What is the maximum aggregate size for coarse aggregate in concrete walls?

What is the maximum aggregate size for coarse aggregate in concrete walls?

• A. 1/3 the narrowest form width.
• B. 1/5 the narrowest form width or 3/4 the clear spacing between rebar.
• C. 1/2 the narrowest form width.
• D. 1/6 the clear spacing between rebar.

Answer: (B)

The main idea is that the largest aggregate used in concrete walls must fit through the forms and around the reinforcing steel to ensure proper placement and compaction. The rule is that the maximum size is limited by two factors: not more than one-fifth of the narrowest dimension of the member (the wall) and not more than three-quarters of the clear spacing between reinforcing bars. In practice, you use the smaller of these two values to set the maximum aggregate size, so that the stones can pass through the tightest gaps and around the bars without causing bridging or voids. This is why the option stating one-fifth of the narrowest form width or three-quarters of the clear spacing between rebar is the correct choice. Larger fractions would permit bigger aggregates that can hinder placement around forms and around rebar, leading to poor compaction and potential voids.

The main idea is that the largest aggregate used in concrete walls must fit through the forms and around the reinforcing steel to ensure proper placement and compaction. The rule is that the maximum size is limited by two factors: not more than one-fifth of the narrowest dimension of the member (the wall) and not more than three-quarters of the clear spacing between reinforcing bars. In practice, you use the smaller of these two values to set the maximum aggregate size, so that the stones can pass through the tightest gaps and around the bars without causing bridging or voids. This is why the option stating one-fifth of the narrowest form width or three-quarters of the clear spacing between rebar is the correct choice. Larger fractions would permit bigger aggregates that can hinder placement around forms and around rebar, leading to poor compaction and potential voids.