(RAS) in Portland Cement Mortar - MDPI

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Apr 19, 2016 - evaluates the effect of RAS in cement mortar when used as ... cement mortar; reclaimed asphalt shingle (RAS); cellulose fiber; toughness;.
sustainability Article

Investigation on the Effect of Recycled Asphalt Shingle (RAS) in Portland Cement Mortar Jinwoo An 1 , Boo Hyun Nam 1, * and Heejung Youn 2, * 1 2

*

Department of Civil, Environmental, and Construction Engineering, University of Central Florida, 12800 Pegasus Drive, Orlando, FL 32816, USA; [email protected] Department of Civil Engineering, School of Urban and Civil Engineering, Hongik University, 94, Wausan-ro, Mapo-gu, Seoul 04066, Korea Correspondence: [email protected] (B.H.N.); [email protected] (H.Y.); Tel.: +1-(407)-823-1361 (B.H.N.); +82-(2)-320-7691 (H.Y.)

Academic Editor: Muge Mukaddes Darwish Received: 4 March 2016; Accepted: 14 April 2016; Published: 19 April 2016

Abstract: Tear-off roofing shingle, referred to as Reclaimed asphalt shingle (RAS), is the byproduct of construction demolition and it is a major solid waste stream in the U.S. Reuse of this byproduct in road construction sector can contribute to the success of materials sustainability as well as landfill conservation. Ground RAS has similar particle distribution as sand and its major component includes aggregate granules, fibers, and asphalt. To promote the beneficial utilization of RAS, this study evaluates the effect of RAS in cement mortar when used as replacement of sand. In addition, the study investigates how cellulose fibers from RAS behave under high alkaline environment during cement hydration process, which may significantly affect mortar’s strength performance. The laboratory study includes measurements of physical, mechanical, and durability behaviors of cement mortar containing RAS replacing sand up to 30%. It was found that the optimum mixture proportions are 5% and 10% for compressive strength and toughness, respectively. Keywords: cement mortar; reclaimed asphalt shingle (RAS); cellulose fiber; toughness; crack propagation

1. Introduction US Environmental Protection Agency (EPA) reported that approximately 250 million tons of wastes were generated in the US during 2010, but only 34% (85 million tons) was either recycled or composed [1]. Roofing shingle is one of construction and demolition (C&D) debris and it is a major solid waste stream in the US. According to the USEPA, total shingle waste generated in the U.S. is approximately 11 million tons per year [2]. Beneficial utilization of byproduct and waste materials in road construction have been made and it contributes to the success of sustainability [3–14]. It consists of roughly 90% representing post-consumer scrap (or tear-off shingles) and 10% comprising post-manufacture scrap [15]. In addition, shingle waste generates up to 8% of the total building-related waste stream and more than 10% of construction and demolition debris [16]; Most of them are being disposed by landfilling, and the estimated cost is up to $60 per ton [17]. Therefore, beneficial reuse of shingle waste can lead to not only land conservation but also cost saving in waste disposal and construction materials. Tear-off roofing shingle, referred as Recycled asphalt shingle (RAS) hereafter, is a complex material. In general the RAS is composed of 40% to 70% of aggregate granules, 20% to 40% of asphalt, and 1% to 25% of fibrous base materials (which can be either cellulose or glass fibers). Figure 1 shows the processing procedure of tear-off roofing shingles from C&D debris to ground RAS that has similar size of sand.

Sustainability 2016, 8, 384; doi:10.3390/su8040384

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Figure 1. Procedure of Recycled asphalt shingle (RAS) processing.

There have been several attempts that beneficially reuse RAS in Hot-Mix Asphalt (HMA), and some of them have shown improvements to mechanical properties of HMA [18–22]. According to Nam et al., the usage of RAS is a good solution to save the virgin binder because shingles contain about 30%–40% of bitumen [20]. Another good reason to use shingle in HMA claimed by Sengoz et al. is that the usage of shingle makes easier compaction of the HMA because the HMA with shingle contains more filler (around 30% of the mass of shingle) [18]; in addition, he also mentioned the lower cracking due to the fibers in the shingle . One more important finding about RAS is that according to Yang et al. the HMA is stiffer at high temperatures than the regular HMA [22]. On the other hand, there has been almost no study on the usage of RAS (consisting of aggregate granules, asphalt, and fiber) in cement-based materials. Instead, there were several studies that evaluates the use of reclaimed asphalt pavement (RAP) in cement-based materials [23–25] and also fibrous base materials in cement-based materials (such as cement paste, mortar and concrete) [26–32]. Regarding RAP, to Mang et al. found several advantages on the usage of RAS in terms of the increment of failure strain, toughness, poison’s ratio, drying shrinkage and coefficient of thermal expansion [23]. Huang et al. concludes that the toughness of Portland cement concrete can be increased by adding RAP as replacement of aggregate [33,34]. On the other hand, however, Abdel-Mohti et al. mentions that compressive strength and flexural strength decrease as the content of RAP increases. The addition of RAP in concrete may reduce the load bearing capacity [24]. Erdem et al. also reports that concrete containing RAP aggregate may not be feasible for structural application [25]. Several researchers report that cellulose fiber provides adequate strength, toughness and the capacity of bonding to cement-based materials because the fibers function as bridge between the cement matrix cracks and transfer the stresses [26–28]. Regarding fibers, fibers might be responsible for the reduction of plastic cracking shrinkage and for some increments on mechanical properties of the cementitious mechanical properties [26]. However, the usage of cellulose fiber in cement-based composites is still limited by durability issue of cellulose fibers. The main problems of cellulose fiber are volume variation due to high water absorption capacity and degradation of cellulose fiber under high alkaline environment [29–32]. This paper investigates the beneficial utilization of RAS in cement mortar when used as replacement of fine aggregate in the mixture. The beneficial and side effects of RAS in mortar were evaluated. For the specimen preparation, the fine aggregate was replaced by RAS with different percentages of 0%, 5%, 10%, 15%, 20%, 25%, and 30%; thus, optimum proportioning (best RAS replacement ratio) was determined for mechanical performance. 2. Materials and Testing Methods 2.1. Materials Physical Properties The cement used in this study was Type I ordinary Portland cement (ASTM C150) with specific gravity of 3.15. The fine aggregate used was sand passing the sieve no. 4 (4.75 mm) with a fineness modulus of 2.36. The specific gravity and water absorption are 2.66 and 2%, respectively. Figure 2a,b shows the pictures of ground RAS and cellulose fibers extracted from RAS, respectively. Figure 2c,d shows those aggregate and fibers in larger magnifications. As seen in Figure 2, RAS has shown irregular

