Scholarly article on topic 'Material development for a sustainable precast concrete block pavement'

Material development for a sustainable precast concrete block pavement Academic research paper on "Civil engineering"

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{"Rubberized concrete" / "Crumb rubber" / "Damage mechanism" / "Material characterization" / "Impact energy"}

Abstract of research paper on Civil engineering, author of scientific article — R. Bharathi Murugan, C. Natarajan, Shen-En Chen

Abstract Portland cement concrete (PCC) and asphalt concrete (AC) are the most common roadway and highway construction materials which are more suitable for continuous slab pavements. The durability of these materials is highly dependent on construction quality and techniques, and both materials are difficult to repair. Heavy rain storms in India have recently revealed several roadway pavement failures and resulted in significant repair costs. Interlocking block type pavements are simpler to construct and maintain than both PCC and AC pavements but, have only been used for slower traffic roads due to weak interlocking at the joints. To improve the quality of block pavements, blocks made of PCC with waste tire crumb rubber partially replacing river sand (fine aggregate) are suggested. The joint interlocks can be further improved by modifying the block geometry. The material is completely recycled and is deemed more superior than concrete pavements when repair and construction techniques and costs are concerned. This paper presents the material characterization of Rubberized Concrete Blocks (RCBs) using crumb rubber particle size ranging from 0.075 mm to 4.75 mm to partially replace the fine aggregates. It also discusses the advantages of RCB over continuous material pavements.

Academic research paper on topic "Material development for a sustainable precast concrete block pavement"

Accepted Manuscript

Material development for a sustainable precast concrete block pavement R. Bharathi Murugan, C. Natarajan, Shen-En Chen

PII: S2095-7564(16)30189-1

DOI: 10.1016/j.jtte.2016.09.001

Reference: JTTE 82

To appear in: Journal of Traffic and Transportation Engineering (English Edition)

Please cite this article as: Bharathi Murugan, R, Natarajan, C., Chen, S.-E., Material development for a sustainable precast concrete block pavement, Journal of Traffic and Transportation Engineering (English Edition) (2016), doi: 10.1016/j.jtte.2016.09.001.

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1 Original research paper

2 Material development for a sustainable precast

3 concrete block pavement

5 R. Bharathi Murugana*, C. Natarajana, Shen-En Chenb

6 a Department of Civil Engineering, National Institute of Technology, Tiruchirappalli, Tamil Nadu, India

7 b Department of Civil and Environmental Engineering, University of North Carolina at Charlotte, Charlotte,

8 NC 28223, USA

9 Abstract

10 Portland cement concrete (PCC) and asphalt concrete (AC) are the most common roadway and highway

11 construction materials which are more suitable for continuous slab pavements. The durability of these

12 materials is highly dependent on construction quality and techniques, and both materials are difficult to

13 repair. Heavy rain storms in India have recently revealed several roadway pavement failures and resulted

14 in significant repair costs. Interlocking block type pavements are simpler to construct and maintain than

15 both PCC and AC pavements but, have only been used for slower traffic roads due to weak interlocking at

16 the joints. To improve the quality of block pavements, blocks made of PCC with waste tire crumb rubber

17 partially replacing river sand (fine aggregate) are suggested. The joint interlocks can be further improved

18 by modifying the block geometry. The material is completely recycled and is deemed more superior than

19 concrete pavements when repair and construction techniques and costs are concerned. This paper

20 presents the material characterization of Rubberized Concrete Blocks (RCB) using crumb rubber particle

21 size ranging from 0.075 mm to 4.75 mm to partially replace the fine aggregates. It also discusses the

22 advantages of RCB over continuous material pavements.

23 Keywords: Rubberized concrete; Crumb rubber; Damage mechanism; Material characterization and

24 Impact energy.

28 'Corresponding author. Tel.: +91 9488024542.

