QUESTION
I’m doing some Finite element Analysis on custom cinder blocks and need to input material properties. Ideally i would like to obtain the properties of concrete mixes typically used in concrete masonry units (CMU).
This is a research project and I’m talking about the CMU made to meet ASTM C-90 standards.
REPLIES
concretemasonry
There is no such definition of a “cinder blok” and very few have been made in the last 60 years and many area have never seen a “cinder block” - It is a slang term used by the uniformed. The only possible exception may be volcanic cinders that are used for specific purposes (color usually) and possibly natural pumic that is also volcanic, but can be more closely specified.
Most of the factors you listed are not a part of the ASTM C90 specifications for a CMU unit and never were. When you are talking about a wall, you must consider the mortar and mortar properties used to determine the wall actions and properties.
The following points are addressed:
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The are 3 different densities, but other can be obtained. The classifications are normal weight (over 125 pcg), medium weight (105-125 pcf) and lightweight (under 105 pcf). At various times the was a classification a lighterweigh category (under 85 pcf), but that is much costlier unit in most areas.
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Compressive strength is measured based on the net area of the masonry unit. The minimum is 1900 psi, but it is very difficult to make one that low. Strengths can range up to over 8000 psi or may specified by the engineer.
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and…
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The are no requirements. I have no idea of any tensile strength tests conducted on a CMU unit. The tensile strength is a rough function of the compressive strength, but is not used in design. The flexural strength of a CMU unit is also similarly meaningless, especially since there is not even a test procedure.
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The modulus of elasticity is usually assumed to be related to the density and compressive strength and many texts and design standards have a range of factor to used for design.
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Permeability is not usually tested and varies widely because of the different types of aggregate, cement content and gradations and admixtures if used.
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Thermal expansion depends on the weight of the block and percentages of the various aggregates used.
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Drying shrinkage is addressed by ATMS C426 and is a test for properties to use in design, if needed.
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Drying shrinkage of reinforced concrete is applicable for masonry units. Reinforced concrete masonry has various core filled with grout and reinforced with spacings between 8" and 4’ o.c.
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The remaining items all related to specific units of different densities and aggregates used for different purposes.
Since CMUs are not used without mortar, any testing or analysis for practical use must also include a composite of the block and mortar without any reinforcement. There have been some theoretical FEA, including the National Concrete Masonry Association, but I don’t think they were ever published because there were too vague factors to be used in any design codes that the engineers participated in writing.
SOURCE
https://www.eng-tips.com/viewthread.cfm?qid=300310
Above is a snippet.