Reduction In Strength Of Concrete Research Articles

Mix design optimisation of self-sealing concrete containing microcapsules with polyurethane shell and water repellent cargo

Despite the robust ability of microcapsules (MIC) to break and release agent for healing/sealing efficacy, the reduction of concrete strength has been a major issue when using MIC. In this study, the optimisation of concrete mix design was initiated with employing three main parameters: MIC size (56, 93 μm), MIC dosage (0, 3, 6% by weight of cement) and water-cement (w/c) ratio (0.40, 0.50, 0.60). The used microcapsules consisted of water repellent agent core acting as a sealing agent and polyurethane as the shell material. Results confirmed the MIC dosage as the most significant factor affecting the mechanical properties, while no significant effect on the MIC size. Further, the MIC effect can be reduced by changing the concrete mix design from low to high w/c. The sealing efficiency of concrete was remarkably improved with the inclusion of MIC and a good bond between the capsules and concrete matrix was attained.

Experimental study on the behavior of eccentrically compressed corrosion-damaged reinforced concrete columns

This paper presents an experimental study of corrosion-damaged reinforced concrete (RC) columns under eccentric compression. Three RC concrete column specimens, identical in geometry, reinforcing steel bars, andconcrete mix, were fabricated. One undamaged control specimen served as the control group, while the othertwo column specimens underwent corrosion due to chloride ion exposure. All specimens were subjected to aminor eccentric compressive load. The test results have revealed the behavior of RC columns damaged by steelcorrosion. Additionally, a comparison of the load-bearing capacity of corrosion-damaged RC columns wasconducted between calculation and experiment. The results indicate a close alignment between calculated andexperimental outcomes. Furthermore, the degree of decrease in the load-bearing capacity of corrosion-damaged RC columns over time was evaluated based on the axial load-moment interaction diagram. This evaluation considered the influence of the reduction in concrete strength and the cross-sectional area of the reinforcement.

STUDY OF STRENGTH REDUCTION OF REINFORCED CONCRETE BEAM UNDER FIRE TESTS

The article presents the results of studies of the regularity of changes in the concrete strength of reinforced concrete beams depending on the heating temperature of its inner layers under fire conditions by interpreting the temperature and deformation measurement results. To obtain the data necessary to identify patterns of concrete strength reduction, we developed a method of fire tests that substantiates the experimental base, design, and number of samples, type, number, and location of measuring devices, as well as the method for statistical processing of measurement data. Based on the developed methodology, we conducted fire tests. As a result of the tests, we obtained a set of measurement results in the form of time dependences of temperature indicators at individual cross-section points and the dependence of the maximum beam deflection on time, which are necessary to identify the coefficients of reduction in concrete strength of reinforced concrete beams under fire test conditions. We then used the proposed method to identify regularities in the reduction of concrete strength of a reinforced concrete beam, which includes interpolation using the obtained temperature indicators at individual points of the cross-section of the beam, which allows us to set the temperature at any point of the cross-section at any control time of measurements based on the approximation of isotherms by parabolas with a variable indicator of their degree. At the next stage, to identify the dependence of the concrete strength of reinforced concrete beams, we used a method based on the compilation of systems of equilibrium equations of internal layers in the cross-section of a reinforced concrete beam, in which the unknown values ​​are the coefficients of reduction of concrete strength for a range of temperatures every 100 °С in the range from 20 °С up to 1200 °С, provided that the reduction factor for the specified heating temperature of the inner layer of concrete is determined by linear interpolation. Using the proposed approach, we obtained appropriate results for a reinforced concrete beam subjected to fire tests. The obtained dependences of the strength reduction coefficient were used to evaluate the fire resistance of reinforced concrete beams and crossbars by the calculation method based on the deformation model. By comparing the obtained data with the data from the literature, we established the adequacy of the calculated data based on the relative deviation and Fisher’s test. The totality of the obtained data allows for improving the calculation method for evaluating reinforced concrete crossbars and beams by increasing the accuracy of the data obtained. Keywords: reinforced concrete beam, fire tests, concrete strength reduction coefficient, fire resistance.

