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A number of seven-year-old, externally stored 500 x 100 x 100 mm concrete beams, some of which had suffered severe cracking due to alkali-silica reaction, have been examined. The concretes were produced using pulverized fuel ash (PFA) at a range of addition levels and contained a fixed proportion of a known reactive sand. Following 7 years of exposure, severe cracking was observed in the specimens without PFA or, with 5 percent PFA, surface crack widths were often in excess of 1 mm and examination of sawn surfaces indicated that the depth of visible cracks was up to 20 mm. Specimens containing 20 percent or more PFA did not exhibit any visible cracking. Expansion measurements, USPV, dynamic modulus of elasticity, and modulus of rupture tests were undertaken, and the results broadly confirm the visual condition of the specimens, with cracked specimens displaying significantly reduced engineering performance. Average carbonation depths were less than 3 mm for all the concrete specimens. However, depths of up to 20 mm were observed at the location of some of the wider cracks. Petrographic examination of thin sections showed evidence that alkali-silica reaction had occurred in all the concretes, but had only led to cracking in the concretes with no PFA or 5 percent PFA. In the concretes containing higher levels of PFA, the sites of gel were rare and there was no evidence of associated damage. Examination of polished sections by quantitative electron probe microanalysis showed differences between ordinary portland cement and PFA concrete in the composition of the alkali-silica gel and the cement hydrates. The gel in pores in the PFA concrete was lower in calcium than that in cracks in the ordinary portland cement concrete. In addition, hydrate rims around alite grains had lower Ca/Si ratios and higher K/Si ratios in PFA concrete. The lower quantity of available calcium in PFA concrete and the increased absorption of potassium by its contributions to the suppression of damaging alkali-silica reaction.

A recent report claimed that ASR expansion was suppressed when calcined clay was added to concrete used in hydroelectric dam construction containing reactive aggregates. The authors report a laboratory study on the effectiveness of metakaolin in preventing ASR. Samples of metakaolin were prepared by calcining china clay (relatively pure kaolin) and several ball clays, all collected from Southwest England. Compression cube strength tests were carried out in which part of the cement content of a 1:6 mixture of aggregate and ordinary portland cement (OPC) was replaced by calcined clay. Results showed that some of the mixtures containing calcined clay exhibited no reduction in the 28-day compressive strength, even when 25 percent of the OPC was replaced. Tests for ASR were conducted using prisms produced in accordance with the Draft British Standard 812, Part 123, containing highly reactive natural aggregates that expansion of 0.450 percent at 12 months. Prisms in which up to 25 weight percent of the OPC was replaced by calcined clay have been monitored over a period of 18 months and have shown no expansion or deleterious surface appearance. As a result of these tests, it is concluded that expansion due to ASR is completely suppressed when sufficient metakaolin is added to the concrete formulation. Metakaolin does not reduce the ultimate compressive strength of the concrete, provided that the feed clay is relatively free of impurity minerals.

Microstructure and mechanical properties of concrete with expansive additives are reported compared with ordinary concrete. Samples of long-term concrete (22 years) were collected from an actual building constructed in 1967 with calcium sulfoaluminate (CSA) used as expansive additive. Hydration products were separated from these samples by using heavy media and analyzed by means of DSC, XRD, and FT-IR. The morphology of the mortar portion was observed by SEM. No differences were detected on the carbonation depth and the compressive strength between CSA concrete and ordinary concrete. Qualitative analysis shows that following carbonation of concretes, C-S-H was changed to silica gel or to C-S-H with low Ca/Si ratio and CaCO3, AL(OH)3 gel, and gypsum. Quantitatively, hydration products in carbonated CSA concrete are larger than in carbonated ordinary concrete. Therefore, decomposition rate of AFt by carbonation is slower than that of C-S-H.

Mortars using heat-resistant glass as aggregate were made using water-binder ratio of 50 percent, replacement ratio of fly ash from 0 to 30 percent by weight, and an alkali content of 1.2 percent weight of cement. Eight fly ashes were used as supplementary cementing materials. These mortars were cured at a temperature of 40 C and a relative humidity more than 95 percent, and the expansion of these mortars was measured. The concentration of soluble alkali ion in fly ash immersed in the solution containing sodium hydroxide and calcium hydroxide was also determined. Expansion of mortar depended on the type and the replacement ratio of fly ash. The concentration of soluble alkali ion in fly ash depended on the type of fly ash. Although expansion of mortar was independent of equivalent sodium oxide content in fly ash, it correlated with the concentration of soluble alkali ion in fly ash. By studying effects of physical/chemical properties and the amorphous silicon dioxide in fly ash, a method to evaluate the expansion of mortars containing fly ash was proposed based on amorphous silicon dioxide, the replacement ratio, and particle diameter of fly ash.

The moisture condition of field concretes exhibiting evidence of alkali-silica reactivity was investigated utilizing relative humidity (RH) measurements. Prior determinations were made on laboratory mortar specimens to determine the threshold level required to sustain expansive reactivity. By comparing measurements of field concretes with the threshold level, environmental field conditions under which expansive reactivity is liable to occur were identified. Results indicated that RH values greater than 80 percent, referenced to 21 to 24 C, are required to support expansive alkali-silica reactivity. Field measurements revealed that most of the concrete in highways and dams in desert areas is sufficiently damp to sustain expansive ASR. Bridge decks and columns in dry climates are sufficiently damp on a seasonal basis to sustain expansive reactions. Massive concrete members indoors in controlled environments may remain sufficiently damp for more than 50 years to permit continued expansive reactivity. Both residual mixing water and external sources of moisture contribute to the moisture condition required for expansion to occur.