While working for a petroleum company in West Africa in the 1970's, US Peace Corps volunteer friends (liberal arts educated couple) assigned to a community development project in a neighboring country and I began a 15-20 day round trip snail mail correspondence on various issues generally associated with my engineering gig. After a few months, I took off a couple of weeks to visit them.
Shortly before they arrived on their station, for some reason, the Soviet embassy had delivered to the community several hundred sacks of what appeared to be Portland cement, most of which were still carefully stacked and dry in a warehouse when I arrived. Much of the correspondence with my PC friends had been related to this ten tonne or so cache of cement and the fact that other than miscellaneous scraps of metal, there was nothing available as a reinforcement material except the planar pattern branches of a local hardwood tree commonly used for small structural slabs of no more than 3 meters of span extent, some of which were decades old and still in service without a problem.
The branches generally were dried for 1.5 to 2 years after cutting and of about 1+ meter sort of square in a trimmed planar aspect ratio of an average of no more than 100 mm thickness; ''thrashing'' with poles of the dry branches broke off weak branchlettes and twigs, as well as removed bark. Slab forming consisted of a crisscrossed pattern of rough wooden planks covered with about 3 layers of trimmed palm fronds. Cement and river aggregate blended to minimum workability and form leakage, was placed in a 20-30 mm layer across the extent of the palm fronds, and the reinforcement branches was shoved down much as is occasionally done with wire mesh reinforcement. Additional layers of paste were applied until 30-40 mm below the finished top of slab surface, at which point, a 3-4 day set was allowed, following which the ''trimmers'' clipped any ''twigs'' that were higher than the planed finished slab surface.
A couple of months before my arrival, I asked my friends to measure the weight of about a 1-2 kg sample of dried branch fragments, then submerge the sample in water for 6 weeks, shake it dry, but still visibly wet, then weigh it again of their postage scale. The ''saturated'' increase in weight was 3 per cent, not bad for an ersatz rebar. When I arrived, we broke up a couple of 15-20 year old abandoned slabs and extracted wood fragments. The concrete bond to the wood was about the same as that to smooth steel wire or rod. Several rather straight pieces between secondary branching points were hewn to a nominally square cross section, then placed as beamlettes with suspended mid-span loads. Outer fiber strength was calculated at about 35 MPa, with elastic modulus of about 150 MPa at a rather sudden rupture with very little indication of ductility, but preceded by some very audible cracking sounds.
We did a couple of ''test'' slabs (as squat latrine covers where a detail around the holes was identified). The branch density typically used historically in the community produced a working ''d'' from finished slab of about 0.65 slab thickness and a branch volume of 15-20 percent of total slab thickness. Aged concrete strength was not determined, but for an assumed effective 28-day compressive strength (some portion of branches included at the top of slab) of about 12 MPa, the historically typical 150 +/- mm thick 3 meter slab was rather balanced in rupture tension and compression in a one way slab analysis for a service load of 100 kg/sm. I worked out a semi-two way slab table of 6 square spans of 3 to 6 meters for the minimum slab thickness of two ranges (150 and 250 kg/sm) of loading and multiples of branch reinforcement quantities for each based on a factor of safety (1.5) of what was customarily used for the 3 meter slabs. Other than the PC volunteers, there were 4 local persons (2 young constructors in their 20's, a nurse and the nominal public works director) who understood the process and my table.
When I left, I put my slide rule away and thought I was finished, but the letters started flowing, several per week. What about holes? (I had a 400 mm square hole detail for the outer 2/3 of the span, but...) What about point loads other than the single center span point load of 200 mm square on a pedestal that I listed? Etc. The Soviet cement was used up in less than a year after my visit; there were not reports of failure.
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Robert Bullard P.E., M.ASCE
President
Ahimsa Technic Inc
Ponce Inlet FL
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Original Message:
Sent: 09-23-2017 09:33
From: Ashish Ganesh
Subject: Rehabililtaion of Concrete Structure
We are planning for the project on rehabilitation of concrete structure subjected to corrosion using bamboo. We are actually naive for the project on a concrete structure. Bamboo has been used as a substitute for steel reinforcement and enough research has not been made on this issue. Does anybody have <g class="gr_ gr_206 gr-alert gr_gramm gr_inline_cards gr_run_anim Grammar only-ins doubleReplace replaceWithoutSep" id="206" data-gr-id="206">idea</g> on this matter? It would be very helpful to move forward if we could get hands-on research paper based on this.
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Ashish Ganesh S.M.ASCE
Bangalore
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