On recovering the second-order convergence of the lattice Boltzmann method with reaction-type source terms

This study derives a method to consistently recover the second-order convergence of the lattice Boltzmann method (LBM), which is frequently degraded by the improper discretisation of required source terms. The work focuses on advection-diffusion models in which the source terms are dependent on the intensity of transported fields. The main findings are applicable to a wide range of formulations within the LBM framework. All considered source terms are interpreted as contributions to the zeroth-moment of the distribution function. These account for sources in a scalar field, such as density, concentration or temperature. In addition to this, certain immersed boundary methods can be interpreted as a source term in their formulation, highlighting a further application for this work. This paper makes three primary contributions to the current state-of-the-art. Firstly, it identifies the differences observed between the ways source terms are included in the LBM schemes present in the literature. The algebraic manipulations are explicitly presented in this paper to clarify the differences observed, and identify their origin. Secondly, it derives in full detail, the implicit relation between the value of the transported macroscopic field, and the sum of the LBM densities. Moreover, this relation is valid for any source term discretization scheme, and three equivalent forms of the second-order accurate collision operator are presented. Finally, closed-form solutions of this implicit relation are shown for a variety of common models. The second-order convergence of the proposed LBM schemes is verified on both linear and non-linear source terms. Commonly used diffusive and acoustic scalings are discussed, and their pitfalls are identified. Moreover, for a simplified case, the competing errors are shown visually with isolines of error in the space of spatial and temporal resolutions

Nowe podejście do oceny wytrzymałości betonu w konstrukcji istniejącej wg PN-EN 13791:2019-12

Zaktualizowana w grudniu 2019 roku norma PN-EN 13791 wprowadza gruntowne zmiany w zasadach oceny wytrzymałości betonu w konstrukcji. W tym artykule przedstawiono zagadnienia dotyczące oceny betonu w konstrukcjach istniejących. Zwrócono uwagę na bardziej precyzyjne zasady dotyczące wyznaczania miejsca pomiarowego i koniecznych w jego obrębie punktów pomiarowych. Precyzyjniejsze są również zasady szacowania wytrzymałości betonu w konstrukcji. W podsumowaniu zestawiono główne różnice pomiędzy starą i aktualną wersją normy.Updated in December 2019, the PN-EN 13791 standard introduces profound changes in the rules for assessing the strength of concrete in construction. This article presents issues regarding the assessment of concrete in existing structures. Attention was drawn to more precise rules regarding the determination of the test region and necessary test location points within it. The rules for estimating the strength of concrete in a structure are also more precise. The summary contains the main differences between the old and the new version of the standard

The possibility of shrinkage strain reduction in cements mortars

The subject of the paper is presentation of action mechanism and effectiveness estimation of different types of chemical admixtures that make it possible to control the course of shrinkage strains associated with cement hydration process. There are presented tests results from the research program realization in which there were used the basic types of admixtures allowing for producing mortars and concretes with reduced or compensated shrinkage. In conducted tests there were applied admixtures based on calcium oxide, multi-molecule alcohol as well as water polymer dispersions (styrene-acrylic co-polymer - SA and styrene-butadiene latex - SBR). Their influence onto the magnitude of shrinkage strain and strength development for cement mortars was analyzed

Beton wyrobem budowlanym

Wskutek ustanowienia betonu wyrobem budowlanym, od 1 stycznia 2021 r. doszły nowe obowiązki dla uczestników procesu budowlanego. Dotyczą przede wszystkim producenta, który zobowiązany jest poddać się obowiązkowej certyfikacji zakładowej kontroli produkcji oraz ma wydać właściwe dokumenty - krajową deklarację właściwości użytkowych i oznakować wyrób znakiem budowlanym. Obowiązkiem odbiorcy natomiast jest sprawdzenie i gromadzenie tych dokumentów. W ślad za nowymi obowiązkami pojawia się ryzyko kontroli ze strony uprawnionych organów.As a result of making concrete a construction product, new obligations have been placed on the participants of the construction process from 1 January 2021. They mainly concern the manufacturer, who is obliged to undergo mandatory factory production control certification and has to issue the relevant documents - a national declaration of performance and label the product with a construction mark. It is the recipient’s responsibility to check and collect these documents. Following the new obligations, there is a chance of inspection by authorized bodies

Ocena betonu wbudowanego w konstrukcję w przypadku wątpliwości co do jego jakości

W grudniu 2019 roku opublikowano nową, gruntownie przeredagowaną wersję normy PN-EN 13791 dotyczącej oceny betonu w konstrukcji. Jedną z możliwości jej wykorzystania jest ocena betonu wbudowanego w konstrukcję w przypadku wątpliwości dotyczących jego jakości. Zupełnie zmieniono zasady planowania tych badań, ale także zasady oceny. Z punktu widzenia użytkowników normy, konieczność ich wdrożenia może na początku wydawać się uciążliwa, ale niewątpliwą zaletą nowej wersji jest dużo większa jednoznaczność i precyzja proponowanych procedur badań i oceny.In December 2019, a new, thoroughly re-edited version of PN-EN 13791 standard regarding the assessment of concrete in construction was published. One of the possibilities of its use is the assessment of concrete embedded in the structure in case of doubts regarding concrete quality. The planning rules for these studies have been completely changed, as well as the evaluation rules. From the point of view of the users of the standard, the need to implement these new rules may seem burdensome at first, but the undoubted advantage of the new version is the much greater clarity and precision of the proposed testing and evaluation procedures