Article

Mechanical Properties and Eco-Efficiency of Steel Fiber Reinforced Alkali-Activated Slag Concrete Sun-Woo Kim 1 , Seok-Joon Jang 2 , Dae-Hyun Kang 2 , Kyung-Lim Ahn 2 and Hyun-Do Yun 2, * Received: 1 October 2015 ; Accepted: 27 October 2015 ; Published: 30 October 2015 Academic Editor: Jorge de Brito 1 2

*

Department of Construction Engineering Education, Chungnam National University, Daejeon 34134, Korea; [email protected] (S.-W.K.) Department of Architectural Engineering, Chungnam National University, Daejeon 34134, Korea; [email protected] (S.-J.J.); [email protected] (D.-H.K); [email protected] (K.-L.A) Correspondence: [email protected]; Tel.: +82-42-821-6281; Fax: +82-42-823-9467

Abstract: Conventional concrete production that uses ordinary Portland cement (OPC) as a binder seems unsustainable due to its high energy consumption, natural resource exhaustion and huge carbon dioxide (CO2 ) emissions. To transform the conventional process of concrete production to a more sustainable process, the replacement of high energy-consumptive PC with new binders such as fly ash and alkali-activated slag (AAS) from available industrial by-products has been recognized as an alternative. This paper investigates the effect of curing conditions and steel fiber inclusion on the compressive and flexural performance of AAS concrete with a specified compressive strength of 40 MPa to evaluate the feasibility of AAS concrete as an alternative to normal concrete for CO2 emission reduction in the concrete industry. Their performances are compared with reference concrete produced using OPC. The eco-efficiency of AAS use for concrete production was also evaluated by binder intensity and CO2 intensity based on the test results and literature data. Test results show that it is possible to produce AAS concrete with compressive and flexural performances comparable to conventional concrete. Wet-curing and steel fiber inclusion improve the mechanical performance of AAS concrete. Also, the utilization of AAS as a sustainable binder can lead to significant CO2 emissions reduction and resources and energy conservation in the concrete industry. Keywords: alkali-activated slag (AAS); mechanical performance; eco-efficiency; ordinary Portland cement (OPC); sustainable binder

1. Introduction Concrete is the most widely used construction material and uses a great amount of cement. Furthermore, anthropogenic CO2 emissions due to the production of cement is rapidly increasing with the increase of urban development. In order to address this, alkali-activated slag (AAS) has been considered as an alternative binder to cement, as well as a way of reusing available industrial by-products. Damineli et al. [1] proposed two indicators which allow measuring the eco-efficiency of cement use, binder intensity and CO2 intensity. Both indicators were tested using two sets of data from literature, one Brazilian and the other from 28 different countries. Yang et al. [2] derived the relationship between the CO2 and binder intensities of different concretes from a regression analysis of a comprehensive database in Korea. However, their applicability was hindered because the AAS concretes obtained with sodium silicate activators exhibit higher drying shrinkage rates than in ordinary Portland cement (OPC). At present, fiber inclusion is commonly accepted as the way to improve shrinkage behavior of AAS concrete [3,4]. In addition to above, many researches have been conducted to improve or enhance the performance of AAS concrete by incorporation of fibers [5–7]. The primary purposes of the fiber inclusion are to control cracking and to increase Materials 2015, 8, 7309–7321; doi:10.3390/ma8115383

www.mdpi.com/journal/materials

Materials 2015, 8, 7309–7321

the fracture toughness of the cement matrix by a bridging action that is controlled by debonding, sliding and pulling-out the reinforcing fibers during both micro and macro-cracking of the matrix. Bernal et al. [5] concluded that alkali-activated slag concrete reinforced with steel fibers shows three times higher flexural toughness than Portland cement concretes at early ages of curing. Aydin and Baradan [6] reported that alkali-activated slag/silica fume mortars present significantly higher mechanical performance than OPC based mortar at the same fiber dosage due to the higher bonding properties between fiber and alkali-activated slag/silica fume mortar interfacial zone compared to OPC mortar. In relation to the use of fibers and development of sustainable materials, the structural behaviors of timber beams have also been studied [8–10]. The aim of this study is to improve the mechanical performance of Ca(OH)2 -based AAS concrete by incorporation of steel fibers because it has been found from other previous research results that microfiber such as polyethylene (PE) or polyvinyl alcohol (PVA) is useful for improving tensile performance of a cementitious composite without coarse aggregate. In this study, concrete was mixed with crushed granite, and therefore steel fibers that have high tensile performance and larger diameter compared to the microfiber were used for mixing the concrete. The effects of incorporation of steel fibers on the compressive and flexural performance of AAS concretes with the main variables being steel fiber volume fraction and curing condition are investigated in this paper. The test results are compared to the OPC concrete specimens, with a view to identifying their performances and potential applications as construction materials. In this study, an alternative fiber-reinforced concrete to OPC concrete with a specified compressive strength value of 40 MPa was produced by using 30 mm length hooked-end steel fibers. The utilization of AAS in concrete will be helpful in reducing environmental problems and greenhouse gas emissions associated with the Portland cement production, and in conserving existing natural resources. 2. Experimental Section 2.1. Materials and Specimen Preparation Ground granulated blast-furnace slag (GGBS) and Type I OPC were used as binders for AAS concrete and ordinary concrete, respectively. The chemical compositions of the GGBS and OPC used in this study are given in Table 1. The specific surfaces for the OPC and the GGBS were 325 and 430 m2 /kg, respectively. The GGBS has a 21.2 µm maximum particle size and an 8.5 µm average particle size. To produce the AAS concrete, AAS binder was produced by the activation of GGBS with calcium hydroxide as the primary activator. Sodium silicate (Na2 SiO3 ) and sodium carbonate (Na2 CO3 ) were used as auxiliary activators. The selection of primary and auxiliary activators was based on studies previously conducted in Korea [2,11,12]. From the chemical composition of GGBS presented in the table, the basicity coefficient (Kb ) and hydration modulus (HM) of GGBS were calculated to be 0.92 and 1.68, respectively. Locally available river sand (maximum particle size of 5 mm) and crushed granite (maximum particle size of 20 mm) were used as fine and coarse aggregates, respectively. The results of sieve analysis for fine and coarse aggregates met the continuous standard curves specified in KS F 2526 [13]. As listed in Table 2, OPC and AAS concretes were prepared with a water-to-binder ratio of 0.55 and a sand-to-coarse aggregate ratio of 0.45. Hooked-end steel fibers shown in Figure 1 were made from mild carbon steel with a tensile strength of 1100 MPa. The fibers were 30 mm long and 0.5 mm in diameter, giving an aspect ratio of 60. The percentage of the steel fiber added ranged from 0%–2.0% by weight of the binder as seen in Table 3. To produce OPC and AAS concretes, the binder and the aggregate were initially dry-mixed for a minute. After the dry-mixing, water including a superplasticizer was added and the time for mixing was planned to be long enough to prevent any segregation in concrete. The required quantities of steel fibers were then added separately in small amounts to avoid fiber balling. The freshly mixed steel fiber-reinforced concrete was poured in two layers into cylindrical (Φ100 mm ˆ 200 mm) and

