Service life estimation of cracked and healed concrete in marine environment

In the aggressive seawater environment, the durability of concrete is strongly influenced by the presence of chlorides and sulfates. Marine structures mostly have an important social function with a high economic impact, which makes durability a key issue. In addition, early-age cracks are a common problem, specifically for massive structural components. Repair of cracks is expensive and often impossible due to inaccessibility. Self-healing concrete is a promising solution to make marine structures more durable. In this study, capsules containing Polyurethane (PU) prepolymers were embedded in the concrete to release their contents when cracks appear. In cracked mortar, the chloride diffusion coefficients in the zone immediately around the crack significantly increased compared to uncracked mortar. The crack width dependency could be introduced into the service life model using a crack effect function. For crack widths in the range of 100 mu m to 300 mu m a service life decrease of around 80% was calculated. Autonomous crack healing had a beneficial influence on the resistance against chloride diffusion. However, for about one third of the cracks the healing mechanism failed, probably due to shifting of the tubes, tubes not rupturing properly, too high capillary forces in the tubes, etc. Nevertheless, on average, the service life of autonomously healed structures by means of encapsulated polyurethane increased with around 100% compared to cracked, unhealed structures. Moreover, in the most beneficial situation of proper healing, a service life increase of 150-550% was obtained, reaching values similar as for sound structures

Influence of chlorides on magnesium sulphate attack for mortars with Portland cement and slag based binders

Sulphate containing environments are aggressive and cause damage to cementitious materials by means of cracking, spalling and strength loss. In realistic conditions, sulphates may be found in combination with e.g. chlorides. Therefore, to predict concrete's durability, it is important to understand the (combined) attack mechanisms and estimate their effect. This study aimed to elucidate especially the influence of chlorides on magnesium sulphate attack at two different relevant temperatures (5 degrees C and 20 degrees C) and for mortars with different binders, including ordinary Portland cement (OPC), high-sulphate resistant Portland cement (HSR) and a binder composed of 50% blast-furnace slag (BFS) and 50% ordinary Portland cement. Mass change measurements were performed to examine the influence of Cl- on MgSO4 attack, and XRD-analyses to identify phase changes. It can be concluded that the influence of Cl- on MgSO4 attack is temperature and binder type dependent. The presence of chlorides does not affect deterioration due to magnesium sulphate for OPC and HSR at an environmental temperature of 20 degrees C, however, it increases the degradation when BFS is used as partial binder and/or when temperature decreases to 5 degrees C. The presence of BFS decreases the formation of a protecting brucite layer and favours decomposition of calcium silicate hydrates to magnesium silicate hydrates. At 5 degrees C the degradation involves thaumasite formation, and is more equal for the different binders and quite severe. (C) 2017 Elsevier Ltd. All rights reserved

Combined effects of chlorides and sulphates on cracked and self-healing concrete in marine environments

Concrete is a well-known construction material with a lot of positive properties such as high compressive strength, low cost, wide applicability, etc. Therefore, it is commonly used for marine constructions. This type of constructions mostly have an important social function with a high economic impact (e.g. bridges, wharfs, piers, tunnels, etc.), which makes durability a key issue. Nevertheless, a lot of damage is reported for constructions in marine environments. In this aggressive environment, the durability of concrete is strongly influenced by the presence of chlorides and sulphates, the main components of sea water. On the one hand, the sulphate attack degrades the concrete directly by forming expansive reaction products as well as strength decreasing reaction products. On the other hand, chlorides attack the concrete indirectly, by initiating corrosion at the reinforcement steel. In addition, earlyage cracks are a common problem, specifically for the massive structural components. These cracks promote the penetration of the aggressive substances. Thus, fast repair of the cracks is desirable. Without appropriate treatment, the amount and size of the cracks will increase. However, repair costs are large and in some cases repair is impossible due to inaccessibility. So in order to investigate the durability of concrete in marine environments, two main focus points can be defined. Firstly, it is important to understand the attack mechanisms occurring in marine environments in detail in order to understand the cause of the deterioration. Secondly, as a possible solution the material characteristics with regard to crack formation should be improved

The influence of sodium and magnesium sulphate on the penetration of chlorides in mortar

