Treating plastic particles for use in concrete includes combining plastic particles with oil to yield a mixture, heating the mixture to yield a heated mixture, cooling the heated mixture to yield a cooled mixture, and removing excess oil from the cooled mixture to yield oil-treated plastic particles (e.g., oil-treated plastic particles for concrete). In one example, the oil is vegetable oil. The vegetable oil can be soybean oil, corn oil, canola oil, safflower oil, peanut oil, olive oil, grape seed oil, cocoa butter, palm oil, rice bran oil, or a combination thereof. The oil can be waste oil (e.g., waste vegetable oil, such as that recovered from restaurants). The plastic particles can be derived from post-consumer plastic, such as recycled plastic. In one example, the post-consumer plastic includes mixed plastics. A concrete composition can include rocks, sand, cement, and the oil-treated plastic particles.