How to carry out a cube test?

Steps to carry concrete cube testing

1. Mix the concrete as per ur design mix

2. Pour to test cube mold, dimensions of 150x150x150mm and the use hand vibrator to conpact it

3. Take siz sample of this cube.

4. Test 3 sample on 7 days, check if you have recive 70% strength from your deaign mix

5. Test remaining 3 samples on 28th day and see if you have achived your design strength.

How to do concrete without a batching plant

concrete been mixed with a european brand winget mixer model 500R and a chinese mixer model JZM500, CAT excavator, excavator bucket is measured and used for loading sand and aggregate to hopper of mixers, kobelco rk250 crane and a tadano TR250 crane been used for hosiitng the buckets and pouring to the second slab. All equipments from YD WORKS, www.yd-mv.com
See the vedio for beter view

For this concrete they been using grade 53 cement, 750 bags of 50kg, and 75 tons of manufacture or crushed aggregate and 113 tons if aggregate. Mixing at a avrage speed of 100 bags per hour.

do you know which brand of concrete pump and batching plant is best? for me i find Putzmeister as best brand around. more about putzmeister in another post.

How to load 1 5 ton concrete block to truck

more details on how load is distributed in other pages

Load diagram

a concrete block been removed and loaded to a dump truck, above is a diagram of how the load act when it been lifted with a nylon rope of 20 mm dia thick, the excavator bucket have a hook on it and roape been hooked there, and this nylon rope is pulling it up word

How to field determination of saturation flow of Traffic

To know traffic flow,  two people are needed to carry out this study, one person needs to have a stop watch or a timer equipped device, and other to record a events with a appropriate software or a notebook computer. details such as area type, width, and grade of the lane being evaluated to be measured and recorded.

thak you need to have a good point for observation with a clear vision without any obstetrical and able to see traffic light, mark a specific point for traffic to enter, than follow below steps:
1. Timer starts the stop watch as green light and record the time
2. recorder immediately notes the last vehicle in the stopped queue and describes the timer and also notes vehicles details such as heavy and light and who turns right and left
3. timer than reads all the vehicles passing
4. timer records all the vehicles that passed and noted
5. width of the lane and slope of approach are then measured and recorded together with any unudal occurrence that might have effected the flow
6. just after the green phase is less than saturation flow, the time considered for calculating the saturation flow is theat between the time the rear axle of the car crosses the reference point t4 and the time the rear axle of the fourth car crosses the reference point tn. below equation can be used

Saturation flow = 3600/((t4-tn)/(n-4))

where n is the number of last vehicle surveyed.

field sheet for direct observation of prevailing saturation flow ratio

steps on How to do New floor screeding

for a new cement/sand floor screeding, its better for the floor if the mix ratio can be 1:4, 1 part cement to 4 parts sand.  if you are not planing to put over load goods or things there is no need for reinforcement, the thickness of the screeding slab can be 50mm or 2 inch thick.

Step 1; do floor blending with a good earth compactor.

Step 2; Using a tube level, bench mark every 2m or 6 feets so that the whole floor is even

Step 3; if your not using a pipe, use the mixed cement and make a trench with a ruler section

 now that there are two side with same height as the above pic, and center is with no cement mix.

Step 4; pour the cement mortar and spread it and using a trowel you can fine smooth it.

Source; www.yd-mv.com

Factors effects Divers while Underwater Concrete

1. Effect of tidal flow

The most important limiting factor which adversely affects a diver's work is the velocity of water flow. A flow of 1 knot has roughly the same effect on a diver as that of an 80 km/h wind acting on a man on land. The maximum tidal flow in which a diver can work effectively is, not surprisingly, about "1 knot. The ability to work in a strong tidal flow is dependent on the work task, the work location and adjacent physical support available to the diver.

2. Visual inspection

A diver looking, as he does, through layers of air, glass and water observes objects apparently larger and closer than they actually are. He is therefore liable to report incorrect dimen-sions if he relies solely on observation, and he should always use a sea-bed ruler. A spirit-level may be used to establish levels in shallow water.

3.Poor visibility

In rivers which run through highly populated or industrialized areas, visibility is often very poor. The converse usually applies in sparsely populated areas. Similarly, in coastal areas near river estuaries, the outflow of polluted rivers may adversely affect visibility many miles offshore although the prospect of good visibility improves further offshore. Apart from pollution caused by man, sand from the sea-bed brought into suspension by storms can reduce visibility to a few centimeters even well offshore. After a few days of good weather this can change to give a visibility in excess of 30m. In poor visibility, high- candlepower lights illuminate only the particles in suspension so the diver sees myriads of bright reflections from the particles. Special low-candlepower lights are available for close inspection in poor visibility. In areas of permanent low visibility, tactile measuring devices are invaluable and the diver's fingers become his eyes.

