Effect of leaching on the composition of hydration phases during chloride exposure of mortar

Mortar specimens were exposed to either a 3% NaCl solution or a 3% NaCl+KOH solution for up to 180 days. Exposure to the NaCl solution provoked much more leaching than the NaCl+KOH exposure. Leaching strongly impacted the chloride ingress profiles. The extended leaching led to a maximum total chloride content almost three times higher and a deeper chloride penetration than exposure with limited leaching after 180 days. The higher maximum chloride content seems to be linked to the enhanced binding capacity of the C-S-H and AFm phases upon moderate leaching as determined by SEM-EDS. The total chloride profile appears to be governed by multi-ion transport and the interaction of chloride with the hydration phases. Service life prediction and performance testing both rely on total chloride profiles and therefore ought to take these interactions into account.publishedVersio

Carbonation resistance of concrete and mortar containing novel low clinker cement

Corrosion of reinforcement steel is a major deterioration mechanism for reinforced concrete structures. Corrosion can be caused by the carbonation of concrete. In this report we test the carbonation resistance of a novel low clinker cement with ground granulated blast-furnace slag (GGBFS) and limestone developed in the EnDurCrete project (CEMII/CM(S-LL)), by comparing its performance to an already commercially available blended cement (CEMII/A-S). We determine and compare the ingress of the carbonation front under accelerated laboratory conditions (1% CO2, 60% RH) on both mortar and concrete, for both cements, after 14, 28 and 90 days. We estimate the carbonation depth using two different techniques: thymolphtalein pH indicator and portlandite profiles determined by thermogravimetric analysis (TGA). In addition, we determine the relative humidity in the samples prior to exposure. The average RH for the mortar and concrete samples prior to exposure was similar. This suggests that mortar samples can be used to describe the moisture state in concrete. The RH ranged between 88 and 92%, which agrees with the level one would obtain by self-desiccation in sealed samples. The portlandite content in the non-carbonated EnDurCrete mortar is lower compared to the reference mortar, as can be expected due to the higher replacement levels with GGBFS. A lower carbonation resistance could be expected because of this, however this was not the case for the concrete samples. The carbonation depth determined by the pH indicator and the portlandite profiles agree well, taking into account the different ways of sampling for the two methods. The carbonation ingress results for mortar and concrete agree well, except for the reference mortar samples which showed a lower carbonation ingress. The reason for this is unknown. Based on the carbonation ingress results obtained on concrete, the EnDurCrete concrete exhibits a similar carbonation resistance as the reference concrete with the commercially available cement. This indicates the possibility to introduce the EnDurCrete cement as a valuable alternative to commercially available cements, providing similar properties and substantial reduction in greenhouse gases during production

Impact of leaching on chloride ingress profiles in concrete

Kloridinitiert armeringskorrosjon er en av hovednedbrytningsmekanismene for armerte betongkonstruksjoner. Klorider trenger igjennom betongoverdekningen over tid og forårsaker korrosjon når de når et kritisk kloridinnhold ved armerings overflaten. Betongens motstand mot kloridinntrenging er derfor avgjørende for levetiden. I denne studien ønsket vi å undersøke effekten utlekking har på kloridinntrengingsprofiler i betong. Betong- og mørtelprøver ble eksponert for to ulike eksponeringsløsninger i 90 dager: 3 % NaCl, og 3 % NaCl tilsatt KOH for å begrense utlekking. Løsningene ble byttet ut ukentlig. Etter eksponering ble kloridprofiler i prøvene bestemt, i tillegg til portlanditt- og kaliumprofiler for å bestemme graden av utlekking. Vi observerte at utlekking fører til betydelig høyere maksimalt kloridinnhold, sammenliknet med prøvene med begrenset utlekking (150 % økning). Kloridinntrengingsdybden var derimot mindre påvirket av utlekking, noe som betyr at levetiden ikke nødvendigvis blir redusert på grunn av utlekking. De totale kloridprofilene er i hovedsak styrt av kloridbinding i prøvene. Det ble demonstrert at dette kan føre til feilaktig estimering av levetid ved bruk av empiriske modeller, derfor burde mer mekanistiske levetidsmodeller tas i bruk

Measurement of the chloride resistance of environmentally friendly and durable concrete

The increasing demand for concrete and thereby Portland cement, creates the need for novel low-clinker Portland composite cements. Concretes prepared with such novel composite cements need to show similar or even improved durability compared to concrete prepared with commonly used Portland composite cements. This study represents a part of the EnDurCrete project that focuses on the durability of concrete produced with novel low-clinker cements, containing high-value industrial by-products. More specifically, we investigated the chloride ingress resistance of such concrete. Concrete cylinders were submitted to chloride ingress by bulk diffusion. The chloride ingress resistance was investigated on concrete samples by %XRF scanning and chloride titration. In addition, the chloride binding capacity of these novel binders was investigated on paste samples by determining chloride binding isotherms for both binders. In the next step of the project, these experimental results will be matched with an advanced model, which is being developed within the project. By combining modelling with experimental verification, we aim to reach a better understanding of the fundamental chloride ingress mechanisms acting on novel types of concrete. The overall goal of the work is to produce a concrete with lower cost, lower environmental footprint and with verified similar or improved durability