Marine environments are very aggressive to concrete, mainly due to the presence of chlorides and sulphates. The influence of sulphates on chloride penetration in mortars was investigated by immersion in combined test solutions containing 165 g/l NaCl and 33.8 g/l SO42- (as MgSO4 or Na2SO4) at temperatures of 5, 20 and 35 degrees C. After immersion periods ranging from 7 weeks up to 37 weeks, chloride profiles were measured by means of potentiometric titrations, XRD analysis and electron probe micro analysis. In general, chloride ions penetrate much deeper into the mortar than sulphate ions. Nevertheless, chloride penetration is clearly influenced by the presence of sulphates in the environment. Sulphate ions compete with chloride ions to bind to aluminate phases. Therefore, the presence of sulphates initially increases chloride diffusion. When magnesium sulphate is present the formation of Mg-related reaction products such as brucite additionally influences the chloride penetration. Later, up to 37 weeks of immersion, a decreasing chloride diffusion is noticed compared to samples exposed to a single chloride solution, due to pore blocking products of the sulphate reaction. Contrarily, immersion periods longer than 37 weeks in combined solutions result in increasing chloride diffusion due to sulphate induced cracking at the outermost layers. Notwithstanding the reciprocal influence of chlorides and sulphates, the magnitude of the effect of sulphate on the chloride diffusion coefficient was limited. Chloride diffusion generally increases with increasing temperature. The presence of sulphates decreases chloride binding even more significantly at 5 and 35 degrees C than at 20 degrees C

Self-healing concrete in aggressive enironments

Although certain crack widths are allowed in reinforced concrete structures, without having immediate effects on the structural stability, they may impair the durability and service life of the structure in the long term. Cracks wider than 10 μm will result, for instance, in a faster penetration of chlorides into the crack and from there onwards into the concrete matrix. Fortunately, the autogenous healing ability of concrete may close cracks of up to 100 μm completely. The further hydration of binder particles, will be supplemented by the deposition of calcium carbonate crystals in case of wet/dry cycles. In case of marine infrastructures in tidal zones, the presence of magnesium sulfates may enhance the crack sealing by means of brucite precipitation. These processes will result in reduced chloride penetration rates. If the cracks are larger than 100 μm or the conditions are not favourable for autogenous healing, autonomous healing mechanisms can be incorporated. In this case, healing is obtained through encapsulated polymeric healing agents, superabsorbent polymers, microbial agents, expansive additives, etc. With encapsulated polyurethane based healing agents, a reduction of the chloride concentration by 75% or more was obtained in a zone with a 300 μm wide crack after chloride diffusion tests, relative to the case in which cracks were not healed. As a result, the service life of reinforced concrete elements in marine environments could be increased with a factor of about 10. Neutron radiography images obtained during a capillary sorption test indicated that release of encapsulated polyurethane in wet conditions was favourable for the polyurethane reaction. As an alternative to the autonomous healing with encapsulated polyurethane, also the incorporation of encapsulated water repellent agents and corrosion inhibitors, has proven to effectively delay reinforcement corrosion during electrochemical measurement campaigns. Accelerated corrosion tests on cracked, manually treated mortar samples, allowed to rapidly screen different agents for their efficiency

Prophylactic use of meloxicam and paracetamol in peripartal sows suffering from postpartum dysgalactia syndrome

Postpartum dysgalactia syndrome (PPDS) is a major economic problem in modern sow farms. General treatment of PPDS consists of the use of oxytocin to promote milk ejection and non-steroidal anti-inflammatory drugs (NSAIDs) to alleviate inflammatory processes. So far, studies investigated the use of a single administration of NSAIDs after parturition in healthy and non-healthy sows. The current study investigated whether administration of meloxicam or paracetamol in sows prior to parturition improves sow and piglet health as well as performance in a farm with PPDS problems in sows. Sixty sows and 978 piglets from a Belgian farrow-to-finish farm were enrolled. Sows were randomly divided into three groups: a non-treated control group, a meloxicam-treated group and a paracetamol-treated group. Treatment was administered orally for 7 days from gestation day 113 onwards. Performance and health parameters investigated in sows were gestation length, farrowing duration, litter characteristics, colostrum yield and quality (Immunoglobulin G), litter weight gain, weaning-to-estrus interval, pregnancy rate, rectal temperature, acute phase proteins and inflammatory markers serum amyloid A, haptoglobin, interferon γ, interleukin 1β and 6 backfat, constipation and feed refusal. Performance and health parameters in piglets were birthweight, average daily weight gain, colostrum intake and mortality. Paracetamol-treated sows showed a significantly (P = 0.04) lower rectal temperature (mean ± SD: 38.09 ± 0.18°C) than the meloxicam-treated sows (38.24 ± 0.18°C), but not than the control group (38.22 ± 0.18°C). Sows of the paracetamol-treated group had a significantly (P = 0.001) longer gestation length (116.3 ± 0.9 days) than sows of the control group (115.3 ± 0.6 days), but not than meloxicam-treated sows (115.9 ± 0.9 days). No significant differences between the three groups were found for all the other parameters. In conclusion, the prophylactic oral administration of either meloxicam or paracetamol for 7 days starting 2 days prior to farrowing did not show beneficial effects on both health and performance parameters of sows and piglets