29 E-mail address: (R.B. Murugan).

32 1 Introduction

33 Conventional modes of roadway and highway pavement construction utilize predominantly in-situ, large

34 dimension and slab-based techniques with either Portland cement concrete or hot mixed asphalt concrete

35 (AC). Due to the wear, tear and abuses of daily traffic, paved roads experience usage damages and

36 require constant maintenance. For example, based on the 2010 capital spending estimate, the US spends

37 $65.3 to $86.3 billion annually for highway condition maintenance (US DOT, 2013). Furthermore, the

38 maintenance of roadways require extended traffic closure periods to complete the patching, overlaying,

39 cutting and curing of materials involved, all resulting in additional financial losses. The key disadvantages

40 of conventional roadway in-situ construction and maintenance are inconveniences to drivers and

41 additional costs associated with extensive site operations. In addition, there is also the seasonal

42 constraint to on-site constructions such as concrete curing or hot mix asphalt placement during low

43 temperatures, that can result in sub-standard products. An alternative pavement technology is the use of

44 block pavements. Despite advances in concrete block pavement technologies, the use of concrete block

45 pavement (CBP) remains limited and must be promoted.

46 State-of-the-art reviews of CBP technologies indicate that modern CBPs' have excellent engineering

47 properties and low life cycle costs. They are easy to construct and maintain, and have a very good

48 aesthetic appearance as compared to conventional pavements (i.e., concrete and asphalt). Additionally

49 CPB's can be easily replaced, thus minimizing the waste of materials and time for construction. This last

50 advantage makes CPB's more sustainable than conventional pavements.

51 The durability of CPB is mainly dependent on the quality and strength of the paving block. However,

52 the block-block interface conditions are also critical to the overall performance of the pavement. The

53 paving blocks can be produced in different grades of concrete, shapes and sizes (Shackel, 1990). Several

54 standards and specifications, such as the Indian Standards (Bureau of Indian Standards, 2006), the

55 British Standards (BS EN 1338:2003) (British Standards Institution, 2003), the ASTM C936/C936M

56 (ASTM, 2015), are available for the detailed definition and basic requirements of the paving blocks. In

57 earlier global standardization efforts, Houben et al. (1984) gave a comprehensive review of all published

58 standards, which documented block thickness of 140 mm in some cases.

59 For typical applications, the small element of precast paving unit is used as a surface course and the

60 bedding sand provides a more flexible response compared to conventional pavements (Singh et al., 2012).

61 Thus, the following factors can influence the structural performance of CBP: (1) paving blocks (i.e., shape,

62 size, thickness and laying pattern); (2) bedding sand (i.e., thickness, grading, angularity and moisture

63 content); (3) base and sub-base (i.e., material type and thickness); and (4) sub-grade (i.e., material type

64 and strength) (Soutsos et al., 2011). Joints can be filled with sand to enhance the interface friction.

65 Polymer filler material can be used to stabilize the joint sand and reduce water infiltration.

66 Loading frequency and scenarios are also critical to the durability of block pavements. The standard IS

67 15658:2006 clearly indicates that the strength and thickness of paving blocks are decided based on the

68 traffic volume. For high volume traffic roads, there is a need to carry large amounts of load, thus requiring

69 stronger and thicker paving blocks. The sub-base and bedding sand thickness are selected based on

70 required bearing capacity of the base course design. For base course with lower bearing capacity, then

71 the required sub-base and bedding sand materials would be more.

72 Manufactured paving blocks have a high compressive strength, but they can still fail during heavy

73 traffic loads due to weaknesses and result in spalling and cracks. Therefore, CPBs require high flexural

74 strength and toughness to sustain a heavy traffic load. However, it is difficult to improve the flexural

75 capacity of conventional concrete block without modifying its material properties. Therefore, there is a

76 need to modify conventional concrete ingredients to improve the toughness of the paving block. In this

77 paper, waste tire crumb rubber mixed with conventional concrete is suggested as a sustainable way to

78 improve block toughness. The result is a Rubberized Concrete Block Pavement (RCBP), which has been

79 shown to have a good resistance to cracking and fracture as compared to conventional concrete (Li et al.,

80 2004; Ling et al., 2009b).

81 Toughness is a parameter that describes the fracture response at a sudden impact load. The

82 toughness of paving blocks can help quantify their resisting properties to cracking induced by frequent

83 wheel impacts. In this study, crack resistance is evaluated based on the impact test suggested by ACI 544.

