p p p p

0.1 SW (%) 10

20

x p p p p

x p p p p

0 p p p p p

0.2 SW (%) 10 p p p p p

20 p p p p p

0 p p p p p

0.3 SW (%) 10 p p p p p

20 p p p p p

0 p p p

10 p p p

20 p p p

– –

– –

– –

0 p p p

10 p p p

20 p p p

– –

– –

– –

Table 3 Programme of experimental mixes with construction and demolition waste (C&DW). Superplasticizer Water/binder ratio

0.35 0.375 0.40 0.45 0.50

0 C&DW (%) 0 p p p p p

0.1 C&DW (%) 10

20

x p p p p

x p p p p

0 p p p p p

0.2 C&DW (%) 10 p p p p p

Table 1 gives the chemical composition of the two types of waste by X-ray fluorescence (XRF) analysis, and Fig. 1 their mineralogical composition as found with X-ray diffraction (XRD). The table shows that both comprised primarily silica (SiO2), although the sum of the alumina (Al2O3) and lime (CaO) contents accounted for over 24% and 27% of the total in SW and C&DW, respectively. While other oxides such as Fe2O3, MgO and sulphates (SO3) were also present, their concentrations were under 2.70%. The C&DW exhibited a much higher loss on ignition (12%) than the SW (0.23%), due primarily to decarbonation of the calcite present in the former. Mineralogically speaking (Fig. 1), ceramic sanitary ware waste contained quartz, feldspar, zircon and hematites, while quartz, calcite and feldspar were identified as the main mineralogical phases in the C&DW. The chemical composition of the Portland cement used (CEM I 52.5 R), supplied by Lafarge from the Toledo factory, Spain, is given in Table 1. The water-based modified polycarboxylate (SIKA ViscoCreteÒ-5920) superplasticizer added was supplied by SIKA, Madrid, Spain.

2.2. Particle size distribution and fineness The particle size distribution of the starting materials (SW, C&DW and OPC) was analysed on a Sympatec HELOS 12A particle size analyser [31]. The findings are shown in Fig. 2. The SW and C&DW particle size distribution curves exhibited two clearly distinguishable peaks, at 3.4 and 13.8 lm, while the main OPC peak was centred at 19.5 lm and had a shoulder at 6.8 lm.

20 p p p p p

0 p p p p p

0.3 C&DW (%) 10 p p p p p

20 p p p p p

Specific surface data were obtained by measuring N2 adsorption isotherms on a Micrometrics ASAP 2000 analyser. As Table 1 shows, at 6.58 m2/g, the C&DW’s surface area was much higher than the 1.36 m2/g found for the SW. The difference in surface area by adsorption is would be related to the higher porosity [31] in the C&DW, which contains a significant amount of cement hydration products. 2.3. Equipment and procedures 2.3.1. Rheology Rheological measurements were taken on a TA Instruments CS5002 rheometer fitted with a specially developed interrupted helical impeller, rotating in a stationary cylinder and operating in controlled shear rate mode. These test conditions have been used in previous studies on high flowability grouts and pastes [31,37]. The shear rate and stress at a series of pre-established shear rates were logged with NavigatorÒ software, after calibration with known liquids to define these two parameters in absolute units. The software provided sufficient flexibility to vary the shear rate suitably over time to ensure that any structure in the paste would be broken down to equilibrium before measurements were taken [38]. The temperature was held at a constant 20 °C by circulating water through a jacket surrounding the outer cylinder. The pastes were mixed by hand for 2 min using 100 g of the blended powder (cement, cement plus SW or cement plus C&DW) and the amount of water (containing dissolved superplasticizer as appropriate) required for water/binder ratios of

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825

Fig. 4. Typical flow curve and evaluation of the yield stress from test 4.

