B. adusta CCBAS 930. The activity of oxidoreductases and levels of phenolic compounds and free radicals were determined during the biotransformation of anthraquinone antibiotics: daunomycin (DNR) and doxorubicin (DOX) by B. adusta strain CCBAS 930. Moreover, phytotoxicity (Lepidium sativum L.), ecotoxicity (Vibrio fischeri), genotoxicity and cytotoxicity of anthraquinone dyes were evaluated before and after biological treatment. More than 80% and 90% of DNR and DOX were removed by biodegradation (decolorization). Initial solutions of DNR and DOX were characterized by eco-, phyto-, geno- and cytotoxicity. Despite efficient decolorization, secondary metabolites, toxic to bacteria, formed during biotransformation of anthracycline antibiotics in B. adusta CCBAS 930 cultures. DNR and DOX metabolites did not increase reactive oxygen species (ROS) production in human fibroblasts and resazurin reduction. DNR metabolites did not change caspase-3 activity.The aim of this study was to evaluate the bioremoval mechanism of anthracycline antibiotics by the white-rot fungus  The development of civilization and accelerated pace of life have led to a global increase in the incidence of cancer in the last decade . MoreoveIn recent years, the amount of pharmaceuticals and their metabolites in wastewater, particularly anti-tumor drugs have increased . DependiBjerkandera adusta is a promising agent in athraquinone derivative biodegradation e.g., anthraquinone dyes, alizarin and anticancer anthracyclines like DNR [Currently, wastewater containing pharmaceuticals is treated using physicochemical methods such as ozonation, adsorption, membrane filtration and electrolysis ,14. In rlike DNR B. adusta CCBAS 930. In this study, we characterized the activity of oxidoreductases , levels of free radicals and phenolic compounds during the biotransformation of DNR and DOX. Moreover, bio-, phyto-, geno- and cytoxicity assays were performed to determine the toxicity of its biotransformation products. Considering that anhracyclines are characterized by a strong pro-oxidant capacity, antioxidant properties during their treatment by B. adusta CCBAS 930 were assessed.Therefore, the aim of this study was to evaluate the mechanism of anthracycline antibiotic bioremoval and detoxification by the white-rot fungus B. adusta CCBAS cultures with the addition of 10 µg/mL of DNR and DOX, their decolorization ranged from 17.30 to 66.16% and 22.91 to 72.50%, respectively. In 20-day-old cultures, B. adusta strain CCBAS 930 removed more than 90% of AQAs. Spectral analysis (200–800 nm) showed that B. adusta CCBAS 930 removed anthracyclines and broke down chromophores, but produced colorless secondary products with maximum absorbance at 216 nm, 271 nm and 364 nm . VP activity, especially measured at pH = 4.5, with and without Mn+2, appeared from the first days of B. adusta CCBAS 930 cultures with both anthracyclines. VP activities measured at pH = 4.5, without or with Mn+2 increased gradually, reaching a maximum of 61–101 and 103–280 U/mg protein on day 20, respectively  and day 10 (5.44–6.44 U/mg protein), respectively. SOD activity in B. adusta CCBAS 930 cultures with DNR and DOX was the highest in the first week . Dioxygenase activities were at a lower level compared to other oxidoreductases. In the presence of DNR and DOX, the maximum 2,3-DO and 1,2-DO activities were recorded at the end of the second week of cultures   .B. adusta strain CCBAS on medium with the addition of DNR and DOX at a concentration of 10 µg/mL. We observed that pH decreased during B. adusta CCBAS 930 cultures in the presence of DNR and DOX from pH = 6.0 to 4.09 and 3.90, respectively.The pH decreased during the 20-day culture of B. adusta CCBAS 930 cultures with DNR and DOX, a systematic increase in the content of phenolic compounds and free radicals was observed. In the third week, the content of phenolic compounds in B. adusta CCBAS 930 cultures with the addition of DNR and DOX decreased to the value characteristic for the initial AQA solutions   A1,B1.B. adusta CCBAS 930 cultures with DNR and DOX. Initial DNR and DOX solutions (10 µg/mL) in the DPPH scavenging assay did not show any antioxidant activity; on the contrary, they showed strong oxidative properties towards trolox (data not shown). Antioxidant activity of post-liquid cultures systematically increased during B. adusta CCBAS 930 cultures with maximum DPPH scavenging activity to the 2nd week (20–46%). After that time, a decrease in their antioxidant activity was recorded  were found in the inhibition of L. sativum seed germination between post-culture fluids after DNR and DOX treatments . Decolorized post-culture fluids with DNR or DOX were characterized by slightly higher, but not statistically significantly different, germination index (GI) than the initial 10 µg/mL DNR and DOX solutions (GI = 35.85 ± 3.33 and 29.88 and 22.06 ± 5.94) (Root growth inhibition (RGI) was at a comparable level (62–69%) for anthracyclines before and after ferences A. Signif ± 5.94) B.V. fischeri bacteria (Microtox) showed that initial media with the addition of DNR and DOX at a concentration of 10 µg/mL were characterized by acute toxicity . Surprisingly, we found significant differences in the toxicity of decolorized post-culture fluids with anthracycline antibiotics. Post-culture fluid with DNR had a similar level of toxicity as the initial 10 µg/mL DNR solution, but in the case of post-culture fluids with DOX, we observed several times higher toxicity (high acute toxicity) against V. fischeri compared to the initial media with the addition of 10 µg/mL DOX  (The ecotoxicity assay with ctively) C.B. adusta CCBAS 930 was also investigated. Our results clearly showed genotoxicity of the initial 10 µg/mL DNR and DOX solutions. The effects were dose-dependent and decreased with increasing sample dilutions. The highest values of CIF factor was noted for DNR and DOX initial solutions at a concentration of 10 µg/mL  .Genotoxicity of anthracyclines before and after treatment by ctively) . After bBJ cell exposure to initial DOX and DNR solutions in medium cause a decrease in resazurin reduction by 50.36 and 48.49% after 24 h, respectively, and 40.36 and 48.40% after 48 h, respectively, compared to Control 1. Conditioned media containing DOX and DNR metabolite did not affect BJ cell metabolism after 24 h compared to Control 1. Only media containing DOX