Electrical Resistivity of Concrete for Durability Evaluation: A Review

Degradation processes in reinforced concrete structures that affect durability are partially controlled by transport of aggressive ions through the concrete microstructure. Ions are charged and the ability of concrete to hold out against transfer of ions greatly relies on its electrical resistivity. Hence, a connection could be expected between electrical resistivity of concrete and the deterioration processes such as increase in permeability and corrosion of embedded steel. Through this paper, an extensive literature review has been done to address relationship between concrete electrical resistivity and its certain durability characteristics. These durability characteristics include chloride diffusivity and corrosion of reinforcement as these have major influence on concrete degradation process. Overall, there exists an inverse or direct proportional correlation between these parameters. Evaluated results, from measuring the concrete electrical resistivity, can also be used as a great indicator to identify early age characteristics of fresh concrete and for evaluation of its properties, determination of moisture content, connectivity of the micropores, and even condition assessment of in-service structures. This paper also reviews and assesses research concerning the influential parameters such as environmental conditions and presence of steel rebar and cracks on measuring electrical resistivity of concrete. Moreover, concrete resistivity concept, application, and its various measurement techniques are introduced

Inter-and Intrarater Reliability of Modified Lateral Scapular Slide Test in Healthy Athletic Men

Objective. The reliability of lateral scapular slide test (LSST) at 90 degrees of abduction is controversial; therefore, in order to achieve more reliability it may be necessary to make changes in this particular position. Methods. Modified lateral scapular slide test (MLSST) was done on thirty male basketball players with two examiners in one session and for the retest with one examiner in the next week. The test was done in 7 positions: arm relaxed at the side (P1), 90 degrees of abduction (P2), 90 degrees of scaption without having a weight in hands (P3), 90 degrees of scaption with having 3 different weights (1, 2, and 4 kg) in hands (P4, P5, and P6, resp.), and 180 degrees of scaption without having a weight in hands (P7). Results. In P1 and P6, the ICC scores indicated the highest level of intrarater reliability. In P2, the ICC scores showed a fair level of intrarater reliability, as the minimum reliability. The maximum and minimum interrater reliability were P1 and P4, respectively. Conclusion. Scaption with loading, as a functional position in the overhead athletes, is a reliable positioning and may be replaced with the third position of the traditional LSST

Antidepressant Potential of Ferula gummosa Essential Oil in Mouse Models

Background and objectives: Earlier researches have exhibited the antioxidant, antinociceptive, and antiepileptic effects of Ferula gummosa. Considering that antioxidants play a key role in the pathogenesis of depression, the antidepressant potential of the F. gummosa essential oil was assessed by using a mouse models. Methods:Lorke’s method was used to access the acute toxicity of the F. gummosa essential oil. The F. gummosa essential oil (5-40 mg/kg), standard agents, and vehicle were administered to animals. The forced-swimming test (FST), tail suspension test (TST), and open-field test (OFT) were used for the evaluation of depression. Results: The F. gummosa essential oil LD50 was found to be 316.22 mg/Kg b.w. β-Pinene, α-pinene, guaiol, δ-3-carene, bulnesol, α-Bisabolol, and β-myrcenewere the major components of the F. gummosaessential oil, respectively. In both FST and TST, 10-40 mg/kg of the essential oil decreased the duration of immobility. Furthermore, 10-40mg/kg of the F. gummosa essential oil enhanced the duration of swimming with no significant effect on the duration of climbing in FST. The F. gummosaessential oil did not change the animal locomotion in the OFT. Conclusion: According to the results, the F. gummosa essential oil showed antidepressant activity similar to fluoxetine which may have a potential clinical value for the treatment of depression

Comparative Study Involving Effect of Curing Regime on Elastic Modulus of Geopolymer Concrete

Geopolymer Concrete (GPC) as a cement-less construction material has attracted worldwide attention due to its lower carbon footprint. There are numerous studies reported on GPC made using different by-products including fly-ash. However, since the use of bottom-ash is comparatively limited, making potassium-based GPC using this waste can be an alternative to Portland Cement Concrete (PCC). In this study, two methods of accelerated curing were used to determine the influence of elevated temperature on the compressive strength of GPC, composed of 50% bottom-ash and 50% fly-ash. GPC specimens were cured using various temperatures including ambient, 30 °C, 45 °C, 60 °C, and 80 °C for 24 h, all followed by 28 days of ambient curing. The highest compressive strength was obtained with steam curing at a temperature of 80 °C for a duration of 24 h. It is of great significance to evaluate elastic modulus of the concrete mixture so that the short-term rigidity of structures subjected to elongation, bending, or compression can be predicted. In this study, a longitudinal Resonant Frequency Test (RFT) as a non-destructive test (NDT) was used to calculate the elastic modulus of both GPC and a comparative PCC mix. Based on the results, PCC had higher resonant frequency (by about 1000 Hz) compared to GPC. A review of empirical models for predicting GPC’s elastic modulus showed that all of the predicted elastic modulus values were lower than experimental values

