Jan Suda

Influence of Micro-Milled Secondary Materials Used as Binders in Low Level Stabilized Cold Recycled Asphalt Mixtures

This paper presents an experimental verification of the alternative options for using by-products or mineral waste materials applied to cold recycled mixtures with low level of stabilisation intended for low-volume road structures. To achieve the necessary refinement and a certain level of reactivity potential, the by-products were activated mechanically, i.e. pulverized in a high-speed disintegrator with respect to the lowest possible energy demands of the process and to the level of wear-and-tear of the working components in the milling machine. Such refined material, with average particle size of 10-15 μm, is applies as an active filler component allowing to partly substitute hydraulic binder in cold recycled mixtures. The application of such materials in structural pavement layers should increase the environmental benefits and result in added economic value. The experimental measurements taken focused on cold recycled mixtures with low level of stabilisation, modified by a combination of binders, or namely cement, mechanically activated concrete from reclaimed concrete pavement slabs originating from the Czech backbone D1 highway modernisation, mechanical-chemically activated fluid ashes from the Pilsen heat plant and foamed bitumen. Both basic volumetric properties and strength and deformation parameters were set for the purposes of evaluation of the characteristic measured in the experimental mixes.

Potentials for Using Mechanically Activated Concrete Powder in Stabilized Granular Pavement Mixtures

Stabilization of granular materials is a common practice in transport infrastructure structures. It is used mainly for improving the roadbed or for achieving higher performance of base layers. The traditional approach is to use cement, lime hydrated, hydraulic road binder or standard fly-ash in mixing with soil or granular material (gravel) to get a hydraulically bond mixture which then shows improved bearing capacity and better resistance to water immersion or frost impacts. However, most of the binders (especially cement) show higher carbon footprint and represent therefore increased socio-economic cost of the structure. On the other hand, yearly many old structures are demolished and waste is created often containing huge volume of concrete material, which can be crushed and reused as a granular material. At the same time this material can be treated by high-speed milling (disintegration) process and it is possible to achieve a partial reactivation of the cement components in the concrete. This paper presents some of the achievements in soil stabilized materials and cold recycling mixtures where activated micromilled concrete powder/fine ground recycled concrete (FGRC) was used as an active filler or a binder substitute. The effect of the micromilled concrete powder with respect to its content or combination with other binders or additives is described further. Regular tests like Proctor Standard, CBR or compressive strength, indirect tensile strength or stiffness determination are done. The effect to act as an alternative binder is studied not only it terms of used content, but also with respect to its impact during test specimen curing. Finally, some recommendations are given in this paper with respect to the practical application of such material.

Potentials for Using Pulverized (Micro-Milled) Mineral Waste Materials as Stabilizing Agents or Fillers in Cold Recycled Mixes

Presented paper introduces alternative solution to use another types of secondary materials or potential waste materials in cold recycled mixes either as active filler, partial miner admixture or a substitute to hydraulic binders. The intention of the study described by this paper is to describe additional potentials of high-speed grinding if applied to selected mineral waste materials. The use of such materials should have also its environmental and economic benefit. Environmentally it might be a solution for treating waste materials or by-products to get solutions with higher technical added value. The preliminary study focused on two types of fine-grained mineral by-products which were pulverized to a size below 50 µm with expected mechanical or mechano-chemical activation. These microfillers were applied to standard cold recycled mixtures which came e.g. from the European research project CoRePaSol (see www.corepasol.eu) and standard tests were performed to evaluate the potentials of using the pulverized limestone or recycled concrete either as active filler or binder substitute. Results are summarized by this paper showing any effect on strength properties, but for several options highlighting improved durability in terms of moisture susceptibility. Higher potential can be expected with pulverized concrete where reactivity of the material might occur as the result of presence of hydrated cement.

Cold bituminous emulsion mixtures - laboratory mix design, trial section job site and monitoring

Presently the road construction engineering focuses on technologies, which allow reducing energy demand of the structures to be built. This is closely linked to cutting the release of CO2 emissions and at the same time to the effort reducing costs for new structures or for rehabilitation works. Cold emulsified asphalt mixtures are a kind of road building material which is defined by using specific type of binder and ambient mixing temperatures. Typical is that their cohesion in the early stage after paving is rather lower and increases gradually during the curing period. Specific properties of these mixes support their use mainly for low-volume roads. These mixes have longer tradition in France and partly in the UK. In the Czech Republic very limited laboratory and practical experience are available for these mixtures. Until recent time there were even no technical specifications giving rules for design and use of these cold mixtures. This paper presents laboratory methodology which was used for cold emulsified asphalt mix design and describes results from such design. Additionally long-term assessment of experimentally evaluated characteristics is included as well. Since the real behavior of such mix in pavement structure cannot be with sufficient credibility described by laboratory tests a trial section was realized in 2014. This should bring additional verification of the experimental findings. For the trial section a low volume road was selected where existing pavement dimensions were known and data about daily average traffic were available. Reconstruction was expected with subsequent monitoring of the new structure with respect to traffic and climatic effects. The trial section was divided into 6 subsections with 5 different options of pavement design to evaluate effects of designed cold bituminous emulsion mixes in wearing and binder course. The mixes were designed in some of the options with 30 % of reclaimed asphalt (RAP). Experience from the first trial section in the Czech Republic and data of site monitoring are presented in this paper.

