# Recycling Waste Paver Blocks in the Manufacture of New Concrete Paver Blocks and Building Bricks
## 1 Introduction  
Waste paving blocks generated from construction projects are one of the major social and environmental issues in Korean society. Several municipalities have policies in place to provide citizens with demolished waste blocks of decent quality, but the recycling rate of blocks remains at around 11%. Additionally, waste blocks with a damaged or poor quality cause environmental issues and social costs such as landfilling and waste storage. Therefore, it is necessary to find an effective way to utilize the continuously generated waste paving blocks. For sustainable development, extensive studies have been conducted on cement composites containing various types of waste. In general, cement composites with various wastes show lower workability and strength in comparison with ones without waste [1, 2]. [PERSON] et al. [3] reported that the slump of concretes with 50% and 100% recycled concrete aggregate was reduced by 45% and 85%, respectively, compared to natural aggregate concrete, and materials segregation was observed when natural aggregate was replaced with recycled aggregate at 100% replacement ratio. In a study using granite waste as a substitute for sand [1], a 10% replacement ratio of sand by granite waste reduced the slump by 50%, and at the 20% replacement ratio, the slump was zero. [PERSON] et al. [4] reported that about 6%, 12%, and 14% more water was required to achieve the same slump at replacement ratios of 10%, 25%, and 40% of the waste brick aggregate, respectively. As can be seen from these previous studies, in many cases, regardless of type, when recycled materials are included, more free water is required to achieve adequate workability, however, an increase in the water-to-cement ratio is the crucial parameter that degrades the properties of cement composites [5]. Although some researchers have achieved their target slump by increasing the dosage of superplasticizers [6], the pronounced detrimentaleffects of superplasticizers on the environment cannot be ignored. In this context, using various wastes for concrete products that do not require workability (i.e., zero-slump) can be considered a more environmentally friendly and viable option. Many studies have focused on evaluating the effect of different types of waste on concrete paving blocks: crumb rubber [7, 8], ceramic waste [9], recycled concrete aggregate [10], and various kinds of ashes [11, 12]. However, little research has been conducted on the recycling of demolished waste paving blocks themselves in the production of new paving blocks and building bricks. Utilizing old waste blocks to make new blocks not only reduces the amount of waste generated but also offsets the slump loss that occurs when recycled materials are included in normal concrete. Therefore, in this study, three different waste paving blocks commonly used as paving materials in Korea were recycled as fine aggregates in a concrete mixture for the production of new pedestrian blocks and building bricks (Figure 1). The aim of this study is (i) to evaluate the applicability of old waste paving blocks for new concrete products; (ii) to propose an optimum replacement ratio that meets the industrial standards for practical application. For this aim, concrete mixtures containing different wastes were prepared, and the main characteristics (i.e., water absorption, flexural strength, and compressive strength) stipulated in the Korean Industrial Standards (KS) for concrete products were analyzed. In addition, other important properties such as density and ultrasonic pulse velocity (UPV) were investigated. The experimental results were compared with the requirements specified in the KS to discuss the use of concrete products containing recycled materials. The significance of this study is to provide immediate and practical value on utilizing waste paving blocks in new concrete products for paving blocks and building bricks.