Mechanical Properties of Epoxy Resin Mortar with Sand ... - MDPI

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Mechanical Properties of Epoxy Resin Mortar with Sand Washing Waste as Filler Dinberu Molla Yemam, Baek-Joong Kim, Ji-Yeon Moon and Chongku Yi * School of Civil, Environmental and Architectural Engineering, Korea University, Anam-dong, Seongbuk-gu, Seoul 02841, Korea; [email protected] (D.M.Y.); [email protected] (B.-J.K.); [email protected] (J.-Y.M.) * Correspondence: [email protected]; Tel.: +82-2-3290-3329 Academic Editor: Jorge de Brito Received: 12 January 2017; Accepted: 22 February 2017; Published: 28 February 2017

Abstract: The objective of this study was to investigate the potential use of sand washing waste as filler for epoxy resin mortar. The mechanical properties of four series of mortars containing epoxy binder at 10, 15, 20, and 25 wt. % mixed with sand blended with sand washing waste filler in the range of 0–20 wt. % were examined. The compressive and flexural strength increased with the increase in epoxy and filler content; however, above epoxy 20 wt. %, slight change was seen in strength due to increase in epoxy and filler content. Modulus of elasticity also linearly increased with the increase in filler content, but the use of epoxy content beyond 20 wt. % decreased the modulus of elasticity of the mortar. For epoxy content at 10 wt. %, poor bond strength lower than 0.8 MPa was observed, and adding filler at 20 wt. % adversely affected the bond strength, in contrast to the mortars containing epoxy at 15, 20, 25 wt. %. The results indicate that the sand washing waste can be used as potential filler for epoxy resin mortar to obtain better mechanical properties by adding the optimum level of sand washing waste filler. Keywords: epoxy resin mortar; polymer binder; filler; mechanical properties

1. Introduction Concrete structures were assumed to be durable and maintenance free; however, in the past few decades, sign of degradation are becoming apparent [1,2] for various reasons, such as environmental loads, faulty material, construction, and design errors which have caused the deterioration of the structures [3–5]. The current practice of the construction industry is inclined towards the repair and retrofit of these deteriorated structures rather than demolition [1,6]. In the United States alone, a significant amount of money is expended in the repair of concrete structures every year [7]. Various materials from conventional Portland cement to polymer binders have been used to perform the repair of concrete structures. Ordinary Portland cement (OPC) is by far the most widely consumed material for the repair and restoration of concrete structures. Despite their vast consumption, OPC-based composites present different shortcomings, such as longer curing time, weak flexural strength, poor bond strength, high shrinkage, low resistance to aggressive environment, and durability problems. These problems of OPC have instigated the use of polymer-based materials as a repair material, which resulted in the introduction of epoxy resin mortar in the repair industry [8]. Epoxy resin mortar has been used as a repair material for the past couple of decades [1,9–12]; however, their consumption did not grow as anticipated due to the high cost of the epoxy resin and the different properties of the epoxy binder and the substrate concrete which caused compatibility problems [11,13,14]. The properties of the epoxy resin mortar depend on the constituents of the mortar. Hence, it is necessary to optimize the mix proportion of the epoxy resin mortar for feasible repair scheme and to avoid or reduce a mismatch in the properties of the repair mortar and the substrate

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concrete [15–19]. Different studies used fillers such as fly ash to reduce the epoxy resin dosage and Materials 2017, 10, 246 2 of 11 make it more economical [20–23]. The recycling industrial wastes sand washing wastethe is epoxy important for sustainable concrete [15–19].ofDifferent studies used such fillersas such as fly ash to reduce resin dosage and development in the construction make it more economical [20–23].industry. Sand washing waste is a waste product of the sand production and a landfill problem. The potential reuse of sand washing waste as a Theprocess, recycling of creates industrial wastes such as sand washing waste is important for sustainable development in the for construction industry.for Sand washing is a waste product the sand supplementary material sand is beneficial reducing thewaste depletion of natural sandof[24,25]. Hence, production andutilized creates ainlandfill problem. Thefor potential sand washing waste as a a sand washing process, waste was this study as filler epoxy reuse resin of mortar. Experimental study of supplementary material for sand is beneficial for reducing the depletion of natural sand [24,25]. the effect of the filler on the mechanical properties of epoxy resin mortar was performed. Hence, a sand washing waste was utilized in this study as filler for epoxy resin mortar. Experimental

study of the effect of the filler on the mechanical properties of epoxy resin mortar was performed. 2. Experiment

In this study, a mortar was prepared by using epoxy resin, sand, and filler; the mechanical 2. Experiment propertiesInofthis thestudy, mortars with different mix proportions were investigated. a mortar was prepared by using epoxy resin, sand, and filler; the mechanical properties of the mortars with different mix proportions were investigated.

2.1. Materials

2.1.two-part Materials epoxy having a Grade 1 viscosity as per ASTM C881 [26] was used as a binder for A manufacturing the mortars in thisa study. 1 shows the detailed of the A two-part epoxy having Grade Table 1 viscosity as per ASTM C881properties [26] was used as aepoxy binderresin for and manufacturing the mortars in this study. Table 1 shows the detailed properties of the epoxy resin its hardener. and its hardener. Table 1. Properties of epoxy resin and its hardener. Table 1. Properties of epoxy resin and its hardener.

