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A new technology for the rehabilitation of wearing course

ART - Asphalt Repair Technology: Simex proposal for low traffic roads maintenance

  Rehabilitation of wearing course
Per la versione in Italiano:
https://www.stradeeautostrade.it/attrezzature-e-componenti/tecnologie-per-interventi-superficiali-di-recupero-funzionale/

Road maintenance is such an important issue that the implications are nowadays also of political nature. Very often the poor state of maintenance affects our roads safety as well as the ride comfort. In an advanced country, no exception should be allowed even on the latter, but certainly safety is the top priority.

The concept of road maintenance is related to pavement life cycle. The following diagram (Figure 1) is one of many available in literature. Simply explained, it means that doing tomorrow what should be done today is much more expensive for Authorities, therefore ultimately for the tax payer, and penalizing for users.

The structural requirements of a pavement include the bearing capacity (necessary to withstand vehicle loads) and durability intended as resistance to degradation. The functional requirements include the grip between tires and the rolling surface and the evenness of road surface; therefore, strictly connected to driving comfort and safety.

Pavement life cycle
1. Pavement life cycle

The concept is certainly not new for professionals and on major roads maintenance is part, although often not to the extent needed, of managing protocols. The so-called minor roads are quite different; as the term minor indicates a mere technical category which, however, does not necessarily reflect the priority within the given community. In essence, we get used to the fact that the roads must be short-lived, not very comfortable and safety delegated only to the due care of drivers.

Thus often, notwithstanding life pavement cycle concept, we see little and poor maintenance, only when situations become unsustainable or dangerous. Then the usual cold asphalt patch laid with a shovel (due to last a few months if not weeks), the absence of sealing in due time, and lastly the laying of a new wearing course on inadequate surfaces or, worse, on roads with deep structural weakness.

These are not solutions rather, at best, palliatives that in any case generate costs but for a very marginal result. There are many types of pavement distress and those are well described in technical literature. As an example, a brief summary follows.

Simex ART 1000 main features
2. Simex ART 1000 main features

Types of pavement distress

Flexible pavement distresses can be grouped in some broad categories:

  • Cracks, depending on type and cause, can be referred to as crocodile cracks, blocks, reflective cracks and others;
  • Unevenness such as deformations, rutting, shearing, depressions, bulges;
  • Stripping, detachments, potholes;
  • Loss of skid resistance due to bleeding or polishing.

As obvious as it may sound, one should bear in mind that a road pavement is a structure and not a simple two-dimensional “strip”; a structure subjected to different loads and stresses and consequently to deformations of various kinds. Unfortunately, that often seems to be forgotten when we observe the current maintenance on our roads, on the secondary ones at least.

Municipalities have limited resources and they therefore try to restore large areas with the little resources available; however, spreading a maintenance budget on an areal basis rather than on the basis of technical priorities does not generate real solutions, at most it mitigates and postpones the problem. 

Crocodile cracks
3. Crocodile cracks at Via Astengo in San Giovanni in Persiceto (Italy)

The Simex proposal

With the above in mind, Simex intended to design an equipment capable of ordinary maintenance with the following objectives, difficult to find in the market today:

  • quality of solution;
  • durability of solution;
  • possibility of recycling the material thus produced in subsequent processes;
  • no environmental impact.

In essence, road repairs that can last an extended period of time, ensuring safety and ride comfort with an operational flexibility not available on the market (https://bit.ly/3voYP2Z).

Specifically, Simex has decided to develop a technology with an operative depth between 5 and 7 cm. Starting from the well-established self-leveling milling technique of the PL series (planers), it makes use of an ecofriendly chemical admixture to regenerate, through a cold process, the RAP produced.

In cooperation with the Department of Civil, Chemical, Environmental and Materials Engineering of the University of Bologna – various laboratory and site tests were carried out, proving the effectiveness of the approach. The model presented at Asphaltica 2021, provides a preview of the equipment that will be launched on the Italian market in the second half of 2022.

Milling depth
4. Milling depth set at 50 mm

Simex method

Simex ART takes care of all the process with a single attachment. The mobile job site with a team of few workers is quick and lean since everything needed can be transported to the site by a single vehicle that carries the skid loader, the attachment, a small roller and a cement spreader.

The site operations are divided into three main phases:

  • first phase where only the milling drum is operated at a depth ranging between 5 and 7 cm, depending on the extent of the pavement distress, spraying water if necessary to ensure dust suppression;
  • phase 2: after distributing the cement, a second pass is carried out activating the second drum, the mixer, which mixes the rap with the admixture (the correct proportional dosage of product is guaranteed by the presence of a speed detection wheel). In this phase, water is sprayed to obtain the correct moisture content of the milled material;
  • finally, phase 3, compaction takes place. The final result is a 100% regenerated pavement, that can be shortly opened to traffic.