Sustainable Concrete Produced with Petroleum Catalyst waste and Polyethylene Glycol as a Self-Healing Agent

Purpose: To evaluate the production of concrete from the partial replacement of Portland cement with petroleum catalyst residue (RC), generated in large quantities by the petrochemical industries, and the addition of polyethylene glycol 400 (PEG 400), with an emphasis on investigating its mechanical properties and durability, considering the technological, scientific and environmental aspects. Theoretical framework: Oil catalyst waste is generated in significant quantities and is classified as non-inert due to its metal ion content, so there is a need to investigate new disposal methods. The use of RC as partial substitute for Portland cement, with the addition of PEG 400 (self-curing agent), was investigated for the production of non-conventional concrete. The waste has pozzolanic activity, enabling improvements in mechanical properties when added to the cement matrix. PEG 400 has properties that can make concrete more effective in terms of water absorption, hydration heat and workability. The search for sustainability leads to research into new construction materials in order to preserve natural resources and reduce environmental impact. The concrete developed can be lower cost and more durable, without any loss of structural strength. Method/design/approach: The use of RC was investigated with partial substitutions of 2%, 5%, 10% and 20% in relation to the total mass of Portland cement for the manufacture of concrete and the addition of polyethylene glycol (PEG 400) as a self-curing agent. The void ratio, water absorption by capillarity and immersion, specific masses and pozzolanicity index of the waste were investigated. Mechanical and morphological characterization tests were also carried out on the concretes developed. Results and conclution: The compressive strength of concrete produced with 2% RC in relation to the total mass of cement and 1.5% PEG 400 increased by 18.3% compared to conventional concrete. An increase in the amount of residue caused a reduction in concrete strength. The sample with 1.5% PEG 400 obtained better workability in the fresh state, which may be due to the polymer acting as a self-healing agent. The images obtained by scanning electron microscopy showed that the samples containing 2% added RC had lower porosity. The study showed that the waste can be used satisfactorily in civil construction and the implementation of this new process can reduce global warming and the scarcity of mineral resources, taking sustainability into account. Research implications: This work contributes to a sustainable circular economy with a new process for using petroleum catalyst waste, with pozzolanic characteristics, in cementitious materials. Originality/value: The results will be promising for the use of petroleum catalyst waste and polyethylene glycol in the production of environmentally sustainable concrete.

Study on the Influence of Shrinkage-Reducing Materials on the Volume Stability of Shotcrete with a Fluorine-Containing Alkali-Free Accelerator.

In contrast to ordinary concrete, shotcrete exhibits greater shrinkage deformation. The utilization of an aluminum fluoride alkali-free accelerator (AF) is prevalent in tunnel engineering, attributed to its economical nature and fast setting and hardening. Currently, there is a dearth of research on the volume stability of aluminum fluoride accelerators, and no relevant studies have been conducted on the application of shrinkage-reducing materials in shotcrete using an aluminum fluoride accelerator. With the use of an aluminum fluoride accelerator, the early strength of shotcrete is reduced, and the addition of a shrinkage-reducing agent (SRA) and super-absorbent polymer (SAP) can also lead to a further reduction in the early strength of concrete. Therefore, this study aims to investigate the influence of these two shrinkage-reducing materials (SRA and SAP) on the workability and mechanical properties of shotcrete. The primary focus of this research is to determine the better compensation effect of the two shrinkage-reducing materials. To accomplish this, the study focuses on assessing the setting time, compressive strength, and volume stability of shotcrete that has been mixed with an aluminum fluoride accelerator using SRA and SAP. Additionally, we also aim to explore the hydration and shrinkage compensation mechanism of these shrinkage-reducing materials on shotcrete by conducting a microscopic test analysis.

