Engineering interfacial strength of polymer coated hydrating cement paste by tuning calcium characteristics

Interfacial strength between cement paste and an acrylic polymer, Poly(methyl methacrylate) (PMMA) primarily originates from the chemical interactions (formation of metal complex) between calcium ions of the cement paste and the ester functional group of PMMA. There are certain parameters, controllable at a construction site and can potentially influence the calcium characteristics of cement paste substrate, thereby affecting the interfacial strength. It is interesting to examine how these parameters can be engineered to enhance interfacial strength. To this end, the present work investigates the role of calcium on the interfacial strength between cement paste and PMMA by evaluating the influence of various parameters at early (2 days) and later (28 days) days of hydration. The parameters considered were w/c ratio, duration of curing, viscosity of PMMA, and use of lime coating. Macro-mechanical experiments such as slant shear and pull-off adhesion tests were performed to measure interfacial adhesive strength. Further, to understand the mechanism of calcium crosslinking in the absence of calcium ions, the effect of removal of pore solution from cement paste on interfacial strength was investigated. The experimental results indicate that the parameters considered have more influence on interfacial strength when PMMA was coated at the early age of hydration than coated at later ages. The trend observed in the interfacial strength is mainly ascribed to the variation in the concentration of calcium ions available for chemical interaction in the different conditions considered.