0.35, 0.375, 0.40, 0.45 and 0.50, and immediately poured into the cylinder, which was mounted on the rheometer. With the NavigatorÒ software running, shear measurements were taken as soon as the impeller was automatically inserted and started up. As shown in Fig. 3 continuous steady shearing at 50 s1 was applied between each successive flow curve determination. An initial 2 min preshear at 50 s1 was followed by test 1, a 5 min preshear by test 2, a further 5 min preshear by test 3, a 10 min preshear by test 4, a 20 min preshear by test 5, and finally a 20 min preshear by test 6 (see Fig. 3). Allowing for the time taken for each flow curve, tests therefore started at 2, 9, 16, 28, 50 and 72 min. Flow curves were plotted using the NavigatorÒ preset speed feature and the stress was measured at 20 shear rates from zero to 10 s1 in 60 s and 20 points from 10 to 200 s1 in 60 s. Tables 2 and 3 list the material combinations used in the experimental programme, where the w/b ratio was 0.35 and the superplasticizer 0%, fluidity was insufficient to run the test in the pastes containing either of the supplementary cementitious materials (SW or C&DW). Consequently, at that w/b ratio, assessment of paste rheology was only possible after the inclusion of the admixture. At the other extreme, pastes at 0.45 and 0.50 w/b ratio were too unstable to test because of sedimentation. The dosages of superplasticizer added were 0.1, 0.2 and 0.3 wt.% of the binder.

2.3.2. Conduction calorimetry The rate of heat evolution [37] and cumulative heat of hydration were determined under isothermal conditions at 20 °C on a Wexham Developments JAF calorimeter. Thirty grams of binder (cement, cement plus SW or cement plus C&DW) were placed in a small plastic bag together with an appropriate quantity of water (containing dissolved superplasticizer as appropriate), sealed and shaken by hand. The bag was carefully placed around the heat sensor and placed in a water bath in the calorimeter chamber. Measurements of temperature differences between the sample and the water bath, consisting of small differences in potential across the thermal sensor, commenced immediately. However, since in this method the rate of heat evolution cannot be determined until the sample and the water bath are in thermal equilibrium meaningful data were only obtained after about 1 h. Hydration continued for about 72 h, by which time the rate of heat evolution had peaked and declined to a low value. At the end of the experiment the equipment was calibrated using the heater built into the calorimeter to convert the voltage readings to rate of heat evolution. The theory underlying both the method and the calibration procedure was developed by Forrester [39].

2.4. Statistical analysis Analysis of covariance (ANCOVA) was used to assess the findings and simultaneously study the effect of all the factors (water/cement ratio, superplasticizer content and measuring time), as well as their interactions, by eliminating the variability generated by the presence of co-variables (type of waste and replacement ratio). The differences between the levels of a given factor were found using the Bonferroni multiple comparison tests.

As the statistical study was conducted with a significance level of a = 0.05, only those factors or co-variables whose p-value was less than 0.05 were regarded to have a significant effect on the results obtained. IBM SPSS Statistics 20 software was used for the statistical analysis.

3. Results and discussion 3.1. Rheology The flow curves (Fig. 4) were analysed with the standard Bingham model (Eq. (1)) [37,40,41] used to study the rheological properties of non-Newtonian fluids such as cement pastes, mortars and concretes:

s ¼ s0 þ lc_

ð1Þ

where s is shear stress; s0 is yield stress, l is plastic viscosity and c_ is shear rate. Fig. 4 shows that the flow curve provided a perfect fit to a straight line for shear rates in the 55–115 s1 range, as observed in prior research by Banfill and Frías [37]. The correlation coefficient (R2) found for this line was over 0.99 in all the samples tested. Fig. 5a–e shows the effect of the superplasticizer content and water/binder ratio on yield stress in all the pastes studied (OPC, SW10, SW20, C&DW10 and C&DW20). Note that yield stress declined with increasing SW or C&DW content [33] and water/binder ratio [33], regardless of the type of supplementary cementitious materials used, revealing the impact of these factors on rheological behaviour. In view of this main effect, only yield stress is reported here. Moreover, depending on the type of waste and, to a lesser extent, the replacement ratio, yield stress reacted differently. The inclusion of SW had a favourable effect on rheological properties, lowering the yield stress respect to the OPC, whereas C&DW increased the yield stress for a given water/binder ratio and superplasticizer dosage. This behaviour is probably due to the effect of binder specific surface [42–44] on water demand, which rose with increasing BET surface area and consequently increased yield stress. The increase in yield stress observed with the increasing percentage of C&DW waste was also found to be related to the

