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Where is min concrete grade for pre-cast (no prestress) walls specified?

Where is min concrete grade for pre-cast (no prestress) walls specified?

(OP)
Friends

I can not find any recommendation on min. grade of concrete for use in pre-cast(no prestress) fences and pre-cast retaining walls, I mean walls in flexure only. It is vaguely shown in most cases and examples that high grade concrete is the usual practice for pre-cast elements

Thanks in advance.

respects
IJR

RE: Where is min concrete grade for pre-cast (no prestress) walls specified?

I include it on the drawings and in the specs... My drawing notes are very comprehensive (and coord with specs); I've too often found drawings without this information so it becomes part of the drawing set. People seem to discard/lose specs 20 years down the road...

Dik

RE: Where is min concrete grade for pre-cast (no prestress) walls specified?

I think he means where is the code guidance on that. If that is the case, it's the same code as any other building concrete, ACI 318 (in the US).
ACI 533 addresses precast wall panels, but that's pretty specific and they don't really require any certain strength.
Usually, precast concrete is required to have a higher strength than cast in place by the designer, but that's a function of the controlled conditions of the yard vs. field work. It's not a code requirement.

RE: Where is min concrete grade for pre-cast (no prestress) walls specified?

Precast concrete elements made in a plant usually have compressive strengths higher than specified because they use proven mix designs and processes that provide adequate strength for stripping and handling that result in ultimate strengths higher than specified because of economics and turning around forms. One factor is the known, established curing methods and cycles that are controlled closely.

An extreme example is the low slump/zero slump or dry tamp concrete where the best products just happen to exceed normal specifications by large percentages. In these cases, more water would provide higher strength, but the product may not be usable. Adding cement is cheap, but the water destroys the accuracy and appearance. Fence materials and some retaining wall systems often fall into this category. In some cases, the strengths are 30% to 50% over minimums because it costs more to produce minimum strength products.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

RE: Where is min concrete grade for pre-cast (no prestress) walls specified?

I don't see any Code specific minimum strength requirement. It all depends on the element which is to be precast. For example, in case of hollowcore slabs, it's always minimum 50Mpa, mostly 60 Mpa concrete as it is related to the method of casting where extruder machine is used and its almost no slump concrete with smaller aggregates, so this is the casting method requirement and like an industry standard. For other elements, like walls, beams or columns which are required to be precast, it depends on the Designer who should consider, apart from the design requirement, strength at transfer (prestress) stage, the initial high strength required when the elements will be tilted in precast yard and will be transported to the erection site. In general, in precast concrete, the activities from precast yard till element's erection are considered by the designer similarly as different construction stages are incorporated in the design of precast members.

IR

RE: Where is min concrete grade for pre-cast (no prestress) walls specified?

ACI provides minimum requirements for structural concrete design or construction. The term structural concrete encompasses plain concrete, reinforced concrete, precast concrete, and also prestressed concrete. Per ACI 318-05, Section 1.1.1 - For structural concrete, f'c shall not be less than 2500 psi. Chapter 16 refers to additional requirements for Precast Concrete but there is no deviation from Section 1.1.1 regarding strength requirements.
Concrete strength of 2500 psi would be the absolute minimum, unless higher strength is recommended in Design Handbook by PCI, ACI-550: Design Recommendations for Precast Concrete Structures, or Standards directly related to Precast Concrete.

RE: Where is min concrete grade for pre-cast (no prestress) walls specified?

DST -

It is just a "boiler plate" specification inserted to provide a complete minimum specification for numerous products under ACI 318.

Normally strengths are much higher for economic purposes (production and handling).

If you need a lower strength such as 2500 psi for some reason, instead of the typical strengths of 3500-4000 psi(or 5000) it should clearly be specified and be expected to pay an additional cost. Much depends on the product and location plus shipping and erecting costs.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

RE: Where is min concrete grade for pre-cast (no prestress) walls specified?

@concretemasonry: The OP is asking where is the minimum grade for precast concrete specified. I was in no way suggesting to use 2500 psi for precast concrete. I was just bringing attention to the ACI code section where the minimum strength of structural concrete is specified.

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