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Estudio de la adición de arcillas calcinadas en la durabilidad de hormigones * Universidad Central de Las Villas, Santa Clara, Cuba ** Escuela Politécnica Federal de Lausana (EPFL), SUIZA Resumen Actualmente son bien conocidas las ventajas económicas y medioambientales de la sustitución del clínker de cemento por otros materiales cementicios suplementarios. Las arcillas calcinadas en forma de metacaolín han recibido por ejemplo especial atención en años recientes. Se conoce que estas adiciones, cuando se añaden a morteros y hormigones, mejoran tanto su resistencia mecánica como su durabilidad. El objetivo de este trabajo es evaluar el comportamiento de las propiedades físico-mecánicas y la durabilidad en microhormigones, empleando arcillas calcinadas y molidas como material sustituyente del 30% en peso del cemento Pórtland ordinario (CPO). Para ello se utilizó una tierra arcillosa, compuesta principalmente por mineral caolín de bajo grado de pureza, para la obtención de arcillas calcinadas como minerales cementicios suplementarios. Los mejores resultados se resistencia a la compresión a los 28 días se obtuvieron para la arcilla sedimentada y calcinada, la cual posee mayor contenido de mineral caolín debido a un proceso de purificación por sedimentación de la materia prima acometido sólo para esta adición. Sin embargo, los ensayos de absorción de agua por capilaridad arrojaron los mejores resultados para el suelo arcilloso calcinado, el cual posee una elevada finura en comparación al resto de los materiales estudiados. Los menores valores mostrados por esta adición, tanto de porosidad capilar como de sorptividad, indican que existió un predominio del fenómeno de la compacidad e impermeabilidad, lograda en la matriz cementicia al usar un material tan fino, por encima del efecto de la reacción puzolánica. Estudios en la microestructura del gel de C-S-H, usando energía dispersiva por rayos-X (EDX), demostraron como el empleo de arcillas calcinadas en sustitución del CPO favorece la formación de productos de hidratación más estables, principalmente monosulfos del tipo hemicarbo y monocarbo, lo cual es conveniente para el hormigón ante la posible acción de diferentes mecanismos de degradación.Palabras Clave: Arcillas calcinadas, durabilidad, absorción capilar, porosidad, productos de hidratación Abstract Currently economical and environmental advantages of cement clinker replacement by other supplementary cementious materials are well known. For example calcined clays, such as metakaolin, have drawn special attention during recent years. It is well known that these admixtures added to mortars and concretes improve mechanical strength as well as durability. The purpose of this study is to evaluate the behavior of physical-mechanical properties and durability in micro-concretes, by employing calcinated and grinded clays as replacement material, by 30% of ordinary Portland cement (OPC). Therefore, clay soil was employed, which is mainly composed by low-purity-kaolin mineral, so as to obtain calcined clays to be used as s...

This article investigates the shear behavior of reinforced concrete beams without transverse reinforcement. Two types of concrete were produced: a Reference Conventional Concrete (RCC) and a Lightweight Self-Consolidating Concrete (LSCC), all with an average 28-day compressive strength (fc) of approximately 30 MPa and characterized by rheological and mechanical tests. Twelve 15 x 30 x 200 cm beams were manufactured for shear failure during a four-point bending test. Concrete properties, longitudinal reinforcement ratios (0.89%, 1.27% and 1.68%) and shear-span to depth ratio (1.87 to 2.71) were determined. The studied beams were compared in terms of cracking pattern, diagonal cracking load, shear strength, specific concrete and longitudinal reinforcement deformation at failure. The strength values obtained experimentally were compared with ABNT NBR 6118 (2014), ACI 318 (2019) and CEN EC-2 (2004). The tested beams of LSCC showed less shear strength when compared to beams of RCC.

The pulp and paper industry increases every year in Brazil, providing an important country position in international market due to its production volume. However, because of this increasing, a large volume of wastes is generated. One of them is a lime mud, resulting from the Kraft chemical pulping production process. Thus, the aim of this study was to evaluate the replacement of hydrated lime by lime mud on laying and coating mortars production, in order to verify its feasibility for possible application in civil construction industry. The 100% hydrated lime replacement mortar reached a 28-day compressive strength of 5.84 MPa. Finally, the results obtained in the experimental program showed that the 100% hydrated lime replacement mortar by lime mud meets the normative requirements for multiple-use mortars.

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As the main components of the building envelope, construction materials have a straight relation with air contaminants from anthropogenic origins. Titanium dioxide has been recently applied in construction industry products since its photocatalytic properties can be used for pollutant degradation purposes. This study evaluated the performance of cement-based mortars with the incorporation of TiO2 nanoparticles and mineral admixtures. Six mortar compositions were defined by considering two reference mixes (with and without TiO2 incorporation), two mineral admixtures (bentonite and metakaolin) as partial cement replacement and one waste from ornamental stone processing in two levels of partial substitution of natural sand. Consistency index, density, and entrained air content of mixtures were investigated at fresh state. Compressive strength, water absorption, sorptivity, and micrographs from scanning electron microscopy were used to characterize mortars at hardened state. It was observed that incorporation of TiO2 does not considerably change mortar's properties at fresh and hardened state, despite a denser microstructure and improved interfacial transition zone. In general, the relation between the water-to-cement ratio and porosity on the performances of TiO2-added mortars was shown, which is strongly related to their photocatalytic efficiency. Metakaolin mixtures were more efficient to NO conversion, and high selectivity was observed for the bentonite mortars.