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As we all need protection from climate changes like Woolen ware in winter and raincoat in monsoon, concrete and steel structures also need similar protection to resist the challenging conditions.

Challenges for concrete needing protection are like this.

1. High humidity,
2. High temperature,
3. Saline conditions,
4. Reinforcement corrosion,
5. Design inadequacy,

Challenges for steel needing protection are like this.

1. Corrosive fumes or splash,
2. Uncalled for stresses generated within the structural matrix,
3. High humidity and temperature,
4. Modification in functionality of the structure.

Both concrete and steel structures are prone to corrosion. Corrosion of concrete is defined as depolarization of cementatious or binding property. Corrosion of steel structure is occurrence of rust on its surface.

Concrete structures:

They are exposed to the challenging conditions at regular intervals. If UAE perspective is considered, then thermal and humidity variations are significant in this region. Hence the methodology for protecting them against getting corroded can be largely divided into two major categories.

In-build resistance to corrosive conditions,

External measures

In-build resistance for concrete matrix can be created by following measures.

Functionality of structure must match the structural design and execution.

Construction by following standard construction practices,

Treatment of construction joints and expansion joints with utmost care.

Structures with special services like water retaining structures, retaining walls, foundations for heavy machinery, mass concrete etc must be constructed by following guidelines provided in Global codes of practices.

Use of construction chemicals should be very critically evaluated before taking into execution.

Rehabilitation / retrofitting / strengthening of concrete members is carried out with help of high grade materials. All of them have tendency of high exotherm generating during polymerization of their ingredients. This has to be brought to balanced thermal equilibrium. Dampening of the surface is the usual method adopted for the purpose.

Curing activity is also called as strength gaining phenomena.

Two points of importance connected with curing are discussed here.

First point is insufficient efforts to compensate for polymerization exotherm. This results in generation of internal and surface cracks through which exotherm heat tries its escape way. Unfortunately some of these cracks turn to be structural cracks at long run and emerges as serious structural defect.

Second point is insufficient time period provided for full polymerization of total quantum of ingredients of the rehabilitation matrix which is also covered under the domain of curing. Polymerization period for each category of rehabilitation material is specific and defined. It is mandatory and essential to allow total polymerization time period. All designed and desired parameters of finally rehabilitated structure are achieved only after this polymerization process is complete. If under any circumstances this period is not allowed before putting the structure to its desired functioning, there are serious chances (with high probability) that the structure might buckle and no more remain capable to sustain the load and other stresses to which the structure would be exposed on later date. This is very typical challenge. No NDT result would be below reject limit. No reinforcement would be found corroded. No external force causing distress would be identified and still the structure may show hollow sound at some local pocket! Internal distress due to buckling or typical shear is the reason for this and insufficient time allowed for polymerization process – curing period – is the reason for the distress as stated above.

Any compromise in curing activity and curing period is a serious threat to the rehabilitated structure which was already damaged and which has been rehabilitated.

Saline conditions causing structural damages in UAE and surrounding areas is major point of concern.

Speed of construction with more thrust on cosmetic value at times induce the inherent defects which can spoil the structure with passage of time.

Absence of special and specific measures to plug / prevent sub-soil water entry to the foundations or basements of the structure is responsible for water ingress at that level which is beginning of end.

Exterior coating for cosmetic and aesthetic value to the structures at UAE and surrounding area must have element to resist saline atmosphere in addition to UV resistance.

Use of FRP bars as structural reinforcement must be extensively explored for construction projects.

ACI CODE-440.11-22: Building Code Requirements for Structural Concrete Reinforced with Glass Fiber-Reinforced Polymer (GFRP) Bars

Damaged structures are first examined for their rehabilitation rather than their demolition and reconstruction.

Designing the scheme or method for structural rehabilitation of such structures demands a special address for structural design dynamics.

Parameters of the damaged structure often reach close to their reject limit and to bring them well within their acceptable limits, demands augmentation of those parameters. This is usually done with external treatment but this is to be validated with the structural design.

For example if the structure is identified to be weak in shear at a particular location then its structural design mechanics can be analysed to find out effects of this weakness on other parameters like bending moment or split shear or ductility etc. This is essential because while designing augmentation measures for weak parameter of shear, it should not happen that other parameter is ignored or not considered for its healthiness. It is imperative that while designing the rehabilitation scheme for compensating one parameter, some other parameter is adversely affected to create new area of structural weakness.