2.1. Materials Physical Properties  The cement used in this study was Type I ordinary Portland cement (ASTM C150) with specific  gravity of 3.15. The fine aggregate used was sand passing the sieve no. 4 (4.75 mm) with a fineness  modulus  of  2.36.  The  specific  gravity  and  water  absorption  are  2.66  and  2%,  respectively.  Figure  Sustainability 2016, 8, 384 3 of 16 2a,b shows the pictures of ground RAS and cellulose fibers extracted from RAS, respectively. Figure  2c,d shows those aggregate and fibers in larger magnifications. As seen in Figure 2, RAS has shown  shape, rough surface texture and highly angular particles [34]. Inparticles  general the RAS composed 40% irregular  shape,  rough  surface  texture  and  highly  angular  [34].  In  is general  the  by RAS  is  to 70% of aggregate granules, 20% to 40% of asphalt, and 1% to 25% of fibrous base materials (which composed by 40% to 70% of aggregate granules, 20% to 40% of asphalt, and 1% to 25% of fibrous  can be either cellulose or glass fibers) [18,19]. base materials (which can be either cellulose or glass fibers) [18,19]. 

(a) 

(b)

(c) 

(d)

Figure 2.2. Pictures Pictures  ground  cellulose  fiber  RAS  with  different  magnifications:  (a)  Figure of of  ground RASRAS  and and  cellulose fiber in RASin with different magnifications: (a) Ground Ground  RAS;  (b)  Cellulose  fibers  in  RAS;  (c)  Aggregate  and  asphalt  binder  in  RAS;  (d)  Cellulose  RAS; (b) Cellulose fibers in RAS; (c) Aggregate and asphalt binder in RAS; (d) Cellulose fibers in RAS. fibers in RAS. 

The basic physical properties of RAS along with cement and fine aggregates are summarized in The basic physical properties of RAS along with cement and fine aggregates are summarized  Table 1. Krivit reported that RAS has a low specific gravity [35]. The low specific gravity is due to the in Table 1. Krivit reported that RAS has a low specific gravity [35]. The low specific gravity is due to  presence of asphalt binder and cellulose fibers, which ranges from 18% to 40% of RAS by weight [35]. the presence of asphalt binder and cellulose fibers, which ranges from 18% to 40% of RAS by weight  The specific gravity of RAS used in this study equals to 2.17, which is lower than normal sand. RAS [35]. The specific gravity of RAS used in this study equals to 2.17, which is lower than normal sand.  has high absorption capacity compared to general fine and coarse aggregates due to the presence of RAS  has  high  absorption  capacity  compared  to  general  fine  and  coarse  aggregates  due  to  the  cellulose fibers and woods that absorbs more water. The water absorption of RAS was found 7% which presence of cellulose fibers and woods that absorbs more water. The water absorption of RAS was  is 3 times higher than sand. found 7% which is 3 times higher than sand.   

  Table 1. Physical properties of Portl and cement, fine aggregate and RAS. Measured Property

Cement

Fine Aggregate (Sand)

RAS

Reference

Fineness modulus Specific gravity (OD) Absorption capacity (%)

N/A 3.15 N/A

2.36 2.66 2.0

2.25 2.17 7.0

ASTM C 33 ASTM C 127 and C128 ASTM C 127 and C128

Table 1. Physical properties of Portl and cement, fine aggregate and RAS. 

Measured Property  Cement Fineness modulus  N/A  Sustainability 2016, 8, 384 Specific gravity (OD)  3.15  Absorption capacity (%)  N/A 

Fine Aggregate (Sand) 2.36  2.66  2.0 

RAS 2.25  2.17  7.0 

Reference  ASTM C 33  4 of 16 ASTM C 127 and C128  ASTM C 127 and C128 

In this ground RAS waswas  used as partial replacement of fineof  aggregate becausebecause  its particle In  this study, study,  ground  RAS  used  as  partial  replacement  fine  aggregate  its  distribution is similar to the required gradation of sand in Portland cement concrete (PCC). Figure 3 particle distribution is similar to the required gradation of sand in Portland cement concrete (PCC).  shows the particle distribution of sand and ground RAS as received. Figure 3 shows the particle distribution of sand and ground RAS as received.   

ASTM High

120

ASTM Low

100 Percent (%) finer

80 60 40 20 0 0.05

0.5 Particle size (log scale)

5  

Figure 3. Gradation curves for fine aggregate (required by ASTM C33 [36]) and ground RAS used in  Figure 3. Gradation curves for fine aggregate (required by ASTM C33 [36]) and ground RAS used in this study.  this study.

2.2. Mixture Proportioning  2.2. Mixture Proportioning A  water‐to‐cement  (w/c)  ratio  of  0.5  was  used  for  all  mortar  samples.  Each  mixture  was  A water-to-cement (w/c) ratio of 0.5 was used for all mortar samples. Each mixture was prepared prepared in 5‐liter (0.005‐m³) batches. RAS was used to replace fine aggregate (sand) in the range  in 5-liter (0.005-m³) batches. RAS was used to replace fine aggregate (sand) in the range from 5 wt% from  5  wt%  to  30  wt%  (with  5  wt%  incremental)  so  that  optimum  replacement  ratio  for  mortar’s  to 30 wt% (with 5 wt% incremental) so that optimum replacement ratio for mortar’s strength and strength and durability are evaluated. Detailed information of mixture proportioning are presented  durability are evaluated. Detailed information of mixture proportioning are presented in Table 2. in Table 2.  Table 2. Mixture proportions of mortar samples per cubic meter. Table 2. Mixture proportions of mortar samples per cubic meter.  Sample Water Cement Fine Aggregate RAS RAS    Slump Fine Aggregate w/c Slump (cm) 3)  Cement (kg/m 3)  Sample ID  w/c  Water (kg/m ID (kg/m3 ) (kg/m3 ) (kg/m3 ) (kg/m3 ) 3 3 C C  R5 R5  R10 R10  R15 R20R15  R25R20  R30R25 

R30 

0.5

0.5 

   

