Characterization and design of asphalt mixtures with asphaltites from Boyacá for use in low traffic volume roads

The high availability of asphaltites in Boyacá and their low cost make this material a viable alternative for low traffic road paving; nevertheless, the traditional way in which this material is used generates, in cases, pavements with deficient behavior. This investigation, presents the results of the mixture design using asphaltites from the municipality of Pesca-Boyacá as well as coarse and fine aggregates produced in the region, 70–80 asphalt cement and slow-break asphalt emulsion. Working formulas for dense mixing in hot and cold and particularly MDF-2 and MDC-2 are presented from the characterization information; as benchmarks to define technical viability for use in low- traffic volume roads, according to NT1 regulation from INVIAS. The mixture design was performed according to the procedures defined in the RAMCODES and MARSHALL methodologies.


Introduction
The deficiency in vial infrastructure is a factor that reduces competitiveness in a region, affecting its development and limiting its inhabitants regarding the possibility of improving their life conditions, this is why it is necessary to seek for viable alternatives for cost reduction in paving works, thus obtaining higher coverage of roads in optimal conditions for communities and ultimately, contribute to the economic and social development of the region.
Keeping in mind the proper use of asphaltites form the municipality of Pesca in the department of Boyacá, this research, undertaken by the research group GRINFAVIAL from the "Masters in Engineering with emphasis in Infrastructure" at the Universidad Pedagógica y Tecnológica de Colombia, intends to perform the characterization of the exploited material in the quarries of Santa Teresa and La Emilia in this municipality, in order to identify the physical and chemical characteristics of this material and thus being able to propose an asphaltic mixtures design for use in low-traffic volume roads.

Asphaltic mixtures
Asphaltic mixtures in hot are defined as the combination of a hydro-carbonated binding agent, aggregates such as mineral dust and, eventually, additives, in such a way that all the particles in the aggregate are thoroughly covered by a uniform film of binding agent. The asphaltic mixture in cold is a mixture of mineral aggregates with or without mineral fillings, along with emulsified or diluted asphalt; the whole process is carried out at environment temperature, (Jimenez, 2009).
In the asphalt mix design include the following materials:  The asphaltic cement 70-80 for MDC-2 and for MDF-2 type is slow-break cationic emulsion.
 Natural asphalt (asphaltite) from the defined quarries in the municipality of Pesca -Boyacá.  The coarse aggregates required for granulometric stabilization are obtained as a product of triturating. The design of hot and cold dense mixtures for roads with low-traffic volume will be obtained using the protocols defined by the MARSHALL and RAMCODES methods; this is done in order to obtain the working formula with optimal percentage of asphalt and that also adjusts to the quality parameters defined by the INVIAS-07.

Material characterization
It is in this chapter that we show the results of characterization of materials used for asphaltic mixtures with natural asphalt form the Santa Teresa and La Emilia quarries in the municipality of Pesca. This way we define the investigation in four work groups, two per quarry, in such a way that a group performs the design of the dense mixture in cold MDF-2 and the other one the dense mixture in hot MDC-2 for each quarry.

Asphaltite characterization
The information obtained from the laboratory shows a fine, improperly gradated material, composed by sandstone impregnated in asphalt, divided in 96% and 4% proportions approximately; this material is fit for the design of asphaltic mixtures, given its physical properties and according to the specifications defined by INVIAS art. 400-07 (see table 1). Experiments performed for chemical characterization of asphaltites were carried out at the carbon laboratory in the UPTC. In this characterization the analysis was performed on asphalt-impregnated sandstone and the bituminous component extracted from asphaltites form the Santa Teresa and La Emilia quarries in Pesca-Boyacá. Likewise, the chemical analysis performed on the sand stones hows an ash-composed material in more than 90% in both quarries; it also shows a material that does not present dilatation or contraction at temperatures up to 520°C. Also, it does not present plastic behavior, maintaining its constant fluidity (30000 dial/min) up to a temperature of 500°C.

Asphaltic mixture design
Starting from material characterization, granulometry was adjusted according to the INVIAS regulation for MDC-2 mixture and NT-1 traffic, thus defining the coarse aggregate and asphaltite percentages for the different groups. (Art 400-07).
For each proposed combination, we determined the optimal asphalt percentage using the Marshall method, according to Illinois methodology. Stability, flow, air voids, mineral aggregate voids and asphalt-filled voids were determined in this briquette; this was made with the intention of verifying with the values established by the INVIAS regulation. Values for stability and flow as main quality check parameters for this asphaltic mixture obtained for the MARSHALL and RAMCODES methods.
Once the optimal asphalt percentage, which included asphaltite, was obtained for each of the asphaltic mixtures and once the compliance of regulations was verified, the definite work formulas and the summary of design for mixtures in each group was summarized in table 4. Mixtures made with an addition of natural asphalt as fine mineral aggregate and asphaltic contribution, show results on control parameters defined in the MARSHALL method, found within the parameter limit (INVIAS art 450-07) thus showing the effect of asphaltite presence, mainly in flow, since this parameter varies with asphaltite content in the work formula.

Conclusions
The information obtained from the characterization experiments in the materials that conform the asphaltic mixture with asphaltite allow us to state that natural asphalt is a material that shows acceptable conditions for cold and hot asphaltic mixture elaboration, with the intention of use in asphalt roads NT1, since the compliance with quality standards was verified, according to regulations from the INVIAS.
Parameters determined for quality control in the asphaltic mixture (stability, flow, air voids, voids in mineral aggregates and asphalt filled voids) comply with values established in the INVIAS regulation, both in the MARSHALL and RAMCODES method, which allows us to state the technical viability of natural asphalt usage from Santa Teresa and la Emilia quarries in Pesca-Boyacá for the design and construction of MDC-2 and MDF-2 rolling layers for NT1 traffic roads. Resulting work formulas for the designed mixtures allow us to ensure that the range defined by the granulometric strip are covered by the technical characteristics observed in the experimented briquettes, thus providing reliability regarding the unavoidable variations of size in aggregate particles and asphaltite.
The results obtained allow us to conclude that asphaltite is a material that proportionally affects quality in a mixture, since its higher volume percentage in the mixture produces higher values in flow, which can generate inadequate behavior from the mixture in the presence of heavy vehicles, slow traffic or high temperatures.