Engineering properties of composite materials

Original Article

Engineering properties of composite materials containing waste ceramic dust from advanced hollow brick production as a partial replacement of Portland cement

Journal of Building Physics 1–18 Ó The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/1744259115597228 jen.sagepub.com

Tereza Kulovana´1, Eva Vejmelkova´1, Jaroslav Pokorny´1, Jamal Akhter Siddique1, Martin Keppert1, Pavla Rovnanı´kova´2, Michal Ondraćˇek2, ˇ erny´1 Zbyneˇk Kersˇner3 and Robert C

Abstract Waste ceramic dust originating in the advanced hollow brick production is applied as a supplementary cementing material replacing a part of Portland cement in concrete. The measurements of mechanical and fracture-mechanical properties, water vapor and liquid water transport parameters, thermal conductivity, specific heat capacity, and freeze/ thaw resistance show that the ceramic dust application does not affect negatively the properties of the analyzed concretes over the whole studied Portland cement replacement range up to 40% by mass. The achievement of such a high limit for the ceramic dust application can be attributed, besides the pozzolanic reaction being initiated already during the time period of 7 to 28 days, to the positive effect of the excess ceramic dust

1

Department of Materials Engineering and Chemistry, Faculty of Civil Engineering, Czech Technical University in Prague, Prague, Czech Republic

2

Institute of Chemistry, Faculty of Civil Engineering, Brno University of Technology, Brno, Czech Republic

3

Institute of Structural Mechanics, Faculty of Civil Engineering, Brno University of Technology, Brno, Czech Republic Corresponding author: ˇ erny´, Department of Materials Engineering and Chemistry, Faculty of Civil Engineering, Czech Robert C Technical University in Prague, Tha´kurova 7, 166 29 Prague 6, Czech Republic. Email: [email protected]

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Journal of Building Physics

in the mixes with a high volume of uniformly distributed air voids. The part of the ceramic additive which cannot participate in the hydration and pozzolanic reactions due to the lack of available Ca2+ acts, apparently, as fine aggregate partially filling the voids, thus contributing to the compaction of the hardened mixes and compensating, to a certain extent, the factual decrease of the amount of binder. Keywords Portland cement, ceramic dust, mechanical and fracture-mechanical properties, hygric and thermal characteristics, freeze/thaw resistance

Introduction Ceramic waste is generated all over the world in large quantities. The ceramic industry itself widely contributes to its production in the form of scrap. For instance, in Europe, the amount of wastes in the different production stages of the ceramic industry reaches 3%–7% of its global production (Pacheco-Torgal and Jalali, 2010). In Argentina, about 2% of the products are refused because of commercial reasons (Lavat et al., 2009). In India, it has been estimated that about 30% of the daily production in the ceramic industry goes waste (Senthamarai and Devadas Manoharan, 2005). These discarded materials, most of which cannot be recycled within the plant, constitute industrial waste which is often landfilled. Milling to a fineness comparable to cement presents a prospective way of how to reuse ceramic waste (Wild, 1996). The obtained ceramic powder, due to its pozzolanic activity (Baronio and Binda, 1997; Pereira-de-Oliveira et al., 2012; Wild et al., 1997), can then be utilized as a partial replacement of cement in concrete. Ground waste clay bricks are probably the most frequently used source of waste ceramics used for that purpose (Naceri and Hamina, 2009; O’Farrell et al., 2006; Toledo Filho et al., 2007; Tydlita´t et al., 2012; Vejmelkova´ et al., 2012). Other possible sources are ceramic sanitary ware (Medina et al., 2013), porcelain stoneware tiles (Bignozzi and Bondua`, 2011), or ceramic demolition waste (Katzer, 2013). A comparison of the performance of several different sources of waste ceramic powder as partial replacement of Portland cement was presented in Pacheco-Torgal and Jalali (2011). The production of red-clay hollow bricks belongs to the sources of ceramic waste which gained on importance continuously during the last decade or two (Reig et al., 2013). The increasing requirements for the thermal insulation properties of building envelopes given by the national standards particularly in Europe led the brick producers to reduce the production of common solid bricks. Brick blocks with more or less complex systems of internal cavities replaced the traditional bricks and became dominant on the building ceramics market (Antoniadis et al., 2012; Arendt et al., 2011; Pavlı´ k et al., 2013, 2014). At the production of hollow bricks, the amount of scrap is similar to the traditional red-clay bricks. However, for advanced types of hollow brick blocks, the


