Behavior of novel cementitious composites for use in sustainable construction and rehabilitation

Cementitious composites are a class of cement-based materials that incorporate a cement paste and other constituents to form a composite material. Cementitious composites may include coarse and/or fine aggregate, admixtures, supplementary cementitious materials (SCMs), or fibers in order to achieve a desired workability, strength, or durability property. Recently, material scientists and engineers have developed a variety of novel cementitious composites for the purpose of new construction, rehabilitation, and reconstruction applications. Such materials can be used to improve the sustainability of civil infrastructure through the use of recycled, repurposed, or low-embodied carbon materials. Since many of the qualification standards and tests that exist are conceived for ordinary portland cement concrete in new construction, there is a need to qualify and test novel cementitious composites in accordance with their conceived use case. It is for this reason that the study of concrete durability and combined deterioration mechanisms is necessary to gain a more comprehensive understanding of the theoretical service life of in-situ repairs and structural elements comprised of novel materials. Gaining insight into the behavior of novel cementitious composites can inform specification development and design. Recently, material scientists and engineers have developed a variety of novel cementitious composites for the purpose of new construction, rehabilitation, and reconstruction applications. Such materials can be used to improve the sustainability of civil infrastructure through the use of recycled, repurposed, or low-embodied carbon materials. Since many of the qualification standards and tests that exist are conceived for ordinary portland cement concrete in new construction, there is a need to qualify and test novel cementitious composites in accordance with their conceived use case. It is for this reason that the study of concrete durability and combined deterioration mechanisms is necessary to gain a more comprehensive understanding of the theoretical service life of in-situ repairs and structural elements comprised of novel materials. Gaining insight into the behavior of novel cementitious composites can inform specification development and design. In this dissertation, mechanical and durability properties of a variety of novel cementitious composites (NCCs) are tested and discussed. Specifically, fiber-reinforced cementitious composites (FRCCs) and recycled aggregate concrete (RAC) materials are investigated in terms of load-displacement and ultimate mechanical strength. Additionally, laboratory testing methodologies are detailed in terms of the applicable concrete qualification tests and their modifications. Further, computational modeling approaches are also considered. The outcomes of the various studies presented herein highlight the importance of the proper adoption and implementation of experimental methods and setups that deliver useful insights when working with NCCs. Furthermore, the properties of NCC constituents for which accurate and repeatable qualification standards do not exist were determined to be sensitive enough to treatment and placement conditions to warrant novel testing program development and control over specific variables. Some of the standard testing procedures for cement composites are directly implemented into the experimental programs, while other procedures are modified to fit the needs of the experiment. In all experiments, constituent variables such as water-cement ratio (w/cm), volume of aggregates, and water content were kept constant, while other experimental mixture design variables are altered in order to capture certain mechanical strength outcomes resulting from mixture composition differences, In one study, the ability of a novel testing setup to capture the effect of an environmental conditioning protocol on bond performance is evaluated. Finally, this dissertation will highlight the importance of qualifying and testing novel cement composites. The testing standards and methodologies selected for qualifying these materials is chosen to capture the desired experimental outputs

Designing Concrete Mixtures With RCA

69A3551847102The use of recycled concrete aggregates (RCA) as a replacement in new concrete has gained popularity worldwide as a method of reducing natural aggregate consumption. Many individual studies have been completed but little work has been done to analyze that work to make broad conclusions on RCA concrete mechanical properties. This report presents the development and analysis of a database of mechanical properties of concrete containing coarse RCA and provides an investigation the applicability of numerically generated recycled concrete aggregate (RCA) systems by varying the material properties. A sensitivity study of RCA systems was conducted through a full-factorial analysis to explore how the mixture design proportions influence the RCA concrete hardened properties. The modeling methodology was adopted by using a computational algorithm that can generate concrete systems with different RCA replacement levels to numerically simulate RAC systems under mechanical loading. Numerically simulated results are compared with an experimental database that has been established, including a substantial data set on RAC mixture design proportions. RAC geometries and material properties were stochastically generated using Monte Carlo simulation methods, resulting in 200 representative numerical models that were subjected to simulated mechanical loading

Effect of Cold Plasma Treatment of Polymer Fibers on the Mechanical Behavior of Fiber-Reinforced Cementitious Composites

Fiber-reinforced cementitious composites (FRCC) are a class of materials made by adding randomly distributed fibers to a cementitious matrix, providing better material toughness through the crack bridging behavior of the fibers. One of the primary concerns with FRCCs is the behavior of the fiber when a crack is formed. The fibers provide a stress-bridging mechanism, which is largely determined by the bond that exists between the concrete and the fiber’s outer surface. While many studies have determined the properties of FRCCs and potential benefits of using specific fiber types, the effects of low temperature or cold plasma treatment of polymer fibers on the mechanical behavior of the composite material are limited. Polymer fibers are notable for their low density, ductility, ease of manufacture, and cost-effectiveness. Despite these advantages, the surface properties of polymers do not enable the bonding potential given by steel or glass fibers when used in untreated FRCC, resulting in pull-out failures before the full displacement capacity of the fiber is utilized. For this reason, modification of the surface characteristics of polymer fibers can aid in higher bonding potential. Plasma treatment is a process wherein surfaces are modified through the kinetics of electrically charged and reactive species in a gaseous discharge environment. This paper is a preliminary study on the use of atmospheric pressure plasma generated at approximately room temperature. This atmospheric, cold plasma treatment is a method for improving the mechanical properties of FRCC using polymeric fibers. In this study, polypropylene and polyvinyl-alcohol fibers were cold plasma treated for 0, 30, 60, and 120 s before being used in cementitious mortar mixtures. Compression and flexure tests were performed using a displacement-based loading protocol to examine the impact of plasma treatment time on the corresponding mechanical performance of the fiber-reinforced cementitious composite. The experimental results obtained from this study indicate that there is a positive correlation between fiber treatment time and post-peak load-carrying capacity, especially for specimens subjected to flexural loading