Type Type Mixing Mixingproportion proportion Specific Specificgravity gravity Color Color Viscosity (mPa·s) Viscosity (mPa·s) Pot life (min) Pot lifetime (min) Hardening (h) Hardening time (h)

Epoxy Resin Hardener Epoxy Resin Hardener 3 3 1 1 1.141.14 ± 0.1 1.02 ± 0.1 ± 0.1 1.02 ± 0.1 Colorless Brown Colorless Brown 550 ± 50 550 ± 50 30 ± 10 at 23 ◦ C 30 ± 10 23 at ◦23 24–36 at C °C 24–36 at 23 °C

SandSand usedused in this study waswas purchased from a local store. The physical in this study purchased from a local store. The physicalproperties propertiesof ofthe thesand sand were were characterized according to ASTM C128and [27]ASTM and ASTM sand was foundtotohave have aa bulk characterized according to ASTM C128 [27] C29 C29 [28];[28]; thethe sand was found 3 , water bulk of 1.52 g/cm3,absorption water absorption of 0.41%, a specific gravity at oven conditionofof2.6, 2.6,and a density ofdensity 1.52 g/cm of 0.41%, a specific gravity at oven drydry condition and a void fraction of 41.28%. Since the epoxy resin mortar was also prepared to repair cracks with void fraction of 41.28%. Since the epoxy resin mortar was also prepared to repair cracks with small small widths, a fine-graded sand with high percentage of particle size less than 600 µm was used. widths, a fine-graded sand with high percentage of particle size less than 600 µm was used. In order to In order to accurately determine the particle size of the sand, a consistent method to that of sand accurately determine the particle size of the sand, a consistent method to that of sand washing waste washing waste (laser diffraction technique) was utilized, and Figure 1 presents the particle (lasersize diffraction technique) was utilized, and Figure 1 presents the particle size distribution. distribution.

Figure 1. Particle size distribution of sand.

Figure 1. Particle size distribution of sand.

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The filler used in this investigation was a sand washing waste that was collected from an The investigation was a sand wastematerial collected The filler used inplant this located investigation was washing waste that waswas collected an aggregates producing in Gyeonggi-do, Korea; the sludge a wastefrom product aggregates producing plant located in Gyeonggi-do, Korea; the sludge material was a waste product of producingprocess. plant located in Gyeonggi-do, Korea; the sludge was a waste product of a sand washing The collected sludge was dried at 110 material °C to remove any moisture, ◦ acrushed sand washing process. The collected sludge was dried atdried 110 C remove moisture, crushed to of a sand The was at to110 °C toany remove any moisture, towashing break offprocess. clusters, andcollected sieved tosludge remove any clusters. The sand washing waste used as break off clusters, and sieved to remove any clusters. The sand washing waste used as filler (Figure 2) 3 crushed to break off clusters, and sieved to remove any clusters. The sand washing waste used as filler (Figure 2) had a bulk density of 1.03 g/cm and specific gravity at oven dry condition of 3 and specific gravity 3 had a bulk density of 1.03 g/cm at oven dry condition of 2.69 according to ASTM filler (Figure 2) tohad a bulk of 1.03 g/cm and specific gravity size at oven dry condition of 2.69 according ASTM C29density and ASTM D854 [29]. The filler particle distribution was also C29 and ASTM D854 [29]. The filler particle size distribution was also determined by using LA-950 2.69 according to ASTM C29 and ASTM D854 [29]. The filler particle size distribution was also determined by using LA-950 laser scattering particle size analyzer manufactured by Horiba, Japan, laser scattering particle manufactured Horiba, Japan, as presentedby in Horiba, Figure 3.Japan, determined by laser scattering particlebysize analyzer manufactured as presented in using FigureLA-950 3.size analyzer as presented in Figure 3.

Figure 2. Sand washing waste used as filler for epoxy resin mortar in this study. Figure 2. Sand washing waste used as filler for epoxy resin mortar in this study. Figure 2. Sand washing waste used as filler for epoxy resin mortar in this study.

Figure 3. Particle size distribution of filler. Figure 3. Particle size distribution of filler. Figure 3. Particle size distribution of filler.

