The industry is experiencing fast-paced advances in grouting procedures and materials as building codes allow new opportunities to explore means and methods for constructing grouted masonry walls. Grout is a mixture of: cementitious material usually portland cement ; aggregate; enough water to cause the mixture to flow readily and without segregation into cores or cavities in the masonry; and sometimes admixtures. Grout is used to give added strength to both reinforced and unreinforced concrete masonry walls by grouting either some or all of the cores.
It is also used to fill bond beams and occasionally to fill the collar joint of a multi-wythe wall. Grout may also be used to stabilize screen walls and other landscape elements.
In reinforced masonry, grout bonds the masonry units and reinforcing steel so that they act together to resist imposed loads. In partially grouted walls, grout is placed only in wall spaces containing steel reinforcement. When all cores, with or without reinforcement, are grouted, the wall is considered solidly grouted. This TEK covers methods for laying the units, placing steel reinforcement and grouting. Figure 1 shows the basic components of a typical reinforced concrete masonry wall.
When walls will be grouted, concrete masonry units must be laid up so that vertical cores are aligned to form an unobstructed, continuous series of vertical spaces within the wall. Head and bed joints must be filled with mortar for the full thickness of the face shell.
If the wall will be partially grouted, those webs adjacent to the cores to be grouted are mortared to confine the grout flow. If the wall will be solidly grouted, the cross webs need not be mortared since the grout flows laterally, filling all spaces.
In certain instances, full head joint mortaring should also be considered when solid grouting since it is unlikely that grout will fill the space between head joints that are only mortared the width of the face shell, i. In cases such as those, open end or open core units see Figure 3 should be considered as there is no space between end webs with these types of units.
Care should be taken to prevent excess mortar from extruding into the grout space. This is because large protrusions can restrict the flow of grout, which will tend to bridge at these locations potentially causing incomplete filling of the grout space. To prevent bridging, grout slump is required to be between 8 and 11 in. This slump may be adjusted under certain conditions such as hot or cold weather installation, low absorption units or other project specific conditions.
Approval should be obtained before adjusting the slump outside the requirements. Using the grout demonstration panel option in Specification for Masonry Structures ref. At the footing, mortar bedding under the first course of block to be grouted should permit grout to come into direct contact with the foundation or bearing surface.
If foundation dowels are present, they should align with the cores of the masonry units. If a dowel interferes with the placement of the units, it may be bent a maximum of 1 in. When walls will be solidly grouted, saw cutting or chipping away a portion of the web to better accommodate the dowel may also be acceptable.
If there is a substantial dowel alignment problem, the project engineer must be notified. Vertical reinforcing steel may be placed before the blocks are laid, or after laying is completed. If reinforcement is placed prior to laying block, the use of open-end A or H- shaped units will allow the units to be easily placed around the reinforcing steel see Figure 3.
When reinforcement is placed after wall erection, reinforcing steel positioners or other adequate devices to hold the reinforcement in place are commonly used, but not required. However, it is required that both horizontal and vertical reinforcement be located within tolerances and secured to prevent displacement during grouting ref.
Laps are made at the end of grout pours and any time the bar has to be spliced. The length of lap splices should be shown on the project drawings. On occasion there may be locations in the structure where splices are prohibited. Those locations are to be clearly marked on the drawing. Reinforcement can be spliced by either contact or noncontact splices.
Noncontact lap splices may be spaced as far apart as one-fifth the required length of the lap but not more than 8 in. This provision accommodates construction interference during installation as well as misplaced dowels. Splices are not required to be tied, however tying is often used as a means to hold bars in place. As the wall is constructed, horizontal reinforcement can be placed in bond beam or lintel units.
If the wall will not be solidly grouted, the grout may be confined within the desired grout area either by using solid bottom masonry bond beam units or by placing plastic or metal screening, expanded metal lath or other approved material in the horizontal bed joint before laying the mortar and units being used to construct the bond beam.
Roofing felt or materials that break the bond between the masonry units and mortar should not be used for grout stops. Standard two-core concrete masonry units can be effectively reinforced when lap splices are not long, since the mason must lift the units over any vertical reinforcing bars that extend above the previously installed masonry. The concrete masonry units illustrated in Figure 3 are examples of shapes that have been developed specifically to accommodate reinforcement.