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total ceramic waste generation is higher. This is related to one of the current trends in the building sector which is using the thin joint technology in the construction of building envelopes. While during the last decades this technology was commonly used for autoclaved aerated concrete, recently it becomes popular also for hollow brick–based envelopes. As the current technologies of hollow brick production do not make it possible to provide sufficiently smooth and even surfaces, the brick blocks have to be ground after leaving the production line. This grinding generates a significant amount of waste ceramic dust which is mostly landfilled, although it has both the composition and granulometry suitable for using as pozzolanic admixture to cement. In this article, we present an application of waste ceramic dust originating in advanced hollow brick production in concrete mix design which has both environmental and economical aspects. The use of ceramic powder as partial replacement of Portland cement in concrete on one hand converts landfilled waste material to a valuable supplementary cementitious material, and on the other contributes to a decrease of overall energy consumption and CO2 emission which accompanies the Portland cement production. The proposed solution is also cost-effective because the waste ceramic dust does not need any further processing and can be used in the form in which it is obtained from the production line.

Materials and mix design Portland cement CEM I 42.5R (Cˇeskomoravsky´ cement, a.s., Mokra´) was used as the main binder in the preparation of concrete mixes. Its specific surface area was 341 m2 kg21, and the chemical composition is given in Table 1. The ceramic dust which was used as a partial replacement of Portland cement in the blended binders was a waste material originating in the hollow brick production (Heluz Brick Industry, Czech Republic). The specific surface area of the ceramic dust was 271 m2 kg21, and its chemical composition is shown in Table 1. Crushed granodiorite was used as coarse aggregate (Olbramovice, 2640 kg m23) and sedimentary river psefites as fine aggregate (Zˇabcˇice, 2580 kg m23). Superplasticizer Dynamon SX 14 was applied to decrease the water/binder ratio, and Mapeplast PT1 was the airentraining agent used for the achievement of better durability properties. The concrete mix was designed basically as air entrained. Contrary to most other mixes of this type, its design involved also the achievement of low water/binder ratio which should lead to an increase of both strength and durability. This could extend its supposed application range in the building practice. Another important factor of the design was the choice of the amount of ceramic dust which could be used as partial replacement of Portland cement without affecting negatively its mechanical and durability properties. Therefore, the Portland cement replacement level was relatively high, up to 40% by mass. The detailed composition of the designed concrete mixes is presented in Table 2.


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Table 1. Chemical composition of cement and ceramic dust (% by mass). Component

Cement

Ceramic dust

SiO2 Al2O3 Fe2O3 CaO MgO SO3 Na2O K2O TiO2 MnO P2O5 Loss on ignition

18.89 4.24 3.83 62.37 0.99 2.31 0.12 1.14 0.30 0.077 0.12 1.52

54.97 14.28 4.77 11.14 3.63 2.07 1.27 3.08 0.55 0.06 0.17 0.00

Table 2. Composition of concrete mixtures (kg m23). Component

REF

CD 10

CD 20

CD 40

CEM I 42.5R Ceramic dust Aggregates 0–4 mm Aggregates 4–8 mm Aggregates 8–16 mm Water Superplasticizer Air-entraining agent

390 – 795 250 695 153 2.9 0.22

351 39 (10%) 795 250 695 153 2.9 0.22

312 78 (20%) 795 250 695 153 2.9 0.22

234 156 (40%) 795 250 695 153 2.9 0.22

REF: reference material.

