Retrofitting of Existing Infrastructure Structures with Advanced Cementitious Materials (ACM's)

Retrofitting of Existing Infrastructure Structures with Advanced Cementitious Materials (ACM's)

Wink, H.P.

Hordijk, D.A. (mentor)
Reitsema, A.D. (mentor)
Savija, B. (mentor)
Grünewald, S. (mentor)
Houben, L. (mentor)

Civil Engineering and Geosciences

Structural Engineering

Concrete Structures/Structural and Building Engineering

2015-09-24

Existing structures are built according to the valid codes at that time and reaching their design life time. The traffic loads and traffic intensity has also increased. In addition, the existing reinforced concrete structures are exposed to degradation mechanisms, like chlorides and carbonation during their lifetime. Existing concrete road infrastructure can have the need to restore the structural performance or the durability. Advanced Ce-mentitious Materials (ACM’s) has the potential for retrofitting due to the increased strength properties and durability. High Performance Concrete (HPC) and especially Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) have increased strength properties and a dense matrix, which prevents the ingress of detrimental substances. Strain Hardening Cementitious Composites (SHCC) has a high tensile strain capacity, whereby the crack widths are limited. The strengthening effect of SHCC retrofitting is negligible. The biggest potential for retrofitting of existing infrastructure with ACM’s is in retrofitting of durability problems. The structural shear strength problems are less severe than originally thought and traditional structural retrofit solutions like FRP lamellas and external prestressing seems to be more feasible and more economic solutions compared to an ACM layer retrofit system. On the other hand, the reinforcement corrosion of concrete structures is expected to increase. Moreover, HPC and UHPFRC both have a dense matrix to prevent the ingress of detrimental substances. SHCC exhibits a large tensile strain capacity and limited crack widths. A specific durability ACM retrofit solution is used in a numerical model (see Figure 1). The durability retrofitting is based on a cast in situ ACM layer on a vertical existing surface, where the time-dependent development of the ACM properties and the interface between the ACM layer and old concrete determine the structural behav-iour. The mechanical properties develop due to the on-going hydration. Shrinkage is the cause of the main stresses in the model and the stresses are partly relaxed by the tensile creep behaviour of the ACM layer. The basic failure modes are debonding of the ACM layer at the free ends and transverse cracking in the ACM layer. A vertical existing surface is used, because vertical surfaces of road infrastructure structures can exhibit dura-bility problems due to de-icing salts in splash water and also tidal zones of marine structures. A parameter study is performed to enhance the understanding of the structural behaviour due to the time-dependent behaviour of the new ACM layer. A thicker ACM layer causes more debonding and transverse crack-ing behaviour, because the total shrinkage displacement is higher which causes higher stresses. A larger shrink-age strain causes higher stresses and more cracking. The creep in the ACM layer causes a stress relaxation. Increased creep compliance results in less severe cracking. The influence of the thickness of the old concrete structure and the length of the ACM retrofitting is limited. A decreased tensile strength and fracture energy of the debonding interface causes a more severe debonding of the ACM layer, because the interface is made weaker. A new ACM layer thickness of 50 mm can be applied without excessive debonding and transverse cracks based on the parameter study of the numerical model. UHPFRC is advised to use for durability retrofitting. It has limited cracking behaviour and a layer of 10 mm is sufficient to prevent the ingress of detrimental substances. The numerical model exhibits in general the expected behaviour. The model has to be improved for a detailed analysis of an ACM retrofit solution. Further research is necessary to the debonding behaviour in the debonding interface. In addition, an experimental program would be necessary to investigate the development of the time-dependent properties of a specific ACM.

retrofitting
existing structures
Advanced Cementitious Materials

http://resolver.tudelft.nl/uuid:b9218b73-ccd5-4cbc-b9d7-326440817b3b

Student theses

master thesis

(c) 2015 Wink, H.P.