metabolite did not affect BJ cell metabolism after 48 h, as measured by the resazurin reduction assay compared to Control 1 .After 24- and 48-h exposure of BJ cells to the medium containing initial DOX and DNR solutions, ROS production was induced by 680.22 and 625.72%, respectively, after 24 h and 457.34 and 372.97%, respectively, after 48 h compared to Control 1. Interestingly, Control 2 fungal medium showed an increase in ROS production by 306.48 and 302.67%, respectively, compared to Control 1 at both tested time intervals. After 24 and 48 h of BJ cell exposure to conditioned medium containing DOX metabolite and DNR metabolite, ROS production decreased compared to the medium containing DOX and DNR  .Caspase-3 activity was not affected after 24 h of BJ cell exposure to the medium containing initial DOX and DNR solutions. Interestingly, caspase-3 activity increased by 34.00 and 56.00%, respectively, at both studied time intervals (24 and 48 h) in the group containing 10% fungal mineral Park Robinson medium (Control 2) compared to Control 1 cells containing 10% PBS. After 48 h, DOX metabolite increased caspase-3 activity compared to Control 1 and DOX-containing group (by 60.54% compared to Control 1) .Viable cells in this assay had a light green fluorescent cytoplasm. Healthy cells with green fluorescent cytoplasm were predominant in the control cultures. After 24 and 48 h, we observed a decrease in cell number in the group treated with DOX and DNR compared to Control 1. We observed an increase in BJ cell number at both time intervals in the cell group exposed to DOX metabolite and DNR metabolite compared to cells exposed to DOX and DNR .B. adusta CCBAS 930 and they explained 79.98–81.53% of data variability. PC1 explained 54.99 and 55.22% of data variability in B. adusta CCBAS 930 cultures with DNR and DOX, respectively. In both cases, PC1 was mainly associated with negatively correlated (p < 0.05) SOR (74.50–87.72%) and GOX (92.76–90.33%) activities and pH (77.06–79.58%) and positively correlated with VP peroxidase activity, measured at pH = 3.0 and pH = 4.5 (with/without Mn+2) (88.22–95.78%). In B. adusta CCBAS 930 cultures with DOX, PC1 was strongly associated with HRP-like (90.30%) and 2,3-DO activity (90.60%). In B. adusta CCBAS 930 cultures with DNR and DOX, PC2 factor explained 24.99% and 26.30% of anthracycline biotransformations, respectively. In B. adusta CCBAS930 cultures with AQAs, PC2 was strongly associated with a higher content of phenolic compounds (73.38–97.48%) and antioxidant properties (83.50–95.80%) for DNR and LiP (74.72%) and MnP (94.61%) activity for DOX. PC2 for DOX treatment in B. adusta CCBAS 930 cultures was associated with higher activities of CAT (86.60%), SOD (72.23%) and 2.3-DO (81.26%)  .B. adusta strain CCBAS 930 to remove these pharmaceuticals from the aquatic environment [B. adusta CCBAS 930. However, the main mechanism of DNR and DOX removal  was associated with color removal through enzymatic oxidation. Previous data indicated the connection between color removal  and biodegradation of color compounds, e.g., synthetic dyes. Color removal of these compounds was visible when the chromophoric center of the dye was cleaved [B. adusta CCBAS 930 cultures with AQAs, we observed a systematic color decrease at an absorbance of 480 nm, but it was slightly increased when oxidized products were formed. Reszka et al. (2003) [Due to the increase in cancer incidence, cytostatics are one of the main environmental problems. Their main sources are hospitals, municipal and industrial wastewater containing non-metabolized or partially metabolized cytostatics and effluents from their production. Since these compounds are not efficiently removed during wastewater treatment, they are found in ground, surface and even drinking water. There is no information in the literature on the biotransformation of anthracycline antibiotics by fungi. Our team was the first to suggest the possibility of using the ironment . Biotran cleaved ,21. Duri. (2003)  showed iB. adusta CCBAS 930 synthesized the following peroxidases: HRP-like, MnP, LiP and VP, but no laccase. Previous data demonstrated that the main oxidoreductases responsible for decolorization and biodegradation of anthraquinone derivatives, e.g., anthraquinone dyes in Bjerkandera sp. were peroxidases [B. adusta CCBAS cultures was related to their biodegradation by extracellular peroxidases, especially VP. Reszka et al.  [2O2 [B. adusta CCBAS, we observed pH decrease, which was strongly correlated (p < 0.05) with increased activities of VP peroxidases. The connection between VP activity, Mn+2 oxidation and guaiacol without and in the presence of Mn+2 and medium pH has been confirmed previously [During biotransformation of DNR and DOX, oxidases ,17,23. O3, 2005) ,24 descr05) [2O2 , pharmac05) [2O2  as well 05) [2O2 ,28. An ieviously .B. adusta CCBAS 930 cultures with anthracycline antibiotics. However, our results indicated that this phenolic compounds showed antioxidant activity, e.g., scavenging activity towards DPPH• radicals. Earlier study indicated that phenolic compounds could be produced during the growth of different white-rot fungi or during xenobiotic biotransformations, e.g., anthraquinone derivatives through the activity of fungal oxidoreductases [B. adusta CCBAS 930 without the addition of anthracycline antibiotics (data not shown). Moreover, previous data have demonstrated that phenols are substrates for dioxygenases that catalyze the cleavage of aromatic rings [p < 0.05) between an increase in hydroxyphenol concentrations and 2,3-DO activity during AQA biotransformation. We observed SOR production during AQA treatment by B. adusta CCBAS 930, but also in control cultures without AQAs (data not shown). This indicated that partial oxygen reduction, with the release of H2O2 molecule was the main source of O•- in fungal cells during the biotransformation of AQAs. It is worth mentioning that free radicals are formed not only due to oxidative stress, but also physiological changes. Even high ROS levels do not adversely affect the growth and development of these fungi as they have an enzymatic mechanism that neutralizes ROS such as SOD, CAT and peroxidase [p < 0.05) between the increase in the level of free radicals during the cultivation of B. adusta CCBAS 930 and higher glucose oxidase activity. H2O2 is then broken down to O2 and H2O by catalase or