Ramendra Bahadur Sinha, Managing Director, Agrani Milestone, explains the remedial measures and challenges faced during slab strengthening of a deflected slab at IIT.

NBCC India Limited undertook the strengthening of a deflected slab at a G+2 storey IIT building for which it employed the services of Agrani Milestone. The building was examined and strengthened using carbon fiber laminates and the cracks were filled with cementitious/epoxy grouts. The load test was done by another IIT on the completed project, and it was found to be satisfactory.

Ramendra Bahadur Sinha, Managing Director

Remedial measures
The construction of the building started in 2016 and was completed up to the second floor slab (i.e. the first floor roof slab) in 2018. Thereafter, cracks were observed in the 1st floor slab (i.e. ground floor roof slab), due to which the construction of the building was put on hold in 2018.

For the ground floor roof slabs of the educational building (LTC-2) of the project (IIT campus), strengthening was done using the FRP system as per the design recommendations of IIT and NBCC, considering some structural and non-structural cracks due to unknown reasons.

Carbon fiber laminates, an excellent material for reinforcing civil engineering and construction works and for designing innovative architectural projects, was suggested to be used. The laminates are extremely strong, and are developed by woven layers of carbon fibers, bonded together by hardened plastic like epoxy resins. High stiffness, high tensile strength, low weight, high chemical resistance, high temperature tolerance, and low thermal expansion make the carbon fiber laminates the right material for durable, strengthening works.

To validate whether after strengthening, the performance of the slab is satisfactory or not, a physical load test was conducted. It checked the performance as per the requirements of IS 456:2000 by examining the deflections at loads up to 1.25 times the design-imposed loads as per IS 875.

Observations
The test comprises of initial loads, reloads, and unloads. The load stage was applied on to the structure and gradually increased up to the maximum required bearing pressure. As per IS 456:2000 RA 2021, after every set of loading, a minimum break of 15 minutes was given for noting the deflection and dial gauge readings.

Ramendra Bahadur Sinha, Managing Director

The slab was subsequently incrementally loaded, corresponding at 25%, 50%, 75% and 100% of the 29.87 ton, i.e. the design imposed load as per IS: 456:2000 RA2021. After 24 hours, the slab was unloaded by 25%, 50%, 75% and 100%.

After 24 hours of removal of the load, recovery of the slab was measured. After and during the load test, the slab was thoroughly checked for cracks. After applying of 100 percent load, the slab was again checked and no crack was found.

Ramendra Bahadur Sinha, Managing Director

Project challenges
The project site was located in a remote area, so Agrani Milestone had to transport the labour and equipment. Sand was to be lifted to the terrace level, which was done skillfully by the workers. Material was procured from FOSROC for the project. Overall, the laminates work was completed in 10 days, excluding the time taken for procurement and load test process.

Such specialised construction is a highly technical job which can be executed only by experts in agencies that have relevant and substantial experience in the field. The project was executed skilfully through organised and pre-planned processes by Agrani Milestone, which has been doing a lot of work (especially with construction chemicals) in top residential, industrial, and infrastructure development segments.
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