Bio: Oğuzhan Çopuroğlu is an academic researcher from Delft University of Technology. The author has contributed to research in topics: Cement & Cementitious. The author has an hindex of 23, co-authored 95 publications receiving 2636 citations.
Papers published on a yearly basis
TL;DR: In this article, a specific group of alkali-resistant spore-forming bacteria related to the genus Bacillus was selected for this purpose, and the bacterial spores directly added to the cement mixture remained viable for a period up to 4 months.
Abstract: The application of concrete is rapidly increasing worldwide and therefore the development of sustainable concrete is urgently needed for environmental reasons. As presently about 7% of the total anthropogenic atmospheric CO 2 emission is due to cement production, mechanisms that would contribute to a longer service life of concrete structures would make the material not only more durable but also more sustainable. One such mechanism that receives increasing attention in recent years is the ability for self-repair, i.e. the autonomous healing of cracks in concrete. In this study we investigated the potential of bacteria to act as self-healing agent in concrete, i.e. their ability to repair occurring cracks. A specific group of alkali-resistant spore-forming bacteria related to the genus Bacillus was selected for this purpose. Bacterial spores directly added to the cement paste mixture remained viable for a period up to 4 months. A continuous decrease in pore size diameter during cement stone setting probably limited life span of spores as pore widths decreased below 1 μm, the typical size of Bacillus spores. However, as bacterial cement stone specimens appeared to produce substantially more crack-plugging minerals than control specimens, the potential application of bacterial spores as self-healing agent appears promising.
TL;DR: In this article, the effect of Rice husk ash (RHA) and silica fume (SF) on the hydration and microstructure development of UHPC was investigated.
Abstract: Rice husk ash (RHA) and silica fume (SF) have a similar chemical composition and a very high specific surface area, but RHA is not an ultra-fine material like SF. The high specific surface area of RHA originates from its internal porosity. For this reason RHA can be expected to behave differently from SF in terms of the hydration and the resulting microstructure of concrete. This still remains unclear in Ultra High Performance Concrete (UHPC). The objective of this research was to study the effect of RHA on the hydration and microstructure development of UHPC. The results are compared to those obtained with a control sample and a sample made with SF. The results show that the addition of RHA can increase the degree of cement hydration in UHPC at later ages. RHA can also refine the pore structure of UHPC and reduce the Ca(OH) 2 content, but less significantly than SF. The thickness of the interface transition zone (ITZ) between sand particles and cement matrix of all samples is very small at the age of 28 days. The compressive strength of the sample made with RHA after 7 days was higher than that of the control sample and the sample made with SF. It is suggested that the porous structure of RHA and the uptake of water in this porous structure results in a kind of is attributable to the internal water curing of the RHA modified mixture.
TL;DR: In this paper, the authors studied the self-healing potential of cement-based materials incorporating calcium sulfoaluminate based expansive additive (CSA) and crystalline additive (CA).
Abstract: This research studies the self-healing potential of cement-based materials incorporating calcium sulfoaluminate based expansive additive (CSA) and crystalline additive (CA). Mortar specimens were used throughout the study. At the age of 28 days, specimens were pre-cracked to introduce a surface crack width of between 100 and 400 μm. Thereafter, the specimens were submerged in water to create a self-healing process. The experimental results indicated that the mixtures with CSA and CA showed favorable surface crack closing ability. The optimal mix design was found to be a ternary blend of Portland cement, 10 wt.% CSA and 1.5 wt.% CA, by which a surface crack width up to about 400 μm was completely closed, and the rate of water passing was dropped to zero within 28 days. It was hypothesized that the amount of leached Ca 2+ from the matrix plays an important role on the precipitation of calcium carbonate which is the major healing product. The analyses showed that those specimens with CSA/CA additions released more Ca 2+ than that control specimen. Moreover, those specimens with additives had higher pH value which would favor calcium carbonate precipitation.