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Fig. 5. Effect of the water/binder ratio and superplasticizer content on yield stress by type and percentage of waste: (a) OPC, (b) SW 10, (c) SW20, (d) C&DW10 and (e) C&DW20.

greater hydration of cement components such as alite and aluminate, physically and chemically induced by calcite [31]. The effect of the superplasticizer on yield stress in pastes with a w/b ratio of 0.40 is depicted in Fig. 6. Here also, increasing admixture content reduced yield stress regardless of the water/binder ratio used. The admixture dosage and type of waste were also observed to modify the effect of the superplasticizer, whose performance may have been impacted by the chemical composition (alkalis, sulfates, C3A and so on) [45–48] and specific surface [49] of the waste. This effect should be investigated more thoroughly in future research. Fig. 7a–e shows the variations in yield stress over time in pastes with a w/b ratio of 0.40. According to the Fig. 6, the loss of paste

fluidity was retarded with rising percentages of superplasticizer, since one of the effects of the admixture is to slow the hydration reaction in cement particles [37]. At the same time, yield stress was observed to remain practically constant in pastes with 20% SW or C&DW at superplasticizer contents of 0.2% and 0.3%. Finally, for lower percentages of admixture (0% and 0.1%), all pastes were found to stiffen with time.

3.2. Conduction calorimetry Fig. 8a and b shows the variation in the rate of heat evolution with different superplasticizer content (0%, 0.1%, 0.2% and 0.3%).

C. Medina et al. / Construction and Building Materials 40 (2013) 822–831

Fig. 6. Variation in yield stress with the amount of superplasticizer in pastes with a w/b ratio of 0.40.

Fig. 7. Variation in yield stress over time for pastes with a water/binder ratio of 0.40: (a) OPC, (b) SW10, (c) SW20, (d) C&DW10 and (e) C&DW20.

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Fig. 8. Conduction calorimetric curves for different proportions of superplasticizer: (a) 0%, (b) 0.1%, (c) 0.2%, and (d) 0.3%.

These curves showed three clearly distinguishable periods: first induction, followed by a stage in which the rate increased to a peak, and lastly deceleration. The induction period was observed to lengthen with higher percentages of admixture, further evidence of the retarding effect of superplasticizers in this initial period [50]. Fig. 8a also shows that total heat was 1% and 5% higher in the pastes containing 10% SW (SW10) and C&DW (C&DW10), respectively, than in the control. This may be explained by the pozzolanic reaction [51,52] in the waste products, which was less intense in the less reactive sanitary ware waste than in construction and demolition waste. The pastes with a replacement ratio of 20% exhibited lower peaks than the control, although the difference was less accentuated in C&DW than in SW. That same pattern of lower peak heat than the control (OPC) was observed with all the other percentages of superplasticizer (see Fig. 8b–d), perhaps because the percentage of cement replaced was not offset by the heat released in the pozzolanic reaction, i.e., the effect of the replacement prevailed over pozzolanic activity [51]. Fig. 9a and b shows the peak rate of heat evolution Wmax versus 1/tmax, the time at which heat peaked for sanitary ware and construction and demolition waste, respectively, as suggested by Wilding et al. [53]. These parameters (Wmax and tmax) are calculated from Fig. 8. If hydration kinetics follows the Avrami–Erofeyev pattern, they suggest that the data should fit a straight line where accelerated hydration is denoted by the points farthest from, and retardation by the points nearest to, the origin. Fig. 9a and b generally confirm this behaviour. Hydration was retarded in all cases in the sanitary ware waste (Fig. 9a) except when the admixture percentage was 0.1%, due perhaps to an adverse effect of small

