ADDITION TO EXISTING CINDER BLOCK CONSTRUCTION 1

[PT99]

I am designing a 1 story addition to a 2 story residence constructed with cinder block in the 1950's.

To strengthen the exterior cinder block walls, I am considering grouting the voids in the cinder units.

Is this a sound idea?. The alternative is to add frame construction adjacent to the walls.

 

[concretemasonry]

Grouting existing CONCRETE block (CMUs) in place is very possible. You probably will not find any "cinder" block. If you are concerned with compression or shear, it may pay to take a look at the properties of the units in place. During the 1950s and 60s, block had an ultimate strength that was often 50 - 100% over minimum strengths. - The manufacturing material handling process was so crude, excessive amounts of cement and a high percentage of solids were used just to handle the uncured units.

You will have material compatibility problems when the wood finishes shrinking. When adding or modifying existing structures compatibility and materials and systems is critical, especially on reidences.

 

[COEngineeer]

Or check out this simpson product.

http://www.simpsonanchors.com/catalog/adhesives/accs/opti-mesh.html

http://www.swijetty.com

Sea Water Intake and Jetty Construction

 

[PT99]

Thanks concretemasonry

My reason for assuming the units were cinder block was that the coloring was dark grey, rather than the light grey used today. The actual construction date was 1948

So, based upon this, is it likely to be cinder or concrete? Should I have the blocks tested for compressive strength in place, with Schmidt hammer, or will it break the block?

Is is possible to grout 16 ft in height?

Do I need to use pumps?

 

[hokie66]

PT99,

Cinders were used as aggregate in some areas of the US, thus the term. But it would be difficult to tell without some testing unless you can find an old hand in your area who can identify the blocks.

 

[concretemasonry]

PT99 -

The main factor is the strength of a wall of a building of this type is the strength of the individual masonry units. If it designed as a reinforced masonry structure, the amount and placement of the steel would be an additional factor. If the steel is just the normal use for continuity, the effect of the steel was usually neglected.

To determine what you have for the block strength, you would have to remove a unit to determine the compressive strength and the physical dimensions (% soild, etc.). A local person looking at the block would not provide any meaningful information.

There is no reliable in-place test for units and a hammer would not provide any good information. The concept of cutting out a prism and testing that poses many problems and can be very unreliable beause of the handling and testing problems.

Since mortar has little effect on the prism strength (f'm), the prism strength can be estimated conservatively by assuming a Type N or Type S mortar, use the unit strength test results and the tables in ACI 530. Some older concrete blocks have incredibly high compressive strengths (2 to 3 times the ASTM C90 minimum or cube strengths of 6000 psi)

You will then have to determine if additional steel reinforcement is needed for flexure or continuity.

Normally, grout is not used to increase the compressive strength of a wall in new construction because it is simpler to just specify a higher strength. If you do use grout, it can easily and economically pumped since the grout has a high slump.

Dick