7310

Materials 2015, 8, 7309–7321

Materials 2015, 8, page–page  prismatic (100 mm ˆ 100 mm ˆ 400 mm) steel moulds for compressive and flexural tests, respectively. For each mix, nine cylinders (three cylinders at each age) and three prisms were cast in steel moulds tests, respectively. For each mix, nine cylinders (three cylinders at each age) and three prisms were  ˝ and 95% relative humidity for 24 h until demoulding. After and kept a mist roomand  at 23 cast  in in  steel  moulds  kept C in  a  mist  room  at  23  °C  and  95%  relative  humidity  for  24  h  until  demoulding, specimens for wet-curing were preserved in water at 23 ˝ C and the other specimens demoulding. After demoulding, specimens for wet‐curing were preserved in water at 23 °C and the  for dry-curing were placed in air at 23 ˘ 5 ˝ C and 50 ˘ 5% relative humidity until 1 day before other specimens for dry‐curing were placed in air at 23 ± 5 °C and 50 ± 5% relative humidity until 1  day before testing. For all mixes, 225 and 75 specimens were made and tested for compressive and  testing. For all mixes, 225 and 75 specimens were made and tested for compressive and flexural flexural properties, respectively.  properties, respectively.

Table 1. Chemical composition (% by mass) of GGBS and OPC.  Table 1. Chemical composition (% by mass) of GGBS and OPC.

Component 

GGBS

OPC 20.9 OPC Silicon Aluminium oxide (Al dioxide (SiO2 ) 2O3) 34.7 13.8  5.39 20.9 AluminiumCalcium oxide (CaO)  oxide (Al2 O3 ) 13.8 40.1  64.7 5.39 Calcium oxide (CaO) 40.1 64.7 Iron oxide (Fe2O3)  0.11  2.38 2.38 Iron oxide (Fe2 O3 ) 0.11 Magnesium oxide (MgO) 4.38  1.51 1.51 Magnesium oxide (MgO) 4.38 2)  0.74 0.74  1.33 1.33 TitaniumTitanium dioxide (TiO dioxide (TiO2 ) Sodium oxide (Na2 O) 0.20 Sodium oxide (Na 2O)  0.20  0.27 0.27 Potassium oxide (K2 O) 0.48 Potassium oxide (K2O)  0.48  0.22 0.22 Sulfur trioxide (SO3 ) 4.83 1.65 Sulfur trioxide (SO 3)  4.83  1.65 5.80 Loss on ignition (LOI) 2.70 Loss on ignition (LOI)  2.70  5.80 2.52 Basicity coefficient (Kb ) 0.92 HydrationBasicity coefficient (K modulus (HM) 1.68 b)  0.92  2.52 3.43 Hydration modulus (HM) 3.43 + Al2 O3 )/SiO2 . Notes: Kb = (CaO + MgO)/(SiO2 + Al2 O3 ); HM =1.68  (CaO + MgO Component Silicon dioxide (SiO2) 

GGBS 34.7 

Notes: Kb = (CaO + MgO)/(SiO2 + Al2O3); HM = (CaO + MgO + Al2O3)/SiO2. 

  Figure 1. Shape of a hooked‐end steel fiber. 

Figure 1. Shape of a hooked-end steel fiber. Table 2. Mixture proportions of OPC and AAS concretes. 

Mix

3) Table 2. Mixture proportionsUnit Weight (kg/m of OPC and AAS concretes. Mix  w/b  S/a W C AAS S G 3) Unit Weight (kg/m OPC  0.55  0.45 205 373 ‐  756 924 w/b S/a AAS  0.55  0.45W 205 ‐  C 373 AAS 756 924 S

G

OPC 0.55 0.45 205 373 756 924 Notes: w/b is water‐to‐binder ratio; S/a is sand‐to‐aggregate ratio; W is water; C is cement; S is sand;   AAS 0.55 0.45 205 373 756 924 and G is coarse aggregate.  Notes: w/b is water-to-binder ratio; S/a is sand-to-aggregate ratio; W is water; C is cement; S is sand; and G is coarse aggregate. Table 3. Variables for mechanical tests. 

Test

Specimen Vf (%) Curing Method 0.0, for 0.5,mechanical 1.0, 1.5, 2.0 tests. Wet-curing  TableOPC 3. Variables Compression  AAS-dry 0.0, 0.5, 1.0, 1.5, 2.0 Dry-curing  AAS-wet 0.0, 0.5, 1.0, 1.5, 2.0 Wet-curing  V f (%) Test Specimen Curing Method OPC 0.0, 0.5, 1.0, 1.5, 2.0 Wet-curing  Flexure  OPC 0.0, 0.5, Wet-curing AAS-wet 0.0, 0.5, 1.0, 1.0, 1.5,1.5, 2.02.0 Wet-curing 

Compression Flexure

AAS-dry 0.0, 0.5, 1.0, 1.5, 2.0 Notes: Vf is steel fiber volume fraction.  AAS-wet 0.0, 0.5, 1.0, 1.5, 2.0 OPC 0.0, 0.5, 1.0, 1.5, 2.0 AAS-wet 0.0, 0.5, 1.0, 1.5, 2.0

3

Notes: V f is steel fiber volume fraction.

7311

Dry-curing Wet-curing Wet-curing Wet-curing

Materials 2015, 8, 7309–7321

2.2. Test Methods Materials 2015, 8, page–page 

The cross-sectional area of each cylinder for compressive test was calculated using an average of three 2.2. Test Methods  diameter measurements taken in two intersecting directions at the mid-height of the specimen. At 3, 7, and 28 days after concrete casting, compressive strength tests of the cylindrical specimens The cross‐sectional area of each cylinder for compressive test was calculated using an average  were of  performed. The cylinders were taken  testedin  intwo  compression as directions  per ASTMat Cthe  39 mid‐height  [14] until failure. three  diameter  measurements  intersecting  of  the  The flexural strength tests were conducted at 28 days in accordance with ASTM C 78 [15]. specimen. At 3, 7, and 28 days after concrete casting, compressive strength tests of the cylindrical  specimens were performed. The cylinders were tested in compression as per ASTM C 39 [14] until 

