Long Term Strength of Rubberized Concrete Paving Blocks

7/28/2019 Long Term Strength of Rubberized Concrete Paving Blocks

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Original citation:

Ling, T.-C., Nor, H.M., Hainin, M.R., Lim, S.-K. (2010) Long term strength of rubberisedconcrete paving blocks.Proceedings of the ICE- Construction Materials; 163 (1): 19-26.http://www.icevirtuallibrary.com/content/article/10.1680/coma.2010.163.1.19

Long term strength of rubberized concrete paving blocksT. C. Ling*, H. M. Nor, M. R. Hainin, S. K. Lim

Abstract

The aim of this study was to investigate the long term strength of rubberized concrete pavingblocks (RCPB). The effect of three curing conditions on compressive strength was studied.Additional strength tests which included flexural and splitting tensile strength were conductedto determine the strength characteristics and to enhance the understanding of the RCPB prop-erties. Four batches of RCPB that replaced sand volume with crumb rubber at 0%, 10%, 20%and 30% were produced in a commercial plant. The results showed that 10% replacement ofcrumb rubber did not show any significant change in compressive strength but slightly im-proved the flexural strength. As the rubber content exceeded 20%, RCPB would cause a great

reduction in strength although ductility increases greatly. It was found that the RCPB speci-mens tested remained intact after failure and did not shatter. Thus, this would be beneficial fortrafficked pavement.

1. Introduction

In engineering and transportation sector, one of the wastes generated is scrap tyres and thisposes serious environmental problem. Recent statistics indicated that there was more than100% increase in the number of registered vehicle in Malaysia within ten years. Therefore, ahuge quantity of waste tyres were abandoned throughout the country annually, which indirect-ly created several problems: (a) become mosquito breeding places, which posed health risks;(b) occupied extensive space in landfills; (c) fire hazard, which would contaminate the air and

soil. In addition, environmental concerns also make it more important to seek and identifyuseful economic and environmental friendly methods for managing these waste tyres in differ-ent applications.

It is no longer a new phenomenon to divert discarded waste tyres into useful material inconcrete for a long term solution. Furthermore, this effort contributes to reservation of naturalmaterials such as aggregate for concrete production. In addition, the main characteristics ofwaste tyres are low density, low stiffness and high deformation, which may improve the prop-erties of normal concrete because it is always a challenge for researchers to design and pro-duce hardened concrete with light weight, high strength and high toughness for concrete blockpavement application.

Various laboratory investigators have shown that the addition of rubber aggregate in wet-cast concrete mixture produces a reduction in the mechanical strength of the rubberized con-

crete.1-13 However, no published data were found in the literature on semi dry-cast rubberizedconcrete produced at commercial plant facilitated with high pressure and vibration makingmachine. In addition, most researches investigated the particular curing conditions for initial28-day, 1-11, 90-day12 and 180-day 13 strength of rubberized concrete.

Tautanji discovered that the incorporation of the rubber aggregates in concrete resulted in areduction of compressive strength of up to 75% and a smaller reduction in flexural strength ofup to 35%.1 Kaloush et al. also showed that the rubberized concrete mixtures lowered thecompressive strength more than the flexural strength at same mixture ratio.2


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First author: [email protected] ; [email protected] Page 2

Eldin and Senouci reported that there were reductions in strength of up to 85% of the com-pressive strength and 65% of the tensile strength were observed when the coarse aggregatewas fully replaced by rubber aggregate. 3 It was found that the reduction in compressivestrength was higher than splitting tensile strength with the increase of rubber aggregate vo-lume content. This early finding was supported by later investigations conducted by some au-thors. 4,5,12

The present experimental study was therefore designed to investigate the effects of curingconditions on the long term compressive strength, flexural and splitting tensile strength ofsemi dry-cast concrete paving block (CPB) produced in a commercial plant. By using a ma-chine with high pressure and vibration facilities, the CPB is expected to be a much more con-sistent product to achieve better dimensional and improved strength. The relationship betweencompressive strength, flexural and splitting-tensile strength in long term performance was in-vestigated and reported.

2. Methods

2.1. Materials

The raw materials used to develop the RCPB and control concrete paving blocks (CCPB)

mixes in this study comprised cement, aggregate, coarse sand, fine sand and crumb rubber.Ordinary Portland cement (OPC) was used throughout the study. The physical and mechanicalproperties of both sand and aggregate are given in Table 1. Crumb rubber is a fine materialand is produced by mechanical shredding with the gradation close to that of sand. Two par-ticle sizes of crumb rubber were used: 1 3 mm and 1 5 mm as partial substitute for finesand and coarse sand in the production of face layer and body layer on CPB, respectively. Theunit weight of 1 3 mm and 1 5 mm dense crumb rubber were 596 kg/m 3 and 606 kg/m3,respectively.

Table 1. Physical and mechanical properties of sand and aggregate

PropertyCCPB & 10-RCPB 20-RCPB & 30-RCPB

Fine sand Coarse sand 3/8" aggregate Fine sand Coarse sand 3/8" aggregate

Silt content (%) 5.61 5.71 - 5.61 7.62 -

Moisture content (%) 5.22 8.5 - 5.22 8.95 -

Fineness modulus 1.77 3.02 - 1.77 2.86 -

Passing 10mm (%) - - 86.15 - - 98.18

Passing 5mm (%) - - 16.18 - - 12.41

Flakiness index - - 17.08 - - 22.07

2.2. Sample preparation

In this study, all samples were manufactured commercially using a mechanized mouldingmachine. Two independent mixers were used with different capacity and worked in parallel toensure facing layer being added for appearance. Table 2 shows the mixing ratio for the com-

ponents of these RCPB. Initially, aggregate, coarse sand, cement and crumb rubber weremixed in body mix mixer, water was then added to the materials and mixed again until the de-sired moisture content for these mixtures was obtained.

The mixtures were transferred from the pan mixer to a feed hopper and closely controlledby an automatic weighting system. The hopper discharged the correct amount of mixture intosteel moulds with internal dimensions of 210 mm length, 105 mm width and 60 mm depth.The mould was filled by the body mix, vibrated and pressed. The face mix was poured intothe mould for second layer, and then final compaction and vibration were applied to ensure


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3

+

=

87.1

5

H

AA

W

C

that uniform concrete was produced. The hydraulic ram was released out of the mould onto amoving conveyor belt and was then loaded onto a rack for curing.

Table 2. Mixing ratio

Mix sym-

bol

Mix proportionCement content

(kg/m3)w/c ratio Rubber content (%) Demolded

fresh density

(kg/m3)Facing(C:S) Body(C:A:S) Facing Body Facing Body Facing Body

CCPB 1:2.3 1:1.8:3.8 617 328 0.23 0.45 0 0 2170

10-RCPB 1:2.1 1:1.8:3.4 585 317 0.23 0.43 8.8 9.7 2140

20-RCPB 1:1.9 1:1.8:3.0 604 274 0.29 0.48 21.6 19.4 2100

30-RCPB 1:1.7 1:1.8:2.6 574 286 0.26 0.39 30.4 29.0 2030

2.3. Curing condition

All the samples prepared in this study were cured under elevated curing temperature for thefirst day. The samples on pallets were then removed from the roller-conveyors mounted on theoutlet side of the press, and on to a lowerator. All samples were then collected and cured atroom temperature for 3, 7, 28, 91,182 and 365 days before being tested. For normal concrete,

curing plays an important role for strength development. The properties and performance ofconcrete are affected under situations where environmental temperatures during concretingand subsequent curing periods are markedly different from those in normal conditions. Thus,three types of curing were adopted in the compressive strength test; mainly (i) air curing, (ii)water curing and (iii) natural weather curing which are described as follows:

(i) Natural air curing in laboratory. Average temperature at 30C with 65% rela-tive humidity.

(ii) Continuous water curing at 26C.(iii) Tropical climate outside laboratory. Temperature ranged from 26C (rainy day)

to 38C (hot day) with humidity ranges from 25% (hot and dry) to 90% (wet).

2.4. Compressive Strength

Almost every country actively involved in the manufacturing of CPB specifies compressivestrength as the most important property to be achieved.14-17 Therefore in this study the com-pressive strength was determined using a Universal Testing Machine with a maximum capaci-ty up to 3000 kN. The load was applied to the nominal area of CPB. Prior to the loading test,the CPB was soft capped with two pieces of plywood. The compressive strength of each spe-cimen was calculated according to the Eq. (1) in MA 20.14 The characteristic strength of fivepaving units based on Eq. (2) is used to determine the reported value. Such a sampling schemeis commonly termed as a variable sampling scheme, as acceptance is based on the variationin property values which are assumed normally distributed.

