Corrosion propagation in cracked reinforced concrete structures

Bezuidenhout, Schalk Ruan (2017-12)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: The durability of a reinforced concrete (RC) structure is significantly influenced by the presence of cracks. Cracks act as pathways that accelerate the ingress of corrosion agents into the concrete to the embedded reinforcement. This causes the acceleration of both the corrosion initiation and propagation stages of degradation. The increase in the corrosion rate in the corrosion propagation stage leads to a reduction in the residual service life of a structure. The overall effect of cracks in RC structures is that the residual service life of a structure is remarkably shortened. In recent years, many researchers have investigated the corrosion of structures in the propagation stage. However, the majority of these investigations are focused on specimens with only one crack and reinforcement rod. This study investigates cracked RC exposed to chloride-induced corrosion. The experimental investigation considers three different reinforcement layouts, namely 1Y10, 2Y10 and 3Y10, and four crack spacings (Sc), as follows: single crack, 70 ≤ Sc ≤ 85 mm, 85< Sc < 100mm ≤ 100 ≤ Sc ≤ 120 mm. Twenty-seven 150 x 150 x 700 mm long beams were sustained in flexural loading to maintain a consistent surface crack width of 0.4 ± 0.1 mm. The specimens were subjected to cyclic ponding for 36 weeks, and were monitored weekly to measure the corrosion rate and corrosion potential. The results indicate that the corrosion rate of the RC members is influenced by a change in reinforcement density. For a given crack spacing, the corrosion rate decreased with an increase in reinforcement density. In addition, the corrosion rates were influenced by different crack spacing. It was also observed that single cracked specimens were susceptible to a higher corrosion rate than the multiply cracked specimens. The combined effect of reinforcement density and crack spacing has shown that apart from a complex relationship between the anode and cathode region, the increase in reinforcement density has a greater in uence on the corrosion rate than the increase in crack spacing. In current practice, the onset of the corrosion propagation stage conservatively marks the end of the structure's serviceable life. A model for determining the residual service life of a structure in the corrosion propagation stage is proposed. This model may be used to gain insight regarding a structure's \corrosion state" for planning maintenance and determining its remaining service life. The study recommends that reinforcement density and crack spacing, accompanied by the prediction of residual service life, should be taken into consideration in the durability design of RC structures.

AFRIKAANSE OPSOMMING: Die duursaamheid van 'n gewapende beton (GB) struktuur word aansienlik beïnvloed deur die teenwoordigheid van krake. Krake dien as weë wat die indringing van roesmiddels in die beton na die bewapening versnel. Dit veroorsaak die versnelling van beide die korrosie-inisiasie en voortsettingsfases van verwering. Die toename in die korrosiesnelheid in die korrosie-voortsettingsfase lei tot 'n afname in die residuele diensleeftyd van 'n struktuur. Die algehele gevolg van krake in GB-strukture is dat die oorblywende leeftyd van 'n struktuur merkwaardig verkort word. In die afgelope jare het baie ondersoeke die korrosie van strukture in die voortsettingsfase bestudeer. Die meerderheid van hierdie ondersoeke is egter op monsters met slegs een kraak en bewapening staaf gefokus. Hierdie studie ondersoek gekraakte GB wat blootgestel is aan chloried-geïnduseerde korrosie. Die eksperimentele ondersoek beskou drie verskillende bewapeningskonfigurasies, naamlik 1Y10, 2Y10 en 3Y10, en vier kraakspasiërings (Sc), soos volg: enkele kraak; 70 ≤ Sc ≤ 85 mm; 85 < Sc < 100mm en 100 ≤ Sc ≤ 120 mm. Monsters in die vorm van 150 x 150 x 700 mm lang balke is deirgans in buiging belas om 'n konsekwente oppervlakkraakwydte van die 0.4 ± 0.1mm te behou. Die monsters is vir 'n periode van 36 weke aan sikliese toediening blootgestel en die korrosietempo en korrosiepotensiaal is weekliks gemeet. Die resultate dui aan dat die korrosiesnelheid van die GB-lede beïnvloed word deur 'n verandering in bewapeningsdigtheid. Vir 'n gegewe kraakspasiëring het die korrosiesnelheid afgeneem met 'n toename in bewapeningsdigtheid. Daarbenewens word die korrosietempo beïnvloed deur kraakspasiëring. Daar is ook opgemerk dat enkel-kraak monsters vatbaar was vir hoër korrosie as veelvoudige-kraak monsters. Die gekombineerde effek van bewapening en kraakspasiëring het getoon dat, afgesien van 'n komplekse verhouding tussen die anode- en katode-gebied, die toename in bewapeningsdigtheid 'n groter invloed op die korrosietempo het as die toename in kraakspasiëring. In die huidige praktyk dui die aanvang van die korrosie-voortplantingsfase konserwatief die einde van die strukturele diensleeftyd aan. 'n Model vir die bepaling van die oorblywende dienslewe van 'n struktuur in die korrosie-voortsettingsfases word voorgestel. Hierdie model kan gebruik word om insig te verkry in 'n struktuur se \korrosietoestand" vir die beplanning van onderhoud en die bepaling van die struktuur se oorblywende diensleeftyd. Die studie beveel aan dat die bewapenings digtheid en kraakspasiërings, tesame met die voorspelling van die oorblywende dienslewe, in ag geneem moet word in die duursaamheidsontwerp van GB-strukture.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102853
This item appears in the following collections: