MODIFICATION OF BINDER WITH ACID - ADVANTAGES AND DISADVANTAGES

Modification (hardening) of binder by an acid extends the upper application limit and protects from possible rutting of a mix. Antistripping agents (ASA), on the other hand, have active amino hydrogens that, on mixing with a binder, help the latter adhere to aggregate surface and minimize moisture damage. It is not uncommon that the two effects that are simultaneously sought are a higher upper limit and a suitable protection from moisture attack. That is, both types of modifiers, acid and ASA, may be present in the same binder. Although each of the two types of modifiers has advantages when used separately, it is not known whether their coexistence in the same binder would enhance each other's benefits, limit the individual advantages of each or may even be detrimental. It is also not known whether there is an optimum amount of each modifier type when both are used together. To address these questions, two parameters were followed: first, the high critical temperature of the binder alone and in presence of each modifier type separately and combined; and second, the pH value of the aqueous layer obtained after extraction with water from the binder toluene solution. The pH measurements are similarly carried out on the binder alone and in presence of each modifier type separately then combined. The pH value provides a quantitative measure of the acidity (or alkalinity) of the water soluble constituents of a binder. This information might serve two purposes: first, an alkaline pH value denotes presence of an ASA and an acidic value denotes an acid; and second, a low pH value points to possible field interactions with an alkaline environment such as a limestone aggregate.