Advances in Materials Science and Engineering

Volume 2016, Article ID 5126436, 9 pages

http://dx.doi.org/10.1155/2016/5126436

## Development of Deflection Prediction Model for Concrete Block Pavement Considering the Block Shapes and Construction Patterns

^{1}College of Transport & Communications, Shanghai Maritime University, 1550 Haigang Avenue, Shanghai 201306, China^{2}Department of Civil and Environmental Engineering, Chung-Ang University, 84 Heukseok-Ro, Dongjak-Gu, Seoul 06974, Republic of Korea^{3}Department of Transportation Engineering, Myongji University, San 38-2 Nam-dong, Yongin-si, Gyeonggi-do 449-728, Republic of Korea

Received 28 December 2015; Revised 12 April 2016; Accepted 19 April 2016

Academic Editor: Peter Majewski

Copyright © 2016 Wuguang Lin et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

Concrete block pavement (CBP) is distinct from typical concrete or asphalt pavements. It is built by using individual blocks with unique construction patterns forming a discrete surface layer to bear traffic loadings. The surface structure of CBP varies depending on the block shapes and construction patterns, so it is hard to apply a general equivalent elastic modulus estimation method to define the surface structural strength. In this study, FEM analysis and dynamic loading test were carried out to develop a deflection prediction model for CBP considering the block shapes and construction patterns. Based on the analysis results, it was found that block shapes did not have much effect on load distribution, whereas construction patterns did. By applying the deflection prediction model to the rutting model for CBP proposed by Sun, the herringbone bond pattern showed the best performance comparing with stretcher bond or basket weave bond pattern. As the load repetition increased to 1.2 million, the rutting depth of CBP constructed by herringbone bond pattern was 2 mm smaller than those constructed by the other two patterns.

#### 1. Introduction

Concrete block pavement (CBP) has been widely used in sidewalks, motorways, and ports because of its aesthetic features and easy maintenance. Unlike continuous concrete pavement or asphalt pavement, CBP can bear traffic loadings with individual blocks constructed in a uniform pattern. The blocks are connected in a continuous structure with joint sand to minimize the rotation and movement of blocks for structural stability. Therefore, CBP should be viewed as a single system in which all components, the surface layer, bedding sand under the joint sand, and underlying layers are taken into account, rather than considering only the blocks as the layer carrying the applied load or providing a wearing layer or roughness [1].

The load bearing capacity of the CBP increases mainly because of shear force at the joints and compressive force caused by dilatancy of the joint sand. In general, CBP bearing capacity also changes over time compared to the initial service life; with traffic loading increase the pavement strain decreases and load bearing capacity increases due to compaction of the sublayers [2, 3]. According to Kuipers [4], the repeated traffic loading causes the rotation of blocks; the construction patterns would affect the performance of CBP when the rotation of blocks at narrow joint intervals reaches its limit. CBP lockup occurs only when a sufficient load is applied over a flexible base. As interlocking efficiency increases, stresses between blocks decrease and are transferred to the substructure. Kuipers [4] proposed that once interlock between the blocks is achieved, the elastic modulus of the joint sand rises around 10 times compared with the initial value. Also the interaction between paving blocks with heavy loading was determined that it could provide increased pavement stiffness and thus increased load dissipation resulting in lower transmitted stress on the subgrade [5].

It is difficult to estimate the elastic modulus of the surface layer because of its discrete property. On the basis of findings from previous studies, Shackel [6] recorded the complex elastic modulus of concrete blocks and bedding sand layers measured in FWD test and laboratory test. The elastic modulus varied widely from 500 MPa to 4,000 MPa depending on conditions such as block shape and testing method. CMAA [7] suggested an initial complex elastic modulus of the surface layer (blocks and bedding sand layer) of 350 MPa (50,750 psi); the complex elastic modulus would rise to 3,100 MPa (450,000 psi) after 10,000 ESALs were applied. Although numerous researchers have presented a wide range of elastic modulus values for the layer of blocks, it seems undesirable to apply only one of them to design CBP structure [8–10].

One of the major structural distresses of a CBP is rutting caused by traffic loading. Rutting of CBPs is the product of horizontal and vertical movements of the blocks. Yasuhisa et al. [11] assessed the conditions of 48 CBPs laid on motorways in service and found that rutting accounted for 40% of all distresses. Panda and Ghosh [12] proved that the vertical load distribution in pavement structures was not significantly affected by construction patterns. It was found that shape, size, and thickness of the blocks have a significant influence on the behavior of CBP [13]. However, Miura et al. [14] found that pavement performance was influenced more by the block shape and laying pattern than the block thickness by using rutting depth as an indicator. Based on the analysis results of finite-element model, Mampearachchi and Gunarathna [15] pointed that the performance of CBP was found to be affected more by the construction pattern. Then the viewpoint was demonstrated by the deflection basins data measured in the field test [16]. Variation of deflection among different laying patterns was significantly high compared with deflection variations of block shapes. The herringbone bond had the lowest and the stack bond showed the largest deflection. Sun [17] developed a rutting prediction model based on a deflection by considering factors such as traffic load, accumulated traffic volume, resilient deflection of pavement, and block thickness. Several prediction models presented in other studies also did not consider the block shapes and construction patterns [18, 19].

