Concrete Technology Essay: Curing Methods and Underwater Placement

This essay provides a detailed overview of concrete curing and underwater concreting techniques. It begins by explaining the importance of curing, emphasizing its role in maintaining moisture, increasing strength, and reducing permeability and cracking. Various on-site curing methods are discussed, including shading, ponding, covering with gunny bags, sprinkling water, steam curing, and membrane curing, highlighting their applications and limitations. The essay also addresses the consequences of improper curing, such as increased chloride ingress, cracking, reduced durability, and lowered strength. Furthermore, it delves into underwater concreting methods like the pump method, toggle bags, bag work, and tremie techniques, detailing their processes and suitability for different projects. The Akashi Kaikyo Bridge is mentioned as an example where tremie concrete was used extensively. Finally, the essay explores sprayed concrete, its properties, advantages, and applications, including its high strength, low permeability, and enhanced bond quality, making it a versatile material for construction and repair. Desklib offers this essay and many more resources for students.

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CONSTRUCTION MANAGEMENT
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Mixture/concrete treatment using cure method.
The process of treatment using cure method is basically a technique in which a mixture of the
cement and sand are treated in a way that prevents the loss of the moisture by keeping it within a
temperature of proper quantity. This particular treatment method normally gives a type of the
sand/cement mixture that has higher strength as well as reduced permeability (Shi, He and Wu
2012). The process of curing is also very essential in controlling cracking, which can affect the
durability of a structure.
Importance of curing concrete
The following are benefits which are associated with the curing of concrete;
i. The availability of water in concrete is very important to facilitate the chemical reaction
which accompanies the setting of concrete. Usually, there is an adequate quantity of
water during mixing of concrete to initiate the hardening of concrete but at the same time
to retain the water till the concrete fully hardness (Kumar, Srikanth and Rao 2012).
ii. Through proper curing of concrete, the impermeability and durability of concrete are
increased while the shrinkage is greatly reduced hence the possibility of cracking is also
reduced.
iii. The process of curing protects the concrete from wind and sun
iv. With proper curing, the resistance of concrete to abrasion is greatly increased
v. The strength of concrete is known to increase with age. If curing is done properly the
increases of strength is sudden and rapid in the early stages and it continuous for an
indefinite period.
How curing of concrete is done on site
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There are distinctive strategies which are connected in the restoring of cement onsite. The usage
of a given system relies upon the idea of work and the climatic conditions where the solid is
being relieved (Memon et al. 2011). The following are a portion of the general techniques which
are utilized in the restoring of cement.
• Shading solid work
• Ponding technique
• Covering the solid with gunny or hessian packs
• A sprinkling of water procedure
• Steam relieving
• Membrane relieving
Sand/Cement mixture shading
The principle point of shading solid work is to keep the dissipation of water from the given
surface even before setting. This system is normally received in circumstances where there is an
expansive solid surface, for example, a street chunk. This procedure is critical in zones which
encounter dry climate request to shield the solid from the warmth, wind and direct sun beams.
This strategy additionally shields the solid surface from the rain. In areas which encounters chilly
climate, the shading system saves the warmth of hydration of the bond and thus forestalling
solidifying of cement under the gentle ice conditions. Shading of the solid surface might be
accomplished by the use of canvas extended on the edges (Espinoza-Hijazin and Lopez
2011).The principle constraint of this innovation is that it has restricted application.
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Protection of the solid mixture with gunny or hessian packs
This is the most widely recognized strategy for restoring concrete, explicitly for basic cement. In
this technique, the solid surfaces which may be uncovered are kept from drying out by covering
them with canvas, void concrete sacks or hessian. The covering of slanting and vertical surfaces
is done cautiously since the surfaces are intermittently wetted. The interim at which the surfaces
are wetted will rely on the rate of dissipation of water. Amid the execution of this innovation, it
ought to be guaranteed that the surfaces of cement are not permitted to dry notwithstanding for a
brief timeframe amid the restoring time frame. Uncommon courses of action for keeping the
surfaces wet must be made at occasions and specific schedules.