(1)

Where C is compressive strength, MPaW is total load at which specimen fail, NH is nominal height of paving unit, mmA is nominal gross plan area, mm

2


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( )DlFk

T

=

868.0

l

FP =

( )4

252

52

42

32

22

1CCCCCC ++++

=

5 54321

CCCCC ++++

=

C

sCk

C 65.1=

(2)Where Ck is the characteristic compressive strength of the lot under test

is the average compressive strength of 5 paving units

s is the unbiased standard deviation of 5paving units

2.5. Splitting tensile strength

A splitting tensile strength is established to derive material strength rather than unit strengthfor CPB according to BS 6717:2001.18 These paving units are tested over the length in orderto test as much as material of the CPB as possible. It measures the ability to resist a shear

force which is the tension generated for instance, in case of spalling. This results also in alarge breaking-surface that can be inspected visually.However, the splitting test has also its limitations. It is very sensitive towards the size of

the aggregate, although this can be seen as an advantage as it causes the splitting test to be abetter performance-related test. Moreover, it is more thickness dependent than the compres-sive strength. This limitation can be overcome by using a correction factor, as shown in Eq.(3).

In this test, theINSTRONUniversal Test Machine with a data acquisition system was used.The loading rate 1.0 mm/min was set for these specimens. The air cured specimens were pre-pared for testing by recording the average of three separate measurements of the specimenslength and thickness. Also required for the splitting tensile tests were two rigid bearers withcontact surfaces having a radius of 75 mm, and two plywood bearing strip (measuring 15 mm

wide, 4 mm thick and 230 mm long) centred between the platens while the test specimen wascentred on top of the plywood strips. Another plywood strip was centred on top of the speci-men and the specimen was then loaded.

Upon failure, the maximum applied load was recorded to calculate the splitting tensilestrength (T) of the specimen according to the following formula:

(3)Where T is the braking load, N

l is the length of the failure plane, mmt is the thickness of the specimen at the failure plane, mmk is the correction factor for the thickness, calculated form the

equation k= 1.3 30(0.18 t/1000)2

The breaking load per unit length of the failure plane, F, in newtons per millimetre(N/mm) was calculated from the following Eq. (4)

(4)


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5

22

3

BD

LF=

l=

F

BD

LE

34

3

2.6. Flexural strength

The compressive strength and splitting tensile strength of CPB, when measured as de-scribed above, are dependent upon the height of the paving units. Generally, the thinner thepaving unit the greater will be the measured strength. Flexural (three-point bending) strength,however, is not affected by paving unit thickness. For this reason, flexural strength is pre-ferred as an index of strength. The test is simpler and consequently cheaper than compression

test. Flexural strength could be regarded as a better criterion for wearing and weathering resis-tance.

There is no doubt that a CPB is more prone to break under traffic (fail in bending) than tobe crushed (fail under compression). Because in normal practice, the CPB were laid in either90 or 45 herringbone pattern to provide geometric lock up on four sides, tend to resist thetendency to lift out but consequently to break of the individual block. Therefore it is essentialto carry out this test because it seems to be a more suitable quality indicator.

Flexural test is when a rectangular CPB is subjected to a transverse force, perpendicular toits longitudinal axis, producing shear and tensile stresses in the CPB. A center line wasmarked on the top of the specimens, using a black felt-tip marker perpendicular to its length.The CPB was tested under a central line load simply supported over a span of 150 mm. 15,18,19

For this test, INSTRONUniversal Test Machine was used as in the splitting tensile strengthtest. A displacement of 0.30 mm/min was set. Each value represents the average of three sam-ples.

During the test, while the load was applied to a center point pivot rod to the specimenwhile being supported by a two support rods until rupture occurs, the deflection and energyabsorption were automatically recorded in the data acquisition system, modulus of rupture(MOR) and modulus of elasticity (MOE) were then calculated. The MOR is as shown in Eq.(5) and expressed in MPa:

(5)

The MOE was calculated using Eq. (6) and expressed in MPa. In these equationsL is the span

length (mm), Fthe maximum applied load (N),B the average width of the sample (mm),D itsaverage thickness (mm), and its average length (mm).

(6)

3. Results and discussions

3.1. Compressive strength

Figs. 1 - 4 show the change in compressive strength of three curing regimes over time up to1 year at varied rubber contents. Fig. 1 shows that the rate of gain in strength is rapid up to 28days of three curing regime. It then slows down with additional curing time. For the 182-day

strength, there was an improvement of about 35%, 37% and 47% over the 28-day strength ofnatural weather, air and water cured, respectively. This behaviour is largely due to the mix-tures low water/cement ratio with good quality finish which certainly produces high density(low air voids content) CCPB. However, the CCPB strength under water and natural weathercuring slightly dropped at 365 days of age.