Based on the particle size distribution of the sand and the filler, the specific surface area and the on the particle size of the sand and the specific area and meanBased size were calculated. Thedistribution specific surface area of sand andfiller, fillerthe were foundsurface to be 1965.57 m2the /m3 Based on the particle size distribution of the sand and the filler, the specific surface area and the3 2 2/m3, and The mean size were m calculated. specific surface area ofµm sand and filler were to becomposition 1965.57 m /m and 140,625.65 the mean size was 450.83 and 21.12 µm. Thefound chemical of3 2 /m mean size were calculated. The specific surface area of sand and filler were found to be 1965.57 m 2/m3, and the mean size was 450.83 µm and 21.12 µm. The chemical composition of and 140,625.65 m the filler and the 2sand3 examined using X-ray Fluorescence manufactured by Horiba, Japan is given andfiller 140,625.65 m sand /m ,examined and the mean size wasFluorescence 450.83 µm and 21.12 µm. The chemical composition of the and the using X-ray manufactured Horiba, Japan given in Table 2. The filler showed a comparable chemical composition as that by of fly ash used asisfiller to the filler and the sand examined using X-ray Fluorescence manufactured by Horiba, Japan is given in in Table polymer 2. The filler showed a comparable chemical composition as that of fly ash used content. as filler to prepare concrete in previous studies [22], and the sand has a majority of silica In Table 2. The filler showed ain comparable chemical[22], composition as that ofafly ash used as fillercontent. to prepare prepare concrete previous studies and the using sand has majority silica In addition,polymer the X-ray diffraction (XRD) spectra was recorded a D/MAX 2200 of VPC manufactured polymer concrete in previous studies [22], and the sand has a majority of silica content. In addition, addition, spectra was recorded using a D/MAX VPC manufactured by Sciencethe ofX-ray Japandiffraction Inc. with a(XRD) continuous scanning speed of 2°/min across 2200 a 2θ range of 5°–80° and theScience X-ray diffraction (XRD) spectra was recorded using a D/MAX 2200across VPC manufactured by Science by of Japan Inc. with a continuous scanning speed of 2°/min a 2θ range of 5°–80° and a Cu/Kα1 target (λ = 1.54059 Å), U = 40 kV, and I = 200 mA. The XRD data is shown in◦Figure 4, which ◦ /min ◦ –80 of Japan Inc. with a continuous scanning speed of 2 across a 2θ range of 5 and a 4, Cu/Kα 1 aidentifies Cu/Kα1 target (λ = 1.54059 Å), U = 40 kV, and I = 200 mA. The XRD data is shown in Figure which the main crystalline phases in the filler as being quartz, albite, and muscovite. target (λ = 1.54059 Å), U = 40 kV, and I = 200 mA. The XRD data is shown in Figure 4, which identifies identifies the main crystalline phases in the filler as being quartz, albite, and muscovite. the main crystalline phases in the filler as being quartz, albite, and muscovite.

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Table 2. Chemical composition of sand and filler (wt. %). Table 2. Chemical composition of sand and filler (wt. %).

Chemical Composition SiO2 Al2 O3 K2 O Chemical Composition SiO2 Al2O3 K2O Sand 87.720 5.915 6.277 Sand 87.720 5.915 6.277 Filler 70.993 18.070 1.792 Filler 70.993 18.070 1.792

Fe2 O3 Fe2O3 6.450 6.450

TiO2 TiO2 0.805 0.805

MnO2 MnO2 0.282 0.282

CaO CaO 1.607 1.607

Figure 4. XRD spectra of filler.

Figure 4. XRD spectra of filler.

2.2. Mix Proportions

2.2. Mix Proportions

Four mortar groups were prepared with epoxy content at 10%, 15%, 20%, and 25% by weight

Four mortar prepared epoxy with epoxy at % 10%, 20%,from and workability 25% by weight fraction of thegroups mortar. were The minimum contentcontent of 10 wt. was15%, selected condition, the maximum content was limited to 25 of wt.10 % due of the epoxy from fraction of theand mortar. The minimum epoxy content wt. to%segregation was selected from workability the mortar mixture. Filler was added to the mortar mix at 10 and 20 wt. % as sand replacement. condition, and the maximum content was limited to 25 wt. % due to segregation of the epoxy from The detailed mix proportion the samples in this study presented in Table the mortar mixture. Filler wasofadded to theinvestigated mortar mix at 10 andis20 wt. % as sand 3.replacement. The detailed mix proportion of the samples investigated in this study is presented in Table 3. Table 3. Mix proportion by weight percent (wt. %) and specimen notation.

* Epoxy by (E) weight Sand percent (S) Sand Washing Fillernotation. (F) TableSpecimen 3. Mix proportion (wt. %) andWaste specimen E10-F0 10.00 E10-F10 10.00 Specimen * Epoxy (E) E10-F20 10.00 E10-F0 10.00 E15-F0 15.00 E10-F10 10.00 E15-F10 15.00 E10-F20 10.00 E15-F20 15.00 E15-F0 15.00 E20-F0 20.00 E15-F10 15.00 E20-F10 20.00 E15-F20 15.00 E20-F20 20.00 E20-F0 20.00 E25-F0 25.00 E20-F10 20.00 E25-F10 25.00 E20-F20 20.00 E25-F20 25.00

90.00 80.00 Sand (S) 70.00 90.00 85.00 80.00 75.00 70.00 65.00 85.00 80.00 75.00 70.00 65.00 60.00 80.00 75.00 70.00 65.00 60.00 55.00

0.00 10.00 Sand Washing Waste Filler (F) 20.00 0.000.00 10.00 10.00 20.00 20.00 0.000.00 10.00 10.00 20.00 20.00 0.000.00 10.00 10.00 20.00 20.00

E25-F0 includes25.00 0.00 * Specimen notation two parts. The75.00 first part is used to identify the epoxy/mortar ratio by 10.00 weight, andE25-F10 the other is used25.00 to identify the65.00 filler/mortar ratio by weight. For example, E20-F10 is a E25-F20 25.00 55.00 specimen having epoxy/mortar = 20% and filler/(sand + filler) = 10%. 20.00 * Specimen notation includes two parts. The first part is used to identify the epoxy/mortar ratio by weight, and the other is used to identify the filler/mortar ratio by weight. For example, E20-F10 is a specimen having epoxy/mortar = 20% and filler/(sand + filler) = 10%.