Punching shear capacity of expanded polystyrene (EPS) lightweight concrete flat slabs without shear reinforcement

This work presents an experimental and theoretical study on the punching shear behavior of Lightweight Concrete Slabs. Lightweight obtained using Expanded polystyrene (EPS) beads as partial coarse aggregate’s replacement, without adding supplementary bonding additives, to reduce concrete density from 2400 to 1800 kg/m3. The EPS content, concrete strength and column aspect ratio were test parameters. Five groups of concrete prepared by partially replacing natural coarse aggregate with 0%, 10%, 20%, 30% and 40% (by volume) of EPS balls. Ten reinforced concrete slabs without shear reinforcement with a monolithic column were tested under concentric loading. The study aimed to examine the effect of the EPS on the density and compressive strength of concrete and eventually on the flat slabs punching capacity. Five series of mixtures identified and compared with conventional normal weight concrete. Results showed that with increasing EPS content, rate of reduction in concrete strength is faster than the reduction in concrete density. Also, showed that the failure base area increased while the concrete density decreased, this yielded a higher punching capacity compared to rate of decrease in the concrete strength. International standards models showed overestimation of punching shear capacity and didnot reflect the reduced concrete strength action of lightweight concrete.

Use of irradiated PET plastic waste for partially replacing cement in concrete?

Portland cement used in the manufacture of concrete is responsible for an estimated 5–8% of the global CO2 emissions. Recently published work (Schaefer et al., 2018) claims that γ-irradiated PET waste powder can be used as a partial replacement of cement in concrete for reducing its CO2 footprint. More specifically, exposure of PET to γ-irradiation at a dosage of 100 kGy alters its crystal structure and chemical composition, which in turn leads to a smaller reduction in concrete strength compared to non-irradiated PET waste. Hence, making it possible for irradiated PET waste to be used as a raw ingredient in the manufacture of concrete while at the same time diverting significant quantities of PET waste from landfills. The aim of this research was to independently assess and verify the above claims. For this purpose, the effect of different low irradiation dosages (0, 10 and 100 kGy) and different replacement levels (2.5 %, 5 % and 10 % by volume) of cement by PET waste on the consistency and mechanical strength of pastes and mortars was determined in a laboratory investigation. XRD, TGA and DSC were also used to study the effect of irradiation on the microstructure of raw PET waste and the microstructure of paste and mortar samples containing irradiated PET waste powder. Our results indicate that use of γ-irradiated PET waste (exposed to an irradiation dosage of up to 100 kGy) for partially replacing cement does not lead to a significant recovery of mechanical strength lost when non-irradiated PET waste is used.

Method for identifying the strength characteristics of concrete of a reinforced concrete crossbar during heating under conditions of fire

This paper proposes a method that makes it possible to study the patterns of changes in the concrete strength of reinforced concrete crossbars depending on the heating temperature under fire conditions by interpreting the results of their standard fire tests. For the implementation of this method, it is proposed to use similar data obtained using mathematical modeling based on the finite element method and given material properties, including the curve of concrete strength reduction recommended by the guidelines, as data included in the set of measurement results during fire tests depending on temperature. Such data are time dependences of temperature indicators at individual cross-section points and time dependence of the maximum deflection of the crossbar. The article proposes an interpolation method that makes it possible to set the temperature at any point of the section based on the approximation of the isotherms by parabolas with a variable indicator of their power. A method based on the mathematical interpretation of temperature indicators obtained using the proposed interpolation method and the curve of the dependence of the maximum deflection on time using a deformation model for describing the stress-strain state is proposed to identify the dependence of the concrete strength of reinforced concrete crossbars. The work also shows that the results obtained using the proposed method of identifying concrete strength reduction coefficients are adequate as their relative error is on average no more than 7 %. Based on the results, the possibility of its application to study the regularities of the decrease in the strength of reinforced concrete crossbars under fire conditions has been proven

