Strange concrete strengths

[karpiozo]

Hi all! I'm quite new to concrete mix designs:

here is my recipe / per m3:

Pebble 4-14 - 1069 kg
Sand (gravelly sand) - 833 kg
Cement: CEM II 42,5 R - 345 kg
Admix: Sika Viscocrete premier
(reduces water around 40%) - 0,51% of cement quantity
Water: - 145 L


I'm getting: 59-61 MPa after 7 days

62-65 MPa after 14

68-70 after 28 days


Is it possible to get such a strength from only 345 kg of cement.
I crushed cubes on two different machines, same results, weighing machinery on the mixer is calibrated properly.

You can see very exact tendency that after 14 days there is not much going on, all the chemical reactions are taking place in first 14 days I think. Is it possible that hydration of the cement, when using admixture that is accelerator, will slow down after 14 days so abruptly?

Any advice more than welcome,

aggregate Soluble Sulphate content : 0,01%

 

[civilperson]

W/C ratios of 0.42 will give good strengths at ultimate cure. The steepness of the strength gain is a function of fineness of cement, temperature of cure and availability of moisture to accelerate the hydration. Ask Sika for lab results to compare your results to, they probably have expertise that no one else has.

 

[Dinosaur]

Accelerated cement mixes typically show slower strength gain than standard mixes after the first few days.