CONCRETE WORK

• Concreting of factory slab

        Concreting of a wide factory slab.Shoud be an altenate slab arragement for concreting .The contraction joint between casted beam to the new slab is produced from bituminous.The finishes is render using a helical rendering machine.

• Concreting pouring

•  What are  concrete pouring mean? To place a fresh concrete from truck or mixer using a various method to the structural element like slab,beam and so ever.

  First of all that is a tradisional method using a wheel barrow or dumper truck or bobcat now collect a fresh concrete from mixer to the place of concrete and by using a scop to fill the concrete to the footing,beam and so on

  This type of pouring are suitable for small project whereby ingnore about quality.Ftom mixed of concrete until pouring of concrete too difficult to control the quality.To control the mixed procedure using a box snd then tranfer it to the placing take a long time to finish the job at the day and also the workers not a robot can doing a job at same quality and msybe morning can get grade 25 of concrete but afternoon the grade down to grade 15.

  This type of pouring still usef for small project not a structure one like base og fence pole,fence beam and a small building like a huts  and project not concern about quality.

  The second method poured used a crane with bucket.The fresh concrete from the ready mix truck pour to the bucket and using a crane to transfer the fresh concrete to the place.This the faster way right now.'But this mehod have a limit depending on the height of the building and distance from between the structure and the truck or mixer.The mobile crane also have a size between 20 T and 40 T depending on the height of the building.

  Right now tall crane are used for high building to transfer and pour the fresh concrete.The bucket also have a size from 1/2 mcu to 1 meter cube.Its depend how big the structure.Normally a site ready mix or imported ready ready are used and this type of pouring more faster snd cheaper and also the quality is there.

  The third method of pouring is using a pipe boom and concrete pump to transfer and pouring if the fresh concrete.Normally fresh concrete from the truck pour to the concrete pump and pumping through the pipe until to the structure.This type of pouring suitable for condition that trucks cant go near to structure may be no road or have an obtruction like many building before and then far the way from the truck place.

  Author have an experience supervised pouring concrete using a boom with concrete pump.Concreting for spill way structure at Batu Dam whick trucks cant go near the structure coz the terrain condition.The most important thing to make sure that the mixed not to dry and can stuck inside the pipe.The stuck concrete can make a concrete pump jamned.To released have to detect which point stucked and dismantle the pipe and then pump the stuck concrete out before continuing concreting and this type of pouring maybe costly and not suitable for small project.

  Pouring have a quality aspect to control it are the height of pouring to the element.To avoid segigration the height between the start point of pour to the final point of pour not more than 4 feet.The second is the pattern of pour like a slab pour that the pouring system  must easy to vibrate that not too thick and not too thin to avoid honeycom.

• Making a cube concrete

            Make a cube concrete for testing.6 nos of 150mm x 150mm x 150mm netal mould are used.The first layer of concrete put in and compact with 25 mm bar,them the second layer with compaction and finally the last layer of concrete.Before concrete set,the numbering and date of cast will write on the top of the cube.By tommorow,all the 3 cube will submerge to the water for the 7 days test and 28 days of test.Today using a ready mix concrete,all the cube test are done at the batching plant.At the 7 days,3 of the cube will send for compression test.

• Supervising a rebound test concrete

            If the 28 days cube test is failed,the rebound hammer test will be carried out to the concrete.If the concrete for beam,each beam have to do the test.Every point at least 12 rebound point will be carried out.From the reading and formula,the grade of concrete will determined.The sound of rebound can show the quality of concrete.If the sound of rebound slow,the low reading of grade and if the high sound of rebound that mean higher grade of concrete

• Calculation a mix concrete with a volume method

            The old method when using a site mix with drum mix machine.The mix 1:2:4 by volume is mean 1 volume for cement,2 volume of sand and 4 volume of aggrigate.Using 1m x1m x1m of timber box,1 bag of cement is contain 2.25 m3,then for sand the volume is 2 x 2.25m3 m= 4.5m3 and also for aggrigate 4 x 2.25 m3=9m3 .Cement is the first item put into the drum follow by the water and the sand using a bucket of JCB equivalent 4.5m3 will put to the drum and 9 m3 of aggrigate will put last.The water is added slowly follow the water ratio.The drum will rotate until can see the perfect mix for concrete.Usually 10 to 15 minutes is the best time for mixing time.

