IJERD – International Journal of Environmental and Rural Development (2011) 2–1

Research article
erdStudy on Evaluating the Hardness of the Sidewalk Pavement
MIE HIGUCHI
Graduate School of Agriculture, Tokyo University of Agriculture, Japan
Email: bamboo @nodai.ac.jp

YASUSHI TAKEUCHI
Faculty of RegionalEnvironmrnt Science, Tokyo University of Agriculture, Japan

HIROMU OKAZAWA
Faculty of RegionalEnvironmrnt Science, Tokyo University of Agriculture, Japan

KEN-ICHI SATO
Fukuoka University, Fukuoka, Japan
Received 15 December 2010

Accepted 27 January 2011

Abstract In Japan, some laws for the pavement, which took into consideration physicallyhandicapped people and senior citizens, were established. In those relevant laws, it isrecommended that safety and comfort for all users should be considered when thesidewalks are designed. But the evaluation method of safety and comfort is not establishedwhen the sidewalk pavement are constructed. Therefore, the objective of this study is toestablish   the   simple   evaluation   method   of   the   pavement’s   hardness   that take into
consideration safety and comfort of users, especially for handicapped people. Moreover,the SB/GB test and the Portable Falling Weight Deflectometer (PFWD) test were carriedout in this study. In SB/GB test, 1 inch steel ball in diameter and a golf ball were used tomeasure SB/GB coefficients that were calculated from the bounce height of each ball. ThePFWD was used to measure elastic moduli of pavement. In the previous study, Takeuchi etal. pointed out that the range of an elastic modulus took into consideration safety andcomfort of users that is 25-80MPa. However it is hard to obtain PFWD because of an
expensive device. By contrast, SB/GB test can be conducted easily by using a golf ball anda steel ball, moreover, it is widely used in Japan. Hence, to simplify the hardness
evaluation of sidewalk pavement, SB/GB coefficients were compared with the elasticmodulus. As the result, it was found that the range of SB/GB coefficients corresponding to
the range of 25-80 MPa in the elastic modulus were around 20-35% in SB coefficient andaround 45-65% in GB coefficient. The range can be used to evaluate a road surface bycheap, easy and convenient equipment.
Keywords sidewalk pavement, universal design, hardness, SB coefficient, GB coefficient,elastic modulus

INTRODUCTION
Japan is seeing its population rapidly aging and the idea of barrier-free access has become widelyaccepted. It is also noted that paved roads in agricultural communities, which are primarily utilized
by resident pedestrians, are a facility that is fundamental to the operation of a broad range ofcommunity activities as well as to the determination of location and active use of social andmodernization infrastructure and service facilities in rural areas. The improvement of roads inagricultural communities allows a faster, smoother, and safer movement of goods and people,thereby expanding socio-economic activities in the community and contributing to higher income
levels and a better living environment for residents.
In Japan, research efforts have been directed to produce pavement that is comfortable and easy
to walk on. Nabeshima et al. (2005) employed the paved surface hardness test (JIS A 6519) in order© ISERD

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to identify a suitable hardness for resilient pedestrian pavement. And it was found that a comfort
zone lies in the measured range of impact acceleration of roughly 80±10 G. Takeuchi et al. (2008)
used this range to pursue structural engineering designs for pedestrian pavement with resilience
performance based on the elastic modulus obtained in Portable FWD testing and the impact
acceleration from hardness testing of paved surfaces. The elastic modulus corresponding to theimpact acceleration within the hardness range that provides safe and comfortable for pedestrians,
including the elderly and wheelchair users, was shown to be from 25 to 80 MPa (Fig.1). The tests
used in the study (the Portable FWD test, which measures the elasticity as a parameter for theamount of physical strain caused by the pavement, and the hardness test of paved surfaces) are noteasy to perform due to their high cost. For this reason the present study employed SB/GB testing,which is popular in Japan. This simple-to-perform test uses a steel ball and a golf ball. However,the sensitivity of this test is limited, and it can show only rough value ranges for different types ofpavement (Fig.2).

