Jan Valentin

Influence of Recycled Concrete Composition on its Elastic Stiffness

The presented study was focused on the influence of the micronized recycled a concrete sleeper on the mechanical properties of fine-grained concrete, specifically on dynamic modulus of elasticity. The tested material consisted of cement CEM I 42.5R (Radotín), crushed bricks fraction 2-5 mm, 0-4 mm sand and micronized recycled concrete fraction 0-0.125 mm. Individual material samples differed in the quantity of cement and finely ground recycled concrete (milled at Ltd. Lavaris, Libčice – Czech Republic). Cement was replaced by the recycled concrete in an amount of 30, 50 and 70 weight percent. Testing was performed on beams of dimensions 40 × 40 × 160 mm by using non-destructive testing – pulse method. The article compares the values obtained between 2-nd and 28-th day.

Impact of selected WMA additives on normal PMB used for a standardized SMA

WMA techniques are well known for many years, even if still not increasingly popular in Europe. In the Czech Republic so far these techniques – mainly different types of wax based additives and surfactants – were used for asphalt concrete and usually in combination with a normal pen grade (70/100 or 50/70). As part of an ongoing research the focus was laid on SMA mixes which are as in any other country used mainly as a top wearing course for pavements with highest loadings and life-time expectations. Even if it is still allowed to use normal distilled bitumen, the best effect is achieved if PMBs are applied. For this reason a typical mix design for SMA11 mix was selected and more than 15 different binders have been used divided in three groups – two where effect of different WMA additives was analysed on PMB 25/55-55 of two selected origins and last group containing a more modified binder (not for WMA) and a 50/70 binder modified by PPA. As WMA additives different waxes have been used, selected surfactants and a nano-based additive. Firstly all bituminous binders were analysed by empirical tests, dynamic viscosity, MSCR and frequency sweep test. Then the mixes were prepared with a temperature reduced by 20-25°C in comparison to reference mix, For all mixes voids content, stiffness, ITSR, rutting and crack propagation was analysed and will be summarized in the paper.

Development and verification of a suitable methodology for stability assessment of bitumen adhesion promoters

Durability of pavement structures represents one of the most important aspects increasingly followed during last years. There are many reasons for this focus, most important are related to public budget constraints and the necessity to develop or rehabilitate road infrastructure. Since many years there has been a stress on using locally available resources which is for asphalt related mainly to the aggregates. On the other hand bitumen comes from a nonrenewable resource which is used to cover many demands of the world’s society. To keep it simple, remaining byproduct is then classified as bitumen what has of course impact on its qualities as well. In case of asphalt pavements durability is related to water and frost resistance of the mix. The water can cause problems if adsorbed by the aggregates. This happens if hydrophilic aggregates are used and the coating by bitumen is not good. For these reasons different additives are used to improve coating and turn the hydrophilic state to a hydrophobic one. Plenty of solutions are available on the market sometimes making the decision for not easy to make a right choice. Since decades test methods have been developed to study durability aspects, adhesion or water susceptibility. In many countries like the Czech Republic simple methods are still used, often based only on observer’s visual opinion and especially often qualifying only the status of a doped bitumen/mix when being produced. This is valid for all test methods defined in EN 12697-11 and similarly also in the national test method used in the Czech Republic. Based on this fact a research project was launched to ideally define a suitable test procedure for evaluating thermal stability and long-term activity of adhesion promoters if used in the bitumen and applied in a mix. This paper is describing how the test method was selected and evaluated, what are the principles the method is based on, if applicable only to the bitumen-aggregate coating quality or analyzing the water/water-frost impacts more. Results are given for the tests done and for assessment of different adhesion promoters. Test protocol is proposed at the end defining necessary conditions.

Analyzing the durability of adhesion stability of asphalt mixtures

Adhesion is one of the fundamental characteristics related to asphalt mixtures. It determines significantly the durability of asphalt mixture and depends not only on the quality of aggregate particles coating but also on the hydrophobity or hydrophility of the aggregates. For this reason often mineral-based or chemical additives are used to improve adhesion between bitumen and aggregate particles. Mainly with the latter group of additives long-term stability is connected. Amine based additives are often used which unfortunately contains easily volatile compounds. If part of the effective substance is evaporated during mixing and paving the later durability can be negatively influences. Therefore it is important not only to assess the adhesion when virgin bitumen and aggregates are used, but also the artificially aged binders or asphalt mixtures have to be evaluated. For this reason long-term research is in progress at the Czech Technical University in Prague focusing on different aggregates (different mineralogy) and different adhesion promoters. Tests are run on virgin materials as well as on specimens long-termly aged (either bitumen by RTFOT+PAV or 3xRTFOT/TFOT, or asphalt mixtures which are usually aged for 5 days at 85°C). For bitumen-aggregate adhesion determination a standardized procedure according to CSN 736161 is performed. For asphalt mixtures the water susceptibility test according to EN 12697-12 is done on Marshall test specimens compacted by 2x25 blows. The paper presents some of the findings, including the impact of long-term ageing effects

