The influence of fly ash as substitute of cement in the durability of concrete

Limitation of transport capacity through the concrete is one of the key points in the improvement of the material’s durability. The use of fly ash as an admixture to concrete is widely extended; a general consensus has been established due to the pore size reduction produced by the ashes. Nevertheless, the importance of the micro-structural and composition changes in mechanical and durable properties is not well defined. In the present study the use of fly ash has been considered as substitute of cement in the design limits. The concrete mechanical properties and its porous structure were evaluated. The tests included porosimetry and water permeability tests. In order to characterize the hydration products and its evolution with time TG and DTA analysis were performed. This work studies the fly ash concrete hydration process, their influence in the porous distribution, and the mechanical and durable properties of the material

La influencia de las cenizas volantes como sustituto parcial del cemento Pórtland en la durabilidad del hormigón: propiedades físicas, difusión del ión cloruro y del dióxido de carbono

La durabilidad del hormigón, está influenciada por la capacidad de transporte de los fluidos en su red porosa. El uso de cenizas volantes en hormigón está extendido por el ahorro económico que supone y los cambios micro-estructurales motivados por la adición. Existe consenso en que las cenizas reducen el tamaño de poro. Aunque, los cambios de composición y micro-estructurales en la durabilidad del material no están completamente claros. En el XXIV Encuentro se presentó un estudio sobre cómo afectaban las cenizas a la permeabilidad y a la estructura porosa. Este trabajo complementa el anterior, extendiendo el estudio a los resultados de los ensayos de carbonatación y difusión de cloruros. Los resultados obtenidos ponen de manifiesto que las cenizas no modifican del mismo modo la carbonatación y la difusión de cloruros. La difusión de cloruros se ve más afectada por los cambios de la estructura porosa. Los iones carbonato interaccionan químicamente con la matriz por lo que su avance se ve afectado por los cambios en composición generados por la reacción puzolánica

Influence of cement properties in the reaction rate and mechanical behavior of concrete with high fl y ash content

The use of fly ash (FA) as an admixture to concrete is broadly extended for two main reasons: the reduction of costs that supposes the substitution of cement and the micro structural changes motivated by the mineral admixture. Regarding this second point, there is a consensus that considers that the ash generates a more compact concrete and a reduction in the size of the pore. However, the measure in which this contributes to the pozzolanic activity or as filler is not well defined. There is also no justification to the influence of the physical parameters, fineness of the grain and free water, in its behavior. This work studies the use of FA as a partial substitute of the cement in concretes of different workability (dry and wet) and the influence in the reactivity of the ash. The concrete of dry consistency which serves as reference uses a cement dose of 250 Kg/m 3 and the concrete of fluid consistency utilized a dose of cement of 350 Kg/m 3 . Two trademark of Portland Cement Type 1 were used. The first reached the resistant class for its fineness of grain and the second one for its composition. Moreover, three doses of FA have been used, and the water/binder ratio was constant in all the mixtures. We have studied the mechanical properties and the micro-structure of the concretes by means of compressive strength tests, mercury intrusion porosimetry (MIP) and thermal analysis (TA). The results of compressive strength tests allow us to observe that concrete mixtures with cements of the same classification and similar dosage of binder do not present the same mechanical behavior. These results show that the effective water/binder ratio has a major role in the development of the mechanical properties of concrete. The study of different dosages using TA, thermo-gravimetry and differential thermal analysis, revealed that the portlandite content is not restrictive in any of the dosages studied. Again, this proves that the rheology of the material influences the reaction rate and content of hydrated cement products. We conclude that the available free water is determinant in the efficiency of pozzolanic reaction. It is so that in accordance to the availability of free water, the ashes can react as an active admixture or simply change the porous distribution. The MIP shows concretes that do not exhibit significant changes in their mechanical behavior, but have suffered significant variation in their porous structur

La influencia de las cenizas volantes como sustituto parcial del cemento Pórtland en la durabilidad del hormigón