Experimental methods As the designed concrete mixes are innovative from the point of view of both using a nontraditional type of pozzolanic admixture and imposing a not very common requirement to produce air-entrained concrete with relatively high strength, a wide range of parameters of hardened concrete is investigated. They include the basic material characteristics, mechanical properties, fracture-mechanical properties, water vapor transport properties, liquid water transport properties, heat transport and storage properties, and freeze/thaw resistance.

Basic material characteristics The basic characterization of the analyzed materials was done using the vacuum water saturation method, capillary water saturation method, mercury intrusion porosimetry, and isothermal heat flow calorimetry.


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In the vacuum water saturation method, bulk density, matrix density, and open porosity were measured according to the procedure described in Roels et al. (2004). Each sample was dried in an oven to remove majority of the physically bound water. After that the samples were placed into the desiccator with deaired water. During 3 h, air was evacuated with vacuum pump from the desiccator. The specimen was kept under water not less than 24 h. From the mass of the dry sample md, the mass of water saturated sample mw, and the mass of the immersed water saturated sample ma, the volume V of the sample was determined from the equation V=

mw ma rl

ð1Þ

where rl is the density of water. The basic physical properties, namely, open porosity c0, bulk density r, and matrix density rmat, of samples were calculated according to the equations c0 = 100 r= rmat =

mw md rl V

ð2Þ

md V

ð3Þ

md

c0 V 1 100

ð4Þ

The capillary-saturation moisture content wcap was determined by the gravimetric method after full immersion of oven dried specimens in water for 7 days using the formula wcap = 100

mw, cap md rl V

ð5Þ

where mw,cap is the mass of capillary water saturated sample. Characterization of the pore structure was performed by mercury intrusion porosimetry. The experiments were carried out using the instruments Pascal 140 and 440 (Thermo Scientific). The range of applied pressure corresponds to the pore radius from 2 nm to 2000 mm. Since the size of the specimens is restricted to the volume of approximately 1 cm3 and the studied materials contained some aggregates about the same size, the porosimetry measurements were performed on samples without coarse aggregates. The hydration heat development was measured using the isothermal heat flow calorimeter TAM air (TA Instruments, New Castle, DE). The reference paste was prepared using the Portland cement CEM I 42.5R (Cˇeskomoravsky´ cement, a.s.), with the water/cement ratio of 0.5. The pastes of blended cements where 10%, 20%, and 40% of mass of Portland cement was replaced by ceramic dust were mixed with the same water/binder ratio of 0.5. The measurement was performed in


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a standard way, using a 20 mL ampoule with the cement specimen which was, together with the water doser, tempered at first inside the calorimeter. Then, water was added into the ampoule and mixed with cement using an externally operated mixer, and the measurement of heat flow was started. The measured data were continuously recorded by a data acquisition system.

Mechanical and fracture-mechanical properties The measurement of mechanical properties was done using the hydraulic testing device VEB WPM Leipzig 3000 kN having a stiff loading frame with the capacity of 3000 kN. The compressive strength was tested according to the standard CˇSN EN 12390-3 (2002); a constant loading rate of 0.2 MPa s21 was imposed on the specimens. The modulus of elasticity in compression was measured using the procedure described in the standard CˇSN EN 12390-13 (2014); the secant initial modulus, measured at first loading, was the obtained parameter. The measurements of compressive strength and modulus of elasticity in compression were done after 28, 90, and 360 days, in order to monitor the effect of the pozzolanic reaction induced by the presence of ceramic dust in the material. The bending strength was determined in accordance with CˇSN EN 12390-5 (2007), with the loading rate of 0.04 MPa s21. The tests were performed after 28 days of standard curing. The effective fracture toughness and the effective toughness were determined using the Effective Crack Model (Karihaloo, 1995) which combines the linear elastic fracture mechanics (LEFM) and crack length approaches. A three-point bending test (CˇSN EN 12390-5, 2007) of a specimen having a central edge notch with a depth of about 1/3 of the depth of the specimen was used in the experiment. The loaded span was equal to 300 mm. The calculation of the critical effective crack length aec was based in the model on the secant compliance of the cracked specimen at the maximal load. The secant stiffness of the specimen at the peak load can be viewed as the initial stiffness of a specimen with a longer initial crack a. The effective fracture toughness KIce is then calculated from LEFM relations for the maximal load and the effective crack length aec . Crack propagation in a real structure, according to this model, begins when the stress intensity factor KI at the effective crack tip reaches the value of fracture toughness, that is, when KI = KIce at a = aec . For the calculation of aec and KIce , only two points from the load–deflection (F–d) diagram are needed: the first is from the initial linear elastic part and the second from the peak. The technique for the calculation of aec employs the formula for the mid-span deflection of a beam loaded by the central force F and the self weight. Young’s modulus E is evaluated by using the formula while constituting the first pair of values F–d and the initial crack length ao within it. An iterative procedure using the reverse expression of the formula provides the value of the critical effective crack length aec from the known values of E and second mentioned pair of values F–d (peak load). The effective toughness Gce is then determined as Gce = (KIce )2 =E.


