Monday, March 19, 2007

Alkali-Silica Reaction Potential of Lahar Sand by Prof. Nelson LLaban

Certain types of aggregate react with cement in concrete, which may affect the performance of the concrete. One of these reactions involves a reaction between alkalies (Na2O and K2O) from cement or from other sources, with hydroxyl, and certain siliceous constituents that may be present in the aggregate. This phenomenon is referred to as “alkali-silica reaction” (ASR). The product of this particular cement-aggregate reaction is a gel-like or crystalline substance called ASR gel. ASR can cause expansion and severe cracking, which leads to loss of strength of concrete structures.
Among the known deleteriously reactive aggregates are silica-rich volcanic and pyroclastic rocks. Lahar deposits from the eruption of Mt. Pinatubo fall under such type of rocks.

1. Appropriate and representative Lahar sand shall be sampled for the analyses to be conducted.
2. Petrographic analysis of the samples shall then be conducted in accordance to ASTM 295, Standard Guide for Petrographic Examination of Aggregates for Concrete.
3. The samples shall likewise be chemically analyzed in accordance to ASTM 289, Standard Test Method for Potential Reactivity of Aggregates (Chemical Method).
4. A concrete mixture of known proportions using the Lahar sand shall be prepared. Mortar bars from the concrete mixture shall be molded and initial measurement of their lengths shall be recorded. Subsequent length measurement of the mortar bars shall be made again after 14 days, and at ages 1, 2, 3, 4, 6, 9, and 12 months and, if necessary, at least every 6 months thereafter. This third test shall be in accordance to ASTM 227, Standard Test Method for Potential Alkali Reactivity of cement-Aggregate Combinations (Mortar-Bar Method)

To determine by petrographic analysis the mineralogical composition of Lahar sand and the presence, if there are any, of potentially reactive components in the sand.
To test by chemical method (ASTM 289) the potential reactivity of Lahar sand, if warranted by the results of the petrographic analysis.
To assess further the ASR potential of Lahar sand through the Mortar Bar test (ASTM 227)..


The rubber is mixed with the aggregate preceding addition of asphalt mix. Since the mixture of the aggregates affects the strength of the concrete, only a small portion of the rubber is mixed with the aggregate. Compressive strength is the main problem of using rubber-based aggregate using a small portion of the aggregate alleviates the need for strength adding admixtures. Shape and size of the aggregate affects the mixture of the asphalt. A standard size aggregate having a size of ¼ inch helps avoids formation of voids. Since the invention of cars the disposing the rubber tires has been a problem. Common techniques like incinerating the rubber tire produce environmental concerns. Developing a way of recycling the discarded rubber tires like using it as a portion of a fine aggregate. Having something the decompose slowly creates wastes in the environment, if the research will prove to be feasible using rubber as aggregate rather than using rock aggregates that destroy rivers and mountains. The procedure using the rubber tire as the aggregate uses dry mixing technique for hot mix asphalt. The rubber tire, which is used in the concrete, is shredded and grounded to produce a fine type of aggregate. It is then mixed with the rock aggregate before the addition of asphalt. The mixture should be mixed thoroughly to remove the voids .The asphalt laid in the pavement must be rolled until it cooled. It is then monitored make sure that the cooling process will not create cracks.