Effects connected to improper curing
When the concrete does not undergo proper curing it results to the following;
i. The probability of ingress of chlorides and the atmospheric chemicals are very high
ii. The cracks will be formed because of the plastic shrinkage, thermal effects, and drying
shrinkage
iii. With poor curing of concrete, the durability of concrete decreases because of high
permeability
iv. Once concrete undergoes improper curing the flexural and compressive strengths are
lowered
v. Poor curing of concrete will increase the rate of carbonation of concrete
vi. Improper curing of concrete reduces the resistance of concrete to frost and weathering
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vii. Improper curing of concrete results to the concrete surfaces being coated with dust and
sand which lowers the abrasion resistance of concrete.
The above issues are very common in parts of the structure which are either directly exposed or
those sections of the structure that possess surfaces perceived to be large in comparison with the
available depth, roads,channels,vertical tubes and the bridges. It is therefore very important to
ensure that naked surfaces are protected prior to setting activities
CONCRETING UNDERWATER
Pouring of concrete in under water is widely demanded in many projects, mainly for the offshore
structures such oil refineries, harbors and jetties and in marine projects, as well as for some
special cases of in-shore structures which are located near the coast, or where the level of
groundwater is near the ground surface(Assaad and Issa 2012)..
Pouring of cement submerged can be helped out effectively through the suitable structure as well
as via picking the most proficient method for setting the solid submerged. Dominant part of the
submerged cement is blended on the ground surface in a customary way and after that set by one
of the numerous techniques for putting. There are numerous strategies for putting the blended
cement submerged which incorporate the conventional techniques, for example, siphoning
strategy and tremie technique. As of now, there are numerous cutting edge strategies for
submerged cementing, for example, grouted totals which are likewise alluded to as a two-
organize solid strategy. Two-arrange solid strategy is characterized as solid which is delivered by
putting the coarse totals in the assigned goal, at that point grouting the voids of the coarse total
with the grout by means of siphoning tubes which are stretched out to the base of the shape; this
normally fills the voids between the totals (Bartos et al. 2014)
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Underwater concrete placement methods
The following are commonly used methods in concrete placement underwater;
Pump method
Toggle bags
Pump method
Bag work
Fig: Diagrammatic illustration of the tremie
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Before the pouring of the solid is begun, a fitting is typically embedded into the cylinder to stop
the solid and the water from blending. This sort of a fitting can be reason made, a shed
vermiculite or a wipe elastic ball. The stream of the solid in the pipe is generally represented by
erosion and gravity with the cylinder, because of that the tremie must be climbed and down to
direct the stream.
Toggle Bags
In the circumstances where little measures of cement are required submerged, for example, for
the fix purposes, the strategy for flip pack is the best thought. By and large, the waterproof sack
is filled in with wet cement, and the measure of this pack is shut with a flip and a rope. At the
setting point, the wet cement is crushed out by a driver, and it is smashed into place .the
utilization of jumpers extraordinary adds to the expenses of activity (Hooton and Bickley 2014).
Bag work
The sacks which are regularly utilized in this system are typically produced using an open-weave
material, for example, hessian. The packs should be half loaded up with the plastic concrete,
fixed and taken submerged whereby they are put by utilization of a jumper. Half filling of the
packs licenses them to be formed into any shape and in the meantime gives them great contact
regions nearby sacks. Grout from the blend sees through the open-finished material and
subsequently enabling the cling to be built up with the adjoining sacks. For extra soundness, the
packs can be spiked together with a little width strengthening bar (Assaad and Issa 2013).
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As a rule, the jumpers as a rule like to deal with sacks of dry-blended cement and to grout up
between packs. In any case, this framework puts a great deal of obligation regarding the jumpers
who are occupied with the position. The dry blend concrete is never completely wetted-out by
the water leaking in with that it is absurd to expect to minimize the solid completely, and the
contact surfaces are exceptionally negligible.
