N. De Belie

Chemical and microbiological tests to simulate sulfuric acid corrosion of polymer-modified concrete

Abstract In certain industrial activities sulfuric acid is used during the production process, which may cause degradation of concrete structures. Another important phenomenon where sulfuric acid is responsible for concrete corrosion is biogenic sulfuric acid corrosion, which occurs often in sewer systems. Because previous investigations have already pointed out the difference between purely chemical sulfuric acid corrosion and biogenic sulfuric acid corrosion two different tests were performed: a chemical test and a microbiological test. Five different concrete compositions were used in the tests, including a reference mixture with high sulfate resistant portland cement and four different polymer cement concrete with a styrene–acrylic ester polymer, an acrylic polymer, a styrene butadiene polymer and a vinylcopolymer, respectively. The concrete composition with the styrene–acrylic ester polymer showed in both tests a higher resistance than the reference mixture while the compositions with the acrylic polymer and the styrene butadiene polymer had a lower resistance than the reference mixture. The concrete composition with the vinylcopolymer did not induce the same results in both tests. The results of the chemical test indicated a slight increase in resistance compared with the reference mixture while the opposite was noticed for the microbiological test.

Repeated Autogenous Healing in Strain-Hardening Cementitious Composites by Using Superabsorbent Polymers

AbstractAutogenous healing is an already-present feature in strain-hardening cementitious materials, but it is an inferior mechanism because it can only heal small cracks in the presence of water. A cementitious material with synthetic microfibers and superabsorbent polymers (SAPs) could provide a solution. In this study, the ability of repeatable promoted autogenous healing in fiber-reinforced, strain-hardening cementitious materials with and without SAPs is investigated by comparing their mechanical properties after they are subjected to two cycles of loading under a four-point-bending test. The results indicate that SAP particles promote self-healing. The main mechanisms of the autogenous healing are the hydration of unhydrated cementitious materials in cracks and the precipitation of calcium carbonate on the crack faces. The healed specimens are able to regain some of their mechanical properties (up to 75%). Even second reloading of those healed samples leads to partial additional regain in mechanical...

Methyl methacrylate as a healing agent for self-healing cementitious materials

Different types of healing agents have already been tested on their efficiency for use in self-healing cementitious materials. Generally, commercial healing agents are used while their properties are adjusted for manual crack repair and not for autonomous crack healing. Consequently, the amount of regain in properties due to self-healing of cracks is limited. In this research, a methyl methacrylate (MMA)-based healing agent was developed specifically for use in self-healing cementitious materials. Various parameters were optimized including the viscosity, curing time, strength, etc. After the desired properties were obtained, the healing agent was encapsulated and screened for its self-healing efficiency. The decrease in water permeability due to autonomous crack healing using MMA as a healing agent was similar to the results obtained for manually healed cracks. First results seem promising: however, further research needs to be undertaken in order to obtain an optimal healing agent ready for use in practice.

Resistance of different types of concrete mixtures to sulfuric acid

The resistance of seven different concrete mixtures against a 0.5% sulfuric acid solution was examined. The difference between high sulfate resistant Portland cement and blast furnace cement, as well as the influence of polymer modifications of the concrete and the addition of silica fume were issues of the investigation. All concrete mixtures were submitted to an alternating immersion and drying during 18 weeks in a 0.5% sulfuric acid solution using a testing apparatus for accelerated degradation tests. The corrosion of the concrete was quantified by measuring the change in dimensions of the test specimens with laser sensors. The mixture with addition of silica fume was most vulnerable to corrosion. Depending on the polymer type used, polymer modification of the concrete resulted in an increase and a decrease in the resistance of the concrete respectively. The concrete made with blast furnace cement had the highest resistance of all tested concrete types.RésuméLa résistance de sept bétons différents à l’action corrosive d’une solution contenant 0,5% d’acide sulfurique a constitué le sujet de cette recherche. La différence entre un ciment Portland à haute résistance aux sulfates et un ciment de haut fourneau, ainsi que l’influence de la modification de polymères et de l’ajovt de fumée de silice ont été examinées. Tous les bétons ont été soumis, en alternance pendant 18 semaines, à une immersion dans la solution sulfurique et à un séchage, au moyen de l’appareil d’essais de corrosion accélérée. L’action de la corrosion a été mesurée avec des lasers mettant en évidence les changements de dimension des éprouvettes. Le béton contenant de la fumée de silice a présenté la moins bonne résistance par rapport aux autres bétons. La résistance du béton augmente ou diminue suivant le type de polymère utilisé. Parmi tous les bétons, c’est le béton fait de ciment de haut fourneau qui a offert la meilleure résistance.

Antimicrobial mortar surfaces for the improvement of hygienic conditions

Aims:  To evaluate the effectiveness of various antimicrobial mortar formulations in inhibiting the growth of a selection of pathogens of environmental and hygienic concern.

Microorganisms versus stony materials: a love–hate relationship

Micro-organisms can have a devastating effect on building materials. They produce a range of organic and inorganic acids and enzymes, inducing solution and alteration of mineral phases. Biofilms alter the water exchange of the material and also mechanical effects add to the biodeterioration. One especially deleterious process in which bacteria are involved, is biogenic sulphuric acid corrosion in sewer systems. On the other hand, some types of bacteria can be used in engineering applications, for example for biological cleaning and bioconsolidation. Bacterially induced carbonate precipitation has been proposed as an environmentally friendly method to consolidate and protect decayed limestone or cementitious materials. The method relies on the bacterially induced formation of a compatible and highly coherent carbonate precipitate. Furthermore, the same principle can be applied for manual or autonomous remediation of cracks in concrete and the bacteria are in this case used as self healing agents.