participates in peroxidase-catalyzed reactions as a co-substrate. Reszka et al. (2005) [•- removal during the degradation of high redox potential compounds, e.g., ligninocelulose and anthraquinone derivatives [We observed high phenolic compound production during ductases . We alsoic rings . It is croxidase . Biosyntroxidase . This wa. (2005)  showed tivatives ,33.B. adusta CCBAS930 cultures.However, xenobiotics such as pharmaceuticals in the environment may contribute to the formation of free radicals. Anthracycline antibiotics readily undergo single-electron reduction, generating semiquinone radicals and superoxide anion radicals. This initiates a cascade of free radical reactions whose products are highly toxic hydrogen peroxide and hydroxyl radical. Due to the universal character of free-radical mechanism of action of anthracyclines, all cells are exposed to harmful effects of radicals generated . In lighB. adusta CCBAS 930 treatment. Using an ecotoxicology assay with Vibrio fischeri, we did not show a reduced toxicity of post-culture liquids obtained after treating 10 µg mL−1 DNR and DOX with B. adusta CCBAS 930. Post-liquid cultures were characterized by a higher toxicity after treatment with B. adusta CCBAS 930. In recent years, various information has been published on the possibility of detoxification of anthraquinone derivatives, e.g., textile dyes by oxidoreductases synthesized by white-rot fungi [B. adusta CCBAS 930 was probably connected with a high concentration of phenolic compounds. On the other hand, we observed that the modification of B. adusta CCBAS 930 culture could significantly reduce the biotoxicity of anthracyclines (data not shown). Previous study indicated that phenolic compounds produced by white-rot fungi exhibited antibacterial activity [Lentinula edodes and Pleurotus ostreatus were characterized by antibacterial activity towards Gram-positive and Gram-negative bacteria [V. fischeri (Microtox) as the main assay to determine the ecotoxicity potential of anthraquinone derivatives in culture fluids after treatment with microfungi cannot be considered as one of the most important toxicological tests.In addition to decolorization degree and activity of oxidoreductases, we also assessed bio-, phyto-, cyto- and genotoxicity of DNR and DOX before and after ot fungi ,34,35. Hot fungi ,37. Baseactivity ,39. Cultbacteria ,39. Morebacteria . In viewB. adusta CCBAS 930 was determined based on the inhibition of seed germination and root elongation. Seed germination and root growth inhibition of L. sativum L. in the presence of initial DNR and DOX solutions or post-culture liquids were at the same levels. There is some information in the literature, on the use of the phytotoxicity assay to determine the detoxification of anthraquinone derivatives by fungi [B. adusta CCBAS 930. Due to the fact that the deficit of drinking water increases with climate change, work is still ongoing on effective methods of municipal and industrial wastewater recycling that will allow for their re-use, e.g., for agricultural irrigation [B. adusta CCBAS 930 for removal of these cytostatic drugs and re-use of the post-culture fluids, e.g., for agricultural irrigation.Phytotoxicity of post-culture fluids of by fungi ,23. Howeby fungi  and a derigation . Our resB. adusta CCBAS 930 treatment both AQAs showed no genotoxicity effect in the SOS Chromotest assay, without and with metabolic activation. A study by Zounková et al. (2007) [B. adusta strain CCBAS 930 may be an alternative or supplement to conventional pharmaceutical wastewater treatment methods.Genotoxicity is also a very important issue in the effective removal of pollutants using biological methods. Genotoxicity and potential promutagenic effects of xenobiotics, e.g., cytostatic drugs, have serious consequences in the future. Previous data indicated that certain amounts of cytostatic drugs pass unmetabolized through the patient. Moreover, cytostatic agents and their metabolites are continuously disposed of not only in hospitals, but also municipal wastewater and end up in the wastewater system ,42. Zhan. (2007)  showed tB. adusta CCBAS 930 treatment in group contained DNR. Our results are comparable to a similar assay involving fungal treatment of anthraquinone derivatives, e.g., textile dyes [B. adusta CCBAS 930 [P. sanguineus did not produce toxic metabolites during dye-containing wastewater treatments. Moreover, our study indicated that the high antioxidant activity was correlated with decrease in SOR levels. This suggested that biotransformation products such as phenols can protect fibroblast cells by ROS during the biological treatment of anthracyclines in B. adusta CCBAS 930 cultures.Additionally, the cytotoxicity assay was carried out before and after fungal treatment. Initial DNR and DOX solutions were also toxic to the BJ skin fibroblast cell line. Control media did not increase ROS production, while media with DNR and DOX strongly enhanced ROS production in BJ skin fibroblasts. The obtained data suggested that both DNR and DNR media caused apoptosis with increasing ROS production, but DNR and DOX metabolites were characterized by low ROS levels and did not activate apoptosis. Previous data demonstrated that high ROS production could lead to the activation of apoptotic processes through the mitochondrial pathway . Low ROSile dyes ,35. No cCBAS 930 . Vanhull2+ and Mg2+, fetal bovine serum (FBS), resazurin, MEM medium without phenol red (≥98%), o-dianisidine (≥95%), veratryl alcohol (96%), 2,6-dimethoxyphenol (99%), ABTS  (≥98%), DPPH• , trolox (97%), peroxidase, type II from horseradish (200 KU) and catechol (≥99%) were purchased from Sigma-Aldrich . All other chemicals and reagents were of analytical grade.Daunomycin hydrochlorine (≥90%), doxorubicin hydrochlorine (≥98%), streptomycin (≥98%), phosphate-buffered saline (PBS) without CaB. adusta strain CCBAS 930 was isolated from black earth soil  from a field near Lublin in south-eastern Poland [The anamorphic n Poland . The expn Poland . Control480nm) measurements of clear post-culturing liquids with DNR and DOX [B. adusta CCBAS 930 cultures. The biosorption assay was performed on 20-day B. adusta CCBAS 930 cultures according to Rybczyńska-Tkaczyk and Korniłowicz-Kowalska (2016) [3 of 70% ethanol to determine the sorption capacity of the biomass and agitated for 24 h . The sorption capacity was estimated