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Concrete - Protecting your structure..
Hi all,
Hope this is of assistance to someone out there at some point in time.
We write this knowing that all too often, concrete quality is overlooked in Bali, and unfortunately often such is exploited by those selling you the product.
Concrete as you probably know is a combination of cement, water and aggregates (sometimes an admixture is added and sometimes flyash is added - but not often in Indonesia). The aggregates are comprised of fine aggregates (sand) and coarse aggregates (batu koral, batu cor, I.e. A bitumen or gravel equivalents). The quality of the "mud" itself ("beton") is one of the most important factors in the integrity of your structure - and when combined with steel reinforcement, you have a monolithic compound (reinforced concrete), which is absolutely, without doubt, the single most important component of your structure. Bricks in Indonesia are mere wall fill, and though they have a certain amount of compressive strength (rather little), such is unreliable and inconsistent and in no circumstances should be counted as anything other than dead weight within the context of your engineer's structural calculations.
Concrete in Indonesia is available in many mix designs and qualities. The most common characterization of these designs is by the compressive strength they are supposed to yield. In Indonesia, the colloquial classification in represented as K###, where ### is equal to the amount of load in kilograms that a single centimeter (by surface area) should be able to be loaded to by a compressive force before failing. That means that a 10cm x 10cm concrete column, poured with K300 should be able to withstand a compressive force of 30 tons (10 x 10 x 300kg) without failing. To achieve these varying grades of mixes (K250, K300, K350, K400, etc) the concrete (or "beton") supplier will adjust their mix design, and their price per cubic meter. Generally speaking, higher grades of concrete have higher volumes of cement, which is the most expensive component of the mud in conventional concrete. Other factors will also affect the volume of cement required - such as aggregate size. The smaller the coarse aggregate for example, the more cement required, as the surface areas requiring bonding increase.
There are many factors that are considered in a mix design, enough to fill several semesters at a tertiary institution, but those details are not the intention of this post.
There are certain applications of concrete whereby K250 may suffice, there are many applications whereby K400 will be required. Most applications should be at least K300. In any case, what's fair is that you are receiving the product you paid for.
Always ensure you collect samples from the pour, on site - enough to test compressive strength at 3 days, 7 days, 14 days, 21 days (optional) and 28 days (essential). Any university with a Civil Engineering Department, including Univeritas Udayana can conduct these tests for you, and you would be surprised just how cheap they are.
Important tips
- Randomly collect these samples. Drivers talk to dispatch and if they see you're regimentally collecting samples on every second truck, you may have your mixes "selectively" dispatched
- Ensure your supplier knows that they'll incur heavy penalties for test results below ordered grade
- It's not a bad practice in Indonesia to "order one grade up" - a penalty for the supplier is nice, but at the end of the day, if the concrete has been poured, you probably have to live with it. Still, apply a penalty based on the ordered grade, not the minimum grade you need
- Always remember, if they think they can cheat you, they probably will
Other tips
- Workability on site is extremely important. A good test result means little if the correct application wasn't achievable. Always perform "slump tests", and be clear with your supplier of your slump requirements. Reject loads that don't fall within range
- Have ample vibration equipment on site - ramming bamboo or steel rebar up and down in the mud is a poor substitute, and on suspended pours, a piece of 22mm rebar rammed too far can take out a chunk of formwork (messy)
- Curing is as important as the application itself. A poorly cured pour will only strengthen to a fraction of its potential. Your lab tests may be fine, but if it wasn't cured properly on site, you have compromised the integrity of your structure. Ponding works well and 28 days is a good duration for suspended slabs
- Try to leave formwork on suspended slabs in place for as long as possible. 21 days is the minimum and 28 days is safe in most applications
There are many other very important aspects of ensuring a quality end product, but hopefully the few tips above may help.
All the best & happy pouring..
Populaire..
Last edited by Populaire; 13-09-2011 at 01:14 AM.
I'm sure this is all excellent and valid information that would serve to support the efforts on building sites all over the world but, and I gotta be honest, if you try pulling this stuff on your personal build here in Bali you will heighten the hilarity value of the surrounding area but you will not achieve anything in terms of building a dog house.
I gather you are speaking from an industry standpoint - but most of the people I know that have built on Bali have done it personally or from a distance (set a local "trusted" build manager to watchover who cheats him the most). When I hear the term "Lab" and "results" I gotta say, my friend, you are soooo on drugs.
This little talk may serve some other purpose perhaps to convince the hoi-peloi that you have clue 1 and 2 of what you are talking about with respect to building but I'm sure you aint never built shit here on the island. Cause then you wouldn't talk so knowingly about "Workability on site is extremely important. A good test result means little if the correct application wasn't achievable."
Workability looks just a tad different friend: I poured my foundations with 45 people over a 18 hour period with burning sun and torrential downpours. When they were done they all said "Besok lagi" and then fucked off for a 3 day Kunigang Ceremony - I had to go to the local Muslim village to find an out of work fisher to come water my green cement for 2 days - who promptly, an hour after starting work, decided that he was kinda hungry and could use some rice and the work was actually kinda hard....
Anyone expecting to build in the method and way you describe should stay home and keep watching Big Brother.
Please don't take this the wrong way - it is just my experience and what the feck to I know?
Hi Markit,
We have built over 750 homes in Indonesia, many in Bali and we, like many other Builders in Indonesia adhere to the practices outlined above, not only sometimes but all the time - on every site and on every pour.
On average we pour over 200 cubic meters of concrete in Bali per month and close to 800 cubic in East Java per month.
