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The effect of different cements and pozzolans on chloride ingress into concrete
Chloride profiles were measured on ten different concrete qualities. The effect of two different cements, an ordinary Portland cement, OPC, and a sulfate-resistent Portland cement, SRPC, with and without inclusion of silica fume and fly ash was investigated. The samples were exposed to a 3 wt% sodium chloride solution for 119 days. Two different preparations before exposure were studied. Both types of preparations consisted of one-day membrane hardening after casting. Af ter this a set of samples were dried for two we eks and then rewetted in tap water for one week before exposure. The other set of samples were stored in tap water one week before exposure to chlorides. The chloride content profile in concrete was measured by removing approximately 1.2 mm thick layers, from the exposed surface, by grinding. The concrete powder, collected from different depths from the surface, was dissolved in an acid and analyzed for chlorides by an ion-selective electrode. The obtained chloride profiles were evaluated in two ways. The first consisted of a simple curve fitting to the solution to Fick's second law, without any special attention to boundary conditions, in order to obtain the so-called effective diffusion constant. The other method of evaluating the measured values consisted of a more detailed hypothesis accounting for dielectrical effects, diffusion of free ions in pore solution, and chemical reaction such as binding of chlorides and dissolution of hydroxide from solid hydration products. Both methods of evaluating the me asur ed data gave the result that the OPC concretes resisted chloride ingress better than SRCP concretes at the same water to binder ratios when stored in water before exposure. The OPC concrete in which 5% of the cement content were replaced by silica fume resisted chloride ingress significantly better than the SRPC with the same relative amount of silica fume. This behavior was independent of curing conditions.
The effect of different cements and pozzolans on chloride ingress into concrete
Chloride profiles were measured on ten different concrete qualities. The effect of two different cements, an ordinary Portland cement, OPC, and a sulfate-resistent Portland cement, SRPC, with and without inclusion of silica fume and fly ash was investigated. The samples were exposed to a 3 wt% sodium chloride solution for 119 days. Two different preparations before exposure were studied. Both types of preparations consisted of one-day membrane hardening after casting. Af ter this a set of samples were dried for two we eks and then rewetted in tap water for one week before exposure. The other set of samples were stored in tap water one week before exposure to chlorides. The chloride content profile in concrete was measured by removing approximately 1.2 mm thick layers, from the exposed surface, by grinding. The concrete powder, collected from different depths from the surface, was dissolved in an acid and analyzed for chlorides by an ion-selective electrode. The obtained chloride profiles were evaluated in two ways. The first consisted of a simple curve fitting to the solution to Fick's second law, without any special attention to boundary conditions, in order to obtain the so-called effective diffusion constant. The other method of evaluating the measured values consisted of a more detailed hypothesis accounting for dielectrical effects, diffusion of free ions in pore solution, and chemical reaction such as binding of chlorides and dissolution of hydroxide from solid hydration products. Both methods of evaluating the me asur ed data gave the result that the OPC concretes resisted chloride ingress better than SRCP concretes at the same water to binder ratios when stored in water before exposure. The OPC concrete in which 5% of the cement content were replaced by silica fume resisted chloride ingress significantly better than the SRPC with the same relative amount of silica fume. This behavior was independent of curing conditions.
The effect of different cements and pozzolans on chloride ingress into concrete
Johannesson, Björn (author)
2000-01-01
other:TVBM-3093
Report TVBM; 3093 (2000) ; ISSN: 0348-7911
Paper
Electronic Resource
English
DDC:
690
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