Brick Debris Dust As an Ecological Filler and Its Effect on the Durability

materials

Article Brick Debris Dust as an Ecological Filler and Its Eﬀect on the Durability of Asphalt Mix

Agnieszka Woszuk , Michał Wróbel , Lidia Bandura and Wojciech Franus * Department of Geotechnical Engineering, Faculty of Civil Engineering and Architecture, Lublin University of Technology, Nadbystrzycka 40, 20–618 Lublin, Poland; [email protected] (A.W.); [email protected] (M.W.); [email protected] (L.B.) * Correspondence: [email protected]; Tel.: +48-815-384-416

Received: 17 October 2020; Accepted: 5 November 2020; Published: 7 November 2020

Abstract: Brick debris is one of the main construction wastes obtained from demolition of buildings. However, this material can be successfully used in the recycling process. The purpose of the study was to determine the brick dust addition effect on asphalt surface service life. An asphalt concrete reference mix was designed for bonding layer and prepared using a Marshall compacting device. In addition, three mixes with combined lime-brick filler were prepared as well as one mix containing only brick filler. The samples were tested for their volumetric properties—density, bulk density, air void content, resistance to water and frost and stiffness modulus with varying test temperatures. It was found that 25% of brick dust addition to the filler did not considerably change the properties of the tested samples, while in the case of 50% filler the replacement stiffness and frost resistance decrease; however, the minimum required value is maintained. It can be concluded that the lime filler can be replaced with up to 50% of brick dust without a negative impact on the properties of asphalt mix. The proposed solution fits into the idea of sustainable development indicating a way of brick debris management.

Keywords: brick debris dust; mineral ﬁller; asphalt mix; air voids; water sensitivity; stiﬀness modulus

1. Introduction A properly formed road network is an important factor in the economic development of each country. For this reason, in many regions, investment in construction of new roads and modernization of existing ones is being increased every year. However, both in Europe and the world, asphalt pavements prevail. In the United States, asphalt mix production increased by 7.8% between 2014 and 2017, while in Europe the value increased by 12.5% [1]. At the same time, the development of road infrastructure is associated with significant consumption of natural resources, including mainly crude oil and mineral aggregates as well as pollution of the environment through the emission of hazardous compounds and the generation of waste materials [2]. Therefore, it is becoming increasingly crucial to use sustainable solutions, for instance warm mix asphalt technology, in the road construction industry [3–5]. Another way to achieve clean asphalt mix production is to use waste materials interchangeably as mineral aggregates [6,7] or as an additive affecting the properties of the asphalt binder [8,9]. Furthermore, the mineral filler, which is ground limestone in a conventional asphalt mix, can be replaced by waste material such as: lime kiln dust [10], waste glass powder [11], fly ash [12], ash from biomass combustion [13], cement and calcium hydroxide [14], waste oyster shells [15], calcium carbide [16] and others [17]. Brick debris is one of the main contributors to building waste. In some countries it represents up to 30% of this waste [18]. In recent years, there have been many studies on the reuse of brick debris. Padmini et al. evaluated the physical properties of brick debris aggregates in comparison to

Materials 2020, 13, 5023; doi:10.3390/ma13215023 www.mdpi.com/journal/materials Materials 2020, 13, 5023 2 of 14 light natural aggregates [19]. Kibriya and Speare found that concrete with crushed bricks has similar compressive, tensile and flexural strengths to concrete with natural aggregates [20]. Poon et al. used 50% addition of crushed brick in the production of paving blocks [21,22]. Moreover, it is possible to use brick debris aggregate in unbound subbase materials as well as cement-stabilised base layers successfully [18,23]. Research studies of asphalt with the addition of ground brick debris were also conducted. Asphalt mastic containing recycled red brick powder at 0 ◦C was found to have higher shear creep stiffness modulus than mastic containing lime filler [24], which may cause low-temperature cracking. Also the results of the research carried out by Wu et al. indicate that the dust from brick debris can have a certain positive effect on the high-temperature performance and, at the same time, a negative effect on the low-temperature properties of asphalt mastic [25]. The tests performed on asphalt concrete asphalt mix type also proved to have higher resistance to permanent deformation with the use of brick dust filler [26]. On the other hand, porous asphalt with the addition of brick dust was characterized by a deeper rut compared to a mixture with lime filler [27]. Differences in test results may result from the use of different testing procedures as well as differences in the properties of individual materials. The physicochemical characteristics are particularly important for a filler that performs numerous important functions in the asphalt mix [28,29]: (1) fills the void spaces between mineral mix grains; (2) stiffens the asphalt forming the mineral filled asphalt together with the binder which binds the aggregate mix grains; (3) improves water tightness and frost resistance of an asphalt mix. The chemical composition of brick debris dust differs significantly from the lime filler commonly used in mineral–asphalt mixtures, which may adversely affect the performance of the mixtures, especially their water resistance. At the same time, environmental aspects speak in favor of the use of waste materials in road construction. In the works published so far, either the influence of brick dust on the properties of asphalt mastic was determined or lime filler was replaced completely by brick dust. The analyses presented in the paper were performed for asphalt mix with brick and lime filler combination in 4 different proportions. The main aim of the study was to determine the brick dust addition effect on the asphalt surface service life defined as resistance to water and frost, considering physical and chemical properties of the brick dust.

2. Experimental Materials The limestone used as the standard mineral ﬁller was acquired from the Bukowa mine (Poland). Dust from brick debris was obtained by grinding brick waste obtained during demolition of old buildings in a laboratory jaw crusher LKS-100 (Testchem, Poland). The physical properties of these materials are summarized in Table1.

Table 1. Physical properties of lime ﬁller and brick debris dust used in the tests.

