20,000 newtons This mix is often used for household projects but may also be utilized for some commercial applications, with a strength rating of 20 newtons after 28 days. As a lightweight mix, GEN 3/C20 concrete contains the most cement of any particular GEN mix. It has a water-to-cement ratio of 0.45 and a sand-to-cement ratio of 1.5. The GEN series consists of seven mixes that vary in the amount of gravel used as a partial replacement for the coarse aggregate (sand). The more gravel used, the less dense the resulting concrete. Gen Concrete's website states that its concrete is suitable for all types of applications, including residential, light-duty commercial, heavy-duty commercial, and industrial. It recommends using a plastic liner or embedding fiberglass rebar in low-stress areas such as driveways, patios, and walkways. Concrete strength is measured in newtons per square millimeter (N/mm2). Lightweight concretes tend to have lower strengths than normal-density concretes. The strength of concrete decreases as it ages because calcium carbonate molecules that make up the majority of cement paste are dissolved by acid compounds present in rain and snow. The amount of calcium carbonate available to create stronger stones over time is reduced due to chemical reactions that occur when soil meets water.