In this study, to develop a deflection prediction model for CBP considering the block shapes and construction patterns, a FEM analysis and a dynamic loading test were performed to analyze load-deflection behavior. By using multiregression analysis, a load distribution model based on the deflection was developed and applied to the rutting model proposed by Sun [17]. Then the calculated rut depth was compared with the rutting results measured from Accelerated Pavement Testing (APT).

#### 2. Rutting Prediction Model

Rutting of CBP mainly happens when using a granular aggregate base, and it is divided into permanent deformation at the base course and at the subgrade. Rutting is caused by repeated loading and is related to permanent deformation which accumulated in additional compaction of bedding sand at an early stage of service and continued traffic loads at the aggregate base, subbase, and subgrade. If a pavement’s substructure (aggregate base, subbase, and subgrade) is relatively weak, shear stress at the joints from a concentrated load exceeds the shear strength at the interlock of the filling sand and blocks, which leads to rut. Rutting at the sublayers deteriorates the performance of the pavement structure and causes poor drainage and roughness. In general, rut depth is a major design standard for CBPs using an aggregate base [17, 20, 21]. Houben et al. [18] presented the rut depth prediction model by taking traffic volume into consideration in the following equation:where RD is rut depth (mm), is the number of load repetitions, and , are model constants.

Huurman and Boomsma [19] defined rut depth occurring at the CBP through strain at the sand layers and the aggregate base. This empirical model mainly reflects the characteristics of materials in the environment condition of Netherlands, as shown inwhere is the number of load repetitions and , , , and are model constants.

It is difficult to accurately estimate the stresses at sublayers of CBP due to the discrete property of the surface layer. Therefore Sun [17] presented a rutting prediction model of CBP by considering factors such as the magnitude of loads, the bearing capacity of structure (resilient deflection), the thickness of block layer, and the number of load repetitions, while the rut depth is relative to both the accumulation of permanent deformation and the lateral distribution of vehicle loads. Based on the regression analysis of test results, the following equation is used for the estimation of the rut depth:where RD is rut depth (mm), is resilient deflection (mm), is load pressure (MPa), is radius of loaded areas (cm), is thickness of block (cm), is number of load repetitions, and is wheel configuration coefficient; for single wheel and = 1.17, 1.25, and 1.34 corresponding to = 8, 10, and 12 cm for dual wheels.

The rutting model of Huurman and Boomsma [19] is an empirical model reflecting the properties of materials suited for Netherlands. However, Sun’s model can predict rutting by calculating the deflection of the pavement structure under diverse conditions for incorporation at the design stage. The allowable design rut depth for CBP with a flexible base varies depending on the location of construction and its function. Allowable rut depth for ports in China is 30 mm [17] and that for motorways is 15 mm [20] in Netherlands and 35 mm [21] in Japan.

#### 3. Methodology to Develop Deflection Prediction Model

##### 3.1. Laboratory Loading Test

As shown in Figure 1, the loading test was conducted in a 1,500 mm × 1,500 mm × 700 mm test pit. In this test, a section with 80 mm blocks for the surface layer, 30 mm for bedding sand, 200 mm aggregate layer, and 300 mm subgrade was used. In order to avoid the loss of bedding sand, a geotextile was placed between the base and bedding sand. Three construction patterns considered in most of the CBP design guide (ASCE 2015) [7, 21] were assessed: stretcher, basket weave, and herringbone bond, which were the same test variables in Mampearachchi and Senadeera’s study [16]. The blocks used in this test were 200 mm × 100 mm × 80 mm rectangular blocks. Flexural strength and dynamic elastic modulus tests were in accordance with ASTM C 78 and ASTM C 215 [22, 23] and were found to be 4.77 MPa and 12.09 GPa, respectively. The bulk density of the blocks was 2.24 kg/mm^{3}. The particle size analysis was performed for the joint sand, bedding sand, and permeable base material [24]. Figure 2 indicates the results of the passing ratio analysis of the base material, bedding sand, and joint sand; the passing ratios of the bedding sand and joint sand met ASTM C 33 and ASTM C 144, respectively, and the base material was uniformly distributed in aggregate sizes ranging from 40 mm to 2 mm [25, 26].