Effect of a Poly-olefin Based Additive on Bitumen and Asphalt Mix Performance

Based on the comparison of the selected characteristics of laboratory prepared modified binders, different blends of bituminous binders with added poly-olefin based additive (PAO) were evaluated alone or in combination with styrene-butadiene-styrene (SBS) polymers. The basic type of bitumen used for the modification was a paving grade 50/70. The second reference binder was an industrially produced polymer-modified bitumen PMB 40/80-85. The properties of bituminous binders were evaluated using selected empirical tests and functional tests on Dynamic Shear Rheometer and viscosity test. Additionally, assessed binder variants were used in a stone mastic asphalt (SMA) mixture, and bitumen properties were compared with performance behavior of the mixture, mainly, stiffness, water susceptibility, resistance to permanent deformations, and behavior in the low temperature range. The results show that the effect of the PAO additive depends mainly on the base binder used. It is a more affordable variant than conventional PMBs from an economic point of view, although the resulting properties with PAO additive are not comparable to those of traditional PMBs. The PAO may be used as a certain intermediate performance product between paving grades and PMB binders.

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.

Alternative Additives for Improving the Functional Characteristics and Performance-Based Behavior of Asphalt Mixes in the Fine-Grained Active Filler Form

Deterioration of asphalt pavements by water immersion and increased moisture content, presents one of the principal issues for pavement technologists. Especially if concentrating on initial phases of the life-cycle of a pavement. Water in the form of rain precipitation and natural air moisture can be harmful to the bonds between bitumen and aggregate particles, which occurs through the medium deteriorated adhesion on the interface of those phases, or the overall deterioration of the adhesion. Even if it might look at the first glance that bituminous binder creates perfectly impermeable layer of particular aggregate particles, in reality the bitumen film makes unstable coating of aggregates in unequal thicknesses and frequencies. Those weakened areas are far more susceptible to water and moisture affects, which enter the asphalt layer on the boundary of aggregates and bituminous binder. To improve the adhesion between bitumen and aggregates and to get in general better functional characteristics of asphalt mixtures large number of available additives exists in civil engineering. First group can be defined as additives which are added directly to the bituminous binder and provides a kind of bitumen modification. Second group includes mineral additives, which may partially or completely replaced fine-grained particles, normally in the form of filler. In this article the objective was set to qualify effect of mechanically activated microfiller originating from limestone by-products or from recycled concrete as a substitute to fine-grained active filler in asphalt mixtures. The research targeted to utilize waste materials and to contribute to the reduction of overall negative impacts to the environment.

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.

Impact of a Poly-olefin Based Additive on Bitumen and Asphalt Mix Performance

Based on the comparison of the selected characteristics of laboratory prepared modified binders, different version of bituminous binders with added poly-olefin based additive (VP) alone or in combination with SBS polymer were assessed. The basic type of bitumen used for the modification was a paving grade 50/70 to which 5 M% and 6 M% or only 1 M% but in combination with a selected type of SBS (quantity of 3 M%) were added. Frequency sweep test (complex shear modulus) and MSCR test was done on virgin and aged binders. Additionally assessed binder variants were used in a SMA mixture and bitumen properties were compared with performance behavior of the mixture – mainly stiffness, water susceptibility and resistance to permanent deformations.

Influence of Asphalt Mixture Ageing and Lowered Laboratory Compaction Rate on Stiffness and Cracking Behavior

Ageing is one of the fundamental phenomena related to bitumen and asphalt mixtures. Traditional problem of asphalt testing is that most of the characterizations done presently reflect ageing only in limited manner. Nevertheless the behavior of a pavement structures is on the other hand dominated by natural effects like ageing. Similarly very important issue related to good job quality is in case of asphalt mixtures the compaction rate of asphalt layers. Compaction rate is often a factor which has very significant impact on the durability, but it is often neglected or the attention which is given to proper compaction is not sufficient enough.