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Specimens were prepared to study the effect of filler on the compressive strength, flexural strength 2.3. Test of Method and modulus elasticity, and bond strength of epoxy resin mortar. The sample preparation was performed as follows. Except for control specimens, dry mixing of sand andstrength, filler was Specimens prepared to study the effectfirst of filler on the compressive flexural Materials 2017, 10, 246were 5 ofperformed 11 strength of elasticity, bondtostrength resin distribution mortar. The sample preparation for 2 min usingand anmodulus automatic mortarand mixer ensureofaepoxy uniform of the sand and filler. Method wasTest performed as follows. Except for control specimens, firstin dry mixing ofbowl sand and Epoxy 2.3. resin and its hardener were manually mixed for 1 min a separate and filler werewas added to performed for 2 min using an automatic mortar mixer to ensure a uniform distribution of the sand Specimens were prepared to study the effect of filler on the compressive strength, flexural the mortar mixer. Mixing was continued for another 2 min, and the mortar mixture was casted as per and filler. Epoxy resinofand its hardener werestrength manually mixedresin for 1mortar. min in aThe separate and were strength and modulus elasticity, andperformed bond of epoxy samplebowl preparation KS F 4043 [30].to Before de-molding was after 24 h, the molded specimens were stored added the mortar mixer. Mixing was continued for another 2 min, and the mortar mixture was in a was performed as follows. Except for ◦control specimens, first dry mixing of sand and filler was controlled environmental chamber at 23 C and 50% RH, and continued curing of the specimen in the casted as per F 4043 Before de-molding was to performed after 24 h, the molded specimens performed for KS 2 min using[30]. an automatic mortar mixer ensure a uniform distribution of the sand same condition was for 6 more days. were stored in performed aresin controlled chamber 23 °Cfor and 50%in RH, and continued curing and filler. Epoxy and itsenvironmental hardener were manuallyatmixed 1 min a separate bowl and wereof the specimen in the same condition was performed for 6 more days. The compressive test of the epoxy resin mortar was conducted according to KS F 4043/EN added to the mortar mixer. Mixing was continued for another 2 min, and the mortar mixture was The compressive test of the epoxy resin mortar was conducted according to KS F 4043/EN 12190 12190 [31]. Three strength samples with dimensions 40 h, mm 40 mmspecimens × 160[31]. mm were casted as percompressive KS F 4043 [30]. Before de-molding wasthe performed after 24 the× molded Three compressive strength samples with the dimensions 40 mm × 40 mm × 160 mm were prepared. wereFirst, storedthe in asample controlled environmental at 23 °C and RH, and continued of flexure prepared. that was curedchamber for seven days was50% broken into halves curing through First, the sample that wascondition cured forwas seven days was into halves through flexure and then the the specimen in the same performed forbroken 6 more days. and then the compressive strength test was performed on the broken halvesusing of thea universal samples using compressive strength was performed on the halves of the to samples The compressive testtest of the epoxy resin mortar wasbroken conducted according KS F 4043/EN 12190 [31]. a universal testing machine (UTM) at arate loading of(Figure 800 N/min testing machine (UTM) at a loading of 800 rate N/min 5A). (Figure 5A). Three compressive strength samples with the dimensions 40 mm × 40 mm × 160 mm were prepared. First, the sample that was cured for seven days was broken into halves through flexure and then the compressive strength test was performed on the broken halves of the samples using a universal testing machine (UTM) at a loading rate of 800 N/min (Figure 5A).

Figure 5. (A) Compressive strength and (B) Flexural strength and modulus of elasticity through

Figure three-point 5. (A) Compressive strength and (B) Flexural strength and modulus of elasticity through bending tests. three-point bending tests. The flexural strength and modulus of Flexural elasticity of three resin mortarsthrough of each mix Figure 5. (A) Compressive strength and (B) strength andepoxy modulus of elasticity proportion were evaluated in accordance to ASTM C580 [32]. Continuous measurements the proportion load tests. three-point bending The flexural strength and modulus of elasticity of three epoxy resin mortars of eachofmix applied and the corresponding deflection that occurred at the mid span were recorded. The maximum were evaluated in accordance to ASTM C580 [32]. Continuous measurements of the load applied loadThe wasflexural used to determine the modulus flexural strength, and the modulus determined from the strength and of elasticity of tangent three epoxy resinwas mortars of each mix and the corresponding deflection that occurred at the mid span were recorded. The maximum load load versus deflection curve. KS F 4043topull-off test method was adopted to measure theload bond proportion were evaluated in accordance ASTM C580 [32]. Continuous measurements of the was used to determine the resin flexural strength, the tangent modulus determined from the load strength of the the corresponding epoxy mortar to ordinary Portland cement concrete. Three specimens of each applied and deflection thatand occurred at the mid span werewas recorded. The maximum versus load deflection curve. KS F 4043 pull-off test method was adopted to measure the bond strength of mix was proportion tested consisted of a concrete of dimensions 100 mm diameter and 70 mm thickness used to determine the flexural strength, and the tangent modulus was determined from the load versus deflection curve. KS F 4043 pull-off test method was adopted to measure the bond as substrate, with 28-day compressive strength of 50 MPa (Figure 6A). The procedure shown in the epoxy resin mortar to ordinary Portland cement concrete. Three specimens of each mix proportion strength thea epoxy resinofmortar to ordinary Portland cement concrete. Three specimens of each Figure 5of was used to prepare the specimens and perform the test. tested consisted of concrete dimensions 100 mm diameter and 70 mm thickness as substrate, with mix proportion tested consisted of a concrete of dimensions 100 mm diameter and 70 mm thickness 28-day compressive strength of 50 MPa (Figure 6A). The procedure shown in Figure 5 was used to as substrate, with 28-day compressive strength of 50 MPa (Figure 6A). The procedure shown in prepareFigure the specimens and perform the test. 5 was used to prepare the specimens and perform the test.