Strength Reduction of Concrete Subjected to High Temperatures: Effects of Various Aggregates

Previous studies on the strength degradation of concrete subjected to high temperatures were analyzed. To analyze the effect of the coarse-aggregate type on strength degradation, data from previous studies were collected, and the coarse aggregate used, physical properties of the aggregate, and heating conditions were analyzed. The concrete types were classified into normal, heavyweight, and lightweight concrete. Their high-temperature characteristics were analyzed and evaluated according to the mixed coarse aggregate. Finally, the correlations derived from the analysis results were compared with the CEB Code. The analysis results were different for different concrete and coarse-aggregate types, and different tendencies from the CEB Code were observed.

Utilisation of aged and unaged basic oxygen furnace steel slag aggregates in pavement quality concrete

ABSTRACT The study presented in the paper evaluated the properties of pavement quality concrete (PQC) containing coarse aggregates made from aged and unaged basic oxygen furnace (BOF) slag. Workability, air content, strength, drying shrinkage, expansion, abrasion resistance and expansive potential of PQC were evaluated. Air content and workability of fresh slag concrete increased marginally. Compressive and flexural strength of the concrete containing aggregates of aged and unaged slag was observed to be less than the strength of normal concrete. The reduction in strength of concrete containing aged slag aggregates was more as compared to the concrete containing unaged slag aggregates due to the presence of a dusty coating around the aged aggregates. The drying shrinkage of the concrete increased with the content of steel slag aggregates. The abrasion resistance of the slag concrete was found to be better than the abrasion resistance of conventional concrete. Deterioration of slag concrete was not observed due to normal water curing up to 90 days. However, accelerated aging of concrete in water at 70°C resulted in the localised cracking and eruptions due to expansion. The study showed that, aged as well as unaged slag aggregates may be used for the preparation of concrete mixtures of required properties for road construction.

Variable compression panel thickness for concrete members under bending and torsion: Experimental study

An experimental study was conducted on the behaviour of eight reinforced and prestressed concrete beams subjected to combined action of bending and torsion. The beams were heavily reinforced in the longitudinal direction so that the height of the concrete compression zone under pure bending would be much larger than the concrete diagonal strut thickness under pure torsion and measurements were done so that behaviour of this compressive zone could be observed. The amount of the reinforcement was designed close to the over-reinforcement limits, as would happen if the cross-section dimensions of an actual structure would be minimized in the design. The ultimate resistances and beam deformations were compared against the results of a plasticity-based space truss model where the panel on the compressive side of the cross-section had variable thickness in order to account for the resultant force demands of both the bending and torsion. Most heavily reinforced beams failed in a brittle manner due to the ineffectiveness of diagonally cracked concrete to resist the high normal stresses arising from the bending. The proposed model gave better predictions than the classical model where the panel thickness was constant, and the results showed the significance of concrete strength reduction factor contribution in ultimate resistance of concrete members under combined bending and torsion.

Test of compressive strength of rubber ceramsite concrete modified by basalt fiber

In order to solve the problem of black pollution in the 21st century, a new type of rubber ceramsite concrete was prepared by crushing the waste rubber tire into granules and adding it into the ceramsite concrete. The basalt fiber was used to modify the rubber for reducing the weakening of the concrete mechanical property caused by the addition of rubber. In this paper, the compressive strength of concrete specimens at 3 and 28 days was measured to discuss the modification effect of single fiber. The results show that the compressive strength of concrete can be improved by adding basalt fiber, and it increases with the increase of adding content. With the increase of rubber replacement rate, the strength of concrete increases first and then decreases, which proves that adding proper amount of rubber can reduce the reduction of concrete strength. The length of basalt fiber also affects the compressive strength of specimens. Basalt fibers of 12 mm length work better than fibers of 9 and 18 mm.

