DEVELOPMENT OF CEMENTITIOUS MATERIALS FOR ADHESION TYPE APPLICATIONS COMPRISING CALCIUM SULFOALUMINATE (CSA) CEMENT AND LATEX POLYMER

The objective of this research was to develop high performing polymer modified calcium sulfoaluminate (CSA) cement materials for use in applications requiring superior adhesion characteristics. Little information is available describing interactions of CSA cement containing minor phase tri-calcium aluminate (C3A) with commonly used admixtures. Given the scarcity of information, a basic approach for developing cementitious materials was followed. The basic approach consisted of four tasks: cement design, admixture design, polymer design and testing developed materials. The iterative, time consuming process is necessary for understanding the influence of specific constituent components on overall system behavior. Results from the cement design task suggest calcium sulfate type influences microstructural characteristics and strength development for materials based upon the experimental CSA cement. Results from the admixture design task suggest lithium carbonate and tartaric acid are effective accelerating and retarding admixtures for hydration reactions including reactants yeelimite, calcium sulfate and water. Results from the polymer design task suggest vinyl acetate / ethylene (VAE) dispersible polymer powders (DPP) are compatible with systems containing the experimental CSA cement and other commonly used admixtures. Additionally, results from the polymer design task highlight a method for specifying the ductile behavior of materials containing the experimental CSA cement as majority hydraulic binding agent. Finally, results from the testing of developed materials task suggests adhesion performance for materials containing the experimental CSA cement can be influenced by adjusting the ratio of polymer to hydraulic binding agent in material formulations. Polymer modified CSA cement mortars demonstrated bond strength resulting in substrate failure when cast over porous concrete substrates. Developed mortars demonstrated consistent bonding performance when applied to non-porous substrate materials, metal and glass. Select polymer modified mortars displayed adhesion bond performance such that the glass substrate materials fractured during pull off testing

In-situ laboratory X-ray diffraction applied to assess cement hydration

In-situ X-ray diffraction (XRD) is a powerful tool to assess the hydration of cementitious materials, providing time-resolved quantitative analysis with reasonable accuracy without disturbing sample. However, the lack of guidelines and well-established procedures for data collection and analysis is the limiting factor for spreading this technique. This paper discussed using in-situ laboratory XRD to assess cement hydration. The first part was dedicated to a literature review on the topic. Then, experimental strategies were discussed, and recommendations related to the data analysis routine were drawn; the advantages and limitations of this technique were also discussed. We can conclude that the critical factors for a successful analysis are the choice of an adequate experimental setup with good statistics and low measurement time, the proper consideration of different amorphous contributions in the XRD pattern, and a good data analysis routine. Independent techniques are highly recommended to support the in-situ XRD data.PID2020-114650RB-I0

Healing Mechanism Investigation of Self-Healing Concrete by Microencapsulated Calcium Nitrate

Durability of reinforced concrete structures depends highly on the integrity of the concrete which protects the structure from the environment. However, concrete is a brittle material and as such it is prone to cracking which allows for detrimental agents to penetrate the structure and produce early deterioration. Embedding microcapsules with chemical healing agents in concrete materials for self-healing applications as well as implementing SMAs as reinforcement of concrete structures for self-closing of cracks are both state-of-the-art techniques with enormous potential for enhancement of concrete infrastructure durability. In this work, both techniques are combined as an alternative for superior self-healing of cracks in concrete materials to prevent early deterioration of structures. The objective of this study was to evaluate the mechanism and effectiveness of microcapsules with encapsulated calcium nitrate on self-healing of unreinforced and reinforced (Steel and SMA) cement mortar. To fulfill this objective, short term healing efficiency (up to 28 days) of unreinforced and reinforced (Steel and SMA) mortar beam specimens with calcium nitrate containing microcapsules were evaluated under different environmental conditions (dry, water submerged, and wet and dry cycles) at different microcapsule dosages. Specimens were cracked by three-point bending test and evaluated during the healing period by light microscopy and Ultrasonic Pulse Velocity (UPV) test. Cracks analyzed ranged from 13 to 387 μm. Water submerged healing conditions yielded the best self-healing results followed by wet and dry cycles. Dry healing conditions did not enable appreciable healing, thereby suggesting the need of external moisture conditions for proper functioning of the self-healing mechanism proposed. Moreover, SMA reinforced specimens (with and without microcapsules) presented an enhanced healing performance at early stages of the healing process likely due to the self-closing effect. Furthermore, the general tendency of healing results suggested that the combination of microcapsules and SMA favored self-healing. Lastly, the healing products generated in cracks were investigated under ESEM-EDS to assess their chemical nature. The overwhelming majority of healing products were identified as likely calcium carbonate in the form of calcite crystals, and a limited quantity of gel-like healing products of possibly CSH chemical nature were also identified