Insights into the Alteration in the Interfacial Performance of Polymer Coating between Clay and Cement Substrates

Abstract

The adhesive strength at the interface of a clay–polymer composite is observed to reduce as a cementitious substrate comes at its proximity. The physical phenomena governing the interfacial behavior of clay–polymer composites is studied at different length scales in the presence and absence of a cementitious substrate. Interfacial adhesion was quantified under both compression and shear mode. This paper presents the suitability of an epoxy coating when sandwiched between two dissimilar substrates such as clay and cement. Experimental and simulation evidences are presented in detail revealing the mechanisms at molecular scale. The extent of polymerization of epoxy oligomers gets unfavorably affected due to the physical interaction of hardener with the hydrating cement paste, as explained through X-ray photoelectron spectroscopy. Experimental and molecular dynamics simulation together revealed that the oxygen of epoxide rings has stronger interaction to calcium cations of cement than interlayer sodium cations in clay gallery. Further, the importance of ring opened C─ OH sites for interaction with siloxane clay surface and its effect on interface strength development is realized. The chemical reaction of epoxy with hardener and its effect on interactions developed at clay surface is explained. Experimental evidence clearly reflects the weak interface formation by epoxy coating in the presence of two dissimilar substrates that is otherwise strong if the substrates are similar. The intricate mechanisms existing at the interface of soil and structure is extensively studied from an elementary perspective. For this, a highly problematic expansive soil and the basic dynamic constituent of a concrete element i.e., cement paste is considered. The influence of an epoxy-based coating on the interfacial interactions between soil and cement shed lights into the essential parameters to be considered for upscaling of the work. The scope of the work is strictly restricted to cement paste at 28 days of curing and at w/c of 0.3, thus ensuring a uniform pore size distribution and surface roughness. Any upscaling of the work undeniably requires consideration of the effect of superplasticizers added in concrete, other polymer functionalities, fluctuations in environmental conditions, and so on.