Test Speciﬁcation Result Lime Filler Brick Debris Dust Grain size [mm] EN (European Standard) 933-10:2009 0–2 0–2 Density [kg/m3] EN 1097-7:2008 2763 2782 Water content [%] EN 1097-5:2008 <1 <1

The bitumen of 35/50 penetration grade was obtained from ORLEN Asfalt Sp. z o.o (Płock, Poland). The following tests were performed in order to characterize the basic bitumen properties: penetration, ring and ball softening point and viscosity. On the basis of the penetration and softening point test results, the penetration index deﬁning the thermal vulnerability of asphalt was calculated. The test results are presented in Table2. Materials 2019, 11, x 3 of 15

Table 2. Properties of the bitumen.

Specification Test Specification Result Materials 2020, 13, 5023 Limits 3 of 14 Penetration (25 °C; 0.1 EN (European Standard) 1426:2009 38.2 35–50 mm) Table 2. Properties of the bitumen. Softening point (°C) EN 1427:2009 55.8 50–58 Viscosity Testat 135 °C ASTM (American Specification Society for Testing and Result Specification Limits Penetration (25 ◦C; 0.1 mm) EN (European Standard) 1426:20090.755 38.2 35–50- Softening(Pa·s) point (◦C)Materials) EN 1427:2009 D 4402 55.8 50–58 Viscosity at 135 C (Pa s) ASTM (American Society for Testing and Materials) D 4402 0.755 - Penetration index◦ · EN 12591:2010 −0.47 - Penetration index EN 12591:2010 0.47 - − Particle size distribution of the aggregates was assessed using the dry sieving method (EN 933-1:2012),Particle while size the distribution mineral filler of particle the aggregates size distribution was assessed was assessed using theusing dry the sieving air jet sieving method method(EN 933-1:2012), (EN 933-10:2009). while the The mineral aggregate filler particlegradation size of distribution the reference was mix assessed asphalt using is given the airin Figure jet sieving 1. Themethod mineral (EN mix 933-10:2009). composition The was aggregate designed gradation using ofthe the grading reference envelope mix asphalt method. is given Sub-threshold in Figure1 . valuesThe mineral apply to mix technical composition requirements was designed effective using in thePoland grading [30]. envelope method. Sub-threshold values apply to technical requirements effective in Poland [30].

100

Passing [%] 50

40 Selected gradation 30 Upper limit 20 Lower limit 10

0 1 2 4 8 16 0.5 5.6 11.2 22.4 31.5 0.063 0.125 0.250 Sieve size [mm]

Figure 1. Aggregate gradation of the reference asphalt mix. Figure 1. Aggregate gradation of the reference asphalt mix. Asphalt concrete mixture for binder course AC 16 W was used as a reference material, abbreviated furtherAsphalt as AC. concrete The amount mixture of asphalt for binder added wascourse 4.5% AC in relation 16 W towas the asphaltused as mix a weight.reference The material, designed abbreviatedmix meets thefurther technical as AC. regulations The amount in force of asphalt in Poland added [30]. was Table 4.5%3 shows in relation the composition to the asphalt of both mix the weight.mineral The mixture designed and themix asphaltmeets the mix. technical regulations in force in Poland [30]. Table 3 shows the composition of both the mineral mixture and the asphalt mix. Table 3. Composition of mineral mixture and asphalt mix. Table 3. Composition of mineral mixture and asphalt mix. Grain Size Type of Aggregate Origin Composition [m%] Grain[mm] Size Type of Aggregate Origin Composition [m%] [mm] Mineral Mixture Asphalt Mix Dolomite 0/4 0–4 Łagów, PolandMineral 24.5 Mixture Asphalt 23.4 Mix Dolomite 2 /0/48 0–4 2–8 Łagów, Łagów, Poland Poland 24.5 37 23.4 35.3 DolomiteDolomite 8/ 162/8 8–162–8 Łagów, Łagów, Poland Poland 3734 35.3 32.5 Limestone filler 0–2 Bukowa mine, Poland 4.5 4.3 Dolomite35/50 asphalt 8/16 8–16 ORLENŁagów, Asfalt Poland Sp. z o.o 34 32.5 4.5 LimestoneTotal filler 0–2 Bukowa mine, Poland 1004.5 4.3 100 35/50 asphalt ORLEN Asfalt Sp. z o.o 4.5 Total 100 100 The tests were carried out for the asphalt mix containing limestone powder as a mineral filler (reference sample) as well as the mixes containing a mixture of limestone and brick filler. Figure2 presents the composition of the particular mixes with the proportions of materials used and summarizes the methodology applied for this study. Materials 2019, 11, x 4 of 15

The tests were carried out for the asphalt mix containing limestone powder as a mineral filler (reference sample) as well as the mixes containing a mixture of limestone and brick filler. Figure 2 Materials 2020, 13, 5023 4 of 14 presents the composition of the particular mixes with the proportions of materials used and summarizes the methodology applied for this study.

