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.

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.

The rapid growth of traffic loads in Latvia increases the demands for asphalt carrying capacity on large motorways. The dolomite and sandstone that can be found in Latvia lacks the mechanical strength and for most of the large motorways the aggregates are imported from other countries causing increase of costs and growth of emissions from transportation. On the other hand, large amounts of Basic Oxygen Furnace (BOF) steel slag aggregates with good qualities are being produced in Latvia and put to waste. During the recent decades, the dolomite sand waste has also been accumulated and its quantity has reached a million of tons and is rapidly increasing. This huge quantity of technological waste needs to be recycled with max efficiency. The lack of experience in the use of steel slag and dolomite sand waste requires an accelerated evaluation of the asphalt performance-based characteristics. This paper presents the testing results of dense graded asphalt concrete AC 11 mixtures made of four types of aggregate: steel slag, dolomite sand waste, conventional imported dolomite aggregates and conventional local crushed quartz sand that were proportioned to develop a mixture that would satisfy the requirements of permanent deformation and stiffness. Analysis of the results showed that the mixes with steel slag and dolomite waste sand or unconventional aggregate combination with dolomite in coarse portion, crushed quartz sand in sand portion plus dolomite waste sand in sand and filler portions had high resistance to plastic deformations and fatigue failure. These mixes can fully satisfy and in some cases significantly overcome the requirements of local asphalt specifications for highly loaded motorways.

The rapid growth of transport load in Latvia increases the demands for asphalt carrying capacity on large motorways. The limestone and sandstone that can be found in Latvia lack the mechanical strength and, for most of the large motorways, the aggregates are imported from other countries causing increase of the costs and growth of emissions from transportation. On the other hand, large amounts of basic oxygen furnace (BOF) steel slag aggregates with good qualities are being produced in Latvia and put to waste. During recent decades, the dolomite sand waste has been accumulating and its quantity has reached a million tons and is rapidly increasing. This huge quantity of technological waste needs to be recycled with maximum efficiency. The lack of experience on the use of steel slag and sand waste requires an accelerated evaluation of the asphalt performance-based characteristics. This paper presents the testing results of different combinations of steel slag, dolomite sand waste, and local limestone aggregates that were proportioned to develop a mixture that would satisfy the requirements of permanent deformation and fatigue. Analysis of the results showed that mixes with steel slag and local limestone in coarse portion and dolomite sand waste in sand and filler portions had high resistance to plastic deformations and good resistance to fatigue failure. These mixes can fully satisfy and, in some cases, significantly overcome the requirements of local asphalt specifications for highly loaded motorways.

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