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A continuous record of the F–d diagram was used for estimation of the value of fracture energy GF. It was obtained according to the RILEM Committee 50-FMC (1985) method; it is the averaged fracture energy of the fracture process through the entire specimen ligament Alig: GF = WF =Alig , where WF is the value of work of fracture, that is, the integral under F–d diagram from the beginning of loading to the rupture of tested specimen.

Hygric, thermal, and durability properties The cup method was used for determination of water vapor transport parameters. The measurement was carried out in steady state under isothermal conditions, using one-dimensional (1D) water vapor diffusion setup, determination of water vapor diffusion flux through the specimen and measuring partial water vapor pressure in the air under and above specific specimen surface (Roels et al., 2004). Two versions of the cup method were employed in the measurements of the water vapor diffusion coefficient. In the first one (dry cup), the sealed cup containing burnt CaCl2 (5% relative humidity) was placed in a controlled climatic chamber at (2560.5)°C and 50% relative humidity and weighed periodically. In the second one (wet cup), the cup containing saturated K2SO4 solution (97% relative humidity) was placed in (2560.5)°C and 50% relative humidity environment. The sealed cups with samples were weighed periodically. The steady state values of mass gain or mass loss were utilized for the determination of water vapor transport properties. The water vapor diffusion coefficient D was calculated from the measured data according to the equation D=

Dm d R T S t M Dpp

ð6Þ

where Dm is the amount of water vapor diffused through the sample, d is the sample thickness, S is the specimen surface, t is the period of time corresponding to the transport of mass of water vapor Dm, Dpp is the difference between partial water vapor pressure in the air under and above specific specimen surface, R is the universal gas constant, M is the molar mass of water, and T is the absolute temperature. On the basis of the diffusion coefficient, the water vapor diffusion resistance factor m and water vapor diffusion permeability d were determined m=

Da D

ð7Þ

M RT

ð8Þ

d=D

where Da is the diffusion coefficient of water vapor in the air.


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Water sorptivity was analyzed using the experimental setup described in Vejmelkova´ et al. (2009). The specimen was water and vapor-proof insulated on four lateral sides and the face side was immersed 1–2 mm in the water, and constant water level in tank was achieved by a Mariotte bottle with two capillary tubes. One of them, inside diameter 2 mm, was ducked under the water level, the second one, inside diameter 5 mm, was above water level. The automatic balance allowed recording the increase of mass. The water absorption coefficient A was then calculated using the formula pffi i=A t ð9Þ where i is the cumulative water absorption and t is the time from the beginning of the suction experiment. The water absorption coefficient was then employed for the calculation of the apparent moisture diffusivity kapp in the form (Kumaran, 1999) 2 A kapp ’ ð10Þ wc w0 where wc is the saturated moisture content and w0 is the initial moisture content. Thermal conductivity l and specific heat capacity c were determined using the commercial device ISOMET 2104 which is equipped with various types of optional probes: needle probes are for porous, fibrous, or soft materials and surface probes are suitable for hard materials. The measurement is based on the analysis of temperature response of the analyzed material to heat flow impulses. The heat flow is induced by electrical heating using resistor heater having a direct thermal contact with the surface of the sample. Calibration data in internal memory ensure interchangeability of probes without affecting the measurement accuracy. Gained data are stored into the internal memory. The measurements were done for dry and water saturated materials to demonstrate the effect of moisture content on the thermal properties. Frost resistance tests were carried out according to CˇSN 73 1322/Z1:1968 (2003). The samples were tested after 28 days of standard curing. The total test required 100 freezing and thawing cycles. One cycle consisted of 4 h freezing at 220 °C and 2 h thawing in 20 °C warm water. Frost resistance coefficient K was determined as the ratio of compressive strength of specimens subjected to 100 freezing and thawing cycles to the strength of reference specimens which did not undergo the frost resistance test.

