Bioconcrete: next generation of self-healing concrete

Concrete is one of the most widely used construction materials and has a high tendency to form cracks. These cracks lead to significant reduction in concrete service life and high replacement costs. Although it is not possible to prevent crack formation, various types of techniques are in place to heal the cracks. It has been shown that some of the current concrete treatment methods such as the application of chemicals and polymers are a source of health and environmental risks, and more importantly, they are effective only in the short term. Thus, treatment methods that are environmentally friendly and long-lasting are in high demand. A microbial self-healing approach is distinguished by its potential for long-lasting, rapid and active crack repair, while also being environmentally friendly. Furthermore, the microbial self-healing approach prevails the other treatment techniques due to the efficient bonding capacity and compatibility with concrete compositions. This study provides an overview of the microbial approaches to produce calcium carbonate (CaCO₃). Prospective challenges in microbial crack treatment are discussed, and recommendations are also given for areas of future research

Induced calcium carbonate precipitation using Bacillus species

Microbially induced calcium carbonate precipitation is an emerging process for the production of self-healing concrete. This study was aimed to investigate the effects and optimum conditions on calcium carbonate biosynthesis. Bacilluslicheniformis, Bacillus sphaericus, yeast extract, urea, calcium chloride and aeration were found to be the most significant factors affecting the biomineralization of calcium carbonate. It was noticed that the morphology of microbial calcium carbonate was mainly affected by the genera of bacteria (cell surface properties), the viscosity of the media and the type of electron acceptors (Ca²⁺). The maximum calcium carbonate concentration of 33.78 g/L was achieved at the optimum conditions This value is the highest concentration reported in the literature

Analyse technico-économique de l'élevage du porc-épic à crête (Hystrix cristata) au Burkina Faso

L'élevage du porc-épic à crête (Hystrix cristata) en Afrique sub-saharienne répond à une problématique de consommation humaine de viande de gibier directement reliée à la valorisation économique et la conservation de la faune sauvage. Les expériences concernant cet élevage, appelé "non conventionnel", et les références scientifiques sur les paramètres zootechniques de cette espèce sont rares. Cette étude a consisté à analyser l'expérience accumulée et les principales données techniques enregistrées à la Ferme de Démonstration de Wédbila au Burkina Faso. L'intervalle moyen entre deux portées est de 171 jours (n=44) et le nombre moyen de petits par portée est de 1,65 (n=88) avec un sex-ratio de 1. Une enquête de terrain a permise de recenser une partie des ressources alimentaires et les quantités consommées par les animaux en captivité. Un protocole expérimental a permis d'obtenir des courbes de croissance moyenne de différents lots d'animaux. Un gain moyen quotidien (GMQ) de 44 g / j (n=35) sur les deux premiers mois de vie des animaux et de 31 g / j (n=26) sur les cinq premiers mois a été enregistré. Le rendement carcasse de l'espèce est estimé à 68,5 %. Un régime alimentaire composé d'environ 3 % de protéines animales à été comparé à un aliment sans protéines sur des animaux en période post sevrage. Aucune différence significative n'a été relevée sur la croissance pondérale. Pour finir, la rentabilité économique de cet élevage dans des conditions déterminées a été démontrée. Le porc-épic à crête semble être un bon candidat à l'élevage commercial de gibier, d'autant plus que ses paramètres zootechniques peuvent être fortement améliorés grâce à de la sélection et qu'un aliment "d'engraissement" adapté peut être mis au point. (Résumé d'auteur

The Effect of Cell Immobilization by Calcium Alginate on Bacterially Induced Calcium Carbonate Precipitation

Microbially induced mineral precipitation is recognized as a widespread phenomenon in nature. A diverse range of minerals including carbonate, sulphides, silicates, and phosphates can be produced through biomineralization. Calcium carbonate (CaCO₃) is one of the most common substances used in various industries and is mostly extracted by mining. In recent years, production of CaCO₃ by bacteria has drawn much attention because it is an environmentally- and health-friendly pathway. Although CaCO₃ can be produced by some genera of bacteria through autotrophic and heterotrophic pathways, the possibility of producing CaCO₃ in different environmental conditions has remained a challenge to determine. In this study, calcium alginate was proposed as a protective carrier to increase the bacterial tolerance to extreme environmental conditions. The model showed that the highest concentration of CaCO₃ is achieved when the bacterial cells are immobilized in the calcium alginate beads fabricated using 1.38% w/v Na-alginate and 0.13 M CaCl₂