84 2R-89. As seen from the test results collected, the impact energy of the paving block is calculated for the

85 first cracking load and the load at complete failure. The ductility index is also measured from the first crack

86 and failure impact energy.

87 The authors of this paper focus on fundamental studies of concrete material modification with the

88 partial replacement of fine aggregates with crumb rubber from waste tires. Crumb rubber is made of

89 shredded waste tires, and, is thus a waste reduction technique to sustains the living environment. Waste

90 tire utilization has been studied as early as the 1990s (Siddique and Naik, 2004). The main advantages of

91 crumb rubber utilization in concrete include lower density, higher impact and toughness resistance,

92 enhanced ductility, and better sound insulation. However, waste tires are very difficult to handle because

93 they are not naturally biodegradable (El-Gammal et al., 2010; Issa and Salem, 2013; Khaloo et al., 2008).

94 Out of the three conventional methods of waste tire handling (i.e., reuse, burning and dumping), the

95 burning of waste tires results in large amounts of Co, NO^ and SO^ emissions. Dumping waste tires can

96 also create serious land hazard and settlement effects (EPA, 1999).

97 Previous efforts to use waste tire for construction applications involved shredding the waste tires into

98 small particles, then using them as concrete aggregate replacements (Siddique and Naik, 2004). In this

99 paper, the authors explore the possible use of waste tire crumb rubber as a partial replacement of fine

100 aggregates by volume in pavement blocks. The study focuses on the use of rubberized concrete blocks in

101 roadway pavement applications.

102 2 Damage mechanisms of pavements

103 Fig. 1 demonstrates the different conceptual failure modes involved in PCC pavement, AC pavement and

104 CBP pavements. In contrast to both PCC and AC pavements, block pavements involve joint action, which

105 may result in hinge formation. This presents the blocks with stress release and preserves their integrity.

106 AC pavement behavior is significantly affected by surface temperature due to solar radiation and ambient

107 conditions, where as such thermal effects are less pronounced in PCC and CBP pavements. RCBP and

108 CBP pavements share similar damage mechanisms. Both AC pavements and RCBP may involve crack

109 tip blunting due to the presence of rubberized material (i.e., rubber in tire and bituminous material in

110 asphalt). As seen in Fig. 1(b), concrete block pavement can be designed to optimize the flexural behavior

111 of the block pavement system and moderate interactions between block and joint behaviors.

Important aspects of rubberized concrete are possible strain softening and fracture arrest mechanisms due to the presence of rubber shreds within the concrete material which is not shown in Fig. 1. A previous study has shown that rubber shreds can reduce the plastic shrinkage cracking of concrete, which can significantly enhance its durability (Twumasi-Boakye, 2014). The proportioning of amount of rubber shreds can help reduce shrinkage behavior and optimize material performance. This study characterizes the block behavior with different proportions of rubber shred mix. (a) (b)

Wheel load i

Single layer PCC pavement

Hinge formation

Dimple rupture for clearagel

Void coalescence for first crack advancing

Void nucleation and growth ;

Stretch zone development:

Plastic zone formation: Notch + fatigue crack :

¡00 o „ooo

O) . «

u S G £

CO O £ ^ w £ £ U


Í-H to

Crack at steady stage

'Onset of facture instability (crack initiation)

/Crack tip blunting

Crack growth A a

122 Fig. 1 Failure modes of different pavements. (a) PCC pavement. (b) Concrete block pavement (Soutsos et

123 al., 2011). (c) AC pavement (Tang, 2014).

125 3 Materials and methods

126 3.1 Materials

127 Ordinary Portland cement 53 grade (OPC 53) conforming to IS 12269:1987 is used throughout this study

128 (Bureau of Indian Standards, 1987). The cement properties were determined, and test results are

129 summarized in Table 1. River sand was used as the original fine aggregate. River sand properties are

130 defined per IS 383:1970, where the specific gravity was found to be 2.65 and fineness modulus of 2.45

131 was used (Bureau of Indian Standards, 1970). Crushed granite stones with a maximum size of 20 mm,

132 specific gravity of 2.63 and fineness modulus of 7.2 were used as coarse aggregates. The shredding of

133 waste tires produced crumb rubber particles that passed through a sieve size of 4.75 mm and was

134 determined to have specific gravity of 0.689.