amounts of the superplasticizer, a question that merits future research. The figure shows that the delay was longer at the higher replacement ratio, although the relationship was not proportional. The superplasticizer, in turn, was found to retard hydration of the pastes near the origin most effectively. The deceleration observed in paste hydration was due primarily to the chemical composition (see Table 1) of the ceramic ware waste, and consistent with prior findings [54–58] on the retarding effect of the presence of certain oxides (ZrO2, ZnO and TiO2) on cement paste hydration. Fig. 9b shows that with C&DW, higher superplasticizer contents induced delays in hydration [37]. At the same time, the inclusion of this waste accelerated cement paste hydration, more intensely with a 20% replacement ratio. This behaviour was directly related to the chemical composition of construction and demolition waste and consistent with the accelerating effect of SO3 and MgO on hydration reactions observed in prior studies [59–61]. 3.3. Statistical analysis Table 4 lists the results of the ANCOVA on the effect of the factors (water/binder ratio, superplasticizer content and measuring time) and co-variables (type of waste and replacement ratio) on the yield stress of the pastes studied. The statistical model accounted for 70% of the variability observed. The data revealed that mixing time, amount of superplasticizer and the water/binder ratio all had a significant (p < 0.05) effect on paste yield stress, as observed in the findings discussed in Section 3.1.

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Fig. 9. Effect of waste (SW and C&DW) and superplasticizer on heat of hydration kinetics.

Table 4 Analysis of covariance data (ANCOVA). Test of inter-subject variability

a

Source of variation

Type III sum of squares

Degrees of freedom

Mean square

F

p

Corrected model Intersection Mixing time W/b ratio Amount of superplasticizer Percentage of waste Type of waste Interaction between percentage and type of waste Error Total Corrected total

82.452a 76.898 2.890 44.281 39.832

7 1 1 1 1

11.778 76.898 2.890 44.281 39.832

169 1.109 41.7 638 574

0.000 0.000 0.000 0.000 0.000

83.9 12.863 785

1 1 1

83.9 12.863 785

1.2 185 11.3

0.272 0.000 0.001

35.204 265.811 117.657

508 516 515

69

R squared = 0.701 (corrected R squared = 0.697).

Of the two co-variables, type of waste had a significant effect (p < 0.05), whereas replacement ratio (p = 0.272 > 0.05) did not and this suggests that, although the two wastes have opposite

effects on rheology, the difference between 10% and 20% replacement is not significant. That the interaction between type of waste and replacement ratio was significant (p = 0.001 < 0.05) confirms the results in Section 3.1. 4. Conclusions The following conclusions can be drawn from the results of the present study. – The addition of ceramic sanitary ware waste (SW) as a partial replacement for cement reduces yield stress, whereas the inclusion of construction and demolition waste (C&DW) increases yield stress. – A reduction in water/binder ratio from 0.375 to 0.35 reduces paste fluidity so much that the paste is not testable without admixtures. – Cement particle hydration is modified depending on the type of ceramic waste: the reaction is accelerated by the inclusion of C&DW and retarded with SW. – The inclusion of the admixture lengthens the induction period and reduces yield stress, more intensely with higher proportions of superplasticizer.

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– The type of waste plays an essential role in paste rheology, and while the replacement ratio has no significant effect, the interaction between these two co-variables affects yield stress significantly. – Based on their effects on paste rheology and heat conduction, low concentrations of sanitary ware and construction and demolition waste can be regarded as feasible new supplementary cementitious materials in concrete manufacture.

