Study on reworked mortars using St Astier NHL 3.5

Mortar mixes prepared: 250 kg/m3 (1:2.5)
Proctors preparation: for each of the above dosages a series of proctors were prepared with normal water addition and tested. Others were prepared with the same mortar 18 hours later reworking the mortar and adding extra water until the required workability was obtained.
Remarks: The water added in re-working was approx. 1/6 of the water used initially to mix the mortars. The reworked mortars were much fatter with a lower bulk density (less 2.6%-4%). The Compressive Strenght of reworked mortars is lower due to the lower bulk density but, if the reworked mortar is compacted more (in practical terms this means that, on a render, it would be pressed harder) and its bulk density increased to that of the normal mortar, the compressive strength increases. In reworked mortars with higher dosages the Compressive Strength is even higher than in standard mortars.
Conclusion It is possible to rework St. Astier NHL mortars. Their performance related to compressive strenght will be lower than standard mortars unless the reworked mortar is tightly applied to return to a bulk density similar to the standard mortar. The reworked mortar has a higher workabilty.

It would not be possible to rework the mortars if the St. Astier binders would contain additions of cement, gypsum or would have a higher content of aluminates as all these would promote an irreversible quicker set.

  Standard Reworked Standard Reworked Standard Reworked
NHL 3.5 Dosage (kg/m3) 250 250 350 350 400 400
Water Add. (liters) 270 270 290 290 305 305
Extra Water   50   50   50
Time for Rework   18 h   18 h   18 h
Density 28 days) Kg/m3 1900 1840 1900 1840 1900 1840
Comp. Strength (N/mm2) 0.93 0.56 1.25 0.81 1.56 1.08
Increased Density Kg/m3)   1900   1900   1900
Comp. Strength
On Increased Density (28 days) N/mm2
  0.77   1.48   1.93
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