Masonry Magazine March 1979 Page. 19
Ready-Mixed Concrete
Transit-mix grout should be rotated continuously from the time the water is added until placement. When a batch mixer is used on the job site, all materials should be mixed thoroughly for at least five minutes. Discard grout not placed within 1-1/2 hours after water is first added to the batch.
Grout Placement
THERE ARE TWO grout placement procedures in general use: (1) low-lift grouting, where the grout is placed in lifts or pours up to 5 ft. in height and no cleanouts are needed; and (2) high-lift grouting, where grout is placed story height and cleanout holes are required at the bottom of each grout space containing reinforcement.
A lift is the layer of grout placed in a single continuous operation. A pour is the entire height of grout placed in one day and may be composed of a number of successively placed grout lifts.
Low-Lift Grouting
THIS IS THE SIMPLEST method of grouting concrete masonry. Figure 1 shows typical reinforced masonry construction with low-lift grouting. Low-lift grouting requires no special concrete block shapes or equipment. The wall is built to scaffold height, or to a bond beam course. Steel reinforcing rods are then placed in the designated hollow cells of the block and the cells are grouted. The level of the grout is stopped at least 1/2 inch from the top of the masonry. The steel reinforcing projects above the top course for sufficient height to provide a lap at the splice of 30 bar diameters.
Move the grout from the mixer to the point of deposit as fast as practical. Use pumping or other placing methods which prevent segregation of the mix and cause a minimum of grout splatter on reinforcement and on masonry unit surfaces not being immediately encased in the grout fill. On small projects, handle and place the grout carefully with buckets equipped with spouts, such as coal scuttles. On large projects, grout pumps or concrete buckets equipped with chutes and handled with lift trucks, are frequently used.
Spaces containing grout should be puddled or vibrated during placement to insure complete filling of the grout space. It takes very little vibration to do the job properly because of the plasticity of the grout. Puddling is usually done with a 1 X 2 in. wooden stick. When highly absorptive masonry units are used, it is advisable to re-rod or revibrate the grout after it has begun to stiffen. The reconsolidation overcomes settlement shrinkage separations of the grout from the reinforcing steel and promotes bond to the masonry walls.
High-Lift Grouting
IN HIGH-LIFT grouting, the grouting operation is done after the concrete masonry wall is laid up to story height. It offers certain advantages, especially on larger projects. One advantage is that a larger volume of grout will be placed at one time, thereby permitting the economical use of more expensive equipment, such as the grout pump. A second advantage, in some instances, is that high-lift grouting permits building the full story height before placing of vertical steel. Less steel is used for splices, and the location of the steel can be easily checked by the inspector prior to grouting.
Vertical cells containing steel reinforcement should be at least 3 inches in dimension. Proper preparation of the grout space before grouting is very important. Remove all foreign materials or debris through cleanout openings at the bottom of all cores containing dowels or vertical reinforcement in hollow-unit masonry and at alternate cores in the units of solid grouted walls. The cleanout openings should be at least 3 by 4 in.
The openings to be made in the face shells of units (cleanouts) should be made before the start of wall laying. A special scored unit is sometimes used to permit easy removal of part of the face shell for cleanout openings. When both sides of concrete block wall are to be exposed to view, it may be necessary to remove the entire face shell of the unit to provide the necessary cleanout opening.
After laying of the masonry units is completed, remove all mortar droppings and projections from the foundation or bearing surface, masonry walls, and reinforcing. The grout spaces are checked for cleanliness and reinforcement position, then the clean-
FIGURE 4 ALTERNATE METHOD OF PROVIDING
CLEANOUT OPENINGS REQUIRED IN
HIGH-LIFT GROUTING
Vertical reinforcement
Dowel
Full cut headers used in
first course to form
continuous cleanout
opening
Full or half brick as
required to support header
units.
Note: Clean out mortar
droppings and form over
opening before filling cores.
FIGURE 5 Unit scored to permit removal of part of face
shell for cleanout openings required in high-lift grouting.