(A) Concrete substrate preparation

(B) Casting of epoxy resin mortar on surface of the substrate

Figure 6. Cont. (A) Concrete substrate preparation

(B) Casting of epoxy resin mortar on surface of the substrate

Figure 6. Cont.

Figure 6. Cont.


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(C) Steel stud was attached on top surface of the epoxy resin

(C) Steel stud was attached on top surface of the epoxy resin (D) Pull-off test set up using universal testing machine mortar using adhesive (D) Pull-off test set up using universal testing machine mortar using adhesive Figure 6. Pull-off test method.

Figure 6. 6. Pull-off test method. Figure Pull-off test method.

3. Results and Discussion

Resultsand andDiscussion Discussion 3.3.Results

3.1. Compressive Strength

3.1. Strength 3.1.Compressive Compressive Strength Figure 7 presents the compressive strength versus filler content results obtained from mortars prepared with three different filler weight fractions at four various epoxy contents. The results

Figure 7 7presents the compressive strength versus filler content results obtained from mortars Figure presents the compressive versus filler content results obtained illustrate that the compressive strengthstrength of the mortar was affected by both its epoxy and from filler mortars prepared with three different filler weight fractions at four various epoxy contents. The prepared with three different filler weight fractions at four various epoxy contents. results content. For mortars prepared with epoxy at 10 wt. %, the compressive strength increased upThe to results illustrate that the compressive strength of the mortar was affected by both its epoxy and filler content. 10 wt. % of filler content then leveled off between 10 wt. % and 20 wt. %, while for mortars prepared illustrate that the compressive strength of the mortar was affected by both its epoxy and filler with epoxy at 15,with 20, and 25 wt. the strength up increased to 20strength wt. %up butincreased a % For mortars prepared epoxy at %, 10epoxy wt.compressive %,at the10compressive strength towith 10 wt. content. For mortars prepared with wt. %, theincreased compressive upofto decreasing rate of increase between filler content of 10 wt. % and 20 wt. %. The mortars showed an filler content between % and 10 20 wt. % %,and while withprepared epoxy 10 wt. % of then filler leveled contentoff then leveled10offwt. between 20 for wt.mortars %, whileprepared for mortars average improvement in compressive strength of 24.46% for epoxy at 10 wt. %, 65.15% for epoxy at atwith 15, 20, and at 2515, wt.20, %,and the 25 compressive increased up increased to 20 wt. % with decreasing epoxy wt. %, the strength compressive strength upbut to 20 wt.a% but with a 15 wt. %, 15.28% for epoxy at 20 wt. %, and 8.60% for epoxy at 25 wt. % due to incorporation of filler rate of increase between filler content of 10 wt. % and 20 wt. %. The mortars showed an averagean decreasing rate of increase between filler content of 10 wt. % and 20 wt. %. The mortars showed when compared to the control group. The increase in epoxy content also enhanced the compressive improvement in compressive strength of 24.46% for epoxy at 10 wt. %, 65.15% for epoxy at 15 wt. %,at average improvement in compressive strength of 24.46% for epoxy at 10 wt. %, 65.15% for strength of the mortar composite, but the rate of increase diminished at epoxy content of 20 wt. % epoxy 15.28% for epoxy at 20 wt. %, and 8.60% for epoxy at 25 wt. % due to incorporation of filler 25 wt. %. canatbe to the decrease in the at void content of the sand with the when 15 wt.and %, 15.28% forThese epoxy 20attributed wt. %, and 8.60% for epoxy 25 wt. % due to incorporation of filler incorporation of the filler in addition to the epoxy binder [22]. Furthermore, it can be noticed thatstrength compared to the control increase epoxy content enhanced the compressive when compared to thegroup. controlThe group. The in increase in epoxyalso content also enhanced the compressive except composite, for the control group, the increase of epoxy content beyond 15 wt. % appears enhance ofstrength the mortar the rate of epoxy content of 20towt. % andthe of the mortar but composite, butincrease the ratediminished of increaseatdiminished at epoxy content of2520wt. wt.%.% compressive strength of the mortar insignificantly. These be attributed in the voiddecrease content of the incorporation of the and can 25 wt. %. These to canthe bedecrease attributed to the in the the sand voidwith content of the sand with the filler in additionoftothe thefiller epoxy [22]. it can be noticed that except control incorporation in binder addition to Furthermore, the epoxy binder [22]. Furthermore, it canfor be the noticed that group, of epoxy content beyondof 15epoxy wt. % content appearsbeyond to enhance the % compressive exceptthe forincrease the control group, the increase 15 wt. appears to strength enhance of the the mortar insignificantly. compressive strength of the mortar insignificantly.

Figure 7. Relationship of compressive strength vs. filler content at different amount of epoxy (10 wt. %, 15 wt. %, 20 wt. %, and 25 wt. %).