Fig. 2 shows that the three curing regime obtained a similar strength at each curing days ofage. As the curing age increased, the compressive strength of the 10-RCPB also increased.However, 91-day and 365-day compressive strength indicated an opposite trend, which ob-served strength decreased at 91 days and then increased again at 182 days of curing age. The


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relative fluctuations in strength with time may be attributed to inherent variations of theseplant 10-RCPB product in the degree of compaction and in the initial accelerated curing andthe storage conditions.

Fig. 1. Development of CCPB compressive strength under different curing condition.

Fig. 2. Development of 10-RCPB compressive strength under different curing condition


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Overall, at 3 days of age, all the samples in CCPB and 10-RCPB met the 28-day compres-sive strength requirement of MA 20 (30 MPa) for 60mm thickness paving block to carry traf-fic load. The main reason for this could be no or small amount of rubber content in CPB andhigh compaction casting method in the commercial plant. From Fig. 3a, it can be observedthat there was effective adhesion between rubber particles and cement matrix. Therefore, itcan be considered that there is no effect upon strength for crumb rubber content less than 10%

by sand volume in 10-RCPB.

Fig. 3. Observation of undisturbed facture surface resulting from compression test (a) 10-RCPB and

(b) 30-RCPB.

As expected, the compressive strength of RCPB greatly depends on the crumb rubber con-tent. Figs. 4 and 5 indicated that as partial replacement of sand with crumb rubber exceeded20% by sand volume it resulted in a significant decrease of compressive strength and did notmeet the minimum strength requirement even until 365 days of age. This could be attributedto the large amount of rubber content in RCPB. At higher volume content of crumb rubberand high compaction during casting, the stress concentrations of the rubber aggregate (low

stiffness) in the RCPB were much higher than the surrounding aggregate particles. After com-paction, when the hydraulic ram was released, it resulted in many microcracks (see Fig. 3b)because rubber particles would be dense (high flexibility) and return to actual size causing therubber particles to bridge the crack surface. Loss of adhesion between the crumb rubber andthe surrounding cement paste also occurred.

Figs. 4 and 5 show that the rate of gain in strength is fairly rapid up to 7 days for air andnatural weather curing RCPB. However, the strength drop at 28 days and then increased again.It is noted that with the increase of curing age from 91 days to 182 days, the strength under airand water curing conditions improved at the same rate. On the other hand, natural weathershows a rapid strength gain from 91 days to 365 days of age by about 1.48 and 1.38 in ratio,for 20-RCPB and 30-RCPB respectively. Comparing the compressive strength of RCPB underthree curing conditions at the age of 365 days, natural weather curing gained the higheststrength followed by air curing and water curing.

In general, the negligible strength difference resulting from the three curing conditions in-dicated that air, water and natural weather curing did not show any significant effect on thestrength development of CCPB and all RCPB samples. However, at 365 days of age, air curedCCPB and 10-RCPB samples gained a the higher strength over natural weather and watercured, while natural weather cured 20-RCPB and 30-RCPB samples gained a higher strengthover air cured and water cured.


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Fig. 4. Development of 20-RCPB compressive strength under different curing condition.

Fig. 5. Development of 30-RCPB compressive strength under different curing condition

The compression tested samples for CCPB and RCPB after testing are shown in Fig. 6. Itcan be observed that the RCPB concrete does not exhibit typical compression failure beha-


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9

vior. The presence of rubber aggregate tends to hold the sample fragments together at fail-ure. This trend becomes more obvious as the rubber content increases.

Fig. 6. Compression tested samples for CCPB and RCPB.

3.2. Splitting tensile strength

The results of the splitting tension tests of the CCPB and RCPB are presented in Fig 7.The results show that the splitting tensile strength of the tested CPB samples varied be-tween 0.72 MPa and 5.25 MPa as the rubber content and curing age increased from 0% to30% and from 1 day to 365 days of age, respectively. It can be observed that the splittingtensile strength decreased with increasing rubber aggregate content in a similar manner tothat observed for the compressive strength. However, the drop in splitting tensile strength

was lower than that obtained when tested in compression. This can be explained throughthe softer rubber aggregate and bonding behaviour of the rubberized concrete matrix. Thisfinding agrees with those of previous investigations. The correlation of splitting tensilestrength and time was also found to be strong compared to the correlation in compressivestrength.

