Halina Garbalińska

The deterioration of strength and thermal properties of autoclaved aerated concrete as a result of capillary moisture

The deterioration of strength and thermal properties of autoclaved aerated concrete as a result of capillary moisture

Porosimetric, Thermal and Strength Tests of Aerated and Nonaerated Concretes

The paper presents the results of porosimetry tests of lightweight concretes, obtained with three research methods. Impact of different porosity structures on the basic thermal and strength properties was also evaluated. Tests were performed, using the pressure gauge method on fresh concrete mixes, as well as using the mercury porosimetry test and optic RapidAir method on specimens prepared from mature composites. The study was conducted on lightweight concretes, based on expanded clay aggregate and fly ash aggregate, in two variants: with non-aerated and aerated cement matrix. In addition, two reference concretes, based on normal aggregate, were prepared, also in two variants of matrix aeration. Changes in thermal conductivity λ and volumetric specific heat cv throughout the first three months of curing of the concretes were examined. Additionally, tests for compressive strength on cubic samples were performed during the first three months of curing. It was found that the pressure gauge method, performed on a fresh mix, gave lowered values of porosity, compared to the other methods. The mercury porosity tests showed high sensitivity in evaluation of pores smaller than 30μm. Unfortunately, this technique is not suitable for analysing pores greater than 300μm. On the other hand, the optical method proves good in evaluation of large pores, greater than 300μm. The paper also presents results of correlation of individual methods of porosity testing. A consolidated graph of the pore structure, derived from both mercury and optical methods, was presented, too. For the all of six tested concretes, differential graphs of porosity, prepared with both methods, show a very broad convergence. The thermal test results indicate usefulness of aeration of the cement matrix of the composites based on lightweight aggregates for the further reduction of the thermal conductivity coefficient λ of the materials. The lowest values of the λ coefficient were obtained for the aerated concretes based of fly ash aggregate. A diminishing influence of aeration on the volumetric heat capacity cv is clearly seen. Simultaneous aeration of the matrix and use of lightweight aggregates brought about also a significant decrease in the average compressive strength fcm of the tested composites.

Wave amplitudes of temperature and heat flux in the surroundings of external walls

S t r e s z c z e n i e W niniejszej pracy poddano analizie zbiór danych dotyczących dynamicznych charakterystyk cieplnych ścian zewnętrznych o różnie dobranej pod względem materiałowym warstwie konstrukcyjnej. Głównym celem pracy było porównanie amplitud wahań fali temperatury wewnętrznej i wewnętrznego strumienia ciepła w zależności od użytego materiału warstwy nośnej. Rozpatrzono przegrody z warstwą konstrukcyjną wykonaną z rozmaitych lekkich kompozytów betonowych, betonów komórkowych oraz betonu zbrojonego. Bardzo dobre właściwości tłumiące przegrody uzyskano dla kompozytów betonowych. Otrzymane dane wykazują, że tego typu rozwiązania zapewniają zdecydowanie mniejsze wahania fali temperatury i strumienia ciepła w porównaniu do materiałów o niskim cieple właściwym. Słowa kluczowe: dynamiczne charakterystyki cieplne, macierz przejścia, lekkie kompozyty betonowe, strumień ciepła * Prof. Halina Garbalińska, M.Sc. Eng. Jarosław Strzałkowski, Department of Building Physics and Building Materials, Faculty of Civil Engineering and Architecture, West Pomeranian University of Technology Szczecin. DOI: 10.4467/2353737XCT.16.212.5961 TECHNICAL TRANSACTIONS CIVIL ENGINEERING 3-B/2016 CZASOPISMO TECHNICZNE BUDOWNICTWO