The assurance of asphalt pavement layer compaction, expressed by ratio between field and laboratory bulk density and air voids content, is one of the main criteria of the durability of asphalt road pavement. Destructive measures should be applied and cores should be taken from the asphalt pavement seeking to determine the representative compaction level of the constructed asphalt layers. New methods are constantly being sought for fast, non-destructive and accurate asphalt layer density and air void determination on road. Ground Penetrating Radar (GPR) can allow determining the qualitative characteristics of asphalt pavement across the entire length of the road without causing damage to the road structure. Relative dielectric permittivity, usually called dielectric value or constant, is the leading property used in GPR applications on road pavement surveys. This article presents GPR measurement results from asphalt base and binder layers of four test sections. GPR measurements were conducted immediately after the end of asphalt layer compaction process. Test points on each layer were selected and density, air void content were determined by drilling cores and testing them in the laboratory. To estimate asphalt layer density and air void content, GPR data were analysed using different existing mathematical models. To justify the reliability of the data measured by GPR, results were checked by comparing them with the results measured directly on cores taken from the asphalt pavement layers.

Warm mix asphalt (WMA) technologies allow significant lowering of the production and paving temperature of the conventional hot mix asphalt (HMA), which promise various benefits, e.g. lowering the greenhouse gas emissions, reduction of energy consumption, improved working conditions, better workability and compaction, etc. However, in order to reach widespread implementation of WMA, it is necessary to prove that it has the same or better mechanical characteristics and long-term performance as HMA. This article presents a laboratory study that has been conducted to evaluate two different WMA technologies -chemical (using Rediset WMX) and organic (using Sasobit) for the use with stone matrix asphalt (SMA). The properties of two types of bitumen after modification with two different dosages of each WMA additive have been tested by traditional empirical test methods and with the Dynamic Shear Rheometer for a wide temperature range. Asphalt testing has been performed for SMA11 type mixture. At first, the necessary changes in testing conditions were determined by means of asphalt stiffness -the results suggested that for adequate comparison with reference HMA, at least two hour asphalt aging is essential before preparing test specimens. The properties of asphalt were determined for specimens that were prepared at four different compaction temperatures by means of two compaction methods -Marshall hammer and gyratory compactor. The test results show that it is possible to reduce the compaction temperature of 155 °C for HMA to at least 125 °C for both WMA products with maintaining similar density and mechanical characteristics at intermediate to high temperatures.

Asphalt pavement in actual circumstances is subjected to the repetitive and changing transport load. As a result of the repetitive load impact, both elastic and plastic deformations occur to the pavement. Accumulation of plastic deformations in one or several layers leads to appearance of permanent deformations or rutting. This type of deformations reduces safety and convenience of traffic. Aim of the research is investigation of the rutting dynamics on the dense graded asphalt concrete (AC) and stone mastic asphalt (SMA) mixtures. The research has been made by using the standard performance test method-wheel tracking test (WTT). Five compositions of the dense graded AC mixture and two compositions of the SMA with the conventional aggregate and one reference mixture AC 11 with the Martin steel slag aggregate have been used in the experiment. The B70/100 unmodified bitumen and SBS modified ModBit 80B has been used for the investigated mixtures. The results have shown poor strain stability of the conventional mixtures with unmodified bitumen under the heavy transport load, in comparison with the reference mixture AC 11 and SMA with modified bitumen. The results of investigating the rutting dynamics under the intensive heavy transport load have shown that the allowed rut depth 25 mm is reached already during the first year of the asphalt pavement exploitation.

Abstract. Warm Mix Asphalt (WMA) production technologies allow lowering the production and paving temperature of the conventional Hot Mix Asphalt (HMA) by at least 20°C without compromising the performance of asphalt. This promises various benefits over HMA, for example, allows to reduce the energy consumption, thus lowering the greenhouse gas emissions, permits to extend the paving season, attain better compaction, provides longer haul distances etc. However, in order to reach widespread implementation of WMA, it is necessary to provide enough information to the decision makers on the benefits of this technology. This article presents an overview of different WMA products and production principles, benefits and drawbacks associated with the technologies. A total of fifteen products that were found to be used in Europe are reported in the paper. However, not all of the technologies are suitable for Latvia, because of the necessary financial investments, climate, local legal provisions and the industry traditions. Potentially most favourable technologies for Latvian conditions are analysed with the reference to local road specifications.

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