2 research outputs found

    Effect of gypsum content in sprayed cementitious matrices: Early age hydration and mechanical properties

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    © 2018 Elsevier Ltd Sprayed materials must present short setting times and a fast early strength development for safety and productivity reasons. In order to improve these characteristics, the construction industry has focused on the development of new formulations of accelerators. Research and improvement of other components of the mix, such as cement or additions, have not advanced at the same rate despite being also crucial for the reaction kinetics. The objective of this work is to evaluate the influence of gypsum content on the hydration and mechanical strength development in sprayed mixes. Sprayed pastes and mortars were prepared with one type of cement, two types of accelerators and different gypsum contents. Kinetics, mechanisms of hydration and mechanical properties were evaluated. Results showed a better performance in sprayed mixes that contain ideal doses of gypsum. Such approach provides valuable information for the improvement of the formulation of cement used in sprayed concrete applications

    Adaptation of the standard EN 196-1 for mortar with accelerator

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    In certain applications, accelerators are added to favour a rapid evolution of mechanical properties in mortar and concrete. In order to assure adequate performance, it is necessary to test the compatibility between the accelerator and other components of the mixture. The EN 934-5 establishes that such evaluation of accelerators should be performed according with the procedure established in the EN 196-1. However, this standard does not take into account the inclusion of the accelerators or the particularities of the mortar produced with these admixtures. The objective of this paper is to adapt the EN 196-1 in order to characterize the strength of mortars with accelerator. First, an experimental parametric study to evaluate the influence of the production procedure on the results was conducted. Based on the results obtained, a modified production process was proposed. Then, a wide experimental program including a total of 40 mixes of mortars with different formulations and contents of accelerators was performed. Based on a statistical analysis, a new admissible variation used to calculate the compressive strength was proposed
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