according to the equation:Qe—biosorption capacity (mg g−1), Ci and Cf—initial and final concentration (mg L−1), m—adsorbent dose (g), V—volume of solution (l).To explain the bioremoval mechanism of anthracycline antibiotics we applied two parameters: decolorization and biosorption degree. Decolorization was estimated by periodic absorbance (A and DOX . Moreovea (2016) . After c460nm = 11,3 M−1 cm−1) in 0.1 M acetate buffer (pH 5.5) with 0.1 mM H2O2 and 0.5 mM ABTS  as a substrate and 35 µL, respectively. The activity of manganese-dependent peroxidase (MnP) was determined by oxidation of 15 µL of 1 mM MnSO4 in 265 µL of sodium malonate  in the presence of 50 µL of the supernatant and 10 µL of 6 mM H2O2, and subsequent determination of the Mn+3–malonic acid complex (ε270nm = 11.590 M−1 cm−1). The activity of lignin peroxidase (LiP) was assayed using 20 mM veratryl alcohol (ε310nm = 9.300 M−1 cm−1) in 40 mM tartrate buffer, pH 3, in the presence of 10 µL of 8 mM H2O2. Versatile peroxidase (VP) activity was determined by the oxidation of 20 mM 2,6-dimethoxyphenols . Mn-independent activity of VP was estimated by the oxidation of 15 µL of 20 mM 2,6-DMP (ε468 = 49.6 M−1 cm−1) in 265 µL 50 mM sodium malonate buffer (pH 3.0 and 4.5) with 10 µL of 6 mM H2O2. Mn-dependent activity of VP was assayed by oxidation of 15 µL 20 mM 2,6-DMP in 250 µL 50 mM sodium malonate buffer (pH 4.5) in the presence of 10 µL of 6 mM H2O2 and 15 µL 0.1 mM MnSO4. The activity of 1,2-dioxygenase  was determined by oxidation of catechol  in phosphate buffer pH 7.5 (50 mM) with the presence of 20 μL of Na2EDTA (20 mM) and 60 μL of supernatant. The activity of 2,3-dioxygenase  was estimated by oxidation of catechol  in phosphate buffer, pH 7.5 (50 mM), and 60 μL of the supernatant. The activities of catalase (CAT) and glucose oxidase (GOX) were estimated according to Korniłłowicz-Kowalska and Rybczyńska (2015) [525nm = 1,86 M−1 cm−1). Activity of CAT was measurement in the presence of 10mM H2O2 .The activities of the following extracellular oxidoreductases: horseradish-type peroxidase (HRP-like), manganese-dependent peroxidase (MnP), lignin peroxidase (LiP), versatile peroxidase (VP) Mn-dependent and Mn-independent activity, laccase (Lac), 2,3-dioxygenase , 2,3-dioxygenase  and superoxide dismutase (SOD) were evaluated using the microplate assay . The acta (2015) . ActivitB. adusta CCBAS 930, but without the addition of anthracyclines served as control in all enzymatic activity assays.Protein concentration was determined according to the Bradford method (1976)  using th740nm according to Singleton and Rossi (1965) [560nm) [The content of PhC was determined spectrophotometrically at Ai (1965)  with a si (1965) . SOR lev [560nm) . Untreat• radical scavenging assay according to Brand-Williams et al. (1995) [• solution in 96% ethanol. Following 30 min incubation at room temperature, sample absorbance was measured (A515nm) using 96% ethanol as a blank sample.Antioxidant activity was measured using the DPPH. (1995) . Each 10The pH of post-culture liquids was measured periodically using potentiometric methods.Lepidium sativum in comparison to controls (distilled water) in a reference soil.Phytotoxkit  was used to determine the direct effects of the untreated and treated DNR and DOX on ermination index (GI) and root growth inhibition (RGI) of seeds of ®  toxicity assay was used to evaluate the inhibition of luminescence of V. fischeri marine bacteria for untreated medium supplemented with DNR and DOX (10 µg/mL) and post-culture liquids of B. adusta CCBAS 930 according to the manufacturer’s protocol.The MicrotoxB. adusta CCBAS 930. Briefly, overnight bacteria cultures were grown in fresh LB medium to an optical density (OD600nm) of 0.5–0.6, diluted 10-fold in double strength LB medium  and mixed (v/v) with the tested compounds, e.g., potential mutagens (or promutagens) and solvents. A negative control (distilled water) was always included in each assay. The bacteria were exposed to different initial concentrations of DOX and DNR and post-liquid cultures of B. adusta CCBAS 930 after anthracycline treatments and cultured for 1.5 h at 37 °C. β-galactosidase  and alkaline phosphatase (AP) were assayed in 96-well plates. Significant genotoxic activity was defined as an adjusted induction factor (CIF) equal or greater than 1.2.The genotoxicity assay was performed using SOS ChromoTest  according to the manufacturer’s protocol. Moreover, the S9 fraction (lyophilized rat liver) was used to estimate the promutagenic potential of tested compounds before and after treatment with 2. Cells were seeded in 96-well culture plates  at a density of 5 × 103 per well and initially cultured before the experiment for 24 h. Subsequently, the medium was changed to a fresh one with an equal amount of conditioned medium  which was always 10% of the total cell culture medium.The human skin fibroblasts cell line BJ (ATCC CRL-2522) was obtained from American Type Culture Collection . BJ cells were maintained in MEM medium without phenol red supplemented with 10% fetal bovine serum (FBS). Cells were maintained at 37 °C in a humidified atmosphere with 5% COThe resazurin reduction cell viability and metabolism assay was performed according to a previously described method . On the 2DCFDA in serum-free and phenol red-free medium for 45 min before conditioned medium treatment. After 24 and 48 h of incubation of the cells with increasing concentrations of compounds (5% CO2 at 37 °C), the culture medium was replaced with fresh medium to remove extracellular residual DCF and studied compounds to reduce the fluorescence background. Cells treated with 0.3% hydrogen peroxide (H2O2) were used as a positive control (result not shown). DCF fluorescence was measured using a microplate reader (FilterMax F5) at maximum excitation and emission spectra of 485 nm and 535 nm, respectively.The ROS measurement was performed according to a previously described method . To deteCaspase-3 activity was assessed according to previous described method Nicholson et al.  