It may happen that after milling the material requires a second pass before being mixed. Indeed, the particle size of the material must have the right distribution before adding the admixture.

1 mm sieve
5. 1 mm sieve
Operational advantages
  • Repair of road surface quickly with long-lasting results;
  • a dynamic and smaller construction site: compact loader + Simex ART, compact roller, cement spreader;
  • no management of resulting RAP or transport costs for new mixes;
  • marginal disruption to traffic.
Environmental advantages
  • Zero impact: 100% of the material is reused on site;
  • asphalt regeneration, which can also be repeated in subsequent maintenance operations;
  • use of eco-friendly materials;
  • no handling or management of special waste.

The mix

From what has been described one may easily recall the traditional in situ cold recycling; with two substantial differences however; the maximum thickness must be less than 10 cm and the road can be opened to traffic in a really short time without laying new material on top, such as a wearing course.

Bringing the concept of cold recycling at wearing course level, required a complete rethinking of the mix and the type of equipment. The structural cold recycling technique, with conventional emulsion or foamed bitumen, requires the subsequent laying of a new wearing course or binder layer for a base course. It also requires large machines that cannot be easily operated in urban or residential areas and with such a limited thickness.

Size distribution of the sample
6. Size distribution of the sample collected in Via Astengo in San Giovanni

Simex therefore envisaged a mix of calibrated size rap (10/12 cm max) added with a special regenerating admixture, to restore the characteristics lost over time, due to oxidation of the existing wearing course; together with a hydraulic binder, typically cement.

This type of product ensures the mix is environmentally friendly and that can be further recycled. Simex goal is to remain open to a wide range of products available in the market but at this stage it was necessary to rely on a widely tested product to eliminate the “chemical unknown”.

Thus, a partnership was born between Simex and Iterchimica, the Italian leading company in the road chemicals industry. The reader may refer to Iterchimica publications for technical information on their Iterlene HP Green.

The challenge arose, however, from the on-site application since previous experiences were all related to mixing in plant or by small concrete mixer with operational steps that are difficult to reproduce on site. 

An example of application

In order to validate the technology, various tests were carried out in the Bologna area, focusing in the first phase on minor types of roads. Although minor those are subject to significant residential and agricultural traffic developed on old rural road structures.

RAP mixed with cement and admixture
7. RAP mixed with cement and admixture

Roads therefore lacking a real design and which have been paved often on poor subgrade. Over time they show various types of distress, causing cracks; hence the possibility for water and ice to carry out the subsequent action. Patches were then carried out with a width of 1 m and an average length of about 4/6 m each.

The surface was trafficable after about 3 hours. A week later cores were taken to verify indirect tensile tests. All gave satisfactory results, above 0.20 N/mm2. A first indication that all was on the right track.

In a second, more advanced, phase the method was tested on medium-traffic roads but characterized by a significant transit of heavy vehicles linked to local industrial activities. Again, all the laboratory support was provided by the University of Bologna.

The following data are obtained from the thesis by Beatrice De Pascale “Innovative cold in-situ recycling of wearing course layers: laboratory and field characterization of 100% RAP asphalt concrete” for the achievement of the master’s degree at the DICAM of the University of Bologna in the academic year 2020/2021 which takes into consideration several experimental sites.

As an example, the job site within the Municipality of San Giovanni in Persiceto (via Astengo) is reported here. The pavement was characterized by an evident cobweb of cracks affecting the entire width of the carriageway.

Final result after compaction
8. Final result after compaction

The working width is 1 meter and the repair length 8 meters. It took 1 hour to rehabilitate that stretch and a half with no handling of materials and marginal labour. The material resulting from the first phase of milling is shown in the photo. Being the repair works relevant to the wearing course only, the machine was set at a depth of 5 cm.

Size distribution analysis was carried out, shown in figure 3.9, using the 1 mm reference sieve; the percentage of passing material was approximately 17%. That is in accordance with the target set in the mix design phase; also indicating that equipment is capable of delivering the rap according to an adequate particle size distribution.

Before starting the second phase, workers laid 1.5% of Portland 32.5 cement and machine was set up for delivering 2.5% of chemical additive. The mixed product after the second step highlights good homogeneity and good dispersion of the admixture.

Once this phase is completed, the material is leveled manually with a special equipment to ensure an even surface. Compaction followed by a compact 600 kg tandem roller.

