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Quality Engineering and Construction

All about quality in building construction industry

In-Situ Field Density Test (Nuclear Method) by Direct Transmission

Equipment: Troxler Model 3440 Surface Moisture Density Gauge

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1. The test location (point) is selected by the client representative in which the soil compaction and density is to be determined.
2. The drill plate is placed over the test location to serve as a guide for the drill rod.
3. The drill rod is driven vertically into the soil to a depth of 150mm to 300mm using a hammer.

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4. The nuclear gauge is placed onto the test location with its source rod placed over the hole.

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5. The hatch is released and the source rod is lowered into the hole.

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6. The test is conducted for a period of 15 seconds. During the test, all personnel are to stay away at least 3m from the area to avoid the radiation effects.

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7. After the test, withdraw the source rod back to its hatch.

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8. After the test, the following information is determined from the nuclear gauge:
a) Bulk Density (Mg/m3)
b) Dry Density (Mg/m3)
c) Moisture Content (%)
d) Degree of Compaction (%)

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Sample Report of In-Situ Density Test by Nuclear Method:

Test 1

Test 2

The test was conducted on different occasions but of the same location. The first test only resulted to mature compaction and did not achieve the client requirement of 95% compaction. After 2 days of continuous compaction using roller, the test result is positive and complied to the required degree of compaction.

Floor screeding works (substrate for marble tiled floor)

This is a comprehensive and photographic method statement of floor screeding works. Screed can be final finish or a substrate of the final floor finishes like homogenous tiles, marble floor or granite floors. This step by step method can be useful for all newbies who would like to learn floor screeding.

The step by step method is listed below:

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Create level pegs on the floor to be screed. This will serve as a guide when leveling the wet screed.

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When the level pegs are dry, clean the floor by using water jet and sweep away the excess water.

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Before screeding starts, ensure that the floor to receive the screed is very clean.

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Prepare the cement mixer and bucket for screed powder mixing.

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Place the screed premix powder to the cement mixer.

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Add water to the mixer on to the amount recommended by the screed powder manufacturer.

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While mixing the screed, prepare and mix bonding agent and OPC.

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Use hand held electric mixer and mix until flowable consistency.

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Pour and spread out the bonding layer over the floor area to be screed.

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The bonding layer must be evenly spread to ensure that all screed will bond to the concrete surface.

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Bring the screed mix unto the floor area until the desired quantity is achieved.

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The screeding must start immediately before the bonding layer lost its tuckiness.

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Use a long straight trowel and begin leveling the screed to desired thickness pressing onto the level pegs.

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Work from sides to sides pressing the screed to compact it.

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Move to the other side and repeat the step above.

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Now move backwards and level the screed in a diagonal position. Always stamp and press the screed for better compaction.

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If the screed thickness is not enough, top up using a trowel and level it. Repeat the steps above until the entire floor is covered with screed.

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The screeding should end at the door area or at the free end where foot or traffic is allowed. Allow the screed to harden and cure for 7 days.

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The finished screed for marble floor substrate should be rough and not trowelled to smooth surface. This is for good bonding between the tile adhesive and the substrate. Before tiling work starts, a good practice to avoid abortive costs is to check for debonding of screed or commonly known as hollowness. If there are any hollowness found, repair is a must to eliminate the problem after tiling works.

The repair of hollowness will be the topic on my next post.

 

 

 

Pull-out test of cast-in channel (Halfen) for curtain wall

Introduction:

Cast-in channels for curtain wall installation are fully embedded in concrete. These channels carry the loads from the curtain wall and transfer them to the main structure. Thus, these cast-in channels shall be tested to demonstrate a minimum performance as required by the engineer.

The testing shall be carried out by an independent, approved laboratory.

 

Equipment used:

– Hydraulic pump complete with calibrated pressure gauges

– Hollow ram hydraulic jack of sufficient capacity

– Reaction test jig

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Requirements:

– Test load: 1.2 … 1.5 x service load (unfactored)

– Alternative test load: characteristic resistance for steel failure as per technical approval (sufficient edge spacing provided)

– Minimum concrete grade as specified

– Required tightening torque to be observed

 

Procedure:

Check that the equipment to be used is duly calibrated with valid certificate.

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Insert T-bolts onto the cast-in channel and set-up the pull-out test jig onto the cast-in channel.