3. Results and Discussion failure. The flexural strength tests were conducted at 28 days in accordance with ASTM C 78 [15].  3.1. Compressive Performance 3. Results and Discussion  Compressive strength versus strain curves of OPC, AAS-dry, and AAS-wet specimens at 28 days 3.1. Compressive Performance  with different fiber contents are presented in Figure 2. The average curves were drawn from the three Compressive  strength  versus in strain  curves  of  OPC, was AAS‐dry,  and  AAS‐wet  specimens  at  28  of test results for each mix. The error the measurement calculated as the standard deviation days with different fiber contents are presented in Figure 2. The average curves were drawn from  the compressive strength from three samples. The maximum standard deviations in the compressive the  three  test  results  for  each  mix.  The  error  in  the  measurement  was  calculated  as  the  standard  strength were 1.56, 2.45, and 3.05 MPa at 3, 7, and 28 days, respectively. As seen in Figure 2a, the deviation of the compressive strength from three samples. The maximum standard deviations in the  descending curvestrength  of OPC-0.0 has 3.05  almost due brittle failure right afterin peak compressive  were  specimen 1.56,  2.45,  and  MPa vanished at  3,  7,  and  28 to days,  respectively.  As  seen  stress,Figure  whereas the other OPC specimens with fiber and all of the AAS specimens have various 2a,  the  descending  curve  of  OPC‐0.0  specimen  has  almost  vanished  due  to  brittle  failure  descending curves as seen in Figure 2a,b. As the steel fiber volume fraction increases, the curve right after peak stress, whereas the other OPC specimens with fiber and all of the AAS specimens  after have various descending curves as seen in Figure 2a,b. As the steel fiber volume fraction increases,  peak stress descended slowly. It can be inferred that the compressive failure mode of concrete the curve after peak stress descended slowly. It can be inferred that the compressive failure mode of  changed from a brittle to a more ductile failure due to the steel fiber inclusion. The effect of steel fibers concrete changed from a brittle to a more ductile failure due to the steel fiber inclusion. The effect of  on the compressive strength of AAS concrete is more noticeable in case of higher fiber inclusion [5]. steel fibers on the compressive strength of AAS concrete is more noticeable in case of higher fiber  Karunanithi and Anandan (2014) reported that the increase of steel fiber inclusion improved the inclusion  [5].  Karunanithi  and  Anandan  (2014)  reported  that  the  increase  of  steel  fiber  inclusion  compressive strength of AAS concrete [16]. As shown in Figure 2b,c, AAS-wet specimens exhibit improved  the  compressive  strength  of  AAS  concrete  [16].  As  shown  in  Figure  2b,c,  AAS‐wet  morespecimens  stable post behavior than AAS-dry specimens. It reflects that water-curing enhances the bond exhibit  more  stable  post  behavior  than  AAS‐dry  specimens.  It  reflects  that  water‐curing  properties in the zone in  between fibers and matrix phase binders enhances  the interfacial bond  properties  the  interfacial  zone the between  fibers  and for the AAS matrix  phase compared for  AAS  to dry-curing. binders compared to dry‐curing. 

  Figure 2. Stress-strain curves of test specimens at 28 days. (a) OPC-wet; (b) AAS-dry; (c) AAS-wet. 4

7312

Materials 2015, 8, 7309–7321 Materials 2015, 8, page–page 

The effects of fiber inclusion on the compressive strengths with age are presented in Figure 3. Figure 2. Stress‐strain curves of test specimens at 28 days. (a) OPC‐wet; (b) AAS‐dry; (c) AAS‐wet.  Until 7 days, OPC-0.5 specimen shows a little less strength than OPC-0.0. At 28 days, however, OPC-0.5 specimens show higher compressive strength value than OPC-0.0. For OPC specimens The effects of fiber inclusion on the compressive strengths with age are presented in Figure 3.  with Until 7 days, OPC‐0.5 specimen shows a little less strength than OPC‐0.0. At 28 days, however, OPC‐0.5  over 1.0% of fiber volume fraction, there is no noticeable increase in the compressive strength specimens show higher compressive strength value than OPC‐0.0. For OPC specimens with over 1.0%  compared to OPC-0.0 specimen. It is thought that the steel fibers were not effectively dispersed in of  fiber  volume  fraction,  there  is  no  noticeable  increase values in  the  of compressive  strength have compared  to  concrete when mixing. However, compressive strength AAS specimens significantly OPC‐0.0 specimen. It is thought that the steel fibers were not effectively dispersed in concrete when  increased by fiber inclusion. At 28 days, the addition of steel fibers in AAS concrete has a significant mixing.  However,  compressive  strength  values  of  AAS  specimens  have  significantly  increased  by  effect on the enhancement of the compressive strength by 1.9%–17.8%. In addition to the fiber fiber inclusion. At 28 days, the addition of steel fibers in AAS concrete has a significant effect on the  inclusion, the compressive strength development of concrete is affected by curing methods; it is clear enhancement  of  the  compressive  strength  by  1.9%–17.8%.  In  addition  to  the  fiber  inclusion,  the  that water-curing is moredevelopment  efficient for of  theconcrete  strength of concrete than as shown compressive  strength  is development affected  by  curing  methods;  it  is dry-curing clear  that  water‐ in Figure 3b,c. curing is more efficient for the strength development of concrete than dry‐curing as shown in Figure 3b,c. 

  Figure 3. Compressive strength development with age (a) 3 days; (b) 7 days; (c) 28 days.  Figure 3. Compressive strength development with age (a) 3 days; (b) 7 days; (c) 28 days.

Figure 4 shows the effect of fiber inclusion on the strain at maximum stress of concrete at each 

Figure 4 shows the effect of fiber inclusion on the strain at maximum stress of concrete at each age. As shown in the figure, the strain value has a tendency to decrease with the age of concrete as  age. As shown in the figure, has a except  tendency tospecimens  decrease at  with the age of concrete as expected.  From  the  results the for strain strain  value at  each  age,  OPC  7  days,  all  specimens  show a similar trend in the strain increase ratio, so it can be inferred that the effect of binder type on  expected. From the results for strain at each age, except OPC specimens at 7 days, all specimens show the  strain  of  concrete  is  negligible.  curing  method, that the  increase  ratio  the  strain  a similar trendcapacity  in the strain increase ratio, so For  it can be inferred the effect of on  binder type of  on the AAS  concrete  is  similar  between  dry‐  and  wet‐curing.  For  strain  values  at  7  days,  regardless  of  strain capacity of concrete is negligible. For curing method, the increase ratio on the strain of AAS curing  methods,  the  AAS‐1.5  specimen  showed  a  noticeably  higher  strain  than  OPC.  The  concrete is similar between dry- and wet-curing. For strain values at 7 days, regardless of curing compressive test results are summarized in Table 4.  methods, the AAS-1.5 specimen showed a noticeably higher strain than OPC. The compressive test results are summarized in Table 4. 5

7313

Materials 2015, 8, 7309–7321 Materials 2015, 8, page–page 

  Figure 4. Variation of compressive strain at maximum stress with age. (a) 3 days; (b) 7 days; (c) 28 days.  Figure 4. Variation of compressive strain at maximum stress with age. (a) 3 days; (b) 7 days; (c) 28 days. Table 4. Compressive test results. 

