Masonry Magazine February 1994 Page. 36
12"
2" to 6"
5" to 8"
8" to 10"
CONCRETE
MORTAR
GROUT
FIGURE 3. Slump tests of concrete, mortar and grout.
material grout would be considered a stepchild of concrete. It has a) high water content, b) high slump, 9 to 11 inches (229 to 279 mm) (Figure 2) and c) is made up of fine materials of sand and pea gravel with the maximum size being 36" (9.6 mm) in diameter.
During the hydration of this material, it gains strength similar to concrete. There is an initial set, approximately 45 minutes and a final set after approximately 4 to 6 hours. The strength gain of the grout in the first 72 hours is rapid and slows down for the next 90 days. The standard strength of concrete and grout is determined after a 28 day period, (4 weeks) after placing.
The minimum strength required for grout is 2000 psi (13.8 MPa). This may be a hardship because 4 weeks after placing the building may be complete. Certainly the masonry will be complete unless it was a major high rise or extensive complex of masonry construction. Testing after 3 or 7 days may provide an indication of the 28 day strength of grout. The 7 day strength which is 60 to 70% of the 28 day strength implies adequate interim results.
What is the mix design for grout?
We should provide the standard mix design as given in the building code for grout. For fine grout it is, by volume, one part portland cement and three parts sand (Figure 3). For coarse grout it's one part portland cement, three parts sand and two parts pea gravel. This would be a standard acceptable mix for most construction projects. (Figure 4)
Grouting limitations
Depending upon the size of grout space, the area of the cell or the width of the grout space, either fine grout or coarse grout can be used.
Fine grout is used where the grout spaces are narrow, two inches or less, or in hollow block that is four or six inches in width.
The maximum grout pour and minimum size of grout space is given in the UBC Table No. 24-G and ACI/ ASCE/TMS Table 4.3.3.4.
Coarse grout that is to be placed by means of a grout pump should have proportions of approximately 70% to 80% sand and 20% to 30% pea gravel.
Coarse grout may be used in grout spaces in brick masonry, two inches or more in horizontal dimensions and the cells in block construction should be four (4) inches or more in both horizontal dimensions.
For special construction projects, where special high strengths are required a design mix would have to be made by a competent laboratory in which the proportion of portland cement, sand and pea gravel were established along with the amount of water or slump and any admixtures required. Accordingly the standard grout which is 2000 psi (13.8 MPa) as required by the building codes, the standard mix is quite adequate.
Now that we have some information about material called grout, how it is used, how is it placed and what are the problems and procedure we should be aware of.
This article is concerned with partially grouted walls. We know that
TAPE
3-3/4"X3-3/4"X7-5/8"
GROUT TEST SPECIMEN
FIGURE 4. Making grout prisms.
COVER UNITS
WITH ABSORBENT
PAPER TOWELING
36 MASONRY-JANUARY/FEBRUARY, 1994