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Ensure that the reaction frame with hydraulic jack is standing in upright position and aligned to the cast-in channel.

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Connect the high pressure tube from the hydraulic pump to the jack.

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Once the set-up is done, start the test and ensure that the pressure/force is set to zero.

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Apply pressure in equal increment as possible until it is set to the required test force/pressure.

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The force/pressure shall be observed and there shall be no reduction within 1 minute to “PASS” the test otherwise it is considered “FAIL”. The concrete surface surrounding the cast-in channel shall be visually inspected for signs of “DAMAGES” or “CRACKS”.

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Record:

The results of the tests shall be recorded and evaluated. The record must contain the following:

– designation of the product or the components

– nature of check or test

– date of testing of the product

– results of test, comparison with requirement

– failure mode, if any:

1 Break of anchor bolt shaft

2 Break-off anchor bolt head

3 Pull through of anchor head

4 Break-off anchor bolt foot

5 Break-out of anchor bolt foot off the channel´s back

6 Break-out of T-bolt off the channel slot

7 Bending up of channel lips

 

Assessment of Concrete Strength by Windsor Probe Test

Introduction:

Penetration resistance test is based on the theory that the depth of penetration of a metal probe (Windsor Probe) fired into a concrete surface depends on the strength of concrete.  However, this relationship is significantly influenced by the properties and proportions of the coarse and fine aggregates. An individual correlation should therefore be prepared for each different concrete to be tested. (BS 1881: Part 207: 1992 Section 9)

The estimated in-situ strength of concrete is derived through empirical formulation from a curve of previous test results. Reliance to one curve or the actual site condition is far off from the assumption could lead to significant error of estimation. Furthermore, design mix of concrete varies from project to project. Thus, it is highly advisable to establish an individual correlation of penetration resistance to compressive strength of specific concrete so that a more reliable estimation can be achieved.

 

Test Brief:

The equipment used in this test is the Windsor Probe Test system using standard power probe. A minimum of 3 test probes located at not less than 175mm from each other was used at each test location. The probes must be located at least 100mm from the edge. The probes were fired into the concrete using driver unit. The protruding length of each probe which was firmly held in the concrete was measured in millimeters. The depth of penetration may be calculated from this value and the length of the probe.

 

Method of Test:

Prepare the area to be tested where the suspected inadequate strength of concrete is located. The concrete should at least 28days old and is in dry condition. If the surface is not relatively flat, grind it off to smooth and even surface.

windsor 1

Load a metal probe to the driver unit and aim to the face of the concrete. Fire and observe that the probe has penetrated to the concrete surface. Note that it is not recommended that the probe would hit embedded reinforcement bars as it will compromise the penetration resistance of concrete.

windsor 2

Repeat and fire other 2 nos of probe each at 175mm apart. It is necessary to remove the concrete which has been raised around the base of the probe to provide a suitable and flat surface.

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Brush off the dust and ensure the surface has no sandy particles which will raise the reference plate.

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Insert the plate and cap then use caliper to measure the protruding length of the probe. Record each probe length and take the average.

windsor 5

 

Conclusion and Recommendation:

The reliability of this test depends upon the data at hand. Remember that this is for estimation purposes only. If you need a more reliable result, one should opt for coring test where an actual representative is tested by compression. After all, the main purpose of the test is to verify the in-situ strength of concrete.

 

I will discuss about more on coring test procedure on my next post.

Cheers!!!

Method Statement of Slab Construction (Cast-In Situ)

Quality Engineering and Construction

This method is meant to help the new graduates understand how to construct a cast-in situ slab. I try to minimize the words and fill many photographic images in sequence as pictures could expound better than words. So here we go.

Erect the slab formwork either using conventional scaffold framing and timber combination or using system formworks.
slab 1
After the slab formwork is done, apply releasing agent using rollers for ease of striking. Meanwhile, the slab reinforcement bars can be brought into the slab formwork ready for installation.
slab 2
Lay the main reinforcement bars of bottom layer of the slab spaced evenly according to design or drawings.
slab 3
Tie the reinforcement bars at both ends to maintain the spacing.
slab 4
Lay the distribution bars and tie them to the main reinforcement bars.
slab 5
Install additional slab reinforcements if there’s any.
slab 6
After completing the bottom layer of slab reinforcement, allow the M&E contractors to lay the concealed…

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Method Statement of Structural Crack Repair Using Epoxy Resin (Pressure Injection)

This is a detailed sequence on how to carry out pressure injection of Epoxy resin to slab soffit cracks using electric pump. All the materials used and procedure are strictly in compliance to manufacturer’s recommendation. Please note that this is not an advertisement of the product featured below. You can use other products such as Tamseal etc.