Figure 2. Methodology scheme used for this work. 3. Research Method 3. Research Method 3.1. Characterization of Lime Filler and Brick Debris Dust 3.1. Characterization of Lime Filler and Brick Debris Dust The chemical analyses were performed on air-dried samples using the energy dispersive X-ray fluorescenceThe chemical method analyses (EDXRF) were employing performed an Epsilon on air-dr 3 spectrometeried samples using applying the theenergy following dispersive parameters: X-ray fluorescenceRTG Rh 9 W, 50method kV and (EDXRF) 1 mA lamp employing (Panalytical, an The Eps Netherlands).ilon 3 spectrometer Elements withinapplying the rangethe following from Na parameters:to Am were includedRTG Rh 9W, in the 50 analyses.kV and 1 mA lamp (Panalytical, The Netherlands). Elements within the rangeParticle from Na size to distributionAm were included was determined in the analyses. using the laser diffraction method (Mastersizer 3000 deviceParticle with Hydrosize distribution G dispersion was unitdetermined with the using range the of laser 0.02 µdiffractionm to 2 mm) method with the(Mastersizer application 3000 of deviceMie theory with andHydro the G following dispersion parameters: unit with the light range refractive of 0.02 μ indexm to 2 of mm) 1.52 with and absorptionthe application coe ffiofcient Mie theoryof 0.1. and The the measurements following parameters: were carried light out refractive with the index speed of of 1.52 1750 and and absorption 700 rpm for coefficient the pump of and0.1. Thestirrer, measurements respectively. were carried out with the speed of 1750 and 700 rpm for the pump and stirrer, respectively.The phase composition of tested fillers was determined by the X-ray diffraction method (XRD) usingThe an phase X’pert composition PROMPD di offfractometer tested fillers along was withdeter PWmined 3050 by/60 the goniometer, X-ray diffraction Cu tube method and graphite (XRD) using an X’pert PROMPD diffractometer along with PW 3050/60 goniometer, Cu tube and graphite monochromator. The test angle (2θ) varied from 5◦ to 65◦. Interstitial spacing parameter dhkl for a particularmonochromator. crystal structureThe test angle was identified (2θ) varied in linefrom with 5° to Bragg’s 65°. Interstitial law. spacing parameter dhkl for a particularThe microstructural crystal structure analysis was identified of the fillersin line waswith performed Bragg’s law. using a Quanta 250 FEG scanning electronThe microscopemicrostructural (SEM) analysis by FEI (Hillsboro,of the fillers OR, was USA). performed using a Quanta 250 FEG scanning electron microscope (SEM) by FEI (Hillsboro, OR, USA). 3.2. Methodology of the Asphalt Mix Tests 3.2. Methodology of the Asphalt Mix Tests The samples were prepared in a Marshall device and had the following dimensions: 63.5 mm heightThe and samples 101.6 mmwere diameter. prepared Before in a Marshall preparation device of theand first had sample, the following the mould dimensions: was heated 63.5 to mm the heightcompaction and 101.6 temperature. mm diameter. The compaction Before preparation temperature of the of thefirst reference sample, mixthe mould asphalt was was heated 140 ◦C to based the compactionon the type oftemperature. asphalt used. The The compaction samples for temperature air voids and of sti theffness reference modulus mix test asphalt were prepared was 140 with °C based75 blows on perthe eachtype side.of asphalt The samples used. The for testssamples of resistance for air voids to indirect and tensilestiffness strength modulus resistance test were to waterprepared and with frost 75 measured blows per by each the ITSR side. (indirect The samples tensile for strength tests of ratio)resistance indicator to indirect were compacted tensile strength using 50 blows per side. Samples were named with the following symbols: L for reference mix containing Materials 2020, 13, 5023 5 of 14 only lime filler, L-B 3:1 (meaning 3:1 ratio of lime to brick filler); L-B 1:1; L-B 1:3 for mixes with combined fillers and B for mix with brick filler. The maximum density of the mix asphalt has been determined by means of the volumetric procedure according to the EN 12697-5:2012 standard. For bulk density of the mix asphalt specimens, the ‘saturated surface-dry’ (‘SSD’) procedure was applied in accordance with the EN 12697-5: 2012 standard. The air voids content in compacted samples was calculated based on the EN 12697-8:2005 standard. The water and frost resistance tests of the concrete asphalts were performed based on the EN 12697-12:2008 standard and Polish technical requirements [30]. This test evaluates the effect of a single freezing cycle of saturated mix asphalt samples on indirect resistance to Marshall-type sample stretching. Ten samples were prepared with every asphalt mix type and divided into two groups: ‘dry set’ and ‘wet set’ of similar heights and bulk density values. The control series samples were conditioned in a laboratory on a flat surface. The second group of samples was exposed to a prolonged effect of water at an increased temperature by placing them in a water bath with the temperature of 40 C for 68 h. Then, the samples were frozen for 16 h at a temperature of 18 C and thawed for ◦ − ◦ 24 h in water at a temperature of 25 ◦C. The samples from both sets were used to test the resistance to indirect tensile strength in the Marshall’s device, according to the EN 12697-23:2009 standard. The ITSR indicator of resistance to water and frost was calculated based on the obtained results according to the following formula: ITS ITSR = w (1) ITSd where:

ITSR—indirect tensile strength ratio [%]

ITSw—the average indirect tensile strength for the wet samples [kPa] ITSd—the average indirect tensile strength for the dry samples [kPa] The study of the stiﬀness modulus was performed according to the EN 12697-26:2012 standard.

The Marshall samples were subject to five-time dynamic load applied to the sample vertically, along the diameter. Maximum force generated a horizontal dislocation of sample equal to 5 µm. The test result was calculated automatically by a control program, as an arithmetic mean from the stiffness modulus for each of 5 force impulse measurements. The sample, after performing the test, was rotated by 90◦ around the horizontal axis and tested again. A reliable stiffness modulus for each sample was a mean average out of two measurements.

4. Results and Discussion

4.1. Characteristics of Brick Debris Dust and Lime Filler

4.1.1. Chemical Composition In the chemical composition of the brick debris, silicon oxide dominates, which is accompanied by a smaller amount of aluminium oxide. Moreover, the presence of MgO, CaO and K2O was detected in a level of several percent (Table4). The main component of the lime ﬁller is calcium oxide.

4.1.2. Mineral Composition The mineral composition of the investigated ﬁllers is shown in Figure3. The main mineral component of the brick debris dust is quartz which can be recognized by the characteristic dhkl = 3.34, 4.26, 1.81, 2.45 Å (26.65, 20.87, 50.16, 36.56, 2θ respectively), accompanied by mullite phase of dhkl = 3.39, 3.42, 5.38, 2.21 Å (26.26, 25.98, 16.44, 40.86, 2θ respectively). Another signiﬁcant phase in the brick debris composition is aluminosilicate glass which can be recognized by the rise of a background line in the range 15–35◦ 2θ. The other, minor components are albite of dhkl = 3.21, 4.03, 3.75 Å (27.73, 22.05, 23.67, Materials 2019, 11, x 6 of 15

