Local post-glacial aggregates must not be excluded from the use for concrete pavements of fast road construction - this is the main conclusion of the II Eastern Road Forum, held March 15-16th in Suwalki in norhern-eastern Poland.
The conference was entitled "Aggregate - Cement - Concrete", what summs up its themes. The territories of north-eastern Poland abound in post-glacial aggregate deposits, such as sand, gravel and grits, which are used, among others, in road construction, but so far mainly in asphalt technology. Specifications for sections of express roads built in this part of the country, being part of the Via Baltica route, require the use of solid rock aggregates. This was explained by the fear of the risk of damage resulting from the alkaline reactivity of these aggregates.
The fact that it is unjustified, both aggregate producers and general contractors said. The former paid attention to the fact that alkaline reactivity also applies to rock raw materials, the latter - to the lack of economic thinking and unnecessary multiplication of logistic problems. As the president of one of the construction companies said during the Forum, in the situation of problems in rail transport resulting from from track closures, the transport of aggregates from Lower Silesia to the construction of the S61 road in the Podlasie and Warmian-Masurian Voivodships is absurd from an economic point of view. The price for transporting a ton of aggregates exceeds the price of the material itself if it were to be picked up in the mine.
The alkaline reactivity of domestic aggregates
The ASR-RID project "Alkaline reactivity of domestic aggregates" is intended to explain problems with the potential alkaline reactivity of aggregates (of various types). It is implemented by a consortium composed of the Institute of Ceramics and Building Materials in Krakow and the Institute of Fundamental Technological Research of the Polish Academy of Sciences. Preliminary findings resulting from research within the framework of the GDDKiA sponsored project, which were presented during the conference in Suwałki, indicate that no increased risk of alkali-aggregate reaction in the post-glacial material was found.
The aim of the project - as Dr Grzegorz Adamski reminded - is to develop criteria for assessing the reactivity of aggregates from various regions of the country, with the possibility of using in the system of control of their production and supply for the production of concrete for structures and road surfaces. The final product is to be technical guidelines for designing concrete with high durability, with particular emphasis on protection against damage caused by the AAR reaction.
The alkaline reactivity of aggregates was determined and evaluated using methods used in aggregate reactivity assessment systems in technologically leading countries. One difficulty was the fact that there are no European standards in this area that are being developed. The project adopted a system based on Amercian ASTM standards.
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Mineral aggregates, produced as aggregates for road infrastructure, from mineral resources exploited in various regions of Poland were subjected to research. These were: granite and basalt grit, traditionally used for structural concretes in road engineering, aggregates from crushed rock raw material, post-glacial sands from the regions of: Warmia and Mazury, Podlasie and West Pomeranien were tested, as well as solid rock material from the province of Lower Silesia. Foreign aggregates were also tested.
Samples from 17 gravel and crushed aggregate production plants and from 14 rock aggregate plants were collected for the study. The plants with significant extraction (at least several hundred thousand Mg / year) and resources enabling mining in the coming years were selected, explained dr Zdzislaw Nazimiec.
The reactivity of these tested aggregates was classified according to the AASHTO methodology (American Association of Highways and Transport Managers). In the ASTM C 1260 study (mortar furnace) aggregates completely crushed from pebbles, extracted in north-eastern Poland were included in this classification in two groups: non-reactive and moderately reactive. 6 cases of confirmed strong reactivity came from plants in other parts of Poland (the project does not reveal the exact names of the plants from which samples were taken). Also gravel aggregates and sands from this region proved to be unreactive.