Compressive Strength (MPa) Strain at Max. Compressive Strength (%) Table 4. Compressive test results. Specimens  3 days  7 days  28 days 3 days 7 days 28 days  wet dry  wet  dry wet wet dry wet dry  wet  Compressive Strength (MPa) Strain at Max. Compressive Strength (%) OPC‐0.0  21.7  ‐  29.2  ‐  36.3 0.212  ‐  0.211 ‐  0.214 Specimens 3 Days 7 Days 28 Days 3 Days 7 Days 28 Days OPC‐0.5 Wet 20.2 Dry ‐  Wet 27.8  Dry ‐  42.2Wet 0.205 Wet ‐  Dry0.186 Wet ‐  Dry 0.225 Wet OPC‐1.0  14.6  ‐  25.5  ‐  34.0 0.241  ‐  0.247 ‐  0.231 OPC-0.0 21.7 29.2 36.3 0.212 0.211 0.214 OPC‐1.5  16.4  ‐  24.5  ‐  35.9 0.486  ‐  0.239 ‐  0.311 OPC-0.5 20.2 27.8 42.2 0.205 0.186 0.225 OPC‐2.0 14.6 18.2  - ‐  25.5 24.2  ‐ - 36.434.0 1.167  OPC-1.0 0.241 ‐  - 1.4130.247 ‐  -0.457 0.231 AAS‐0.0 16.4 14.3  - 21.8  24.5 22.0  31.8 0.236  -0.207 0.311 OPC-1.5 - 34.635.9 0.290  0.486 0.195 - 0.2090.239 AAS‐0.5  15.5  24.8  23.0  35.9 39.3 0.245  0.238 0.227 0.225  OPC-2.0 18.2 24.2 36.4 1.167 1.413 -0.238 0.457 AAS‐1.0  15.8  23.4  25.5  34.6 34.7 0.285  0.246 0.272 0.228  0.219 0.207 AAS-0.0 14.3 21.8 22.0 31.8 34.6 0.290 0.195 0.209 0.236 AAS-0.5 35.9 42.339.3 0.692  0.245 0.5610.2380.6970.227 AAS‐1.5 15.5 17.5 24.827.8  23.0 28.5  38.1 0.333  0.225 0.334 0.238 AAS-1.0 34.6 41.434.7 1.020  0.285 0.7190.2460.8830.272 AAS‐2.0 15.8 23.5 23.431.8  25.5 34.6  40.1 0.480  0.228 0.447 0.219 AAS-1.5 17.5 27.8 28.5 38.1 42.3 0.692 0.561 0.697 0.333 0.334 AAS-2.0 23.5 31.8 1.020 0.719 0.883 0.480by  fiber  0.447 The  compressive  strength 34.6 values  40.1 of  AAS 41.4 concrete  were  significantly  increased  inclusion whereas OPC concrete shows no noticeable change in the compressive strength. It can be  noted  that  lateral  confinement  by  steel  fiber concrete is  improved  due  to the  smaller  particle by size  of  GGBS  The compressive strength values of AAS were significantly increased fiber inclusion compared to OPC. Furthermore, the increase ratio in compressive strength for AAS concrete with  whereas OPC concrete shows no noticeable change in the compressive strength. It can be noted that wet‐curing is higher than that with dry‐curing. This indicates that wet‐curing enhances the bonding  lateral confinement by steel fiber is improved due to the smaller particle size of GGBS compared to properties  between  fiber  and  mortar  phase  for  AAS  based  binders.  Figure  5  shows  SEM  OPC.micrographs of the steel fiber–matrix transition zone. From the micrographs in the figure, it is clear  Furthermore, the increase ratio in compressive strength for AAS concrete with wet-curing is higher than thatAAS  withbinder  dry-curing. This indicates that wet-curing thecoarse.  bonding that  using  turns  the  surface  of  the  steel  fiber  from enhances smooth  to  The properties SEM  between fiber and mortar phase for AAS based binders. Figure 5 shows SEM micrographs of the steel micrographs also confirmed that the bond property in the interfacial zone between steel fibers and 

fiber–matrix transition zone. From the micrographs in the figure, it is clear that using AAS binder turns the surface of the steel fiber from smooth 6to coarse. The SEM micrographs also confirmed that the bond property in the interfacial zone between steel fibers and matrix phase for AAS binders is better than that for OPC based binders. These enhanced bond characteristics of alkali activated 7314

Materials 2015, 8, 7309–7321 Materials 2015, 8, page–page  Materials 2015, 8, page–page 

matrix  phase  AAS  binders in is other better research than  that results for  OPC  based Shi binders.  These  bond  that binders have alsofor  been reported [17,18]. and Xie [17]enhanced  also reported characteristics of alkali activated binders have also been reported in other research results [17,18].  ´ matrix  phase  for dense AAS  binders  is  better  than  that zone for  OPC  based  These  enhanced  bond  can the formation of the and uniform transition in the Na2binders.  SiO3 activated slag mortars Shi  and  Xie  [17]  also  reported  that  the  formation  of  the  dense  and  uniform  transition  zone  in  the  characteristics of alkali activated binders have also been reported in other research results [17,18].  be attributed to several factors such as the water reducing function of Na2 SiO3 and the high initial Na 2SiO3−  activated  slag  mortars  can  be  attributed  to  several  factors  such  as  the  water  reducing  Shi  and  Xie  [17]  also  reported  that  the  formation  of  the  dense  and  uniform  transition  zone  in  the  concentration of [SiO ]4´ in the pore solution. function of Na 2SiO43 and the high initial concentration of [SiO4]4− in the pore solution.  − Na2SiO3   activated  slag  mortars  can  be  attributed  to  several  factors  such  as  the  water  reducing  function of Na2SiO3 and the high initial concentration of [SiO4]4− in the pore solution. 

(a) 

   

(b) 

(c) 

(a)  (b)  (c)  Figure 5. SEM micrographs of steel fiber–matrix transition zone. (a) OPC‐wet; (b) AAS‐dry; (c) AAS‐wet.  Figure 5. SEM micrographs of steel fiber–matrix transition zone. (a) OPC-wet; (b) AAS-dry; (c) AAS-wet. Figure 5. SEM micrographs of steel fiber–matrix transition zone. (a) OPC‐wet; (b) AAS‐dry; (c) AAS‐wet. 

