Análisis de propiedades del transporte de humedad en bloques de hormigón

The moisture absorption properties in the concrete blocks have a significant influence on the performance of the penetration of rainwater. Knowledge of these properties is necessary to have technical information that allows the construction of walls with long life. In this paper we conducted a comparative analysis of two structural concrete blocks in relation to their physical properties and moisture transport: open porosity, specific mass and the initial rate of absorption (IRA), the total absorption and uptake versus time, obtaining the sorptivity as code for measuring the absorption accurate and reliable. The results obtained show that the sorptivity in the case of concrete block D2 is not applicable and presents the absorption average curve versus time as a characterization parameter with great potential, once can be observed the behavior of the blocks from the initial time to saturation, showing the characteristics between the different block types analyzed.Las propiedades de absorción de humedad de los bloques de hormigón tienen influencias significativas en el comportamiento a la penetración de agua de lluvia. El conocimiento de estas propiedades es necesario para poder contar con información técnica que permita la construcción de paredes con vida útil prolongada. En el presente articulo se realizó un análisis comparativo de dos bloques de hormigón estructurales en relación a sus propiedades físicas y de transporte de humedad: porosidad abierta, masa especifica así como la tasa inicial de absorción (IRA), absorción total y la absorción en función del tiempo, con la obtención de la sorptividad como código de medición preciso y confiable. Los resultados mostraron que la sorptividad no es aplicable en el caso de los bloques de hormigón D2 y se presenta la curva media de absorción en función del tiempo como un nuevo parámetro de caracterización que permite analizar el comportamiento y las peculiaridades de los bloques desde el instante inicial hasta la saturación

Effect of alkalis content on calcium sulfoaluminate (CSA) cement hydration

The behavior of sulfoaluminate (CSA) cements hydrated in neutral or alkaline solutions (0 M, 0.1 M, 1 M, 4 M and 8 M NaOH) was studied. 2-d, 28-d and 90-d mechanical strengths were determined, as well as the reaction rate by isothermal conduction calorimetry. The reaction products were characterised with XRD, DTA and SEM. The findings revealed differences in performance depending on whether hydration transpired at pH ≤ 14 (0.1 and 1 M) or pH > 14 (4 M and 8 M). To 0.1 M and 1 M, there is an improvement of mechanical strength than in water-hydrated pastes. The majority reaction products in these conditions were ettringite and microcrystalline aluminium hydroxide. Mechanical strength was lower in the high alkalinity (4 M and 8 M) than in the reference pastes, mainly due to the formation of different reaction products. Ettringite was unstable at 4 M and failed to form at 8 M, whilst thenardite and U-phase were detected in the 28d and later materials hydrated at both concentrations.This study was partially supported by the Brazilian National Council for Scientific and Technological Development (CNPq) under project 208380/2017-5, and CAPES. Financial support for this study was also furnished by the Spanish Ministry of the Economy and Competitiveness and FEDER under research project BIA2016-76466-R.Peer reviewe

Effect of chloride salts on sulfoaluminate cement hydration

The effect of including 5 % chloride salts (NaCl and CaCl2) on calcium sulfoaluminate cement hydration was studied. The rate of heat release, setting times and mechanical strength were determined in 2 d, 28 d and 90 d cement pastes. The hydration products formed at those ages were identified with XRD and SEM. Hydration reactions were hastened and early age strength heightened with 5 % NaCl. In contrast, 5 % CaCl2 retarded setting times, although it also increased later age compressive strength. The predominant reaction products found in both cases were ettringite and AH3. Chloraluminates such as Friedel’s salt were not observed to form at any of the ages studied. Gypsum precipitation, absent in the reference sample (CSA cement+water), was detected in the presence of chloride salts, however

Use of raw-state bottom ash for aggregates in construction materials

The recycling of raw-state bottom ash as it is holds an advantage from an economic and environmental standpoint in that it omits pre-processes such as milling and wetting. Its physical and chemical properties are first characterized for the purpose, and then the use of raw-state bottom ash for aggregates in construction materials is proposed. Preplaced aggregate concrete or dry-mixing concrete scheme can be selectively applied according to the particle size requirement of bottom ash aggregate. Preplaced bottom ash aggregate concrete is produced by placing the bottom ash aggregate in formwork and injecting grout to fill the voids. To ensure the injectability of the grout, relatively large-sized particles, greater than 5mm, are recommended to be used. In the case of dry-mixing concrete, this is originally designed for manufacturing concrete masonry units and concrete blocks with a low water-to-cement ratio and consolidated zero-slump concrete using a mechanized vibrating mold. The experimental results show that bottom ash aggregate concrete has moderate compressive strength with a low density