After 24Calcein AM staining was performed to measure intracellular esterase activity in neocortical cell cultures 24 and 48 h after treatment with Control 1, Control 2, DOX, DOX metabolite, DNR and DNR metabolite diluted in MEM medium containing 10% FBS using a fluorescence microscope  .Data are presented as means ± standard deviation (SD) of three  and six (cell cultures and cytotoxicity assays) independent experiments. Data were analyzed using one-way analysis of variance (ANOVA) followed by Tukey’s multiple comparison procedure and Principal Component Analysis (PCA)   using STB. adusta strain CCBAS 930 exhibited biotransformation activity towards anthracycline antibiotics such as DNR and DOX. This activity was mainly related to the production of extracellular HRP-like and VP peroxidases. Our study showed that DNR and DOX were toxic for Vibrio fischeri bacteria, L. sativum L. seeds and BJ skin fibroblasts cell line before biotransformation. Our study suggested a ROS-dependent cytotoxicity mechanism associated with caspase-3 activity. Biotransformation products, e.g., phenols can protect fibroblast cells by ROS during biological treatment of anthracyclines in B. adusta CCBAS 930 cultures. Moreover, phenols formed during anthracycline biotransformations showed antioxidant activity. It can be assumed that not only oxidoreductases, but also phenolic compounds formed during biotransformation of anthraquinone derivatives were responsible for the detoxification of these compounds. Based on these results, further studies require the characterization of the main VP peroxidase involved in anthracycline bioremoval. Since no phytotoxicity after AQA treatment with B. adusta CCBAS 930 was recorded, it is also planned to conduct a pilot study on the use of post-culture liquids for agricultural irrigation after anthracycline removal.In conclusion, it should be emphasized that the


The main objective of this research is to investigate the effect of water content in concrete on the velocities of ultrasonic waves (P- and S-waves) and mechanical properties (elastic modulus and compressive strength) of concrete. For this study, concrete specimens (100 mm × 200 mm cylinders) were fabricated with three different water-to-binder ratios . These cylinders were then submerged in water to be saturated in different degrees from 25% to 100% with an interval of 25% saturation. Another set of cylinders was also oven-dried to represent the dry condition. The dynamic properties of concrete were then assessed using a measurement of elastic wave accordance with ASTM C597-16 and using resonance tests following ASTM C215-19, before and after immersion in water. The static properties of saturated concrete were also assessed by the uniaxial compressive testing according to ASTM C39/C39M-20 and ASTM C469/C469M-14. It was observed that the saturation level of concrete affected the two ultrasonic wave velocities and the two static mechanical properties of concrete in various ways. The relationship between P-wave velocity and compressive strength of concrete was highly sensitive to saturation condition of concrete. In contrast, S-wave velocity of concrete was closely correlated with compressive strength of concrete, which was much less sensitive to water saturation level compared to P-wave velocity of concrete. Finally, it was noticed that water saturation condition only little affects the relationship between the dynamic and elastic moduli of elasticity of concrete studies in this study. Concrete, a heterogeneous and porous material, comprises several types of voids   that cancf, and elastic modulus of concrete, cE) [A significant part of the evaluation of the state of conservation and structural performance of these structures is the assessment of their actual mechanical properties  . These pMany nondestructive evaluation (NDE) methods are already being utilized for structural health monitoring of concrete infrastructures. Indeed, there are already books that discuss the use of NDE methods in evaluating different structures and materials ,5,6,7. Ocf) and UPV can be affected by various factors such as physical properties of the cement paste, type and size of aggregate, curing conditions, concrete age, and mixture proportions. Therefore, the correlation between cf and P-wave velocity must be calibrated for each specific concrete mixture proportion. Even if applied to the same concrete mixture, P-wave velocity of concrete could be affected by various parameters such as the confinement conditions, environmental effects and heterogeneity of concrete that are not easily considered in the relationship between UPV and cf. Moreover, it has been demonstrated by previous researchers that the increasing moisture content (or water saturation level) affects the static properties of concrete and P-wave velocity of concrete in different ways. Some researchers corroborated that the compressive strength decreases as the saturation level increases [Previous researchers have established empirical relationships that relate the UPV parameters and static mechanical properties of concrete. Until now, P-wave velocity measurements have been predominantly utilized to evaluate UPV of concrete in the laboratory and the field practice. However, it is, at times, not easy to correctly evaluate mechanical properties from P-wave velocity measurements because of theoretical and practical difficulties ,18. For ncreases ,21,22,23ncreases ,23,24 obncreases ,26 have ncreases  observedncreases  found ouncreases  studies cf and cE) with less sensitivity to other material and environmental effects. Voigt et al. [In contrast, theoretically, shear wave propagation in porous material is not sensitive to water content in pore systems or in confinement conditions of concrete but, until recently, there was a scarcity of available equipment for measurement of shear waves. Regardless of this, there have been experimental results demonstrating that S-wave velocity shows good correlation to mechanical properties of concrete  and two mechanical properties of concrete (compressive strength and elastic modulus of concrete). Consequently, the study would relate the dynamic and static mechanical properties, particularly to the compressive strength and the static modulus of elasticity of concrete with various saturation levels. Specifically, this research will propose a relationship between S-wave velocity and compressive strength.In general, the methodology for this study followed the flowchart shown in A series of cylindrical specimens, with 200 mm height and 100 mm diameter, was manufactured for the experiment. In this study, the concrete is composed of crushed granite with a maximum size of 25 mm, crushed sand, Type I Portland cement, and additional