Pump strategy
Siphon strategy alludes to the method of siphoning the solid straightforwardly into its last
position, and it for the most part includes both vertical and level conveyance of cement in a shut
arrangement of release pipes. The siphoning of cement has the advantage of being productive
with potential sparing work and time. In the ongoing past siphoning, the procedure has been
generally connected for the above water structures development due to the numerous headways
of siphoning innovation and hardware utilized. Siphoning concrete specifically submerged is the
actually defective system. Regardless of whether solid shadow water is possible, despite
everything it includes a great deal of dangers and conceivably poor solid quality. For the
ventures which include enormous submerged cementing, the siphoning strategies ought not to be
allowed. In any case, the siphoning innovation is an extremely incredible method for conveying
the solid to submerged.
Akashi Kaikyo Bridge
This scaffold is otherwise called pearl connect; it is the longest suspended extension on the
planet. Akash Bridge is situated in Japan. The two key pinnacle establishment of this extension
are expansive, twofold – divider steel; caissons loaded up with tremie concrete. The task required
an expansive volume of tremie cement to be put up to 57m beneath the water surface.
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Sand/Cement mixture sprayed
Showered solid alludes to the blend of concrete, totals, and water that are anticipated
pneumatically from a spout into place to produce a thick homogenous mass. The splashed
cement abnormally fuses admixtures and may likewise incorporate increases or filaments or a
blend of these two. The first term which was utilized to allude to showered concrete was Gunit,
with time different terms have grown, for example, 'splashed solid,' 'shot cement' and 'shotcrete.
In any case, the present acknowledgment is that 'shotcrete' is utilized in the USA and the term
'splashed cement is utilized in Europe. Introduced in the right path by the accomplished
implements, the splashed cement generally furnishes fashioners and constructors with a versatile
and financially savvy procedure to make and fix solid structures.
Properties and preferences of splashed cement
Splashed cement normally shows special properties s which is some sense makes it prevalent
poured concrete. By and by, these properties are because of the diverse techniques that are
connected amid blending, transporting and position and not the essential contrasts in parts
materials.
Little concrete to water ratio
Splashed cement by and large has brought down water to bond proportion than the poured
cement.
High quality with fast quality gain
Shown cement can be relied upon to accomplish high compressive quality, especially with low
bond to water proportion and the thick compaction accomplished by the fast of utilization. The
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quick quality gain can likewise be accomplished, especially while applying plant clustered
materials.
Little penetrability
The rapid of situation more often than not guarantees amazing compaction and high-thickness
joined with low by porousness and the water retention. The above procedure accomplishes a
homogeneous development material having brilliant stop obstruction, high level of scraped area
and a low surface splitting (Gjørv 2014).
Enhanced bond quality and attachment
Fitting surface readiness is vital in the numerous activities that I did in the development business.
Having a supposition that the substrate is legitimately arranged then it is programmed that the
security quality is extraordinarily made strides. Additionally, the utilization of holding operators
and coatings is as a rule of no utilization and, under even conditions harming to the bond.
Rapid with high-yield
Splashed cement can accomplish high volumes at an a lot quicker rate and in the meantime
conservative.
The utilization of splashed solid help in lessening formwork costs
Making an examination between they poured cement and they showered concrete, the splashed
cement requires significantly less formwork when contrasted with they poured concrete.
Specifically, whenever bended or natural shapes are to be accomplished by the fashioner.
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Ordinary applications and employments of splashed cement
 The precedents beneath show the one of a kind flexibility of splashed cement
 New development
 Domes and shell rooftops
 Silo structures
 Bank vaults
 Blast verification structures
 Retaining dividers
 Barrel vaulting
 Caissons
Underground development
 Storage supplies
 Tunnel Lining
Water holding structures
 River and ocean dividers
 Dams and supplies
 Swimming pools
 Water towers
 Canal Lining
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 Drainage and water system channels
Defensive coatings
 Refractory linings
 Fire insurance to auxiliary steelwork
 Pipeline encasements
 Soil and shake adjustment
Fix on reinforcing
 Fire harmed structures
 Housing
 Concrete harmed by support consumption
 Bridges
 Cooling towers
The dry procedure
In this procedure, they splashed cement is foreordained by the proportion of bond and total
without the expansion of water. The blend is then sustained into a reason structured machine,
pressurized and after that brought into a high-speed air stream and passed on through adaptable
cylinders to the splashing spout. At the spout, I finely atomized shower of plain water is added to
the surge of the materials to hydrate the bond and profile the correct blend consistency.