Detecting the Activation of a Self-Healing Mechanism in Concrete by Acoustic Emission and Digital Image Correlation

Autonomous crack healing in concrete is obtained when encapsulated healing agent is embedded into the material. Cracking damage in concrete elements ruptures the capsules and activates the healing process by healing agent release. Previously, the strength and stiffness recovery as well as the sealing efficiency after autonomous crack repair was well established. However, the mechanisms that trigger capsule breakage remain unknown. In parallel, the conditions under which the crack interacts with embedded capsules stay black-box. In this research, an experimental approach implementing an advanced optical and acoustic method sets up scopes to monitor and justify the crack formation and capsule breakage of concrete samples tested under three-point bending. Digital Image Correlation was used to visualize the crack opening. The optical information was the basis for an extensive and analytical study of the damage by Acoustic Emission analysis. The influence of embedding capsules on the concrete fracture process, the location of capsule damage, and the differentiation between emissions due to capsule rupture and crack formation are presented in this research. A profound observation of the capsules performance provides a clear view of the healing activation process.

Cleaning of concrete fouled by lichens with the aid of Thiobacilli

Concrete specimens weathered for over a decade in the moderate Belgian climate, showing a black organic outer layer that mainly consisted of lichens, were cleaned with a new biological technique. A mixture of sulphur oxidising bacteria of the genusThiobacillus supplemented with an appropriate nutrient was applied to a fouled concrete surface, either by sprinkling or by submersion. The aim was to remove the fouled layer in such a way that the surface is uniformly cleaned. The general effect of the technique was evaluated by colorimetry and microscopy. Two sets of weathered concrete specimens, containing blast furnace slag cement or ordinary portland cement, were investigated. The effectiveness of the technique depended on the cement type of the concrete specimens. The effect on the ordinary portland cement concrete specimens was in some cases up to a factor 2 stronger than the result on the blast furnace slag cement specimens. The sprinkling treatment was about 50% as effective as the submersion treatment but was very promising in the case of in situ acidification. A side effect was the formation of a gypsum layer on some of the specimens, resulting in a whiter colour.

Differences in chewing sounds of dry-crisp snacks by multivariate data analysis

Abstract Chewing sounds of different types of dry-crisp snacks (two types of potato chips, prawn crackers, cornflakes and low calorie snacks from extruded starch) were analysed to assess differences in sound emission patterns. The emitted sounds were recorded by a microphone placed over the ear canal. The first bite and the first subsequent chew were selected from the time signal and a fast Fourier transformation provided the power spectra. Different multivariate analysis techniques were used for classification of the snack groups. This included principal component analysis (PCA) and unfold partial least-squares (PLS) algorithms, as well as multi-way techniques such as three-way PLS, three-way PCA (Tucker3), and parallel factor analysis (PARAFAC) on the first bite and subsequent chew. The models were evaluated by calculating the classification errors and the root mean square error of prediction (RMSEP) for independent validation sets. It appeared that the logarithm of the power spectra obtained from the chewing sounds could be used successfully to distinguish the different snack groups. When different chewers were used, recalibration of the models was necessary. Multi-way models distinguished better between chewing sounds of different snack groups than PCA on bite or chew separately and than unfold PLS. From all three-way models applied, N-PLS with three components showed the best classification capabilities, resulting in classification errors of 14–18%. The major amount of incorrect classifications was due to one type of potato chips that had a very irregular shape, resulting in a wide variation of the emitted sounds.

RESISTANCE OF CONCRETE WITH LIMESTONE SAND OR POLYMER ADDITIONS TO FEED ACIDS

By using limestone sand or polymer additions in the concrete mix, it was attempted to reduce the deterioration of concrete floors in pig houses by lactic and acetic acid. To simulate in a standardized and automated way chemical attack by those acids and abrasion caused by animals and cleaning, a testing apparatus for accelerated degradation tests was developed. Concrete cylinders mounted on rotating axles were turning through containers with simulation liquid. After each attack cycle the concrete was brushed with rotary brushes. Concrete degradation was measured with laser sensors connected to a computer and the average attack depth and the Ra-value, which is a measure of surface roughness, were calculated. Results of previous experiments, showing that concrete with blast furnace slag cement was much more resistant than the reference concrete with ordinary portland cement, were confirmed. The use of limestone sand and possibly limestone aggregates led to a quicker neutralization of the aggressive liquid, but was insufficient to reduce the average attack depth. When limestone sand and limestone aggregates were used, the increase in concrete roughness was smaller than for concrete with limestone sand and gravel aggregates. Addition of 10% polymers to the concrete mix increased the resistance significantly, when care was taken that the polymer cement concrete (PCC) didn’t contain too much air voids. The most resistant PCC, containing a styrol acrylic acid ester showed after six cycles an average attack depth 12 times smaller than the reference concrete. Furthermore the potential benefit of the polymers was probably underestimated, as an investigation with the scanning electron microscope showed that the emulsified polymer had not completely formed a film.