Chloride induced corrosion and concrete carbonation of 3D printed concrete with reinforced connections

Malan, Jean De'M (2022-04)

Thesis (MEng)--Stellenbosch Univeristy, 2022.

Thesis

AFRIKAANSE OPSOMMING: Die duursaamheid van gewapende betonstrukture word bepaal deur die betonbedekking se vermoë om die binnedring van chloriede en koolstofdioksied in mariene en stedelike omgewings te weerstaan. Die binnedring van hierdie kontaminante verlaag die pH van die beton, breek die beskermende passiewe laag van die staal af en inisieer die aktiewe korrosie-stadium. Die hoë korrosie-lesings tydens aktiewe korrosie lei tot vinnige vermindering van die staal, wat die kapasiteit van die struktuur verminder en uiteindelik die lewensduur van die struktuur verlaag. Baie navorsing is al uitgevoer oor betonkarbonering en chloried-geïnduseerde korrosie van gekraakte en ongekraakte gegote strukture. Die teenwoordigheid van krake is bekend daarvoor om die lewensduur van strukture te verkort. Outomatisering is onlangs in die konstruksiebedryf bekendgestel, spesifiek met verwysing na additiewe vervaardiging. Drie-dimensionele betondruk is die mees toegepaste additiewe vervaardigingstegniek in die konstruksiebedryf en die gebrek aan samesmelting by die grensgebiede tussen opeenvolgende gedrukte lae is prominent, veral as 'n verloopstyd tussen betonlae toegepas word. Die verloopstyd verwys na die tyd tussen die druk van opeenvolgende lae. Aangesien drie-dimensionele betondruk 'n nuut geïmplimenteerde konstruksiemetode is, is beperkte navorsing oor die duursaamheid van drie-dimensionele betondruk-strukture beskikbaar. Hierdie studie ondersoek die duursaamheid van drie-dimensionele betondruk met betrekking tot betonkarbonasie (versnelde betonkarbonasie toets) en chloried-geïnduseerde (deur sikliese benatting en droging met ‘n soutoplossing) korrosie om die effek van die grensgebiede te kwantifiseer. Die effek van 'n verloopstyd, wat wissel van 0 tot 30 minute, word ook in ag geneem en die resultate word vergelyk met konvensionele gegote beton wat uit dieselfde materiaal bestaan. Die duursaamheid word gemeet deur chloried-geïnduseerde korrosie, versnelde betonkarbonasie en om duursaamheidsindekstoetse uit te voer. Buigsterkte-toetse word ook uitgevoer om die gebrek aan samesmelting se teenwoordigheid by die grensgebiede te kwantifiseer. Die resultate van buigsterkte en duursaamheidstoetse toon dat die gegote beton beter as die drie-dimensionele betondruk presteer. Hoër korrosiesnelhede, groter karbonasie dieptes, laer kwaliteit duursaamheidsindeksresultate en laer buigsterkte, as gevolg van die gebrek aan samesmelting teenwoordig by die grensgebiede, is in drie-dimensionele betondrukproefstukke gemeet. Die buigsterkte en duursaamheidsprestasie neem ook af met 'n toename in verloopstyd wat toegeskryf word aan die gebrek aan samesmelting wat deur die verloopstyd veroorsaak word. Twee voorspellingsmodelle van die beton karbonasie diepte en chloriede konsentrasieprofiele, met behulp van die duursaamheidsindeks-resultate as insetparameters, word aangepas om die effek van die grensgebiede en verloopstyd in drie-dimensionele betondruk in ag te neem. Hierdie modelle kan gebruik word om die tyd tot aktiewe karbonasie en chloried-geïnduseerde korrosie stadium te voorspel.

ENGLISH SUMMARY: The durability of reinforced concrete structures is dependent on the ability of the concrete cover to combat the ingress of chlorides and carbon dioxide in marine and urban environments. The ingress of these contaminants reduces the pH of the concrete, breaks down the protective passive layer of the reinforcement and initiates the corrosion propagation stage. The high corrosion rates during the propagation stage result in fast degradation of the reinforcement, reducing the structural load-carrying ability and ultimately reducing the structural service life. A vast amount of research has been conducted over the years regarding concrete carbonation and chloride-induced corrosion of cracked and uncracked cast structures. The presence of cracks has been shown to reduce the service life. Recently, automation has been introduced to the construction industry, specifically referring to additive manufacturing. Three-dimensional concrete printing is the most applied additive manufacturing technique in the construction industry and the lack of fusion at the interlayer region between subsequent printed layers is prominent, especially when a pass time is introduced between concrete layers. The pass time refers to the time between the printing of subsequent layers. As three-dimensional concrete printing is a newly implemented construction method, limited research is available regarding the durability of such three-dimensional concrete printing structures. This study investigates the durability of three-dimensional printed concrete with regard to concrete carbonation (accelerated concrete carbonation testing) and chloride-induced corrosion (via cyclic wetting and drying with a saline solution) to quantify the effect of the interlayer region. The effect of a pass time, varying from 0 to 30 min, is also considered and the results are compared to conventional cast concrete consisting of the same material. The durability performance is measured by conducting chloride-induced corrosion, accelerated concrete carbonation and durability index testing. Flexural strength tests are also conducted to quantify the lack of fusion present at the interlayer region. The flexural strength and durability performance results show that the cast concrete outperforms three-dimensional concrete printing. The three-dimensional concrete printing samples resulted in higher corrosion rates, greater carbonation depths, lower quality durability index values and lower flexural strengths owing to the lack of fusion present at the interlayer region. The flexural strength and durability performance also decreases with an increase in pass time, which is attributed to the lack of fusion induced by the pass time. Two models for predicting the concrete carbonation depth and chloride concentration profiles are adapted to incorporate the effect of the interlayer region and pass time present in three-dimensional concrete printing, using the durability index results as input parameters. These models can be used to predict the time to carbonation and chloride-induced corrosion initiation.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/124567
This item appears in the following collections: