Petrography of aggregates in Luzon, Philippines: Identification of components and deleterious materials

Abstract

Petrography is one of a series of standard tests used to assess an aggregate’s components, mechanical qualities, durability, chemical stability, and alkali reactivity. In this study, aggregate materials were collected from rock exposures and/or alluvial deposits from four areas near Metro Manila, Philippines: Bulacan, Rizal, Pampanga, and Zambales. Transmitted light microscopy was conducted to identify rock types and characterise physical and chemical properties that may present potential problems when used as aggregate materials. The results show that the aggregates vary in terms of rock types and alteration type. Samples from Bulacan are mostly porphyritic basalt and fine to coarse-grained sandstone with veinlets of silica and carbonate. The presence of cavities and microfractures caused mainly by vesicles from the volcanic rocks was also observed. Rizal aggregates are composed predominantly of chloritized basalts and andesites with minor clastic rocks and tuffs. The aggregates from Zambales are products of erosion of the Zambales Ophiolite, mixed with the lahar deposits from the Pinatubo eruption. On the other hand, Pampanga aggregates are mostly lahar deposits, containing pumice, a poor choice for aggregate composition due to its low hardness, brittleness and vesiculated texture. Aside from the lithological classification, potentially alkali-reactive constituents were also observed in selected samples from the four sampling areas.