cementitious materials (slag cement and fly ash). There were different water-to-binder ratios (W/B) of 0.52, 0.35, and 0.26, used in this study, resulting in three different design compressive strengths of 24, 40, and 70 MPa, respectively. The concrete mixtures  were manufactured with ready-mixed concrete and the quantities are tabulated in The standard concrete cylinder specimens were subjected to different levels of saturation and moisture content. The saturation curve was initially generated to reach a specific level of saturation. There were five target saturation levels for this study—two standard saturation levels of oven-dry (OD) and saturated-surface dry (SSD), and three other degrees of saturation . The control factors for this procedure were the mix proportion and the immersion time in water. For this method, three specimens from each design mix were used with a total of nine cylindrical specimens. After the specimens were cured under water for at least 150 days, they were put inside the electronic oven for at least 72 h to dry with constant temperature of 105 °C. The mass of the specimens was recorded thirty minutes after they were taken out from the oven. Then, they were placed in small tanks in groups and tap water was added slowly to ensure that the specimens were still submerged in water after the initial absorption of water by the concrete. The mass of the specimens was recorded every 30 min for the first ten hours. The specimens were taken out from the tanks and then excess water was wiped using a wet cloth. After mass was recorded, the cylinders were put back into the water for continuous immersion. After which, mass was recorded every 24 h until the tenth day of immersion time. The total immersion time of the specimens was 240 h. The degree of saturation was calculated using Equation (1).ed state .The saturation curve initially developed from this procedure, shown in In this section, the variables for the experiment were the degree of saturation and the design mix proportions. The materials and experimental groups were similar with those used in the development of water saturation curve explained in the previous section. There were a total of fifteen experimental groups set up for this measurement. Five specimens from each design mix, for each saturation level, were used for testing giving a total of 75 specimens. Moreover, the frequencies of the transducers used for this study were 40 kHz and 50 kHz, which gave a wavelength less than the length of the cylinders used for the experiment.The P-wave velocity (constrained compressive velocity) of concrete cylinders with five different saturation levels was evaluated using the standard test method following ASTM C 597-16 . The stupV is the velocity of wave propagation, d is the distance between transducers, at is the time of first wave arrival, and dt is the delay time, calculated during calibration of the probes. Delay time was determined when time for the first arrival wave was registered when the two transducers were positioned against each other. From the measured ultrasonic signals, the arrival of transient stress waves through cylinders was calculated using the modified threshold process [ process . In this process . Then, aS,UPV, was measured using the P-wave velocity method depicted in the previous section but using a pair of S-wave transducers (40 kHz) . The S-wave transducer had a diameter of 84 mm and a length of 114 mm and a weight of 340 g, which is portable and can be operated by a single person. It has an eight dry point shear wave sensor array, which does not require extra coupling agent (such as a viscous and sticky coupling gel), which minimizes the effect of coupling conditions between concrete surface and the transducer. The dry contact feature of shear wave sensors significantly ensured reliable and consistent data acquisition and significantly improved the test speed. Typical impulse signals produced by a source transducer and an ultrasonic wave measured by a receiving transducer for the S-wave velocity measurement is shown in The S-wave velocity of concrete, VTrf and longitudinal Lf modes [A free–free resonant (FFR) frequency test was used in this study to measure the wave velocities through a concrete cylinder specimen. The FFR test set up for this study following ASTM C215-19  is shownfL modes .Trf and Lf are the required resonance frequencies for transverse and longitudinal modes, respectively, determined by the resonance test; L is the length of the cylindrical specimen , as follows [EK is a correction factor to address the scattering effect of stress waves in a 200 mm × 100 mm concrete specimen  as follows [imen see  and KG i follows :(5)KG= 0 follows :(6)KE= −0L) to determine axial strain from the evaluated deformations. The load and deformation data measured by the load cell and the extensometers were digitized by a data acquisition equipment  with a sampling frequency of 100 Hz. The compressive strength and elastic modulus of the cylindrical specimens were determined using a universal testing machine , with a capacity of 2000 kN, after the measurement of stress wave velocities. The specimens were at the age of around 226–263 days at the time of testing. The compressive strengths and elastic moduli were measured under displacement control in accordance with ASTM C39/C39M-20  and ASTMThe concrete modulus of elasticity is characterized as the chord modulus from the stress–strain curve and is determined using Equation (9), which is called the static modulus of elasticity of concrete in this study.CV), two shear wave velocities from the UPV test  and resonance frequency test , and constrained compressive wave velocity (PV)) from the submerged concrete as the water saturation increases from 0% (OD condition) to 100% (SSD condition) with intervals of 25%. Equations (2)–(4) were used to calculate PV, CV, and S,RFV, respectively, while S,UPVV was measured using the same concept of Equation (2) using the time domain signal of shear wave measurement from the UPV test. Overall, the unconstrained wave velocity (CV) and the constrained compressive wave velocity (PV) increase as the water saturation of concrete increased. All mixes of concrete cylinders exhibited a gradual increase of PV as the water saturation level increased from 25% to 75% with MIX 1 increasing by about 5.2%, MIX 2 by 7.7% and MIX 3 by around 10%. Then an abrupt