Mix designs for cold recycled pavement materials considering local weather and traffic conditions

Cold recycling is a road rehabilitation procedure/technique, where the reclaimed road material from rehabilitated pavements is recycled completely and used in the new structure with only small contents of new road materials. This is done preferably in-situ to save time, costs and environment. However, internationally various mix design procedures were developed since decades resulting in diverse contents of bituminous binders (emulsion or foamed bitumen) and/or mineral binders (cement or hydraulic road binder). The different material compositions result in diverse mechanical material properties and demand for different pavement designs. Based on an international comparison of cold recycling experience, commons and differences were elaborated during European CoRePaSol project funded by the CEDR. The existing definitions of various cold recycled materials were assessed and supplemented in order to introduce clear material definitions in future European specification documents. Based on intensive test campaigns suitable assessment procedures are proposed to address these materials. At the same time based on local traffic and weather conditions as well as availability of source materials, a decision model is proposed for choosing the optimum cold recycling material for the given rehabilitation project.

The Effects of Bituminous Binders on Cold Recycled Mixes Prepared by the Foamed Bitumen Technology

The foamed bitumen technology is experiencing a global renaissance and rather extensive development of innovative approaches with respect to both, its application and research, is clearly visible. However, the variability of available bituminous binders for utilization within the technology is quite large; therefore, a general methodology of quality parameters determination for foamed bitumen and the requirements for mixes bound by this type of binder must be specified.In general different types of pen grade bituminous binders can be used for producing the foam. Besides the pen grades which are defined by penetration and also its viscosity, the source of the bitumen can have important effect on final foamed bitumen quality given especially by its expansion ratio and stability of the foam as well. Experimental study has been done to compare different types of bitumen from different sources to assess the effects on the foamed bitumen and on cold recycled mixes produced by these binders. In parallel the effect of a suitable foaming agent has been assessed as well. The foamed bitumen was analyzed by its expansion ration, half time defining the stability of the foam and the so called foam index. Cold recycled mixes were produced with one type of reclaimed asphalt material and different foamed bituminous binders. For the mix assessment mainly indirect tensile strength, water susceptibility and stiffness modulus have been considered. Results and comparison of the evaluated effects are presented in this paper.

Experimental Assessment of Fly-ash Stabilized Mixes Exposed to Freezing and Water Immersion

The utilization of fly-ash stabilizers, fly ash from fluidized combustion and other solid products of combustion, and desulphurization arising during the production of electricity have a good potential for use in the roadbed structures of pavement structures. With a lower density and high shear strength, fly ash reduces the ground subsidence and pressure on supporting constructions during the construction of roadbed structures. In the coming years, an increased focus on the use of these materials can be expected with regard to the continuation of the road infrastructure construction. One of the possible factors blocking the use of some types of fly ashes is their relatively little resistance to repeated contact with water and resulting volume changes. Their water sensitivity is well known. Given the negative properties of fly ash, which occur mainly in repeated contact with water, it was decided to pay attention to the testing of the resistance of these mixes to the combined effect of freezing and water within the experimental activity. Fly-ash stabilized mixes were designed with the use of ashes from two combustion technologies with different contents of binder and also including the influence of selected chemical additives and binders such as lime hydrated or mineral admixtures such as chemomechanically activated dolomitic lime.

Impact of the Compaction Method Applied on Selected Characteristics of Cold Recycled Asphalt Mixes

The quality of cold recycled asphalt mixes in most European countries is currently characterized primarily by indirect tensile strength or stiffness assessed after the defined curing period. These characteristics are usually supplemented by residual values of both parameters after immersion in water. This way of assessing quality empirically is very simple, fast, and well-established. Conversely, it also has some unnoticed weaknesses. A major disadvantage is probably the strong dependency on various factors like, e.g., the method of test specimen compaction. Technical specifications in different European countries prescribe the preparation of test specimens by using different equipment that is based on static, dynamic, or slow rotational compaction (gyratory compactor). The laboratory compaction method applied naturally affects bulk density and voids content, thus directly influencing the values of indirect strength or stiffness modulus as well. This paper focuses on the assessment of cylindrical test specimen preparation and its effect on quality determination for cold recycled asphalt mixes. The specimens were prepared by a static pressure compacting machine, Marshall hammer and gyratory compactor. Two mixes were used, one of them containing bituminous emulsion and the other one with bituminous foam, whereas the cement content was identical.