135 Table 1 Cement properties.

Sl. No. Properties Results IS 12269:1987 requirements

1 Normal consistency 31% -

2 Specific gravity 3.14 -

3 Initial setting time (min) 65 Not < 30

final setting time (min) 280 Not > 600

4 Fineness (m2/kg) 320 225

5 Compressive strength

7 d (N/mm2) 38.60 37.00

28 d (N/mm2) 56.96 53.00

137 3.2 Mix proportion

138 UNI-Paver 50 mm thick paving blocks were manufactured at a local plant for compressive strength and

139 flexural strength tests. To determine the static strength and moduli parameters, cylinders with a 150 mm

140 diameter and 300 mm height were cast. An M20 grade concrete with a cement, fine aggregate and coarse

141 aggregate ratio of 1:1.89:2.88 and water to cement ratio of 0.5 were used as the control. Table 2 shows

142 the concrete mix design used in this study.

143 Table 2 Concrete mix design.

Sl. No. Mix ID Crumb rubber replacement (%) Mix ratio C:FA:CA:CR Slump (mm)

1 R0 Control mix 1:1.89:2.88:0.00 48

2 R5 5% FA replaced by CR 1:1.78:2.88:0.09 50

3 R10 10% FA replaced by CR 1:1.71:2.88:0.18 52

4 R15 15% FA replaced by CR 1:1.62:2.88:0.27 56

5 R20 20% FA replaced by CR 1:1.53:2.88:0.36 61

6 R25 25% FA replaced by CR 1:1.44:2.88:0.45 69

144 Note: C: Cement; FA: Fine aggregate; CA: Coarse aggregate; CR: Crumb rubber.

146 3.3 Test methods

147 In this paper, waste tire fines are mixed in PCC blocks with different percentage replacements of fine

148 aggregates (i.e., 5%, 10%, 15%, 20% and 25%). The blocks were then tested for compressive strength,

149 flexural strength, static modulus of elasticity and impact energy. The results comparing concrete with

150 crumb rubber and normal concrete without rubber are presented in the following.

151 The compressive strength and flexural strength test was performed in accordance with IS 15658:2006

152 and the static modulus of elasticity test was performed in accordance with IS 456:2000 (Bureau of Indian

153 Standards, 2000, 2006). The IS 456:2000 recommends an empirical relation between the static modulus

154 of elasticity and compressive strength of concrete, expressed below as Eq. (1).

160 161 162

168 169

E = 5000f (1)

where Ec is static modulus of elasticity in MPa, fck is characteristic compressive strength of concrete at 28 d in MPa. IS 456:2000 further suggests that the flexural strength, f, of concrete can be defined as Eq. (2).

f = 0-7f (2)

Guidelines from ACI committee suggest that the impact energy from a load can be determined via the free fall of a drop weight onto the center of at paving block (ACI, 1999). A 4.54 kg weight was lifted to 0.457 m above the specimen and then released. The drop weight impact testing machine is shown in Fig. 2. The weight was dropped repeatedly, and the blows required to produce the first visible crack and complete failure of the specimens were noted. The impact energy is then calculated for each paving block using the following equation.

v = V 2(0.9 g )h

where U is impact energy, n is number of blows, m is weight of the hammer (4.54 kg), v is drop weight hammer velocity, g is gravitational acceleration, and h is drop height (0.457 m). A factor of 0.9 was used to account for the effect of air resistance and friction between the lifting weight and guided rails.



Base plate

171 Fig. 2 Impact testing machine.

173 4 Material characterization results

174 4.1 Workability

175 Table 2 shows that the addition of crumb rubber increased the concrete's slump, indicating that the crumb

176 rubber improved the workability of the concrete material. Since crumb rubber does not absorb water as

177 compared to river sand, less water is needed for rubberized concrete to achieve good workability.