Fig. 1 Relationship between impact acceleration and elastic modulus

Fig. 2 Relationship between SB and GB coefficient of each pavement
In order to create a pedestrian environment that is safe and comfortable for senior citizens andthe physically handicapped, there is a need to establish a simple testing protocol for pavement
elasticity. This paper reports on our SB/GB testing of different paving materials for pedestrian
traffic as well as Portable FWD testing for the purpose of developing a simple method to measurepavement resilience to evaluate the comfort level for pedestrians.
SAMPLE LOCATIONIn this study, 57 types of pavement were randomly selected as samples. The sample locations arethe Setagaya Campus of Tokyo University of Agriculture, the Nanakuma Campus of Fukuoka© ISERD

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University, Sakuragaoka Junior High School, Karasuyamagawa Ryokudo, Togasira Jutaku inIbaragi, and pedestrian pavements in their surrounding areas, as well as specialty paving in a trackfield.
Table 1 Sample locations and pavement types
Type of pavement

Number of samples

ResilientConcrete slab
Clay-based
ILB
Artificial turfAsphalt

2765322Type of pavement
Soil
Synthetic resin mixed
TileWoodgrass
Other

Number ofsamples
222213The types of pavement in those locations are shown in Table 1. For the discussion of test
results, the measurement data produced by the Pedestrian Pavement Sub-Committee, Pavement
Engineering Committee, Japan Society of Civil Engineers were also included.
TEST METHOD
SB/GB tests and Portable FWD tests were conducted for the purpose of measuring the resilience ofthe paved surface.
SB/GB test
A golf ball and a steel ball are dropped from a height of 100 cm (H) to the paved surface and theirrespective rebounding heights are measured. The free fall is repeated 5 times for each paving
material, and the three most similar rebounds are used to calculate the mean value for reboundingheights (H0). SB and GB coefficients are obtained using H0 in Eq.1. It is believed that the GB
coefficient reflects impact absorbance, while the SB coefficient represents rebound resilience. It is
widely held that the smaller these factors are, the less bodily impact a pedestrian would receive.
The tests were all performed in accordance with the instructions in the Handbook of Pavement
Survey and Testing (Japan Road Association, 2007).
Fig.3 and Fig. 4 show the schematics of the SB/GB tester and how the test was done.
SB coefficient and GB coefficient % H0
100H(1)Fig. 3 SB/GB tester detail© ISERD

Fig. 4 SB/GB testing in situ

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Portable Falling Weight Deflectometer (PFWD) test
Portable FWD testing involves a load cell that is lifted up by hand and dropped to cause an impacton the paved surface; the impact load and deflection are to be measured. With the loading radius (r)at 0.05 m and the weight at 5 kg, the test was conducted by changing the dropping height to 5levels from 10 to 50 cm. For each height, the cell was dropped 3 times or more until three similar
peak deflection values were obtained. The elastic modulus, EPFWD [MPa], was calculated using Eq.2
based on the maximum deflection, D[m], and the maximum load intensity, q [N/m2], that wasderived from the maximum load, P [N] divided by the loading area, A[m2]. EPFWD refers to the rateof stress-dependent change of displacement. In the case of pavements that incorporate rubber chips,measurements   didn’t   stabilize   before   the   load   level   reached   3000   N;;   their   EPFWD [MPa] werecalculated from the measurements obtained with the maximum load at around 4000 N. EPFWD[MPa], represents a value when the subsurface layers are deemed to be a single layer. In addition,the Poisson ratio, ν, is assumed to be 0.4.
Fig.5 and Fig. 6 show the Portable FWD tester and actual testing.
EPFWD  1  2 r  q2 D

106 

1  P 102(2)62 Dr

Fig. 5 PFWD tester detailFig. 6 PFWD testing in situ

RESULTS AND DISCUSSION
The test data were plotted to show the relationship between SB and GB coefficients (Fig. 7).
Statistical analysis classified the data roughly into five groups. It was then decided to exclude thesamples where the paved surface is not consolidated, such as artificial turf and soil-based paving,
including those akin to clay-based paving and some tile pavements for which the data was rather
isolated in the Figures. These samples had uneven top layer surfaces, and test results showed little
stability and no correlation between the SB and GB coefficients. Data for the remaining pavement
samples were used to calculate the relationships between SB coefficient and elastic modulus (Fig. 8),and GB coefficient and elastic modulus (Fig. 9). These Figures show that both SB and GB
coefficients have a linear relationship with elastic modulus in single-logarithmic plotting. Although
Takeuchi et al. (2008) did not find any correlations between SB coefficient and elastic modulus, thisstudy involved more varied pavement samples, which likely produced the linear relationships ofFigs. 8 and 9. The dotted line in each Figs. 8 and 9 represents an approximated curve, while thesolid lines depict the upper and lower limits of the 99% confidence interval.