Durability and Self-Sealing Examination of Concretes Modified with Crystalline Waterproofing Admixtures

Repairing concrete structures costs billions of dollars every year all around the globe. For overcoming durability concerns and creating enduring economical structures, chemical admixtures, as a unique solution, have recently attracted a lot of interest. As permeability of a concrete structure is considered to play a significant role in its durability, Permeability Reducing Admixtures (PRA) is one of the ideal solutions for protecting structures exposed to water and waterborne chemicals. Different products have been developed to protect concrete structures against water penetration, which, based on their chemistry, performance, and functionality, have been categorized into PRA. As it has previously been tested by authors and proven to be a promising solution, a hydrophilic Crystalline Waterproofing Admixtures (CWA) has been considered for this study. This paper aims to investigate how this product affects concrete’s overall freeze–thaw resistance, self-sealing, and corrosion resistance. Various testing methods have been utilized to examine the performance of CWA mixtures, including the linear polarization resistance, resonance frequency testing, half-cell potential, and self-sealing test. The reinforcement corrosion potential and rate measurements indicated superior performance for CWA-treated samples. After being exposed to 300 freeze–thaw cycles, concrete mixes containing CWA—even non-air-entrained ones—showed a Durability Factor (DF) of more than 80% with no signs of failure, while non-air-entrained control samples indicated the lowest DF (below 60%) but the greatest mass loss. The major causes are a reduction in solution permeability and lack of water availability in the concrete matrix—due to the presence of CWA crystals. Furthermore, evidence from the self-sealing test suggests that CWA-treated specimens can seal wider cracks and at a faster rate

Inventive Microstructural and Durability Investigation of Cementitious Composites Involving Crystalline Waterproofing Admixtures and Portland Limestone Cement

The durability of a cement-based material is mainly dependent on its permeability. Modifications of porosity, pore-structure and pore-connectivity could have significant impacts on permeability improvement, which eventually leads to more durable materials. One of the most efficient solutions in this regard is to use permeability reducing admixtures (PRA). Among these admixtures for those structures exposed to hydro-static pressure, crystalline waterproofing admixtures (CWA) have been serving in the construction industries for decades and according to ACI 212—chemical admixtures’ report, it has proven its capability in permeability reduction and durability-enhancement. However, there is substantial research being done on its durability properties at the macro level but very limited information available regarding its microstructural features and chemical characteristics at the micro level. Hence, this paper presents one of the first reported attempts to characterize microstructural and chemical elements of hydration products for cementitious composites with CWA called K, P and X using Scanning Electron Microscopy (SEM). Backscattered SEM images taken from a polished-section of one CWA type—K—admixture were analyzed in ImageJ to obtain paste matrix porosity, indicating a lower value for the CWA-K mixture. X-ray analysis and SEM micrographs of polished sections were examined to identify chemical compositions based on atomic ratio plots and brightness differences in backscatter-SEM images. To detect chemical elements and the nature of formed crystals, the fractured surfaces of three different CWA mixtures were examined. Cementitious composites with K admixture indicated needle-like crystal formation—though different from ettringite; X and P admixtures showed sulfur peaks in Energy Dispersive Spectrum (EDS) spectra, like ettringite. SEM images and X-ray analyses of mixtures incorporating Portland Limestone Cement (PLC) indicated lower-than-average porosity but showed different Si/Ca and Al/Ca atomic ratios

Self-Healing Potential and Post-Cracking Tensile Behavior of Polypropylene Fiber-Reinforced Cementitious Composites

The use of synthetic fibers as reinforcement in fiber-reinforced cementitious composites (FRCC) demonstrates a combination of better ductile response vis-à-vis metallic ones, enhanced durability in a high pH environment, and resistance to corrosion as well as self-healing capabilities. This study explores the effect of macro- and micro-scale polypropylene (PP) fibers on post-crack energy, ductility, and the self-healing potential of FRCC. Laboratory results indicate a significant change in fracture response, i.e., loss in ductility as curing time increases. PP fiber samples cured for 2 days demonstrated ductile fracture behavior, controllable crack growth during tensile testing, post-cracking behavior, and a regain in strength owing to FRCC’s self-healing mechanism. Different mixes of FRCC suggest an economical mixing methodology, where the strong bond between the PP fibers and cementitious matrix plays a key role in improving the tensile strength of the mortar. Additionally, the micro PP fiber samples demonstrate resistance to micro-crack propagation, observed as an increase in peak load value and shape deformation during compression and tensile tests. Notably, low volume fraction of macro-scale PP fibers in FRCC revealed higher post-crack energy than the higher dosage of micro-scale PP fibers. Lastly, few samples with a crack of < 0.5 mm exhibited a self-healing mechanism, and upon testing, the healed specimens illustrated higher strain values