Over the recent years the amount of fast destruction defects of cement paste matrix has increased markedly for exposed concrete structures of highway and airport pavements. The accelerated destruction of silicate structure is unusual due to its irregular occurrence. It only occurs at 30 to 50% of newly built pavements (in continuous segments). The issue is applicable to loaded as well as unloaded pavements. Detailed diagnostics found that the probable cause is based on concurrently occurring expansive reactions in capillaries, cracks and pores in the cement paste matrix. In defect spots the presence of several expansive substances was proven, wherein the biggest question poses the unexpectedly high potassium concentration. Potassium is only contained at best in trace amounts in road concrete input components in the Czech Republic. Neither existing regulations nor standards sufficiently deal with this type of defects of cement concretes. If they mention the existence of this issue at all, they are just limited to recommendations. Since the modification of the existing commercially produced cements to pavements is still improbable, the solutions to this issue seem problematic.
The evaluation of the bearing capacity of asphalt pavements is usually performed by analysing the deflections measured by a Falling Weight Deflectometer (FWD). The deflection changes with the pavement temperature. In evaluation is necessary to consider the thermal gradient of pavement and perform the temperature correction. The article contains an analysis of effects of the pavement temperature on FWD results on the long-term monitored sections. The temperature correction was performed on measured deflections or back-calculated elasticity moduli. The moduli recalculated to the temperature of 20 °C according to both procedures were similar. Comparison of moduli determined by recalculation to moduli backcalculated from the deflection bowls measured at the temperature of 20 °C, has proven smaller differences for the moduli determined from the deflection bowl corrected to the temperature of 20 °C.
The California Bearing Ratio (CBR) is a test designed to measure the bearing capacity of the subgrade during a construction of roads. It has also been used as a baring capacity test for unpaved aircraft runways and other transport areas. Nowadays, CBR is used as a proof and control test in evaluating the bearing capacity of subgrade and structural layers of roads. A distinction is made between the laboratory test and the in-situ test, which is nowadays no longer widely used. This is due to several reasons. It is primarily about the physical demands of performing the test. Another limiting factor is that it can only be used in case of fine-grained materials.
This paper deals with the development of an automatic lightweight dynamic cone penetrometer, verification of its functionality in the laboratory geotechnical field, describing the progress and results of comparative measurements with mechanical DCP. Also, the CBR values obtained by the classical way from the collected samples and the CBR obtained by recalculation from the measured values by the automatic DCP in-situ will be compared.
AbstraktV dnešní době je kladen stále větší důraz na ochranu životního prostředí. Tyto nároky se samozřejmě nevyhnuly ani silničnímu stavitelství. Pro výstavbu většiny pozemních komunikací se využívají asfaltové kryty, přičemž při výrobě těchto směsí je potřeba dosáhnout vysokých teplot, což je energeticky náročné a zároveň dochází k zatěžování životního prostředí. Aby se tyto negativní vlivy co nejvíce snížily, rostou snahy o snížení pracovních teplot se zachováním vlastností směsí. Výsledkem jsou tzv. teplé asfaltové směsi (Warm Mix Asphalt -WMA). Cílem tohoto článku je seznámení se základními metodami snižování pracovní teploty s konkrétním zaměřením na technologii pěnoasfaltu a jejím využitím v České republice.
Klíčová slovaAsfaltová směs, asfaltové pojivo, asfaltový beton, pěnoasfalt
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