Steel

civil techniques

Steel corrosion control methods

abbu riyaz 30 Apr, 2023

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.

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.

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

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

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.

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

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

Methods of Ground Water Control in Excavations

abbu riyaz 30 Apr, 2023

The Methods of Ground Water Control in Excavations explains in this post. These techniques use to prevent groundwater entering into construction like, piling for bridges, tunneling, marine structures, underground structures. The groundwater causes extreme geotechnical problems in excavations like sand running for most of the construction projects. These issues caused by groundwater increase construction budget and extend construction time.

Methods of Ground Water Control in Excavations

There are two major Methods of Ground Water Control in Excavation explains as follows,

Pumping technique
exclusion technique

1. Pumping technique

It is highly expensive by Utilization of large capacity pumps which are not economical to consider in the critical situations.

2. Exclusion Methods to Control Ground Water in Excavations

There is a number of techniques by which groundwater exclusion are obtaining:

Forming impervious barriers

Chemical consolidation for controlling groundwater in excavation

Groundwater control by compressed air

Freezing groundwater control.

In these, we provide methods to prevent groundwater entering in construction by using Forming impervious barriers.

3. Forming impervious barriers

In this technique, permeability reduces by creating an impervious barrier.

An impervious barrier with lower end close by expandable plug & upper end seals on the surface drives into the soil. And grout is force into the pipe and drive out the plug and wide fissures with grout.

Application

Drill a hole in advance, insert a lance for grouting to carry out by a bottom-up method or top-down method.
Gout upper part by a lance inserted into the hole. After its setting time grout lower part of the pipe.
After grouting, preventing groundwater from entering into the excavation of piling, the normal procedure implies out for constructions.

Chemical consolidation for controlling groundwater in excavation

Chemical consolidation method is suitable for sandy gravels and fine grading sands. The most usual chemical material used for chemical consolidation is the sodium silicate.

Control Ground Water in Excavation by Compressed Air Method

There are several factors that motivate the application of compressed air to control groundwater in excavations. Compress air techniques are for controlling groundwater in excavations of tunnels and shafts.