CCPB and 10-RCPB show that the rate of gain in splitting tensile strength up to 28 daysis rapid and there was considerable strength gain over time. Both 20-RCPB and 30-RCPBhad similar rate gain in splitting tensile strength which is slow at early age and then re-mained relatively constant from 28 to 365 days. Overall, the CCPB showed a slightly high-er strength than the 10-RCPB with partial replacement of 10% sand volume with crumbrubber. Both types of CPB exceeded the splitting tensile strength requirement described inBS 6717 at the early age (28 days). A great reduction of splitting tensile strength was ob-

served when rubber content reached 20% of the total sand volume. General average reduc-tion of approximately 53% and 75% of splitting tensile strength for 20-RCPB and 30-RCPB were observed, respectively. Therefore RCPB with higher content of crumb rubberfailed to meet the requirement for splitting tensile strength.

The splitting tension tested samples for CCPB and 30-RCPB are shown in Fig. 8. Itcan be observed that, as for the compressive strength tests, the RCPB does not exhibit typi-cal compression failure behaviour. The CCPB shows a clean split of the sample into twohalves, whereas the rubber aggregate tends to produce a less well defined failure.


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Fig. 7. Long-term splitting tensile strength development.

Fig. 8. Splitting tension tested samples for (a) CCPB and (b) 30-RCPB.

3.3. Flexural strength

As in the case of compressive and splitting tensile strengths, the relationship betweenflexural strength and rubber content with respect to the curing age was studied and the re-sults are shown in Fig. 9. The results show that the flexural strength slightly improved ap-proximately 10% for 10-RCPB compared to the 10-CCPB. The improvement in flexuralstrength is limited to relatively small rubber aggregate contents. This variation is unclearand difficult to ascertain on the basis of the published data. Despite this disparity, the testresults suggest that further investigation of the possibility of increased flexural strength isneeded. However, the previous investigations indicated the opposite trend, a reduction inflexural strength, even at low rubber contents. The low flexural strength obtained was dueto weak bonding between the cement paste and rubber particles.


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At higher volume of sand replaced by crumb rubber, the flexural strength was reduced by32% and 48% for 20-RCPB and 30-RCPB, respectively. Therefore, the relative flexuralstrength FR/FC (FR and FC being the flexural strengths of RCPB and CCPB, respectively) islower than that relative splitting tensile strength. All CPB specimens exceeded the flexuralstrength requirement prescribed by T-44 specification of 3 MPa from early age,21 exceptfor those made with the 30% replacement of rubber content which only achieved the value

from 182 days.As expected, the inclusion of crumb rubber decreased the MOE for the CPB. Generally,

CCPB and 10-RCPB mixed with low rubber volume tend to be brittle when MOE valuewas higher, and RCPB mixed with higher volume of crumb rubber tend to be ductile orflexible when MOE values were lower.

In all cases, it was found that the MOE increased as the modulus of rupture (MOR) in-creased. In Fig. 10, similar ratio of MOE to MOR was obtained for all RCPB samples re-gardless of the percentage used in the CPB. Therefore it can be explained that the additionof 10% crumb rubber significantly increased the MOR. The fact that existing CPB is muchweaker in tension than in compression makes rubberized CPB important and has potentialfor use in trafficked pavement application instead of sidewalks.

Fig. 9. Long-term flexural strength development.

The flexural strength samples for CCPB and 10-RCPB are shown in Fig. 11. Fig. 11ashows a clear breaking from the tension zone in the middle of the CCPB. However, it isobserved that for 10-RCPB, during the three points bending testing, initial cracking fromthe tension zone were apparent in the lower portion of the block. At the end of the testing,it was found that the block was not fully broken into two halves under the loss of bottomsupport condition (Fig. 11b). The enhanced toughness by adding rubber aggregate can alsobe demonstrated by the effort required to fully open the RCPB.


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Fig. 10. Modulus of elasticity versus modulus of rupture.

Fig. 11. Flexural tested samples for (a) CCPB and (b) 10-RCPB.

3.4. Splitting tension-compression, flexural-compression, and flexural-splitting tension

relationship

The correlation between splitting tension-compression and flexural-compression in thisexperiment are shown in Fig. 12. The correlation coefficient (R2) between the splitting ten-sile and compressive strength was 0.85 while for flexural and compressive strength, the(R2) was 0.92 which was much higher.