180 180  180 180  180 180  180 180 180 

180  180 180 180  180 

360 360 360 360 360

360  360  360  360  360 360  360 360  360 

(kg/m )  760  722  684  646  608  570 532 570  532 

760 722 684 646 608

(kg/m )  ‐  38  76  114  190 152  228 190  228  38 76 114 152

(cm)  18 18  16 16  15 15  13 11 13  11  10 810  8 

Fine aggregate and RAS used in this study meets the grading requirement of ASTM C33. Figure 3 Fine  and  RAS  used  in  study  meets  the  grading  requirement  of C33 ASTM  C33.  shows theaggregate  particle size distributions of this  fine aggregate with the corresponding ASTM grading Figure 3 shows the particle size distributions of fine aggregate with the corresponding ASTM C33  requirements and also the gradation of ground RAS used in this study. The aggregate granules used in grading  requirements  and particles also  the coated gradation  ground  RAS ground used  in coal this  study.  The  aggregate  RAS is likely crushed rock with of  ceramic oxides, slag, backsurfacer sand, granules used in RAS is likely crushed rock particles coated with ceramic oxides, ground coal slag,  or mineral filler [34]. Based on the sieve analysis, RAS has slightly more fine aggregates than typical backsurfacer  or  mineral  fine aggregatesand,  (see Figure 3). filler  [34].  Based  on  the  sieve  analysis,  RAS  has  slightly  more  fine  aggregates than typical fine aggregate (see Figure 3).  2.3. Properties of Fresh Mortar Several testing methods were employed to investigate properties of early cement hydration when RAS was used in replacement of fine aggregate. The selected tests include measurements of heat of hydration (ASTM C186 [37]), setting time (ASTM C807 [38]) and Porosity (ASTM C1754 [39]). A

2.3. Properties of Fresh Mortar  Several  testing  methods  were  employed  to  investigate  properties  of  early  cement  hydration  when RAS was used in replacement of fine aggregate. The selected tests include measurements of  Sustainability 2016, 8, 384 5 of 16 heat  of  hydration  (ASTM  C186  [37]),  setting  time  (ASTM  C807  [38])  and  Porosity  (ASTM  C1754  [39]). A thermometer with four‐channel data logger provided by Omega was used to measure heat  of  hydration. with Vicat  consistency  apparatus  of  Humboldt  Mfg. was Co. used was to used  to  measure  the  initial  thermometer four-channel data logger provided by Omega measure heat of hydration. setting time of mortar mixture. All results were compared with a control sample that includes 0%  Vicat consistency apparatus of Humboldt Mfg. Co. was used to measure the initial setting time of RAS (mortar with only Portland cement and sand).  mortar mixture. All results were compared with a control sample that includes 0% RAS (mortar with only Portland cement and sand). 2.4. Properties of Harden Mortar  2.4. Properties of Harden Mortar Mechanical  behaviors  of  RAS‐combined  mortar  samples  were  investigated  by  compressive  strength  (ASTM  C109  [40]), of flexural  strength  (ASTM  [41]),  and investigated indirect  toughness  tests.  The  Mechanical behaviors RAS-combined mortar C348  samples were by compressive sample size for the compressive strength test was 5 cm × 5 cm × 5 cm (cubic) and the sample size for  strength (ASTM C109 [40]), flexural strength (ASTM C348 [41]), and indirect toughness tests. The the flexural strength test was 5 cm × 10 cm × 2.5 cm. After these mechanical tests, visual survey was  sample size for the compressive strength test was 5 cm ˆ 5 cm ˆ 5 cm (cubic) and the sample size conducted  on  fractured  surface  investigate  of  strength  change  to  RAS  in  for the flexural strength test was 5to cm ˆ 10 cm ˆany  2.5 mechanism  cm. After these mechanical tests,due  visual survey cement  matrix.  on As fractured a  means  of  durability  investigation,  porosity  measurement  (ASTM due C1754  [39])  was conducted surface to investigate any mechanism of strength change to RAS was conducted.  in cement matrix. As a means of durability investigation, porosity measurement (ASTM C1754 [39]) was conducted. 2.5. Degradation Check of RAS at High pH  2.5. Degradation Check of RAS at High pH RAS  contains  significant  amount  of  cellulose  fibers  (approximately  7  wt%  by  weight).  This  RAS contains significant amountof  of cellulose wt% by weight). This study study  investigated  the  behavior  cellulose fibers fiber (approximately contained  in 7RAS  under  high  alkaline  investigated the behavior of cellulose fiber contained in RAS under high alkaline environment where environment where cement hydration process produces high pH (in the range of 12 to 13). High pH  cement hydration process is  produces highto  pH (in the2  range of 12 towhich  13). High pH during during  cement  hydration  mainly  due  Ca(OH) (portlandite),  is  byproduct  of  cement cement  hydration is mainly due to Ca(OH)2 (portlandite), which is byproduct of cement hydration. 500 µm of hydration. 500 μm of distilled water and 20 grams of pure sodium hydroxide (NaOH) were used to  distilled water and 20 grams of pure sodium hydroxide (NaOH) were used to make sodium hydroxide make sodium hydroxide solution with a pH of 12.5. 50 grams of cellulose fibers extracted from RAS  solution with a pH of 50 grams of cellulose fibers extracted RAS wereAfter  submerged in sodium were  submerged  in 12.5. sodium  hydroxide  (NaOH)  solution  from for  7  days.  7  days  of  the  hydroxide (NaOH) solution forwere  7 days. After with  7 days thesieve  submergence, cellulose fiberswith  weredistilled  filtered submergence,  cellulose  fibers  filtered  a  of fine  (75  μm  sieve),  washed  with fine air  sieve (75 to  µmremove  sieve),the  washed with distilled water and air driedmicroscope  to removewas  the sodium water a and  dried  sodium  hydroxide.  A  high‐resolution  used  to  hydroxide. A high-resolution microscope was used to investigate the condition of cellulose fibers after investigate the condition of cellulose fibers after the degradation under high pH. Figure 4 shows a  the degradation under high pH. Figure 4 shows a schematic illustration of the laboratory testing to schematic illustration of the laboratory testing to investigate the behavior of cellulose fibers in high  investigate the behavior of cellulose fibers in high pH condition. pH condition. 

  Figure 4. Test setup for investigating the behavior of cellulose fibers in high pH condition. Figure 4. Test setup for investigating the behavior of cellulose fibers in high pH condition. 

3. Results and Discussion  3. Results and Discussion 3.1. Heat of Hydration 3.1. Heat of Hydration  The tested onon  thethe  mortar samples thatthat  contain 10%,10%,  20%,20%,  and 30% RAS, The heat heat of of hydration hydration was was  tested  mortar  samples  contain  and of 30%  of  and the results compared with the control sample. Allsample.  results shown in Figure 5 illustrate that5  RAS,  and  the  were results  were  compared  with  the  control  All  results  shown  in  Figure  the heat of hydration decreases as the replacement percentage of RAS increases in the mix. The control illustrate that the heat of hydration decreases as the replacement percentage of RAS increases in the  sample exhibits regular behavior of cement hydration with two humps of which the second one is about the temperature around 29.5 ˝ C. On the other hand, the RAS-combined mixtures (all three cases) show a clear decrement in the heat of hydration. One of main causes for the reduction of hydration

