**1. Introduction**

The urban expansion leads to the rise of building construction, especially in developing countries. Therefore, the use of concrete which is the primary material in such construction is also increasing [1]. This results in an increase in the use of natural crushed stone which constitutes two-thirds of the total weight of concrete. Moreover, 5–10 percent of the concrete used in construction has turned into waste [2]. However, the inappropriate disposal of leftover concrete such as dumping it at a landfill and using it in the landfilling process has been widely practiced. This leads to more problems in the future. To tackle the problem, the concept of turning the leftover into aggregate used in concrete is developed.

The sources of aggregate waste from the construction industry come from three main sources: building demolition waste, laboratory waste, and precast concrete waste. [3] The behavior of recycled aggregate concrete differs from that of natural aggregate concrete [4,5] in terms of compressive strength, the efficiency of fresh concrete, chloride penetration, etc. The concrete properties have been tested over and over; however, there has been no explanation of how concrete behavior from various sources is linked to its actual behavior.

This research aimed to analyze the behavior of concrete made from various types of recycled aggregate from different sources in terms of compressive strength and chloride penetration through an image processing technique.

#### *1.1. Chloride Penetration Behavior*

The longer the concrete is in use, the higher the probability of water and air penetrating it becomes. Ref. [6] The presence of water and air is the cause of other undesirable compounds [7,8]. For example, chloride in the water might be found in the concrete. The most undesirable effect of chloride is that it can react with passive film covering the reinforcement, resulting in the passive film deteriorating. As a result, the reinforcement without the passive film will react with the penetrating water and air and will eventually rust. This

in turn makes the reinforcement occupy a greater volume of the concrete, allowing more air and water to penetrate the concrete. This process, as a chain reaction, accelerates the deterioration of the concrete and reinforcement. [9–11]

According to the EN 1744-1 [12] Test for Chemical Properties of Aggregate, ASTM C33 [13] Standard Specification for Concrete Aggregate, the amount of chloride in natural aggregate must be less than 0.01 percent and can be up to 0.03–0.15 percent in recycled aggregate by wet chemistry method. This is because chloride content might be present in mortar waste in recycled aggregate or the recycled aggregate itself was previously used where chloride content was present [14]. This results in the increase in water absorption of the concrete corresponding with the amount of the recycled aggregate. This also applies to the chloride penetration ratio of the concrete. According to previous studies, [15] the problem of chloride penetration behavior could be solved by decreasing the water over cement ratio. This would help the concrete yield the desirable strength. Moreover, the research conducted by [16] found that the type of recycled aggregate also plays a role in the chloride penetration behavior of concrete, with the chloride penetration of fine aggregate higher than that of coarse aggregate.