It was also found that the flexural strength of RCPB decreased with increasing rubberaggregate content in a manner similar to that observed for the compressive strength. How-ever, at higher strength, reduction rate of compressive strength was steeper than that of theflexural and splitting tensile strength.


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Similar to conventional concrete, RCPB specimens tested in bending (flexural strength)demonstrated a higher indirect tensile strength as compared to that obtained by splittingtension test. The results also confirmed that the relationship between tensile and compres-sive strength depends on the way in which the tensile strength is measured.

The average ratio of splitting tensile to compressive strength ranged from 0.106 to 0.102,0.102 to 0.089, 0.122 to 0.084 and 0.057 to 0.091, for CCPB, 10-RCPB, 20-RCPB and 30-

RCPB, respectively, as curing age increased from 1 day to 365 days of age. All the RCPB,except for 30-RCPB showed that the ratio continued to decrease with an increase in curingage, which means that compressive strength gain higher strength at the later age than thatobtained in splitting tensile strength. This tendency was particularly strong because the cor-responding strength was lower when the crumb rubber replacement ratio achieved 30%.

The average ratio of bending to compressive strength ranged from 0.127 to 0.137, 0.121to 0.145, 0.175 to 0.190 and 0.165 to 0.225, for CCPB, 10-RCPB, 20-RCPB and 30-RCPB,respectively, as curing age increased from 1 day to 365 days of age. These results indicatedthat curing age affects flexural more than compressive strength, leading to an increase inthe bending-compression ratio. Additionally, the later-age results confirmed the fact thatthe ratio of tensile to compressive strength increases as the rubber content in RCPB in-

creases.Since flexural test is found to give higher values for bending strength than splitting ten-sile test, it is always of interest to establish a relationship between the two parameters.Moreover, engineers and researchers have found the importance of the relationship be-tween splitting tensile and flexural strength. Therefore investigations were conducted todevelop a mathematical relationship between both strengths of the CPB in this study. Fig.13 shows the variation of the bending strength with the splitting tensile strength. The anal-ysis established an equation and is expressed as

= 0.90(T) + 1.5 (6)

Fig. 12. Relationship of long-term compressive strength to flexural and splitting tensile strength.


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Fig. 13. Long-term flexural strength versus splitting tensile strength.

4. Conclusions

The semi dry-cast production of RCPB at commercial plants did not pose any difficultiesin terms of mixing, casting, and that good quality finish can be achieved. However, increas-ing the rubber aggregate content from 20% increases the deformability of the mixture re-sulting in poor quality finish.

As expected, the target compressive and splitting tensile strengths were achieved for thecontrol and mixes incorporating low content of rubber aggregate. However, higher re-placement of sand with rubber particles, as in 20-RCPB and 30-RCPB, caused a great re-duction in strengths which is not steady and is inconsistent with those of previous investi-gations. The reduction in splitting tensile strength is found lower than that obtained incompression test.

The test results were similar to that observed from preceding strength tests, which showthat the use of rubber aggregate exceeded 20% in CPB produces a significant reduction inflexural strength. However, if the amount of rubber in the concrete is limited to 10%, anenhancement of flexural strength exists in RCPB which could be favorable for traffickedconcrete block pavements. However, 20-RCPB and 30-RCPB can still be produced withpotential use at places where high strength of concrete is not as important, such as side-

walks.In all failure strength tests, the RCPB specimens stayed intact (did not shatter) indicat-

ing that rubber particles capable to absorb significant plastic energy and withstanding largedeformations without full disintegration. This process will continue until the stresses over-come the bond between the cement paste and the rubber aggregates. This behaviour may bebeneficial for a pavement structure that requires good impact resistance properties particu-larly in port application. Because impact loading by stacked containers can result in pointloads of up to 23,000 kg (50,000 lb) at each corner which could induce individual blockcracking and eventually damage the CPB.


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Comparing the three curing regimes at long term age, air cured samples gain the slightlyhigher strength over natural weather and water cured samples for CCPB and 10-RCPB,while natural weather cured samples gained higher strength than water and air cured sam-ples for 20-RCPB and 30-RCPB. Nevertheless, high volume of daily production of CPBmakes natural weather curing to be more economic and applicable.

A good correlation between splitting tension-compression, flexural-compression and

flexural-splitting tension are found. A valuable relationship of long term strength wouldproduce benefits for both researchers and pavement designer.

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Long Term Strength of Rubberized Concrete Paving Blocks

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