TL;DR: In this article, a modified mathematical equation, based on Fick's 1st law of diffusion, is used to evaluate CO 2 diffusion coefficient of concrete and the required cover depth of concrete is estimated by using the applicative methods of reliability and stochastic concepts to take microclimatic conditions into consideration.
Abstract: In the recent years, global warming has dramatically increased the atmospheric carbon-dioxide (CO 2 ) concentration and temperature. As a consequence of this, carbonation has become one of the most critical durability issues for concrete structures in urban environment. In this study, the climate scenario IS92a recommended by Intergovernmental Panel on Climate Change (IPCC) is used for evaluating the effect of CO 2 concentration on carbonation of concrete. A modified mathematical equation, based on Fick's 1st law of diffusion, is used to evaluate CO 2 diffusion coefficient of concrete. The required cover depth of concrete is estimated by using the applicative methods of reliability and stochastic concepts to take microclimatic conditions into consideration. The tolerance of cover depth should be considered in order to prevent carbonation-induced corrosion. From the relationship between the weight loss of reinforcement and corrosion current density for a given time, the tolerance of cover depth to prevent carbonation-induced corrosion is suggested. It was observed that corrosion occurs when the distance between carbonation front and reinforcement bar surface (the uncarbonated depth) is
TL;DR: In this paper, an innovative approach to improve the fiber distribution by adjusting the mixing sequence was explored, and the adjusted mixing sequence increased the tensile strain capacity and ultimate tensile strength of ECC and improved fiber distribution.
Abstract: Engineered cementitious composites (ECC) is a class of ultra ductile fiber reinforced cementitious composites, characterized by high ductility and tight crack width control. The polyvinyl alcohol (PVA) fiber with a diameter of 39 μm and a length of 6–12 mm is often used. Unlike plain concrete and normal fiber reinforced concrete, ECC shows a strain-hardening behavior under tensile load. Apart from the mix design, the fiber distribution is another crucial factor for the mechanical properties of ECC, especially the ductility. In order to obtain a good fiber distribution, the plastic viscosity of the ECC mortar before adding fibers needs to be controlled, for example, by adjusting water-to-powder ratio or chemical admixtures. However, such adjustments have some limitations and may result in poor mechanical properties of ECC. This research explores an innovative approach to improve the fiber distribution by adjusting the mixing sequence. With the standard mixing sequence, fibers are added after all solid and liquid materials are mixed. The undesirable plastic viscosity before the fiber addition may cause poor fiber distribution and results in poor hardened properties. With the adjusted mixing sequence, the mix of solid materials with the liquid material is divided into two steps and the addition of fibers is between the two steps. In this paper, the influence of different water mixing sequences is investigated by comparing the experimental results of the uniaxial tensile test and the fiber distribution analysis. Compared with the standard mixing sequence, the adjusted mixing sequence increases the tensile strain capacity and ultimate tensile strength of ECC and improves the fiber distribution. This concept is further applied in the development of ECC with high volume of sand.
01 Jan 2016
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TL;DR: In this paper, the use of microbially induced carbonates as a binder material, i.e., biocementation, is discussed, for the improvement of compressive strength and the remediation of cracks.
Abstract: Evidence of microbial involvement in carbonate precipitation has led to the exploration of this process in the field of construction materials. One of the first patented applications concerned the protection of ornamental stone by means of a microbially deposited carbonate layer, i.e. biodeposition. The promising results of this technique encouraged different research groups to evaluate alternative approaches, each group commenting on the original patent and promoting its bacterial strain or method as the best performing. The goal of this review is to provide an in-depth comparison of these different approaches. Special attention was paid to the research background that could account for the choice of the microorganism and the metabolic pathway proposed. In addition, evaluation of the various methodologies allowed for a clear interpretation of the differences observed in effectiveness. Furthermore, recommendations to improve the in situ feasibility of the biodeposition method are postulated. In the second part of this paper, the use of microbially induced carbonates as a binder material, i.e. biocementation, is discussed. Bacteria have been added to concrete for the improvement of compressive strength and the remediation of cracks. Current studies are evaluating the potential of bacteria as self-healing agents for the autonomous decrease of permeability of concrete upon crack formation.
