|
Grout is often identified by its application. Some
examples are: bonded prestressed tendon grout, auger
cast pile grout, masonry grout, and pre-placed aggregate
grout. Controlled low strength material
(flowable fill) is a type of grout.
WHY Does Delamination Occur?
Grout is used to fill space or cavities and provide continuity
between building elements. In some applications,
grout will act in a structural capacity. In projects
where small quantities of grout are required, it is proportioned
and mixed on site. The ready mixed concrete
producer is generally called upon when large
quantities are needed.
HOW to Specify Grout?
ASTM C 476 for masonry grout dictates proportions
by loose volumes and is convenient for small quantities
of grout mixed on site. These grout mixtures have
high cement contents and tend to produce much higher
strengths4 than specified in ACI 5305 or Model Codes.
When grout is ordered from a ready mixed concrete
producer, the specifications should be based on consistency
and compressive strength. Converting loose
volume proportions into batch weights per cubic yard is
subject to errors and can lead to controversies on the job.
Specifications should address the addition of any
required admixtures for grout. Conditions of delivery,
such as temperature, time limits, and policies on
job site addition of water, should be specified. Testing
frequency and methods of acceptance must be covered
in specifications.
HOW to Test Grout
The consistency of grout affects its strength and other
properties. It is critical that grout consistency permit
the complete filling of void space without segregation
of ingredients.
Consistency of masonry grout may be measured with a
slump cone (ASTM C 143), and slumps of 8-11 in. are
suggested. This is particularly applicable for grouts
containing 1/2 in. or smaller coarse aggregate.
For grouts without aggregate, or only fine aggregate
passing a No. 8 sieve, consistency is best determined
with a flow cone (ASTM C 939). For flow values exceeding
35 seconds, use the flow table in ASTM C 109,
so modified to use 5 drops in 3 seconds.
Masonry grout (“blockfill”) for strength tests specimens
should be cast in molds formed by masonry units having
the same absorption characteristics and moisture
content as the units used in construction (ASTM C
1019). Never use nonabsorbent cube or cylinder molds
for this purpose.
Strength of other types of grout is determined using 2
in. cubes per ASTM C 942. Method C 942 allows for
field preparation, recognizes fluid consistency, and also
affords a means for determining compressive strength
of grouts that contain expansive agents or grout
fluidifiers. This is extremely important since “expansive”
grouts can lose substantial compressive strengths
if cubes are not confined. However, cylindrical specimens
(6 x 12 in. or 4 x 8 in.), may give more reliable
results for grouts containing coarse aggregate.
Special application grouts often require modification
of standard test procedures. All such modifications
should be noted in the specifications and discussed
prior to the start of the job.
|