Skip

Engineering FAQs

Frequently Asked Questions - Engineering

Is the welding of steel reinforcement permitted?

Are nominal size concrete wall ties acceptable?

What types of wall ties are acceptable for use in constructing concrete walls and are patching of the wall tie ends required?

What are the requirements for proper curing of concrete?

What are the minimum requirements that a contractor must meet, for documenting the proper concrete mix used in cast-in-place concrete projects?

Can fiber mesh be used in lieu of steel reinforcement?

Do prequalified designs require design approval?

What are the minimum requirements for soil bearing capacity?

Can steel reinforcement bars be heated and bent to desired shapes?

Can additional water be added to the concrete mix after arrival onsite?


Q. Is the welding of steel reinforcement permitted?

A. No. Manufactured materials that contain the welding of reinforcement steel that is inherent within their design, such as welded wire fabric are acceptable products. Precast concrete will continue to be manufactured to their specific specifications.


Q. Are nominal size concrete wall ties acceptable?

A. No. Wall ties used in the forming of cast-in-place concrete walls are made in nominal or full dimensions. An 8-inch nominal wall tie does not measure a full 8 inches in width and therefore, when used, will not result in an 8-inch thick concrete wall. An 8-inch full wall tie, as the name implies, does measure a full 8 inches and will result in an 8-inch thick concrete wall. Therefore, nominal size wall ties are not acceptable, full dimension wall ties are required.


Q. What types of wall ties are acceptable for use in constructing concrete walls and are patching of the wall tie ends required?

A. Concrete wall ties are typically flat with a notched break area or round. Wall tie ends must be broken off and patched with a concrete epoxy or polymer modified cement. Patching is required on both the inside and outside of concrete structures.


Q. What are the requirements for proper curing of concrete?

A. Curing must be accomplished by protecting the concrete from drying during the curing period by leaving forms in place, spraying or sprinkling the concrete with water, covering with wet burlap or plastic sheeting, or by use of a curing compound. The protection must be applied immediately after the initial set of the concrete. A minimum curing period of 3 days is required when atmospheric temperatures are at or above 55º F or 7 days when the atmospheric temperature is below 55º F. Concrete must be kept from freezing during the curing period.


Q. What are the minimum requirements that a contractor must meet, for documenting the proper concrete mix used in cast-in-place concrete projects?

A. Concrete mix tickets are required for all concrete projects. Mix tickets should include the mix strength, type of cement, type of admixtures, time loaded, time load arrived at job site, and time unloading is complete. If this information is not included on the ticket, the concrete supplier shall provide documentation with the minimum information for the design mix.


Q. Can fiber mesh be used in lieu of steel reinforcement?

A. No. Fiber mesh is used to control cracking during the curing process. It may be used in addition to steel reinforcement, but not as a replacement.


Q. Do prequalified designs require design approval?

A. Yes. Prequalified engineering designs are to be used as part of a site-specific design. The site-specific design must be reviewed and approved by someone with the appropriate engineering approval authority. The vendor must supply to the field office all appropriate construction drawings, notes, details, and construction specifications prior to construction for engineering approval. In situations where a different prequalified design is being substituted into an already approved site design, all documentation must be provided by the vendor and the design reviewed and reapproved prior to start of any construction.


Q. What are the minimum requirements for soil bearing capacity?

A. Criteria for allowable soil bearing capacity based on foundation description are contained in the Waste Storage Facility conservation practice standard (code 313) Table 1-Presumptive Allowable Bearing Stress Values. Site soil investigations are to include a soil foundation description that corresponds to Table 1. The actual soil bearing (allowable stress) capacity for the site must meet or exceed the soil bearing capacity required by the design. When the actual soil bearing capacity (based on foundation description) is less than that required by the design, the design cannot be used unless site specific testing for soil bearing capacity is performed. The site soil bearing capacity must meet or exceed the required soil bearing capacity for the planned design. Testing is to be performed by a qualified geotechnical engineering representative. A copy of the test report must be kept on file with the engineering plans. The testing must be complete prior to start of construction.


Q. Can steel reinforcement bars be heated and bent to desired shapes?

A. No. Reinforcing steel shall be bent cold. Bars that fracture or crack during bending shall be replaced.


Q. Can additional water be added to the concrete mix after arrival onsite?

A. Each concrete supplier has different mixing procedures. Some plants add all mix water prior to leaving the plant. Some add a portion at the plant with additional to be added onsite. It is important to determine the applicable procedure prior to placing concrete. No water is to be added that exceeds the amount used for the design mix. Most concrete tickets require contractor waiver signature to add more water, however this should not be allowed.


Contact

Allan Stahl
State Conservation Engineer
Phone: 443.482.2912
Email: allan.stahl@md.usda.gov