Masonry Magazine January 1970 Page.18
FIGURE 1 TYPICAL REINFORCED CONCRETE MASONRY CONSTRUCTION
USING THE LOW-LIFT GROUTING TECHNIQUE
Vertical steel-Lap 30 bar diameters at splices; hold in position at intervals of 192 diameters.
Steel in Bond Beams is set in place as wall is laid up.
Place metal lath under bond beam to confine grout.
Floor Slab.
Footing.
Stop grout 1½" from top.
Place grout in lifts not to exceed four feet; puddle or vibrate in place.
Cells containing steel are filled solidly with grout; vertical cells should provide a continuous cavity, free of mortar droppings, and at least 2 x 3 inches in size.
Place mortar on cross webs adjacent to cells which will be grouted to prvent leakage.
When hollow-core masonry units are being filled, you can generally ignore the hydrostatic or fluid pressure exerted by the freshly placed grout. Therefore, it is necessary that mortar in hollow unit masonry walls cure only 24 hours before grouting. When filling the cavity in two-wythe masonry, do not pour grout until the mortar has cured at least 3 days. In cold damp weather or periods of heavy rains, the masonry should cure at least 5 days.
Grout
GROUT FOR USE in concrete masonry walls should comply with ASTM C 476 "Specifications for Mortar and Grout for Reinforced Masonry." Table 1 lists the proportion requirements of this specification.
The choice of fine or coarse grout depends mainly on the minimum horizontal cross-sectional dimensions of the grout space. Building codes vary with respect to minimum dimensions of grout spaces and maximum size of aggregate in grout. The smallest space to be grouted should be at least 2 x 3 inches. In this case, fine grout (sand aggregate) should be used. When the minimum horizontal dimension of the space is 4 in., use coarse grout (containing pea gravel). Also use coarse grout for 2-wythe masonry walls if the continuous clear space between wythes is at least 2 inches.
Cement content of grout usually ranges from 6 to 8 bags of portland cement per cubic yard of grout. Grouts placed by pump have cement contents near the higher range.
If the minimum dimensions of the grout space exceed 5 to 6 in., as may occur in pilasters or columns, the cavities can be filled with conventional concrete with maximum aggregate sized to 1 in. Some specifying agencies stipulate that % in. gravel should be used when the grout space is greater than 4 in. However, the choice of the maximum size of the aggregate should be consistent with the particular job conditions to insure satisfactory placement of the concrete fill and proper embedment of the reinforcement.
All grout should be of fluid consistency; that is, it should be as fluid as possible without segregation of the materials. When the slump is measured using ASTM C 143, "Method of Test for slump of Portland Cement Concrete," the desired range is 8 in. for units with low absorption, up to 10 in. for units with high absorption.
Wherever possible grout or concrete fill should be batched, mixed, and delivered in accordance with the requirements for transit-mixed concrete, ASTM C 94, "Specification for 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 ½ 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 4 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 is composed of a number of successively placed grout lifts.
Wherever possible grouting should be done from the inside face of the masonry.
Low-lift Grouting
THIS IS THE SIMPLEST and most common method of grouting concrete masonry. Figure 1 shows typical reinforced masonry construction with low-lift grouting. Low-lift grouting required no special concrete block shapes or equipment. The wall is built to scaffold height, or to a bond beam course, but not more than 4 ft. Steel reinforcing rods are placed in the proper hollow cells of the block and the cells are grouted. The level of the grout is stopped 1 ½ inches from the top of the masonry. The steel reinforcing sticks up above the wall a 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