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mix. The control sample exhibits regular behavior of cement hydration with two humps of which  6 of 16 the  second  one  is  about  the  temperature  around  29.5  °C.  On  the  other  hand,  the  RAS‐combined  mixtures (all three cases) show a clear decrement in the heat of hydration. One of main causes for  the  can reduction  of  hydration  heat  can  be  related  to  the of higher  water  absorption  capacity  of  RAS  heat be related to the higher water absorption capacity RAS compared to sand. RAS is composed compared  to  sand.  RAS  composed  several  materials  fiber  and  pieces  wood  of several materials such is  cellulose fiberof and pieces of woodsuch  thatcellulose  can largely absorb water. of  Table 1 that can largely absorb water. Table 1 shows that the absorption capacity of RAS is 3 times higher  shows that the absorption capacity of RAS is 3 times higher than fine aggregate which is sand. Effective than fine aggregate which is sand. Effective water in the cement matrix decreases due to the high  water in the cement matrix decreases due to the high absorption; thus, cement grains in the mix may absorption; thus, cement grains in the mix may be hindered to fully react with water during early  be hindered to fully react with water during early hydration process. In addition, Table 2 shows hydration  process.  In  increased, addition,  Table  shows  that  as This the  RAS  content  might increased,  slump  have  that as the RAS content slump2 have decreased. phenomenon be due to higher decreased. capacity This  phenomenon  due  to  higher  absorption  capacity  of fully cellulose  fibers  the and  absorption of cellulosemight  fibersbe  and pieces of wood in RAS. In order to investigate pieces  of  wood  in  RAS.  In  order  to  fully  investigate  the  effect  of  RAS  as  is,  the  study  does  not  effect of RAS as is, the study does not include pre-processing on RAS such as removal of deleterious include  pre‐processing  on  RAS  such  as  removal  of  deleterious  materials  or leads water  materials or water correction. Another observation is that the replacement of RAS to correction.  the retard Another  is  that  replacement  RAS  leads  to  the  retard  cement  hydration.  of cement observation  hydration. The peakthe  temperature hasof  been delayed gradually byof  increasing the amountThe  of peak temperature has been delayed gradually by increasing the amount of RAS replacement.  RAS replacement.

Temperature (C)

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32 31 30 29 28 27 26 25 24 23 22

Mortar (Control) Mortar (10% RAS) Mortar (20% RAS) Mortar (30% RAS)

0

2

4

6

8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 Time (hour)

 

Figure 5. Heat of hydration with RAS (10%, 20% and 30% of RAS). Figure 5. Heat of hydration with RAS (10%, 20% and 30% of RAS). 

3.2. Setting Time  3.2. Setting Time The setting setting time time of of mortar mortar was was analyzed analyzed for for all all mixtures mixtures (0%, (0%, 10%, 10%, 20%, 20%, and and 30% 30% of of RAS RAS  The replacement).  The  results  of  setting  time  are  summarized  in  Table  3.  ASTM  C807  recommends  to  replacement). The results of setting time are summarized in Table 3. ASTM C807 recommends to measure only the initial setting, thus the final setting was not recorded.  measure only the initial setting, thus the final setting was not recorded. Table 3. Setting time of mortar samples containing RAS.  Table 3. Setting time of mortar samples containing RAS.

Sample Time (mins) Time (mins) Control  210  Control 210 10% RAS  200  10% RAS 200 20% RAS  200  20% RAS 200 30% RAS  195  30% RAS 195 Sample

As  the  replacement  percentage  of  RAS  increases  from  0%  to  30%,  the  setting  time  decreases  As the replacement percentage of RAS increases from 0% to 30%, the setting time decreases from from 210 min to 195 min. It can be explained by two reasons. The first reason is that fibers of RAS in  210 to 195 min. It canresist  be explained by twoof reasons. Theapparatus  first reason isforming  that fibers of RASof  infiber  the the min mortar  mixture  may  to  the  needle  the  setting  by  a  matrix  mortar mixture may resist to the needle of the setting apparatus by forming a matrix of fiber bridges. bridges. The second reason might be the un‐hydrated cement grains in the mortar mixture due to  The second reason might be the un-hydrated cement grains in the mortar mixture due to the high the high absorption capacity of RAS. Fibers in RAS are hydrophilic materials and can absorb more  absorption of RAS. Fibers actual  in RAScement  are hydrophilic and can absorb more water than water  than capacity sand.  Consequently,  grains  to materials be  hydrated  become  less  and  the  initial  sand. Consequently, actual cement grains to be hydrated become less and the initial cement hydration (representing the initial setting time) occurs faster when the replacement ratio of RAS is increased.

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Sustainability 2016, 8, 384 7 of 16 cement hydration (representing the initial setting time) occurs faster when the replacement ratio of 

RAS is increased.  3.3. Compressive Strength Measurement 3.3. Compressive Strength Measurement  The results  results of  of compressive  compressive strength  strength test  testare  areshown  shownin  inFigure  Figure6. 6.Overall,  Overall, the usage RAS The  the  usage  of  of RAS  in  in cement mortar causes reduction in compressive strength. As the percentage of RAS in the mix cement  mortar  causes  reduction  in  compressive  strength.  As  the  percentage  of  RAS  in  the  mix  increases the strength decreases. Interestingly, the 5%the  replacement exhibits the maximum increases  the compressive compressive  strength  decreases.  Interestingly,  5%  replacement  exhibits  the  compressive strength, which is slightly higher than the control. The control and 5% replacement maximum  compressive  strength,  which  is  slightly  higher  than  the  control.  The  control  and  5%  shows the compressive of 23.62 and 23.65 MPa,and  respectively. However, this increment might replacement  shows  the strength compressive  strength  of  23.62  23.65  MPa,  respectively.  However,  this  possibly be caused by experimental errors such as mixing, vibrating and pouring time. After the increment might possibly be caused by experimental errors such as mixing, vibrating and pouring  5% replacement, the compressive strength proportionally decreases with increasing the RAS content, time. After the 5% replacement, the compressive strength proportionally decreases with increasing  exhibiting 17.80 MPa for the 30% replacement. The mechanism to control mortar strength includes the RAS content, exhibiting 17.80 MPa for the 30% replacement. The mechanism to control mortar  asphalt film around aggregate, degradation of cellulose fiber, filler effect, and any combination of these. strength includes asphalt film around aggregate, degradation of cellulose fiber, filler effect, and any  RAS used in this studyRAS  has finer than has  sandfiner  (see particles  Figure 3),than  thussand  a slight effect combination  of  these.  used particles in  this  study  (see filler Figure  3), occurs, thus  a  resulting in a slight increase of the strength from 0% to 5% RAS. However, the effect of asphalt film and slight filler effect occurs, resulting in a slight increase of the strength from 0% to 5% RAS. However,  cellulose fiber become dominant and the strength decreases with increasing the RAS content. More the  effect  of  asphalt  film  and  cellulose  fiber  become  dominant  and  the  strength  decreases  with  discussionsthe  on the effects of asphalt and cellulose fiber degradation at high environment are increasing  RAS  content.  More  film discussions  on  the  effects  of  asphalt  film pH and  cellulose  fiber  presented later sections. degradation at high pH environment are presented later sections.   

