The Success of repair and rehabilitation of Structures depends on the specific plans designed for it. Concrete Structures: Protection, Repair and Rehabilitation procedures depend on evaluating the condition of concrete in the structure, relating the condition of the concrete to the underlying causes of distresses and selecting appropriate repair material and method for any deficiency found and using the selected materials and methods to repair or rehabilitate the structure.
STP Ltd has been associated with Repair & Rehabilitation of numerous structures. One such structure was a Chemical plant in India. During an evaluation by STP Ltd Engineers, it was found that the Structure has several distresses.
Reasons for Distress & Causal Mechanisms :
The basic distresses, which are visible, are a) Cracks and b) Spallings. The reasons for these distresses are due to aggressive chemicals ingress inside the concrete structure.
The Chemicals penetration helps corrosion of the steel reinforcement. As the rust has more volume than the original steel bar, the rust causes tension in the surrounding concrete. As the cover of concrete is limited on the outer side, the resultant tensile force causes cracks formation and the crack permit easier entry of water and oxygen to form more rusting. Resulting in more increase in volume and the cracks in concrete get wider and wider. The surrounding concrete becomes partly disintegrated which finally causes spalling.
The porosity of the surrounding concrete plays an important part as concrete having more porosity which may be due to inadequate compaction allowing easier passage of water and oxygen. This perhaps explains the different degree of distress of similar members.
Conveyer Belt Area shows severe spalling due to effect of chemicals
Concrete Surface Preparation: Remove the damaged / loose concrete from the soffit of the conveyor belt structure. Wash the concrete surface thoroughly with water jet then spray on the prepared concrete surface 20% Oxalic Acid, let it dry then followed by washing with water jet the next day. Rust to be removed with wire brush / ShaliRustOff, then apply Zinc Rich Primer on the reinforcement ( Note: where Reinforcement has gone/corroded beyond 10%, similar dia , extra reinforcement needs to be added/welded with suitable overlaps (min 16 times the Dia of the bar) apply Primer coat of ShaliCrete, on the wet slurry coat surface apply single component ShaliFix MC (Micro Concrete ) which will give the compressive strength of 50 Mpa maximum, average thickness of 25mm including repairing of the surface with STP ShaliFix MC & leave the surface for 12 hours to become dry. After 12 hours wet curing with water for 3 days of ShaliFix MC. On the dried surface of ShaliFix MC (Micro Concrete) applying primer ShaliPrime penetration after checking the moisture content on the surface which should be below 5%, applying STP ShaliKote NES two component Chemical resistant Phenol Novolac Based Epoxy Coating.
DM Water Drainage Treatment
Removing all the damaged/cracked/ spalled concrete from RCC Structural members by tapping with light hammer/chip-ping withchisel/High-pressure water jet etc. Cleaning and removing all loose and defective concrete/materials using appropriate tools and equipment along with cleaning of reinforced steel. Repair of cracks & Crevices with STP ShaliScreed ARM (Two-component Acid resistant mortar). Application of primer ShaliPrime Penetration on the bone-dry surface (moisture <5%) Application of first coat of STP ShaliKote NES Micacious (Severe Chemical resistance epoxy), after 16 to 20 hrs apply the second coat of STP ShaliKote NES Micacious. Total thickness will be 300 microns.
Neutralization & Acid Pit Treatment
Repair of cracks & Crevices with Shali Screed ARM (Two- component Acid resistant mortar). Application of primer ShaliPrime Penetration on bone-dry surface (moisture <5%) Application of first coat of STP ShaliKote NES Micacious ( Severe Chemical resistance epoxy), after 16 to 20 hours apply second coat of STP ShaliKote NES Micacious
Filling of cracks ShaliCrete Modified Mortar (PMC) in the ratio ShaliCrete: Cement: Sand (1:2:5), including treating the pipe penetrations. Saturating with water and applying ShaliCem EWP in two coats at 2.5 kg per Sq.m for 1.5 mm thickness with fibre glass cloth sandwiched between two layers and curing the same. (positive side application) providing 25mm protective plaster admixed with ShaliPlast LW+ @ 200ml per bag of cement
The most important after detailed investigations are correct diagnosis. STP Ltd Engineers found the causes of distress and adopted the correct repair strategy. Therefore, analysis of the inspection and detailed investigations are the most important component of Repair & Rehabilitation of structures.
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