Destruction of concrete by nitrification

Summary Nitrification was studied, using samples of asbestos concrete plates and water, both taken from a cooling tower, in which ammonia-containing water had been circulated for several years. Almost the entire nitrifying activity and the majority of autotrophic nitrifying bacteria were found to be located in the coating, covering the asbestos concrete plates. When sprinkled over these plates, the H⁺-concentration of such ammonia-containing water increased from neutrality to about pH 5.3 and this pH was maintained as long as nitrification was feasible. Death of microorganisms and lack of either ammonia or oxygen caused a rapid decrease of H⁺-concentration, which was obviously due to concrete destruction. The temporary acidification observed in the medium resulted from both acid-producing microbial nitrification and acid consuming concrete dissolution, with both reactions counteracting each other. The amount of nitric acid required to maintain a low pH in presence of concrete was determined by automatic titration. The obtained result indicated that considerable amounts of nitric acid might have been formed in the cooling system, which could well account for the observed damage.     

Microfouling studies on experimental test blocks of steel-making slag and concrete exposed to seawater off Chiba, Japan

Microfouling studies with the emphasis on microalgae (Bacillariophyceae) were carried out on test blocks of steel-making slag in comparison with concrete. Two types of slag test blocks, with and without fly-ash as an additional source of silica, and concrete test blocks of size 75 x 26 x 26 mm were used to study microfouling build-up for a period of 30 d, with intermittent samplings after 1, 2, 3, 7, 14 and 21 d. The species composition, cell density, biomass and surface pH of the test pieces were determined, in addition to the hydrographic parameters of the water column. Microfouling studies showed higher numbers of algal species as well as a greater cell density on the slag than on the concrete blocks. This was true with respect to biomass measured as dry weight also. Colonization was significantly delayed in the case of concrete. Navicula spp. and Nitzschia spp. were the initial colonizers on all three types of substrata and were the dominant genera throughout the study period. While the number of species increased, several disappeared after colonization, as a part of community build-up. The surface pH of the slag blocks was near neutral, whilst that of the concrete was highly alkaline during the initial period of exposure. This alkaline surface reduced the rate of species colonization on the concrete blocks initially. The study showed severe biofouling on the slag blocks compared to concrete and thus they were considered an environmentally benign construction material for land protection. The use of slag as the construction material for land protection would greatly reduce the expense compared to concrete.     

Identification and characterization of alkali-tolerant clostridia isolated from biodeteriorated casein-containing building materials

Summary Reports on malodour in buildings constructed in the late 1970s gave rise to thorough investigations on the possible role of vapours of chemical compounds emitted by building materials. The odour could be related to the use of casein as an additive to improve the fluidity of concrete materials used as a self-levelling floor topping compound. Casein was suggested to be degraded by microorganisms, resulting in an accumulation of malodorous substances in the topping compounds.Bacteria isolated from biodeteriorated concrete materials containing caseins exhibited unusual tolerance towards high pH. Two dominant species were found among a total of 80 sporeforming, anaerobic isolates from concrete and raw products of caseins, namely Clostridium bifermentans and Clostridium sporogenes. C. bifermentans had a maximal pH tolerance of 12.2 while C. sporogenes could reproduce up to pH 11.7. The study includes the identification of the clostridia with API multitest as well as an investigation of the volatile organic acid and monoamine patterns. About 100 cfu clostridia/g material could be obtained during the isolation procedures.     

pH variations during growth of Acidithiobacillus thiooxidans in buffered media designed for an assay to evaluate concrete biodeterioration

The pH of two buffered media having their initial pH ranging between 3.5 and 8.5 was monitored during growth of Acidithiobacillus thiooxidans. The first media was buffered with tricyclic phosphate whereas the second one contained phosphate ions and thus exhibited a stronger buffer capacity. Bacterial growth was not observed in any of the two media when the initial pH was higher than 5.5. On the other hand, for initial pH lower than 5.5, bacterial growth induced pH drops in both media. This drop was preceded by a lag phase during which the pH remained unchanged. However, in the medium buffered with phosphate ions, the lag periods were longer. As these media were developed for designing a bioleaching test to evaluate concrete biodeterioration caused by A. thiooxidans, the medium containing tricyclic phosphate appeared to be the most appropriate.     

