Al-Mutlaq, Fahad Mohammed (2011)
Ph.D. thesis, University of Birmingham.
Electric arc furnace dust (EAFD) is a by-product of the electric steelmaking industry produced in large quantities around the world. In Saudi Arabia, a form of EAFD known as Bag House Dust (BHD) is being used in small amounts as concrete additive, because higher levels of addition caused excessive retardation of setting and hardening. The use of this material is recent, therefore little is known about its effects on durability. This research aims to examine effects of BHD additions on certain properties of cement pastes, mortars and concretes, particularly those believed to affect the susceptibility of embedded steel reinforcement to chloride-induced corrosion as this is a major cause of degradation of reinforced concrete structures in the Arabian Gulf region.
Studies of the effects of 2 % BHD addition on pore solution chemistry of hydrated-cement pastes with various levels of internal chloride contamination indicated that both free chloride concentration and hydroxyl ion concentration increased. Electrochemical monitoring of the corrosion behaviour of embedded steel in chloride-contaminated mortars showed that the rates of corrosion were reduced slightly in the presence of BHD.
Measurements of the coarse capillary porosities of hydrated-cement pastes revealed significantly lower results in 2-3 % BHD-specimens compared to plain cement pastes. Attempts to measure the consequent changes in apparent diffusion coefficients of chloride in related concrete specimens showed that the BHD additions caused no adverse effects on chloride penetration rates.
Electrochemical monitoring of the corrosion behaviour of steel bars embedded in mortars exposed to chloride ingress at 20 °C and 40 °C demonstrated that the threshold chloride level for the initiation of crevice corrosion was significantly increased by the presence of BHD. This was thought to be partly influenced by BHD in reducing bleeding which affects the integrity of the layer of hydration products formed around the steel surface.
Having found that 2-3.5 % BHD additions had no detrimental effects on the properties studied, the possibility of using chloride-free accelerators to increase levels of BHD addition without causing excessive retardation of cement hydration was investigated. Calcium nitrite and calcium formate were both found to be reasonably effective in increasing the rates of hardening of specimens with 8 % addition of BHD.
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