Acknowledgments This research was funded by the Spanish Ministry for Science and Innovation under Project BIA2010-21194-C03-01 and by Heriot-Watt University, Edinburgh, Scotland. The authors wish to thank SIKA (Madrid, Spain) and Lafarge Cements (Toledo, Spain) for providing the materials for this project. We also want to thank Santiago Angulo for his collaboration in the statistical analysis. Finally, we are grateful to Ewan Szadurski for his help in the utilization of calorimeter. References [1] Meral C, Benmore CJ, Monteiro PJM. The study of disorder and nanocrystallinity in C–S–H, supplementary cementitious materials and geopolymers using pair distribution function analysis. Cem Concr Res 2011;41(7):696–710. [2] European Commission. Cement, lime and magnesium oxide manufacturing industries [on line, May 2010]. [3] European Standard EN 197–1:2011. Cement – Part 1: Composition, specifications and conformity criteria for common cements. p. 40. [4] Hammond G, Jones C. Inventory of carbon & energy (ICE). United Kingdom: University of Bath; 2008. p. 64. [5] Park CK, Noh MH, Park TH. Rheological properties of cementitious materials containing mineral admixtures. Cem Concr Res 2005;35(5):842–9. [6] Schneider M, Romer M, Tschudin M, Bolio H. Sustainable cement production– present and future. Cem Concr Res 2011;41(7):642–50. [7] Ganesan K, Rajagopal K, Thangavel K. Rice husk ash blended cement: assessment of optimal level of replacement for strength and permeability properties of concrete. Constr Build Mater 2008;22(8):1675–83. [8] Rodríguez de Sensale G. Effect of rice-husk ash on durability of cementitious materials. Cem Concr Compos 2010;32(9):718–25. [9] Frias M, Villar-Cocina E, de Rojas MIS, Valencia-Morales E. The effect that different pozzolanic activity methods has on the kinetic constants of the pozzolanic reaction in sugar cane straw-clay ash/lime systems: application of a kinetic-diffusive model. Cem Concr Res 2005;35(11):2137–42. [10] Villar-Cocina E, Frias M, Valencia-Morales E, de Rojas MIS. An evaluation of different kinetic models for determining the kinetic coefficients in sugar cane straw-clay ash/lime system. Adv Cem Res 2006;18(1):17–26. [11] Frías M, Villar E, Savastano H. Brazilian sugar cane bagasse ashes from the cogeneration industry as active pozzolans for cement manufacture. Cem Concr Compos 2011;33(4):490–6. [12] Shao YX, Lefort T, Moras S, Rodriguez D. Studies on concrete containing ground waste glass. Cem Concr Res 2000;30(1):91–100. [13] Pereira-de-Oliveira LA, Castro-Gomes JP, Santos PMS. The potential pozzolanic activity of glass and red-clay ceramic waste as cement mortars components. Constr Build Mater 2012;31:197–203. [14] Frias M, Rodriguez C. Effect of incorporating ferroalloy industry wastes as complementary cementing materials on the properties of blended cement matrices. Cem Concr Compos 2008;30(3):212–9. [15] Frias M, Sánchez de Rojas MI, Santamaría J, Rodríguez C. Recycling of silicomanganese slag as pozzolanic material in Portland cements: basic and engineering properties. Cem Concr Res 2006;36(3):487–91. [16] Vegas I, Frias M, Urreta J, San Jose JT. Obtaining a pozzolanic addition from the controlled calcination of paper mill sludge. Performance in cement matrices. Mater De Constr 2006;56(283):49–60. [17] Frias M, Rodriguez O, Vegas I, Vigil R. Properties of calcined clay waste and its influence on blended cement behavior. J Am Ceram Soc 2008;91(4):1226–30. [18] Frías M, de la Villa RV, Sánchez de Rojas MI, Medina C, Juan Valdés A. Scientific Aspects of Kaolinite based coal mining wastes in Pozzolan/Ca(OH)2 system. J Am Ceram Soc 2012;95(1):386–91. [19] Frías M, Sanchez de Rojas MI, García R, Juan Valdés A, Medina C. Effect of activated coal mining wastes on the properties of blended cement. Cem Concr Compos 2012;34(5):678–83. [20] Kim YJ, Choi YW. Utilization of waste concrete powder as a substitution material for cement. Constr Build Mater 2012;30:500–4. [21] Ay N, Unal M. The use of waste ceramic tile in cement production. Cem Concr Res 2000;30(3):497–9.

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