Compressive strength (MPa)

30

7 days

25

28 days

20 15 10 5 0 0

5

10

15

20

25

30

Percentage of replaced RAS (%)

 

Percentage of strength increment (%)

(a)

35% 30% 25% 20% 15% 10% 5% 0%

y = 0.024x + 0.1246 R² = 0.8982

0

5 10 15 20 25 Percentage of replaced RAS (%)

30  

(b) Figure 6. Results of compressive strength test: (a) compressive strength of mortars containing RAS  Figure 6. Results of compressive strength test: (a) compressive strength of mortars containing RAS and and (b) percentage of strength increment from 7 days to 28 days.  (b) percentage of strength increment from 7 days to 28 days.

Another observation is that the difference in compressive strength between 7 and 28 days. The  Another observation that the difference in compressive strength between ratio  7 andincreases.  28 days. difference  between  7  and is28‐day  strengths  increases  as  the  RAS  replacement  The difference between 7 and 28-day strengths increases as the RAS replacement ratio increases.

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Considering  the  strength  increment  is  one  of  indicators  of  cement  hydration  process,  this  trend  Considering the strength increment is one of indicators of cement hydration process, this trend indicates that higher RAS replacement cause larger amount of cement hydration after 7 days. Figure  indicates that RAS replacement largerfrom  amount of cement afteris 7the  days. Figure 6a 6a  shows  the higher percentage  of  strength cause increment  7  days  to  28 hydration days,  which  ratio  of  the  shows the percentage of strength increment from 7 days to 28 days, which is the ratio of the strength strength difference between 7 and 28 days to the 7‐day strength. Asphalt binder in RAS may retard  difference betweenin  7 and 28stage  daysbut  to the strength. Asphalt binder in RAS retard cement cement  hydration  early  the 7-day hydration  continues  after  7  days.  This may later‐stage  cement  hydration in early stage but the hydration continues after 7 days. This later-stage cement hydration hydration combined with the filler effect obviously causes the strength increment after 7 days.   combined with the filler effect obviously causes the strength increment after 7 days. 3.4. Porosity Measurement  3.4. Porosity Measurement The  results  of  porosity  testing  are  shown  in  Figure  7.  Since  Portland  cement  hydrates  and  The results of porosity testing are shown in Figure 7. Since Portland cement hydrates and consumes unbound water in the mixture over time, the voids due to unbound water in the mixture  consumes unbound water in the mixture over time, the voids due to unbound water in the mixture is being reduced in process of time. Figure 7 shows that all the results of porosity measurements at  is being reduced in process of time. Figure 7 shows that all the results of porosity measurements 28  days  are  lower  than  those  measured  at  7  days.  Interestingly,  the  control  and  5%  replacement  at 28 days are lower than those measured at 7 days. Interestingly, the control and 5% replacement shows  relatively  high  porosity  values  at  7  days  and  significant  reduction  in  porosity  at  28  days.  shows relatively high porosity values at 7 days and significant reduction in porosity at 28 days. Other Other mortar samples including RAS more than 5% shows smaller reduction in porosity as cement  mortar samples including RAS more than 5% shows smaller reduction in porosity as cement hydration hydration  proceeds  from  7  days  to  28  days.  The  30%  replacement  exhibits  almost  same  porosity  proceeds from 7 days to 28 days. The 30% replacement exhibits almost same porosity between 7 days between 7 days and 28 days. This can be explained by that the mortar including RAS less than 5%  and 28 days. This can be explained by that the mortar including RAS less than 5% produces significant produces  significant  amount  of  cement  hydration  but  higher  amount  of  RAS  has  limited  level  of  amount of cement hydration but higher amount of RAS has limited level of cement hydration. Another cement  hydration.  Another  observation  is  that  the  mortar  containing  5%  RAS  at  28  days  has  the  observation is that the mortar containing 5% RAS at 28 days has the lowest porosity, which is 29.6%. It lowest  porosity,  which  is  29.6%.  It  is  an  important  note  that  the  mortar  containing  5%  RAS  is an important note that the mortar containing 5% RAS produces the highest compressive strength. produces the highest compressive strength. As discussed in Section 3.3, the RAS used in this study  As discussed in Section 3.3, the RAS used in this study contains finer particles than sand. As a result, a contains finer particles than sand. As a result, a filler effect likely occurred and led to lower porosity  filler effect likely occurred and led to lower porosity at 5% RAS at 28 days, resulting in the highest at 5% RAS at 28 days, resulting in the highest compressive strength at 5% RAS (see Figure 6a).  compressive strength at 5% RAS (see Figure 6a).

7days 28 days

35

Porosity (%)

33 31 29 27 0

5 10 15 20 25 30 Percentage of replaced RAS (%)

 

Figure 7. Porosity of mortars containing RAS. Figure 7. Porosity of mortars containing RAS. 

3.5. Flexural Strength 3.5. Flexural Strength  Figure the results of flexural strength test. The strength reduction in flexural Figure 88 presents presents  the  results  of  flexural  strength  test. trend The  of trend  of  strength  reduction  in  strength similar to results compressive test. This reduction bereduction  explainedcan  by the flexural  is strength  is  the similar  to of the  results  of strength compressive  strength  test.  can This  be  aggregate coated by asphalt film and material degradation of cellulose fibers. In general, the bonding explained by the aggregate coated by asphalt film and material degradation of cellulose fibers. In  between film and cementasphalt  paste matrix is weaker than thematrix  bonding regular general,  asphalt the  bonding  between  film  and  cement  paste  is between weaker  than  the aggregate bonding  between regular aggregate and cement paste matrix [11]. Cellulose fibers are also being degraded  and cement paste matrix [11]. Cellulose fibers are also being degraded under high pH environment. under high pH environment. More details of the degradation mechanism are discussed Section 3.6.  More details of the degradation mechanism are discussed Section 3.6. Although the overall pattern of Although  the  overall  pattern  flexural  in  decline, shows the  mortar  with  10%  RAS  flexural strength is in decline, theof  mortar withstrength  10% RASis  replacement higher flexural strength replacement  shows  higher  flexural  than  the  RAS  replacement.  than the mortar incorporating 5% RASstrength  replacement. Onemortar  possibleincorporating  explanation of5%  this increment might One  explanation  increment  might there be  the  fiber‐cement  bonding  in  the  mortar.  be thepossible  fiber-cement bondingof  in this  the mortar. Although might be a degradation of cellulose fibers Although  might  be ofa cement degradation  of  some cellulose  fibers  due  function to  high  pH  of  cement  due to highthere  pH condition mixture, of fibers might as a condition  bridge in the mortar mixture,  In some  fibers  might  as  a  bridge  in RAS the  mortar  samples.  In athis  sense,  it  is  samples. thisof  sense, it is very function  recommendable to use with glass fibers as replacement ofvery  fine recommendable to use RAS with glass fibers as a replacement of fine aggregates. Since glass fiber 