TL;DR: In this article, a two-component bio-chemical self-healing agent consisting of bacterial spores and calcium lactate is released from the particle by crack ingress water, which results in physical closure of micro cracks.
Abstract: Crack formation is a commonly observed phenomenon in concrete structures. Although micro crack formation hardly affects structural properties of constructions, increased permeability due to micro crack networking may substantially reduce the durability of concrete structures due to risk of ingress of aggressive substances particularly in moist environments. In order to increase the often observed autogenous crack-healing potential of concrete, specific healing agents can be incorporated in the concrete matrix. The aim of this study was to quantify the crack-healing potential of a specific and novel two-component bio-chemical self-healing agent embedded in porous expanded clay particles, which act as reservoir particles and replace part of regular concrete aggregates. Upon crack formation the two-component bio-chemical agent consisting of bacterial spores and calcium lactate are released from the particle by crack ingress water. Subsequent bacterially mediated calcium carbonate formation results in physical closure of micro cracks. Experimental results showed crack-healing of up to 0.46 mm-wide cracks in bacterial concrete but only up to 0.18 mm-wide cracks in control specimens after 100 days submersion in water. That the observed doubling of crack-healing potential was indeed due to metabolic activity of bacteria was supported by oxygen profile measurements which revealed O2 consumption by bacteria-based but not by control specimens. We therefore conclude that this novel bio-chemical self-healing agent shows potential for particularly increasing durability aspects of concrete constructions in wet environments.
TL;DR: In this paper, the use of a biological repair technique is investigated in concrete repair by means of water permeability tests, ultrasound transmission measurements and visual examination, and it was shown that pure bacteria cultures were not able to bridge the cracks.
Abstract: As synthetic polymers, currently used for concrete repair, may be harmful to the environment, the use of a biological repair technique is investigated in this study. Ureolytic bacteria such as Bacillus sphaericus are able to precipitate CaCO3 in their micro-environment by conversion of urea into ammonium and carbonate. The bacterial degradation of urea locally increases the pH and promotes the microbial deposition of carbonate as calcium carbonate in a calcium rich environment. These precipitated crystals can thus fill the cracks. The crack healing potential of bacteria and traditional repair techniques are compared in this research by means of water permeability tests, ultrasound transmission measurements and visual examination. Thermogravimetric analysis showed that bacteria were able to precipitate CaCO3 crystals inside the cracks. It was seen that pure bacteria cultures were not able to bridge the cracks. However, when bacteria were protected in silica gel, cracks were filled completely.
TL;DR: In this article, the theoretical principles, raw materials, mixture design methods, and preparation techniques for UHPC are reviewed, including reduction in porosity, improvement in microstructure, enhancement in homogeneity, and increase in toughness.
Abstract: Ultra high performance concrete (UHPC) refers to cement-based materials exhibiting compressive strength higher than 150 MPa, high ductility, and excellent durability. This paper reviews the theoretical principles, raw materials, mixture design methods, and preparation techniques for UHPC. Reduction in porosity, improvement in microstructure, enhancement in homogeneity, and increase in toughness are four basic principles for UHPC design. Raw materials, preparation technique, and curing regimes have significant influence on properties of UHPC. The use of widely available supplementary cementitious materials, such as fly ash and slag for partial/complete replacement of cement and silica fume, could significantly reduce the materials cost without sacrifice of strength. The use of high temperature curing results in denser microstructure and better performance than room temperature curing does, but obviously limits its applications of UHPC. Thus, preparation of UHPC using widely available raw materials, common technology, such as conventional casting and room temperature curing, are trends for production of UHPC.