Structural rehabilitation is a 360⁰ process which requires all round analytical approach to design a sound scheme for making it totally successful when implemented at site.

Accord Specialities Contracting LLC works with this applied knowledge background to execute every assignment of structural rehabilitation with perfect understanding the logic and design philosophy for making it a success in achieving desired functional life of the rehabilitated elements, members and the structure as a whole.

Structural rehabilitation of damaged concrete structures often calls for injection of specified grouting material inside concrete core. This injection is always done with specified pressure. How important that pressure is?

It is indeed very important.

When an under-pressure activity is to be taken up, its necessity is to be properly addressed. Injection method is to be sought for only under special situations where other methods are not found effective. Injection operation under pressure is a blind work. One won’t know the path followed by the material being injected although it would have a reason for its selection based on observations and results of non destructive testing. This calls for its meticulous execution at field so that the activity happening beyond our vision, happens to the benefit of the damaged structure.

Pressure at which the grout is to be injected within the core concrete must be very precise and optimum. It should be just adequate for the grout (with its known viscosity) to reach and to plug the crevice of the core concrete mass. It should also be not very high for pushing the grout for plugging the crevice because if it is higher than required, it would exert additional pressure on the walls of crevices as a result of which the crevices would expand before getting plugged. Of course the crevices would be plugged during the injection process but (as said earlier,) it may create the stresses due to excessive pressure in that case through the crevices which might add a new dimension to the damage.

Always be careful while carrying out injection operation to rehabilitate the damaged concrete members.    

Cementatious structures are often found with (excessive) hidden humidity even after the curing period is complete. This is a serious factor affecting the functional performance of that structure or member.

• It affects binding action and hence integrity of the concrete matrix.

Integrity of a member is of utmost importance for its long functional life. Hidden humidity within the member affects hard binding action of concrete ingredients and then the integrity deteriorates. 

• It attacks reinforcement steel and corrodes it.

Reinforcement steel exposed to humidity at a close distance can easily corrode fast.

• It affects the stability of protective or decorative resinous coating applied on the surface of structure or member. It also obstructs the process of development of bond between the mother surface and any other treatment to be applied on the surface of structure or member.

Any resinous protective or decorative coating or treatment must be applied on the member only after its internal humidity has been completely evaporated.

• It affects the plans to modify or refurbish the structure or member to take additional load or for change of the functionality of structure or member.

Members having hidden humidity for any reason for a long time is normally not found fit for its structural or functional modification. This becomes a big challenge especially for industries.

When a damaged or underperforming structure is taken up for its structural rehabilitation / retrofitting / strengthening, its execution requires to be planned considering surrounding climate and weather conditions. It is briefly addressed below.

1. Ideally atmospheric temperature during such activities should be in the range of 27⁰ C to 35⁰ C. This is significant especially when the activity involves repair material having high exothermic polymerisation process. Lower atmospheric temperature than 27⁰ C or higher than 35⁰ C, has tendency to disturb thermal equilibrium between temperature of rehabilitation mass and atmospheric temperature.
   1. Use of ice is one of the essentials for taking up of these activities under high temperature.
   1. Concealing of conduits carrying cold water within the concrete matrix (by taking it into consideration right from design stage) and continuously blowing cold water throughout the activity of placing of micro-concrete; helps in minimising the adverse effects due to high temperature within the matrix as well as outside temperature.
2. Atmospheric humidity also affects the velocity of polymerisation process. Polymerisation slows down during high humidity and hence rehabilitation activity can be scheduled when atmospheric humidity is normal as per the meteorological data. When resinous materials are involved in structural rehabilitation activity, polymerisation of its different ingredients drastically slows down under high humidity.
3. However if it becomes absolutely necessary to execute the activity during high humidity, then the proportioning of water:powder ratio would need to be adjusted as per manufacturer’s advice.

We at Accord Specialities Contracting LLC have am inborne practice of keeping a close watch on surrounding atmospheric conditions affecting structural rehabilitation / retrofit / strengthening activities to execute them with all precautionary measures so that the rehabilitated structure performs as desired.

Accord Specialities Contracting LLC – one stop solution for structural rehabilitation / retrofitting / strengthening.