3.2. Flexural Performance 

3.2. Flexural Performance

3.2. Flexural Performance  A  flexural  strength‐deflection  curve  itself  may  be  quite  sensitive  in  distinguishing  amongst  A flexural strength-deflection curve be quite  quitesensitive  sensitive distinguishing amongst different fiber inclusions, and the curve roughly indicates differences in the toughness performance  A  flexural  strength‐deflection  curve itself itself may may  be  in in distinguishing  amongst  of concrete with different fiber volume fractions. Figure 6 shows flexural strength‐deflection curves  different fiber inclusions, and the curve roughly indicates differences in the toughness performance different fiber inclusions, and the curve roughly indicates differences in the toughness performance  for  all  specimens.  All  the  are fractions. the  average  values  for  three  specimens.  As  expected,  the  of concrete with different fibercurves  volume Figure 6 shows flexural strength-deflection curves of concrete with different fiber volume fractions. Figure 6 shows flexural strength‐deflection curves  ultimate  strength  is  higher  for  concrete  with  more  fiber  volume  fractions,  due  to  bridging  action.  for allfor  specimens. All the are the average values for three specimens. As expected, the ultimate all  specimens.  All curves the  curves  are  the  average  values  for  three  specimens.  As  expected,  the  However,  there  was  no  significant  effect  of  binder  type  or  fiber  inclusion  on to  the  first  cracking  ultimate  strength  is  higher  for  concrete  with  more  fiber  volume  fractions,  due  bridging  action.  strength is higher for concrete with more fiber volume fractions, due to bridging action. However, strengths.   there  was  no  significant  effect  of  binder  type  or  fiber  inclusion  on  the  first  cracking  thereHowever,  was no significant effect of binder type or fiber inclusion on the first cracking strengths. The The  ultimate  strength  was  noticeably  improved  when  the  fiber  volume  fraction  was  above  1.0%.   strengths.   ultimate strength was noticeably improved when the fiber volume fraction was above 1.0%. In In  particular,  AAS‐1.5  and  AAS‐2.0  specimens  showed  very  similar  flexural  as  The  ultimate AAS‐1.0,  strength  was  noticeably  improved  when  the  fiber  volume  fraction  was  behavior  above  1.0%.   particular, AAS-1.0, AAS-1.5 and AAS-2.0 specimens showed very similar flexural behavior as shown shown in Figure 6a, whereas the ultimate strengths of AAS‐0.0 and AAS‐0.5 specimens were lower  In  particular,  AAS‐1.0,  AAS‐1.5  and  AAS‐2.0  specimens  showed  very  similar  flexural  behavior  as  in Figure 6a, whereas the ultimate strengths of AAS-0.0 and AAS-0.5 specimens were lower than than those of OPC‐0.0 and OPC‐0.5 specimens due to lower compressive strengths. In Table 5, first  shown in Figure 6a, whereas the ultimate strengths of AAS‐0.0 and AAS‐0.5 specimens were lower  thosecrack strength (f of OPC-0.0 and OPC-0.5 specimens fdue to lower compressive strengths. In Table 5, firstf) crack f), first crack deflection (δ ), ultimate strength (f f), and deflection at the peak load (δ than those of OPC‐0.0 and OPC‐0.5 specimens due to lower compressive strengths. In Table 5, first  are given. As shown in flexural responses in Figure 6, the descending portion of the curve is steeper  strength (ff ), first crack deflection (δf ), ultimate strength (ff ), and deflection at the peak load (δf) f ) are f), first crack deflection (δ f), ultimate strength (f f), and deflection at the peak load (δ crack strength (f when the ultimate strength is higher. Therefore, it can be inferred that the residual strength beyond  given. As shown in flexural responses in Figure 6, the descending portion of the curve is steeper are given. As shown in flexural responses in Figure 6, the descending portion of the curve is steeper  when the ultimate strength is higher. Therefore, it can be inferred that the residual strength beyond  whenthe peak load decreases faster so that the post‐crack toughness changes.  the ultimate strength is higher. Therefore, it can be inferred that the residual strength beyond the peak load decreases faster so that the post‐crack toughness changes.  the peak load decreases faster so that the post-crack toughness changes.

  Figure  6.  Flexural  strength‐deflection  curves  of  test  specimens  at  28  days.  (a)  OPC  specimens;   (b) AAS specimens.  Figure  6.  Flexural  strength‐deflection  curves  of  test  specimens  at  28  days.  (a)  OPC  specimens;  

 

Figure 6. Flexural strength-deflection curves of test specimens at 28 days. (a) OPC specimens; (b) AAS specimens.  (b) AAS specimens. 7

7

7315

Materials 2015, 8, 7309–7321 Materials 2015, 8, page–page 

Table 5. Strengths and deflections at both first crack and peak load. Table 5. Strengths and deflections at both first crack and peak load. 

Specimen OPC-0.0 OPC-0.5 OPC-1.0 OPC-1.5 OPC-2.0 AAS-0.0 AAS-0.5 AAS-1.0 AAS-1.5 AAS-2.0

First Crack First crack  ff (MPa) δf (mm) Specimen  ff (MPa) δf (mm) 6.329 0.049 OPC‐0.0  6.329  0.049  6.577 0.047 OPC‐0.5  6.577  0.047  5.755 0.042 OPC‐1.0  5.755  0.042  5.064 0.047 OPC‐1.5  5.064  0.055 0.047  6.646 OPC‐2.0  6.646  0.050 0.055  5.501 4.674 AAS‐0.0  5.501  0.044 0.050  5.249 AAS‐0.5  4.674  0.029 0.044  5.910 AAS‐1.0  5.249  0.019 0.029  4.180 AAS‐1.5  5.910  0.047 0.019  AAS‐2.0  4.180  0.047 

Peak Load Peak load  fu (MPa) δu (mm) fu (MPa) δu (mm) 6.329 0.049 6.329  0.049  8.197 1.303 8.197 10.5571.303  0.531 10.557 10.8550.531  1.035 10.855 13.1301.035  2.221 13.130 5.5012.221  0.050 1.145 5.501  6.6380.050  0.705 6.638 11.6151.145  1.427 11.615 11.7140.705  0.931 11.714 13.2621.427 

13.262 

0.931 

ASTM C1018 [19] is the most common method used for evaluating the flexural toughness of FRC ASTM  C1018  [19]  is  the  most  common  method  used  for  evaluating  the  flexural  toughness  of  (fiber reinforced concrete). In this study, the ASTM flexural toughness indices and the ASTM residual FRC (fiber reinforced concrete). In this study, the ASTM flexural toughness indices and the ASTM  strength factors are adopted for calculating the post-crack toughness of test specimens. The ASTM residual  strength  factors  are  adopted  for  calculating  the  post‐crack  toughness  of  test  specimens.   specifies the flexural toughness indices as I5 (3δ), I10 (5.5δ), I20 10(10.5δ), (15.5δ),30and I50 (25.5δ). For The ASTM specifies the flexural toughness indices as I 5 (3δ), I  (5.5δ), II2030 (10.5δ), I  (15.5δ), and I 50  the residual strength factors, R5,10 , R10,20 , R20,30 and R30,50 are also specified in the ASTM. In this paper, (25.5δ). For the residual strength factors, R 5,10, R10,20, R 20,30 and R30,50 are also specified in the ASTM.   for the flexural toughness indices and residual strength factors, I100 (50δ), I200 (100δ),200R In this paper, for the flexural toughness indices and residual strength factors, I 100 (50δ), I  (100δ),  50,100 , and R50,100 R100,200 were added consider overall flexural response including the deflection at peak load of test , and R 100,200to  were added to consider overall flexural response including the deflection at peak  load  of For test  specimens.  For  the  R50,100   and the R100,200   added,  factors  reduced  as  per  the  specimens. the R50,100 and R100,200 added, factors werethe  reduced aswere  per the following equations: following equations: 

R50,100 “ = 2 × (I 2 ˆ pI100 100 R50,100  − I´50I) 50 q

(1)

(1)

R100,200 “= 2 × (I 2 ˆ pI200 R100,200   − I´100I) 100 q 200

(2)

(2)

Figure  7  shows  the  effect  of  binder  on ASTM the  ASTM  toughness  indices  all  specimens.   Figure 7 shows the effect of binder typetype  on the toughness indices for for  all specimens. All are All  are  average  values  for  three  specimens.  It  can  be  seen  that  the  ASTM  toughness  indices  are  average values for three specimens. It can be seen that the ASTM toughness indices are particularly particularly  sensitive  in  distinguishing  amongst  different  fiber  volume  fractions,  is  more  sensitive in distinguishing amongst different fiber volume fractions, which is morewhich  obvious when the obvious  when  the  fiber  volume  fraction  is  higher  than  1.0%.  AAS  specimens  exhibit  similar  or  fiber volume fraction is higher than 1.0%. AAS specimens exhibit similar or higher toughness index higher toughness index than OPC specimens, regardless of fiber volume fraction. In particular, for  than OPC specimens, regardless of fiber volume fraction. In particular, for R50,100 and R100,200 which R50,100 and R100,200 which are toughness indices added in this paper, the difference of indices between  are toughness added inwas  this widened.  paper, theThis  difference of indices between and OPC specimens AAS  and indices OPC  specimens  means  that  the  AAS  binder AAS is  more  efficient  for  was widened. This means that the AAS binder is more efficient for bonding in the interfacial zone bonding in the interfacial zone between steel fibers and the matrix phase than OPC binder during  between steel fibers and the matrix phase than OPC binder during post-cracking behavior. post‐cracking behavior. 

