Studies on natural aggregates unsaturated polyester composite materials: increasing the resistance through reducing the moisture of the aggregates

Abstract

The main objective of the present investigation is to develop a new building material, a polymeric mortar (PM), that we have named Polialbero, after the words Polymer and Albero (a rare and special rock).

The Albero natural aggregates used always came from the same kind of crushed or sifted rock: the row material came form a quarry under exploitation in Alcalá de Guadaira (Seville). The aggregate used in our tests always had the same grain mixture, sifting to eliminate sizes over 5mm and under 0.16 mm. The granulation used was corrected to have the highest compacity possible.

In spite of the fact that the Albero rock is rather homogeneous in natural quarries, its characteristics as row material differ depending on the area and level in an interval that was considered acceptable.

We also had to face another difficulty: the moisture degree of Albero. This rock has in general a considerable quantity of moisture: moisture degrees over 10% are not rare in rainy weather, decreasing up to five points less in hot weather.

It is also important to point out the difficulty of totally drying the grains. They easily become darker when they are heated for a long time, becoming what is called (due to the shade) toasted or burnt Albero.

The conglomerating mixes used in our experiences and tests were always composed of a standard commercial polyester resin mixed with an aggregate made of sifted Albero with a variable granulometry over 0.16 mm and under 5mm.

For the very first experiments the aggregates were not dried before their addition to the polymeric mortar. The natural moisture degrees of the aggregates (as they are served directly from the quarry) is used, as we wanted to establish a hypothesis as similar as possible to a real working site, were sometimes facilities for drying the aggregates are not available.

The moisture degree of the aggregates of a polymeric mortar is very important, as it has a great influence in the final strength. It has been experimentally demonstrated (Ohama 1973), moisture degrees over 0,1% have a negative influence on polyester P on Polyester PM mechanical strengths, and thoughtfully in PCs in general.

Based on this, it was considered to be interesting to analyse the Polialbero characteristics under different moisture degrees of the aggregates. In the frame of this investigation, we have established a practical classification to identify different moisture degrees of the aggregate. This rate, based on average moisture percentages in expressed in the table enclosed:

ALBERO MOISTURE CLASSIFICATION Qualification HA-0 HA-1 HA-2 HA-3 HA-4 % of moisture <1 1-4 4-6 6-9 >9 Albero Type Dry Half dry Half wet Wet Very wet or soaked

Table 1: Classification of Albero moisture degree

The present work intends to establish the influence of moisture in Albero polymeric mortars, through testing different aggregates with different moisture degrees. The compression strength can be increased up to a 35% when using fully dried Albero, compared to the one with 4-6% moisture degree