Material used in this crack repair:

crack 13 Epoxy Resin

crack 14Putty

Demonstration Process:

1. Locate the crack and drill 13mm dia holes along the crack at 300mm interval.

crack 1

2. Insert the nipples to the drilled holes and tighten it to prevent from pull-off action when the pressure gets higher.

crack 2

3. Apply Estorex Putty from end to end of the crack line by using trowel or spatula. Wait for the putty to dry in about 5hrs.

crack 3

4. The crack line must be sealed with Estorex Putty to prevent the epoxy grout from oozing during pressure injection. Ensure that the crack line is dry before starting any epoxy injection.

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5. Fill in Part A (Estofill Base) compound to the funnel of the electric pump. The mixing ratio by weight is 3 parts of Estofill Base and 1 part of Estofill Hardener.

crack 5

6. And then fill-in Part B compound (Estofill Hardener). Mix thoroughly until a uniform mixture is achieved.

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7. Install the injection tube to the nipple.

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8. Once ready, start pumping the epoxy grout to the injection nipples until the pressure goes up. Pumping may take up to 5 minutes to fill-in depending on the extent and depth of the crack

crack 8

9. Observe and control the pressure not to reach higher than 10bars.

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10. While pumping the epoxy resin into the cracks, the pump will not show any increase in pressure. Only when the cracks are filled up will the pressure start to rise. If the cracks are small, the pressure can rise very fast in some instances hence it is quite difficult to control.

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11. Transfer the injection hose to the next nipple and repeat steps from 8 to 10.

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12. A good practice is to clean the electric pump and injection hose by using thinner. This is always done before the first pumping and after using before the break period. It is mainly to remove any compound left in the pump and prevent blockage.

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Method Statement of Column Construction (cast-in king-post of temporary deck/bridge)

In some cases, temporary structures are deemed permanent when its location and purpose coincides with the master plan. Design have to be modified in order to cater the influence of such temporary structure. Most of them are king posts supporting temporary deck for crane or pump car parking. RC columns reinforcements should be changed to smaller sizes when the steel area and inertia of the steel king-post is considered. This is on the design change part but on this article, I will show you the actual construction of RC column with cast-in king-post. I will go through some of the steps and some tips on how to get a good finished concrete quality of RC column. As usual I will show some actual photos to help the readers understand the important steps and procedures.

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For good bonding between steel column and concrete, wash thoroughly using high pressured water jet to remove dusts and oil.

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Ensure that the base construction joint is roughened and clean before closing of formwork.

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Close the formwork once the rebars are inspected and cleanliness is accepted by the client representative.

column 6

To prevent bulging surface and column deformation due to concrete pressure, install walers at maximum of 600mm distributed along the column height.

column 7

Check the column formwork verticality and braces should be enough to prevent from swaying during concrete placement. Gaps must be sealed to prevent grout loss. Remember that the aim is to have a good finished concrete quality. Concrete workers handling the vibration pokers must be trained on how to compact wet concrete for vertical elements. Pouring shall be done in layers of 1m and vibration draw-out at 1m per second. Too much vibration will lead to segregation and less vibration may cause honeycomb. Only when no more air bubbles should the compaction would stop.

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When concreting is done, remove the supports, walers and formwork after 24hrs.

column 11

When the formwork is removed, you should notice that a good concrete surface quality is achieved.

At this stage, a post-pour inspection should be carried out by the engineer to record the quality of concrete. A clearance is given when there are no defects recorded like honeycomb, minor grout loss and bulging surface. If such defects are found, it should be rectified and re-inspected before a clearance is given to proceed the next stage of work.

I think that is all that I can share for this topic. Please feel free to comment and share this post if you find it useful.

I hope you enjoyed reading my post.