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The upper limit, 80 MPa, and the lower limit, 25 MPa, of the elasticity range identified byTakeuchi et al. (2008) as appropriate for pedestrian comfort from their hardness testing wereplotted on the horizontal axis and vertically extended in each chart to intersect the upper and lower
limit lines of the confidence interval to obtain the values of SB and GB coefficients at theintersecting points. In Figs. 8 and 9 the horizontal arrowed solid lines show the range on thevertical axis that corresponds to the range of elastic modulus values and within the confidence
interval. In SB and GB tests, results significantly vary depending on the surface condition of thepaving material due to the small mass of the measuring apparatus (steel and golf balls). It istherefore assumed that the statistical distribution of data should be taken into account in assessing
relationships between results of Portable FWD tests and SB/GB tests where load levels are not thesame. Thus the ranges of SB coefficient and GB coefficient to fit the comfort range of elastic
modulus were obtained at the confidence interval based on confidence levels of 90%, 95%, and99%. The measurements obtained in this study are considered to indicate that SB/GB testing ofpavements having resilience within the suitable range will produce measurements that fall within
the range described in Fig. 8, which has 20% to 35% in SB coefficient and 45% to 65% in GB
coefficient and overlaps partially with the range of polyurethane-based paving.

Fig. 7 Relationship between SB and GB coefficients

Fig. 8 Relationship between elastic
modulus and SB coefficient© ISERD

Fig. 9 Relationship between elastic
modulus and GB coefficient81

IJERD – International Journal of Environmental and Rural Development (2011) 2–1

Fig. 10 Indexes commonly used and range of proper hardness
CONCLUSION
The test results suggest the following:(1) Pavement resilience can be evaluated using only SB/GB tests because SB coefficient and GBcoefficient show correlations with elastic modulus.
(2) The appropriate range of elasticity indicated by SB/GB tests is 20% to 35% in SB coefficientand 45% to 65% in GB coefficient.
These values are, however, applicable only to those pavements containing resin and the like,since the data exclude clay-based materials. We intend to collect more data in order to investigate
the reliability of the SB/GB data further. We also plan to study the properties of clay-based
pavements in order to revisit the definition of the appropriate hardness range.
ACKNOWLEDGEMENTS
We would like to express our gratitude to members of the Pedestrian Pavement Sub-Committee,Committee on Pavement Engineering, Japan Society of Civil Engineering. The authors are also
grateful for the field assistance provided by students of the laboratory of Hydro-structure
Engineering, Tokyo University of Agriculture and of the Road & Geotechnical Laboratory ofFukuoka University.
This research was supported by Grant-in Aid for challenging Exploratory Research(20658056) and Grant-in Aid for Scientific Research (B) (22360175) from the Ministry ofEducation, Culture, Sports, Science and Technology (MEXT), Japan.
REFERENCES
Japan Road Association (2000) Pavement performance rating system in separate volume, Rating system of
the performance index to determine as needed, 218-222 (in Japanese).
Japan Road Association (2007) The handbook of pavement survey and testing, the first volume, 126-129 (inJapanese).
Nabeshima, M. and Yamada, M. (2005) Range of proper hardness for aged about walkway pavement,
Official journals quarterly of the Japan Society of Civil Engineers, 788-67, 117-126.
Tanaka, K. and Uchida, K. (1989) Evaluation of comfortability and safety on pedestrian road pavement,
Annual report of Inst. Civil Engineering of Tokyo Metropolitan Government, 15-26.
Takeuchi, Y., Sato, K., Aoki, M. and Yaginuma, H. (2008) Hardness evaluation of the sidewalk pavement
using Portable FWD tester, the proceeding of the 64th JSCE Annual Meeting of the Japan Society ofCivil Engineers, (CD-ROMS).

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