Evaluation of ASR Resistance of Fly Ash-Slag Combinations Using the Modified ASTM C1260 Test Method

摘要

Supplementary cementitious materials (SCM) such as fly ash, ground granulated blast furnace slag and silica fume are now being extensively used in concrete primarily to enhance mechanical strength and improve resistance to chemical attack, resulting in more durable concrete. Ever since alkali silica reactivity (ASR) was identified in concrete some six decades ago, structure deterioration due to ASR has been extensively documented. Moreover, it has been well established that partial replacement of portland cement by fly ash or slag reduces the expansion due to ASR. Little data are available, however, on the effect of fly ash-slag combinations on ASR resistance. The ASR testing program is an in-house modification of the ASTM C 1260 test. The modifications can be more closely identified with actual field conditions. In this study three different strengths of NaOH test solution (1N, 0.5N, and 0.25N) were used to measure the expansion characteristics of mortar bars made with a reactive aggregate. The other variables included high alkali content cement and a 28-d testing period (instead of 14 d). These parameters were then used to evaluate ASR resistance of ternary blends with varying proportions of portland cement, fly ash, and slag. The portland cement replacement was 30%, 50%, and 70%. A set of plain cement mortar bars was also tested in conjunction with the ternary mixes. The results of ASR resistance of fly ash-slag combinations using the modified ASTM C 1260 test are presented.