            Today the the site mix are not allow but trial design mix with cube test result will submitted for approval before usage as a structural mix.

• Curing a cast concrete at the past time

        Curing is the process to slow down the chemistry process in the concrete.Rapid harden can coz cracking at the top or part of the concrete.During last time a moist gunny sack is using to cover the structure for curing process.last time gunny sack easy to buy compare today time.Today water jetting is the most popular to do a curing process.

• How to honey comb column,bulging beam.

            Honey comb occured when the only the aggrigate cover a little bit of cement without a sand.Poor vibration is the main coz and concreting from the higher point can produced seggration between the material.Last time ,the tiny openiing at the middle of column formwork are prepare for concreting to avoid seggritation .If the percentage of honey comb bigger,the structure will be demolish.If less than 5 %,only the honey comb area will be reinstated.

• Footing without form work

            Coz of formwork not shown in the structure drawing,many builders not prepared for it.The only excavate follow the size of structure and fixing a re bar and after that doing a concreting.The soil are act as formwork.One of the fuction of formwork as a mould to the concrete,The soil not have a strength to retain the vibration and the cement water can flow to the cavity between soil particels .The cement water ratio control the binding between sand and aggrigate and can reduce the strength of concrete.One project author insist to excavate the unformwork concrete footing.The shape of footing not in shape but looklike oblong.All the footing are instruct to demolish.

Type of concrete structure :

 

1.Concrete Pavement :I remember in 1987 when I am in final year in varsity,one of my clique got a thesis about concrete pavement.That time Malaysian dont have any kind of concrete pavement in elsewere in the country do all the references was from the books and journals from the oversees so lucky my clique was done the thesis succesfully and got the degree.

Yesterday in the facebook one of the website as shown or can click at read at above described that concrete pavement were introduced in Malaysia at year 1999 eleven year passed 1987 that time my clique done the thesis.

According to the website only 3 places of road were introduced and lately no place or highway used this type of pavement.Why?

Let me describe that the structure of pavement from below are same only different at the top finishes.Concrete pavement used a concrete as top layer  compare to wearing course as top layer for flexible pavement.

Readers can go to the many website to know further detail of differences or major differences between them.Rigid pavement refer to whatever concrete pavement snd flexible pavement refer to whatever macadam pavement.

One of the weakness about concrete pavement when pass by the pavement make big noise and when at rain time at the corner maybe canout of the road.

That why maybe concrete not wide used as pavement but this is only my opinion not a real fact but maybe can rectify or modify for future used like a rubber  from waste tyres mixed with concrete to more flexible and less noise.

Hopely in future time the rubcon pavement ate widely used in the world.

2.Concreting of column

 Column is the superstructure element in building.The function of column is to tranfer all the dead load and live load from wall 1st floor slab.There are 2 type of column short column and slender column .Many shape of column such as rectangular,circle ,L shape to the odd like oval and etcs.

How to cast and erect it,?Works involve to make a column is

1.setting out

• Normally they are using a tradisional method,using tape and string and marktaw to the slab.the alignment always to be check whether the grid is out in centre or in

2.rebar

• Rebar installation is very easy.the prefabricated rebar is lifted and fixed to the position.the bottom lapping always to be check.the 25mm concrete cover must be fixed around link and through the height of column.the re bar of column consist of 4 or more main bar and a number of link from bottom to top.

3.formwork

• Formwork erection using plumbob as tradisional method to get the straight verticality or theodalite as modern equipment.then the formwork will strut in 4 or 2 direction to firm or lock it into position.last time the hole at 4 ft interval  in height will do for concreting purpose to avoid seggration and then to avoid honey com at the bottom of the column especially for small size of column.

4.concrete

• actually the best way for laying  a concrete is using a chute to avoid seggration but not practise for small project.they just pour from the top using bucket and vibrate or hit the formwork to compact it.the site of vibrator also must be small for small size of column.

5.formwork dismantle 

• after one day cast,the formwork can dismantle using a right tool and equipment.always check the hney com,if worse,the colum must demolish to make anew one and if less just cover with cement grout.