Underwater floodlights are likely to be useless in shallow water where daylight has not penetrated. The effective use of floodlights is primarily limited to night work or at intakes and other areas where natural light cannot penetrate.

4. The underwater season

In the summer months, weeds and other marine growth are at their most prolific, particularly in shallow coastal waters. Inspection of outfalls and other structures is therefore best carried out in the early spring.

5. Fatigue

Breathing underwater involves appreciable effort. The muscles of the rib cage which draw air into the lungs have to work harder to ventilate the lungs with the denser air. With the demand-valve systems, some effort is also required to activate the tilt valve. The effort required to swim underwater is heavy and trials have shown that a diver in standard diving apparatus uses approximately the same effort when walking as the under- water swimmer. Two hours is considered the maximum time a diver can work efficiently using a demand-valve breathing system. Provided that he is working in one area, 4 h duration is possible in helmet gear.

6.Sickness

Of necessity, divers are required to have a high degree of physical fitness and, generally, they are very rarely ill. However, working in cold water and experiencing temperature changes exposes them to the common cold. This can be serious since the presence of mucus in the Eustachian tubes can prevent 'clearing his ears'. He is then unable to balance the pressure across his ear drums and the drums are forced inwards. The forcing can cause damage or infection of the ear. Consequently, divers should not dive with a head cold.

How to prepare concrete staircase form work or shuttering work

The stair case which has 6 steps before landing, width of the stair case 850mm, step height 176mm, steps 200mm.  stair case step one start after floor height of 150mm

Drawing of sample stair case

leveling step one of form work

side view of staircase shuttering work

stair case bottom support of shuttering/form work

The most important thing to take note while preparing form work is that; 

1. The ply wood is secure and timber is enough to support concrete weight and vibration while pouring, so the last pic shows the bracing given to support the concrete. the pics were taken few hours before completing the whole form-work.

2. Making sure the first step is level, using a sprite level, so that it ensures the fact that next steps will be leveled. 

3. Take accurate measurements from the last end of the step one to the grid line, and top end of the step to the grid line, in this sample it measure 820mm at bottom and top against the grid line.

4. for easy construction of form work, use 2inch x 1.5inch straight timbers, and nail or screw them together. 

concrete poured to stair case form work and left for curing

setting up cantilever beam for landing

Use of Admixtures (chemicals) in Mixing Cement concrete

 


Chemicals or Admixtures when concreting is widely used all over the world today. admixtures are chemicals which are added to cement while or after concrete has been mixed with Aggregates and Sand. there are various types admixtures, and each admixture has its own use, the amount of admixture added to concrete is dependent to the type of chemicals used in it. 


Most of the admixtures are ready to use, no need of doing your own experiments on it. 


ASTM C 494, “Standard Specification for Chemical Admixtures for Concrete,” classifies admixtures into seven types as follows;

Type A - Water-reducing admixtures;
Type B - Retarding admixtures;
Type C - Accelerating admixtures;
Type D -  Water-reducing and retarding admixture;
Type E -  Water-reducing and accelerating admixtures;
Type F - Water-reducing, high-range, admixtures; and
Type G - Water-reducing, high-range, and retarding admixtures




Type A - Water-reducing admixtures
this type will reduce the amount of water needed for the mix, there for it increases the concrete strength,  its useful when concrete is been pumped by pump or tremi. Type A reduces water content by 5 to 15%, Typically the dosage rate of Type A water-reducers range from 130 to 390 mL per 100 kg (2 to 6 fl oz. per 100 lb) of cementitious materials. Higher dosages may result in excessive retardation of the concrete setting time.


Type B - Retarding admixtures and Type D -  Water-reducing and retarding admixture

Both of this is to offset the unwanted effect of temperature, since cement is exothermic and weather temperature place a roll too, this formula is needed on hotter weather conditions,  factors depending are; admixture concentration, dosage rate, concrete proportions, and ambient and concrete temperatures.


Type C - Accelerating admixtures and Type E -  Water-reducing and accelerating admixtures

both this shortens the setting time and accelerates the early strength of concrete. mostly used in freezing temperatures. 