Effect of Normal and Rubberized Concrete Properties on the Behavior of RC Columns Strengthened with EB CFRP Laminates and Welded Wire Mesh under Static Axial Loading.

The huge amounts of old and damaged tires spread worldwide has caused many complex environmental risks. The old tires have been converted to crumb rubber (CR) and tire recycled steel fiber (RSF) to facilitate their use. This study used CR to partially replace natural sand in reinforced (RC) columns. Externally bonded (EB) carbon-fiber-reinforced polymer (CFRP) laminates, welded wire mesh (WWM), and RSF were used to enhance the axial behavior of the tested columns to overcome the concrete deficiencies resulting from the inclusion of the CR instead of natural sand. Eighteen columns were prepared and tested to discuss the effects of strengthening type, CR content, RSF, and strengthening area on the axial behavior of the RC columns. Certain columns were internally reinforced with WWM, while others were externally strengthened with EB CFRP laminates. Partially or fully EB CFRP laminates were used to strengthen the columns. Moreover, one column was cast with NC and 0.2% RSF to investigate the role of RSF in confining the column. The results demonstrated a concrete strength reduction for the rubberized concrete (CRC) as the CR content increased. Conversely, the strengthened columns experienced higher load capacities than the corresponding un-strengthened ones cast with the same concrete mix. Moreover, adding 2% RSF to the NC mix could enhance the column capacity, although it decreased the concrete strength. Furthermore, using two CFRP layers increased the load capacity and ductility of the strengthened columns. The strengthened column cast with 50% CR showed the highest load efficiency (334.3% compared to the un-strengthened one).

The influence of granite powder waste and the addition of fly ash on concrete bleeding

AbstractBleeding is a common problem in concrete slabs, and may lead to serious damage. The goal of this article is to understand the impact of alternative binders and their properties on the bleeding of concrete. Therefore, the impact of the type of binder on the bleeding process is investigated. The results show that the addition of granite powder or fly ash allows for the increased control of the bleeding process. It was found that a finer particle size distribution (PSD), an increased specific surface area (SSA), and a higher bulk density may reduce the amount of dispensed water in the concrete mix. Furthermore, the use of additives with an increased SSA leads to even a 30% reduction of the bleeding rate of mixes. The utilization of additives with a finer PSD than cement enables a 37% reduction of the bleeding rate of mixes. The influence of bleeding on compressive strength was assessed using destructive and non‐destructive tests: Replacing 30% of cement with granite powder leads to a 30% reduction of concrete strength after 28 days of curing; on the other hand, replacing 30% of cement with siliceous fly ash leads to an 18% reduction of strength. Importantly, bleeding was also found to lead to the heterogeneity of the physical and mechanical properties across the concrete section. Consequently, the proper control of the bleeding process leads to more homogeneous properties of concrete across its cross‐section.

Assessment of lifetime seismic resilience of a long-span cable-stayed bridge exposed to structural corrosion

The present paper proposed a probabilistic methodology for evaluating the lifetime seismic resilience of the cable-stayed bridge considering the effect of structural corrosion. In this proposed methodology, the deteriorating processes, including the corrosion of steel bars, the reduction of concrete strength, and the corrosion of high-strength stay cables, were considered. Then, the nonlinear static analysis was conducted to directly relate the reduced seismic capacities with the pre-defined damage states to facilitate seismic fragility analysis. Furthermore, the serviceability reliability analysis of a cable-stayed bridge was implemented to improve the quantification of the long-term and post-earthquake functionality loss. The proposed methodology was illustrated by a typical sea-crossing cable-stayed bridge, including the structural corrosion under seismic hazards. The detrimental effect of the deteriorating process on seismic resilience and loss of the cable-stayed bridge was investigated. It is concluded that the lifetime seismic resilience can be overestimated, excluding the long-term functionality loss due to structural corrosion, and the deteriorating process has a significant impact on the seismic resilience of the cable-stayed bridge at large seismic intensities.