Changes in the immunoglobulin M conformation in media with different degrees of acidity

The pH-dependent conformational changes in immunoglobulin M were studied by differential spectrophotometry. It was found that the state of chromophores (tryptophan and tyrosine) which reflects conformational changes of the structure alters stepwise in the course of acidification. The native structure is not restored by neutralization. The recovery of the native structure was obtained only at pH approximately 6.5 of the IgM solution. A possible explanation of concrete conformational transitions during the pH change is proposed. These changes were shown to be similar for IgM and IgG.     

Design of concrete : Setting a new basis for improving both durability and environmental performance

CO₂ emissions from cement production currently represent around 6% of global CO₂ emissions. However, cement concrete absorbs CO₂ from the atmosphere because of carbonation (i.e., penetration of atmospheric CO₂ inside bulk concrete). Carbonation has beneficial effects on the mechanical resistance of cement concrete. However, carbonation also has adverse effects because it provokes a decrease in pH that favors later corrosion of reinforcing bars and thus reduces service life. Current European standards provide recommendations concerning reinforcing concrete covers, but these are not based on actual service‐life durations. Thanks to a previously developed carbonation model combined with sensitivity analysis and LCA, we compare Climate Change indicators of 1 m² of reinforced concrete cover over a 100‐years service life exposed to XC4 conditions in Madrid, obtained on one hand by using current standards and on the other hand with concrete‐cover depths calculated with our carbonation model. Our results show that cement strength class is a key parameter to both increase durability and decrease climate‐change impacts. When the carbonation model is used to optimize both durability and climate‐change impacts, it drives to considerable and significant improvements. Finally, climate‐change indicators predicted from our carbonation model are not linearly linked to carbon intensity of cements, which is a current argument of so‐called “green cements.” The values of indicators presented in this article cannot be generalized: They mainly depend on the geographical location. However, the model and key action levers are general. Using high cement strength classes and low water‐to‐cement ratios allows use of lower concrete‐cover depths and thus save amounts of concrete compared to the standard. This generates an important benefit in terms of climate‐change impacts for identical service lives and improved mechanical resistance. Thus, considering the huge impact of cement and construction industry on climate change, we plead for a revision of standards which, instead of thresholds based on simplified models, should provide certified tools enabling the best design for every situation. This article met the requirements for a gold/gold JIE data openness badge described at http://jie.click/badges.     

Succession of sulfur-oxidizing bacteria in the microbial community on corroding concrete in sewer systems

Microbially induced concrete corrosion (MICC) in sewer systems has been a serious problem for a long time. A better understanding of the succession of microbial community members responsible for the production of sulfuric acid is essential for the efficient control of MICC. In this study, the succession of sulfur-oxidizing bacteria (SOB) in the bacterial community on corroding concrete in a sewer system in situ was investigated over 1 year by culture-independent 16S rRNA gene-based molecular techniques. Results revealed that at least six phylotypes of SOB species were involved in the MICC process, and the predominant SOB species shifted in the following order: Thiothrix sp., Thiobacillus plumbophilus, Thiomonas intermedia, Halothiobacillus neapolitanus, Acidiphilium acidophilum, and Acidithiobacillus thiooxidans. A. thiooxidans, a hyperacidophilic SOB, was the most dominant (accounting for 70% of EUB338-mixed probe-hybridized cells) in the heavily corroded concrete after 1 year. This succession of SOB species could be dependent on the pH of the concrete surface as well as on trophic properties (e.g., autotrophic or mixotrophic) and on the ability of the SOB to utilize different sulfur compounds (e.g., H2S, S0, and S2O3(2-)). In addition, diverse heterotrophic bacterial species (e.g., halo-tolerant, neutrophilic, and acidophilic bacteria) were associated with these SOB. The microbial succession of these microorganisms was involved in the colonization of the concrete and the production of sulfuric acid. Furthermore, the vertical distribution of microbial community members revealed that A. thiooxidans was the most dominant throughout the heavily corroded concrete (gypsum) layer and that A. thiooxidans was most abundant at the highest surface (1.5-mm) layer and decreased logarithmically with depth because of oxygen and H2S transport limitations. This suggested that the production of sulfuric acid by A. thiooxidans occurred mainly on the concrete surface and the sulfuric acid produced penetrated through the corroded concrete layer and reacted with the sound concrete below.     