Compression tests cost less than a McDonalds Happy Meal and the university labs provide detailed reports that include the type of shear experienced in each test. In Bali our tests are done at Universitas Udayana (in Jimbaran) and in Java they're done at Petra (Surabaya). Most Builders in Indonesia have Civil Engineers on their team - we have eight full time CE's. The CE's calculate and 'design' the structure of ALL BUILDINGS based on presumed loads plus a rather large margin of safety. It is imperative to ensure that the product arriving on site is as per the specification outlined in the structural design.
If you don't conduct these tests, you could be pouring concrete with a fraction of the required strength. Steel rebar is also checked rigorously during installation by the CE's and directly prior to any pour. Most builders will have at least one CE on site during a pour. If you haven't verified the integrity of your concrete and the reinforcement within it, your structure may be standing by the grace of luck and a prayer.
It maybe difficult to believe Markit, but proper industry practices exist even in Bali. Unfortunately though, as in your experience they're not even considered a possibility, or perhaps at the time were just overlooked. These aren't difficult steps and if you do not have a Builder or Project Manager capable of arranging these tests then doing so yourself is rather simple and very cheap.
All the best..
Populaire
that's very helpful tips, thanks to share..
Might be starting to build soon....hmm...whose advice should I be listening to.
Thanks Populaire - I might be in contact in the not so distant future.
This sound standard in the west but Bali????? Can you tell me how many concrete batching plants there are in Bali????Originally Posted by Populaire
Last time I checked they said that they only deliver to big projects.
And Penalty or your money back I wish you well. As you say if its poured you will have to live with it, so why do the tests???? In the west if it fails you have to replace it, no chance of just living with it. Or do you just pay more & have the results come back in spec?????
There are two houses being built around the corner from me, both will be big dollar homes. One had a crane & pile driver come in to do the foundation, the other had 10 men with the biggest hand post hole borers I have ever seen, one used a backhoe to clean the block the other used 25 men with shovels. I will wait to see which house will come out on top, maybe 2-3 years time, I will have to post some picture on there progress.
Hi Fred,
In South Bali there is Ready Con and Karya Beton. Both of which we pay in arrears - post the 28 day test.
If you'd done a 100m3 pour for a specification of K300 and you ordered K350, it's unlikely you'd get a product from either of these providers that tests less than K320, even on a bad day. But, IF you did get some tests come in at K280 for example, even in the West you would not leap to demolish 100m3 of concrete immediately (which would significantly damage any sub-structure). You would first consult your CE's and get them to run the calculations again - prior to formwork removal on suspended slabs. If ETAPS showed that the lowered grade of concrete was still within the allowable margin of safety, you would unlikely demolish the work. As a owner-builder, you'd penalise the supplier and keep the change. As a builder, you would pass that report to your client and the calculation that displays an adequate margin of safety still exists and you would credit them the penalty.
Now, in the event the re-calculation shows that the minimum margin of safety has been breached - there are still dozens of options that would exist before you had to commit yourself to demolishing 250 tons of concrete. For example, you could look at reducing spans by adding support columns, you could reduce dead load by replacing overhead structure with light structure, etc, etc. Whatever choice is made, a CE would be intimately involved.
Turning a blind eye to avoid the hassles of implementing a structurally sound solution hardly seems like a logical argument. Many builders offer structural warranties - our firm provides a comprehensive 10 year warranty on structure, extendible to 13 years, so the decision to overlook such would be a foolish gamble.
Ready-mix providers don't only deliver to large projects, though for smaller pours you may incur a higher cubic rate, plus the fixed costs of pump rental if such is required.
Testing of manually mixed concrete should also be undertaken consistently - though you may not have recourse against a ready-mix supplier, you will still have the information you need to ensure you can avoid a costly and potentially dangerous progression.
All the best..
Populaire
So if there is only 2 ready-mix plants in the south then you would have to say that not many builders have taken to the idea? I was thinking with all the construction in Bali you need 4-6 ready-mix plants to keep up with demand. Everything here comes down to price on small projects, large project a engineer would always be on site but a house project???? So the houses you build must be very expensive???
practice and theory..two totally different things in the west..overhere on Bali that difference only becomes bigger.
would have love to see a concrete truck (with those rotating things on the back right) try and make it up to where I life...
no way no how, I would still be waiting for him to get here and start building
don't read between the lines..i think the words are clear enough...:)
Hi Fred,
Not sure what the point of your post is. The majority of construction in Bali is obviously in the South.
That said,
- we have not stated that manually mixed concrete is any lower in quality than ready-mix
- we have not stated that we never use a manual mix - we do in some cases - but in every case, be it ready-mix or a manual mix, we always test it
- we have not stated that an Engineer is always on site, but rather they're regularly on site to check key installations (and preferably during pours)
- economies of scale explains why larger builders are able to have a permanent team of engineers
- owner-builders should still have an engineer, if only a consulting engineer doing their calculations and checking their rebar installations (and preferably their pours also)
- on occasion we'll have small pours and like anyone else, pay a slightly higher cost when the daily pump rental is factored in - we don't incur higher volume rates
- logistically, it's not difficult to group your pours to find efficiencies
The post was not intended to be argumentative, it was intended to be informative.
If you've been offended because you didn't adhere to the basic principles of sound design, sound application and sound QA, we apologize.
In Indonesia, as where anywhere else in the world, professions in construction exist. If you appointed your Gardener as your Forman (Mandor), your Driver as your Engineer and recruited your workers (Tukang) from a Car Salon - don't attribute their performance to the often misrepresented, "that's how they build in Bali!".
All the best..
Populaire
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