Experimental results and discussion Basic material characteristics The bulk density decreased with the increasing content of ceramic dust in concrete (Table 3), but as the matrix density decreased as well, the increase of open porosity was only up to 6%, when compared with the reference mix. Similarly, the


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Table 3. Basic physical properties. Material

Bulk density (kg m23)

Matrix density (kg m23)

Open porosity (% m3 m23)

Capillary-saturation moisture content (% m3 m23)

REF CD 10 CD 20 CD 40

2095 2072 2044 2005

2422 2409 2380 2345

13.5 13.9 14.1 14.4

12.7 13.2 13.3 13.1


capillary-saturation moisture content of the mixes containing ceramic dust increased only up to 5%. This was the first indication of a successful mix design because the porosity is known to affect significantly the mechanical properties of cement-based composites. All analyzed hardened concrete mixes had a significant amount of fine pores up to 10 nm (Figure 1); these are typical pores appearing in the cement gel. The pore size distribution curves exhibited also three less distinct maxima, the first at ;100 nm, the second at ;1 mm, and the third at ;10 mm. While the first one was highest for CD 10 containing 10% ceramic dust in the binder and CD 40 with the 40% dosage, the second one was most pronounced for CD 20 with 20% ceramic dust, and the third one was highest for the reference mix and decreased with the increasing ceramic dust dosage. The relatively high amount of capillary pores in the range of 1–100 mm was, apparently, a consequence of the addition of airentraining agent in the mix. The heat flow (representing the hydration heat power) at both the first local maximum corresponding to the first phase of C3A hydration and the first local minimum characterizing the dormant phase differed only slightly for the mixes with up to 20% ceramic dust content in the binder but a noticeable decrease was observed for CD 40 (Figure 2). The time of occurrence of both the first local maximum (;6 min) and first local minimum (;2–3 h) was not affected by the presence of ceramic dust in the binder. The heat flow at the second maximum corresponding to the C3S hydration decreased with the increasing dosage of ceramic dust but the time of occurrence of the second maximum was similar for all mixes, ;12 h (Figure 3). The third maximum corresponding to the second phase of C3A hydration, that is, the transformation of the AFt to AFm phase, was for the reference mix manifested in a not very distinct form, only as a shoulder on the decreasing part of the heat flow versus time curve (Figure 3). For the cements with the ceramic dust dosage of 10% and 20%, the third peak was more pronounced, and for CD 40 it was already higher than the second maximum. The time of occurrence of the third maximum, which was within the range of 20–25 h, decreased with the increasing amount of ceramics in the mix.


10


0.009 CD 10

Incremental pore volume [cm 3/g]

0.008

CD 20 CD 40

0.007

REF 0.006 0.005 0.004 0.003 0.002 0.001 0.000 0.001

0.01

0.1 1 Pore diameter [μm]

10

100

Figure 1. Pore size distribution.

0.06 REF CD 10

0.05

CD 20 CD 40

Heat flow [W]

0.04

0.03

0.02

0.01

0 0

1

2

3

4

5

Time [h] Figure 2. Hydration heat development—detail of the first local maximum and first local minimum.


