Use of buffer treatment to utilize local non-alkali tolerant bacteria in microbial induced calcium carbonate sedimentation in concrete crack repair

Concrete often suffers cracks due to its low tensile strength. The repair process can vary ranging from surface coating, grouting, and strengthening. Microbial induced calcium carbonate sedimentation process (MICP) is a process of utilizing non-pathogenic bacteria to produce calcium carbonate through its urease activity in crack repair (filling). It is known as an alternative crack repair method that does not utilize Portland cement. In general, the bacteria used in MICP are alkali tolerant bacteria that have a higher chance of surviving the high alkalinity environment in concrete. However, in some regions, alkali tolerant bacteria are difficult to acquire and unavailable locally. This study introduced a technique to utilize non-alkali tolerant bacteria in MICP using buffer treatment. Instead of injecting bacteria directly onto the crack surface, the buffer solution was applied onto the crack surface prior to the bacteria injection. Results from the laboratory indicated a higher bacteria survival rate when the buffer treatment was applied to the medium. For the crack filling, with the buffer treatment, the crack was completely filled within 21–28 days. The microstructure results also showed that the crystal deposits from both laboratory and crack surface were similar in both physical appearance and phase composition

Seismic strengthening of low strength concrete columns using high ductile metal strap confinement : a case study of Kindergarten school in Northern Thailand

The 2014 Chaing Rai earthquake (Thailand) caused extensive damage in many reinforced concrete (RC) buildings built before the introduction of modern seismic design guidelines. Much of the damage on these buildings was attributed to the inadequate capacity and/or ductility of columns. As a result, suitable and cost-effective strengthening techniques for such substandard elements are necessary. This article presents a case study on the seismic strengthening of a one-story RC kindergarten school located in Ampor Pan, Chaing Rai province. The building was partially damaged during the afore-mentioned earthquake, which led to cracking in walls, columns, and beam-column joints. As part of the initial assessment, innovative repair solutions were sought to minimize construction time, labor, and material cost. Accordingly, an innovative strengthening technique that uses Post-tension Metal Strapping (PTMS) was proposed to strengthen the damaged RC elements. This article presents details of the structural assessment performed on the building, as well as details of the PTMS strengthening strategy, which was applied for the first time in a real full-scale structure. This article contributes towards the validation and application of the PTMS strengthening on real structures, which had not been possible until now

BENDING, BUCKLING AND FREE VIBRATION ANALYSES OF NANOBEAM-SUBSTRATE MEDIUM SYSTEMS

This study presents a newly developed size-dependent beam-substrate medium model for bending, buckling, and free-vibration analyses of nanobeams resting on elastic substrate media. The Euler-Bernoulli beam theory describes the beam-section kinematics and the Winkler-foundation model represents interaction between the beam and its underlying substrate medium. The reformulated strain-gradient elasticity theory possessing three non-classical material constants is employed to address the beam-bulk material small-scale effect. The first and second constants is associated with the strain-gradient and couple-stress effects, respectively while the third constant is related to the velocity-gradient effect. The Gurtin-Murdoch surface elasticity theory is adopted to account for the surface-free energy. To obtain the system governing equation as well as corresponding boundary conditions, Hamilton’s principle is called for. Three numerical simulations are presented to characterize the influences of the material small-scale effect, the surface-energy effect, and the surrounding substrate medium on bending, buckling, and free vibration responses of nanobeam-substrate medium systems. The first simulation focuses on the bending response and shows the ability of the proposed model to eliminate the paradoxical characteristic inherent to nanobeam models proposed in the literature. The second and third simulations perform the sensitivity investigation of the system parameters on the buckling load and the natural frequency, respectively. All analytical results reveal that both material small-scale and surface-energy effects consistently stiffen the system response while the velocity-gradient effect weakens the system response. Furthermore, these sized-scale effects are more pronounced when the underlying substrate medium becomes softer

Self-compacting steel fibers reinforced geopolymer: Study on mechanical properties and durability against acid and chloride attacks

This study aimed to investigate the effects of steel fibers on the properties of self-compacting geopolymer (SCG), including flowability and fillability, compressive and flexural strength, and durability against harmful chemical substances such as acids and chloride. In the first stage, the study involved determining the optimum fiber content for geopolymer that meets the criteria for self-compacting concrete. The second stage involved investigating the mechanical properties and durability of self-compacting fiber-reinforced geopolymer (SCFRG). For SCG, the binder phase consisted of fly ash and slag at different proportions, while for SCFRG, the geopolymer was mixed with hooked-end steel fiber at 0.5–1.5% by volume fractions. The study found that adding 0.5% to 1.5% steel fibers by volume fraction to create self-compacting fiber-reinforced geopolymer (SCFRG) improved compressive strength by 8.7%, toughness by 88%, and residual strength by 83.7%. However, it slightly reduced slump and filling ratio while increasing T50. Both SCG and SCFRG's durability were assessed by immersing samples in 5% concentration chemical solutions, resulting in weight loss to varying degrees depending on the type of chemical. In terms of weight loss, immersion in 5% sodium chloride showed no effect, while immersion in 5% magnesium sulfate and 5% sulfuric acid resulted in a reduction in weight compared to samples cured in ambient conditions. Additionally, SCFRG samples submerged in MgSO4, H2SO4, and NaCl demonstrated relatively stable compressive strength when compared to ambient samples. The addition of steel fibers to SCG reduced the chloride penetration depth and diffusivity, indicating better resistance to chloride ion penetration. In summary, the study demonstrated that although the addition of steel fibers decreased flowability and fillability, it potentially improved the mechanical and durability properties of self-compacting geopolymer

Eco-friendly 3D Printing Mortar with Low Cement Content: Investigation on Printability and Mechanical Properties