179 4.2 Compressive strength

180 The 28-day compressive strength, on the other hand, reduced with increasing crumb rubber replacement.

181 Fig. 3 shows the decreasing strength versus increasing rubber replacement. This observation is

182 consistent with several previous studies. 25% of rubber replacement represents a strength reduction of

183 nearly 50%. The decrease in 28-day compressive strength of concrete with 5%, 10%, 15%, 20% and 25%

184 waste tire crumb rubber was observed to be 7.85%, 13.34%, 21.92%, 29.90% and 46.44%, respectively,

185 when compared to normal concrete without rubber replacement. The strength reduction due to crumb

186 rubber addition may result from the fact that at first the rubber particles are much softer than the cement

187 paste, resulting in rapid crack propagation around the rubber particles. This leads to failure in the rubber-

188 cement matrix. Since rubber particles have more air content, they can increase the voids within the

189 concrete and decrease the compressive strength of the paving block (Al-Mutain et al., 2010; ; Guneyisi et

190 al., 2004; Khatib and Bayomy, 1999).

5 10 15 20

Crumb rubber content (%)

Fig. 3 Compressive strength as a function of crumb rubber replacement. 4.3 Modulus of elasticity

200 201

202 203

To determine the rubber crump replacement effect on the Young's modulus, a value is computed from Eq. (1) and compared to the test results, which are shown in Fig. 4. The modulus for normal concrete is 29.43 MPa at 28 d, and the modulus decreases with increasing rubber content. Fig. 4 clearly shows that the measured moduli of elasticity are lower than the calculated values. Generally, normal concrete is more brittle when the modulus of elasticity is higher, and concrete mixed with a large volume of rubber is more ductile or flexible when the modulus of elasticity values are lower (Ling et al., 2009a). Therefore, it is proven that the addition of a low volume of crumb rubber into concrete notably increases the modulus of elasticity.

S 30 fr 25

I 20 %

[723 By experiment

Fwl By experience (IS 456:2000)

R0 R5 RIO R15 R20 R25 Mix ID

Fig. 4 Static modulus of elasticity as a function of crumb rubber replacement.

205 4.4 Flexural strength

206 A comparison of flexural strength and the computed values from Eq. (2) is shown in Fig. 5, where the

207 experimental results peak at 5.2 MPa for R15 rubber replacement concrete. The improvement in flexural

208 strength is limited to relatively small amounts of rubber crumb. In general, normal concrete is more brittle

209 with a higher modulus of elasticity when compared to rubberized concrete mixed with large volumes of

210 rubber, thus demonstrating a more flexible behavior (Ling et al., 2009a). However, empirical results

211 according to IS 456:2000 show a consistent decreasing flexural strength with increasing rubber

212 replacement contents, which contradicts the experimental results.

■G 4


1223 By experiment

Km By experience (IS 456:2000)

R0 R5 R10 R15 R20 R25 Mix ID

Fig. 5 Flexural strength as a function of crumb rubber replacement.

215 The authors believe that the flexural strength increase of RCB concrete demonstrates a possible

216 bridging of rubber within the fracture zone, resulting in the arrest of fracture propagation. This

217 phenomenon is described as "strain hardening" in fiber-reinforced concrete under tension, where the

218 tensile behavior has demonstrated the fiber bridging within propagating cracks (Fantilli et al., 2009).

219 Soranakom and Mobasher (2007) describe the post-crack flexural responses of fiber reinforced concrete

220 as "deflection softening" or "deflection hardening" because of the effective activation of tensile responses

221 within the embedded fiber bridging, which is a function of the amount of fiber and the anchor strength of

222 the fibers. The material characterization tests performed in this study demonstrate the flexural

223 performance of RCB material, validating earlier speculation that block pavements using RCB can benefit

224 from both the joint interaction and flexural strength of individual blocks.

226 4.5 Impact energy

227 The number of blows required to produce the first visible crack and complete failure for each type of

228 paving block are presented in Table 3. Based on the number of blows the first crack impact energy and

229 failure impact energy were calculated using Eq. (3) and plotted in Fig. 6. Compared to conventional

230 concrete paving blocks, the first crack impact energy increased by 34.48%, 51.23%, 71.92%, 91.62% and

231 112.31%. The failure impact energy increased by 35.81%, 53.02%, 74.88%, 96.27% and 118.14% to 5%,

232 10%, 15%, 20% and 25% of sand replaced by crumb rubber by volume, respectively.

