Investigation of Differences in Deterioration of Two North Carolina Bridges Due211 to Alkali-Silica Reactivity (ASR)

摘要

A previous investigation of the extent of alkali silica reactivity (ASR) in North211u001eCarolina highway structures found a distinct difference in the extent of ASR in 211u001ecores from different parts of two separate bridges which contained reactive 211u001eaggregates. In one bridge, differences were found to be directly related to the 211u001ealkali content of the concrete. When the total equivalent alkali content of the 211u001ecement was greateer than 0.6%, deleterious expansion and significant cracking 211u001eoccurred. When the alkali content was less than 0.55%, no deleterious cracking 211u001eoccurred even though ASR was present. When the alkali content of the cement was 211u001eless than 0.4%, essentially no ASR was found. More ettringite was found than 211u001eexpected in one location in concrete with very low alkali content (less than 211u001e0.4%). In the other bridge, along the coast, the differences were due to the use 211u001eof different coarse aggregates in the concrete, including a mixture of reactive 211u001eand non-reactive aggregates along or in combination in varying amounts. An 211u001eadditional finding is that, due to the seawater exposure, the alkali content of 211u001ethe concrete is so high that ASR cannot be mitigated by controlling the alkali 211u001econtent of the cement. Ettringite, due to the seawater exposure, was found to 211u001ehave caused some cracking, but the damage was secondary in many cases and 211u001econsiderably less severe than that due to ASR.