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Normal/Medium weight masonry 1
- Thread starter WWTEng
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concretemasonry
Structural
In my experience (35 years), the vast majority is normal weight block. This has been the most common density is national studies over the past 50+ years.
In some markets, weight is a concern because of union requirements and construction practices and medium weight block are common because of perceived contractors cost opinions.
Lightweight block are used mainly for insulation, fire ratings and in some cases for appearance, texture and acoustics, but these requirements can by architects.
The lighter the masonry units the higher the material cost.
All block must meet the minimal ASTM C90 requirements for strength and all types can be obtained at higher strengths. The higher the block density, the higher the maximum compressive strength, but normally the engineers specifications are very easy to meet. I have seen hollow block prisms with a net compressive strength of and a f'm of 4800 psi, but there was no need to make them, even for 20 story partially grouted apartment buildings.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
In some markets, weight is a concern because of union requirements and construction practices and medium weight block are common because of perceived contractors cost opinions.
Lightweight block are used mainly for insulation, fire ratings and in some cases for appearance, texture and acoustics, but these requirements can by architects.
The lighter the masonry units the higher the material cost.
All block must meet the minimal ASTM C90 requirements for strength and all types can be obtained at higher strengths. The higher the block density, the higher the maximum compressive strength, but normally the engineers specifications are very easy to meet. I have seen hollow block prisms with a net compressive strength of and a f'm of 4800 psi, but there was no need to make them, even for 20 story partially grouted apartment buildings.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
msquared48
Structural
I like to think that engineers are normal, but then...
Never spec'd any CMU other than normal.
Mike McCann
MMC Engineering
Never spec'd any CMU other than normal.
Mike McCann
MMC Engineering
JedClampett
Structural
Another aspect is that the lightweight, while cheaper to build, is harder to finish. Lightweight means a rougher surface (kind of makes sense) that's tougher to make look nice.
I never realized this until an architect showed me them side by side.
I never realized this until an architect showed me them side by side.
- Thread starter
- #5
concretemasonry
Structural
Jed -
Lightweight block do not necessarily have a rougher or coarser texture. The texture of the surface is a function of the particle shape and the gradation. The particle shape is not covered by any ASTM standard and the gradation is a very wide range of values and can be over-ridden by proof of long term performance.
A few decades ago, architects required sample of the coarsest and finest surface proposed for supplying. Some required two sample (coarsest and finest) and requested them to be partially cut so he could split the block, keep one half and give the other half to the supplier. It was based on the acoustics, appearance (exposed block in churches, schools and some hospitals. Also, the large spaces (auditoriums, theaters, etc where there may be a wide range of frequencies, the project specification were unique and often forced the use of a mult-wythe wall with different textures or strength on either side. - A small part of the industry, but extremely critial.
A second criteria for the texture was the finishing (especially paint)cost since painting contractors will price according to the products in place and labor and materials required.
For normal weight block for high strength applications, the cheapest way to increase the compressive strength is to add more water (not cement) to the mix during manufacture, but the production cost increases and the appearance quality decreases.
Despite all of these minor points the frequency of use has not changed through the years and there are regional differences.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
Lightweight block do not necessarily have a rougher or coarser texture. The texture of the surface is a function of the particle shape and the gradation. The particle shape is not covered by any ASTM standard and the gradation is a very wide range of values and can be over-ridden by proof of long term performance.
A few decades ago, architects required sample of the coarsest and finest surface proposed for supplying. Some required two sample (coarsest and finest) and requested them to be partially cut so he could split the block, keep one half and give the other half to the supplier. It was based on the acoustics, appearance (exposed block in churches, schools and some hospitals. Also, the large spaces (auditoriums, theaters, etc where there may be a wide range of frequencies, the project specification were unique and often forced the use of a mult-wythe wall with different textures or strength on either side. - A small part of the industry, but extremely critial.
A second criteria for the texture was the finishing (especially paint)cost since painting contractors will price according to the products in place and labor and materials required.
For normal weight block for high strength applications, the cheapest way to increase the compressive strength is to add more water (not cement) to the mix during manufacture, but the production cost increases and the appearance quality decreases.
Despite all of these minor points the frequency of use has not changed through the years and there are regional differences.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
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