increase in wave velocity was observed from a saturation level of 75% until approximate full saturation by about 16.3% and 12.5% for MIX 1 and MIX 2, respectively. MIX 3 continued to exhibit a gradual increase of about 11.5% at approximate fully saturated state. For CV, all mixes generally exhibited a gradual increase in velocity as the level of saturation became higher with an average increase of about 3–5.7% of the velocity when fully dried. In contrast, the values of the shear wave velocities from both the UPV and resonance tests were almost constant as the concrete cylinders become more saturated. MIX 2 and MIX 3 showed a decrease  in shear wave velocity  as the cylinders became fully saturated while MIX 1 demonstrated a very slight increase of about 1.3%. In the case of VS, MIX 2 and 3 showed an increase in the values by around 1.8% and 2.8%, respectively, while MIX 1 showed a decrease in value by about 1.5%.PV and CV) as well. The effect of saturated water in concrete can be explained by Biot’s theory . The proγ is the ratio of the P-wave and S-wave velocities from the UPV test. When the concrete cylinders are completely dried, the dynamic Poisson’s ratios are in the range of 0.25–0.35 across all mixes. These values are higher than the typical reported values of Poisson’s ratio. One of the possible reasons is the difficulty in picking up the accurate time for the arrival of the first wave, especially for shear wave velocities. Higher values of dynamic Poisson’s ratio in this study may be attributed to the lower values of measured shear wave velocity according to the criteria of determining the first arrival of S-wave velocity in this study. When the saturation level increased from the oven-dry conditions (0% saturation) to the SSD conditions (100% saturation), the dynamic Poisson’s ratio increased by 32.36%, 22.02%, and 31.56% for the MIX 1, 2, and 3, respectively. The values of the dynamic Poisson’s ratio were used to evaluate the dynamic elastic modulus of concrete in the next section. The measured wave velocities of concrete give estimated values of the dynamic Poisson’s ratios. The variation of the dynamic Poisson’s ratios of concrete with respect to the saturation condition of the concrete is illustrated in Lf) as follows,D is a constant reliant on the specimen’s dimensions and Poisson’s ratio of concrete specimens ; M is the mass of the specimen in kg; L is the length of the specimen in m; and d is the diameter of the specimen in m. In this study, d,LRE value from a concrete cylinder is presented as an open circle and the average of d,LRE values obtained from concrete cylinders for the same concrete mixture proportion and saturation condition are presented as dash lines. The resonance modulus slightly increased as the saturation level also increased. At the full saturation level (100%), the increase in the dynamic elastic modulus was about 7.1%–12.3%, with the highest increase in MIX 1, followed by MIX 2 then MIX 3. From 0 to 25%, the increase was very minimal for MIX 2 with the rate of 0.4% while for MIX 1 and 3, the rates were 8.3% and 7.2%, respectively. The values of the dynamic elastic modulus from 25% to 75% were fluctuating although their coefficients of variation were within the reasonable values ranging from 1.6% to 3.5% for Mix 1, 1.1% to 3.0% for MIX 2, and 0.5% to 2.1% for Mix 3. Note that another resonance modulus based on the measured transverse resonance frequency (TRf)  were dependent on the value of the Poisson’s ratio. As discussed in d,PE. However, as can be observed from the graph, there is only a minimal effect of the Poisson’s ratio to the said parameter. Meanwhile, dynamic modulus d,LRE also showed the same behavior when the saturation level increased. From this assessment, it can be inferred that Poisson’s ratio does not greatly affect the values of the dynamic elastic moduli. Therefore, it can be deduced from this observation that the saturation condition greatly affects the values of the dynamic Poisson’s ratio and consequently, the dynamic elastic modulus but not as much as with the Poisson’s ratio.For comparison, two additional dynamic elastic moduli were calculated using Equations (12) and (13) using the values of P- and S-wave velocities measured by ultrasonic pulse velocity measurements, which are called the velocity moduli.a and b are the best-fit constants according to regression analysis performed in the curve fitting toolbox in MATLAB using the nonlinear least squares method. The curve fitting analysis was done separately for each saturation condition across all mixes. The parameters of the best-fit curves for the experimental data of this study are summarized in It was observed that the relationship between dynamic and static elastic moduli of concrete was affected by water saturation levels in concrete. For example, at the completely dry state, the static modulus of concrete was about 83% of the dynamic modulus for MIX 1, 87% for MIX 2, and 94% for MIX 3. At the fully saturated condition, the difference between the static and dynamic elastic moduli increased. At 100% saturation, static elastic modulus was about 75% of the dynamic elastic modulus for MIX 1, 80% for MIX 2, and 84% for MIX 3. As determined by the experimental aspects of this study, the equation relating the static and dynamic elastic moduli of concrete saturated with water was attained by non-linear regression using the power function relationship:3. The equation proposed by Popovics [3. In general, comparing the two previous equations, the equation proposed by Lydon and Balendran [Popovics  recommenPopovics  takes inalendran  agrees bcf) and P-wave velocity (PV) of concrete cylinders made with the three different mixture proportions  at the five different water saturation conditions . Consistent with the observation from Popovics [cf and PV was highly sensitive to the saturation condition of concrete. Consequently, there are many relationships that can be formed between cf and PV. For the fixed saturation level of concrete, the concrete made with lower water-to-binder (W/B) resulted in higher values in both cf and pV. For comparison, the best-fit curves relating the cf and pV of concrete at the saturation levels of 0, 25, 50, 75, and 100% are shown as dashed lines with black, blue, green, orange, and red dashed lines, respectively. In contrast, for the fixed concrete mixture, the water saturation