Grafted β-Cyclodextrin Methoxy Polyethylene Glycol Copolymers as Superplasticizing Admixtures for Cement Mortar

Synthetic-based plasticizers are often used in the masonry industry to improve the rheological and mechanical properties of mortar, but these systems are neither sustainable nor eco-friendly. In this study, several copolymers were prepared that contain grafted β-cyclodextrin (βCD) and its modified forms (HprβCD, FβCD, SucβCD, and CarβCD) were grafted onto methoxy polyethylene glycol (MPEG) and were evaluated as hybrid bio-based plasticizing admixtures for cement mortar. The grafted copolymers were characterized by IR/1H NMR spectroscopy, powder XRD, TGA, and DSC. Their performance as admixtures were evaluated based on flowability, consistency, rheological parameters, and mechanical properties of mortar in fresh and hardened states. Spectral (27Al and 29Si NMR, XRD) measurements of the cementitious samples provided insight on the intermolecular interactions of the mortar components. At low concentrations, 1.0 wt %, the copolymers were effective plasticizers, increasing the mortar fluidity in comparison to the control sample without admixtures. At a 0.30: 1 water-to-cement ratio, the water reduction capacity was up to 20%, keeping the mortar flow within an appropriate range. Besides, hydration-related behavior was indirectly assessed through strength development and spectroscopic analyses. The mortar sample with HprβCD-MPEG had a higher compressive strength when the admixture concentration was changed from 1% (31 MPa) to 2% (40 MPa) showing the capacity of the copolymer as a strength enhancer. The copolymers CarβCD-MPEG (35 MPa) and FβCD-MPEG (42 MPa) also reached the compressive strength typical for a 28 day mortar sample, whereas a lower value was noted for the 7 day control (30 MPa). Relative to commercial superplasticizers, the graft copolymers showed high potential as suitable alternatives for conventional fully non-renewable admixtures.