Tailoring the Properties of Calcium Aluminate Macro-Defect-Free Cements: From Brittle to Ductile Behavior
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JMEPEG https://doi.org/10.1007/s11665-019-04430-3
Tailoring the Properties of Calcium Aluminate Macro-Defect-Free Cements: From Brittle to Ductile Behavior Raffaella DellÕAversano and Alberto DÕAmore (Submitted April 23, 2019; in revised form August 23, 2019) Cementitious macro-defect-free (MDF) materials can be obtained processing a mixture of a water-soluble polymer, namely polyvinyl alcohol (PVA) and the calcium aluminate cement. Based on process techniques typical of plastics, the MDF products can be obtained in complex forms and, thanks to the reduced water to cement ratio, w/c, their strength is very high compared to standard cements. However, these materials show both the sensitivity typical of water-soluble polymers, presenting a low glass transition temperature (Tg), and the brittle behavior typical of ceramic materials and therefore low toughness. The aim of this work is to modify the mechanical properties of MDF cements by tuning their unacceptable brittle behavior. Water solution of carboxylate styrene butadiene rubber is used as reactive additives, and different mixture formulations are tested changing the rubber-like content both with respect to the fixed water content and PVA amounts. It is shown that the modifications of the organic phase imply small or negligible effects on paste formation of different recipes as detected by the torque–time responses. From flexural and fracture toughness tests, a wide range of responses was observed, and depending on the particular recipe, the mechanical behavior can be tuned from a brittle to a ductile behavior. Keywords
macro-defect-free cements, mixing analysis, mechanical properties, toughening
1. Introduction Low tensile strength and low fracture toughness are the main drawbacks of traditional cast cement-based materials compared to plastics and metals. The excess water provides a sufficient workability, but when water evaporates the cement becomes more porous which significantly reduces its tensile strength. Eventually, the tensile strength of common Portlandbased cements (PC) is one order of magnitude lower that the compressive strength. Instead, MDF cements are characterized by high elastic modulus and tensile strength, namely E 3.5 GPa and rr 150 MPa, respectively, and, thanks to their potential, these materials have been the subject of numerous studies after being developed in the early 1980s (Ref 1-5). In these materials, the plastic mass is achieved with a high shear stresses mixing process typical of plastics processing thanks to the plasticization of a water-soluble polymer, namely polyvinyl alcohol (PVA), in the calcium aluminate cement (CAC), and a small amount of glycerol in a water/cement ratio, w/c 0.1. It was well established that the cross-linking reaction occurs between polymer and hydrating cement and this cross-linking plays an important role in the achievement of high strength. Moreover, hot pressing during processing accelerates crossRaffaella DellÕAversano and Alberto DÕAmore, Department of Engineering, University of Campania ‘‘Luigi
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