ASSESSMENT OF CONCRETEBEAMS WITH

HONEYCOMBED ZONE(S)By: T.P.Bharath

Guide: Mr. M.U. Kiran

Introduction• Reinforced and pre-stressed concrete are widely used for the

construction of infrastructures, such as power plants, bridges, etc.•Most of the time, quality of the concrete mix is guaranteed,

but due to the congestion of reinforcement and the quality control exercised during placing and vibrating, honeycombs and voids are likely to be present in the hardened concrete.•Non Destructive Testing & Evaluation (NDT&E) in

reinforced concrete (RC) structures plays a very important role which includes identification of defects such as honeycombs, voids, cracks, etc., and, thickness measurement, location of reinforcements, ducts, etc.,

Assessment Using Non Destructive Testing

Using Ground Penetrating Radar (GPR)

•Ground penetrating radar (GPR) is a non-destructive testing methodology that employs the transmission and reception of radio waves to detect inhomogeneities in many different media.• The application of ground penetrating radar (GPR) for the

investigation of concrete structures is well known and has been in widespread use for a number of years.• Current applications for structural engineers most commonly

include locating spacing and depth of reinforcing steel, post tensioning cables or anchors, measuring rebar cover, mapping voids, and clearing areas prior to cutting, coring and trenching.

Basic Components of a GPR

(A)(A)

(B)(B)

(C)(C)

(A) Monitor: XV monitor with a transreflective screen

(B) Antenna: 500 MHz antenna

(C) Control Unit: 32 bit processor controls transmitter

Receiver timing, stores raw radar data.

Typical Radargram obtained from GPR of a Reinforced Concrete Beam.

• Roberts, R., et. al. (2010) found out that GPR, when appropriate equipment, data collection, and data processing techniques are employed, is very useful for detecting and characterizing surface voids.

• It was also found that buried voids can be detected after as little as 3 days of curing, depending on the concrete.

• The detectability of the buried voids increases as the concrete cures.

• ZHOU, X et. al. (2012) found out that In contrast, the GPR technology achieves a better performance in detecting voids within plastic ducts of post-tensioned concrete structures.

• Ékes, C. (2007) concludes that due to the key advantages, including safety, the ability to scan large areas quickly and cost-effectively together with only one sided access, real time results, and digital data storage, GPR technology is expected to play an ever increasing role in structural evaluations and infrastructure monitoring, with new technical developments pushing the capabilities of the technology even further.

Assessment by Experimental Work

• Omar, W. (1998) carried out Experimental investigations on the effect of a honeycombed zone(s) on shear behavior and shear capacity of a concrete beam.

• Honeycombed zone(s) was deliberately introduced at a number of locations within the high shear region of a beam.

• In this study, the effects on the shear capacity of a concrete beam are investigated when a honeycombed zone is present in the high shear region.

• Tests were carried out on rectangular beams with a honeycombed zone introduced at various locations within the high shear region of the beam.

• The honeycombed zone was square with the size of about a third of the effective depth of the beam.

• Two strengths of normal concrete were investigated, with average strengths of about 50 N/mm2 and 35 N/mm2 .

• The average strengths of the honeycombed concrete were about 23 N/mm2 and 12 N/mm2.

• The study found that, in a beam with a honeycombed zone, a diagonal crack could form early and the shear capacity of a beam could be reduced. The severity of these effects varies with the location of the honeycombed zone.

References

• Ékes, C. (2007). GPR: A NEW TOOL FOR STRUCTURAL HEALTH MONITORING OF INFRASTRUCTURE. Terraprobe Geoscience Corp., Kanada.

• Omar, W. (1998). The shear assessment of concrete beams with a honeycombed zone present in the high shear region (Doctoral dissertation, University of Birmingham).

• Roberts, R., Corcoran, K., Arvanitis, M., & Schutz, A. (2010). Insulated concrete form void detection using ground penetrating radar. In Structural faults and repair conference. Edinburgh, Scotland, UK.

• ZHOU, X., WANG, Z., & ZHANG, D. (2012) DETECTING VOIDS IN GROUTED TENDON DUCTS OF POST-TENSIONED CONCRETE STRUCTURES USING THREE DIFFERENT METHODS. (Last accessed from Google on 13th Nov 2014)

Thank You..