Compression strength tests

Submitted by T_Nhien on Thu, 14/06/2018 - 20:48

Dear Geoffrey,

do you know whether there is a lab/institute in Chiang Mai who can conduct compression strength tests for blocks?

thanks & best regards,
Nhien

Submitted by geoffrey on Sat, 16/06/2018 - 08:52

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It is appropriate to test the compressive strength of compressed earth blocks when they are to be used in load-bearing walls. In Thailand blocks are typically of sizes: 25 x 12.5 x 10 cm or 30 x 15 x 10 cm. They should be between 1 and 3 MPa strength after 28 days. At the CVBT we test our blocks at 7 days to 2 MPa because we want feedback for production sooner and for confidence.

Unfortunately, compressive strength testing equipment designed for standard 15 cm concrete cubes (typically having compressive strengths of 20 to 40 MPa) will not give meaningful readings in the much lower strength range of compressed earth blocks. The Center for Vocational Building Technology makes a Compression Tester, model CT5, that works well with compressed earth blocks.

Thank you for your reply. The blocks I want to test are lightweight insulating concrete and therefore are not intended as load-bearing wall. I am looking at compressive strength between 0.35-0.6 MPa (30/60days) for these blocks. Is It possible to accurately test these blocks with your CT5 for low compressive strength blocks?

Compressive strength is Force / Area.  The area in question is the net cross-sectional area of the specimen you are testing. The nominal area is the length multiplied by the width. From this subtract the area of vertical corner chamfers, vertical grooves and vertical internal cavities. We actually have a variation of the CT5 that we use to measure very low forces. I'm sure that we have, or can come up with, a configuration of equipment that can meet your needs. I'd like to know the dimensions of your block so that I can know which configuration you need.

Please understand that we it is appropriate to test blocks for compressive strength. If you are making panels then the characteristic that we need to be interested in is the tensile (aka, bending) strength. That requires a very different setup for testing.

I have already done the tensile test but would like to do compressive strength test as well. the current dimension of my blocks are 35 x 14 x 8 cm, however for the compression strength test I can make blocks of 30 x 15 x 10 to match with the size of your CT5. Thank you for your support.

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