masonry cracks and leaks .. also wideslab design

huangyhg

masonry cracks and leaks .. also wideslab design
we are in a tropical country and experiences lots of rainfall... our usual problems about masonry are masonry cracks and also leaks especially on the interface of solid concrete and masonry. any suggestions?
also, can anybody help me in the design of wideslabs? wideslabs are precast slabs poured half ( or less ) and installed on the structural frame. the slab will then be used as a form on which the on site concrete will be poured. the slab will ultimately become a part of the structure. this can be done both as a prestressed or conventional way. i'm interested on the conventional method using wire mesh girders.
find a job or post a job opening
from my experience the slabs are designed as either prestressed or reinforced concrete slabs for the total  depth. the wire mesh girders are used to give the slabs the capacity to span between supports until the insitu topping is poured. they also provide continunity between the precast and insitu concrete. if you are using a prestressed slab you will need to be careful at the transfer of prestress into the slab as the flat depth could cause the slab to snap due to the prestressing force
as for the masonry do you construct your buildings in cavity construction ?
kieran
in ages past we used a greater proportion of lime in masonry mortars.  this produced:
- greater workability in the plastic mortar,
- greater flexibility in the set mortar (therefore fewer cracks) and
- greater ability to self heal the cracks that did form.

suitable proportions of cement:lime:aggregate are:
1:1:6 for conditions of severe frost and exposure
1:2:9 for most normal work in exposed conditions
1:3:12 for internal work only
mortars for structural work should, of course, be properly specified from the appropriate codes.
properly detailed contraction joints at suitable intervals in masonry walls will allow the cracks to be dealt with at the design stage.
if all else fails, make sure you have plenty of silicone mastic.
proper expansion joints between the concrete and the masonry are crucial, and can be retro-fitted.  single-wythe masonry will always be a problem in wet areas, so the best solution is to add a veneer with a cavity to control the water infiltration.  also check roof parapets, since this is an easy place for water penetration.
all,
thanks!!!! i'll try the options you have suggested for our r&d evaluation.
kieran,
by cavity construction, if you mean two separate chb walls... we are using only one; filled with mortar... usually using 6" thk. or sometimes evg / 3d panels.
other suggestions still appreciated when available.
ksd
dear ksdphilippines,
   a beam of 150mm. depth and thick ness same as wall will help to prevent the dampness to enter.for already existing building the cracked portion , the plaster is removed racked about 100mm on both sides of the crack  fix a chicken wire mesh and cover it with 1:3 plaster.this will invariabley keep the moister away.
pechetty.
i have done used pechetty's method countless times here in tanzania.in 50% of the cases the plaster cracks not at the treated joint, but where the chicken mesh ends!the most effective method is plastering the crack on one side and finishing up on the opposite side the next.wait a few days for curing.you should get a "trained" crack which can be treated with a flexible mastic.basically it will not be an eyesore.
regards mooslim