Dos

1. Design the structural rehabilitation scheme and methodology after systematically assessing, evaluating and analysing the structural damages.
2. Ensure availability of total quantity of tools, tackles, equipment and construction consumables before starting the work.
3. Ensure overall safety measures for the structure when a part of it is being taken up for rehabilitation.
4. Ensure transfer of load of additional rehabilitation mass upto the foundation.
5. Ensure compatibility of construction chemicals with surrounding environment and core conditions.
6. Ensure appropriate and optimum pressure for injection grouting activity commensurate with the properties of material which is being injected.
7. Ensure scaffolding, strutting and supporting the formwork to receive free flow rehabilitation mass because its heat of exotherm exerts huge pressure on the formwork.
8. Ensure application of resinous applications only under moisture free conditions.
9. Protect the rehabilitated structure with protective coating to safeguard the rehabilitated structure from corrosive conditions.

Don’ts:

1. Ensure that the rehabilitation activity doesn’t cause environmental hazards.
2. Avoid total thickness build up of more than 50 mm for application of polymer modified mortar.
3. Avoid loading the rehabilitated member before its stipulated setting and curing period.
4. Avoid execution under humid or high temperature period.
5. Avoid over-safe design for structural rehabilitation as it is uneconomical and may prove to be unsafe for the rehabilitated member at long run.

Whenever concrete or steel structure is found damaged, its damage assessment followed by analysis / evaluation of the assessment is the first step done.

Then methodology for retrofitting / rehabilitating / strengthening of the member/s is prepared.

This requires a fundamental knowledge of design engineering for quantifying the quantum deterioration of respective parameters of the member.

Execution of the assignment with designed method, requires more of an applied knowledge. Basic steps to be followed for this execution include the following:

• Surface preparation,

Experience for assessing the force required to prepare the surface by scabbling or chipping off the damaged surface; is the key for this step of work. This is achieved with having gained applied knowledge.

• Pre-execution action,

Prepared surface would require priming as per design requirement. Preparing the priming material and its application is better judged with experience. This is achieved with having gained applied knowledge.

• Execution of retrofit / rehabilitation / strengthening activity,

This is the most important stage. The properties of material selected for retrofit / rehabilitation / strengthening activity play a pivotal role in its preparation for application. Factors like viscosity, yield, honeycomb combat, handling exotherm during hydration etc are few of many factors which can be better controlled under close visual observation. This is achieved with having gained applied knowledge.  

• Post execution care.

Any structural rehabilitation task is incomplete without post execution care. Exotherm dissipation, curing of rehabilitated member, making the member ready for reinstatement of final finishes etc are the factors covered under post execution care. As like factors mentioned above, even this is not a part of any text book. This is achieved with having gained applied knowledge.

 It is hence mandatory to amalgamate design engineering and applied knowledge in appropriate proportion for a successfully carrying out the task of retrofitting / rehabilitating / strengthening the damaged concrete / steel member in better than the best manner.

Accord Specialities Contracting LLC is proud to state here that we possess such professionally amalgamated blend of design engineering and applied knowledge for successful execution of each assignment of retrofitting / rehabilitating / strengthening the damaged concrete / steel member.

Reinforced Concrete consists of aggregates bound under cement paste and reinforcement steel.

Cement paste is a result of physical reaction followed by a chemical reaction.

Bond of reinforcement with concrete matrix; makes it an integral part of reinforced concrete.

Damage to the reinforced concrete matrix is similar to a wound on body. It may either begin from ingredients of concrete or from steel but once it begins, it spreads like cancer and covers the complete member.

Treatment of damaged concrete begins with reaching at the root cause of the damage for which testing is necessary just like pathology laboratory tests for human body. This is essential to ensure that concrete matrix wound won’t repeat with the same root cause.

Little different from human anatomy, treatment of damaged concrete can’t replace the damaged part in totality. Hence its core has to be strengthened or treated for the identified damages and certainly its skin is to be repaired and strengthened.

Skin concrete (cover concrete) retrofit has to be designed and executed with a very special concept. Skin concrete (cover concrete) encompasses or envelops the core concrete. This very phenomena plays very vital part in rehabilitating the damaged concrete member. Even if it is not feasible to rectify few inferior parameters of the core concrete, the extra strong skin concrete (cover concrete) will encompass / envelop the core concrete and the member would be available through out its designed functional life.