Laboratory evaluation of large-scale decontamination approaches

Aims: To evaluate the effectiveness of two spray‐based decontamination methods for surface contamination reduction and to determine the potential for contamination spread by these methods. Methods and Results: Material coupons (treated plywood and concrete) were contaminated with c. 1 × 10⁷ spores of Bacillus atrophaeus by aerosol deposition. Decontaminants (pH‐adjusted bleach or Spor‐Klenz^® RTU) were applied to coupons by either backpack sprayer or gas‐powered sprayer. Contact time, reapplication frequency and rinse method were also varied. In addition to surface removal efficacy, partitioning of contamination between the rinsate and aerosol fractions was determined. Results indicated that pH‐adjusted bleach was effective (≥6 logs reduction) when two applications and a 30 min contact time were administered, regardless of the decontaminant application method or material. Spor‐Klenz^® RTU was effective on wood, but achieved ≤3 logs reduction on concrete. A shortened application procedure with pH‐adjusted bleach resulted in lower efficacy on wood, and a greater apparent potential for contamination spread. Conclusions: Consideration of material surface type is important when selecting a decontaminant. Also, achieving conditions that effectively inactivate surface biological contamination are critical to preventing the spread of contamination. Significance and Impact of the Study: Results presented here are intended to help development of remediation plans following a biological contamination incident.     

Si amelioration of Al toxicity in barley (Hordeum vulgare L.) growing in two Andosols

The influence of silicon on aluminium toxicity in barley (Hordeum vulgare L. cv. Shunrai) was studied in two Andosols. Silicon sources were a solution of sodium metasilicate with pH adjusted to 5.0, silica gel, and an industrial waste, porous hydrated calcium silicate. The waste is produced in large amounts in the manufacturing processes of autoclaved light concrete, and has been used as a silicon source for rice plants. The addition of the waste increased the concentration of Si in the soil solution, soil pH and amelioration of aluminium toxicity was observed. The addition of silica gel and sodium metasilicate solution to both soils increased significantly (p<0.05) the Si concentration of the soil solutions, but no amelioration of aluminium toxicity was observed. An amelioration of aluminium toxicity by the waste porous hydrated calcium silicate was probably due to the increase in soil pH rather than to the increase of silicon concentration in the soil solution.     

Succession of Sulfur-Oxidizing Bacteria in the Microbial Community on Corroding Concrete in Sewer Systems

Microbially induced concrete corrosion (MICC) in sewer systems has been a serious problem for a long time. A better understanding of the succession of microbial community members responsible for the production of sulfuric acid is essential for the efficient control of MICC. In this study, the succession of sulfur-oxidizing bacteria (SOB) in the bacterial community on corroding concrete in a sewer system in situ was investigated over 1 year by culture-independent 16S rRNA gene-based molecular techniques. Results revealed that at least six phylotypes of SOB species were involved in the MICC process, and the predominant SOB species shifted in the following order: Thiothrix sp., Thiobacillus plumbophilus, Thiomonas intermedia, Halothiobacillus neapolitanus, Acidiphilium acidophilum, and Acidithiobacillus thiooxidans. A. thiooxidans, a hyperacidophilic SOB, was the most dominant (accounting for 70% of EUB338-mixed probe-hybridized cells) in the heavily corroded concrete after 1 year. This succession of SOB species could be dependent on the pH of the concrete surface as well as on trophic properties (e.g., autotrophic or mixotrophic) and on the ability of the SOB to utilize different sulfur compounds (e.g., H₂S, S⁰, and S₂O₃²⁻). In addition, diverse heterotrophic bacterial species (e.g., halo-tolerant, neutrophilic, and acidophilic bacteria) were associated with these SOB. The microbial succession of these microorganisms was involved in the colonization of the concrete and the production of sulfuric acid. Furthermore, the vertical distribution of microbial community members revealed that A. thiooxidans was the most dominant throughout the heavily corroded concrete (gypsum) layer and that A. thiooxidans was most abundant at the highest surface (1.5-mm) layer and decreased logarithmically with depth because of oxygen and H₂S transport limitations. This suggested that the production of sulfuric acid by A. thiooxidans occurred mainly on the concrete surface and the sulfuric acid produced penetrated through the corroded concrete layer and reacted with the sound concrete below.     

Structural properties of the neutral and monoanionic forms of xanthosine,highly relevant to their substrate properties with various enzyme systems

The monoanions of the 6-oxopurines guanine (Gua) and hypoxanthine (Hx), and their nucleosides, pKa approximately 9 due to dissociation of the N(1)-H, are predominantly in their neutral forms at physiological pH. By contrast, the monoanions of the 6-oxopurine xanthine (Xan) and xanthosine (Xao), were long ago proposed to involve dissociation of the N(3)-H, with pKa values of 7.5 and 5.7, respectively, so that, at physiological pH, the former is mixture of the neutral and monoanionic species, and the latter predominantly the monoanion. We have employed multi-dimensional heteronuclear NMR spectroscopy, which fully confirms the proposed mode of monoanion formation in Xao (and, by implication, in Xan), further supported by the results of ab initio quantum mechanical calculations, and additionally extended to determination of the preferred conformational parameters in solution for the neutral and monoanionic species. These findings are highly relevant to the modes of binding, and to the substrate properties, of Xan, Xao and its 5'-phosphate (XMP) in numerous enzyme systems, hitherto virtually ignored, and illustrated by several concrete examples.     