Plastic dilation rate characteristic of concrete confined with steel tube

The use of external confining devices to confine concrete has become widely used. One of the purposes is to gain additional concrete strength and ductility. Although there are many types of external confining devices, in this paper, the attention is limited to the use of the steel tube as an external confining device. One of the main objectives of this research is to study the plastic dilation rate behavior of concrete-filled-steel-tube (CFST) columns. The experimental data for the plastic dilation rate is extracted, and compared with the authors concrete plasticity model. In the authors’ previous research, the calibration of the plastic dilation rate model was based on confined concrete tested under both active and passive confinement using FRP wraps. Since the behavior of the steel tube and the FRP materials are different, the author’s plastic dilation rate model needs to be re-evaluated for CFST columns. Comparisons of the extracted experimental plastic dilation rates with the model prediction for CFST specimens with normal strength concrete show good agreement and requires no adjustment in the formulation. However, for a specimen with 80 MPa concrete, the proposed formulation shows slightly lower plastic dilation rates. More experimental data for CFST using high strength concretes is required for further investigation. For the sake of completeness, the overall response of two CFST specimens is also evaluated using an in-house three-dimensional non-linear finite element analysis (3D-NLFEA) using the author’s proposed plasticity formulation for confined concrete

A Thorough Review of Sand Dunes in Iran and Their Relationship to Certain Climatic Features

IntroductionSand covers around 20% of the world's drylands, and 97% of it is found in the sandy land of the arid region of the earth. Different landforms are created by the wind in these regions. Sand dunes are a landform that is mentioned in arid lands. Knowing the distribution of sand in these areas is crucial because wind erosion can cause a lot of damage. The significance of studying sand dunes lies in its impact on water and soil resources, plants and animals, human infrastructure, and roads. In Iran, various researchers and related organizations have reported various areas of the sand dunes. Different tools and methods have been utilized by these researchers, including aerial photos, topographic maps, satellite images, and field visits. This study was conducted to improve accuracy and update the existing maps due to the differences between the maps provided by previous researchers. By providing a new map of sand dunes distribution in Iran, more precise information can be obtained. Precipitation, temperature, evapotranspiration, and UNEP aridity index were used to calculate climate characteristics for Iran's sand dunes. Material and MethodsRemote sensing was used to export the sand dunes distribution map in this research using the Google earth engine system. The image collection of the OLI sensor of the Landsat 8 satellite was used. The process of image classification involved introducing 4000 points as training points. The land use map of Iran was exported after verifying and calculating the overall accuracy and kappa coefficient, which were 0.91 and 0.89, respectively. The map's sand dune class was imported into ArcMap. The maps of the distribution of sand dunes obtained from previous researchers were compared with the obtained map. The boundary of sand dunes was modified by drawing 1020 polygons using vision recognition. We aim was always to utilize the most up-to-date satellite images for visual interpretation. Due to differences in tools and study time, and the prepared maps based on different criteria, there are numerous differences between the maps in practice. The research utilized up-to-date satellite images and geological maps, topography, hand-planted forests, residential lands, agricultural lands, and land use as auxiliary maps. In the next step, the long-term climate maps prepared by Jamab's consulting engineers for the period of 1350 to 1390 were used to investigate climate characteristics such as temperature, precipitation, evaporation and transpiration and UNEP aridity index. The mentioned maps were interpolated and classified in ArcMap for this purpose. The distribution of the country's sand dunes was examined in each of the categories mentioned in the climatic indicators. Results and DiscussionBased on the result, the updated area of Iran's sand dunes is 5.15 mha which includes the sand sheets and different forms of sand dunes such as barchans, star dunes and nebkas. Based on this, the provinces of Kerman, Sistan and Baluchistan, Isfahan, South Khorasan and Yazd respectively, with an area of about 1000000, 700000 and 590000 ha, have allocated the largest area of sand dunes in the country. There are some differences in the obtained results compared to the previous maps of sand dunes. In Dehlran city in Ilam province, some regions that were previously considered sand dunes have now become agricultural lands, for instance. The border modification resulted in a 366% increase in the area of Qaen city in South Khorasan province. According to climate data, sand dunes are distributed in three climates that are hyper- arid, arid, and semi-arid. The highest and lowest amount of precipitation can be found in Farashband city in Fars province and Hirmand city in Sistan and Baluchestan Province, respectively. The range of precipitation changes is ranging from 6 to 312 mm.  The hottest sand dunes are located in Shahrud city in Semnan province and the coldest sand dunes are located in Buin Zahra city in Qazvin Province. The temperature of sand dunes is in the ranges of 10 to 28.5 °C. the dominant thermal regime of sand dunes is thermic, which covers about 68% of the sand dunes in 8 provinces. Hyperthermic thermal regime dominates 31% of sand dunes in 7 provinces. Only about 1% of sand dunes have mesic thermal regime which are scattered in 3 provinces. The range of changes in evapotranspiration in the sand dunes of Iran is between 1500 to 4000 mm per year. Evaluating the UNEP aridity index showed that 89% of the sand seas are classified as hyper arid and 11% of them is in arid class. The result of this research by determining the location of sand seas and their climate classification, will help the administrators to locate appropriate areas for reclamation and wind erosion control projects, especially the biological project

