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Concrete repairs

Causes of Cracks in concrete structures
Concrete repairs

Causes of Cracks in concrete structures

7 Apr, 2018

Causes of Cracks in concrete structures

There are many Causes of Cracks in concrete structures, they are

  • Thermal movement
  • The permeability of concrete.
  • Corrosion of Reinforcement
  • Creep
  • Moisture Movement
  • Structural design and specifications
  • Poor Construction practices.
  • Improper maintenance

Causes of Cracks in concrete structures

1.Thermal movement

All materials expand on heating and contract on cooling. The thermal movement depends on temperature variations, dimensions, a coefficient of thermal expansion and physical properties of materials. The external exposed to direct solar radiation and the roof subject to thermal variation is liable to cracking.

Remedial Measures:

Thermal joints avoid by expansion joints, control joints and slip joints.

2.The Permeability of concrete

Concrete permeability controls by factors like water-cement ratio, water hydration, curing, air voids, micro-cracks and continues exposure to thermal variations.

3.Corrosion of Reinforcement

Concrete provides protection to reinforcing steel. Steel will not corrode as concrete around it is impervious. And does not allow moisture or chlorides to penetrate within the coverage area. A properly designed and constructed concrete is initially water-tight. The reinforcement steel protects by a physical barrier of the concrete cover having low permeability and high density.

Remedial Measures:

Increase the concrete cover with proper materials like plastic, concrete, readymade cover blocks, etc., instead of using stones and wood pieces. Increased concrete cover over the reinforcing bar reduces corrosion.

use concrete with low permeability.

4.Creep

Concrete subjected to loading exhibits a slow time-dependent deformation known as creep. Creep increases with increase in water and cement content, water-cement ratio and temperature. It decreases with increase in humidity of surrounding atmosphere and age of material at the time of loading. Use of admixtures and pozzolanas in concrete increases creep. Amount of creep in steel increases with rising in temperature.

5.Moisture Movement

Shrinkage occurs in all building materials that are cement/lime based. Heavy aggregate concrete shows less shrinkage than lightweight aggregate concrete.

Materials with pores in the structure in the form of intermolecular space expand on absorbing moisture and shrink on drying. These movements are cyclic in nature and causes by increase or decrease in inter pore pressure with moisture changes.

Remedial Measures:

Shrinkage cracks in masonry minimize by avoiding the use of rich cement mortar in masonry.

Plastering of masonry after proper curing.

6.Structural design and specifications

Cracks in concrete forms due to poor structural design and specifications. At the starting of design first, consider the environmental conditions existing around the building site. It is important to determine the type of foundations, the type of concrete materials use in concrete. And the grade of concrete depending on chemicals present in groundwater and sub­soil. Closely spaced of reinforcement steel bars due to inadequate detailing causes segregation.

precautions while designing

specification for concrete materials and concrete.

Proper quality and thickness of concrete cover around the reinforcement steel.

Reinforcement Cover

proper reinforcement layout and detailing

7.Poor Construction practices

Construction should design and supervise only by civil engineers or persons having proper knowledge and experience in construction practices. People without construction knowledge are engaging nowadays to supervise construction works and to carry out construction works.

Lack of good construction practices due to ignorance, carelessness, greed or negligence.

For a healthy building, it is necessary to ensure good quality materials selection and good construction practices.

Some of the main causes for poor construction practices

  • Using poor quality materials
  • improper selection of materials
  • cheap and nonstandard materials
  • improper concrete mix
  • Inadequate control on various steps of concrete products such as batching, mixing, transporting, placing, finishing and curing
  • Inadequate quality control and supervision causing large voids(honeycomb)
  • Improper construction joints between
  • Addition of excess water in concrete and mortar mixes.
  • Poor quality of plumbing and sanitation materials and practices.

8.improper Maintenance

Buildings should maintain at regular interval of time properly to avoid damages. Attend Leakages as earliest as possible before corrosion of steel inside concrete starts. The external painting of the building helps in protecting the building against moisture and other chemical attacks. Necessary water-proofing and protective coating on reinforcement steel or concrete.

Steel corrosion control methods
civil techniques

Steel corrosion control methods

7 Apr, 2018

Steel Corrosion control methods are essential to prevent damage and the failure of structures. 40% of failure of structures are by corrosion of inner steel. Steel corrosion control methods carry mostly in the structure that locates in coastal areas. And steel structures like tower transmission lines, cell phone towers, etc.

Steel reinforcement corrosion control methods

There are many causes of corrosion. It relates to the quality of concrete and quality of construction. The first step in corrosion of steel is to provide good quality of concrete. The quality of concrete materials, mixing and compaction and workmanship help to control the steel corrosion.

Steel reinforcement corrosion control methods

Quality in construction reduces corrosion. There are various methods, they are

Steel corrosion control methods

  • Cement-Polymer Composite Coated Rebars (CPCC)
  • Fusion Bonded Epoxy Coated Rebars (FBEC)
  • Corrosion Resistant Steel Deformed Rebars (CRSD)

1. CPCC

It set in concrete surrounds by an alkaline medium. A cement base coating is more useful for steel corrosion control. Apply two coats of cement polymer on rebar.

