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Strength of Brick Masonry

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suited  to  walls  or  partitions  in  hospitals,  dairies, laboratories, and other structures requiring sanitary conditions  and  ease  of  cleaning. Fire  brick  is  made  from  a  special  type  of  clay. This  clay  is  very  pure  and  uniform  and  is  able  to withstand the high temperatures of fireplaces, boilers, and  similar  constructions.    Fire bricks are generally huger than other structural bricks and are often hand molded. Cored  bricks  have  ten  holes—two  rows  of  five holes  each-extending  through  their  beds  to  reduce weight.    Walls built from cored brick are not much different in strength than walls built from solid brick. Also, both have about the same resistance to moisture penetration.  Whether  cored  or  solid,  use  the  more available brick that meets building requirements. European brick has strength and durability about equal to U.S. clay brick. This is particularly true of the English and Dutch types. Sand-lime brick is made from a lean mixture of slaked  lime  and  fine  sand.  Sand-lime  bricks  are molded  under  mechanical  pressure  and  are  hardened under  steam  pressure. These   bricks   are   used extensively  in  Germany. STRENGTH OF BRICK MASONRY The main factors governing the strength of a brick structure  include  brick  strength,  mortar  strength  and elasticity, bricklayer workmanship, brick uniformity, and  the  method  used  to  lay  brick.  In  this  section, we’ll cover strength and elasticity. Workmanship is covered  separately  in  the  next  section. The strength of a single brick masonry unit varies widely,  depending  on  its  ingredients  and  manu- facturing  method. Brick  can  have  an  ultimate compressive  strength  as  low  as  1,600  psi.  On  the other hand, some well-burned brick has compressive strength  exceeding  15,000  psi. Because  portland-cement-lime  mortar  is  normally stronger than the brick, brick masonry laid with this mortar  is  stronger  than  an  individual  brick  unit.  The load-carrying  capacity  of  a  wall  or  column  made  with plain lime mortar is less than half that made with portland-cement-lime   mortar.   The   compressive working strength of a brick wall or column laid with plain   lime   mortar   normally   ranges   from   500   to 600 psi. For mortar to bond to brick properly, sufficient water  must  be  present  to  completely  hydrate  the portland  cement  in  the  mortar.  Bricks  sometimes have  high  absorption  rates,  and,  if  not  properly treated,  can  “suck”  the  water  out  of  the  mortar, preventing complete hydration. Here is a quick field test to determine brick absorptive qualities. Using a medicine dropper, place 20 drops of water in a l-inch circle (about the size of a quarter) on a brick. A brick that absorbs all the water in less than 1 1/2 minutes will suck the water out of the mortar when laid. To correct this condition, thoroughly wet the bricks and allow  time  for  the  surfaces  to  air-dry  before  placing. BRICKLAYING  METHODS Good  bricklaying  procedure  depends  on  good workmanship  and  efficiency. Efficiency    involves doing  the  work  with  the  fewest  possible  motions. Each  motion  should  have  a  purpose  and  should accomplish   a   definite   result.   After   learning   the fundamentals,  every  Builder  should  develop  methods for achieving maximum efficiency. The work must be arranged in such a way that the Builder is continually supplied  with  brick  and  mortar.  The  scaffolding required must be planned before the work begins. It must  be  built  in  such  a  way  as  to  cause  the  least interference  with  other  crewmembers. Bricks should always be stacked on planks; they should  never  be  piled  directly  on  uneven  or  soft ground. Do not store bricks on scaffolds or runways. This  does  not,  however,  prohibit  placing  normal supplies  on  scaffolding  during  actual  bricklaying operations.  Except  where  stacked  in  sheds,  brick piles should never be more than 7 feet high. When a pile  of  brick  reaches  a  height  of  4  feet,  it  must  be tapered back 1 inch in every foot of height above the 4-foot  level.  The  tops  of  brick  piles  must  be  kept level,  and  the  taper  must  be  maintained  during unpiling  operations. MASONRY TERMS To  efficiently  and  effectively  lay  bricks,  you  must be familiar with the terms that identify the position of masonry  units  and  mortar  joints  in  a  wall.  The following  list,  which  is  referenced  to  figure  8-32, provides  some  of  the  basic  terms  you  will  encounter. Course—  One  of  several  continuous,  hori- zontal  layers  (or  rows)  of  masonry  units bonded  together. 8-26



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