La durabilidad del hormigón, especialmente del hormigón armado, está muy influenciada por la capacidad de transporte de líquidos y gases a través de su red porosa. El uso de cenizas volantes como adición del hormigón está ampliamente extendido por dos razones: el ahorro económico que supone la reducción del cemento empleado y los cambios microestructurales motivados por la adición. Sobre este segundo punto existe consenso en considerar que las cenizas generan un hormigón más compacto y una reducción del tamaño medio del poro. Sin embargo, la importancia relativa de los cambios de composición y microestructurales en las propiedades mecánicas y la durabilidad del material no están completamente claras. Este trabajo estudia la influencia de las cenizas volantes y las propiedades del cemento en el comportamiento mecánico y durable del hormigón. Se ha estudiado el uso de las cenizas volantes como sustituto parcial del cemento en distintas condiciones. Por un lado, se ha investigado la influencia de dos contenidos de cemento: 250 y 350 Kg por m3 de hormigón. Además, se han empleado dos cementos de igual designación pero distinto origen. En todos los casos se han empleado distintos contenidos de cenizas. Para este fin se prepararon probetas de hormigón a las que se les examinaron los mecanismos de transporte a través del hormigón, las propiedades mecánicas y las características físico‐químicas. El estudio de los mecanismos de transporte expuso las muestras del hormigón a tres tipos de ataque: penetración de dióxido de carbono, penetración del ión cloruro y penetración de agua bajo presión. Los ensayos de las propiedades mecánicas comprobaron las resistencias a compresión y tracción indirecta y el módulo de elasticidad en compresión. La caracterización físico‐química incluyó análisis térmicos (termogravimétricos y termodiferenciales) y porosimetría por intrusión de mercurio. Los resultados obtenidos ponen de manifiesto que la incorporación de cenizas como sustituto parcial del cemento Pórtland varía el comportamiento del hormigón en función de las características físicas y químicas de los cementos empleados, a pesar de que éstos estén catalogados bajo la misma designación de cementos comunes. Las cenizas volantes, empleadas adecuadamente, constituyen una adición activa que puede mejorar las propiedades durables y mecánicas de los hormigones en la mayoría de los casos. Sin embargo, el empleo de la ceniza volante, sin estudiar los efectos de la misma en el cemento que reemplaza, puede ocasionar comportamientos inesperados y adversos en el hormigón. The durability of concrete, especially of reinforced concrete, is influenced by the concrete’s ability to carry liquids and gases through it’s porous network. The use of fly ash as a concrete admixture is widespread for two reasons: the economic savings resulting from the reduction of cement used; and micro‐structural changes driven by the admixture. On this second point there is consensus in considering that the ashes generate a denser concrete and a reduction in the average size of the pore. However, the relative importance of the shifting composition and microstructural mechanical properties, and durability of the material are not entirely clear. This research examines the influence of fly ash and cement properties in the mechanical behavior and durability of concrete. The use of fly ash as a partial substitute for cement in different conditions has been studied. One aspect of this research has been the influence of two cement contents: 250, and 350 Kg/m3. In addition, two cements with the same designation but different origin have been used. In all cases, different ash contents have been used. Several mixtures were tested to understand the concrete transport mechanisms, mechanical properties, and micro‐structural characteristics. Concrete samples were exposed to three attacks: penetration of carbon dioxide; penetration of chloride ion; and penetration of water under pressure. The mechanical properties were tested to observe their development: compressive strength; tensile strength; and elasticity modulus. Micro‐structural characterization included thermal analysis (thermo‐gravimetric and thermodifferential) and mercury intrusion porosimetry. The results show that the incorporation of fly ash as a partial substitute of Portland cement can improve the concrete properties. But, its behavior varies depending on the physical and chemical properties of cements, even if they are classified under the same designation. The fly ash, used properly, is an admixture that can improve mechanical properties and durability of concrete in most cases. However, the use of fly ash, without previous research is not recommended

Study of the influence of Portland cement on the properties of concrete with fly ash

Concrete made with Portland cement is one of the most used construction material in the world. Engineers and scientists are always looking to improve its sustainable properties. The durability of concrete is a determining factor in the service life of a structure. The durability of cement based materials is strongly influenced by its porous structure. Previous research has shown that the use of fly ash in concrete mixtures as partial substitution of Portland cement produces a pozzolanic reaction that changes concrete’s micro-structure. As a concrete mineral admixture, fly ash improves concrete’s mechanical properties and durability while providing economic and environmental benefits. The objective of this paper is to present the results of a study that investigated the influence of fly ash on the durability of concrete mixed with ASTM C150: Type I cements. The methodology included mixing three different ASTM C150: Type I cements with three different percentages of fly ash each for a total of 9 different combinations. Durability, physical, and mechanical properties tests were performed on the concrete samples from each mix. The results indicate that the performance of concrete with fly ash varies based on the characteristics of the cement used and the amount of fly ash used in the mixture. Based on the results of this study, it can be concluded that the best result for experimental concrete with 25% fly ash substitution were obtained with concrete Y (C3S = 55.31%), while with 50% fly ash substitution the best results were obtained with cement Z (C3S = 77.04%). These combinations increase the concrete’s durability while reducing costs and providing environmental benefits. This paper contributes to the body of knowledge by increasing the understanding of the influence of cement properties in fly ash on the durability of concrete.Non UBCUnreviewedFacultyOthe

Direct observation of the dead-cone effect in quantum chromodynamics

The direct measurement of the QCD dead cone in charm quark fragmentation is reported, using iterative declustering of jets tagged with a fully reconstructed charmed hadron