Figure 7. Relationship of compressive strength vs. filler content at different amount of epoxy (10 wt. %, Figure 7. Relationship of compressive strength vs. filler content at different amount of epoxy (10 wt. %, 15 wt. %, 20 wt. %, and 25 wt. %). 15 wt. %, 20 wt. %, and 25 wt. %).


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Thecompressive compressivestrength strengthisisaatraditionally traditionallyexamined examinedproperty propertyof ofrepair repairmaterial materialfor forconcrete concrete The structures.Mostly Mostlyititisisexpected expected that ratio compressive strength of repair mortar to that structures. that thethe ratio of of thethe compressive strength of repair mortar to that of theof the substrate concrete should be equal to or higher than one. Furthermore, KS F 4043 suggests substrate concrete should be equal to or higher than one. Furthermore, KS F 4043 suggests a minimuma minimum compressive 40 MPa epoxyused resin for structures. repair of concrete compressive strength of 40strength MPa forof epoxy resinfor mortars formortars repair ofused concrete All the structures. All E10-F0 the samples except E10-F0 showed a compressive strength above 40 MPa. samples except showed a compressive strength above 40 MPa. 3.2. 3.2.Flexural FlexuralStrength Strength The Theflexural flexuralstrength strengthofofmortar mortarmixes mixesprepared preparedwith withvarying varyingfiller fillercontent contentatatgiven givenamount amountofof epoxy Figure 8. 8. The flexural strength of the mortar altered withwith respect to thetofiller and epoxyisispresented presentedinin Figure The flexural strength of the mortar altered respect the filler epoxy content. EvenEven though the rate of increase slightly decreased between 1010 wt. and epoxy content. though the rate of increase slightly decreased between wt.%%and and20 20wt. wt.%, %, aamore linear increase in flexural strength with R2 value of 0.942 and 0.957 was observed for mortar more linear increase in flexural strength with R2 value of 0.942 and 0.957 was observed for mortar containing containingepoxy epoxyatat10 10wt. wt.%%and and15 15wt. wt.%. %.For Formortars mortarsprepared preparedwith withepoxy epoxyatat20 20wt. wt.%%and and25 25wt. wt.%, %, the increased linearly linearlyup uptoto2020wt. wt.%%ofoffiller filler content with values of 0.995 theflexural flexural strength strength increased content with thethe R2 R2 values of 0.995 and and 0.999, respectively. mortars showed averagerise riseininflexural flexuralstrength strength of of 44.6% for 0.999, respectively. TheThe mortars showed anan average for epoxy epoxyatat 10 10wt. wt.%, %,65.78% 65.78%for forepoxy epoxyatat15 15wt. wt.%, %,17.61% 17.61%for forepoxy epoxyatat20 20wt. wt.%, %,and and19.51% 19.51%for forepoxy epoxyatat25 25wt. wt.% % due duetotoincorporation incorporationofoffiller fillerwhen whencompared comparedtotothe thecontrol controlgroup. group.The Theflexural flexuralstrength strengthofofthe themortar mortar seems seemstotobe beslightly slightlybeyond beyond15 15wt. wt.%%ofofepoxy epoxycontent. content.In Ingeneral, general,ititcan canbe beconcluded concludedthat thataalinearly linearly proportional proportionalrelationship relationshipwas wasexhibited exhibitedbetween betweenflexural flexuralstrength strengthand andthe thefiller fillercontent contentup uptoto20 20wt. wt.% % ofofthe epoxy resin mortar. the epoxy resin mortar.

Figure 8. Relationship of flexural strength vs. filler content at different amounts of epoxy (10, 15, 20, Figure 8. Relationship of flexural strength vs. filler content at different amounts of epoxy (10, 15, 20, and 25 wt. %). and 25 wt. %).

The strength of repair materials to withstand a bending load is stated as flexural strength. The strength ofofrepair materials to withstand a bending loadthe is substrate stated as concrete flexural should strength. Generally, the ratio the flexural strength of the repair mortar and be Generally, the ratio of the flexural strength of the repair mortar and the substrate concrete should higher than one, whereas KS F 4043 specifies 10 MPa as the minimum flexural strength value for be higher thanmortars one, whereas KS Frestoration 4043 specifies 10 MPa as the minimum flexural value for epoxy resin used for of concrete structures. In our study,strength all mortar mixes epoxy resinexhibited mortars used for restoration of concrete structures. In our study, all mortar mixes prepared prepared a flexural strength much higher than 10 MPa. exhibited a flexural strength much higher than 10 MPa. 3.3. Modulus of Elasticity (MoE) 3.3. Modulus of Elasticity (MoE) The tangent modulus of elasticity of the epoxy resin mortars was determined from the load The tangent modulus of elasticity of the epoxy resin mortars was determined from the load versus versus deflection relation obtained via three-point bending test. Figure 9 shows the influence of filler deflection relation obtained via three-point bending test. Figure 9 shows the influence of filler content content on the MoE of the mortars prepared with different epoxy content (10 wt. %, 15 wt. %, 20 wt. %, on the MoE of the mortars prepared with different epoxy content (10 wt. %, 15 wt. %, 20 wt. %, and and 25 wt. %). It can be noticed that a linear trend was observed as that of flexural strength results 25 wt. %). It can be noticed that a linear trend was observed as that of flexural strength results between between MoE and filler content with R2 value of 0.998, 0.999, 0.966, and 0.999 for epoxy content at 10, 15, 20, and 25 wt. %, respectively. The addition of filler resulted in an average increase in MoE of