A stress-strain model for uniaxial and confined concrete under compression

Analytical models for the full stress-strain relationship of confined and unconfined concrete in compression are required for the numerical simulation of the structural behavior of reinforced concrete structural elements. There are many analytical models presented in the literature, which are generally empirical and are based on tests either on plain concrete specimens or reinforced concrete columns. This paper reviews some widely used analytical models calibrated using triaxial test results on plain concrete and compares their predictions with available test data on uniaxial and triaxial compression on specimens with different specimen height, width or diameter and concrete strength. The model prediction's for the peak stress and corresponding strain due to confinement are also compared. The residual stress level and the post-peak fracture energy under confinement are discussed. Estimates of the post-peak fracture energy per unit area are obtained from available experimental data showing that the post-peak fracture energy varies with confinement. The size effect on the softening behavior of uniaxial and triaxially loaded plain concrete specimens with different aspect ratios, heights and level of confinement, are also discussed. A new analytical model for unconfined and confined concrete is introduced which tries to address the limitations in previous models. The proposed model is capable of predicting the behavior of normal strength concrete, as well as high strength concrete and incorporates allowances for size effects dependent on specimen height and aspect ratio. Comparisons are made between the proposed new model, the models of others in the literature, and available compression triaxial and uniaxial test results. © 2012

Size effect in confined concrete

Compressive size effect tests have been mainly conducted on uniaxial compression tests. However, softening in concrete happens not only in uniaxial compression but also under triaxial compression. The present study shows that the post-peak compressive fracture energy per unit area, is influenced by the level of confinement in triaxial loading. The results estimated from the literature show an increasing fracture energy with increasing confinement until a limit is reached, at a confinement ratio of about 10 to 20% after which it decreases until it becomes zero. The fracture energy, the specimen height, aspect ratio and the confinement level is shown to influence the softening behavior of both uniaxially and triaxially loaded concrete. A new stress strain model is proposed for unconfined and confined concrete. The proposed model takes account of size effects dependent on specimen height and aspect ratio. The model is compared to experimental data and shows excellent agreement

Lateral behavior of concrete

Lateral expansion is a factor defining the level of confinement in reinforced concrete columns. Therefore, predicting the lateral strain relationship with axial strain becomes an important issue. Measuring lateral strains in experiments is difficult and only few report experimental lateral strains. Among the existing analytical formulations, two recent models are compared with available test results in this paper with shortcomings highlighted. A new analytical model is proposed here for lateral strain axial strain relationship and is based on the supposition that the concrete behaves linear elastic in the early stages of loading and then nonlinear hardening up to the peak stress and then volumetric expansion. The proposal for the lateral strain axial strain relationship after the peak stress is mainly based on the hypothesis that the plastic lateral strain varies linearly with the plastic axial strain and it is shown that this is related to the lateral confinement level

Lateral strain of confined concrete incorporating size effect

The lateral and axial strain relationship plays an important part in predicting the confinement of confined columns. Measuring lateral strains in compressive experiments proves to be difficult which mean few reliable results are available. A lateral strain versus axial strain model is proposed based on the supposition that the concrete behaves linear elastically in the early stages of loading, nonlinear hardening up to the peak stress after which the inelastic lateral strain vary linearly with the inelastic axial strain. The lateral to axial inelastic strain ratio is shown to be a function of the lateral confinement level and related to the failure mechanism. Moreover, size effect is also discussed from the lateral strain versus axial strain perspective