How to Make ground water well

what is a ground water well, thats the a very traditional method used to in collecting water where the other sources of water or rivers are far away, if u wanna know a lot more about more technical detail and kids of wells used for ground water.

firstly you'll need is good form-work to preppier the cylinder part of it, so what was used is a steel framing with 1.2meter (4 feet) in diameter and 1.2m (4FT) in height as in the pic shown, this type of shuttering or form work has two parts init, external shuttering and internal shuttering. all the steel shuttering is bolted together with 9mmx 25mm bolts at each connection, always we have to prepare the internal shuttering first.

after u have carefully prepared the internal shuttering its time to start with the steel work, steel used for vertical is 10mm deformed bar at 150mm spacing, and horizontal as rings its 6mm round bar at spacing of 150mm. since the wall thickness of this well is 120mm, make sure to add a wooden block in between the shuttering before u completely bolts it.

once the steel bars are been handled, insert the cover blocks so that the steel bars wont be touching the form work, what have been used for cover blocks is 35mm small blocks around 2inch by 2 inch, if u wanna knw how to make simple concrete cover blocks visit bigatoll.come, well any how making a cover block is pretty simple.

after u have completed the steel work, concrete cover blocks its time for you to place the external covering for the form work. if you wanna find out how much of concrete needed for 1m³ of concrete visit yd-mv.com this website has a free concrete calculator. now start mixing the concrete in the ratio of 1:2:3. make sure its a bit wet like 60% water, this will help you to get rid if the honey combing that will occur, but dont forget to use a mechanical vibrator, good vibration has to be done after each load of concrete has been poured into this shuttering.

once the concrete has been poured, give the form work 24 hours to dry out, than carefully remove the bolts and remove the shuttering, Always remove internal form work first than external form work, this is because the concrete haven't got its full strength and giving 1 day means its surface is dry. so there will be cracks if u try removing the external first. so keep in mind internal than external. leave the concrete for curing with wool bags till 7 days, so it will reach the peak of strength starts to gain. spray water 2 times a day so that it will keep wet and no thermal crackings occurs.

while the 7 day period is there, use that time to cast a new concrete cylinder part for your well, if you have heavy machinery than it will be a advantage for you, but if u dont u have to wait till the 7 day period is over than to put the form work on top of it to precast a new concrete.

if you have an excavator, excavate the place where you want to keep the well, mark the location of the well, than dig the place till water or more than water, in this case water depth was something like 1.2 meters, since Maldives is a flat land water table is petty high and the island is 1meter above sea level.

when the excavation is done, place the pre caste concrete in side the hole, use a crane or a the excavator, while lifting heavy objects you must be very careful, cos every where there are nut cases running around.

excavating ground water well

Source: Courtesy of YD Works

once the well is placed, start another concrete on top of this well with connection the rods or place another concrete cylinder on top of it. once the pieces is placed, start manual excavation from inside of the well, the more soil u remove underneath the concrete, it will slowly starts to sink down, ground water well are sinks like this and its called the sinking method.

in this case YD Works used a mini dredger pump of 4", this pump can suck water with soil, this way some soil underneath the concrete wells will come plus there will be one labor always digging the soil and sand out of it. once the sinking starts try not to stop digging till your done, while your digging the soil around the external surface is been pulled down to your shovel, there will be a gap forming between the external surface and the ground, once that gap is started to from that means its ready to sink, if u get stuck sprey some water to the bottom that way soil erosion will occur giving you more sand to pull up.

top concrete cover plate been laid

Source: Courtesy of YD Works

pre cast concrete cover is 150mm thick and steel of 10mm deformed bar been placed at 150mm spacing both ways, there is an opening of 2ft by 2 ft, a concrete cover has to be made so that no one falls in it, this cover is cast with 6mm steel bar with 80mm spacing T/B.

there you go, now thats a short way on how to build ground water well, now please visit bigatoll.com and find out more other stuff. we would like to thank YD Works for providing us with the pics and detail info on how the work has to be done, bigatoll.com send regards and thanks to YD Works.

Method of underwater concreting - Tremie method

This is a method on how to place concrete underwater, this method place a big role in offshore concreting, since cement looses its strength and fade away under water, Tremie method is to be used. Tremie Concrete is done by using a formwork/pipe which will have one end of the formwork/pipe above water and other bottom end immersed under the water and with the help of gravity. 

A tremie is a watertight pipe, generally 250mm in diameter, having a funnel shape hopper at its upper end and a loose plug at the bottom or discharge end. The valve at the discharge end is used to de-water the tremie and control the distribution of the concrete. The tremie is supported on a working platform above water level, and to facilitate the placing it is built up in 1 to 3.5m section.

During the concreting, air and water must be exclude from the tremie by keeping the pipe full of concrete all the time; and for this reason the capacity of the hopper should be at least equal to that of the tremie pipe. In charging the tremie a plug formed of paper is first inserted into the pipe as the hopper is filled the pressure of fresh concrete forces the plug down the pipe, and the water in the tremie I displaced by concrete.

