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Title: Non-destructive approach for sprayed concrete lining strength monitoring
Author: Ahuja, Vishwajeet
ISNI:       0000 0004 7425 5508
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2017
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Sprayed concrete lining (SCL) is an important part of soft ground tunnelling. It provides immediate ground support and maintains tunnel stability. A quick set and rapid strength development of freshly sprayed concrete are crucial for maintaining SCL integrity. An inadequate strength development leads to the SCL failure and tunnel instability. This poses serious health and safety risks to construction workers and nearby structures. Therefore, early age strength development monitoring forms a crucial aspect of SCL construction. Currently used testing methods, namely needle penetrometer, stud-driving and uniaxial compressive testing of cored samples, are of destructive nature. To avoid damage to the freshly sprayed lining and to mitigate safety hazards to testing operatives, testing is performed on test panels. Current test methods, however, test a very small part of the sprayed concrete. Since the temperature histories of the lining section are different from the test panels, the outcomes are local in nature and provide an incomplete picture of the SCL strength gain. Thus, there remains a need for a test method with a capability of testing large volumes of the sprayed concrete works remotely, holistically and non- destructively. The maturity method is well established for normal concretes and allows maturity and hence strength to be calculated from a temperature history. A new method called Strength Monitoring Using Thermal Imaging seeks to apply this principle to accelerated sprayed concrete using an Arrhenius equation based maturity function, but there are significant challenges to overcome to obtain the input parameters. This research establishes a thermo-chemo-mechanical evaluation methodology for obtaining the input parameters and verifies its reliability through two detailed case studies on live tunnelling projects. The two-staged methodology involved thermo-chemical evaluation of a total of twelve cement pastes, through isothermal calorimetry and thermogravimetry, and thermo-mechanical evaluation of two sprayed concrete mixes, through strength testing and thermal imaging of more than fifty test panels. The thermo-chemical evaluation revealed that the sprayed concrete has very different hydration kinetics at different temperatures and the reference temperature approach is not valid for the maturity assessments. The maturity modelling procedure was modified to account for kinetics variability. The thermo-mechanical evaluation revealed that sprayed concrete holds a multilinear strength – maturity relationship as against a single linear relationship for plain concrete.
Supervisor: Not available Sponsor: University of Warwick
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TA Engineering (General). Civil engineering (General)