# Performance Evaluation of Bedding Sand and Load Transfer Characteristic of Concrete Block Pavements
###### Abstract
Joint sand is one of the components of the surface layer of concrete block pavement that promotes the load transfer between blocks and distributes the concentrated load. Horizontal interlocking between blocks directly affects the structural strength against horizontal load, depending on the joint material, joint width, block shape, and construction pattern, and exhibits the load transfer between blocks [11]. According to the Japan Interlocking Block Pavement Engineering Association (JIPEA), the load transfer characteristics between blocks are evaluated by measuring the load transfer efficiency (LTE) [12]. In addition, the degree of the filling of the joint sand is a very important factor in expanding the stress area at the bottom of the pavement and minimizing the spalling that occurs when angled portions of adjacent blocks collide with each other directly due to external impact. According to the previous literature, a homogeneous, well-filled joint 2-3 mm wide is required to achieve the optimal load distribution [13]. The rotation of the block due to an external load causes \"arching thrust\" and provides a high load-bearing capacity through additional rotation suppression of the constraint conditions [14]. [PERSON] et al. (2006) studied the amount of deflection and stress distribution of block pavement according to the joint width, finding that the amounts of deflection in 2 mm and 5 mm joint widths were similar and the stress dispersion was effective when the width was 2 mm [15]. In addition, as the number of compactions increases, the load transfer efficiency and joint width increases, and the joint sand should have a larger maximum particle diameter [16]. It turns out that the loss of joint sand is the main cause of high deflection, broken blocks, and block movement. Among others, it is seen as a decisive factor in the movement of blocks [17]. [PERSON] (2003) used a light falling weight deflectometer (LFWD) to evaluate the LTE of joints for examining the difference in bearing capacity of concrete block pavements according to block dimensions [18]. The load was imposed at the block center to compare the deflection that occurred at the block joint to that of the load directly applied to the adjacent block. According to advanced research, the role of sand in concrete block pavement design has been defined, which is shown in Figure 1 from the perspective of LTE. The basic physical properties of sand to be evaluated include moisture content, water absorption, durability, hardness, and friction between particles. The particle size distribution of bedding sand reflects the traffic load conditions, bedding layer thickness, and bedding material density. Density determines the shear resistance, permeability, and moisture sensitivity of a material. When using joint sand, it is important to know not only how the shear resistance resists traffic loading, but also whether it is well filled in the gaps to facilitate an effective load transfer between blocks. Therefore, in this study, composition analysis by sand type and shear resistance according to the grading of bedding sand were evaluated. In addition, the load transfer characteristics and the rotational interlocking effect between blocks according to the degree of joint filling were evaluated using a non-destructive method.