Strategies for Waste Recycling: The Mechanical Performance of Concrete Based on Limestone and Plastic Waste

Recycling is among the best management strategies to avoid dispersion of several types of wastes in the environment. Research in recycling strategies is gaining increased importance in view of Circular Economy principles. The exploitation of waste, or byproducts, as alternative aggregate in concrete, results in a reduction in the exploitation of scarce natural resources. On the other hand, a productive use of waste leads to a reduction in the landfilling of waste material through the transformation of waste into a resource. In this frame of reference, the paper discusses how to use concrete as a container of waste focusing on the waste produced in limestone quarries and taking the challenge of introducing plastic waste into ordinary concrete mixes. To prove the possibility of reaching this objective with acceptable loss of performance, the mechanical characteristics of concrete mixed with additional alternative aggregates classified as waste are investigated and discussed in this paper through the presentation of two experimental campaigns. The first experimental investigation refers to concrete made with fine limestone waste used as a replacement for fine aggregate (sand), while the second experimental program refers to the inclusion of three types of plastic wastes in the concrete. Different mixes with different percentages of wastes are investigated to identify possible fields of application. The experimental results indicate that use of limestone quarry waste and use of plastic waste are possible within significant percentage ranges, having recognized a limited reduction of concrete strength that makes concrete itself appropriate for different practical applications.

Properties of Lime-Cement Concrete Containing Various Amounts of Waste Tire Powder under Different Ground Moisture Conditions.

Lime-cement concrete (LCC) is a non-structural concrete in which lime and cement are used as the main binders. However, although LCC has many applications in reducing the settlement of foundations and providing a support layer for shallow foundations, little research has been conducted to evaluate its behaviour in various moisture conditions. Previous researchers have studied the feasibility of using waste tires in conventional concrete to alleviate their negative environmental impacts. However, in field projects, rubber has not been widely used because its application leads to the strength reduction of concrete. In the case of LCC, attaining high strengths is not required and thus application of waste tire particles sounds reasonable. This research evaluated the impact of various rubber powder contents on the fresh, geotechnical and durability properties of LCC at different saturation degrees induced by the capillary action and groundwater level increment, which has not been studied before. The results of more than 320 tests showed that the application of tire powder increases workability and decreases the water absorption of LCC. Moreover, all 60-day cured specimens exposed to 100% saturation degree experienced a strength reduction of less than 10% by using rubber powder contents varying from 0 to 20%. Moreover, increasing the saturation degree from 0 to 100% decreased the average compressive strength by 13.5 and 22% for 60-day cured samples of two different mix designs. The results of this research confirm that LCC containing up to 10% rubber powder could be promisingly used underneath or close to the groundwater table without its strength and geotechnical properties being jeopardized due to rubber employment and/or exposure to ground moisture.

Probabilistic models of concrete compressive strength and elastic modulus with rubber aggregates

The disposal of waste rubber products is a significant issue globally and it poses a serious threat to the environment creating long-term ecological problems. The possible use of rubber aggregates in concrete is a valid alternative to obtain a green construction material. This paper develops probabilistic models for the concrete Strength Reduction Factor (SRF) and Elastic modulus Reduction Factor (ERF) accounting for the amount of rubber aggregates as well as several variables defining the mix design. Three different rubber aggregate types are considered, namely fine and coarse replaced individually and fine and coarse replaced simultaneously. A total of 644 sets of concrete compressive strength and elastic modulus tests are collected from the literature for the model calibration. The paper presents a discussion about the formulation of the models, variance stabilizing transformations, model calibration, and model selection. Once formulated, we calibrate the probabilistic models using data from experimental tests. The unknown model parameters are estimated using a Bayesian approach implemented using A Markov Chain Monte Carlo (MCMC) simulation method. The proposed probabilistic models are used to evaluate the reliability of rubberized concrete structures. As an illustration, the proposed probabilistic models are used to estimate the reliability of an example column made of rubberized concrete under compressive axial force and of an example one-way slab made of rubberized concrete under distributed load.

