Preliminary Studies on a Lightweight Porous Cement-Based Composite – Gel Concrete

Abstract

This paper presents some preliminary results of research on light, highly porous cement composites – gel concretes. A material based on Portland cement was tested, the very high porosity of which (over 60%) was obtained by direct gelatinization of starch in a liquid cement slurry. A composite based solely on cement and concretes produced with the addition of metakaolin or zeolite was tested. The basic properties of the concretes obtained in this way were determined, i.e., the volume density in a dry state, the thermal properties, and the compressive strength. In the case of the thermal properties, tests were performed on specimens dried to constant mass, while the test itself was carried out at an average temperature of 10°C. The tests employed an Isomet 2114 apparatus, which uses a non-stationary heat flow technique. The thermal conductivity coefficients and the volumetric specific heat were determined. The compressive strength tests were carried out on cubic specimens with a side of 4 cm after 28 days of curing by air-drying. Four specimens of each type of composite were tested. For composites based solely on Portland cement, the sorption properties of the material were also tested. For this purpose, the method of dynamic water vapor sorption (DVS) was used. As a result, graphs of the sorption and desorption of individual composites of different densities were obtained. Preliminary qualitative tests were also carried out using an electron microscope. The use of the starch gelatinization process directly in the cement slurry made it possible to obtain a very homogeneous material, in which the initial, temporary structure was starch gel, around which, after exceeding the setting time of the cement, the target cement-based structure was formed – gel concrete. The tested materials are innovative, having excellent thermal properties, comparable mechanical properties to lightweight concretes of the same densities, and is formed using an easily available, relatively cheap admixture in the form of starch. They can be used to produce small masonry elements, such as blocks for external walls or other typical prefabricated lightweight concrete elements.