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MoE and filler content with R2 value of 0.998, 0.999, 0.966, and 0.999 for epoxy content at 10, 15, 20, 51.5% at 10atwt. %, 54.47% for epoxy at resulted 15 wt. %,%,11.10% for epoxy atat20 %, and 7.29% and 51.5% 25for wt.epoxy %, epoxy respectively. ofepoxy filler an average increase in wt. MoE 51.5% for for 10 wt.The %, addition 54.47% for at 15 wt. in 11.10% for epoxy 20 wt. %,ofand 7.29% for epoxy at 25 wt. % when compared to the control group. Besides the substantial improvement in epoxy 10 wt.at%, for epoxy at 15 wt. %,control 11.10%group. for epoxy at 20the wt.substantial %, and 7.29% for epoxyin at foratepoxy 25 54.47% wt. % when compared to the Besides improvement the MoE of mortar containing epoxy at 10 wt.wt. % Besides and 1515 wt. MoE with 25 wt. when compared to the control the substantial improvement MoE of the%MoE of mortar containing epoxy atgroup. 10 % and wt.%, %,a ahigher higherrate rateof ofincrease increaseinin inthe MoE with the increase in filler content was observed compared containing at wt. % % mortar at 10 wt. %observed and 15when wt. %, acompared higher to rate of increase in MoEepoxy with the increase the containing increase in epoxy filler content was when tomortars mortars containing epoxy at 20 20 wt. and 25 wt. %. The increase in MoE can be attributed to the increased stiffness of the mortar when the andcontent 25 wt. %. Theobserved increase in MoEcompared can be attributed to the increasedepoxy stiffness in filler was when to mortars containing at of 20the wt.mortar % andwhen 25 wt.the %. filler is added. filler is added. The increase in MoE can be attributed to the increased stiffness of the mortar when the filler is added.

Figure 9. Effect of filler content on the modulus of elasticity of epoxy resin mortars at different Figure 9. ofoffiller content onon thethe modulus of elasticity of epoxy resin mortars at different amount Figure 9. Effect Effect filler content of elasticity of epoxy resin mortars at different amount of epoxy (10, 15, 20, and 25 wt.modulus %). of epoxy (10, 15, 20, and 25 wt. %). amount of epoxy (10, 15, 20, and 25 wt. %).

The density of the epoxy resin mortar three-point bending test beams were determined by The density ofmass the epoxy epoxy resin mortar mortar three-point bending test beams beams were determined by The density the resin bending test were by measuring theof and volume in orderthree-point to understand the relation between thedetermined MoE and the measuring mass and order to understand the relation theand MoE and theand density measuring the mass andvolume volume in order to understand the relation between the MoE the densitythe of the hardened beam in samples. Figure 10 indicates a plot ofbetween the density MoE versus filler of the hardened beam samples. Figure 10 indicates a plotThe ofathe density andsamples MoE versus filler content for the mortars with different epoxy density of density the showed a content similar density of the hardened beam samples. Figure 10content. indicates plot of the and MoE versus filler trend increase in filler content as that of theThe MoE. Thesamples results show thataasimilar linear correlation for the mortars with different epoxy content. The density ofdensity the showed trend with content forwith the the mortars with different epoxy content. of the samples showed a similar 2 value of 0.919 exists between the MoE and the density of the samples. 2 with R the increase in filler content as that of theasMoE. results that a linear with R value trend with the increase in filler content that The of the MoE.show The results showcorrelation that a linear correlation of 0.919 existsof between the MoE and the of the the density samples.of the samples. with R2 value 0.919 exists between the density MoE and

Figure 10. Relationship between modulus of elasticity (MoE) and density of sample.

Figure Figure 10. 10. Relationship Relationshipbetween between modulus modulus of of elasticity elasticity (MoE) (MoE) and and density density of of sample. sample.