  Figure 7. Comparison of toughness indices.  Figure 7. Comparison of toughness indices.

Figure 8 shows the effect of binder type on the ASTM residual strength factors for all specimens. 8 As shown in the figure, AAS binder could be better for residual strength of FRC than OPC binder. It

7316

Materials 2015, 8, page–page  Materials 2015, 8, 7309–7321

Figure  8  shows  the  effect  of  binder  type  on  the  ASTM  residual  strength  factors  for  all  specimens.  As  shown in  the  figure,  AAS  binder  could  be  better  for  residual strength  of FRC  than  can bebinder.  thoughtIt that distribution the tension zone in  would be enhanced to the OPC  can the be internal thought stress that  the  internal  in stress  distribution  the  tension  zone  due would  be  formation of the dense and uniform transition zone in the matrix as seen in Figure 5. enhanced due to the formation of the dense and uniform transition zone in the matrix as seen in Figure 5. 

  Figure 8. Comparison of residual strength factors.  Figure 8. Comparison of residual strength factors.

3.3. Eco‐Efficiency of Alkali‐Activated Slag  3.3. Eco-Efficiency of Alkali-Activated Slag Korea LCI Database Information Network [20] and Japanese database [21] were referred to in  Korea LCI Database Information Network [20] and Japanese database [21] were referred to in order  to  evaluate evaluate the the CO CO22  emissions  of  concrete. concrete.  Tables  show  CO CO22  evaluation  OPC  order to emissions of Tables 6  6 and  and 77  show evaluation of  of the  the OPC and the AAS concrete, respectively. As listed in the tables, the CO 2 emission of the AAS concrete is  and the AAS concrete, respectively. As listed in the tables, the CO2 emission of the AAS concrete 15%~24%  of of that  of of the  lower  CO CO22  is 15%~24% that theOPC  OPCconcrete  concretebecause  becausethe  theAAS  AASbased  based binder  binder has  has about  about 97%  97% lower emission than the OPC based binder. The CO 2 emissions of concretes considering fiber inclusion are  emission than the OPC based binder. The CO2 emissions of concretes considering fiber inclusion are compared in Table 8.  compared in Table 8. To compare environmental efficiency, a binder intensity (bi) and CO2 intensity (ci) were proposed To  compare  environmental  efficiency,  a  binder  intensity yields (bi)  and  CO2  intensity  (ci)  were  by Damineli BL et al. [1]. It was reported that the binder intensity the efficiency of using clinker proposed by Damineli BL et al. [1]. It was reported that the binder intensity yields the efficiency of  and other hard to find clinker substitutes. The CO2 intensity permits an estimation of the mix design’s using clinker and other hard to find clinker substitutes. The CO 2 intensity permits an estimation of  global warming potential. The indices are calculated as: the mix design’s global warming potential. The indices are calculated as:  bܾ bi (3) ܾ݅“ൌ p   (3) ‫݌‬ cܿ ciܿ݅“ൌ   p‫݌‬

(4) (4)

where b is the total consumption of binder materials (kg/m (kg/m3) emitted to  ) emitted to where b is the total consumption of binder materials (kg/m33),), c is the total CO c is the total CO22 (kg/m produce, and p is the compressive strength (MPa) at 28 days.  produce, and p is the compressive strength (MPa) at 28 days. Table 6. CO Table 6. CO22 evaluation of OPC concrete.  evaluation of OPC concrete.

Material and Production Material and Production Item  A BB A∙B A A¨ B Item 3 3 -kg/kg kg/m3 kg/m3 COCO CO 2‐kg/kg CO 2 ‐kg/m 2 2 -kg/m OPC  373 373  0.944  352.1  352.1 OPC 0.944 Sand 0.0026 2.0 Sand  756 756  0.0026  2.0  Coarse 924 0.0075 6.9 Coarse  924  0.0075  ´4 6.9  Water 205 0.0 1.96 ˆ 10 Water  205  1.96 × 10−4 0.0  Admixture 0.1492 0.25 0.0 Admixture 2258 0.1492 0.25  0.0  Conc. production 0.008 18.1 2258  0.008  18.1  Sum Conc. production – – 379.2 Wet-curing – 38.5 – –– Sum  379.2 3 Total * = 417.7 CO -kg/m 2 – – 38.5 Wet‐curing  Note: * CO2 emission of steel fiber (1.6 CO is not included. 3  2 -kg/kg) Total * = 417.7 CO 2‐kg/m

Note: * CO2 emission of steel fiber (1.6 CO2‐kg/kg) is not included. 

9 7317

Materials 2015, 8, 7309–7321

Table 7. CO2 evaluation of AAS concrete. Materials 2015, 8, page–page 

Material and Production A¨ B CO2 -kg/kg CO2 -kg/m3 Material and production GGBS 373 9.9 Item  A B0.0265 A∙B Sand 756 0.0026 2.0 3 3 kg/m CO2‐kg/kg CO2‐kg/m Coarse 924 0.0075 6.9 GGBS  373  0.0265  Water 205 0.0 1.96 ˆ 10´4 9.9  Sand  0.1492 756  0.0026  2.0  Admixture 0.25 0.0 924  0.0075  6.9  Conc. production Coarse  2258 0.008 18.1 Water  – 205  1.96 × 10–−4 0.0  Sum 36.9 Dry-curing 0.0 Admixture – 0.1492 0.25  – 0.0  Wet-curing Conc. production – 38.5 2258  0.008 – 18.1  3 Total * = 36.9 CO –2 -kg/m for – AAS-dry;36.9 Sum  3 for AAS-wet 75.4 CO -kg/m 2 – – 0.0 Dry‐curing  Note: * Wet‐curing  CO2 emission of steel– fiber (1.6 CO– included. 38.5 2 -kg/kg) is not Total * = 36.9 CO2‐kg/m3 for AAS‐dry; 75.4 CO2‐kg/m3 for AAS‐wet  Table 8. Final CO2 emission of concrete with fiber inclusion. Item

A 2 evaluation of AAS concrete.  B Table 7. CO kg/m3

Note: * CO2 emission of steel fiber (1.6 CO2‐kg/kg) is not included. 

