Tricalcium aluminate (C3A) is a chemical compound found in cement. It is responsible for early strength development and contributes to the initial setting time of cement. However, it also has some negative effects on the properties of cement, one of which is its susceptibility to sulfate attack.

Less resistance to sulfate attack:
Sulfates can react with C3A to form a compound called calcium sulfoaluminate hydrate (ettringite). This reaction can cause expansion and cracking of concrete, leading to reduced durability and strength. C3A-rich cement is more susceptible to this type of sulfate attack, as it contains more C3A to react with sulfates. Therefore, C3A content is typically limited in cement to reduce the risk of sulfate attack.

Hydrates rapidly:
C3A is known to hydrate rapidly, meaning that it reacts quickly with water to form calcium aluminate hydrates. This rapid hydration can cause a sudden increase in temperature (known as heat of hydration) and can lead to the formation of cracks in the early stages of concrete curing. Therefore, cement manufacturers often limit the amount of C3A in their products to reduce the risk of excessive heat generation.

Generates less heat of hydration:
Contrary to the given option, C3A is known to generate more heat of hydration than other cement compounds, such as tricalcium silicate (C3S) and dicalcium silicate (C2S). This can be a problem in large concrete structures or in hot climates, where the heat generated during curing can cause cracking and reduced durability. Therefore, cement manufacturers often use a combination of C3S, C2S, and C3A to optimize the heat of hydration and other properties of their products.

Increases:
The given option is incomplete and unclear. It is unclear what property of C3A is supposed to "increase." Therefore, it is not possible to provide a detailed explanation for this option.

Overall, while C3A is an important component of cement, its effects on the properties of concrete must be carefully managed to ensure optimal performance and durability.