The road was then opened to traffic. A few hours for laying and curing are certainly advantageous but the material immediately develops all the mechanical properties necessary to ensure safe traffic flow. Grip test was also carried out for this purpose. Figure 9 shows the result for the pendulum value.

The results for the macro-texture are reported in Figure 10.

  • Skid resistance test
    9 Skid resistance test
    9. Skid resistance test
  • Macrotexture values
    10 Macrotexture values
    10. Macrotexture values

Tests on cores

Various cores were taken at different job sites. Figure 11 is an example of the result in via Astengo.

From a first visual analysis it is possible to observe that there is no clear separation between the new wear and the old pavement, an indication that the new layer is well bonded to the old underlying. Air voids content for each core is shown below.

The results from the indirect tensile strength tests are shown in Figure 13. Considering an ITS of 0.35 MPa as a reference value, the values ​​are well beyond the requirement and therefore able to ensure adequate performance for the patch. To sum up, the Simex rehabilitation method translates into durability and safety.

All results in small and dynamic road construction jobsite: no need to deploy large machines, with no impact on traffic, minimal labor and a single vehicle carrying all the necessary equipment.

rehabilitation of wearing course

  • rehabilitation of wearing course
    rehabilitation of wearing course
    11. Core taken at Via Astengo in San Giovanni
  • rehabilitation of wearing course
    rehabilitation of wearing course
    12. Air void content for each sample
  • rehabilitation of wearing course
    rehabilitation of wearing course
    13. ITS test results

Furthermore, no material carried from/to the site as existing pavement is fully reused. A sustainable approach that simplifies the process by cutting down costs, reusing only existing materials that can be recycled again in subsequent maintenance cycles.

ART available to contractors in the road maintenance business: the test by Tolomio Srl

On Monday 21 February 2022, a test took place in San Giovanni in Persiceto (BO), in Via Tivoli, which involved Simex R&D department and Tolomio srl, a company from Borgoricco (PD), specialized in road construction and public infrastructure sector.

For many years, Tolomio has been looking with interest at the regeneration techniques of damaged asphalt from a sustainable perspective and has started a specific project called “Restreet”. For this reason, the company asked to test the Simex asphalt regeneration technology, trying out the ART 1000 for the first time.

rehabilitation of wearing course
14. Asphalt distress

The company carried out a first test on a damaged surface of 8 m in length and a second of 3 m, using the 1 m drum width. In both cases, a milling depth of 70 mm was set. After an initial training on the product, Tolomio performed the operation as developed by Simex R&D department for ART 1000.

In summary, after milling, thanks to the second integrated drum and the admixture mixing system, the regenerated RAP was ready for the subsequent compaction phase. The company decided to use a natural plant-based admixture of its own, demonstrating that the ART technology can match with various additives designed for the cold regeneration of RAP.

In both tests, the result was largely satisfactory, obtaining the complete rehabilitation of pavement distress quickly and above all making the rehabilitated stretch of road immediately driven on.

rehabilitation of wearing course
15. Simex ART 1000 in action

Simex interviewed Fabio Tolomio, Technical Director of Tolomio Srl for a further study.

“Simex”: “What are the main operational advantages of Simex ART for the in-situ asphalt regeneration methods, such as your “Restreet”?”.

“Fabio Tolomio”: “Simex ART allows to streamline and improve the regeneration procedure, but above all allows to tackle any existing road situation and adapt it to the needs by choosing the most suitable grain size”.

“Simex”: “To what extent, according to your experience, can the regeneration of the wearing course bring benefits to the managing authorities of the road networks?”.

“FT”: “As far as our daily experience, the idea envisaged allows all managing authorities to increase road safety level, at any time of the year (even in winter below 0 ° C), reducing costs from 30 to 50% compared to traditional maintenance and with zero environmental impact.

rehabilitation of wearing course

  • rehabilitation of wearing course
    rehabilitation of wearing course
    16A. Regenerated asphalt before compaction
  • rehabilitation of wearing course
    rehabilitation of wearing course
    16B. Regenerated asphalt after compaction
“Simex”: “What is the demand for this type of operation for your areas today and which cases would you recommend it for?”.

“FT”: “It has limitless potential, that can be used on any type of pavement distress (alligator cracking, deformation, pavement unevenness), therefore in any road situation. Our commercial proposal, which involves patented technologies, aims at single customized operations, as from a minimum of 1 m2”.


Rehabilitation of wearing course
Per la versione in Italiano:
https://www.stradeeautostrade.it/attrezzature-e-componenti/tecnologie-per-interventi-superficiali-di-recupero-funzionale/