Thread: Concrete - Protecting your structure..

Yes yes Yes ..., all 100% true populaire and all your argument thereafter also , all it takes a bit of extra planning (in fact all the main work is in the planning ) and preparation and supervision , and all you say is acheivable . There is a place and nessecity for hand batched concrete pours here in Bali , but most of these suffer from poor planning and knowledge and supervision , but jobs can be utilised to make many pours happen on the same day as to take advantage of concrete pours and using the truck .
Recently , I watched (in horror) an upper deck and many columns get poured by hand mix . No vibrator , inconsistant mixes , 2 hour lunch break halfway through , dark arrived 3/4 done and panic set in ..., ring up for more people , mixes got more inconsistant rush the job more . In all the slab had more cold joints than an igloo , in time the reo bars will all rust out , leak ..., and not once after the concrete had set did anyone cover the freshly poured slab or even wet it down to slow the cure this should be done often at for at least a week or two , especially seeing as this deck was meant to be acting as a roof also.

Where there is a will , there is a way ..., when I ask indo tukung " why they do some crucial errors the way they do " ( ie; from a western educated and trained veiwpoint ) .......................................,

( note , before you tear strips from me -I always ask in a friendly and inquisitive way, and im never judgemental nor put myself on a pedestal when I ask. I learnt most of my bahasa indo from village fishermen or tukungs over the years , by asking and observing is my way of learning their ways , good or bad .) ,

......................................, The reply from the tukung is always the same - ie " thats the way we always do it " , in other words ...., they dont know any better or dont care ..., its always one or the other or both. Begitu is not the right answer unless you accept that it is , or you oblivious to know any different .

Also there is no excuse for not screeding and trowling the finished slab to a smooth finish, even to a broom finish if tiling over later . The topping they do afterwards is a complete joke , unless you like the look of cracked mortar .

Ps , I know what im talking about , as does Populaire ...,
Im a registered builder from homes to medium rise construction , with 29 years onsite experience , with the last 6 involved with civil and specialised formwork.

Originally Posted by Populaire

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..