# Mechanical Properties of Cement Composites Using Modified Plastics by Gamma Irradiation
## 1 Introduction  
Recently, the demand for high strength and lightness of construction members has been increasing due to the progress of large-scale construction structures. Previous studies have shown that the strength of cement composites follows by inducing a reduction in the unit volume mass of the lightweight cement composites [1, 2, 3, 4]. In general, in order to induce the weight of cement composites, there is a method of using lightweight aggregates. Studies related to methods for weight reduction using lightweight aggregates such as rubber lightweight aggregates and plastic lightweight aggregates are being actively conducted. Among them, plastic aggregates seem to need measures to recycle such plastics, as the use of plastic containers has increased due to the recent spread and prolonged coronavirus, resulting in more plastic waste. Since waste plastics have relatively high strength and small unit volume, they appear to have advantageous aggregate properties to produce lightweight cement composites, but plastic aggregates have disadvantageous surface properties [5, 6]. In order to use plastic aggregates in a more efficient way, it is applied to various fields such as medicine, bio, industry, environment, and construction. Based on prior research, gamma-ray irradiation technology was applied to induce and reform cross-linkage of plastic pellets to be used as aggregates [7, 8]. According to [PERSON] et al. (2007), the method of grafting radiation to a polymer material improves its physical, chemical and mechanical properties, and it is described as an economical and eco-friendly method. Moreover, [PERSON] et al. (2008) stated that as the gamma irradiation dose increases, there is an increase in tensile stress and compressive stress in a plastic region, and [PERSON] et al. (1999) described an increase in abrasion resistance of an ultra-high molecular weight composite irradiated with gamma rays.  
The method of using gamma irradiation technology is eco-friendly and can improve the physical, chemical, and mechanical properties of polymer materials. Conversely, due to the lack of gamma-ray irradiation facilities domestically and internationally, it is expensive to irradiate gamma rays. Therefore, it is judged that it is necessary to develop a plan to use the natural radiation generated from the solar rays and to measure the irradiation dose for it.  
There have been no studies on evaluating physical properties of modified plastic aggregates using gamma-ray irradiation applied to cement composites. Therefore, gamma rays were irradiated onto plastic types such as poly propylene (PP), poly ethylene (PE), and acrylonitrile butadiene styrene (ABS) pellets. As a result, the surface modification of the plastic aggregates was analyzed. The purpose of this study was to evaluate the suitability of the modified plastic aggregate technology by conducting unit volume mass and flexural/compressive strength tests of cement composites that secured strength and lightness by applying modified plastic aggregates through gamma irradiation.  
In this study, poly propylene (PP), poly ethylene (PE), and acrylonitrile butadiene (ABS) pellets, which are recently most commonly used as plastic containers, were manufactured by extrusion method. By using this, a lightweight cement composite was manufactured to evaluate the physical performance, and in order to determine the cause, the change in surface properties of plastic aggregate according to gamma ray irradiation was analyzed.