Products in CPCC are:

  • De-rusting Solution
  • Alkaline Powder
  • Phosphating Jelly
  • Inhibitor Solution
  • Sealing Solution

2. FBEC

Steel reinforcement corrosion control methods

It produces from 100% solid finely ground fuse powder particles. At heating, it melts to form an adherent film. There is no primer film provide in FBEC rebars. It makes a medium of weakness in the path of a bond between rebar and concrete.

Epoxy coats the rebar by

  • Melts
  • Flows
  • Gels
  • Cures
  • Cools
  • Stick to coat

Steel corrosion control methods

3. CRSD

Corrosion begins with the formation of an initial layer of rust. On common rust on normal rebars, the CRSD rust is self-renewing. The protective oxide is fine texture, tightly stick and a barrier to moisture, oxygen, carbon dioxide, Sulphur dioxide. And chloride prevents corrosion.

Steel corrosion control methods

Use corrosion resistance bars to prevent corrosion of concrete structures, damage, and failure of structures. This increases the strength and lifespan of structures.

Screed in concrete construction
Concrete repairs

Screed in concrete construction

21 Mar, 2018

Screed in concrete construction

Screed in concrete construction is a process of cutting off the excess wet concrete. And to bring top surface slab to a proper level. And to provide a good smooth floor. A screed is a flat board uses to smoothen the concrete.

Screed in concrete construction

Properties and composition of the screed

A screed is a construction element constructs in a range of thickness. Its purpose is to bring the surface of the flooring to the design height. And to provide a suitable surface for installing the specific flooring.

The screed is a flat board or an aluminum tool. It uses to smoothen the concrete after it places over a surface.

Screed in concrete construction

A screed makes from pre-blended mortar mixes with binders. They set as guides for straight edges. And helps in bringing the surface of floor concrete to the required level.

The screed is hard in nature. This resists the stresses and the distortion causing on the spreading and leveling of the floor topping.

Specifications of an effective screed

  1. Acts as a substrate, important for fixing the specified flooring
  2. It is laying on schedule
  3. shows durability under various service conditions

The service conditions specify it is external or internal for civil, commercial and industrial flooring purpose.

Screed in concrete construction

Composition of Screed

The major components of screed show good performance

  • Admixtures for mixing it with water, liquid and powdered superplasticizers, cement, and aggregates.
  • Special binders to mix with water and aggregates.
  • Mixes of aggregates in a granulometric curve to make the screeds.
  • Special pre-blended mortars to mix with water.

Advantages

  • Improve the quality of concrete
  • Reduce repairs
  • Lower costs
  • Improvement of health and safety
  • Elimination of vibrators
  • Reduce of noise around the site
  • Thinner concrete
  • Good durability and
  • Quality of concrete
  • Ease of placing
  • Reduce equipment and
  • Labors
Roof Repairs
Concrete repairs

Roof Repairs

7 Apr, 2018

Roof Repairs – Repairs of Roof for Damages and Leakages

 

Roof repair

Reasons of Roof Repairing

1. Leakages

The main reason for a leak is joint on the roof. In the sloping roof, the leakages are at the joints and junctions.

The reasons for roof leakages are wear and tear. Along with wear and tear, harsh weather cause leakages. In the flat roof, leakage is by poor workmanship, cold joints in the concrete.

2. Damages

Roofs of Asbestos Sheet and Polycarbonate materials leak if joints get loose by the wind. Connecting screws loosen up making up holes bigger creating leakages.

Damage roof are not take care, water seeps into roofs and accumulates underneath roof seeps into beams, through ceilings, into the home. Damage is by the broke, loose, missing, or water-logged surface.

If water penetrates to roof for a long period of time, a home’s structure gets damage. To avoid unnecessary water damage, the roof to maintain regularly. And the damage must replace quickly.

Deciding on Roof Repair vs. Roof Replacement

The repairing of the roof is a better option. This option is better because of lesser cost application. Sometimes even after repairing, there is a need for replacement of roof which costs more. It is a better option for roof replacement if there is heavy damage. Another consideration to take of is the age of the roof. If it is more than 20 to 25 years old than better to select the option of roof replacement rather than repair.

Methods of Flat Roof Repairs

Residential Flat Roof Repair

1. Rubber Roofing Repair

Roof Repairs

Rubbing roofing includes products like EPDM, modified bitumen and other roofing products available as thin, rubber-like material. For minor leaks and holes, the roofer is typically using a primer and adhesive patch to seal the damaged area.

Alternatively, the roofer may use a specially-designed glue to repair small holes or cracks. Larger repairs often require replacing an entire section of rubber roofing and resealing the seams.

2. Built-up Roofing Repair

Roof Repair

Apply a metal mesh patch along with additional layers of asphalt material to solve most leaks and cracking problems.

Apply a water and UV-resistant coating to protect the roof from future damage.

Flat roof repairs are temporary in nature. It extends the life of the roof for more years. completely replace if the flat roof has started to fail.

3. Tile Roof Repair

To avoid replacing an entire roof, quickly repair tile. As a tile has warped, cracked, fallen, or become chipped, repair it.