基于芽胞的混凝土微生物原位修复技术研究进展

混凝土是最广泛使用的现代建筑材料,在应力作用下易于开裂,使混凝土结构具有渗透性,影响其耐用性和完整性,进而缩短使用寿命.混凝土微生物原位修复技术是一种廉价、有效、绿色的方式,因其具有良好的生物相容性、延长混凝土服役寿命、减少经济损失与环境污染等特点,已成为研究热点.其中,芽胞杆菌因良好的生物矿化能力且其芽胞具有极强的环...     

Effect of overlaying rubber on fully slatted concrete floors on hoof health and lying postures in finishing dairy-origin bulls offered two contrasting diets

Fully slatted concrete floors are labour-efficient, cost-effective and thus common in beef cattle housing. However, the welfare of cattle accommodated on them has been questioned. The objective of this study was to evaluate the effect of floor and diet on hoof health and lying behaviours of housed dairy-origin bulls, from a mean age of 8 months to slaughter at 15.5 months old. Forty-eight bulls, which had a mean initial live weight of 212 (SD = 23.7) kg, were allocated to one of four treatments, which consisted of two floors and two diets arranged in a 2 × 2 factorial design. The floors evaluated were a fully slatted concrete floor and a fully slatted concrete floor overlaid with rubber, while the diets offered were either a high concentrate diet or a grass-silage-based diet supplemented with concentrates. The mean total duration of the study was 216 days. Floor had no significant effect on claw measurements measured on day 62 or 139. However, bulls accommodated on slats overlaid with rubber had a tendency to have a higher front toe length measured pre-slaughter than those accommodated on concrete slats (P = 0.063). Floor had no significant effect on the net growth of toes or heels during the duration of the study. The number of bruises (P < 0.01) and the bruising score (P < 0.05) were significantly higher on day 62 in bulls accommodated on fully slatted concrete floors than on concrete slats overlaid with rubber, but there was no significant effect of floor on these parameters on day 139 or at the measurement taken pre-slaughter. There was a tendency for bulls accommodated on concrete slats to have a higher probability of having sole bruising at the end of the experiment than those accommodated on slats overlaid with rubber (P = 0.052). Diet had no significant effect on toe length or heel height, number of bruises, or overall bruising score at any time point of the study. There was little evidence in the current study to suggest that bulls lying on fully slatted concrete floors could not express lying postures similar to those on concrete slats overlaid with rubber.     

The use of pH indicators to identify suitable environments for freezing samples in aqueous and mixed aqueous/nonaqueous solutions

The colours of frozen solutions containing pH indicators are shown to provide a test for changes in pH in the solvent environment which occur on freezing. Yeast alcohol dehydrogenase loses activity on freezing in phosphate buffer (a buffer in which pH indicator colour changes shows a marked decrease in pH on freezing) but when frozen in bis-tris, Hepes, or N-glycylglycine buffers (all of which show little change in the colour of universal pH indicator and hence of pH on freezing) is stable on freezing. The effects of freezing in different buffer systems on the rate of decomposition of NADPH, and on the rate hydrolysis of 4-nitrophenyl acetate, are rationalised in terms of the pH shifts in these buffers which were determined using universal pH indicator. It is proposed that a major reason for the instability of samples on freezing is the pH changes which occur when some systems are frozen. From the results a general scheme for selecting the best environment for safely freezing samples is proposed which is based on the use of pH indicators.     

