Technical Guide
Repairs To Structures
Repairs to reinforced concrete structural members like columns, beams and slabs is becoming increasingly necessary, on account of the corrosion of reinforcement steel. Corrosion leads to several other distressing aspects like cracking, spalling, delamination etc. Repairs to these damages calls for special techniques and materials. Proper identification of the extent of repair is the first step. Removal of damaged plaster, concrete or mortar follows. At same time it is also essential to support or prop various elements, so that during repairs there is no possibility of unforeseen yielding of any structural elements.
REPAIR TYPES
(a) Minors
Minor repairs can generally be looked upon as those that do not require attending to the structural skeleton. Such repairs as water proofing, replastering, filling up non-structural cracks can be minor jobs.
(b) Major
Major repairs would need to tackle with the structural skeleton - at least attend to some of its members. This calls for an evaluation of the likely extent of repairs and strengthening measures required. A proper plan of the execution of the job, the choice of materials and method need to be decided.
The following sections explain typical repair items like:
1. Cleaning & surface preparation
2. Preparation of repair materials
3. Use of Bonding coat
4. Execution of repairs
5. Curing
6. Guidance or Supporting Systems.
7. Safety precaution
Preparation of Repair Material
The range of chemicals available for repairs are many. Some are to be used as they are, or "off-the-pack" whereas others require to be "prepared". The preparation would generally involve addition of water or cement or both sand is another material often added.
The prepared materials could be broadly classified as mortars, grout or slurries
POLYMER CEMENT BONDING COAT (PCBC)
To prepare a polymer based bonding coat, take 1 part cement and 1 part Polymer based chemicals (by weight) and mix thoroughly. Use a mechanical mixer preferably. The materials thus mixed, form a thick slurry, of a consistency easily applicable by brush. The slurry thus prepared is ready for use as a bonding material.
The surface on which the bonding coat is to be applied, has to be cleaned with a water jet approximately 24 hours prior to application. This will help in making the substrata, slightly moist.
After application of the slurry on the requisite surface, place the next screed or mortar etc. that is to come over it. ("wet on wet" application)
Note:
The slurry is prepared using Polymer based chemicals only as the mixing liquid. ( Do not add any water).
The cement to be used should be fresh and OPC only.
POLYMER MODIFIED CEMENT MORTAR (PMCM)
To prepare a composite mortar of Polymer and cement base, use 1 kg Polymer based chemicals, 5 kg (fresh) Cement, 15 Kg Quartz sand (graded). This is same as using 1 bag of cement (of 50 Kgs), 10 Kg Polymer based chemicals and 150 Kgs of graded sand.
First dry mix the cement and sand in a mixer. Separately mix Polymer based chemicals with the requisite quantity of water. Then add this water-polymer mix to the cement-sand in the mixer and mix for 3 minutes at least use a mechanical mixer. (see item 3 of note below). The mortar is now ready for use.
POLYMER CEMENT GROUT (PCG)
To prepare a polymer based cement grout, use 1 kg Polymer based chemicals, 3 kg Cement (fresh) and 2 kg water. Mix Polymer based chemicals and water first and add this to the cement using a mechanical mixer till slurry of uniform consistency is formed. This is now ready for use.
(Important: see item 2 of 'Note' below)
POLYMER RICH CEMENT MORTAR (PRCM)
To prepare this mortar, use 2 kg Polymer based chemicals, 5 kg cement (fresh) and 15 kg quartz sand (graded). Mix the three ingredients (without addition of any water) preferably in a mechanical mixer, till a soft mix of uniform consistency is formed. This is now ready for use.
General Precautions
Prepare only as much quantity of material as can be used in 30 minutes.
Use fresh Cement only.
CURING:
Curing is best achieved by a fine spray of water. Curing should begin after 24 hours of application & continue for 3 days.
NOTE:
1. Clean all tools with water immediately after use.
2. The mixes given above are by way of general recommendations. For special mix designs using Polymer based chemicals you may please get in touch with Edifice Erection's Engineer .
3. The mixer consists of a shaft with spiral blades, filled in place of the drill-bit of the hand held electric drill,