Thanks,

Rey Joy Mangubat

Marble Floor: You got to be perfect

 

Polished marble floor may be the best choice of finishes but a lot can go wrong. It’s tideous with loads of areas need to control right from cutting and production, to selection, to handling and delivery, to installation and to polishing. Marble as a natural stone has characteristics which sometimes cannot be avoided during the selection. There are crystal lines that are deep and quite few are shallow. So even though we knew that the marble is solid during the selection, it would somehow come out as many pin holes after grinding. Some holes and fissures are too small that when epoxy is applied during polishing are covered but some are too big. So manual application of glue is necessary. Marble also easily reacts with oxide and other household chemicals so stains are always found after the installation. It cannot be avoided but could be removed using cleaning agents. You can use products from Primalas to remove the stains if you can afford but other economical brands can also be found in the market. Just decide wisely so won’t end up scratching your head. Another common defects are chipped edges and movement cracks. These are the defects which need high level of skill. Patching the chips and cracks might be as easy as it sounds but the difficult thing upfront is to match the colour of the filler and the parent material. Sometimes it looks alright during application of glue but when it dries you can notice the difference in colour tone. So you have to try and try until you get it right. If you have time constraints then you must get it right first time. That is the key for a good quality product. Be careful not to break the marble after installation. If broken, you need to remove and replace it with new marble. And replacing marble is not an easy task. You need to get the right colour tone in a group so it is not so obvious. The tricky part is when you need to match the light to dark colour distribution. Not many contractors can get it right but there are few who can do it but it comes with a big price.

Method Statement of Slab Construction (Cast-In Situ)

This method is meant to help the new graduates understand how to construct a cast-in situ slab. I try to minimize the words and fill many photographic images in sequence as pictures could expound better than words. So here we go.

Erect the slab formwork either using conventional scaffold framing and timber combination or using system formworks.
slab 1
After the slab formwork is done, apply releasing agent using rollers for ease of striking. Meanwhile, the slab reinforcement bars can be brought into the slab formwork ready for installation.
slab 2
Lay the main reinforcement bars of bottom layer of the slab spaced evenly according to design or drawings.
slab 3
Tie the reinforcement bars at both ends to maintain the spacing.
slab 4
Lay the distribution bars and tie them to the main reinforcement bars.
slab 5
Install additional slab reinforcements if there’s any.
slab 6
After completing the bottom layer of slab reinforcement, allow the M&E contractors to lay the concealed services.
slab 8
Install bar chairs acting as spacers between top and bottom reinforcements.
slab 7
Lay the top reinforcements with distribution bars fixed on first and the main reinforcements on the upper layer (transverse direction).
slab 9
After completing the slab top reinforcements, clean and blow away the dust by using compressed air.
slab 10
Meantime, the surveyor must check the formwork level and install the markings for the concrete level.
slab 11
After the formwork level measurements are done, furnish the copy from the surveyor and locate the area which varies from the correct level.
slab 12
After the adjustment is done, do a routine formwork inspection to check the stability of the frames and runners.
slab 14
Ensure the slab level markers are fixed nice and tight so that it will not move during the concrete pouring operation.
slab 13
Check all the formwork gaps and ensure that they are plugged before concrete placement. Concrete slurry will flow through the gaps and will lead to grout loss if not rectified.
slab 15
Spray water to the formwork and reinforcements to lower down the temperature. Wet concrete temperature must be less than 35deg Celsius during pouring.
slab 16
Prepare the vibrator machine while waiting for the concrete truck to come. It is always good to have a back-up vibrator if in case something goes wrong.
slab 17

All concrete trucks must report to the cube room for slump test. The arrival time will be recorded.

slab 18

Check the slump height whether it is within the tolerance, if not the concrete would be rejected. A note to the D.O. reflecting the slump stating  “REJECTED”.

slab 18.1

Only those trucks that passed the slump test would be allowed to unload the concrete.

slab 17.1

slab 17.2

Meanwhile, make test cube samples for the concrete batch. Normally for slab, cube must be taken at every 50 cu.m. (refer to project specification). Total 3 + 3 cubes shall be made for 7-day and 28-day test, respectively. You can make extra cubes if you want just for the purpose of earlier test like 3-day test or for water absorption test if you are using waterproofing admixture.

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Proceed to concrete placement and maintain sufficient light when the operation reaches dusk or even until midnight.

slab 20

On the next day, check the concrete slab surface and ensure it is sufficiently dry after 12hrs. If not, no traffic shall be allowed until its hard enough.
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Spray water and flood the concrete to cure and repeat when it’s needed.

slab 22

Please feel free to comment and share your thoughts to improve the procedures above.

Thanks,

Rey Joy Mangubat

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