Studies on Cement Pastes Exposed to Water and Solutions of Biological Waste

Agnieszka Sujak,Krzysztof Pilarski,Michał Pyzalski,Tomasz Brylewski,Paweł Murzyn,Karol Durczak

doi:10.3390/ma15051931

Agnieszka Sujak, Krzysztof Pilarski + Show 4 more

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https://doi.org/10.3390/ma15051931

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Abstract

The paper presents studies on the early stages of biological corrosion of ordinary Portland cements (OPC) subjected to the reactive media from the agricultural industry. For ten months, cement pastes of CEM I type with various chemical compositions were exposed to pig slurry, and water was used as a reference. The phase composition and structure of hydrating cement pastes were characterized by X-ray diffraction (XRD), thermal analysis (DTA/TG/DTG/EGA), and infrared spectroscopy (FT-IR). The mechanical strength of the cement pastes was examined. A 10 to 16% decrease in the mechanical strength of the samples subjected to pig slurry was observed. The results indicated the presence of thaumasite (C3S·CO2·SO3·15H2O) as a biological corrosion product, likely formed by the reaction of cement components with living matter resulting from the presence of bacteria in pig slurry. Apart from thaumasite, portlandite (Ca(OH)2)—the product of hydration—as well as ettringite (C3A·3CaSO4·32H2O) were also observed. The study showed the increase in the calcium carbonate (CaCO3) phase. The occurrence of unreacted phases of cement clinker, i.e., dicalcium silicate (C2S) and tricalcium aluminate (C3A), in the samples was confirmed. The presence of thaumasite phase and the exposure condition-dependent disappearance of CSH phase (calcium silicate hydrate), resulting from the hydration of the cements, were demonstrated.

Highlights

Depending on the exposure conditions of the tested cement pastes, the diffraction patterns show clear changes in the relative intensity of the reflections coming from these phases, confirming the variable ratio of the mass fraction of portlandite to calcite
In samples immersed in pig slurry, there is a noticeable decrease in the intensity of reflections attributed to the portlandite phase, with a simultaneous increase in the intensity of the peaks characteristic of calcite
The use of different exposure conditions for pastes made of Portland cements (OPC)

Summary

Introduction

Finding alternative energy sources poses a serious challenge to the scientists dedicated to environmental protection and sustainable development policies [1]. The agricultural industry has become an excellent source of reagents for the production of biological gases generated from wastes [2]. Most reactors used for the production of biological gases using waste from the agricultural industry are made of non-biodegradable plastics. From the scientific and application point of view, concrete biogas reactors in which energy gases are obtained should be built from cements with increased surface resistance to biological corrosion. This means that extremely durable concretes are required. Thanks to its specific microstructure, the migration of aggressive ions that have a destructive effect on the durability of the hardened monolith can be eliminated [3]

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