MgO 1.29 0.21 Al2O3 9.68 0.15

Materials 2020, 13, 5023 SiO2 76.19 0.27 6 of 14 P2O5 0.00 0.02 SO3 0.04 0.04 2θ respectively), hematite dhklK2O= 2.70, 2.51, 1,843.00 Å (33.11, 35.61, 49.41, 0.00 2θ, respectively), and secondary crystallized calcite of dhkl CaO= 3.04, 2.07, 2.284.54 Å (29.40, 43.16, 39.42, 74.68 2 θ, respectively). The mineral composition of the lime ﬁllerTiO is2 less complex.0.84 Apart from the calcite 0.00phase which dominates, a small amount of quartz can be recognized,Fe2O3 as well4.13 as trace amount of 0.06dolomite of dhkl = 2.89, 2.19, 2.01 Å (30.97, 41.16, 44.96, 2θ, respectively). 4.1.2. Mineral Composition Table 4. Chemical composition of the tested ﬁllers. The mineral composition of the investigated fillers is shown in Figure 3. The main mineral component of the brick debris dust is quartzBrick which Debris can be recognized Lime Filler by the characteristic dhkl = 3.34, 4.26, 1.81, 2.45 Å (26.65, 20.87, 50.16, 36.56, 2[%θ respectively), of Weight] accompanied by mullite phase of dhkl = 3.39, 3.42, 5.38, 2.21 Å (26.26, 25.98,MgO 16.44, 40.86, 1.29 2θ respectively). 0.21 Another significant phase in the brick debris composition is Alaluminosilicate2O3 9.68glass which can 0.15 be recognized by the rise of a background line in the range 15–35°SiO2 2θ. The other,76.19 minor components 0.27 are albite of dhkl = 3.21, 4.03, P O 0.00 0.02 3.75 Å (27.73, 22.05, 23.67, 2θ respectively),2 5 hematite dhkl = 2.70, 2.51, 1,84 Å (33.11, 35.61, 49.41, 2θ, SO3 0.04 0.04 respectively), and secondary crystallized calcite of dhkl = 3.04, 2.07, 2.28 Å (29.40, 43.16, 39.42, 2θ, K2O 3.00 0.00 respectively). The mineral compositionCaO of the lime 4.54 filler is less complex. 74.68 Apart from the calcite phase which dominates, a small amountTiO 2of quartz can0.84 be recognized, 0.00as well as trace amount of dolomite of dhkl = 2.89, 2.19, 2.01 Å (30.97,Fe 41.16,2O3 44.96, 2θ4.13, respectively). 0.06

Figure 3. X-ray diffraction (XRD) patterns of the tested fillers. Figure 3. X-ray diffraction (XRD) patterns of the tested fillers. 4.1.3. Scanning Electron Microscopy (SEM) 4.1.3. Scanning Electron Microscopy (SEM) The microstructural morphology of the brick debris dust and the lime filler is presented in Figure4a,b, respectively. SEM images indicate that more fine grains are present in the lime filler. The grains in the lime filler are in the size of about 10 µm and their shape is irregular. Interestingly, Materials 2019, 11, x 7 of 15 Materials 2019, 11, x 7 of 15 The microstructural morphology of the brick debris dust and the lime filler is presented in The microstructural morphology of the brick debris dust and the lime filler is presented in MaterialsFigure2020 4a,b,, 13 respectively., 5023 SEM images indicate that more fine grains are present in the lime filler.7 of The 14 Figuregrains 4a,b, in the respectively. lime filler are SEM in imagesthe size indicate of about that 10 moreμm and fine their grains shape are presentis irregular. in the Interestingly, lime filler. The the grainsbrick debrisin the islime characterized filler are in bythe the size grains of about often 10 exceeding μm and their30 μ mshape and theiris irregular. surface Interestingly,is heterogeneous, the thebrickrough brick debris and debris theis characterized isshape characterized is sharp-edged by bythe the grains in grains comparison often often exceeding exceeding to the 30lime 30 μµm filler.m and and their their surface surface is is heterogeneous, heterogeneous, roughrough andand thethe shapeshape isis sharp-edgedsharp-edged inin comparisoncomparison toto thethe limelime filler.filler.

(a) (b) (a) (b) Figure 4. Scanning electron microscopy images of (a) brick debris dust and (b) lime filler. Figure 4. Scanning electron microscopy images of (a)) brickbrick debrisdebris dustdust andand ((b)) limelime filler.filler. 4.1.4. Grading 4.1.4.4.1.4. Grading FigureFigure5 presents5 presents the the particle particle size size distribution distribution (PSD) (PSD) of two of two fillers fillers used used in the in study. the study. Particle Particle size size Figuredistribution 5 presents of the the brick particle debris size dust distribution is bimodal (PSD)with one of twoclear fillers dominant used peakin the with study. a maximum Particle distributionsize distribution of the of brickthe brick debris debris dust dust is bimodal is bimodal with with one one clear clear dominant dominant peak peak with with a maximum a maximum at at about µ40 μm which means that grains of this size make the greatest contribution. The second peak aboutat about 40 40m μm which which means means that that grains grains of of this this size size make make the the greatest greatest contribution. contribution. TheThe secondsecond peakpeak isis relatively relatively small small withwith aa maximummaximum at around 120 120 μµmm suggesting suggesting a a small small amount amount of of larger larger grains grains in isthe relatively brick debris. small withParticle a maximum size distribution at around of 120the μlimem suggesting filler is also a small bimodal, amount however of larger two grains distinct in inthe the brick brick debris. debris. Particle Particle size size distribution distribution of of the the lime lime filler filler is is also also bimodal, however twotwo distinctdistinct peaks can be distinguished. The first one is slightly higher and has its maximum at the valueµ of 5 peakspeaks cancan bebe distinguished. distinguished. The The first first one one is is slightly slightly higher higher and and has has its maximumits maximum at the at valuethe value of 5 ofm, 5 andμm, the and second the second one at one around at around 80 µm. 80 The μm. PSD The curve PSD revealscurve reveals that the that granulation the granulation of the lime of the filler lime is μfillerm, and is less the homogeneous second one at that around granulation 80 μm. ofThe the PSD brick curve debris reveals dust. that the granulation of the lime lessfiller homogeneous is less homogeneous that granulation that granulation of the brick of the debris brick dust. debris dust.