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Sustainability 2016, 8, 384 9 of 16 Sustainability 2016, 8, 384  9 of 15  has more resistibility to high pH condition than cellulose fiber, mortar with RAS containing glass 

Flexural strength Flexural strength (MPa)(MPa)

fiber may increase the flexural strength.  has more resistibility to high pH condition than cellulose fiber, mortar with RAS containing glass  aggregates. Since glass fiber has more resistibility to high pH condition than cellulose fiber, mortar fiber may increase the flexural strength.  with RAS containing glass 6.0 fiber may increase the flexural strength. 7 days

5.0 6.0

28 days 7 days

4.0 5.0

28 days

3.0 4.0 2.0 3.0 1.0 2.0 0.0 1.0

0

5

25

30

0

Percentage of replaced RAS (%) 5 10 15 20 25

30

0.0

10

15

20

Figure 8. Flexural strength test for the mortar specimens containing RAS.  Percentage of replaced RAS (%)

   

Figure 8. Flexural strength test for the mortar specimens containing RAS.  3.6. Effect of RAS in Cement Mortar  Figure 8. Flexural strength test for the mortar specimens containing RAS.

This section presents discussions on how RAS reacts with cement and behaves in the cement  3.6. Effect of RAS in Cement Mortar  3.6. Effect of RAS in Cement Mortar matrix.  Important  mechanisms  involve  effects  of  asphalt  binder  and  cellulose  fiber  on  cement  This section presents discussions on how RAS reacts with cement and behaves in the cement  mortar.  This section presents discussions on how RAS reacts with cement and behaves in the cement matrix.  Important mechanisms mechanisms  involve  effects  of  asphalt  binder  and  cellulose  on  mortar. cement  matrix. Important involve effects of asphalt binder and cellulose fiber onfiber  cement mortar.  3.6.1. Influence of the Asphalt Binder  3.6.1. Influence of the Asphalt Binder The bonding between asphalt and cement paste matrix is generally weaker than the bonding  3.6.1. Influence of the Asphalt Binder  The bonding between asphalt and cement paste matrix is generally weaker than the bonding between regular sand and cement paste matrix [11]. Thus, crack may propagate around the asphalt  The bonding between asphalt and cement paste matrix is generally weaker than the bonding  between regular sand and cement paste in  matrix [11].9b)  Thus, maythe  propagate around the asphalt film film  surrounding  aggregates  (shown  Figure  not crack through  aggregate  particle  (shown  in  between regular sand and cement paste matrix [11]. Thus, crack may propagate around the asphalt  surrounding  aggregates (shown in Figure 9b) not through the aggregate particle (shown in Figure 9a). Figure 9a).  film  surrounding  aggregates  (shown  in  Figure  9b)  not  through  the  aggregate  particle  (shown  in  Figure 9a).   

  (a)   (a)

  (b) Figure 9. Crack propagation in Mortar with sand (a) and RAS (b) [33].  (b) with sand (a) and RAS (b) [33]. Figure 9. Crack propagation in Mortar Figure 9. Crack propagation in Mortar with sand (a) and RAS (b) [33]. 

 

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This mechanism will decrease the overall compressive strength of mortar since the crack resistance This  mechanism  will  decrease  the  overall  compressive  strength  of  mortar  since  the  crack  by the bonding between harden paste and aggregate may not be fully developed. Figure 10 supports resistance by the bonding between harden paste and aggregate may not be fully developed. Figure  the10 supports the phenomenon that a crack propagates around the asphalt layers. Figure 10d clearly  phenomenon that a crack propagates around the asphalt layers. Figure 10d clearly shows asphalt film in the fractured surface (meaning no split of aggregate) while Figure 10c shows split aggregates in shows asphalt film in the fractured surface (meaning no split of aggregate) while Figure 10c shows  thesplit aggregates in the fracture section of the control mortar sample.  fracture section of the control mortar sample.

(a) 

(b)

(c) 

(d)

Figure 10. Photographs of mortar sections: (a) Fracture section (Control); (b) Fracture section (R15);  Figure 10. Photographs of mortar sections: (a) Fracture section (Control); (b) Fracture section (R15); (c) Split aggregates (Control); (d) Asphalt layer in mortar (R15).  (c) Split aggregates (Control); (d) Asphalt layer in mortar (R15).

The asphalt film layers, an interface between harden cement paste and RAS aggregate, might  The asphalt film layers, an interface between harden cement paste and RAS aggregate, might impede the crack propagation. While the crack detours around the side of the RAS aggregate due to  impede the crack propagation. While the crack detours around the side of the RAS aggregate due the asphalt layer, the fracture energy to mobilize crack initiation and propagation might increase. In  to the asphalt layer, the fracture energy to mobilize crack initiation and propagation might increase. order to check this mechanism, the toughness of mortar samples was measured. In this study, the  In order to check this mechanism, the toughness of mortar samples was measured. In this study, the area of force–displacement curve of flexural test at 28 days was used as an indirect toughness index.  Figure  11  shows  the  results  of  of indirect  toughness  flexural  testing  at  28  days.  It  was  area of force–displacement curve flexural test at 28index  days from  was used as an indirect toughness index. found that the mortar samples containing 5% and 10% RAS have larger areas compared to that of  Figure 11 shows the results of indirect toughness index from flexural testing at 28 days. It was found thatthe control sample, which indicates that the asphalt film layer requires larger energy to fracture the  the mortar samples containing 5% and 10% RAS have larger areas compared to that of the control specimen  and  also  more  behavior.  all  mortar  containing  shows  sample, which indicates thatductile  the asphalt filmAlthough  layer requires largersamples  energy to fracture RAS  the specimen lower  flexural  strength  than  the  control,  the  mortar  samples  containing  10%  RAS  exhibited  the  and also more ductile behavior. Although all mortar samples containing RAS shows lower flexural highest “toughness”.  strength than the control, the mortar samples containing 10% RAS exhibited the highest “toughness”.