234 Table 3 Impact test results for plain and rubber mixed concrete.

Mix ID No. of blows Average no. of blows Impact energy (J) Average impact energy (J) Ductility Index Average ductility index

First crack Failure First Failure crack First crack (N1) Failure (N2) First First crack crack N2/N1 Average of N2/N1

22 25 399.96 454.50 1.136

23 25 418.14 454.50 1.086

R0 26 27 24.2 25.6 472.68 490.86 439.96 465.41 1.038 1.059

22 22 399.96 399.45 1.000

28 29 509.04 527.22 1.035

39 41 709.02 745.38 1.051

36 42 654.48 763.56 1.166

R5 38 43 38.2 41.4 690.84 781.74 694.48 752.66 1.131 1.085

38 40 690.84 727.20 1.052

40 41 727.20 745.38 1.025

45 48 818.10 872.64 1.066

48 49 872.64 890.82 1.020

R10 46 48 45.6 49.6 836.28 872.64 829.01 901.73 1.043 1.091

47 49 854.46 890.82 1.042

42 54 763.56 981.73 1.285

51 56 927.19 1018.09 1.098

52 57 945.37 1036.27 1.096

R15 54 62 52.6 58.0 981.73 1127.17 956.27 1054.45 1.148 1.102

56 60 1018.01 1090.81 1.071

50 55 909.01 999.91 1.100

59 66 1072.63 1199.89 1.118

60 65 1090.81 1181.71 1.083

R20 62 69 59.2 65.4 1127.17 1254.43 1076.26 1188.98 1.112 1.104

58 64 1054.45 1163.53 1.103

57 63 1036.27 1145.35 1.105

63 70 1145.35 1272.61 1.111

65 72 1181.71 1308.97 1.107

R25 66 73 63.8 70.8 1199.89 1327.15 1159.89 1287.15 1.106 1.109

64 70 1163.53 1272.61 1.093

61 69 1108.99 1254.43 1.131

E3 First crack E23 Failure

R0 R5 RIO R15 R20 R25 Mix ID

Fig. 6 Impact energy of paving block.

239 With an increasing replacement percentage of shredded rubber, there is an increase in the impact

240 energy of paving blocks, which is observed by other researchers such as Nilli and Afroughsabet (2010),

241 Yildirim et al. (2010), and Al-Tayeb et al. (2012). This trend holds true for both impact energies at first

242 crack and at failure. The impact resistance of R25 is approximately twice that of R0 because crumb

243 rubber absorbs more energy. This proves that rubber acts as a fibre and an effective crack arrestor, when

244 an impact load is encountered. Thus plain concrete exhibits an early brittle failure when compared to fibre

245 reinforced concrete which shows better ductile properties (Swamy and Jojagha, 1982). The failure mode

246 of concrete depends on the cement matrix strength, aggregate strength and bond strength of the fibre with

247 aggregate matrix.

248 4.6 Ductility index

249 There are different definitions for ductility index including one based on displacement measurements

250 (Maghsoudi and Bengar, 2011). In this case, the ductility index is defined as the ratio of energy absorbed

251 at failure to energy absorbed at first crack (Senthilvdivel et al., 2014). Fig. 7 shows variations in the

252 ductility index of the wet cast paving blocks based on the crumb rubber replacements at various

253 percentages. An increase in the ductility index value is observed when the percentage of crumb rubber in

254 concrete mix increases. The percentages of sand replacement by crumb rubber (i.e., 5%, 10%, 15%, 20%

255 and 25%) and the associated increases within the ductility index are 0.93%, 1.16%, 1.82%, 2.3% and

256 2.94%, respectively.

R0 R5 RIO R15 R20 R25

257 Mix ID

258 Fig. 7 Ductility index of paving block.

260 5 Discussions

261 A modified block response diagram is shown in Fig. 8 to demonstrate the micro-macro behavior of the

262 likely moderation of block flexural responses and joint interlocking (hinge formation) mechanisms that

263 resist over-bearing wheel loads. As shown in Fig. 8, the block/joint system provides a more uniform

264 response against wheel loads with flexural hardening, and, at the same time, allows block separation at

265 the ultimate load. Thus, a stronger response system is created using RCB's.

