Concrete repairs

civil techniques

Screed in concrete construction

abbu riyaz 30 Apr, 2023

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.

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.

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

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

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

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

civil techniques

Reinforcement Cover

abbu riyaz 30 Apr, 2023

Reinforcement Cover

Reinforcement Cover is essential to the steel reinforcement bars. Bars are surrounding sufficient impermeable concrete to protect from corrosion. And to allow the combined strength of the reinforcement and concrete to be effective.

Place the steel bars into position after Binding. keep the bars at a correct distance from the surface with spacers. Pour concrete and erect formwork. Steel place close to the surface become exposed to moisture and forms corrosion.

Spacers

Spacers are of plastic, mortar, and steel. Plastic spacers make to fit particular bar size and give specified depths of cover. Small mortar blocks use to tie the reinforcement bars using soft iron binding wire. If ends of ties bent away from the surface of concrete, wire cause corrosion of reinforcement. The structure is not in a corrosive atmosphere and exposes to water, use steel spacers. The required amount of cover is to specify.

Pre-Concrete Checks for Reinforcement

The pre-concrete check for reinforcement is essential.

It is in two parts.

The first part is a visual inspection.
The second part by a surveyor.

Visual Inspection

Visual inspection is simply seeing materials as it is in the correct form. And the materials are free from damages. Some f them are as follows.

Check cover thickness Using a steel tape and spacers which falls or brakes and replace it.

Check the reinforcement bars are free of excessive rust and not cover in mud from foot traffic.

The bottom of the concrete pour is free of debris including the cutoffs from the steel tying bars.

check for under-bent bars and allow the correct cover and correct spacing.

Image show reinforcement has not place correctly in the concrete formwork.

Images show correct way of placing of reinforcement in the concrete form works.

Surveyor

The second part carries out by a surveyor. Surveyor checks the steel levels against required levels. make to pour if levels are satisfactory.

civil techniques

RCC Columns Pedestals and Footings

abbu riyaz 30 Apr, 2023

RCC Columns Pedestals and Footings is to give good strength and durability to structural members. Improper concrete leads to corrosion of steel by pores, cracks in concrete. This cause concrete not to achieve its strength in the setting. This leads failure of columns, pedestals, footings during occupancy of the structure.

RCC Columns Pedestals and Footings work inspection

Inspection for strength, leakage, and finish.
Reinforcement inspection, lap length, correct lapping.
Inspection of concrete cover.
Alignment of the structural member.
Availability of sufficient construction material at the site.
Availability of vibrators.
Proper safety PPEs and safety measures.
A Proper ratio of mix
Availability of slump testing equipment.
Availability of cube casting equipment.

After the inspection concreting work starts.

1. Concrete cover

Concreting of RCC columns, pedestals and footings starts from the center of vertical bars and go towards the ends.

2. Vibration

Vibrate concrete at regular intervals to spread evenly on all sides. Avoid Over vibration of concrete. Over vibration of concrete leads to segregation of coarse aggregates which settles at the bottom making the mix weak.

3. key

Provide proper keys in the center of column reinforcement and walls. This is to provide a proper grip between concrete of stem part with footing, walls, foundations. Apply 1:1 ratio of cement and sand slurry. This avoids separation of stem/ wall where a cold joint forms.

4. Starters

After concreting of the footing in a day or two starters for column and wall to cast with proper alignment. And again the upper surface of starter is making rough. In green concrete, place coarse aggregate outside and part goes inside by the spread and light press. This measure provides a proper grip on the surfaces.

5. Dowel

Dowel to Insert between the outer main bar of wall and column. It provides grip between old and new concrete surfaces. This dowel is 600 to 800 mm cut pieces of bars. Inserts in green/wet concrete such a way that half-length is projecting and half-length is inside concrete.

civil techniques

Roof Repairs

abbu riyaz 30 Apr, 2023

The Roof repairs and repairing methods explains in these post. There are various methods follows for rectification of old roof cracks, damages etc,. Instead of demolition of old damages roofs, several alternations carries to extend the life of structure.

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

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

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.

civil techniques

Repairing Concrete Column Cracks and Damages

abbu riyaz 30 Apr, 2023

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.

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.

civil techniques

Corrosion protection

abbu riyaz 30 Apr, 2023

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

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

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

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.