Carbonation induced corrosion in integral and non-integral surface treated lightweight foam concrete

Mubatapasango, Marlin (2017-12)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Carbonation induced corrosion is a concern in reinforced lightweight foam concrete (R/LWFC) as a result of air entrainment. Concerns arise from whether the air voids increase diffusivity of carbon dioxide (CO2) into LWFC. The effect of carbonation is the destruction of the protective cover for the steel reinforcement. LWFC is a low density concrete in which at least 20 per cent air by volume is entrained in a base mix comprising water, cement and a filler. The air entrainment is achieved by adding stable foam to the base mix. LWFC is a versatile construction material whose density can be altered by using various amounts of entrained air to suit the required function, structural or non-structural. The significant amount of air entrainment give LWFC its advantages of high strength to weight ratio and improved insulating properties. While progress in LWFC on mix designs and suitable compressive strengths for structural use has been made, other properties such as durability have not been adequately explored. In normal weight concrete, surface treatment has been used to improve durability, little research has been conducted on the efficacy of surface treatment agent on the durability of LWFC. Surface treatments are applied either during mixing (integral) or after curing (non-integral). This study investigates the durability of R/LWFC with a particular focus on carbonation and whether surface treatment can be used to limit corrosion induced by carbonation. The influence of surface treatment on the lightweight foamed concrete is also characterised. In this investigation R/LWFC is used with a target casting density of 1400 kg/m3 for testing changes in microstructure via CT scans, compressive strength, penetration depth (carbonation front and silane) and half-cell potential corrosion measurement. Application of integral and non-integral surface treatment is done and the effects on the R/LWFC and evaluated against results from control samples. CT scanning is used for investigating the effect of surface treatment on the lightweight foam concrete. An accelerated carbonation set-up is used to investigate carbonation resistance. Phenolphthalein indicator solution is used to determine the depth of carbonation. Integral surface treatment affected the size and distribution of voids compared to non-integral treatment. Consequently, the compressive strengths observed for integral surface treatment were higher than for control and non-integral treatment. The shape of the voids in integral and non-integral surface treated concrete were similar. Integral surface treatment provided the highest resistance to carbonation followed by the non-integral surface treatment. High levels of carbonation and carbonation rates were observed for control samples. The observed half-cell potentials showed that integral treatment resulted in high carbonation resistance. Little difference was observed between control samples and non-integral treatment. This investigation concluded that surface treatment can be used in lightweight foamed concrete to improve its durability against carbonation. The use of integral surface treatment in lightweight foam concrete resulted in additional benefits in increased compressive strengths thereby increasing its strength to weight ratio.

AFRIKAANSE OPSOMMING: Koolstof-geïnduseerde korrosie is 'n besorgdheid in gewapende ligte skuimbeton (G / LSB) as gevolg van luginrigting. Bekommernisse ontstaan uit of die lugruimtes diffusiwiteit van koolstofdioksied (CO2) in LSB verhoog. Die effek van karbonering is die vernietiging van die beskermende omhulsel vir die staalversterking. LSB is 'n lae digtheid beton waarin minstens 20 persent lug per volume in 'n basismengsel bestaan wat water, sement en 'n vulstof bevat. Die lugverbindings word behaal deur stabiele skuim by die basismengsel te voeg. LSB is 'n veelsydige konstruksiemateriaal waarvan die digtheid verander kan word deur gebruik te maak van verskillende hoeveelhede ingehokte lug om die vereiste funksie, strukturele of nie-strukturele, te pas. Die aansienlike hoeveelheid luginvoeding gee LSB sy voordele van hoë sterkte tot gewigsverhouding en verbeterde isolerende eienskappe. Alhoewel vordering gemaak is in LSB op mengontwerpe en geskikte druksterkte vir strukturele gebruik, is ander eienskappe soos duursaamheid nog agter gelaat. In normale gewigsbeton is oppervlakbehandeling gebruik om duursaamheid te verbeter. Geen ondersoek is gedoen na die effektiwiteit van oppervlakbehandelingsmiddel op die duursaamheid van LWFC nie. Oppervlaktebehandelings word toegedien gedurende meng (integraal) of na genesing (nie-integraal). Hierdie studie ondersoek die duursaamheid van R / LSB met 'n spesifieke fokus op karbonering en of oppervlakbehandeling gebruik kan word om die korrosie wat deur koolsuur veroorsaak word, te beperk. Die invloed van oppervlakbehandeling op die liggewig skuimbeton word ook gekenmerk. In hierdie ondersoek word R / LSB gebruik met 'n teikengietdigtheid van 1400 kg / m3 vir die toetsing van veranderinge in mikrostruktuur deur middel van RT-skanderings, druksterkte, penetrasie diepte (carbonation front en silaan) en half-sel potensiële korrosie meting. Toepassing van integrale en nie-integrale oppervlakbehandeling word gedoen en die effekte op die R / LSB en geëvalueer teen die resultate van kontrole monsters. RT-skanderings word gebruik om die effek van oppervlakbehandeling op die ligte skuimbeton te ondersoek. 'N Versnelde koolstofopstelling word gebruik om koolstofasiet weerstand te ondersoek. Fenolftaleïen-indikatoroplossing word gebruik om die diepte van karbonering te bepaal. Integrale oppervlakbehandeling het die grootte en verspreiding van holtes beïnvloed in vergelyking met nie-integrale behandeling. Gevolglik was die druksterkte waargeneem vir integrale oppervlakbehandeling hoër as vir beheer en nie-integrale behandeling. Die vorm van die holtes in integrale en nie-integrale oppervlak behandelde beton was soortgelyk. Integrale oppervlakbehandeling het die hoogste weerstand teen koolsuurwerk gevolg, gevolg deur die nie-integrale oppervlakbehandeling. Hoë vlakke van karbonasie en koolstofasietempo's is waargeneem vir kontrole monsters. Die waargenome halfsellepotensiale het getoon dat integrale behandeling tot hoë koolsuurweerstand gelei het. Daar is min verskil tussen kontrole monsters en nie-integrale behandeling. Hierdie ondersoek het tot die gevolgtrekking gekom dat oppervlakbehandeling gebruik kan word in ligte skuimbeton om sy duursaamheid teen koolsuur te verbeter. Die gebruik van integrale oppervlaktebehandeling in liggewigskuimbeton het bykomende voordele in verhoogde druksterkte tot gevolg gehad, waardeur die sterkte tot gewigsverhouding daarvan verhoog is.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102986
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