Flexural bending

267 Fig. 8 Flexural hardening and joint interlock in the load bearing mechanism of RCBP.

269 The current study only involves the testing of a single block element and does not accurately reflect

270 the block-block-base interactions. Fig. 8 shows that the flexural response of the loaded individual block

271 may lie opposite to the formation of the joint hinge, resulting in reduced stress at the joints. This

272 mechanism is missing in continuous slab pavements and further proves the advantage of using blocked

273 pavements in roadway loading. However, such tests require multiple block elements and are beyond the

274 scope of this paper.

275 Additional enhancements to improve the impact resistance of pavement blocks, including the

276 placement of black toppings on block pavements have also been introduced for airplane runways, which

277 can also be considered for highway and road way applications.

279 6 Summary and conclusions

280 This paper dicusses a series of tests conducted to characterize concrete pavement blocks made with

281 partial replacement of fine aggregates with waste rubber in the form of fine shredded crumbs. The tests

282 conducted include strength tests and determinations of the modulus of elasticity and compressive and

283 flexural strengths. Comparisons to conventional concrete blocks include derived parameters, such as the

284 impact energy and ductility index. The test results support the initial assumption that rubberized concrete

285 pavement blocks have superior toughness and strength compared to conventional concrete blocks. These

286 blocks help mechanize the combined load bearing mechanisms that combine the hinge formation at joints

287 and flexural bending of blocks. Observations from this study are summarized as follows.

288 • A series of tests investigate the behavior of concrete containing fine waste tire crumb rubber. The

289 following conclusions are drawn based on the test results of this study, which show that there is

290 an increase in slump values when crumb rubber content increases up to 25%. This means that

291 the workability of rubberized concrete improves due to the addition of rubber crumbs and is

292 acceptable in terms of the ease of handling, the placing and finishing of wet concrete as

293 compared to normal concrete.

294 • Compressive strength is reduced with increasing rubber content, and the static modulus of

295 elasticity of rubberized concrete is lower than normal concrete. However, the flexural strength of

296 concrete increases up to 15% of the crumb rubber replacement. When the percentage of crumb

297 rubber replacement increases over 15%, the flexural strength begins to decrease. An explanation

298 may be based on tension strain hardening.

299 • If the suggested fracture arrest by the embedded rubber crumb/fiber, then the integration of

300 flexural hardening and joint interlocking would make RCBP a superior roadway pavement system.

301 Future studies should focus on demonstrating the global behaviors of a block pavement system

302 with joint response monitoring.

303 • The impact resistance of the paving blocks was calculated in two stages: (i) first cracks impact

304 resistance and (ii) failure impact resistance. Both stages of impact resistance were increased by

305 the replacement of sand with crumb rubber up to 25% by volume of sand. The ductility index also

306 increased when the crumb rubber content increased up to 25%.

307 • The incorporation of rubber content to concrete, changes, the failure pattern from a brittle mode to

308 ductile mode, which displays the beneficial effects of Portland cement block with crumb rubber,

309 used in absorbing vibrations.

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R. Bharathi Murugan holds a M. E (Structural Engineering), is pursuing his PhD at National Institute of Technology, Tiruchirappalli, Tamil Nadu, India. His research interests include special concretes, sustainable construction materials, pavement materials and utilization of waste materials in concrete.

Dr. C. Natarajan holds PhD degrees in civil engineering from IIT Madras, India. He is a professor in the Department of Civil Engineering at National Institute of Technology, Tiruchirappalli, Tamil Nadu, India. His research interests pertain to the domains of forensic investigation, size effects on beam, traditional structures, corrosion resistance in concrete and pavement materials. His publications in these areas are well cited. 398

Dr. Shen- En Chen holds PhD degrees in civil engineering from West Virginia University, USA. He is a professor in the Department of Civil and Environmental Engineering at University of North Carolina at Charlotte, USA. His research interests pertain to the domains of power transmission structures, carbon storage in geological formations, remote sensing for bridge monitoring and forensic investigation His publications in these areas are well cited.