Mix OPC AAS AAS

CO22 emission of concrete with fiber inclusion.  Emission with Fiber Volume Fractions (CO2 -kg/kg) Curing Table 8. Final CO 0.0% 0.5% 1.0% 1.5% 2.0% Method Curing  CO2 Emission with Fiber Volume Fractions (CO2‐kg/kg)  417.7 420.6 423.6 426.6 429.6 Mix  wet 0.0%  0.5%  1.0% 42.9 1.5%  45.9 2.0%  method  dry 36.9 39.9 48.9 OPC  wetwet  417.7  420.6  423.6 81.4 426.6  84.4 429.6  75.4 78.4 87.4 AAS  dry  36.9  39.9  42.9  45.9  48.9  AAS  wet  75.4  78.4  81.4  84.4  87.4 

The binder intensity with variables and the relationship between the binder intensity and compressive are presented in Figure seen in Figure 9a,the  it binder  is clearintensity  that theand  binder The  strength binder  intensity  with  variables  and 9. the As relationship  between  intensity can be reduced by wet-curing fiber case 9a,  of concrete lessbinder  than 1.0% compressive  strength  are  presented  in and Figure  9. inclusion. As  seen  in In Figure  it  is  clear with that  the  of fiber volume fraction, OPC specimens have lower binder intensity compared to AAS specimens. intensity can be reduced by wet‐curing and fiber inclusion. In case of concrete with less than 1.0% of  fiber  volume  specimens  have  lower  binder  intensity ofcompared  to  AAS  specimens.  However, as fiberfraction,  volume OPC  fraction increases, the binder intensities AAS specimens are lower than However, as fiber volume fraction increases, the binder intensities of AAS specimens are lower than  those of OPC specimens. It can be inferred that AAS binder can enhance performance, especially those  of  OPC  specimens.  It  can  be  inferred  that the AAS  binder  can  enhance  performance,  the compressive strength of concrete, and reduce total amount of binder necessary especially  to achieve the the  compressive  strength  of  concrete,  and  reduce  the  total  amount  of  binder  necessary  to  achieve  performance required. The best-fit curves in previous research [2] are adopted to compare the binder the performance required. The best‐fit curves in previous research [2] are adopted to compare the  intensity in this study and are presented in Figure 9b. As shown in the figure, the binder intensity binder  intensity  in  this  study  and  are  presented  in  Figure  9b.  As  shown  in  the  figure,  the  binder  calculated in this study is below the best-fit curve of OPC (Yang et al., 2013). AAS concrete has lower intensity calculated in this study is below the best‐fit curve of OPC (Yang et al., 2013). AAS concrete  binder intensity compared to compared  OPC concrete even though itthough  was reported that Ca(OH) AA 2 -based has lower  binder  intensity  to  OPC  concrete  even  it  was reported  that  Ca(OH) 2‐ GGBSbased AA GGBS concrete requires a greater amount of binder in order to obtain the same compressive  concrete requires a greater amount of binder in order to obtain the same compressive strength as OPC concrete [2]. strength as OPC concrete [2]. 

  Figure 9. Comparison of binder intensity (bi). (a) fiber volume fraction; (b) compressive strength. 

Figure 9. Comparison of binder intensity (bi). (a) fiber volume fraction; (b) compressive strength. 10

7318

Materials 2015, 8, 7309–7321

Materials 2015, 8, page–page 

Figure thethe  COCO withwith  variables and the relationship betweenbetween  the CO2 intensity 2 intensity Figure 10 10 shows shows  2  intensity  variables  and  the  relationship  the  CO2  and compressive strength. As estimated in Table 8, the CO intensity of AAS concrete is about intensity  and  compressive  strength.  As  estimated in  Table 8, 2the CO2  intensity  of  AAS  concrete  is  20%–25% of that of  of OPC concrete. In view of curing method, shown in wet-curing about  20%–25%  that  of  OPC  concrete.  In the view  of  the  curing asmethod,  as Figure shown 10a, in  Figure  10a,   increases theincreases  CO2 intensity by 40%–50% by  compared to compared  dry-curing to  because electric equipment is wet‐curing  the  CO 2  intensity  40%–50%  dry‐curing  because  electric  needed to maintain the water at a constant temperature for curing. The best-fit curves in previous equipment is needed to maintain the water at a constant temperature for curing. The best‐fit curves  research [2] are adopted to compare the CO2 intensity in2 intensity in this study and are presented in  this study and are presented in Figure 10b. in previous research [2] are adopted to compare the CO As shown in the figure, it is indicated that the estimated CO for OPC is around for  the OPC  best-fit 2 intensity Figure  10b.  As  shown  in  the  figure,  it  is  indicated  that  the  estimated  CO2  intensity  is  curve. However, there is little difference between the curves because Yang et al. [2] considered CO2 around the best‐fit curve. However, there is little difference between the curves because Yang et al. [2]  emitted in production and transport as c. In this study, CO2 emitted for transport was omitted because considered CO 2 emitted in production and transport as c. In this study, CO 2 emitted for transport  the CO emission is influenced by the transportation distance between the plant and construction 2 was  omitted  because  the  CO2  emission  is  influenced  by  the  transportation  distance  between  the  sites. In this study, CO2sites.  emitted in production (cradle to gate) was considered to gate)  calculate plant  and  construction  In  this  study,  CO2only   emitted  in  production  only  (cradle  to  was  CO intensity (ci), and the best-fit curves for AAS-wet and -dry lie under the curve proposed by 2 considered  to  calculate  CO2  intensity  (ci),  and  the  best‐fit  curves  for  AAS‐wet  and  ‐dry  lie  under  the  Yang et al. [2]. curve proposed by Yang et al. [2]. 

  Figure 10. Comparison of CO2 intensity (ci). (a) Fiber volume fraction; (b) compressive strength.  Figure 10. Comparison of CO2 intensity (ci). (a) Fiber volume fraction; (b) compressive strength.