For concreting, the tremie pipe is lowered into position and the discharge end is kept as deeply submerged beneath the surface of freshly placed concrete as the placed concrete as the head of concrete in tremie permits. As concreting proceeds the pipe is raised slightly and the concrete flows outwards. Care should be taken to maintain continuity of concreting without breaking the seal provided by the concrete cover over the discharge end. Should this seal is broken, the tremie should be lift and plugged before concreting is recommended. The tremie should never be moved laterally though freshly placed concrete. It should be lifted vertically above the surface of concrete and shifted to its new position.

When large quantities of concrete are to be placed continuously, it is preferable to place concrete simultaneously and uniformly through a battery of tremies, rather than shift a single tremies from point to point. It has been recommended that the spacing of tremies be between 3.5 and 5m and that the end tremies should be about 2.5m from the formwork. The risk of segregation and non-uniform stiffening can be minimized by maintaining the surface of concrete in the forms as level as possible and by providing a continuous and rapid flow of concrete.




How is the Underwater Concrete Mixes?

For Structural concrete following must be considered 

• Coarse Aggregate: Gravel of 3/4” (20mm) max. size.  Use 50-55 % of the total aggregate by weight.
• Sand, 45-50% of the total aggregate by weight.
• Cement: Type II ASTM (moderate heat of hydration), 600 lbs/yd3
• Pozzolans: ASTM 616 Type N or F, 100 lbs/ yd3
• Water/Cement Ratio: 0.42 (0.45 Maximum).
• ƒWater-Reducing Admixture (preferably it is also plasticizer):  Do not use superplasticizers.
• ƒAir-Entrainment Admixtures:  To give 6% total air.
• ƒRetarding Admixture:  To increase setting time to 4-24 hours, as required.
• ƒSlump:  6 1/2" ± 1"
• ƒThis mix will develop compressive strength in the range of 5,600 – 7,000 psi at 28 days.

Method of underwater concreting - Tremie method (inside view)

Basic principle behind Method of underwater concreting - Tremie method

Maldives bridge work using this method

Conditions of underwater concrete

Concrete poured underwater must have good workability and, thus, should meet the following conditions:

(1) The mixture must incorporate the proper proportions of sand and gravel (preferably not crushed material) in a rich paste of Portland cement and freshwater.

(2) The mixing water must not exceed 5.5 gallons per bag of cement. (Mixing water includes the water entering the batch in the form of free, surface moisture on the sand and/or gravel; this free water must, therefore, be deducted from the total water to be
added.) If the aggregate particles are surface-dry and not saturated, they will absorb some of the gross mixing water; allowance must, therefore, be made for extra mixing water, taking care that the W/C ratio of 5.5 gallons per bag is not exceeded.

(3) The mixture should not contain less than 8 bags and not more than 10 bags of cement per cubic yard of ASTM Type V concrete.
- Type V is the recommended product for such structures because of its high resistance to sulfate attack (a form of disintegration occurring in seawater and other high salt environments)

(4) For improved workability, the concrete should incorporate an admixture to provide not less than 3°% and not more than 6% entrained air as determined
by standard ASTM methods.

(5) The sand and gravel should be physically sound, and the maximum gravel size should be 3/4 inch The aggregate should be graded as indicated in Table 1 .


(6) The formwork in which the concrete is poured must be rigid, carefully fitted, and designed so that no underwater currents can pass through it. Provision must be made for the seawater displaced by the concrete to escape from within the form. Timber is generally the most suitable material for construction of the formwork. Joints between the formwork and the intact portion of a structure should be caulked.

(7) Low temperatures during mixing and curing of concrete (i.e., below 50°F) can delay strength development for periods as long as one year and so should be avoided.

(8) An enclosed chute or "trunk" should be specified so that there is no mixing with water during placement

Underwater concrete

Placing of concrete in water is a very difficult operation all aspects from mixing transportation placing and control of the work have to be carefully evaluated and should only be preformed be very experienced engineers and workers the aim in placing concrete underwater is to keep the fresh concrete and water a part as much as possible during the placing of the concrete, and to avoid a rapid flow of either of them and when they come in contact. So that cement will not be washed out.
For this reasons, the correct placing method is the most important factor with respect to final quality.


Underwater concreting is not a new technique: it has been experimented with since about 1850. In 1910 the Norwegian August Gunderson, took a Norwegians patent on a method of underwater casting for concrete columns and the like. In the same year, the method was tried for the first time In Norway for underwater concreting of reinforced structure. This method is, nowadays, the Maine underwater concreting method and is known as termite pipe method.