10.0 10.0 9.0 9.0 8.0 brick debris 8.0 brick debris 7.0 lime filler 7.0 lime filler 6.0 6.0 5.0 5.0 4.0 4.0 3.0 3.0 2.0 Percentage by volume [%] volume by Percentage 2.0 Percentage by volume [%] volume by Percentage 1.0 1.0 0.0 0.0 0.1 1 10 100 1000 0.1 1 10 100 1000 Particle size [μm] Particle size [μm] Figure 5. Grading curves of the tested ﬁllers. Figure 5. Grading curves of the tested fillers. Figure 5. Grading curves of the tested fillers.

Materials 2019, 11, x 8 of 15

4.2. Properties of Asphalt Mix

4.2.1. Effect of Brick Debris Dust Addition on Volumetric Properties of Asphalt Mix The results of volumetric properties tests are presented in Figures 6 and 7. Mean value of the maximum density of the reference mix L was 2483 kg/m3, while the bulk density was 2390 kg/m3. The value of maximum density increased from 2481 kg/m3 to 2499 kg/m3 along with a rising amount of brick dust. In the samples in which the traditional filler was replaced by 25% brick debris, the volumetric properties were comparable to those of the reference samples. Increasing the share of brick dust resulted in a steep reduction of bulk density to 2380 kg/m3 (50% and 75% of brick filler) and further to 2370 kg/m3 (100% brick filler). Also, the content of air voids increased to 4.4%, 4.6% and 5.2%, respectively, while in both reference sample L and L-B 3:1 sample the value equaled 3.7%. Considering the comparable density of the lime filler and brick dust, minor changes in the maximum density values were expected. The trend observed in the research is different from that expected, probably as a result of the chemical composition of brick dust with a very high SiO2 content (76.19%), which negatively affects the properties of the obtained asphalt mastic and in particular the adhesion to the aggregate. Subsequently, the density of asphalt mix decreases, which is reflected in the bulk density and air void content values of asphalt mixes [31]. Also the particle shape of the filler has a significant impact on asphalt mix compaction process [32,33]. Particles of the Materials 2020, 13, 5023 8 of 14 lime filler used in the study are finer and have a more regular shape than those of brick dust (Figure 4). It could be seen from the SEM results that the surface of recycled brick powder is much rougher. 4.2.What Properties is more, of Asphalt its particle Mix size distribution (Figure 5) is more homogeneous than that of the limestone powder. Both observations suggest that the recycled brick powder may exhibit better adsorption 4.2.1.abilities Effect than of Brick the Debrislimestone Dust filler. Addition As indicated on Volumetric by Zulkati Properties et al., of Asphaltthe filler Mix with sufficiently large diameterThe results and ofregular volumetric shape properties grains acts tests as both are presentedlubricating in and Figures fractioning6 and7. agent, Mean which value offacilitates the maximumthe movement density of of the the aggregates reference and mix consequently L was 2483 kg increases/m3, while the the compaction bulk density susceptibility was 2390 of kg asphalt/m3. Themix value [33]. of maximumHowever, density the surface increased of frombrick 2481debris kg/ mdust3 to 2499is more kg/m rough,3 along withwhich a risingresults amount in greater of brickadsorption dust. In the capacity samples than in which a lime the filler traditional [34]. The filler meth wasodology replaced of sample by 25% preparation brick debris, is the also volumetric important. propertiesAccording were to comparablethe technical to regulations those of the in referenceforce in Poland, samples. all Increasingsamples were the sharecompacted of brick at dust140 °C, resultedwhereas in aWu steep et reductional. indicate of that bulk the density average to 2380comp kgaction/m3 (50% temperature and 75% of of an brick asphalt filler) mix and containing further to 2370brick kgdust/m 3should(100% be brick 6.5 °C filler). higher Also, than the that content of mixes of aircontaining voids increased lime filler to [25]. 4.4%, 4.6% and 5.2%, respectively, while in both reference sample L and L-B 3:1 sample the value equaled 3.7%.

Materials 2019, 11, x 9 of 15 Figure 6. Maximum density and bulk density results of the studied mixes.

Figure 6. Maximum density and bulk density results of the studied mixes.

Figure 7. Air void content of the studied mixes. Figure 7. Air void content of the studied mixes. Considering the comparable density of the lime filler and brick dust, minor changes in the maximum4.2.2. density Effect of values Brick wereDebris expected. Dust Addition The trend on Water observed and Frost in the Resistance research isand diff Indirecterent from Tensile that expected,Strength probably of Asphalt as a result Mixtures of the chemical composition of brick dust with a very high SiO2 content (76.19%), which negatively affects the properties of the obtained asphalt mastic and in particular the The results of the strength properties test and resistance to water and frost are shown in Figures adhesion to the aggregate. Subsequently, the density of asphalt mix decreases, which is reflected in the 8 and 9. The reference asphalt mix L had the highest indirect tensile strength values of 770.1 MPa for bulk density and air void content values of asphalt mixes [31]. Also the particle shape of the filler has a dry samples and 679.2 MPa for wet samples, respectively. The decrease in strength as a result of significant impact on asphalt mix compaction process [32,33]. Particles of the lime filler used in the water and frost was the lowest in samples with lime filler, so the ITSR index reached 88.1%. The use study are finer and have a more regular shape than those of brick dust (Figure4). It could be seen from of dust from brick debris as a filler resulted in a reduction in the strength of the produced mixture as well as lower water and frost resistance. Samples in which the lime filler was half replaced by brick filler (L-B 1:1) were the weakest in terms of strength (dry samples—668.2 MPa). Taking into account the resistance to water and frost, a decrease in the ITSR parameter from 85.1% to 78.7% was observed with the increase in the share of brick dust in the filler. One of the key factors influencing water and frost resistance is the adhesion of asphalt to aggregates, including fillers. Bonding of the asphalt mix components to a large extent depends on the chemical and mineral composition of fillers. Materials that exhibit hydrophobic properties adhere very effectively to the asphalt. In turn, natural aggregates used in road construction are hydrophilic to varying degrees (water attracting), but also lipophilic (fat attracting). Asphalt binder has a hydrophobic character and, therefore, if the applied filler shows more affinity to water than to bitumen (high hydrophilicity), the asphalt mastic produced will not be durable. In addition, the created joints will be additionally weakened by water during the operation of the pavement. As noted by Nciri et al., a filler with with a high calcium content is naturally a material which forms strong bonds in contact with hydrophobic organic compound (i.e., asphalt binder) [15]. This theory can explain the higher tensile strength values of asphalt mixes with calcium filler in which calcium carbonate (Table 4) occurs in the form of calcite (Figure 3). In contrast, the chemical composition of brick dust is mainly SiO2 (Table 4) in the form of quartz (Figure 3). Moreover, the surface of silica materials is characterized by the occurrence of hydroxyl groups providing hydrophilic character. Both the acidity of this material and its hydrophilic character adversely affect the asphalt adhesion to the aggregate, which is reflected in a decrease in tensile strength and resistance to water and frost. A decrease in water and frost resistance can lead to premature degradation of the road surface. However, the use of brick dust is an interesting recycling method. Therefore, it is necessary to determine the optimal amount of brick dust in the mixed filler. Considering the requirements of ITSR for the binding layer, (at least 80%) it is possible to replace up to 50% of the lime filler with brick debris dust (Figure 9).

