Abstract
The polymer cement mortar (PCM) overlay method is a promising solution for strengthening deteriorated concrete structures in which the occurrence of premature debonding at the interfaces prevents the strengthened structures from achieving full serviceability. The purpose of this study is to improve the concrete–PCM interfacial bond to prevent premature debonding. There are two main focuses of this study: (i) investigation of the effectiveness of adding 5% silica fume to PCM in forming a chemical connection between concrete and PCM, based on a direct single-surface shear test using two roughness levels of concrete (smooth and rough) and microstructure analysis and (ii) performance evaluation of the bond between substrate concrete and a PCM overlay with/without silica fume at early ages and with different moisture conditions at the interface, based on a bi-surface shear test using rough substrate concrete surface. The inclusion of 5% silica fume with PCM caused an improvement in the interfacial strength (approximately 113% relative to the normal PCM in cases of without primer), with a smooth concrete substrate surface where mechanical bonding had less influence. In addition, lower Ca/Si values in the interface of modified 5% silica PCM specimens compared to the normal PCM specimens quantified by energy-dispersive X-ray spectroscopy (EDS) indicate the formation of a chemical connection at the concrete–PCM interface by transforming harmful Ca(OH)2 into more C-S-H which strongly improves the bonding strength. As a repair layer mortar, the positive influence of silica fume in modified 5% silica PCM specimens was also found at early ages and with different moisture conditions at the interface compared to the normal PCM. In conclusion, the addition of silica fume to the PCM caused chemical connection at the concrete–PCM interface and improved the interfacial performance.
Highlights
Existing reinforced concrete (RC) structures are at risk of deterioration due to exposure to severe environmental conditions, unseen mechanical loadings, natural disasters, etc
Several strengthening techniques based on practical experience and scientific research have been proposed over recent decades, such as continuous fibre sheet bonding, steel plate bonding, and fibre-reinforced polymer jacketing [1,2,3]
To overcome some of these obstacles, innovative strengthening systems based on the cement matrix, such as textile-reinforced concrete [4], textile reinforced mortar [5], fibre reinforced concrete [6], mineral-based composites [7], fibre reinforced cementitious mortar [8,9], and polymer cement mortar (PCM) [10,11,12] can be found in the technical literature
Summary
Existing reinforced concrete (RC) structures are at risk of deterioration due to exposure to severe environmental conditions, unseen mechanical loadings, natural disasters, etc. Several strengthening techniques based on practical experience and scientific research have been proposed over recent decades, such as continuous fibre sheet bonding, steel plate bonding, and fibre-reinforced polymer jacketing [1,2,3] These techniques have some unavoidable drawbacks due to the use of epoxy resin, such as low permeability, poor fire resistance, difficulty to apply to humid surfaces, and susceptibility to UV radiation. The coalescence of polymer particles in PCM reduces the porosity by filling all the pores and providing better adhesion with concrete than ordinary mortar [20,21] This strengthening method is advantageous, as overlaying to the slab bottom surface enables the construction without any interruption in traffic and in any weather conditions
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