In concrete masonry, which of the following ingredients increases compressive strength?

In concrete masonry, the primary ingredient responsible for increasing compressive strength is cement. Cement is a binding agent that, when mixed with water, sand, and aggregate, undergoes a chemical process known as hydration. This process forms a solid matrix that holds the aggregates together and contributes significantly to the overall strength of the concrete.

Cement is essential because it provides the necessary chemical reactions to create a solid mass. The more cement used, relative to the other ingredients, generally results in higher compressive strength up to a certain point, beyond which the addition of more cement can have diminishing returns or can even be counterproductive if not balanced with the right proportions of water and aggregates.

The role of other ingredients is important as well. For instance, while sand and gravel serve as the aggregates that provide volume and bulk, they do not contribute the same binding properties as cement. Water is crucial for the hydration process but must be carefully measured, as too much can weaken the mix, while too little can hinder the epoxy reaction that fortifies the concrete.

Thus, the role of cement is central in enhancing the compressive strength of concrete masonry, making it the correct choice in this context.