Insights on failure modes of calcium-silicate-hydrate interface strengthened by polyacrylamides: Structure, dynamic and mechanical properties

Abstract

Abstract Hydrolytic reaction of polymers influences the interfacial bonding of cement-polymer composites. The interfacial deterioration mechanism of the calcium silicate hydrates (C–S–H) incorporated by multi-layered Polyacrylamides (PAM) is revealed by molecular dynamics (MD) simulation. To consider the influence of hydrolysis reaction, the amide groups (CONH2) of PAM is transformed to deprotonated carboxyl groups (–COO−) with the substituted ratio of 100% (fully hydrolysis (FH)), 75% (higher hydrolysis degree (HH)) and 50% (lower hydrolysis degree (LH)). Simulation results reveal that the interfacial chemical bonds are mainly attributed to Ca-O bonds, that is the calcium atoms play a predominated role in connecting with the silicate chains and oxygen-containing functional groups in PAM. Also, in the interior region of multi-layers polymers, hydrolytic reaction can transform the weak H-bonds connection to stable ionic bond connection, which strengthens the inter-polymer network at a high hydrolytic degree. Furthermore, uniaxial tensile modeling results exhibit that the failure mode is greatly dependent on hydrolytic degree for C–S–H/PAM composites. The hydrolytic reaction of PAM not only strengthens interfacial strength but also enhance the ductility of C–S–H/PAM composites. While at a low hydrolytic degree, the composite is stretched to fracture in the interior region of PAM polymers, failure happens at the interface of C–S–H and PAM at a high hydrolytic state. The properties of C–S–H/PAM composites decoded at the atomic scale level might guide the organic–inorganic composites with enhanced mechanical properties and durability.