Initial Power Because of early strength improvement, the strength of 53 grade does not increase much after 28 days. After 28 days, 33-grade and 43-grade cement continue to build strength. 33 and 43-grade cement will eventually achieve the same ultimate strength as 53-grade cement. Price Cement costs more for higher grades. Generally, low-cost cements are lower in quality. They may be less refined or have larger particles than high-quality cements. Low-cost cements tend to harden faster so they must be mixed with water before being placed in the mold. Higher Final Strength The extra silicon added to 53-grade cement allows it to develop greater initial strength. This means that a sample of 53-grade cement placed in a test tube could support more weight than a sample of 33-grade cement. When exposed to air, both cements would harden but the silicon in the 53-grade cement would begin to dissolve, releasing more calcium silicate hydrate (C-S-H) gel into its interior. This extra cross-linking of molecules creates a stronger cement that can hold more weight before breaking. The extra silicon in 53-grade cement also makes it more resistant to chemical attack. Chemicals such as sulfur dioxide gas used by some coal-fired plants to control acid rain would react with the calcium carbonate present in both types of cement to create calcium sulfate hemihydrates.