Compare the manner in which the aggregate particles become bonded together in clay-based mixtures during firing and in cements during setting.

Clay-based mixtures, such as ceramics and pottery, bond together during the firing process due to the presence of water and clay minerals. These minerals, primarily composed of silicates (e.g. kaolinite), have a layered structure with some interlayer water. When the clays are mixed with water, a plastic mass is formed, allowing the shaping of the material. During firing, the temperature increases, causing the interlayer and physically bound water to evaporate, which contracts the clay and leads to densification. At higher temperatures, the clay minerals begin to decompose, forming amorphous aluminosilicates and new crystalline phases. These new phases diffuse, react with each other, and melt, leading to the formation of glassy phases that help bond the aggregate particles together.

Cements, such as Portland cement, are made from a mixture of calcium silicates, aluminates, and other minerals. When they are mixed with water, a chemical reaction called hydration occurs. The calcium silicates and aluminates react with water to form a hydrated calcium-silicate-hydrate (C-S-H) gel and calcium hydroxide. The C-S-H gel is the primary bonding agent that binds the aggregate particles together, giving the cement its strength. This binding process takes place during the setting and hardening stages, during which the cement slowly loses workability and gains strength as the reaction progresses.

The bonding processes in clay-based mixtures and cements are different in several ways: 1. Clay-based mixtures undergo a thermal process that involves heating to high temperatures, while cements bond through a chemical reaction called hydration that occurs at room temperature. 2. The main bonding mechanism in clay mixtures is the formation of glassy phases through the decomposition and melting of clay minerals, while in cements, the primary bonding agent is the C-S-H gel formed through hydration. 3. The process of forming bonds in clay mixtures requires physically incorporated water to evaporate, whereas in cements, water is chemically incorporated into the structure through the reactions of hydration.