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Indirect toughness index (N · mm) Indirect toughness index (N · mm)

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2500

2500 2000 2000 1500 1500 1000 1000 500 500

0 0

0 0

5 5

10 15 20 (%) 10 RAS15content 20 RAS content (%)

25 25

30 30

Figure 11. Indirect toughness index of mortar samples containing RAS.  Figure 11. Indirect toughness index of mortar samples containing RAS. Figure 11. Indirect toughness index of mortar samples containing RAS. 

   

3.6.2. Influence of the Cellulose Fiber  3.6.2. Influence of the Cellulose Fiber 3.6.2. Influence of the Cellulose Fiber  The  effect  of  cellulose  fiber  in  cementitious  material  can  be  either  increase  or  decrease  of  The effect of cellulose fiber in cementitious material can fibers  be either increase or decrease of compressive  strength.  Figure  12  shows  the  existence  of  RAS’s  in  cement  matrix.  The  main  The  effect  of  cellulose  fiber  in  cementitious  material  can  be  either  increase  or  decrease  of  compressive strength. Figure 12 shows existence of RAS’sgravity  fibers inof cement matrix. The main cause cause  of  that  decreased  strength  is the that  low  specific  the  fibers  causes  a  lack  of  compressive  strength.  Figure  12  shows  the  existence  of  RAS’s  fibers  in  cement  matrix.  The  main  of that decreased strength is that low specific gravity of the fibers causes a lack of homogeneity in homogeneity  in  the  mixture  [42].  On  the  other  hand,  there  might  be  a  positive  effect  of  cellulous  cause  of  that  decreased  strength  is  that  low  specific  gravity  of  the  fibers  causes  a  lack  of  the mixture [42]. On other mixture.  hand, there might a positive effect cellulous replacement in fiber  replacement  in the cement  When  the becellulous  fiber  is  of mixed  well  fiber in  the  cement  paste  homogeneity  in  the  mixture  [42].  On  the  other  hand,  there  might  be  a  positive  effect  of  cellulous  cement mixture. When the cellulous fiber is mixed well in the cement paste matrix, those fibers can matrix, those fibers can form the fiber‐cement matrix bonding; hence, the fiber network can increase  fiber  replacement  in  cement  mixture.  When  the  cellulous  fiber  is  mixed  well  in  the  cement  paste  form the fiber-cement matrix bonding; hence, the fiber network can increase the compressive strength the compressive strength of mortar. As shown in Figure 6, the mortar sample containing 5% RAS  matrix, those fibers can form the fiber‐cement matrix bonding; hence, the fiber network can increase  of mortar. As shown in Figure 6, the mortar sample containing 5% RAS exhibited a slight higher exhibited a slight higher compressive strength than the control, the positive effect of fiber is quite  the compressive strength of mortar. As shown in Figure 6, the mortar sample containing 5% RAS  compressive strengthof  than theat  control, the positive effect ofcan  fiberbe  is one  quiteof  small. Degradation of fiberlow  at small.  Degradation  fiber  high  alkaline  condition  mechanism  to  explain  exhibited a slight higher compressive strength than the control, the positive effect of fiber is quite  high alkaline condition can be one of mechanism to explain low positive effect of cellulose fibers. positive effect of cellulose fibers.    small.  Degradation  of  fiber  at  high  alkaline  condition  can  be  one  of  mechanism  to  explain  low  positive effect of cellulose fibers.   

(a) 

(b) 

   

Figure 12. 12. Photographs Photographs  of mortar mortar section: section:  (a) (a)  Fracture Fracture  section section  (R15) (R15) and and  (b) Fracture Fracture section section with with  (a) of (b) (b) Figure cellulose fiber (R15).  cellulose fiber (R15). of  mortar  section:  (a)  Fracture  section  (R15)  and  (b)  Fracture  section  with  Figure  12.  Photographs  cellulose fiber (R15). 

Cement  hydration  creates  high  pH  condition  (pH  12–13)  in  the  cement  mixture  due  to  Cement hydration creates high pH condition (pH 12–13) in the cement mixture due to byproducts byproducts of hydroxyl ions and calcium hydroxide (Ca(OH)2). This high pH condition may cause  creates hydroxide high  pH (Ca(OH) condition  (pH high 12–13)  in  the  cement  mixture  due  to  ofCement  hydroxylhydration  ions and calcium pH condition may cause the degradation 2 ). This the  degradation  of  cellulose  fibers  in  RAS  when  fibers  are  incorporated  in  the  cement  mixture.  byproducts of hydroxyl ions and calcium hydroxide (Ca(OH) 2). This high pH condition may cause  of cellulose fibers in RAS when fibers are incorporated in the cement mixture. Figure 13a shows a Figure  13a  shows  a  diagrammatic  sketch  of  cellulose  fiberʹs  alkaline  degradation  process  [43].  To  the diagrammatic degradation  of  cellulose  fibers  in  RAS  when  fibers  are  incorporated  cement  mixture.  sketch of cellulose fiber's alkaline degradation process [43].in Tothe  verify the degradation verify the degradation of cellulose fiber in high pH condition, high alkaline solution was prepared  Figure  13a  shows  a  in diagrammatic  sketch  of  cellulose  fiberʹs  alkaline  [43].  To  of cellulose fiber high pH condition, high alkaline solution was degradation  prepared by process  dissolving sodium by dissolving sodium hydroxide (NaOH) in distill water. Manually collected cellulose fibers (50 g)  verify the degradation of cellulose fiber in high pH condition, high alkaline solution was prepared  hydroxide (NaOH) in distill water. Manually collected cellulose fibers (50 g) from RAS were submerged from  RAS  were  submerged  in  high  alkaline  solution  (measured  pH  was  12.5)  for  7  days.  Figures  by dissolving sodium hydroxide (NaOH) in distill water. Manually collected cellulose fibers (50 g)  in high alkaline solution (measured pH was 12.5) for 7 days. Figure 13b,c shows the comparison of from  RAS  were  submerged  in  high  alkaline  solution  (measured  pH  was  12.5)  for  7  days.  Figures 

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cellulose fibers in RAS before and after the chemical process. The same amount of cellulose fibers was 13b and 13c shows the comparison of cellulose fibers in RAS before and after the chemical process.  tested and same magnification used to tested  check the of fibers. Although it to  is very hard The  same  amount  of  cellulose was fibers  was  and conditions same  magnification  was  used  check  the  to quantify of  thefibers.  reduction of length all fibers, the length the  of the fiber after chemical processthe  is conditions  Although  it  is of very  hard  to  quantify  reduction  of  the length  of  all  fibers,  generally reduced. The reduction of fibers can be seen and compared with the same fibers and same length  of  the  fiber  after  the  chemical  process  is  generally  reduced.  The  reduction  of  fibers  can  be  magnification in Figure 13. seen and compared with the same fibers and same magnification in Figure 13. 