No matter the size unit, however, a variety of block types are available, including: Header, bond, lintel, closer, jamb, kerf, sash, bull-nosed, beveled-end, and acoustical block. Next, I will discuss the methods of construction of both walls and piers, including the different types of reinforcement, which is determined by the design loads expected at the Project Site, and the particular in-service application. See the Diagrams below for the following discussion on walls.
As mentioned above, CMU walls are constructed by laying the block courses in a running-bond pattern. This spacing is determined by the applicable wind, seismic, and snow loads, and as the application demands.
The vertical dowels are embedded in the supporting elements of the foundation base, which is reinforced cast-in-place concrete consisting of either continuous or pad footings, grade-beams, or thickened slabs. This Specification is in turn referenced by the Building Code enforced at the building site, which in the U. Bar size is also determined by the design loads and demand. A bond-beam course is laid at the top of walls, which has a U-shaped trough which is filled with horizontally reinforced grout.
Where the blockwork will be below grade in-service and subjected to contact with the soil, a weatherproof sealant should be applied. Per ACI , CMU walls constructed as described above are considered to be properly detailed for seismic applications. Next, I turn the focus to square CMU columns or piers. As mentioned, these piers are constructed of column block, which is square and has only 1 cell.
The typical method of reinforcement of a CMU pier is to use several vertical hooked dowels embedded in the foundation and spliced in the same manner as with walls. Again, the bar size is dependent on the loading and demand. By joining you are opting in to receive e-mail. Promoting, selling, recruiting, coursework and thesis posting is forbidden. Students Click Here.
Related Projects. This was a local city limitation. On a similar project now and would like to know what your experience is using 4" cmu and if you had issues placing steel and grouting cells. What is your take on this?. To me is fine and the numbers check for in plane loading, shear and moment. We don't use reinforced 4" blocks at all for anything structural. In the same boat as JAE - 8" block is the smallest I've used for structural purposes. I would never use it for a bearing wall.
Even for solid concrete, the minimum thickness for a bearing wall is 5. Unless this is a screen wall, as in for a dumpster, I would not use 4".
Heck, with the truck drivers I have seen in our area, I would use3 nothing less than 24" block for the dumpster walls! We use 4" cmu only for fences around houses here, and the block has zero reinforcing in it - however there are H-pilasters spaced about 12' oc with 2- 4 verts.
ACI , Table 1. I'm not sure if there's any way to meet it with 4 inch blocks. Most that 4" CMUs are not made for reinforcement, but can be. If you go by the normal standards the units may work for reinforcement, but units are made with tapered core and a face shell wider at the bottom. In many areas, contractors will desire an almost closed core for ease of laying and mortar spreading the weight is not a factor.
Unfortunately, this does not work well with grout filling and rebar placement. What works on paper is not acceptable. The 6" mm units are very common in many areas in the world using the normal unit dimensions for engineered units because of the demand, especially when higher strengths f'm may be required. The 4" from the Jim Amrhein book is an example of what may be done with 4" block and the international designers may have studied from him or attended seminars and caused the local use of masonry.
They did use 6" on many highly loaded walls and switched to 4" for some interior bearing walls to replace the 6" poured walls on high rises.
Because of the number of load bearing walls, the cost was not a factor and the engineers were usually employed by developers with an ear on square footage of floors and compatibility with floor plans starting in the 's. The 6" units are so practical that they are the most common for high performance engineered construction in many areas. Dick Engineer and international traveler interested in construction techniques, problems and proper design. I am surprised ACI allows 4" block for load bearing walls, but I have only used it for bathroom partitions Where are you located where this even calcs out for a two story building?
To add to concretemasonry's thoughts, even if you could get it to calc out, my experience with partially grouted CMU is that sometimes even 8" CMU is a challenge when it comes to quality control of proper rebar location and good grout consolidation. Also, I think it would impossible to have a lap splice.
I don't see it being very practical to have a hooked bar in your footing that extends up 8 to 10 feet, and then how do you lap it with the second story walls?
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