PSI - Issue 64

Eric Williams et al. / Procedia Structural Integrity 64 (2024) 1573–1580 Williams, Annooz, and Myers / Structural Integrity Procedia 00 (2024) 000 – 000

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bond behavior of MKPC coated rebars. The research team is currently testing MKPC coated mild steel 13 mm (#4) and 19 mm (#6) bars with more consistent lug patterns and with reduced mil coating thicknesses as well as three different varied d b lengths to better understand the influence of these variables. 3.2 Pull-out comparison to ACI empirical bond strength Using the ACI 318-19 empirical estimate for the development length to reach yield in the mild steel bar and the measured concrete properties, one can then estimating the bar capacity for the experimental bonded length (5d b ), From this one can finally estimate of the pull-out capacity. For the 19 mm uncoated mild steel bars, this results in a 6.6 MPa average bond strength and 3.0 MPa average bond strength for the 13 mm uncoated mild steel bar. Based upon the experimental results in Figure 3, all tested specimens exceeded the ACI 318 predicted bond strength extrapolated from the ACI development length equation. Which is known to be conservative. 4. Conclusions When considering at the results of just the 19 mm rebar, MKPC-coated rebar performs very well compared to steel rebar and epoxy-coated rebar. The results are much less impressive for 13 mm rebar; however, this is attributed to the loss of mechanical advantage of the rebar lugs due to the thickness of the MKPC coating. Based upon prior multiple research studies including Ichinose et al. (2004), bars with smaller diameters have higher bond strength than bars with larger diameters. This is due to smaller diameter bars with the same properties having a larger ratio of surface area to cross-sectional area. In future testing with a modified thinner coating, it is expected this trend will result. As the size of the data base increases and more bar sizes are tested, a model similar to the one developed Ichinose et al. (2004) could be created to predict the bond stress and/or suggest a calibration factor to current models for other rebar sizes with MPKC coating. Based on the work of Zhang et al. (2023), the research team anticipates that reduced mil thicknesses will still provide the needed anti-corrosion protection required to be competitive or better than epoxy coated rebars from a corrosion protection perspective and also improve the bond performance. Current ongoing experiments are in process using an MKPC mixture with a higher water content, so the coating will be thinner when applied. These additional tests also include changes to reduce some of the larger standard deviations observed in the experimental work by increasing the number of replicants per specimen type and reducing the quantity of batches of concrete in which the specimens were fabricated. Future investigations are needed to include investigating the bond performance of MKPC under aggressive environments as it relates to bond even though corrosion studies by Zhang et al. (2023) showed little degradation to the rebar coating under accelerated rebar corrosion studies. Magnesium potassium phosphate cement (MKPC) demonstrates great potential as a corrosion resistant coating for steel rebar. MKPC coated bar bond performance is comparable to steel and epoxy-coated rebar at larger bar sizes, and is believed to have this same potential for smaller bar sizes with a thinner coating, which is being investigated currently. MKPC bonds well both with concrete and concrete repair materials, indicating its potential for use in new construction and repair. With future testing, it is believed these claims will be strengthened. Acknowledgements The support of the Concrete Reinforcing Steel Institute (CRSI) is gratefully noted to support this research investigation. In addition, the support of Dr. Wenyu Liao at Missouri S&T who assisted the graduate student in the MKPC coating of several rebars is gratefully acknowledged. The research team also expresses its deepest gratitude to the support staff and technicians in the Dept of Civil, Arch. and Envir. Engineering (CArEE), the Missouri Center for Transportation Innovation (MCTI) and the Center for Infrastructure Engineering Studies (CIES) at Missouri S&T. The lab technician at Missouri S&T provided crucial assistance and technical expertise during the experimental phases of this project.