[peteeng]

Hi Mud - a bending test for modulus can be tricky. It would be good to do an aluminium sample to the same test to check the accuracy of the lab test. What E did you get? and yes most compression tests of high solid ratio samples test high as the aggregate transfers lots of strain via contact vs through the epoxy. Tensile tests are the better path. The things that could go wrong with 4 point flexure are as follows:
1) The beam is too short and it does not follow the "long" beam or std beam flexure formula. Its then a short beam or a "shear beam" and uses a different formula
2) The calc data includes (0,0) which creates a large error in the calculation. The calculation should measure the slope of the curve not try to estimate the actual modulus. Then the slope is used to calculate modulus via the geometry. This is a common error with automated load/deflection systems
3) The depth to width ratio of the sample is incorrect and again it is then shear dominate which means the std deflection beam formula will not represent how it deflects
4) The deflection is measured via the cross bridge deflection vs its actual centre deflection. Most times this is OK but it has to be checked. ie as the cross bridge is pushing down on the two load points the beam deflects more in the middle then the top bolster does. If they attached a linear measurement device to the centre of the beam then all good
5) They need to test the beam in two directions to check the sample is not biased. "small" samples of this sort of stuff are often biased due to segregation and settling in the mould

Maybe others I can't think of at the moment.. If the test data is available happy to look at it...

cheers Peter

Granite and epoxy top published value say 40GPa average value say 30GPa so you got less then say 36/3=12GPa??

granite E=70 epoxy E=3.5 and you may have top solid volume ratio of 80% so (70x0.8x0.5) + (3.5*0.2) = 29GPa tops... (70x0.65x0.5) +(3.5*0.35)= 24GPa typical. To get 40GPa need to test in compression or use high modulus aggregate...

concrete can get higher as its E=27GPa vs epoxy at 3.5GPa and the aggregate addition is about the same so overall E can be much higher... My first test will be an ALOX/epoxy cantilever... Mould nearly done...

[Mud_]

What do EG mix manufacturer say about the results?

They should be pretty keen to sort it out

No answers yet, but short of them admitting an issue with the supplied materials I don't think anything constructive will result. I may name and shame if it's a lost cause.

{...}

Appreciate the detailed comments - I don't suspect the lab has made a mistake as the unexpected values spurred a detailed sanity check, but I'll confirm if the material is so wildly disappointing or if there was a mistake.

Epoxy was on the order of 10%, and yes, E around your 12GPa guess (cannot be more specific unfortunately, but way off expectations!).