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0.02 REF CD 10 CD 20

0.015

Heat flow [W]

CD 40

0.01

0.005

0 0

10

20

30

40

50

Time [h] Figure 3. Hydration heat development—detail of the second and third local maximum.

The hydration heat development in blended cements containing ceramic dust was investigated very rarely and a direct comparison was not possible. In the only paper published in the relevant literature sources, Tydlita´t et al. (2012) studied blended binders containing finely ground red ceramics but they added also a superplasticizer to their binders which prolonged significantly the whole process of hydration, making a possible comparison almost useless. The enhanced third maxima shifted toward lower times were observed in Rahhal and Talero (2008) for the Portland cement-metakaolin blends which could be considered as closest in composition to our blended cements. These features were attributed to the dilution of the silicate phase due to the replacement of Portland cement by the respective metakaolin and to the synergistic calorific effect produced between the C3A from Portland cement and the Al2O3 from the metakaolin, which was verified by X-ray diffraction (XRD), monitoring of the AFm phase evolution. Similar mechanisms could play an important role also in the case of the Portland cement-ceramic dust blends investigated in this article.

Mechanical and fracture-mechanical properties The 28 days compressive strength, fc, of concretes with 10% and 20% ceramic dust content decreased by 12%–13%, as compared with the reference material (REF),


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Table 4. Compressive strength (MPa). Material

28 days

90 days

360 days


39.5 34.5 34.1 40.0

42.5 42.6 43.4 43.1

45.6 46.2 47.8 44.5


Table 5. Modulus of elasticity in compression (GPa). Material

28 days

90 days

360 days


26.5 25.0 25.5 25.0

28.5 26.5 28.5 28.0

29.5 29.0 28.0 28.5


but CD 40 achieved a similar fc value as REF (Table 4). The compressive strength of all analyzed concretes increased with time up to 360 days. This increase was most pronounced for CD 10 and CD 20 within the 28–90 days time period, which was, apparently, a manifestation of the pozzolanic reaction. The high compressive strength of CD 40 after 28 days could be caused by the dual role of the ceramic dust in the designed concrete mixes. As it was reported in Tydlita´t et al. (2012), during the first week after mixing the direct involvement of red ceramic powder in the hydration process, as manifested by the hydration heat production, is limited to approximately 20% Portland cement replacement level; for higher ceramics content, its effectiveness as a binder decreases fast. The calorimetric measurements presented in this article basically confirmed this finding. A part of the excess ceramic dust can take part in the pozzolanic reaction with Ca(OH)2 in later times (Baronio and Binda, 1997). However, for the blended binders with high ceramic contents there is still its certain amount available which can act as very fine filler, fittingly completing the granulometric curve of the aggregates. In the concrete mixes analyzed in this article, this effect was most distinct in the CD 40 mix; the compaction of its microstructure indicated by the more homogeneous pore structure (Figure 1) was clearly due to the filling of the voids by the excess ceramic dust particles. The slower strength increase of CD 40 after 28 days was probably a consequence of the lower amount of Ca(OH)2 available; a major part of it could be consumed already during the first 28 days time period. The modulus of elasticity in compression of materials containing ceramic dust was after 28 days slightly lower than the reference concrete; after 90 and 360 days, the differences were similar, typically up to 5% (Table 5). The bending strength of


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Table 6. Bending strength after 28 days. Material

REF

CD 10

CD 20

CD 40

Bending strength (MPa)

8.7

8.7

8.4

8.4


Table 7. Fracture-mechanical properties. Material

Effective fracture toughness (MPa m1/2)

Static modulus of elasticity in bending (MPa)

Effective toughness (N m21)

Specific fracture energy (J m22)