Impact of leaching on chloride ingress profiles in concrete

To investigate the effect of leaching on chloride ingress profiles in concrete and mortar, we exposed concrete and mortar specimens for 90 and 180 days to two different exposure solutions: 3% NaCl, and 3% NaCl with KOH added to limit leaching. The solutions were replaced weekly. After exposure, we determined total chloride profiles to investigate the chloride ingress, and portlandite profiles to assess the extent of leaching. The results showed that leaching during exposure greatly affects the chloride ingress profiles in mortar and concrete. We found that leaching leads to considerably higher maximum total chloride content and deeper chloride penetration into the concrete than in the specimens where leaching was limited. We recommend therefore that leaching should be taken into account in standard laboratory testing and that more mechanistic service life models should be used to take into account the impact of leaching

Experimental carbonation study for a durability assessment of novel cementitious materials

Durability predictions of concrete structures are derived from experience-based requirements and descriptive exposure classes. To support durability predictions, a numerical model related to the carbonation resistance of concrete was developed. The model couples the rate of carbonation with the drying rate. This paper presents the accelerated carbonation and moisture transport experiments performed to calibrate and verify the numerical model. They were conducted on mortars with a water-cement ratio of either 0.6 or 0.5, incorporating either a novel cement CEM II/C (S-LL) (EnM group) or commercially available CEM II/A-S cement (RefM group). The carbonation rate was determined by visual assessment and thermogravimetric analysis (TGA). Moisture transport experiments, consisting of drying and resaturation, utilized the gravimetric method. Higher carbonation rates expressed in mm/day(−0.5) were found in the EnM group than in the RefM group. However, the TGA showed that the initial portlandite (CH) content was lower in the EnM than in the RefM, which could explain the difference in carbonation rates. The resaturation experiments indicate an increase in the suction porosity in the carbonated specimens compared to the non-carbonated specimens. The study concludes that low clinker content causes lower resistance to carbonation, since less CH is available in the surface layers; thus, the carbonation front progresses more rapidly towards the core

Experimental carbonation study for a durability assessment of novel cementitious materials

Durability predictions of concrete structures are derived from experience-based requirements and descriptive exposure classes. To support durability predictions, a numerical model related to the carbonation resistance of concrete was developed. The model couples the rate of carbonation with the drying rate. This paper presents the accelerated carbonation and moisture transport experiments performed to calibrate and verify the numerical model. They were conducted on mortars with a water-cement ratio of either 0.6 or 0.5, incorporating either a novel cement CEM II/C (S-LL) (EnM group) or commercially available CEM II/A-S cement (RefM group). The carbonation rate was determined by visual assessment and thermogravimetric analysis (TGA). Moisture transport experiments, consisting of drying and resaturation, utilized the gravimetric method. Higher carbonation rates expressed in mm/day−0.5 were found in the EnM group than in the RefM group. However, the TGA showed that the initial portlandite (CH) content was lower in the EnM than in the RefM, which could explain the difference in carbonation rates. The resaturation experiments indicate an increase in the suction porosity in the carbonated specimens compared to the non-carbonated specimens. The study concludes that low clinker content causes lower resistance to carbonation, since less CH is available in the surface layers; thus, the carbonation front progresses more rapidly towards the core

Effect of leaching on the composition of hydration phases during chloride exposure of mortar

Mortar specimens were exposed to either a 3% NaCl solution or a 3% NaCl+KOH solution for up to 180 days. Exposure to the NaCl solution provoked much more leaching than the NaCl+KOH exposure. Leaching strongly impacted the chloride ingress profiles. The extended leaching led to a maximum total chloride content almost three times higher and a deeper chloride penetration than exposure with limited leaching after 180 days. The higher maximum chloride content seems to be linked to the enhanced binding capacity of the C-S-H and AFm phases upon moderate leaching as determined by SEM-EDS. The total chloride profile appears to be governed by multi-ion transport and the interaction of chloride with the hydration phases. Service life prediction and performance testing both rely on total chloride profiles and therefore ought to take these interactions into account

Effect of leaching on the composition of hydration phases during chloride exposure of mortar

Mortar specimens were exposed to either a 3% NaCl solution or a 3% NaCl+KOH solution for up to 180 days. Exposure to the NaCl solution provoked much more leaching than the NaCl+KOH exposure. Leaching strongly impacted the chloride ingress profiles. The extended leaching led to a maximum total chloride content almost three times higher and a deeper chloride penetration than exposure with limited leaching after 180 days. The higher maximum chloride content seems to be linked to the enhanced binding capacity of the C-S-H and AFm phases upon moderate leaching as determined by SEM-EDS. The total chloride profile appears to be governed by multi-ion transport and the interaction of chloride with the hydration phases. Service life prediction and performance testing both rely on total chloride profiles and therefore ought to take these interactions into account