Naming a Lego World. The Role of Language in the Acquisition of Abstract Concepts

While embodied approaches of cognition have proved to be successful in explaining concrete concepts and words, they have more difficulties in accounting for abstract concepts and words, and several proposals have been put forward. This work aims to test the Words As Tools proposal, according to which both abstract and concrete concepts are grounded in perception, action and emotional systems, but linguistic information is more important for abstract than for concrete concept representation, due to the different ways they are acquired: while for the acquisition of the latter linguistic information might play a role, for the acquisition of the former it is instead crucial. We investigated the acquisition of concrete and abstract concepts and words, and verified its impact on conceptual representation. In Experiment 1, participants explored and categorized novel concrete and abstract entities, and were taught a novel label for each category. Later they performed a categorical recognition task and an image-word matching task to verify a) whether and how the introduction of language changed the previously formed categories, b) whether language had a major weight for abstract than for concrete words representation, and c) whether this difference had consequences on bodily responses. The results confirm that, even though both concrete and abstract concepts are grounded, language facilitates the acquisition of the latter and plays a major role in their representation, resulting in faster responses with the mouth, typically associated with language production. Experiment 2 was a rating test aiming to verify whether the findings of Experiment 1 were simply due to heterogeneity, i.e. to the fact that the members of abstract categories were more heterogeneous than those of concrete categories. The results confirmed the effectiveness of our operationalization, showing that abstract concepts are more associated with the mouth and concrete ones with the hand, independently from heterogeneity.     

Autogenic succession in boreal mires — A review

The main features of autogenic bog development are discussed. Using extensive literature the changes in vegetation, surface topography, soil environment and hydrology are characterized. Oligotrophy and low pH seem to be the most important factors directing bog succession. The decrease in decomposition rates correlates with increase of the content of dissolved oxygen in the soil water. Due to substantial changes in local environment bog succession should be considered first of all as an ecosystem process. In comparison with mineral land communities bog succession is characterized by more deterministic development. Both successional convergence and divergence are observed. In every case the concrete character of bog dynamics depends on the spatial and temporal scales of investigation.     

Composting of straw in small units

Summary Straw could be composted satisfactorily in 4 to 5 months in small concrete cells holding 30 lb. material (dry basis), providing the straw was thoroughly moistened and sufficient easily available nitrogeneous material added to give an initial carbon/nitrogen ratio of 40. During the composting process about half the dry matter was lost. Results were similar to those obtained using large cells holding 1500 lb. straw. Wire units holding 100 lb. straw were unsatisfactory. Changes in dry matter, carbon/nitrogen ratio, temperature, soluble inorganic nitrogen, and pH of composts prepared with various accelerators are reported.     

Effect of K+ on the membrane functions of an alkalophilic Bacillus

We have examined the involvement of K+ in the membrane functions of a facultatively alkalophilic Bacillus at neutral and alkaline pH. The effects of K+ on membrane functions, such as maintenance of the membrane potential, leucine uptake and respiratory activity, were dependent on the external pH. K+ uptake, which induced alkalinization of the cytoplasm, is suggested to be electrogenic at neutral pH and 'electroneutral' at alkaline pH, resulting in a similar level of net accumulation. We suggest that the bacterial membrane is highly permeable to K+ at neutral pH, compared to alkaline pH, which results in a pH-dependent effect of K+ on the above membrane functions.     

Purification and properties of phosphofructokinase from fruits of Lycopersicon esculentum

A procedure is described using affinity chromatography on Blue Sepharose and on an immobilized ATP column by which phosphofructokinase has been purified by 260-fold from tomato fruits. The properties of the enzyme are affected by the pH at which the preparation is made and maintained. At the pH optimum, pH 8.0, the enzyme is very heterogeneous with up to three forms present differing in MW. At pH 7.5 a single major form of MW 180 000 is present, and evidence that raising the pH to 8.0 promotes dissociation of the enzyme is discussed.     

Behavioural and physical effects of flooring on piglets and sows

Three different floor surface treatments in farrowing pens, viz. concrete, epoxypainted concrete and floor covered with a rubber mat, were studied with regard to their effects on the behaviour of the sows and piglets, and also knee damage suffered by the piglets.The data were studied in three parts: (1) the analysis of animal behaviour (2) knee wounds and (3) the association between knee wounds and behaviour. The analysis of behaviour showed that floors covered with rubber mats were the best for lying-comfort of the sows, the epoxy-painted concrete floor being too slippery. It was also observed that the piglets moved around most on the floor covered with rubber mats.The different floor treatments did not influence the number of knee wounds on the front legs of the piglets. From three days of age the incidence of wounds decreased by three percent per day. The wound diameters were greatest on the rubber mats and smallest on the concrete floors. The diameters of the wounds increased up to an age of ten days, after which they decreased. Wound depth was less on the concrete flooring than on the rubber mats.There is an association between the number of wounds and the lying-time of the animals. In further work, the behaviour of the piglets should be studied in the first three or four days of life in relation to floor structures and quality of bedding.