Materials 2020, 13, 5023 9 of 14 the SEM results that the surface of recycled brick powder is much rougher. What is more, its particle size distribution (Figure5) is more homogeneous than that of the limestone powder. Both observations suggest that the recycled brick powder may exhibit better adsorption abilities than the limestone filler. As indicated by Zulkati et al., the filler with sufficiently large diameter and regular shape grains acts as both lubricating and fractioning agent, which facilitates the movement of the aggregates and consequently increases the compaction susceptibility of asphalt mix [33]. However, the surface of brick debris dust is more rough, which results in greater adsorption capacity than a lime filler [34]. The methodology of sample preparation is also important. According to the technical regulations in force in Poland, all samples were compacted at 140 ◦C, whereas Wu et al. indicate that the average compaction temperature of an asphalt mix containing brick dust should be 6.5 ◦C higher than that of mixes containing lime filler [25].

4.2.2. Effect of Brick Debris Dust Addition on Water and Frost Resistance and Indirect Tensile Strength of Asphalt Mixtures The results of the strength properties test and resistance to water and frost are shown in Figures8 and9. The reference asphalt mix L had the highest indirect tensile strength values of 770.1 MPa for dry samples and 679.2 MPa for wet samples, respectively. The decrease in strength as a result of water and frost was the lowest in samples with lime filler, so the ITSR index reached 88.1%. The use of dust from brick debris as a filler resulted in a reduction in the strength of the produced mixture as well as lower water and frost resistance. Samples in which the lime filler was half replaced by brick filler (L-B 1:1) were the weakest in terms of strength (dry samples—668.2 MPa). Taking into account the resistance to waterMaterials and frost,2019, 11 a, decreasex in the ITSR parameter from 85.1% to 78.7% was observed with the increase10 of 15 in the share of brick dust in the filler.

Figure 8. Indirect tensile strength of the studied mixes for the dry and wet samples. Figure 8. Indirect tensile strength of the studied mixes for the dry and wet samples. One of the key factors influencing water and frost resistance is the adhesion of asphalt to aggregates, including fillers. Bonding of the asphalt mix components to a large extent depends on the chemical and mineral composition100 of fillers. Materials that exhibit hydrophobic properties adhere very effectively to 88.1 the asphalt. In90 turn, natural aggregates used85.1 in road construction82.6 are hydrophilic to varying degrees (water attracting), but also lipophilic (fat attracting). Asphalt binder has79.6 a hydrophobic78.7 character 80 and, therefore, if the applied filler shows more affinity to water than to bitumen (high hydrophilicity), 70 the asphalt mastic produced will not be durable. In addition, the created joints will be additionally weakened by water60 during the operation of the pavement. As noted by50 Nciri et al., a filler with with a high calcium content is naturally a material which forms

strong bondsITSR [%] in40 contact with hydrophobic organic compound (i.e., asphalt binder) [15]. This theory can explain the30 higher tensile strength values of asphalt mixes with calcium ﬁller in which calcium 20 10 0 L L-B 3:1 L-B 1:1 L-B 1:3 B Sample type

Figure 9. Water and frost resistance of studied mixes measured with indirect tensile strength ratio (ITSR) indicator.

4.2.3. Effect of Brick Debris Dust Addition on Stiffness Modulus of Asphalt Mixtures The mean values of stiffness modulus are presented in Figure 10. Reference sample L had the highest value of stiffness modulus at both subzero (−2 °C) and average temperatures (+10 °C). Below 0 °C, the decrease of stiffness modulus was observed for samples containing brick filler. The values were from 16,886 MPa for L-B 3:1 samples to 15,605 MPa for B samples. Considering the fact that road surfaces become stiffer over time [35], the results obtained should be treated positively in terms of asphalt mix low-temperature cracking resistance. The stiffness of reference samples (L) at a temperature of +23 °C was 4298 MPa. The replacement of the lime filler with brick debris dust caused a change in stiffness at that temperature ranging from +1.3% to −7.9%. However, for samples where the lime filler has been replaced by brick dust by no more than 50%, the stiffness remains close to the level of reference samples. Due to the fact that asphalt mixes of high stiffness modulus at positive temperatures are more resistant to permanent deformations [36], it can be concluded that adding more than 50% of brick dust into the filler is more likely to cause rutting in the road surface. Based on the equivalent temperature of

Materials 2019, 11, x 10 of 15

Materials 2020, 13, 5023 10 of 14 carbonate (Table4) occurs in the form of calcite (Figure3). In contrast, the chemical composition of brick dust is mainly SiO2 (Table4) in the form of quartz (Figure3). Moreover, the surface of silica materials is characterized by the occurrence of hydroxyl groups providing hydrophilic character. Both the acidity of this material and its hydrophilic character adversely aﬀect the asphalt adhesion to the aggregate, Figure 8. Indirect tensile strength of the studied mixes for the dry and wet samples. which is reﬂected in a decrease in tensile strength and resistance to water and frost.