1.31 1.50 1.42 1.28

33.8 32.4 31.6 33.3

52.1 69.6 63.8 48.9

227 218 203 212


all studied concretes after 28 days was, once again, very similar; the differences were within a 3% range (Table 6). The effective fracture toughness and effective toughness were highest for the CD 10 and CD 20 mixes, 15%–30% higher than REF (Table 7). The mix with 40% ceramic dust in the binder achieved slightly lower values than the reference concrete. The static modulus of elasticity in bending of the analyzed mixes differed only within a 6% range, the lowest value was found for CD 20. The specific fracture energy followed a similar trend as the static modulus, with the differences up to 10%. Taking into consideration the experimental results obtained for the mechanical and fracture-mechanical parameters, one can see that all studied hardened concrete mixes performed in a satisfactory way. The application of ceramic dust instead of a part of Portland cement did not lead to any substantial worsening of concrete properties. Therefore, the practical limit for the effective use of ceramic dust as partial replacement of Portland cement was as high as 40% by mass. This limit was significantly higher than the compressive strength–based limits identified by other investigators; O’Farrell et al. (2006), Toledo Filho et al. (2007), and Vejmelkova´ et al. (2012) found independently for different concrete types 20% as an effective maximum. The apparent reason for the observed differences can be found in the production technology. Contrary to the concretes analyzed in O’Farrell et al. (2006), Toledo Filho et al. (2007), and Vejmelkova´ et al. (2012), the mixes in this article were designed as air entrained; thus containing a high volume of uniformly distributed air voids already in the initial hydration phases. Therefore, the part of the ceramic dust which could not take part in the hydration and pozzolanic reactions


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Table 8. Water vapor transport properties. Material


Dry-cup method

Wet-cup method 2 21

d (s)

D (m s

1.42E212 1.48E212 1.55E212 1.60E212

1.95E207 2.03E207 2.13E207 2.20E207

)

m (–)

d (s)

D (m2 s21)

m (–)

117.860 113.082 107.975 104.601

1.90E212 1.95E212 2.10E212 2.30E212

2.61E207 2.68E207 2.89E207 3.16E207

88.085 85.826 79.696 72.766


Table 9. Water transport properties. Material

Water absorption coefficient (kg m22 s21/2)

Apparent moisture diffusivity (m2 s21)


0.0138 0.0129 0.0121 0.0112

7.994E209 7.295E209 5.197E209 4.430E209


due to the lack of available Ca2+ could act effectively as fine aggregate partially filling the voids created by the air-entraining agent and contributing to the compaction of the hardening mixes and compensating, to a certain extent, the factual decrease of the amount of binder.

Hygric, thermal, and durability properties The water vapor diffusion coefficient and water vapor diffusion permeability increased with the increasing ceramic dust dosage in both the dry-cup and wet-cup arrangement, the maximum difference being ;20% (Table 8). The water vapor diffusion resistance factor followed an opposite trend, in accordance with its definition relation to equation (7). This agreed with the measurement of open porosity which increased correspondingly (Table 3). On the other hand, the liquid water transport parameters, namely, the water absorption coefficient and apparent moisture diffusivity, exhibited a decrease in the whole range of cement replacement levels up to 40%, with a maximum difference of ;20% (Table 9). This correlated well with the measurements of pore size distribution (Figure 1) where the peak found at ;10 mm was highest for the reference mix and decreased with the increasing ceramic dust dosage. The amount of capillary pores was thus the decisive factor for the observed changes in liquid water transport characteristics.


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Table 10. Thermal properties. Material

ldry (W m21 K21)

cdry (J kg21 K21)

lsat (W m21 K21)

csat (J kg21 K21)