The conventional approach to achieving optimal printability and buildability in 3D printing mortar relies heavily on cement, which is both costly and environmentally detrimental due to substantial carbon emissions from its production. This study aims to mitigate these issues by investigating the viability of slag as a partial substitute for cement, with the goal of developing an eco-friendly alternative. The newly formulated mortar, featuring a 30% reduction in cement content (from 830 to 581 kg/m3) and the inclusion of 0.10% micro-fibers, exhibits properties comparable to conventional 3D printing mortar. The research is structured into two parts: Part 1 focuses on determining the optimal fiber content, while Part 2 delves into the investigation of fiber-reinforced mortar with reduced cement content for 3D printing. Criteria were established to ensure mortar flow at 115%, initial printable time below 60 minutes, and 7-day compressive strength exceeding 28 MPa. Part 1 results indicate that a fiber content of 0.1% by volume meets the specified requirements. In Part 2, it was observed that increasing the slag replacement percentage extended the initial printable time and time gap. However, even at a 30% replacement rate, the initial printable time remained within the acceptable range, partially attributed to the presence of fibers in the mix. Additionally, higher slag content led to increased flow and reduced filament height in the mixes. Notably, all formulations surpassed the 7-day compressive strength threshold. These findings underscore the potential of slag as a sustainable alternative to cement in 3D printing fiber-reinforced mortar, offering promising prospects for environmentally friendly construction practices

Effect of graphene oxide nanoparticles on blast load resistance of steel fiber reinforced concrete

Concrete structures may occasionally be subjected to both intentional or unintentional explosions which could cause casualties and damage to properties. Advance research on protective structures are important to enhance blast resistance of materials, and to protect life and properties. This study investigated the effect of graphene oxide nanoparticles (GO) on enhancing the blast resistance of fiber reinforced cement mortar (FRM). GO in solution was incorporated in steel fiber reinforced mortar at the rate of 0, 0.025, 0.050, 0.075, and 0.100 % by weight of cement. A series of experiments were carried out consisting of 2 stages: Stage 1) workability, setting time, compressive and flexural strength, and microstructure using SEM and XRD processes, and Stage 2) blasting loading test. The optimum GO dosage giving the highest compressive and flexural strengths from the 1st stage was determined and chosen to continue on the 2nd stage (blast loading test). The blasting tests were performed on panel specimens (500mmx1000mmx60mm) using TNT weighing ½ lb. (226.7 grams) with three different standoff distances of 340, 400, and 460 mm. Results from Stage 1 on both flexural and compression tests indicated an optimum GO content of 0.025% by weight of cement. The workability was found to decrease with the increasing the GO content. The SEM images also revealed that the addition of GO nanoparticles reduced the porosity in the mortar matrix. For the blasting test, three damage patterns were observed: complete flexural failure, partial damage (flexural cracking), and no major damage, depending on the standoff distance and specimen type. The addition of GO can reduce the maximum and permanent deflections of the panel under blast loading. FRM panels with GO at 0.025% tested at the standoff distance of 460 mm showed the lowest level of damage

Static and Free Vibration Analyses of Single-Walled Carbon Nanotube (SWCNT)-Substrate Medium Systems

This paper proposes a novel nanobar-substrate medium model for static and free vibration analyses of single-walled carbon nanotube (SWCNT) systems embedded in the elastic substrate medium. The modified strain-gradient elasticity theory is utilized to account for the material small-scale effect while the Gurtin-Murdoch surface theory is employed to represent the sur-face-energy effect. The Winkler-foundation model is assigned to consider interactive mechanism between the nanobar and its surrounding substrate medium. Hamilton’s principle is called for to consistently derive the system governing equation, initial conditions, and classical as well as non-classical boundary conditions. Two numerical simulations are employed to demonstrate the essence of the material small-scale effect, the surface-energy effect, and the surrounding substrate medium on static and free vibration responses of single-walled carbon nanotube (SWCNT)-substrate medium systems. The simulation results show that the material small-scale effect, the surface-energy effect, and the interaction between the substrate and the structure lead to a system-stiffness enhancement both in static and free vibration analyses

Characteristic and Allowable Compressive Strengths of Dendrocalamus Sericeus Bamboo Culms with/without Node Using Artificial Neural Networks

The strength of construction material is a crucial consideration in the process of structural design and construction. Conventional materials such as concrete or steel have been widely utilized due to their predictable material performance. However, a significant obstacle to the widespread use of bamboo in structural elements lies in the challenge of its standardization. Many previous research studies have explored bamboo’s load bearing capacity, but the information remains limited due to variations in species, size, age, physical properties, moisture content, and other factors, making it difficult to predict their load-bearing capacity. This study aims to propose Artificial Neural Network (ANN) models to predict ultimate compressive load and compressive strength of Dendrocalamus Sericeus bamboo culm. Additionally, for structural design purposes, the proposed ANN models were employed to determine the characteristic and allowable compressive strengths. As a first step, experimental data from compressive tests in the literature were used for training and developing the ANN model. To investigate the effect of the node on compressive loading capacities, the test data were separated into two datasets, “Node” samples and “Internode” samples. Through the training process, ANN models were finally proposed, and the R-square values for the prediction of ultimate compressive load and compressive strength from the proposed ANN models were significantly higher than those obtained from the linear regression analyses used in the literature. Subsequently, the characteristic and allowable compressive strengths were calculated and compared to the strengths obtained from the experiment data, revealing a difference of approximately only 8.0%. Overall, the ANN models presented in this study offer promising predictive ability for both ultimate compressive load and compressive strength of Dendrocalamus Sericeus bamboo culm, as well as for determining characteristic and allowable strengths. Hence, ANN models are suggested to be adopted as a tool for the design and construction of bamboo buildings