32
Geotechnical News •June 2015
THE GROUT LINE
add more weight to the structure than
absolutely necessary, and where large
quantities of injected grout are ex-
pected, capacity of the foundations to
carry the additional load should be con-
firmed. Very old structures have often
undergone previous settlement during
their life, and have little capacity for
additional loading. Even small addi-
tions of dead weight can initiate further
movement. In this regard, where large
cavities must be filled, expansive poly-
mer foams have been used, in order to
minimize the additional load.
Cementitious grouts should not only
have strength on the order of the mor-
tar, but also be completely stable (no
settlement of solids or bleed) and free
of shrinkage. Use of viscosity modify-
ing admixtures to
provide thixot-
ropy to the grout
will greatly assist
in limiting travel
and leakage of
the grout within the structure. In addi-
tion to cement and admixtures, typical-
ly used mixes contain up to about four
parts of sand, and are usually injected
in a thick slurry consistency. To pro-
vide stability and shrinkage resistance,
the water:cement ratio should be kept
as low as practicable and high range
water reducing admixtures are advan-
tageous. The exact consistency will de-
pend upon the nature of structure, pur-
pose of the injection, and particulars of
the void system, and can vary between
a thin fluid to a thick slurry.
Because leakage, which can very much
detract from the aesthetics of exposed
surfaces is such a problem, it is best to
repoint or seal exposed joints prior to
any grout injection, Figure 12. This is
especially important when resin grouts
are used as they can be extremely dif-
ficult if not impossible to remove.
Masonry is a composite of different
elements, all held together with the
mortar. The elements can be of vary-
ing size, stiffness, and strength. The
Figure 9. Urethane injection; defects are intercepted at
depth and grout returns to surface can be quite messy.
Figure 10. Large and sometimes continuous voids are
common in older masonry.
Figure 11. Grout leakage is usually a huge problem
when injecting grout into masonry.
Figure 12. It is good practice to repoint and seal masonry
surfaces prior to injection.
