Bio-Inspired and Low-Content Polymer Cement Mortar for Structural Rehabilitation

Use of polymers as partial replacement for Portland cement in cement mortar and concrete can diminish several drawbacks of these composites such as low tensile strength and strain capacity, high permeability and low adhesion. Main reasons for the use of polymers are to improve damage tolerance, adhesion, and resistance to water permeation. Various polymers with a wide range of physical and mechanical properties have been used in fabrication of cementitious composites. Typical polymer content for such composites is 5% to 20% (by the weight of cement) for both mortar and concrete. There are also drawbacks associated with the use of PMMs which become critical at higher P/C ratios. These limitations include but are not limited to high cost; vulnerability to high temperatures, chemical attack, and UV radiation; and storage and handling issues such as odor, toxicity, flammability, and combustibility. Therefore, finding ways to reduce these drawbacks and maintain the advantages PMMs have to offer is of great interest to engineers and researchers. In this work dopamine (DA) is introduced as a potential monomer for production of high-performance polymer-modified mortar (PMM) composites at small polymer-cement (P/C) ratios of 0.1-0.5%, i.e. two orders of magnitude smaller than P/C ratios used in common practice. Formation of a PDA-cement co-matrix is examined and different factors affecting the characteristics of such system are discussed. In particular, the role of P/C ratio in formation and distribution of PDA network and effect of PDA network on mechanical properties of PDA-cement systems are studied and different mechanisms are discussed. 7- and 28-day compressive strength and splitting tensile strength of newly-formulated composites were tested at different P/C. Morphology and microstructure of PDA-cement matrix were studied using scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX) analysis of samples obtained from fracture surfaces. The effect of PDA on drying shrinkage and early-age cracking resistance of mortar was also evaluated using ASTM ring test. Incorporation of PDA at P/C of 0.5% improved compressive strength, tensile strength, and shrinkage cracking on average by 55%, 27%, and 69%, respectively

Functionalized Graphitic Nanoreinforcement for Cement Composites

Physical and mechanical properties of graphitic nanomaterials, in particular multiwalled carbon nanotubes (MWCNTs) and graphene nano-platelets (GNPs) make them promising candidates for nanoreinforcement of cement composites. The two key challenges associated with the incorporation of MWCNTs and GNPs are to attain uniform dispersion and interfacial bonding within the composite matrix. The effects of three main-stream dispersion techniques (namely, ultrasonication, acid-etching, and surfactant-coating) on the mechanical properties and microstructure of MWCNT- and GNP-cement composites were experimentally studied. Compressive strength tests and different characterization techniques including dynamic light scattering, Raman spectroscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron spectroscopy were employed to evaluate the dispersion and embedment of nanoreinforcement in cement mortar and paste. As a result of significant and consistent compressive strength enhancements, further supported with material characterization results, acid-etching and surfactantcoating were selected as suitable functionalization techniques to manufacture MWCNTand GNP-cement composites, respectively. The validity of the selected functionalization techniques was further investigated through bending tests on single-edge notched cement paste beams. The results were studied with respect to flexural strength and stiffness. In addition, the effects of incorporating well-dispersed acid-etched MWCNTs on the fracture behavior of cement paste were studied through bending tests on notched beam samples. This research contributes to filling the gap in understanding whether dispersibility of MWCNTs and GNPs in aqueous solutions by means of well-known dispersion and functionalization techniques results in good dispersion and embedment (i.e., resulting in consistent and repeatable enhancement in relevant mechanical properties) in cement matrices. This gap is addressed by presenting new experimental evidence on improved mechanical properties as well as supporting evidence from material characterization tests, in particular for the case of GNP-reinforced mortar and cement paste. A novel contribution of this work is offered by the results of digital image correlation measurements aimed at visualizing full-field strain maps from the area surrounding the notch in cement paste beams. These results provide insight into the morphology and evolution of the fracture process zone in nanoreinforced cement paste vis-à-vis unreinforced counterparts, and constitute new evidence on the potential fracture toughening effect of MWCNTs

Applied TEM Approach for Micro/Nanostructural Characterization of Carbon Nanotube Reinforced Cementitious Composites

A novel colloidal technique for transmission electron microscopy (TEM) of graphitic nano-reinforced cementitious (GNRC) composites was developed. Single-walled and multiwalled nanotubes (SWNTs and MWNTs) were functionalized using an acid etching technique to obtain stable aqueous suspensions that were incorporated in the mix design of a cement paste. Effective functionalization was demonstrated by Raman spectroscopic measurements and time resolved dynamic light scattering measurements. The functionalized nano-reinforcement and binding characteristics were observed at the nanoscale for the first time using high resolution TEM imaging. Functionalized CNTs were found to be well distributed and preferentially associated with the cementitious matrix. This newly developed colloidal technique for TEM imaging of GNRC composites is a viable approach to characterize the interfacial compatibility between graphitic nano-reinforcement and cementitious matrices