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3.4. 3.4.Bond BondStrength Strength The bond strength ofof epoxy resin mortar toto substrate concrete was determined using a pull-off The bond strength epoxy resin mortar substrate concrete was determined using a pull-off test. test.AAhigh highstrength strengthconcrete concretewith witha a28-days 28-dayscompressive compressivestrength strengthofof5050MPa MPawas wasprepared preparedasasa a substrate execute test. modes substratetoto executethis this test.Depending Dependingononwhich whichsection sectionisisthe theweakest, weakest,one oneofofthe thethree three modesofof failures (de-bonding) (failure inin the epoxy mortar, failure atat the interface ofof epoxy resin mortar failures (de-bonding) (failure the epoxyresin resin mortar, failure the interface epoxy resin mortar and substrate concrete, and failure in the concrete substrate) could occur when the pull-off test on theon and substrate concrete, and failure in the concrete substrate) could occur when the pull-off test epoxy resin mortar-bonded concrete is performed. the epoxy resin mortar-bonded concrete is performed. Figure 1111 indicates the pull-off test results ofof concrete bonded with epoxy resin mortar containing Figure indicates the pull-off test results concrete bonded with epoxy resin mortar containing varying weight fractions of filler at four different epoxy amounts. For epoxy at 10 wt. %, varying weight fractions of filler at four different epoxy amounts. For epoxy at 10 wt. %,allallthe the failures occurred at at the mortar/substrate failures occurred the mortar/substrateconcrete concreteinterface, interface,and andthe thebond bondstrength strengthseemed seemedtotoslightly slightly increase with the addition ofof 1010 wt. the bond strength considerably dropped atat 2020 wt. increase with the addition wt.%;%;however, however, the bond strength considerably dropped wt.%% ofoffiller content bond between mortar and concrete filler contenttotothe theextent extentthat thatfailure failureofofthe the bond betweenthe theepoxy epoxyresin resin mortar and concrete occurred byby anan insignificant load application. E10-F20 specified asas occurred insignificant load application.Hence, Hence,the thebond bondstrength strengthofof E10-F20was was specified zero. The mortars prepared with epoxy at 15 wt. % showed two modes of failure: all the samples zero. The mortars prepared with epoxy at 15 wt. % showed two modes of failure: all the samples except those containing filler atat 2020 wt. %% exhibited a afailure inin the ofofepoxy mortar and except those containing filler wt. exhibited failure theinterface interface epoxyresin resin mortar and substrate concrete, whereas thethe samples prepared withwith fillerfiller at 20atwt. demonstrated a failure in thein substrate concrete, whereas samples prepared 20 % wt. % demonstrated a failure substrate concrete. The bond strength of the of mortar at 15 wt. % showed a lineara increase with filler the substrate concrete. The bond strength the mortar at 15 wt. % showed linear increase with content up to 20up wt.to%. 20 andat2520wt. %,25 allwt. the %, failure occurred the substrate filler content 20For wt.epoxy %. Foratepoxy and all the failurein occurred in theconcrete; substrate the failuresthe seems to occur in the interfacial of the zone coarse the substrate concrete; failures seems to occur in thetransition interfacialzone transition ofaggregate the coarseinaggregate in the concrete. Hence, the effect of the filler content on the adhesion property of epoxy resin concrete substrate concrete. Hence, effect of filler content on the adhesion property ofmortar epoxy to resin mortar was clearly understood, because the failure was mainly governed by the governed intrinsic property of the to not concrete was not clearly understood, because the failure was mainly by the intrinsic concrete [33,34]. property of the concrete [33,34].

Figure 11. Effect of filler content on the bond strength of epoxy resin mortar at different amounts of Figure 11. Effect of filler content on the bond strength of epoxy resin mortar at different amounts of epoxy (10, 15, 20, and 25 wt. %) to substrate concrete. epoxy (10, 15, 20, and 25 wt. %) to substrate concrete.

Bond strength of repair material is an important property that holds the repair mortar and the Bond repair material is an important property thata holds therepair repairwork mortar the substratestrength concreteofbonded as a unit. Hence, in order to have durable ofand concrete substrate concrete bonded as a unit. Hence, in order to have a durable repair work of concrete structures, the mortars used should have adequate adhesion to avoid bond failure between the structures, thethe mortars used because should have adequate adhesion to avoid failure between the repair repair and substrate of the stresses developed due bond to internal and external loads. and the substrate because of the stresses developed due to internal and external loads. KS F 4043 KS F 4043 suggests a minimum of 1.5 MPa bond strength of the epoxy resin mortar used for the suggests a minimum of 1.5 MPa bond In strength of the the epoxy resinresin mortar usedprepared for the maintenance maintenance of concrete structure. this study, epoxy mortar with 10 wt.of% concrete structure. In this the epoxy resin0.8 mortar 10samples wt. % epoxy showed epoxy showed poor bondstudy, strength lower than MPa.prepared Whereas with all the with epoxy at poor 15, 20, bond strength lower than 0.8 MPa. Whereas all the samples with epoxy at 15, 20, and 25 wt. % showed and 25 wt. % showed a bond strength higher than 1.5 MPa. a bond strength higher than 1.5 MPa.

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4. Conclusions This study investigated the effect of filler on the mechanical and adhesion properties of epoxy resin mortar. The following conclusions were drawn based on the experimental results obtained. (1)

(2)

(3) (4)

The compressive strength, flexural strength and modulus of elasticity value of epoxy mortar containing filler up to 20 wt. % improved by an average of 1.08–1.66, 1.18–1.66, and 1.07–1.54 times, respectively, at different weight fraction of epoxy in the range of 10–25 wt. % when compared to the control specimens. It was observed that when filler is used at optimum level, it can improve bond strength; all the mortars except those prepared with epoxy at 10 wt. % showed a good bond strength higher than 1.5 MPa. It can be established that sand washing waste can be used as potential filler for epoxy resin mortar to obtain better compressive, flexural, stiffness, and bond strength. This study does not cover all the parameters required to examine repair materials for concrete structures; further investigations on compatibility issues such as dimensional change stability of the epoxy resin mortar containing sand washing waste filler is required.

Acknowledgments: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2015R1D1A1A01060892). Author Contributions: Chongku Yi conceived and designed the experiments; Ji-Yeon Moon and Dinberu Molla Yemam performed the experiments; Dinberu Molla Yemam and Baek-Joong Kim analyzed the data; Dinberu Molla Yemam wrote the paper. Authorship must be limited to those who have contributed substantially to the work reported. Conflicts of Interest: The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

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