Someone asked me this the other day and I did not know for sure. At several locations in Bangalore where columns are coming up, you see the pillar covered with a jute/gunny wrapping and workers wetting this sack from a bucket and mug or some kind of bottle etc. Does anybody here have the expertise to comment on how good this methodology is? Input will be appreciated.
Thanks.
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Not mature enough
Not an expert in civil engineering but the way construction is being done in general doesnt inspire me with confidence. I can visibly notice the professionalism in safety, quality of tools and equipment vastly inferior from the rest of the world. Just heard about this now confirming my fears. We are turning this out to be some massive pre BC pyramid of egypt with lives being lost and all that. The ease with which complex structures are being built around the world, these incidents shows our civil engineers in primitive light. We can clearly see that in the state of our infrastructure. At the same time we wont mature if we dont get our act together and build these things oursleves. Sridharan was clear when he said we dont have such massive engineering experience in India and we have to get our local companies exposure to international scale projects.
Some help from Wikipedia
Not an expert but to help you and having used the method of wrapping jute bags/ and also dry rolled paddy ropes for keeping the pillars/fresh concrete structures like flooring, masonry covered walls etc., wet for curing purpose for their becoming harder and more durable and also to give you a technical background, the following is
From Wikipedia, the free encyclopedia
Concrete is a construction material composed of cement (commonly Portland cement) as well as other cementitious materials such as fly ash and slag cement, aggregate (generally a coarse aggregate such as gravel, limestone, or granite, plus a fine aggregate such as sand), water, and chemical admixtures. The word concrete comes from the Latin word "concretus" (meaning compact or condensed), the past participle of "concresco", from "com-" (together) and "cresco" (to grow).
Concrete solidifies and hardens after mixing with water and placement due to a chemical process known as hydration. The water reacts with the cement, which bonds the other components together, eventually creating a stone-like material. Concrete is used to make pavements, architectural structures, foundations, motorways/roads, bridges/overpasses, parking structures, brick/block walls and footings for gates, fences and poles.
- Vasanth Mysoremath
Curing
Yes - it is common procedure to use gunny sacks soaked in water or curing compound to cure the concrete or tie the sack and pour water on it. Curing compounds may be sprayed directly on concrete but are not as effective as leaving wet gunny sacks in place for a longer time.
idontspam - different people (engineer, contractor, safety official) are responsible for different aspects of the project. The reinforcement splaying out may be because of pouring concrete from a greater height or not forming it correctly and so on. Without knowing all the facts, it is probably not right to blame one particular person or entity.
thank you.for answers - next level of detail
Okay, so I understand that moisture is important for curing. For the concrete, the loss of moisture is from the surface, so applying a barrier that can retain moisture and compensate for the evaposrative loss is what is being tried.
What I am wondering is - how repeatable is the process of this gunny wrapping and human wetting using very elementary tools? If I am using a plastic bottle to splash water on gunny sack around a big pillar... what are the chances that I will not get it (a) uniformly wet (b) Sufficiently wet such that it remains wet until the next round of wetting.
This seems to be more like the way our maid does the dishes. Every once in a while, something gets left behind. While washing the vessel once again is easily done, a weak spot in a concrete pillar is weak for life, is it not.
Can folks comment on: (a) Is this the international practise to wet concrete (b) Have there been studies on how effective this method is?
Not an enquiry cmte
Without knowing all the facts, it is probably not right to blame one particular person or entity.
Please read my comment again. I have passed judgement based on the visual observation on the variety and primitiveness of tools and equipment used and practices in construction of some of the infrastructure projects. The accident in question may or may not have arisen due to the the tools and practices but the collapse supports the argument that something is definitely wrong if this must have happened. The primitivemess of some of the practices and tools a worker is equipped with in construction sites is clearly visible in comparision with similar labourers elsewhere in the developed world. My judgement also stems from the observation of the kind of engineering infrastructure we witness starting from the practice of laying streets, pavements, primitiveness of traffic markers etc. My argument is also not about curing technique of one pillar in the question. It is broader and I hope the point is appreciated in such a light.
QC
sanjayv - That is quality control. Curing links 1 and 2 (first one is a little dramatic but conveys the concept) provide some more information. Some experienced engineers agree that gunny-sack water-based curing is more effective - it is practised less as it is very labour intensive and labour is expensive in developed countries. Workers need to be skilled, responsible and not get lazy. Contractor and site engineer have to constantly check quality but cannot do it at all locations at all times. Same as in a manufacturing factory. Post-install, regular maintenance of structure is also very important - if problems come to light, they can be rectified before too late. Again, quality control and maintenance issues.
idontspam - was responsing to these incidents shows our civil engineers in primitive light. Dont want to get into a battle of words. Developed country workers were not born with power tools. The skill, non-laziness, QC and safety matter more (to a certain extent) than the available tools.
will stop here. cheers and no offense to anybody.
Disagree and no offense taken
Developed country workers were not born with power tools.
I stand by my statement. These incidents if caused due to the poor practices that are existing in the industry it does show our civil engineers in poor light. Construction companies in Africa do not have access to power tools because they are poor and hence the quality of the infrastructure shows up. There is no harm in calling that primitive. You cannot get the consistent mix of asphalt if you dont have an automated mixer. No amount of enthusiasm can substitute for it. If our labourers carry earth on their heads instead of tippers we should have the guts to admit it is primitive even if it gets the job done in a longer and inhumane way. Admit we can get better instead of getting offended. I dont want to see us any less we have the same brains the rest of the people in the world have. We are only not using it the same effect.
he skill, non-laziness, QC and safety matter more (to a certain extent) than the available tools.
Disagree completely. If it is found that the primitiveness is preventing us from executing mega structures like metro we should take it on the chin and try and get better instead of feeling offended. Like I said you can build the metro by hands like the pyrimids were built with loss of life and all or you could get the tools required to do the job and make easy on all.
GIGO
Read here to see how lack of adequate tools and inhumane practices in every profession contributes to low quality of output. I quote
"Low-ranking officers often work in difficult conditions. They are required to be on call 24 hours a day, every day. Instead of shifts, many work long hours, sometimes live in tents or filthy barracks. Many are separated from their families for long stretches of time. They often lack necessary equipment, including vehicles, mobile phones, investigative tools and even paper on which to record complaints and make notes."
Summary thus far
Okay... so as I understand it - current soaking and gunny bags method can work, but is labour intensive, requires non-lazy workers, more stringent quality control from engineer and contractor. So the big lacuna in knowledge is that is we do not know how strong a typical structure constructed with this method in India are. If there are issues found later during use, if problem is not catastrophic in nature, fixes can be made.
@n Since you sem to understand the civil engineering aspects here (are you in the profession?), are there methods of non destructive testing and inspection of final structures? How often is that used in India? The thing is, we have to be concerned about this infrastructure. Our country has not exactly made a name in "quality" and following"standards" in most spheres of life.
As an example, if you go to a regular hardware store to buy any product [ what are the chances of getting anything based on spec? Unless you buy very expensive plumbing fittings, what are the chances everything threads well together without a lot of sealant material (thread, teflon tape etc.). As an engineer who has worked in the country and outside - in my profession, there are un-necessary issues faced everyday because of a total lack of respect for quality, standardization and safety.
My 2 cents on the tweetanator's comments. Tools are important in all professions. I will agree 100%. Consider the roads that are machine laid nowadays ... are'nt those much better quality than the old, gang crew laid roads from the past. I feel they are.