This process are repeat for 1st floor until the desire storey of the building.

Innovation from concrete technology

Maybe 1st or world record that 10 storey building can completed in 28 hours time.The 10 storey apartment using a modular unit system like a lego system using a several unit of mobile crane completed with fully furnish unit apartment in less than one day.

What a modular unit system?.The modular units are prepare in the factory and each unit will assemble storey by storey at the site until completed.The modular unit consists a several unit of room and the sizing of modular unit are loooklike a 40 footer cabin which easy to load and unload a unit for assembling purpose.

Each modular completed with ceiling,partition,wall and slab and completed with finishing like tiles terrazo and so on and also completed with hidden electrical wiring and plumbing and also completed with painting.So the modular unit was completed in the factory snd cart by a long vehicle to the site.At the site the foundation was ready and all the connection using high grade stainless steel bolt amd nut and also all the frame for modular unit are from stainless steel which stronger than a normally mild steel.

But the 28 hours are not include the preparation of a sub structure work.Building more than 2 storey always need piling for their foundation.And depending on the type of pile,the duration to complete the piling work are 1 or 2 weeks time.So maybe the 28 hours are not include sub structure and testing and commisioning works.

For the super structure works using modular unit the 28 hours time to complete 10 storey building are the world record so far but also the design must limited to 10 floor only or limited wind speed and also limited to a specific earthquake movement but also what code of practise for this kind of building to follow.Actually to built these type of building outside from that country are impossible coz no code of practise to follow or any guidance to design and contruct.

May be future in several of years the code of practise are ready and all the country all over the world can built these type of building as many as they can.Why not,fastest and cheapest!

Thank to the technology and continues innovation in civil and structural engineering and more and more new innovation coming in future to pushing the limit of our thinking.

Safety factor for concrete work:

Yesterday at Ipoh,a mandur calling for a senior supevisor died when falling down from 2 meter high.The incident not in the building .The 58 year old mandur died during checking a concrete quality(maybe) but suddenly fell down from the concrete truck mixer and died according worse injured at head.

Why must checking the quality of concrete at the certain height?

Normally practise at Malaysia,the quality of fresh concrete from a batching plant at site are using a slump test only where the dropping reading are between 25 mm to 75 mm depend on the grade of concrete.The slump test were doing by the fresh concrete were fill in the cone shape container and compact with the special bar until the container full and the cone will extract and concrete will drop .The drop level will measure.If the concrete drop more than 75 mm,the concrete will reject and send back to the batching plant.

The quantity of the concrete in the truck also cannot seen by visual .At the top of the truck the condition is wet,slippery and strong vibration and dangerous for someone who at the time standing there when the truck will bring out the fresh concrete.The SOP ,when the fresh concrete have a abnormaly condition like quality or volume,that batch of concrete must send back to the batching plant.

No need to check inside the mixer and can cause a dangerous to the mandur or personnel incharge for quality.According to OSHA department,the site will stop until further investigation will carry out.The OSHA said before commencement any work at construction site ,the risk assessment must carry out to prevent accident.

What is the risk assessment?

A risk assessment is  thoroughly looks at workplace to identify that things,situations,processes,etc that may cause harm or accident to the people.After identification.analyze and evaluate how likely and severe the works is.

There are 5 important step to prepare the risk assessment:

1. Identify the hazard such as accident,chemical attack and etcs
2. Decide who might be harm and how
3. Evaluate the risks and decide precautions
4. Record the finding and implement them
5. Review and update the assessment

As the mandur accident actually no special risk assessment were made before but for a truck mixer driver,there are a special risk assessment.Example of the risk assessment are

1. The common hazard is slips,trips and fall from the trucks platform(only these kind of hazard will discuss,there are many including chemical and body posture and etcs)
2. 50% injuries are from these hazard
3. Slippery surface,unsure footing,damage ladder and walkways and unsure hand and foothold during climb and desceding truck cab and platform

With and age 58,the mandur maybe have a item no.3 experience before falling down.But the question is why the mandur climbing up the truck and for what purpose?

We wait for the investigation finding did by the authority.