100 88.1 90 85.1 82.6 79.6 78.7 80 70 60 50

ITSR [%] 40 30 20 10 0 L L-B 3:1 L-B 1:1 L-B 1:3 B Sample type

Figure 9. Water and frost resistance of studied mixes measured with indirect tensile strength ratio Figure(ITSR) indicator.9. Water and frost resistance of studied mixes measured with indirect tensile strength ratio (ITSR) indicator. A decrease in water and frost resistance can lead to premature degradation of the road surface. 4.2.3.However, Effect the of useBrick of brickDebris dust Dust is anAddition interesting on Stiffness recycling Modulus method. Therefore,of Asphalt itMixtures is necessary to determine the optimal amount of brick dust in the mixed filler. Considering the requirements of ITSR for the bindingThe layer,mean (atvalues least of 80%) stiffness it is possible modulus to are replace presented up to 50%in Figure of the 10. lime Reference filler with sample brick debrisL had dustthe highest(Figure 9value). of stiffness modulus at both subzero (−2 °C) and average temperatures (+10 °C). Below 0 °C, the decrease of stiffness modulus was observed for samples containing brick filler. The values were4.2.3. from Effect 16,886 of Brick MPa Debris for L-B Dust 3:1 Addition samples on to Sti15,605ffness MPa Modulus for B ofsamples. Asphalt Considering Mixtures the fact that road surfaces become stiffer over time [35], the results obtained should be treated positively in terms The mean values of stiffness modulus are presented in Figure 10. Reference sample L had of asphalt mix low-temperature cracking resistance. the highest value of stiffness modulus at both subzero ( 2 ◦C) and average temperatures (+10 ◦C). The stiffness of reference samples (L) at a temperature− of +23 °C was 4298 MPa. The Below 0 ◦C, the decrease of stiffness modulus was observed for samples containing brick filler. The replacement of the lime filler with brick debris dust caused a change in stiffness at that temperature values were from 16,886 MPa for L-B 3:1 samples to 15,605 MPa for B samples. Considering the fact ranging from +1.3% to −7.9%. However, for samples where the lime filler has been replaced by brick that road surfaces become stiffer over time [35], the results obtained should be treated positively in dust by no more than 50%, the stiffness remains close to the level of reference samples. Due to the terms of asphalt mix low-temperature cracking resistance. fact that asphalt mixes of high stiffness modulus at positive temperatures are more resistant to The stiffness of reference samples (L) at a temperature of +23 ◦C was 4298 MPa. The replacement permanent deformations [36], it can be concluded that adding more than 50% of brick dust into the of the lime filler with brick debris dust caused a change in stiffness at that temperature ranging from filler is more likely to cause rutting in the road surface. Based on the equivalent temperature of +1.3% to 7.9%. However, for samples where the lime filler has been replaced by brick dust by no more − than 50%, the stiffness remains close to the level of reference samples. Due to the fact that asphalt mixes of high stiffness modulus at positive temperatures are more resistant to permanent deformations [36], it can be concluded that adding more than 50% of brick dust into the filler is more likely to cause rutting in the road surface. Based on the equivalent temperature of softening and cracking of asphalt material, Wu et al. found that the advantage of asphalt mastic containing brick dust is its resistance to high temperatures and the disadvantage is low-temperature properties [25]. Due to divergent conclusions resulting from the tests of asphalt mastics described in the literature and the analysis of the results obtained, these properties should be examined according to the procedures in force in this field. The analyses mentioned above are based on generally known probable correlations described in the literature. Nonetheless, it is worth noting that a material with originally low mechanical properties Materials 2019, 11, x 11 of 15

softening and cracking of asphalt material, Wu et al. found that the advantage of asphalt mastic containing brick dust is its resistance to high temperatures and the disadvantage is low-temperature properties [25]. Due to divergent conclusions resulting from the tests of asphalt mastics described in the literature and the analysis of the results obtained, these properties should be examined according to the procedures in force in this field. The analyses mentioned above are based on generally known probable correlations described in the literature. Nonetheless, it is worth noting that a material with originally low mechanical properties can stiffen faster than a material with high initial stiffness. The stiffness of mineral– asphalt mixtures and its change over time is mainly influenced by the type of asphalt, including chemical composition and molecular structure. However, as indicated by Gandhi et al., even when Materials 2020, 13, 5023 11 of 14 the same type of asphalt was applied, the change of stiffness for the aged samples was different for various aggregates and other warm mix asphalt additives [37]. can stiffen fasterAs expected, than a materialthe stiffness with of high asphalt initial mix sti withffness. the Theaddition stiff nessof brick of mineral–asphalt dust decreased with mixtures the and its changeincrease over of voids time in is the mainly samples influenced [35,38]. Asphalt by the typechanges of asphalt,its properties including over time chemical due to composition oxidation processes. In layers of asphalt pavements with a higher air void content, the oxidation of the asphalt and molecular structure. However, as indicated by Gandhi et al., even when the same type of asphalt binder is expected to be more intense. In consequence, these mixtures, despite their lower initial was applied, the change of stiffness for the aged samples was different for various aggregates and other stiffness, can stiffen faster. warm mix asphalt additives [37].

