The study used the method of accelerated mortar bar test to study alkali aggregate reaction (ASR) with sandstone aggregate. Both fly ash and slag can inhibit the expansion of mortar bar. Results show that 50% slag can inhibit ASR reluctantly, but 10% fly ash and 20% slag can inhibit ASR very well, and the inhibitory effect of fly ash is far better than slag. Because of the high content of CaO in slag, it has inhibit and promote aspects, when the ASR is fierce, slag can inhibit ASR, otherwise slag can promote ASR.
In order to study the effects of slate powder on mineral admixtures in suppressing ASR of slate aggregate, refer to the following methods: accelerated mortar bar test in “Standard for Constructional Quality Acceptance of Railway Concrete Engineering” TB10424-2010 and “Durability Design of Railway Concrete Structures” TB10005-2010, as well as an improved steam curing method. The text has studied the expansion of the specimens that are made from slate aggregate with different powder contents and specimens using slate powder as admixtures. The results show : When powder content in aggregate is less than 20%, it dose not have adverse effects; ASR of high-activity slate aggregate can be suppressed by using 30% fly ash and 5% silica fume as mineral admixtures; when the mineral admixtures are effective, a certain amount of powder mixed with admixtures can contribute to suppression; the main mechanism that slate powder can suppress ASR is that alkali in concrete can be consumed and physically diluted by slate powder.
The influence of the content of matekaolin powder and fly ash in cement on controlling ASR was evaluated using Accelerated Mortar Bar Test (AMBT). Replacing cement with matekaolin powder to the extent of 5%,10%,15%,20%,25%,and with fly ash to the extent of 10%,20%,30%,35%,40%, 45% respectively. The result show that matekaolin powder and fly ash both can control Alkali-aggregate activity but to different degrees. Small amount of metakaolin powder exerts significant influence, whereas only when the proportion of fly ash is up to 35%, can it control ASR effectively. The effect and mechanism of the control of the extension of glass aggregate activity was studied by means of SEM analysis.
The effectiveness of fly ash in suppressing expansion due to alkali-silica reaction (ASR) of sandstone are studied respectively based on accelerated mortar bar test and concrete prism test. The mechanism of fly ash in inhibiting the ASR of sandstone is examined by scanning electron microscope (SEM) and energy dispersive analysis of x-ray (EDAX). Moreover, the reliability of fly ash in inhibiting ASR of sandstone was discussed through concrete strength and frost resistance tests. Results indicate that the replacement amount of fly ash is 20%, the expansion due to ASR can be decreased to the critical value of a non-reactive aggregate. The reason why fly ash can inhibit the alkali reactivity for the sandstone is that the strong reaction between alkali and fly ash dissipates the alkali, and the products of alkali-silica-aluminate gels are non-expansible. For the concrete specimens suffered from accelerated ASR tests, their strength and frost resistance are decreased with the increment of fly ash replacement.
The effects of Al2O3 and Al(OH)3 on expansion due to alkali-silica reaction (ASR) were tested by using Accelerated Mortar Bar Test and through prolonging the curing age, and the ffect was compared with silicon fume and fly ash. The results show that ASR can be inhibited effectively by proper content of silicious admixtures within 14 days, but can not in long term, while it can be inhibited by proper content of Al2O3 and Al(OH)3 not only within 14 days but also in long term. The composite of silicious admixtures and aluminous admixtures has synergetic effect on inhibiting ASR, and there exists a value of Al2O3/SiO2 with which ASR is suppressed best. For the composite, ASR is suppressed mainly by silicious admixtures in early age and mainly by aluminous admixtures in long term.
Influence of Limestone Mineral Addition in Cements on the Efficacy of SCMs in Mitigating Alkali-Silica Reaction Assessed by Accelerated Mortar Bar Test