TECHNOLOGICALITY OF FORM SYSTEMS AT DIFFERENT METHODS OF CONCRETE PREPARATION

It is shown that many scientific publications and researches in the field of monolithic house-building aredevoted to increase of efficiency of use of formwork systems as the most labor and economically expensive area. It isnoted that up to 50 % of the costs are for formwork, including the cost of renting or purchasing, its installation,maintenance, storage and remuneration. It is presented that with the development of formwork systems their technologyis improved, in particular the regulatory framework is improved to reduce the complexity of the work, adjustments aremade to the size of the formwork, it becomes more uniform, reduces the number of connections, increases the turnoverof formwork systems, which also reduces costs.It is shown that a very important issue, inseparable from monolithichousing is the improvement of design with the composition of concrete and concrete mixtures. One of the promisingУкраїнський журнал будівництва та архітектури, № 4 (004), 2021, ISSN (Print) 2710-0367, ISSN (Online) 2710-0375 17 areas of technology improvement is to reduce the time of the set of design strength. The question of the accelerated setof durability by concrete at hardening is very actual in the conditions of the market and high cost of rent of a timbering.Predicting the accelerated growth of concrete strength, respectively, will establish the morning timing of removal offormwork systems. The graph of dependence of time of a set of durability by concrete, for example at activation ofcement suspension in an electromagnetic field in comparison with standard data of hardening is specified. The reductionof the term (days) of keeping concrete in the formwork is shown, it improves the manufacturability of its use,accordingly it causes a reduction of all costs, incl. reduction of construction time and, accordingly, acceleratedmovement of funds and economic profit due to the earlier commissioning of facilities.The area of perspectiveresearches on establishment of interrelation of indicators of efficiency from parameters of object and technology isformulated. This gives a theoretical justification for further computational experiments. The object of research is theproduction processes with the use of collapsible formwork systems for frame-monolithic construction. The subject ofthe study are indicators of manufacturability of the use of formwork systems. The purpose of scientific and appliedresearch is the ability to show the increase of manufacturability of construction by ensuring the normative turnover offormwork by intensifying the hardening of concrete in frame-monolithic construction with a reduction in the duration ofthe strength of concrete. As a result of research the following tasks were defined: the area of further researches isformulated, ways of reduction of the basic technical and economic indicators are offered, the expedient theoreticalsubstantiation of the further computational experiments is proved.

The effect of isolated Bacillus ureolytic bacteria in improving the bio-healing of concrete cracks

BackgroundReinforcement corrosion and the concrete strength reduction are critical problems that resulted from crack creation in concrete. Very expensive and hazardous technologies based on chemical materials have been provided for repairing the cracks. Recently, crack repair using bio-catalysis precipitating bacteria has been developed as a viable and ecofriendly alternative technique. The main target of this study was to select and identify bacterial isolates with high urease activity to use in filling the cracks by the precipitation of CaCO3.ResultsTwo endospore-forming and alkali-resistant ureolytic bacteria were combined with concrete to tolerate the mechanical stresses generated by mixing. The two isolates designated as (B1 and B2) were selected and identified as Bacillus wiedmannii strain FSL W8-0169 and Bacillus paramycoides strain MCCC 1A04098, respectively, using 16SrDNA gene sequencing. Both bacterial species completely heal cracks in fully destructed concrete and significant enhancement in compressive strength was illustrated. The calcite filling of cracks and CaCO3 crystals that were screened using a scanning electron microscope may explain the crack healing and the enhancement in concrete strength.ConclusionsBacillus wiedmannii strain FSL W8-0169 and Bacillus paramycoides strain MCCC 1A04098 can be inserted with the concrete to improve the compressive strength and the self-healing of cracks. The two ureolytic bacterial strains can be used to protect water buildings from exposure to frequent cracks.