Figure 10. Average stiffness modulus values of studied mixes. Figure 10. Average stiffness modulus values of studied mixes. As expected, the stiffness of asphalt mix with the addition of brick dust decreased with the increase of voids4.3. in theStatistical samples Data [ 35Analysis,38]. Asphalt changes its properties over time due to oxidation processes. In layers ofThe asphalt one-way pavements analysis of with variance a higher (ANOVA) air void method content, was implemented the oxidation for of statistical the asphalt analysis binder of is expectedparticular to be test more group intense. results. In This consequence, parametric thesetool allows mixtures, the comparison despite their of more lower than initial two groups stiffness, can stiffenseparated faster. by the categories of one variable being an extension of the t-test used to compare two independent groups. The results of the ANOVA analysis are presented in Table 5. The p values 4.3. Statisticalindicate Data thatAnalysis the results are statistically significant in every test (p < 0.05). Moreover, to indicate the Thereplicability one-way analysis of the particular of variance tests, (ANOVA) in Table method 6 standard was deviation implemented values for for statistical each group analysis were of presented. particular test group results. This parametric tool allows the comparison of more than two groups separated by the categoriesTable of5. Analysis one variable of variance being (ANOVA) an extension analysis on of the the particulart-test tests. used to compare two independent groups. The results of the ANOVA analysis are presented in Table5. The p values indicate Test Type Origin SS df MS F p Test F that the results are statistically significant in every test (p < 0.05). Moreover, to indicate the replicability Intergroups 721 4 180 80 1.54E-07 3.478 of the particular tests,Density in Table 6 standard deviation values for each group were presented. Intragroups 23 10 2 Bulk density Intergroups 837 4 209 18 1.34E-04 3.478 Table 5. Analysis of variance (ANOVA) analysis on the particular tests.

Test Type Origin SS df MS F p Test F Intergroups 721 4 180 80 1.54 10 7 3.478 Density × − Intragroups 23 10 2 Intergroups 837 4 209 18 1.34 10 4 3.478 Bulk density × − Intragroups 114 10 11.4 Intergroups 55,728 4 13,932 8.657 0.0008 3.056 Indirect tensile strength (wet) Intragroups 24,140 15 1609 Intergroups 28,469 4 7117 6.141 0.0039 3.056 Indirect tensile strength (dry) Intragroups 17,385 15 1159 Intergroups 705,714 4 176,428 3.103 0.0333 2.759 Stiffness modulus at 23 C ◦ Intragroups 1,421,308 25 56,852 Intergroups 23,202,499 4 5,800,625 17.806 4.94 10 7 2.759 Stiffness modulus at 10 C × − ◦ Intragroups 8,144,274 25 325,771 Intergroups 10,638,660 4 2,659,665 4.344 0.0084 2.759 Stiffness modulus at 2 C − ◦ Intragroups 15,307,063 25 612,283 SS: Sum of the squared deviations; df: Degree of freedom; MS: Mean square; F: F-value; p: p-value. Test F: Test F-value. Materials 2020, 13, 5023 12 of 14

Table 6. Standard deviation values for particular groups of samples.

Standard Deviation Values Test L L-B 3:1 L-B 1:1 L-B 1:3 B Density 1.2 1.2 2.1 0.6 2.0 Bulk density 3.0 3.2 2.5 2.5 5.0 ITSw 42 60 34 18 34 ITSd 25 34 27 38 44 Stiffness at 23 ◦C 218 329 211 139 254 Stiffness at 10 ◦C 585 429 763 262 672 Stiffness at 2 C 385 1072 1258 299 306 − ◦ ITSw: Indirect tensile strength for wet samples; ITSd: Indirect tensile strength for dry samples.

5. Conclusions The paper presents the influence of brick debris dust addition on the properties of asphalt mix. The use of mixed lime-brick filler could contribute to the increase in recycling of brick debris obtained from the demolition of old buildings and structures. On the basis of the experimental work conducted, the following conclusions can be drawn: Along with the increase in the quantity of brick filler, a decrease in the bulk density was generally observed, which may be the result of irregular-shaped grains of brick, and thus reduced compaction susceptibility. Replacement of the lime filler with brick dust in the amount of 25% did not affect the volumetric properties of asphalt mix, specifically maximum density, bulk density and air void content. Further increase in the percentage of brick dust caused a decrease in bulk density and increase in maximum density as well as air voids. Both the chemical character and the mineral composition determine the strength of the bitumen-filler bond. A high proportion of silica in the brick, which has an acidic and hydrophilic chemical character, is associated with a reduction in the binding force between the filler and binder. Therefore, the addition of brick dust filler resulted in a decreased tensile strength of asphalt mix along with lower resistance to water and frost. However, the ITSR value required by technical regulations was maintained in mixtures with mixed filler containing up to 50% brick dust. The results of the stiffness modulus tests of asphalt mix suggest that the addition of brick dust will have a positive effect on the resistance to low-temperature cracking. At the same time the resistance to permanent deformation should not change if the amount of brick dust in the filler does not exceed 50%. The analysis of the examined physico-mechanical properties of asphalt mix indicates that brick debris dust can be used as a material in the mixed filler, while its percentage should not exceed 50%. Both the acidity of brick dust and its hydrophilic nature in regard to water have a negative impact on the adhesion to the asphalt, which is reflected in the properties of the mineral–asphalt mixture and, as a consequence, reduced service life of the road surface. Conversely, parameters such as homogeneous filler gradation and rough grain surface ensure good adhesion between the binder and the filler, which to some extent may compensate for the negative effect of the chemical nature of the brick filler surface on the asphalt mix properties. Application of an appropriate ratio of dust from brick debris allows the design of an asphalt mix with good performance parameters. The proposed solution fits the idea of sustainable development, indicating a means of brick debris management.

Author Contributions: Conceptualization, A.W.; Data curation, M.W. and L.B.; Formal analysis, A.W. and L.B.; Funding acquisition, A.W.; Investigation, M.W.; Methodology, A.W. and L.B.; Supervision, A.W. and W.F.; Visualization, M.W.; Writing—original draft, A.W., M.W., L.B. and W.F.; Writing—review & editing, A.W., M.W., L.B. and W.F. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the National Centre for Research and Development of Poland grant number LIDER/5/0013/L-9/17/NCBR/2018. Conﬂicts of Interest: The authors declare no conﬂict of interest. Materials 2020, 13, 5023 13 of 14

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