 

(a)

(b) 

(c)

Figure 13. Illustration of degradation process of cellulose fiber in high alkaline: (a) and photos of  Figure 13. Illustration of degradation process of cellulose fiber in high alkaline: (a) and photos of cellulose fibers before; (b) and after; (c) exposed to high alkaline solution for 3 days.  cellulose fibers before; (b) and after; (c) exposed to high alkaline solution for 3 days.

Several researchers studied fiber mixed cementitious composites such as mortar and concrete  Several researchers studied fiber mixed cementitious composites such as mortar and concrete contain either cellulous, glass fibers or both in the past. The results of their studies and this study  contain either cellulous, glass fibers or both in the past. The results of their studies and this study were compared in Table 4 to show the differences and similarities. Table 4 shows the comparison of  were compared in Table 4 to show the differences and similarities. Table 4 shows the comparison of compressive and flexural strengths of this study and other studies.  compressive and flexural strengths of this study and other studies. Table 4. Comparison of compressive and flexural strengths of this and other studies [44–46].  Table 4. Comparison of compressive and flexural strengths of this and other studies [44–46]. Mortar  Mortar (Current  (Current Study)  Study) C C  R5

R5 

R10

R10  R15 R20

R15 

R25

R20  R30 R25  R30 

Mortar Compressive Compressive Strength  Strength 23.64 23.64  (100%) (100%)  23.65 23.65  (100%)

Flexural  Flexural Strength  Strength 5.1  5.1 (100%)

(100%)  4.4  21.8(100%)  (92.2%) 4.6(86.3%)  (90.2%) 21.8  4.6  21.34 4.1 (80.4%) (90.3%) (92.2%)  (90.2%)  4.1  19.521.34  (82.5%) 3.9 (76.5%) (90.3%)  (80.4%)  18.25 3.6 (70.6%) (77.2%) 19.5  3.9  17.9 (75.7%) 3.6 (70.6%) (82.5%)  (76.5%)  3.6  18.25 (77.2%)  (70.6%)  17.9    3.6  (75.7%)  (70.6%)  4.4 (86.3%)

[45]  Mortar [45] (Hemp (Hemp  Fiber) Fiber) 

Control Control  Hemp Hemp  fiber 1% Hemp fiber 1%  fiber 2% Hemp  Hemp fiber 4% fiber 2%  Hemp Hemp  fiber10%

fiber 4%  Hemp  fiber10% 

Mortar Compressive  Flexural Compressive Flexural Mortar [46]  [46] Compressive Strength  Flexural Strength Compressive Flexural Strength Strength Strength  Strength Strength  (Glass (Glass  Strength (MPa)  (MPa)  Fiber) (MPa) (MPa) Fiber)  32.4  9.1  70.2  6.57  32.4 (100%) 9.1 (100%) Control 6.57 (100%) Control  70.2 (100%) (100%)  (100%)  (100%)  (100%)  7.78 Glass 32.3 (99.7%) 8.2 (90.1%) 57.58 (82%) 32.3  8.2  Glass  57.58  7.78  fiber 3% (118.4%) Glass 50.46 8.37 (99.7%)  5.6 (61.5%) (90.1%)  fiber 3%  (82%)  (118.4%)  27.2 (83.9%) fiber 5% (71.9%) (127.4%) 27.2  5.6  Glass  50.46  Basalt 57.15 8.728.37  25.1 (77.5%) 5.6 (61.5%) 3% (81.4%) (132.7%) (83.9%)  (61.5%)  Fiber fiber 5%  (71.9%)  (127.4%)  Basalt 52.10 8.538.72  57.15  25.1  5.6  Basalt  16.1 (49.7%) 5.9 (64.8%) Fiber 5% (74.2%) (129.8%) Fiber 3%  (81.4%)  (132.7%)  (77.5%)  (61.5%)  16.1  5.9  Basalt  52.10  8.53  (49.7%)  (64.8%)  Fiber 5%  (74.2%)  (129.8%) 

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As shown in Table 4, compressive and flexural strengths of mortars which contain hemp fiber (one of cellulose fibers) were gradually decreased due to the degradation of cellulose fiber in high pH condition as we discussed [45]. However, flexural strengths of mortars which contain either glass or basalt fibers were increased up to 132.7% compared to the control mortar sample. This result can be explained by the bridging effect of glass and basalt fibers. Glass and basalt fibers have higher resistance to alkali attack than cellulose fiber so that these fibers could function as bridges. Which means that RAS contains either glass or basalt fiber may increase the flexural strength of mortar. On the other hand, compressive strengths of mortar which contain glass and basalt fiber had been deceased [46]. Greater amount of glass and basalt fibers may cause to increase the viscosity of fresh cement matrix. In addition, this higher viscosity may allow the entrapment of residual air bubble while material mixing [47]. 4. Conclusions The present work investigated the effect of RAS when used as replacement of fine aggregate in cement mortar samples. Laboratory testing procedure includes measurements of physical, mechanical, and durability properties/behaviors of RAS-mixed mortar specimens. In addition, the visual survey on the fractured surface of mortar was conducted to evaluate how RAS behaves in the cement matrix. Lastly, the degradation of cellulose fibers at high pH (due to byproduct of cement hydration) was investigated. The following conclusions have been drawn from this study. ‚







The particle size distributions of ground RAS meets ASTM C33 grading requirements of fine aggregate for Portland cement concrete (PCC); thus, ground RAS as received could be used as replacement of sand in mortar and PCC. Overall the usage of RAS in mortar causes reduction in compressive and flexural strengths, which can be explained by the mechanism that high absorption capacity of RAS may cause reduced effective water to participate in cement hydration. It is concluded that an optimum mixture proportion for compressive strength of mortar is 5% and that for toughness is 10% RAS replacement. The asphalt film layer by RAS likely impedes the crack propagation so that the mortar samples containing RAS shows more ductile behavior than the control under flexural loading; however, the improvement is slight. The alkaline degradation of cellulose fibers due to high pH condition in cement matrix can cause the disconnection of discrete cellulose fiber-cement matrix. Thus, bridging effect of cellulose fibers in the cement matrix may not be significant. However, reusing RAS containing glass fibers in cementitious materials can result in positive influence because glass fiber has higher resistance to alkali attack than cellulose fiber.

Acknowledgments: This work was supported by National Research Foundation of Korea (NRF) funded by Ministry of Science, ICT & Future Planning (NRF-2013R1A1A1011983). Author Contributions: Jinwoo An conducted the laboratory experiments; Heejung Youn and Boo Hyun Nam designed the experiments and analyzed the data. Conflicts of Interest: The authors declare no conflict of interest.

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