Direct observation of the dead-cone effect in quantum chromodynamics

At particle collider experiments, elementary particle interactions with large momentum transfer produce quarks and gluons (known as partons) whose evolution is governed by the strong force, as described by the theory of quantum chromodynamics (QCD) [1]. The vacuum is not transparent to the partons and induces gluon radiation and quark pair production in a process that can be described as a parton shower [2]. Studying the pattern of the parton shower is one of the key experimental tools in understanding the properties of QCD. This pattern is expected to depend on the mass of the initiating parton, through a phenomenon known as the dead-cone effect, which predicts a suppression of the gluon spectrum emitted by a heavy quark of mass m and energy E, within a cone of angular size m/E around the emitter [3]. A direct observation of the dead-cone effect in QCD has not been possible until now, due to the challenge of reconstructing the cascading quarks and gluons from the experimentally accessible bound hadronic states. Here we show the first direct observation of the QCD dead-cone by using new iterative declustering techniques [4, 5] to reconstruct the parton shower of charm quarks. This result confirms a fundamental feature of QCD, which is derived more generally from its origin as a gauge quantum field theory. Furthermore, the measurement of a dead-cone angle constitutes the first direct experimental observation of the non-zero mass of the charm quark, which is a fundamental constant in the standard model of particle physics.The direct measurement of the QCD dead cone in charm quark fragmentation is reported, using iterative declustering of jets tagged with a fully reconstructed charmed hadron.In particle collider experiments, elementary particle interactions with large momentum transfer produce quarks and gluons (known as partons) whose evolution is governed by the strong force, as described by the theory of quantum chromodynamics (QCD). These partons subsequently emit further partons in a process that can be described as a parton shower which culminates in the formation of detectable hadrons. Studying the pattern of the parton shower is one of the key experimental tools for testing QCD. This pattern is expected to depend on the mass of the initiating parton, through a phenomenon known as the dead-cone effect, which predicts a suppression of the gluon spectrum emitted by a heavy quark of mass $m_{\rm{Q}}$ and energy $E$, within a cone of angular size $m_{\rm{Q}}$/$E$ around the emitter. Previously, a direct observation of the dead-cone effect in QCD had not been possible, owing to the challenge of reconstructing the cascading quarks and gluons from the experimentally accessible hadrons. We report the direct observation of the QCD dead cone by using new iterative declustering techniques to reconstruct the parton shower of charm quarks. This result confirms a fundamental feature of QCD. Furthermore, the measurement of a dead-cone angle constitutes a direct experimental observation of the non-zero mass of the charm quark, which is a fundamental constant in the standard model of particle physics

Σ(1385)± resonance production in Pb–Pb collisions at √sNN = 5.02 TeV

Hadronic resonances are used to probe the hadron gas produced in the late stage of heavy-ion collisions since they decay on the same timescale, of the order of 1 to 10 fm/c, as the decoupling time of the system. In the hadron gas, (pseudo)elastic scatterings among the products of resonances that decayed before the kinetic freeze-out and regeneration processes counteract each other, the net effect depending on the resonance lifetime, the duration of the hadronic phase, and the hadronic cross sections at play. In this context, the Σ(1385)± particle is of particular interest as models predict that regeneration dominates over rescattering despite its relatively short lifetime of about 5.5 fm/c. The first measurement of the Σ(1385)± resonance production at midrapidity in Pb-Pb collisions at sNN−−−√=5.02 TeV with the ALICE detector is presented in this Letter. The resonances are reconstructed via their hadronic decay channel, Λπ, as a function of the transverse momentum (pT) and the collision centrality. The results are discussed in comparison with the measured yield of pions and with expectations from the statistical hadronization model as well as commonly employed event generators, including PYTHIA8/Angantyr and EPOS3 coupled to the UrQMD hadronic cascade afterburner. None of the models can describe the data. For Σ(1385)±, a similar behaviour as K∗(892)0 is observed in data unlike the predictions of EPOS3 with afterburner

Measurement of the lifetime and Λ separation energy of 3ΛH

The most precise measurements to date of the 3ΛH lifetime τ and Λ separation energy BΛ are obtained using the data sample of Pb-Pb collisions at √= 5.02 TeV collected by ALICE at the LHC. The 3ΛH is reconsNN structed via its charged two-body mesonic decay channel (3ΛH→ 3He + π− and the charge-conjugate process). The measured values τ=[253±11 (stat.)±6 (syst.)] ps and BΛ=[102±63 (stat.)±67 (syst.)] keV are compatible with predictions from effective field theories and confirm that the 3ΛH structure is consistent with a weakly-bound system

Investigation of K+K− interactions via femtoscopy in Pb-Pb collisions at √sNN = 2.76 TeV at the CERN Large Hadron Collider

Femtoscopic correlations of non-identical charged kaons (K+K−) are studied in Pb−Pb collisions at a center-of-mass energy per nucleon−nucleon collision sNN−−−√=2.76 TeV by ALICE at the LHC. One-dimensional K+K− correlation functions are analyzed in three centrality classes and eight intervals of particle-pair transverse momentum. The Lednický and Luboshitz interaction model used in the K+K− analysis includes the final-state Coulomb interactions between kaons and the final-state interaction through a0(980) and f0(980) resonances. The mass of f0(980) and coupling were extracted from the fit to K+K− correlation functions using the femtoscopic technique for the first time. The measured mass and width of the f0(980) resonance are consistent with other published measurements. The height of the ϕ(1020) meson peak present in the K+K− correlation function rapidly decreases with increasing source radius, qualitatively in agreement with an inverse volume dependence. A phenomenological fit to this trend suggests that the ϕ(1020) meson yield is dominated by particles produced directly from the hadronization of the system. The small fraction subsequently produced by FSI could not be precisely quantified with data presented in this paper and will be assessed in future work