Block
- Concrete Masonry Unit (CMU)
- Fundamental component of a masonry wall
- Strength of the block is a key component in the strength of the wall
- Check local manufacturers for available typical block strength
- Typically CMU comes in “normal weight”, “medium weight” or “lightweight”
- check with local suppliers for regional preferences
- CMU now with reduced web thickness for improved R-values
Mortar
- “Mortar” and “grout” are not synonyms
- Workable paste used to bind construction blocks together
- Becomes hard when it sets
- Typically made from a mixture of sand, a binder such as cement or lime, and water
- Not as strong as CMU (does not need to be)
- Purpose is to be the “glue”
- Type “S” or “N” (and others)
- Mortar cement has more tensile strength than masonry cement
- Mortar cement is better for unreinforced masonry walls
Grout
- “Grout” and “mortar” are not synonyms and are NOT the same
- Essentially fluid concrete
- Fills cores of CMU, especially when there is reinforcement in the cores
- Generally composed of a mixture of water, cement, sand, pea gravel
- Fine grout or coarse grout –applied as a thick liquid, and hardens over time
- Must be 2000 psi minimum and greater than f’m
- Can be similar strength as CMU, but does not need to be
- Fine grout must be used as per code requirements when the grout space is too congested by reinforcing steel or other obstructions that would impede the flow of grout as intended down the entire column
- Coarse grout is based on fine grout mix proportions with 1-2 parts additional (3/8″) coarse aggregate added
- Self-consolidating grout (SCG) is a specially-formulated grout for use with reinforced masonry. It is very flowable, easy to install, increases the masonry’s moisture-resistance, and has less shrinkage than conventional grout. SCG is specifically permitted to be used by the Structural Masonry Specification (TMS 602), which is referenced by the IBC Codes
Vertical Reinforcement
- Strengthens wall: masonry (CMU, grout, mortar) is good in compression, but bad in tension – reinforcement is great in tension.
- Reinforced cells must be grouted to bind reinforcement to CMU .
- Generally needed at exterior walls.
- Reinforced bars are typically ASTM A615, fy = 60ksi; they can be ASTM A706 grade if welding is required.
- Contractor would prefer to use 2 smaller bars vs 1 larger bar .
- Bar sizes need to consider laps. For a portion of the wall height, there will be twice the reinforcement in each cell.
- If larger bars are required and laps will not fit, use reinforcing couplers. The couplers must be designed for at least 125% of the yield strength of the bar.
- Bar sizes are limited by the following criteria: the area of reinforcing must be less than or equal to 4% of the cell area (8% at laps); the bar diameter must be less than or equal to 1/8 of the least nominal member dimension; and the bar can be no larger than a #9.
- Size CMU appropriately so rebar fit into cell with proper grout cover.
(2) #8 in a 8” CMU. There is not enough clearance for proper grout cover. This could lead to diminished wall strength and cracks in the CMU.
Horizontal Joint Reinforcement
- Primarily for crack control
- Typically spaced 16” o.c. vertically
- Common to use hook and eye type to engage veneer
- For wire reinforcement, minimum cover = 5/8″ when exposed to weather or earth or 1/2″ otherwise
- Stainless or galvanized
- The minimum wire size is W1.1; the maximum wire diameter is equal to 1/2 the size of the bed joint
- For joint reinforcing used as shear reinforcing, the minimum amount is (2) 3/16″ wires at 16″ in Seismic Design Categories A & B; 8″ spacing in SDC C, D, E, or F
