Effect of varying silica-limestone sand fines on the physical-mechanical performance of concrete

The use of crushed limestone sand in the concrete industry will be quite possible and imperative for environmental reasons. Many researchers around the world have found that concrete based on 50% substitution of river sand by limestone sand gives better physico-mechanical characteristics. The main objective of this investigation is to search for an optimal percentage of silica-limestone fines resulting from the substitution of half in quantity of alluvial sand by crushed limestone sand in ordinary concrete. The proportions of fines that were tested in this work are 6%, 8%, 10%, 12% and 14%. The obtained results revealed that concrete based on silica-limestone sand and containing 14% of the same type of fines strongly improves the different mechanical strengths and participates in the reduction of 10% and 13%, of the coefficient of capillary absorption and of the porosity accessible to water, respectively, compared to the control concrete. In addition, good statistical relationships between the studied parameters were also found

Understanding the Microstructure of Mortars for Cultural Heritage Using X-ray CT and MIP

In this study, the microstructure of mock-up mortar specimens for a historic environment, composed of different mixtures, was studied using mercury intrusion porosity (MIP) and microcomputed tomography (µCT), highlighting the advantages and drawbacks of both techniques. Porosity, sphericity, and pores size distribution were studied, evaluating changes according to mortar composition (aerial and hydraulic binders, quartz sand, and crushed limestone aggregate). The µCT results were rendered using 3D visualization software, which provides complementary information for the interpretation of the data obtained using 3D data-analysis software. Moreover, µCT contributes to the interpretation of MIP results of mortars. On the other hand, MIP showed significant ink-bottle effects in lime and cement mortars samples that should be taken into account when interpreting the results. Moreover, the MIP results highlighted how gypsum mortar samples display a porosity distribution that is best studied using this technique. This multi-analytical approach provides important insights into the interpretation of the porosimetric data obtained. This is crucial in the characterization of mortars and provides key information for the study of building materials and cultural heritage conservation.

Bitumen aging on the surface of crushed limestone at high temperatures

In road structural layers, mixtures of crushed limestone with oil bitumen are used as a structural material (black crushed stone), or as a part of asphalt concrete organic-mineral mixtures. Since limestone deposits are located in a great number of regions, their increased use makes it possible to reduce transportation costs in the estimated road construction cost. In the meantime, it is necessary to conduct a study of the aging of bitumen-mineral mixtures during their preparation and use in road structures when using local limestone materials. This article presents the results of the studies, during which the effect of bitumen aging on some properties of bitumen-mineral mixtures was studied using a new method. The developed method for studying bitumen aging compares favorably with the already known methods and is protected by the Patent of the Russian Federation No. 2654954. Due to this method, it becomes possible to study the effect of aging on the values of any indicator according to a single model – both complex (e.g. asphalt concrete) and simple systems (crushed stone-bitumen, sand-bitumen, etc.). This approach provides a more accurate prediction of the material behavior both during preparation and service in road structures. The execution of work involves the preliminary establishment of the optimal bitumen and crushed stone ratio, at which the highest average density and ultimate compressive strength at +20 °C is provided. Laboratory testing of samples indicated the dynamic pattern of the value of the aging coefficient and the aging rate in terms of the ultimate compressive strength at +50 °C and the elastic modulus.