The tile falls or becomes warped, repair tiles without replacing the entire roof. Water begins to seep underneath any damage roof tiles and result in replacing the entire roof.

If there are any signs of water damage inside the home, tile roof is beyond repair. Water penetrates to home’s structure, it is too late to simply repair the damaged tiles.

Cost of a Residential Flat Roof Repair

The cost of repairing the roof is affordable and depends upon the extent of damage, location of the project. If compromise with small repair its good way to save money, and not beneficial in a long way. The cost of repairing is more than replacing in the major residential flat.

Precautions

Precautions to roof damage are to clean the roof of loose leaves, tree limb, standing water on a regular basis. And repair leak soon as possible. This avoids further damage to the roof.

Repairing Concrete Column Cracks and Damages
civil techniques

Repairing Concrete Column Cracks and Damages

7 Apr, 2018

Repairing concrete column cracks and damages is essential. The column concrete damages are becoming critical in mass structures like shopping malls, commercial buildings. To carry out the column repair identify the axial dead load, live load, and horizontal load.

Repairing concrete columns are two category

  • Surface or cosmetic  –  covers local deterioration
  • structural repair –   strengthens the affected columns.

Repairing Concrete Methods for cracks and damages

1. Unloading Columns

unloading the column is necessary. Entire cross-section of the repair column is capable of carrying the reintroduce design load. Without unloading, new repair does not carry any load. Drying shrinkage of new material reduces the share of the load.

2. Redistribution of the Load

In corrosion of reinforcement and concrete deterioration, Redistribute a load of column concrete with alternative supports for repair.

 3. Supplemental Reinforcing Steel

 

The supplemental vertical bar to fix outside the original cage with extra ties. Provide adequate cover and Place Apartment’s bars outside the tie bars to increase column dimensions. Use Hairpin ties, of stainless steel laterally to support the supplemental bars. Column ties cannot disturb at the repair of the longitudinal bars as it causes buckling.

4. Concrete Removal

Remove concrete within a column cage and unload the column. If not, the longitudinal bars are buckle and compression failure of column take place.

Repairing Concrete

5. Corroded Reinforcing Steel

It’s not necessary to remove the corrode reinforcing bar with the reduce cross-sectional area if the loss is supplement with additional reinforcing bars. The partially corrode reinforcing bars are thoroughly clean by sandblasting to obtain the bare metal. The bars with excessive corrosion is replacing with fresh reinforcement having full laps on both sides.

6. Corroded Ties

Replace the corrode ties by adding stainless steel hairpin ties that are anchor into the concrete. It is often necessary to deposit extra material around columns to provide an adequate cover over the supplemental ties.

7. Low-strength Concrete

Where the concrete strength is low, resulting in insufficient load-carrying capacity, several alternatives are available:

  • Shore the column and remove and replace the in-place concrete.
  • Shore column and increase the size of the column to reduce bending stresses, and increase confinement on placed weak concrete.
  • Wrap the column with carbon- or glass-reinforced plastic.
  • Install a supplemental column.
Corrosion protection
civil techniques

Corrosion protection

7 Apr, 2018

Corrosion protection of underwater pile is essential in aqua construction. Eliminating this corrosion problem is very hard, the corrosion is control by using corrosion protection methods.

Corrosion Protection Methods for Underwater Piles

Protective Coatings for Underwater Piles

Protective coating for underwater piles is necessary as it causes corrosion of piles. The Corrosion protection of underwater pile methods provides a great solution to corrosion of underwater piles.

The surface of pile comes in contact with water, corrosion in piles forms. To protect the piles from coming in contact with water, the pile is cover with non-porous material which is anti-corrosive. There is some non-corrosive chemical materials use in corrosion of underwater piles. Several chemical coating uses for corrosion protection.

The different types of coatings employes for underwater piles are mention below:

  • High build Epoxy coatings
  • Zinc Rich epoxy primer
  • FRP composites
  • Inorganic zinc silicate primers

1. High Build Epoxy Coatings

Corrosion protection

These epoxy coatings are abrasion and chemical resistant. These epoxy coatings provide a high level of service and more tolerant ambient weather conditions. And most effective in maintaining the damage area and breakdown of a coating system.

2. Zinc Rich Epoxy Primers

Zinc Rich epoxy primer is a mixture of  Inorganic Zinc Silicates Primer and High Build Epoxy Coating. It provides a high level of service and more tolerant ambient weather conditions. And most effective in maintaining the damage area and breakdown of a coating system.

3. Application of FRP Composites for Corrosion Protection of Underwater Piles

Corrosion protection

FRP a mix of wet concrete is economic to repair on substructure parts. Repair of this parts requires the enlargement to accommodate new ties. Completely corroded part of the elements should remove by using FRP.

spreading of corrosion to other piles are protect by FRP. The aesthetics of FRP repair is one of its unheralded benefits.

4. Inorganic Zinc Silicates Primers

Corrosion protection

The structure below the splash zone always immerse in water are commonly not coat with cathodic protective layers. There are numerous types of anti-corrosive pigment primers in which inorganic zinc silicate is the best. It arrests rust creep or undercutting of the coating surrounding.

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