Carbon fiber reinforced polymer(CFRP) are a cost-effective system for strengthening concrete slabs and decks, or correcting design and construction errors that result in excessive deflection and sagging of slabs.

Carbon fiber reinforced polymer(CFRP) advanatges for strengthening slabs:

• Increased the modulus of rupture in the positive and negative bending moment area of the slat

• Increase the rigidity of the board and reduce the use load of deflection

• Reduce crack width and improve durability

• Covering a small part of the floor surface with CFRP may be sufficient to reinforce the entire floor

• The use of carbon fiber reinforced plastic will not reduce the air clearance (for example, in the parking lot)

• Compared with traditional reinforcement methods (such as injecting epoxy resin into the cracks), CFRP has a lower cost.

Project for slab strengthening with CFRP

A high-rise residential building has 2 floors underground and 18 floors above ground. The upper part adopts cast-in-place shear wall structure. Each floor of the upper structure has 3 large-span floor slabs of 5.3 mx8.0 m, a total of 54 blocks, with a floor height of 5.4 m. Infill walls are built on the floor to divide the space. During the infill wall masonry process, it was found that the bottom of the large-span floor slab and the surrounding slab surface of the shear wall produced a large number of cracks, the maximum deflection reached 52mm. The original design of the floor slab concrete strength grade is C30, the slab thickness is 130mm, and the protective layer thickness is 15 mm.

Reinforcement scheme design

Since the main structure of the residential building has been completed and is undergoing renovation, the construction period is relatively tight, so it is impossible to remove all 54 large slabs and re-pouring. Moreover, the construction unit cannot change the net height of the original structure when it is required to reinforce it, so the method of adding secondary beams to reduce the span of the floor cannot be used for reinforcement.

After comprehensively considering the above-mentioned limitations, the large-span floor slab is reinforced with the following methods. First remove the wall of the large-span floor slab. The cracks of the concrete floor slab are sealed by chemical grouting, the concrete laminate is poured after the reinforcement is planted on the slab surface, and unidirectional carbon fiber cloth is pasted on the bottom of the slab for reinforcement. However, due to the pouring of the laminated layer, the deflection of the floor slab will further increase after the load is applied later, which may cause the deflection of the floor slab to exceed the allowable deflection, which cannot meet the requirements, and the deflection of some floor slabs before reinforcement does not meet the requirements. Therefore, it is necessary to carry out the jacking treatment for the floor slab with the current deflection greater than f before the reinforcement treatment.

Structural strengthening materials

200g unidirectional carbon fiber fabric

carbon fiber adhesive

crack injection

Reinforcement effect

The reinforcement treatment of the large-span floor slab has a shared construction period of 35 days and 880 labors. After the reinforcement treatment was completed, the construction unit randomly inspected 2 reinforced floor slabs, carried out on-site pile loading tests and observed their deflection and cracks. The deflection observation results were all less than 2mm, and no cracks were found. So far, the carbon fiber reinforced floor slab has been in normal use for more than one year, and the deflection and cracks are observed to be no abnormalities, which proves that the reinforcement measures are reliable.