4. Conclusions  4. Conclusions In this study, AAS was used as an alternative binder to OPC in order to reduce environmental  In this study, AAS was used as an alternative binder to OPC in order to reduce environmental impact  of  concrete.  To  estimate  eco‐efficiency  of  AAS  based  binder,  compressive  tests  were  impact of concrete. To estimate eco-efficiency of AAS based binder, compressive tests were conducted conducted  and  the  effects of fiber inclusion  and  wet‐curing  on  the  two indicators (bi and  ci)  were  and the effects of fiber inclusion and wet-curing on the two indicators (bi and ci) were evaluated. The evaluated.   following observations and conclusions can be made and drawn on the basis of the compressive test The  following  observations  and  conclusions  can  be  made  and  drawn  on  the  basis  of  the  results and intensity estimation in this study. compressive test results and intensity estimation in this study.  1. AAS based binders may provide similar compressive performance with a lower fiber content 1. AAS  based  binders  may  provide  similar  compressive  performance  with  a  lower  fiber  due to better dispersion and enhanced bond characteristics in the steel fiber–matrix content  due fiber to  better  fiber  dispersion  and  enhanced  bond  characteristics  in  the  steel  fiber– transition zone. Furthermore, the wet-curing method is very helpful for the performance matrix  transition  zone.  Furthermore,  the  wet‐curing  method  is  very  helpful  for  the  enhancement of AAS with steel fibers. performance enhancement of AAS with steel fibers.  2.2.It It  can bebe  inferred can  inferred that that AAS AAS binder binder can can enhance enhance performance, performance, especially especially the the  compressive compressive  strength of concrete, and can reduce the total amount of binder necessary strength  of  concrete,  and  can  reduce  the  total  amount  of  binder  necessary to to achieve achieve  the the  performance required. performance required.  3.3.Based on on  the results of theof  ASTM toughness index and residual strength factor, it isfactor,  concluded Based  the  results  the  ASTM  toughness  index  and  residual  strength  it  is  that AAS binder is more efficient for bonding in the interfacial zone between steel fibers and concluded  that  AAS  binder  is  more  efficient  for  bonding  in  the  interfacial  zone  between  matrix than matrix  OPC binder post-cracking behavior. This is because theThis  internal stress steel phase fibers and  phase in than  OPC  binder in post‐cracking  behavior.  is  because  distribution in the tension zone would be enhanced due to the formation of the dense and the internal stress distribution in the tension zone would be enhanced due to the formation  uniform transition zone in the matrix. of the dense and uniform transition zone in the matrix. 

4. The significant effects of fiber inclusion and wet‐curing on the eco‐efficiency of AAS were  confirmed  on  the  basis  of  the  binder  intensity  and  CO2  intensity.  It  indicates  that  more  economic  and  eco‐efficient  fiber  reinforced  composites  with  AAS  can  be  produced.  In  the  7319 11

Materials 2015, 8, 7309–7321

4. The significant effects of fiber inclusion and wet-curing on the eco-efficiency of AAS were confirmed on the basis of the binder intensity and CO2 intensity. It indicates that more economic and eco-efficient fiber reinforced composites with AAS can be produced. In the future, additional studies on the mechanical properties of AAS concrete under fatigue and creep are needed. Acknowledgments: The work was financially supported by the General Researcher Support Program (No. NRF-2013R1A1A2066034) through a National Research Foundation (NRF) grant funded by the Korea Ministry of Education (MOE). Author Contributions: Sun-Woo Kim is a main writer of the manuscript and advised the experiments. Seok-Joon Jang, Dae-Hyun Kang, and Kyung-Lim Ahn performed the experiments and assisted the research. Hyun-Do Yun is a consultant to the research and supervised the entire research work. All authors were involved in the test results analysis and in the finalizing of the manuscript. Conflicts of Interest: The authors declare no conflict of interest. References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

Damineli, B.L.; Kemeid, F.M.; Aguiar, P.S.; John, V.M. Measuring the eco-efficiency of cement use. Cem. Concr. Compos. 2010, 32, 555–562. [CrossRef] Yang, K.H.; Song, J.K.; Song, K.I. Assessment of CO2 reduction of alkali-activated concrete. J. Clean. Prod. 2013, 39, 265–272. [CrossRef] Alcaide, J.S.; Alcocel, E.G.; Puertas, F.; Lapuente, R.; Garces, P. Carbon fiber-reinforced, alkali-activated slag mortars. Mater. Constr. 2007, 57, 33–48. Puertas, F.; Gil-Maroto, A.; Palacios, M.; Amat, T. Alkali-activated slag mortars reinforced with AR glassfibre. Performance and properties. Mater. Constr. 2006, 56, 79–90. Bernal, S; Gutierrez, R.D.; Delvasto, S.; Rodriguez, E. Performance of an alkali-activated slag concrete reinforced with steel fibers. Constr. Build. Mater. 2010, 24, 208–214. Aydın, S.; Baradan, B. The effect of fiber properties on high performance alkali-activated slag/silica fume mortars. Compos. B Eng. 2013, 45, 63–69. [CrossRef] Silva, F.J.; Thaumaturgo, C. Fiber reinforcement and fracture response in geopolymeric mortars. Fatigue Fract. Eng. Mater. Struct. 2003, 26, 167–172. [CrossRef] Fossetti, M.; Minafò, G.; Papia, M. Flexural behaviour of glulam timber beams reinforced with FRP cords. Constr. Build. Mater. 2015, 95, 54–64. [CrossRef] Raftery, G.M.; Rodd, P.D. FRP reinforcement of low-grade glulam timber bonded with wood adhesive. Constr. Build. Mater. 2015, 91, 116–125. [CrossRef] Andor, K.; Lengyel, A.; Polgár, R.; Fodor, T.; Karácsonyi, Z. Experimental and statistical analysis of spruce timber beams reinforced with CFRP fabric. Constr. Build. Mater. 2015, 99, 200–207. [CrossRef] Yang, K.H.; Cho, A.R.; Song, J.K.; Nam, S.H. Hydration products and strength development of calcium hydroxide-based alkali-activated slag mortars. Constr. Build. Mater. 2012, 29, 410–419. [CrossRef] Yang, K.H.; Cho, A.R.; Song, J.K. Effect of water–binder ratio on the mechanical properties of calcium hydroxide-based alkali-activated slag concrete. Constr. Build. Mater. 2012, 29, 504–511. [CrossRef] Korea Agency for Technology and Standards (KATS). KS F 2526 Concrete Aggregate; Korea Agency for Technology and Standards (KATS): Seoul, Korea, 2007; pp. 1–9. American Society for Testing Materials. Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens; ASTM C39; ASTM International: West Conshohocken, PA, USA, 2005. American Society for Testing Materials. Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading); ASTM C78; ASTM International: West Conshohocken, PA, USA, 2010. Karunanithi, S.; Anandan, S. Flexural Toughness Properties of Reinforced Steel Fibre Incorporated Alkali Activated Slag Concrete. Adv. Civ. Eng. 2014, 2014. [CrossRef] Shi, C.; Xie, P. Interface between cement paste and quartz sand in alkali-activated slag mortars. Cem. Concr. Res. 1998, 28, 887–896. [CrossRef] Hu, S.; Wang, H.; Zhang, G.; Ding, Q. Bonding and abrasion resistance of geopolymeric repair material made with steel slag. Cem. Concr. Compos. 2008, 30, 239–244. [CrossRef]

7320

Materials 2015, 8, 7309–7321

19.

20. 21.

American Society for Testing Materials. Standard Test for Flexural Toughness and First-Crack Strength of Fiber Reinforced Concrete (Using Beam with Third Point Loading); ASTM C1018; ASTM International: West Conshohocken, PA, USA, 1997. Korea Environmental Industry & Technology Institute. Korea LCI Database Information Network; Korea, 2013. Available online: http://www.edp.or.kr/lcidb (accessed on 1 October 2015). Sakai, K.; Kawai, K. JSCE Guidelines for Concrete No. 7; Recommendation of Environmental Performance Verification for Concrete Structures, Japan Society of Civil Engineering: Tokyo, Japan, 2006. © 2015 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons by Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).

7321