165 / 2022-04-30 10:47:37

INFLUENCE OF SILICA FUME WITH PCM AS A REPAIR MATERIAL ON THE PCM-CONCRETE INTERFACIAL BOND

Polymer cement mortar, overlay method, premature debonding, interfacial strength, silica fume

Performance degradation of existing concrete infrastructures due to adverse environmental or mechanical conditions made strengthening a global issue. The polymer cement mortar (PCM) overlay method is a promising solution for strengthening the deteriorated concrete structures. In this method, the substrate concrete-PCM bond is considered a threshold and the occurrence of premature debonding at the concrete-PCM interface prevents the strengthened structures from achieving full serviceability and designed load-carrying capacity. This study investigated the effectiveness of adding 5% silica fume in forming chemical connection at the substrate concrete-PCM interface, subsequently on improving the concrete-PCM interfacial bonding strength to prevent premature debonding.



The splitting tensile and direct single-surface shear tests were selected as test methods along with microstructure analysis using X-ray diffraction (XRD) and thermogravimeter-differential thermal analysis (TG-DTA). Concrete substrate with a rough and smooth surface were used to understand more precisely the chemical bonding at the interface concerning mechanical bonding had less influence at smooth surface. Primers were also utilized to understand the effectiveness of modified 5% silica PCM because the use of primer can act as a protective layer of the substrate concrete to resists silica fume to perform its function in expected way to improve interfacial bond.



The silica fume inclusion greatly increased the splitting tensile strength by 16.3% and 22.3% [Fig.1(a)] compared to the normal PCM for smooth and rough surfaces, respectively (without primer cases). The interfacial shear strength increases even higher, approximately 113.7% and 29.4% relative to the normal PCM on the smooth and rough concrete surfaces, respectively [Fig.1(c)]. While using primer at the interface, only a slight variation in the interfacial strength for the normal and modified cases was observed in tension [Fig.1(b)] and in shear [Fig.1(d)], which can be considered as experimental scatter. The use of primer results in a protective layer that prevents the small silica fume particles from filling the gaps among the cement particles of the substrate and hinders the flow of the water required for hydration to the cured concrete, thus, silica fume cannot perform in the expected way to strengthen the interface (micro-filling effect or chemical connection). An increase of interfacial strength with silica fume inclusion (no primer cases) with the smooth surface where mechanical bonding had less influence indicates a higher possibility of chemical connection at the concrete-PCM interface by transformation of harmful Ca(OH)₂ into more C-S-H. The XRD results of normal and modified specimen presented in Fig.1(e) indicates some qualitative differences in the hydration rate (the peak intensity in the region of 2θ = 18° that considered as a measurement of Ca(OH)₂ intensity) due to the incorporation of silica fume in PCM. From TG-DT analysis [Fig.1(f)], the amount of both free Ca(OH)₂ and CaCO₃ was found higher in the normal PCM cases compared to modified 5% silica PCM cases. This finding indicates an increase in the extend of bond formation between silica compound and free Ca(OH)₂ (modified 5% silica PCM cases) compared to the bond formation in without silica fume (normal PCM) cases. In conclusion, the addition of silica fume to the PCM improves the interfacial performance.