The wet procedure
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The wet procedure of showered concrete is comprised of a blend of bond and totals and blended
with water before it is being siphoned through a cylinder to the release spout. Once in the release
spout, high-speed air is connected to impel the blend into the position.
Constituent's materials
Admixtures
Splashed cement is comprised of admixtures, which are added primarily to upgrade the
properties of the new blend and the solidified cement. A portion of the blends that are included
incorporate; quickening agents, plasticizers and super plasticizers, Hydration control admixtures
and retarders.
Fibers
The strands are added to the splashed cement to affect one or the majority of the accompanying
material properties;
i. Control of them is breaking
ii. Control of plastic shrinkage breaking
iii. Enhancement scraped area and effects opposition
iv. To enhance imperviousness to fire
v. To enhance malleability and durability
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vi. To upgrade malleable and flexural quality
Treatment operators
Fluid relieving operators ought to be indicated to boost hydration of the concrete by lessening
water dissipation.
As a rule, there are two kinds of restoring specialists;
 External shower connected to fix operators
 Internal relieving and blends
Immersed surface-dry
The immersed surface dry is characterized as the condition in which the surface of the particles is
dry, however the antiparticles voids are soaked with water. In this condition, totals won't
influence the free water substance of the composite material. The water retention by mass is
characterized as the mass of the immersed surface example, and the mass of the broiler driest
example is gotten by the accompanying equation.
SSD stands for saturated surface-dry and it describes a condition in which concrete surface must
be brought to when assignment product is to be applied to it. The service is saturated surface dry
when the complete is saturated with water to a depth of several millimeters, but the other service
is devoid of free water as it had been dried with a tower.
This kind of surface condition is very crucial when applying cement product to the existing
concrete. This is because the saturation usually prevents rapid drying and weakening of the
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products and its bond to the surface. Just a significance removal of free water from the surface
prevents dilution and weakening of the product in exactly the location where our strength is most
important and bond interface.
Fig: diagrammatic representative of aggregate in SSD condition.
Concrete Trial
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References
Assaad, J.J. and Issa, C.A., 2012. Bond strength of epoxy-coated bars in underwater
concrete. Construction and Building Materials, 30, pp.667-674.
Assaad, J.J. and Issa, C.A., 2013. Mechanisms of strength loss in underwater concrete. Materials
and structures, 46(10), pp.1613-1629.
Bartos, P.J., Cleland, D.J. and Marrs, D.L. eds., 2014. Production methods and workability of
concrete. CRC Press.
Espinoza-Hijazin, G. and Lopez, M., 2011. Extending internal curing to concrete mixtures with
W/C higher than 0.42. Construction and Building Materials, 25(3), pp.1236-1242.
Gjørv, O.E., 2014. Durability design of concrete structures in severe environments. CRC Press.
Hooton, R.D. and Bickley, J.A., 2014. Design for durability: the key to improving concrete
sustainability. Construction and Building Materials, 67, pp.422-430.
Kumar, M.J., Srikanth, M. and Rao, K.J., 2012. Strength characteristics of self-curing
concrete. International Journal of Research in Engineering and Technology ISSN, pp.2319-1163.
Memon, F.A., Nuruddin, M.F., Demie, S. and Shafiq, N., 2011. Effect of curing conditions on
the strength of fly ash-based self-compacting geopolymer concrete. World Acad Sci Eng
Technol, 80, pp.860-863.
Shi, C., He, F. and Wu, Y., 2012. Effect of pre-conditioning on CO2 curing of lightweight
concrete blocks mixtures. Construction and Building materials, 26(1), pp.257-267.
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