Browsing by Keyword "Compressive strength"
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Item Effect of ternary cements containing thermally activated paper sludge and fly ash on the texture of C-S-H gel(2012-05) Goñi, S.; Frias, M.; Vegas, I.; García, R.; Vigil De La Villa, R.; GENERALThe texture of the C-S-H gels formed in ternary cement blends containing thermally activated paper sludge (APS), fly ash (FA) from coal combustion and Ordinary Portland Cement (OPC) was studied by means of the specific surface area (SSA) and pore-size distribution (PSD), which were measured by the sorption isotherms of nitrogen gas and the BET method. Two differentiated zones in the PSD of the C-S-H gel at ∼10-20 nm and ∼5 nm were observed. The proportion of such zones depends on the age of hydration and amount of OPC replacement. The incorporation of the additions (APS and FA) clearly revealed an increase in both porosity and SSA. This effect decreased with the progress of hydration together with a refinement of the nano-porous structure of C-S-H. High correlations were found among these nanostructure characteristics of the C-S-H gel and mechanical strengths.Item Quantitative correlations among textural characteristics of C-S-H gel and mechanical properties: Case of ternary Portland cements containing activated paper sludge and fly ash(2012-09) Goñi, S.; Frias, M.; Vegas, I.; García, R.; De La Villa, R. Vigil; GENERALThe hydraulic activity of ternary Portland cements containing different proportions of commercial thermally activated paper sludge (APS(I)) and fly ash (FA) from coal combustion was evaluated from the textural characterization of the C-S-H gels formed during hydration. The study was accomplished by means of the specific surface area (SSA) and pore-size distribution (PSD), which were measured by the sorption isotherms of nitrogen gas and the BET method. The microstructure was characterized by scanning electron microscopy (SEM). The incorporation of such admixtures (APS and FA) clearly revealed an increase in both porosity and SSA. This effect decreased with the progress of hydration, together with a refinement of the nano-porous structure of C-S-H. In addition, high correlations were found between nano-structural characteristics of the C-S-H gel and mechanical compressive strengths.Item Recycled Self-Compacting Concrete: Mechanical Behavior and Durability(American Concrete Institute, 2022-07-01) Revilla-Cuesta, Víctor; Skaf, Marta; Chica, José A.; Serrano-López, Roberto; Ortega-López, Vanesa; Coffetti, Denny; Coppola, Luigi; Holland, Terence; SGIncreasing sustainability is currently one of the main objectives of the construction sector. One of the most widespread sustainable practices to reach this goal is the recycling of industrial residues within concrete mixes. What began as a practice to produce low-quality concrete has now spread, for example, to Self-Compacting Concrete (SCC), which has a high flowability in the fresh state. Recycled Concrete Aggregate (RCA) is a waste that can be used to develop SCC of good mechanical performance. RCA produced from the crushing of rejected precast components for the prefabricated concrete industry is assessed in this study. It was demonstrated that the addition of 100 % coarse RCA and 50 % fine RCA contributed to the production of an SCC with adequate flowability and an optimal mechanical and durability behavior. To do so, the design of the mixture, its flowability, its strength behavior at different curing ages and its performance in freeze/thaw, moist/dry and sulfate-attack tests are discussed. The study is complemented by analyzing the interaction of RCA with different natural fine aggregates, such as siliceous or limestone sand. It is concluded that the SCC developed with large amounts of RCA was of sufficient strength and durability for general usage.Item VALIDATION OF ULTRASONIC PULSE TO QUALITY CONTROL OF RECYCLED AGGREGATE SELF-COMPACTING CONCRETE(University of Cantabria - Building Technology R&D Group, 2022) Revilla-Cuesta, Víctor; Santamaría, Amaia; Espinosa, Ana B.; Chica, José A.; Manso, Juan M.; Ortega-López, Vanesa; Blanco, Haydee; Boffill, Yosbel; Lombillo, Ignacio; SGOne of the main operations in any civil work is to verify that the concrete supplied and placed on site reaches the required minimum compressive strength. This verification is usually performed statistically through the preparation and testing of a large number of specimens. However, its indirect control is also useful due to its simplicity, ease of execution, and low cost. One of the most common methods to perform this operation is the measurement of the Ultrasonic Pulse Velocity (UPV) of the cast concrete, checking that its value corresponds to the necessary concrete’s strength class. This study aims to analyze whether this indirect measurement, widely used in vibrated concrete produced with natural aggregate, is also valid when large quantities of Recycled Concrete Aggregate (RCA) are added to Self-Compacting Concrete (SCC). For this purpose, six SCC mixes were produced with 100% coarse RCA and variable fine RCA contents (0%, 50%, and 100%). In addition, two different types of powder were used: Limestone filler <0.063 mm and limestone fines 0/0.5 mm. The determination of the compressive strength and the UPV at 7 and 28 days in all mixes allowed demonstrating the existence of a close relationship between these two magnitudes in this type of concrete. It was even possible to develop highly accurate simple-regression models to interrelate both variables. These findings show that the use of SCC with RCA in engineering works would still allow the control of compressive strength using one of the most common traditional techniques, the ultrasonic pulse.