Questions from the Field is a selection of questions NPCA Technical Services engineers received from calls, emails and plant evaluations.

Frances asks: What resources are there to support the use of Type IL cement in sanitary structures? We have a local sewer agency questioning us.

NPCA technical experts answer: Most jurisdictions recognize or specify ASTM C478 – Standard Specification for Circular Precast Reinforced Concrete Manhole Sections for sanitary manholes. The current version of that, ASTM C478-22, states in section 4.1.2.:

4.1.2 Cementitious Materials:

4.1.2.1 Cement — Cement shall conform to the requirements for portland cement
of Specification C150/C150M, or shall be portland blast-furnace slag cement,
portland-limestone cement, or portland-pozzolan cement conforming to the requirements of Specification C595/C595M, except that the pozzolan constituent of the Type IP portland-pozzolan cement shall be fly ash.

Based on this paragraph (4.1.2.1) in ASTM C478, the use of a Type IL portland limestone cement, which is defined in ASTM C595 – Standard Specification for Blended Hydraulic Cements, is acceptable for the use in circular precast reinforced concrete manhole sections.
Provide your mill certificate to show that Type IL cement conforms to requirements of C596 and, consequently, C478.

Horatio asks: Can I use plastic zip ties to tie my rebar cages together?

NPCA technical experts answer:

While using plastic zip ties is not a recommended standard practice, NPCA is not aware of a specification that prohibits its use. Instead, the requirement is that all steel be held in place so that steel clearances and spacings are maintained during pouring and that the material holding the steel would not cause long-term harm to the concrete (plastic shouldn’t).

However, NPCA would advise whoever is proposing the use of plastic zip ties that a cage that is “held rigidly in place” is best defined by ASTM A184 Section 6.1, which requires connections to withstand a 150 pounds perpendicular force without loosening the connection. Most common zip ties would not meet this 150 pounds requirement.

It might also be worth mentioning that a pigtail tying tool and a box of 500-plus tie wires can be had for about $40, which is on par with a similar number of adequately sized zip ties.