Papers by Keyword: Charge Passed

Abstract: In this paper, permeability of concrete after loading at various stress levels, including recycled aggregate concrete (RAC) and natural aggregate concrete (NAC) (at W/B ratio of 0.586 and 0.250), is measured by means of surface infiltration experiment and chloride penetrating test to study the effect of loading size on permeability of recycled aggregate concrete. The results show that there exists a critical stress ratio value of around 0.65 to 0.75 for NAC at W/B ratio of 0.586, and among the four types of RAC, the critical stress ratio exists only in 60R50, while the water permeability coefficient increases linearly with the stress ratio for the other 3 types of RAC. The charge passed of RAC increases with the W/B ratio, and the more the recycled aggregates mixed, the higher the charge passed. As the stress ratio increases, the charge passed increases slightly in samples at W/B ratio of 0.25, while the charge passed of samples at W/B ratio of 0.586, whether NAC or RAC, increases almost linearly.

Abstract: Charge passed of mortars with different aggregate volume fractions was tested according to ASTM C1202, and the differential expression of the Ohm law was introduced to explain the relationship between charge passed data and aggregate fractions.Cl- penetration depth of the corresponding mortars and concretes was measured to illustrate the influence of the aggregate volume fraction on their chloride permeability. It was shown that the charge passed of mortar was negatively correlated with aggregate volume fractions, and high aggregate fraction bearing concrete with low charge passed did not necessarily mean low permeability. As a result, the influence of aggregate fraction on charge passed should be taken into consideration when charge passed data was employed to evaluate Cl- permeability of concrete.

Abstract: Mineral powders play positive role in improving the durability of concrete subjected to alkaline and saline corrosion, where sulphate ion and chloride ion coexisted may cause serious deterioration to the reinforced concrete structures. Metakaolin, slag, fly ash and natural zeolite mixed in appropriate proportion were tested in inhibiting the deterioration. It is found that the composite powder might decreased AAR and the charge passed of concrete effectively，the while the 7d and 28d strength of cement and concrete are improved as well.

Abstract: Sulphate ion and chloride ion existed in the alkaline saline soils may cause serious problems on the durability of reinforced concrete structures, while it is found that superfine mineral powder plays positive role in the precaution of the alkaline saline corrosion. A composite cement named high performance cement (H.P.C) composed of clinker, metakaolin and fly ash powder in appropriate proportions is developed with good performance in preventing concrete from alkaline saline soil corrosion. Mortar bar test and visual examination showed that the cement could effectively control AAR and sulphate ion related expansion, and the charge passed tested according to ASTM C1202 was decreased to “negligible” level for concrete with W/B ratio of 0.3, and “very low” grade for concrete with W/B ratio of 0.45 and 0.55 when the high performance cement was used. Other properties such as low hydration heat and anti-freezing properties, as well as the uniformity of the fresh concrete (with no bleeding and segregation), made it an important material in the construction of concrete structure in alkaline saline soils.