1.617 1.570 1.530 1.493

741 765 757 796

2.370 2.240 2.237 2.220

932 995 1052 1069


The results obtained for the water vapor diffusion parameters were in a qualitative agreement with the measurements of oxygen permeability reported by Pacheco-Torgal and Jalali (2011), who found its 10% increase for concrete with 20% of ceramic brick powder. A similarly good agreement was observed for the liquid water transfer properties; Toledo Filho et al. (2007) reported the water sorptivity of mortar to decrease with the increasing amount of ground brick up to 40% of mass of cement and Pacheco-Torgal and Jalali (2011) found a 10% decrease of water permeability of concrete with 20% of ceramic brick powder. The thermal conductivity in dry state, ldry, decreased with the increasing content of ceramic dust in the mix, the difference between REF and CD 40 was ;8% (Table 10). This was in accordance with the open porosity measurements (Table 3). The thermal conductivity in capillary water saturated state, lsat, followed a similar trend, with a maximum difference of ;6%. The effect of moisture content on the thermal conductivity values was very significant for all analyzed mixes; an almost 50% increase was observed when comparing the ldry and lsat values. This finding can have important consequences for the building-physics-related analyses of structures built of the concretes designed in this article. The specific heat capacity in dry state, cdry, slightly increased with the increasing ceramic dust content in the mix, the maximum difference being ;7% (Table 10). The specific heat capacity in capillary water saturated state, csat, showed similar feature, with a maximum increase of ;15%. The significant increase of the specific heat capacity with increasing moisture content which was up to ;35% for different concrete mixes can be attributed to the high-specific heat capacity of water. The freeze/thaw resistance of all analyzed concrete mixes was excellent (Table 11). The frost resistance coefficient K safely met the standard criterion of K . 0.75. The highest K value exhibited the CD 20 mix with 20% ceramic dust content but also the mix with the lowest K, CD 10, performed very well. These results were in accordance with our previous studies achieved for high performance concrete containing fine-ground red ceramics (Vejmelkova´ et al., 2012), no other references were found in the common literature sources. Summarizing the results of the measurements of hygric, thermal, and durability properties, one can see that similar to the mechanical and fracture-mechanical properties, the ceramic dust application did not affect negatively the properties of


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Table 11. Frost resistance coefficient K. Material

K


0.91 0.83 0.96 0.88


the analyzed concretes over the whole studied Portland cement replacement range up to 40% by mass.

Conclusion The application of waste ceramic dust originating in the advanced hollow brick production in concrete mix design was presented as a prospective solution with sound environmental and economical aspects. The first argument in that respect was the conversion of a landfilled waste material to a valuable supplementary cementing material, contributing to a decrease of overall energy consumption, and CO2 emission related to the Portland cement production. The second was its costeffectiveness because the waste ceramic dust does not need any further processing and can be used in the form in which it is obtained from the production line. As the designed concrete mixes were innovative from the point of view of both using a nontraditional type of pozzolanic admixture and imposing a not very common requirement to produce air-entrained concrete with relatively high strength, a wide range of parameters of hardened concrete was investigated. They included the basic material characteristics, mechanical properties, fracture-mechanical properties, water vapor transport properties, liquid water transport properties, heat transport and storage properties, and freeze/thaw resistance. The experimental results showed that the effective limit for the use of ceramic dust in the analyzed hardened concrete mixes was relatively high. It was found not to affect negatively the properties of the analyzed concretes over the whole studied Portland cement replacement range up to 40% by mass, contrary to the most previous studies where only 20% replacement level was recommended in most cases. The main reason for this improved performance of the ceramic dust was identified in its dual role in the designed concrete mixes. Apparently, the part of the ceramic additive which could not participate in the hydration and pozzolanic reactions due to the lack of available Ca2+ acted as fine aggregate partially filling the voids, thus contributing to the compaction of the hardened mixes and compensating, to a certain extent, the factual decrease of the amount of binder. The designed concrete mixes are characteristic by a combination of relatively high compressive strength (35–40 MPa after 28 days) and high frost resistance


Kulovana´ et al.

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coefficient (over 0.80). This makes them suitable candidates for a variety of applications in the building practice. The cost-effectiveness of the mix design, together with the environmental considerations, presents another bonus which is to be taken into account. Declaration of conflicting interests The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article

Funding This research was supported by the European social fund within the framework of realizing the project ‘‘Support of inter-sectoral mobility and quality enhancement of research teams at Czech Technical University in Prague,’’ CZ.1.07/2.3.00/30.0034, the Ministry of Education, Youth and Sports of the Czech Republic, under project No LO1408 ‘‘AdMaS UP— Advanced Building Materials, Structures and Technologies,’’ and by the Czech Science Foundation, under project No 14-04522S.

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