Evaluation of penetration of the aggregate in the bases for surface treatments
Using the penetrometer ball as quality control element base treatment.
In the path that is being traced at the national level to standardize design criteria for surface treatments, we believe the inclusion of the ball penetrometer test is of utmost importance. It determines if the base is in proper condition to receive initial treatment, or if it requires additional work. It is also an indicator of the degree of compaction that has been achieved and the moisture contained in the base. The test was originally developed by South Africans and is also used in Australia and New Zealand to quantitatively measure the penetration potential of aggregate into the base.
En este frío mes de Agosto, junto con Lucio Borelli de CVC, pusimos a prueba este equipo de medición en diversas superficies: bases granulares no ligadas, bases estabilizadas con ligantes (cemento Portland y asfalto espumado) y mezclas asfálticas. A continuación se ilustran algunas de las conclusiones, acompañadas de fotos de la experiencia.
In the initial treatments (surface treatments on bases), the subsidence of the aggregate on the surface always occurs, to a greater or lesser extent. The degree of penetration will depend on the base material, its humidity, compaction and the traffic to which it will be subjected. Not taking these parameters into account results in exudate in the short term, becoming particularly evident in the tracks. The explanation for this phenomenon is intuitive: the tire pressure sinks the stone into a base that allows it and the voids that correspond to the asphalt and the air (to achieve the macrotexture of the wearing course) are occupied by the material of base, causing the asphalt to surface through the stone, which results in exudation in the tracks.
El ensayo que se propone es muy sencillo y de fácil aplicación: consiste en la penetración de una bola de 19 mm de diámetro que es golpeada por un martillo normalizado lanzado de una altura conocida (Australian Standards: AG-PT/T251 – Ball Penetration Test). El valor de penetración queda registrado en el aparato, ya sea en un indicador electrónico o en una regla graduada (que viene incorporada).
Los resultados de este ensayo se utilizan para ajustar la cantidad de ligante a regar o para seleccionar un tratamiento correctivo previo al definitivo. Su uso más importante es quizá el de establecer el límite en el que no se pueden realizar gravillados sin antes recompactar o estabilizar la base, dado que su riesgo de falla es muy elevado.
La primera y más importante de las conclusiones es que la preparación de la base es un factor determinante en los resultados. Un problema común es que las bases presentan un exceso de finos en la parte superior que genera que la bola penetre con facilidad. Aunque parecen estar lisas y homogéneas inicialmente, tan pronto como se barren, una gran cantidad de este material fino se dispersa, dejando una superficie áspera e inconsistente que es problemática para ejecutar un tratamiento.
Another issue to consider is the humidity at the time of the test: if the surface is visibly wet, the penetration gives higher values. We could corroborate this by testing the same surface early in the morning and close to noon. In some cases, the conditions of the base at the time of the test are good, but when a primer is applied, due to capillarity and temperature differences, humidity begins to increase in the first 5 cm, affecting the penetration result.
Developing