Since 1980s, admixtures that increase the cohesion of the concrete and make direct contact with water passable without signification changing the properties of the concrete have been developed and are widely used. The ant washed out (AWO) admixtures.

E.g. Rescan T from Norway and similar product, has certain properties that influence the fresh concrete, and the setting and hardening of it knowledge about this properties
is crucial for all parties involved.

How many days is it for curing?

The recommended minimum curing time is 28 days, but most contractors typically wait only 7 to 14 days just to save time and money, but depending on the size of the concrete its very important to cure for 28days cos it will gain full or almost full strength.

pouring water (curing) of concrete after it been poured

What is the name given for the procedure of pouring water on concrete?
its called curing, a processed where concrete is left moist due to the exothermic reaction that takes place which may give cracks on the concrete.

Why Cure?
The major objective of concrete curing applications is to prevent the rapid loss of water from the concrete. As concrete loses water due to evaporation from the top surface, differential drying shrinkage can occur. This is a major contributor to shrinkage cracking. The application of curing methods reduces the loss of water from the surface of the concrete. It also permits more complete hydration of cement in the concrete itself. Minimizing evaporation also helps control the temperature of the concrete during its early-age stage.

Curing operations should begin after the water sheen disappears from the surface, and after any texturing operations have been completed. In the case of a curing compound, the membrane formed by the compound should not be disturbed after it is placed.

Rapid Drying Conditions
In rapid drying conditions, a light water fog may be necessary to maintain moist surface conditions prior to the application of curing methods. Light water fogging can be accomplished during a short period of time when the concrete surface begins to dry but before the curing operations can begin, such as prior to texturing operations have been completed.

Use of Ambient Weather Condition Information
Ambient weather conditions, such as wind speed, relative humidity, and air temperature can interact with the temperature of the concrete to cause excessive water evaporation from the concrete surface. Since different curing methods provide different levels of protection, knowing the amount of protection required is important in determining the method to use. In order to know the required level of protection, the ambient conditions and concrete temperature must be known. A portable weather station that records the ambient conditions and automatically predicts evaporative water from the concrete surface can be an invaluable tool for controlling water loss from the concrete surface. Such a tool can also warn in advance when conditions approach predefined limits of evaporation.
Curing Methods
Various concrete curing methods are available, and each provides different levels of protection. A single coat of liquid curing compound generally provides the least protection, but additional coats can improve its performance. Polyethylene sheets, cotton mats and wet burlap provide additional protection.

Liquid Curing Compound

White-pigmented, liquid membrane curing compound is used most often due to its low cost and ease of application. It does not require great amounts of labor, nor does it expensive, bulky material, such as cotton mats. It's disadvantages are that it provides the least amount of protection, and the membrane can be ruptured inadvertently.

The liquid curing compound should be white, to avoid excess heat absorption from the sun (Figure 4.1). Also, the white color enables construction workers to check more easily for coverage uniformity and gaps in the coverage. The liquid compound must be constantly agitated during application to ensure that the mixture is applied correctly. The curing compound spraying operation should be shielded from the wind throughout the process.

The compound must cover all exposed surfaces, including the sides of the pavement slab. The compound should not, however, be applied into any joints in the pavement. For ultra-thin whitetopping, curing compound should be applied at twice the normal application rate, due to its extra sensitivity to drying shrinkage.

Figure 4.1 - White-Pigmented, Liquid Membrane Curing Compound.

Plastic or Waterproof Paper

Plastic, or polyethylene, sheeting provides good protection to the concrete from water evaporation from the surface (Figure 4.2). It requires more labor than liquid curing compound, yet it is not as bulky as cotton mats or burlap. Waterproof paper may also be used in the same manner described here for plastic sheeting, but is not as common.

The plastic sheeting must not have any rips or tears through which water can escape. The sheets should overlap to provide full coverage for the concrete surface. Just as with curing compound, the sheeting should cover all exposed concrete surfaces, including the edges of the pavement slab. Active methods must be used to hold the sheeting in place. Do not assume that they will remain in place of their own accord.

Figure 4.2 - Polyethylene Sheeting Used as a Curing Method.

Cotton Mats or Burlap

Cotton mats represent a great increase in evaporation protection, both by providing additional moisture if needed, and by protecting the concrete from ambient conditions such as low humidity, high wind speeds, and high temperatures. Cotton mats and wet burlap must be kept continually moist. When the mats get dry they can become more harmful than without them due to "wicking" action which draws moisture from the concrete into the mat.