level of concrete affected pV and cf in different ways: as increasing water saturation level, PV increased while cf decreased. The best-fit curves relating the cf and pV of concrete with MIX 1, 2, and 3 with various saturation levels from 0% to 100% in intervals of 25% are shown as solid lines with blue, black, and red lines, respectively, in Popovics , the relS,UPVV) measured from the UPV test and the compressive strength (cf) of water saturated concrete. Overall, S,UPVV increased as cf increases from MIX 1 to MIX 3. For comparison, the best-fit curves relating the cf and S,UPVV of concrete at the saturation levels of 0, 25, 50, 75, and 100% are shown as dashed lines with black, blue, green, orange, and red dashed lines, respectively, in S,UPVV and cf had a minimal change as the concrete becomes saturated and this observation is true for all mixes. As stated in the study of Lee et al. [cf and S,UPVV was determined by the nonlinear exponential function as follows,In contrast, e et al. , in theoa = 0.1445, b = 0.0027 with the least R-square equal to 0.867. The RMSE between the predicted compressive strength based on the recommended equation and the measured compressive strength from the experiment was 9.3 MPa. The value of RMSE was about 40%, 25%, and 15% of the design compressive strength of concrete MIX 1, 2, and 3, respectively. The considerable level of RMSE in this study could be attributed to several experimental uncertainties associated with compressive strength of concrete  and (16)) from previous studies and the proposed equation from this research (The compressive strength of concrete from all mix proportions decreased as the saturation level increased. Among the three concrete mix proportions, MIX 3 established the highest reduction in compressive strength, followed by MIX 2 and then MIX 1. In this study, it could be interpreted that the lowest water-to-cement ratio would be more sensitive to the increased water saturation. However, it is suggested that further investigation on the effect of water saturation should be done involving the porosity and different material constituents of concrete materials.The relationship between the stress wave velocities and the compressive strength was also investigated. The compressive strength decreased as the P-wave velocities increased. This observation was true for all the mix proportions used in this study. P-wave was greatly affected by the amount of water present in the concrete and other factors as shown in this study. Thus, estimation of compressive strength using P-wave velocity was not considered a proper method. In contrast, shear wave velocity was closely correlated with compressive strength of concrete, which was much less sensitive to water saturation level compared to compressive velocity.This study was based on the laboratory investigations and might not fully represent the environmental factors affecting concrete in the field. This study only focused on water saturation. Saturation with different liquid may affect the behavior of concrete when the saturation level increases. Hence, it is also suggested that further investigations using other fluid that may affect concrete be investigated, such as chloride, among others.This experiment was conducted to investigate the effect of the water saturation to the dynamic and static mechanical properties of concrete. Three different mix proportions of concrete were investigated with five different degrees of saturation from completely dry to approximate fully saturated conditions. The nondestructive test methods used in the investigation of the dynamic properties of concrete were the ultrasonic pulse velocity test and the resonance test. Detailed below are the conclusions attained in this study:


The behavior of fiber-reinforced polymer (FRP) bars under compression is not fully understood yet due to the limited research in this area. However, the long-term durability, weathering resistance, and exceptional mechanical properties of FRP bars justify the need for their use in compression members. The main objectives of this study are to evaluate the mechanical properties of glass FRP (GFRP) and basalt FRP (BFRP) bars under compression and examine their performances as main longitudinal reinforcements in reinforced concrete (RC) columns. In the first part of this research, a series of static compression tests were conducted on GFRP and BFRP bars of different diameters. The second part of this research numerically investigated the behavior of FRP-RC columns under concentric and eccentric loading using the mechanical properties of the FRP bars obtained experimentally. Nonlinear finite element models were developed to simulate the compressive behavior of the concrete columns reinforced with GFRP and BFRP bars. The FE models were verified with the experimental results conducted previously. The verified FE models are then utilized to conduct a parametric analysis considering two different column geometries and cross-sections, five reinforcement ratios, two concrete compressive strengths, three types of ties materials, and several loading eccentricities to develop a set of interaction diagrams that may provide valuable data for design purposes. The results indicated that the FRP bars could have a significant contribution to the overall capacity of FRP-RC columns by up to 35% of the total force at failure, depending on the reinforcement ratio. The performance of both the GFRP- and BFRP-RC columns was almost similar in terms of capacity, deflection, and bar strength contribution.  In recent years, fiber-reinforced polymer (FRP) bars have been used to reinforce concrete members in tension, while their contribution in compression has been neglected due to insufficient research. The main advantages of FRP bars in comparison with steel are their very light density, larger strength, and most importantly that they do not corrode even in harsh environments. The mechanical and physical properties of FRPs are controlled by their micro-structural configuration and the properties of their constituents. FRP composites are ideal for structural applications where high strength-to-weight and stiffness-to-weight ratios are required . HoweverMany studies had also been conducted to evaluate the durability ,5,6,7,8,For the research that investigated the behavior of FRP bars under compression, different setups have been made, with varying ways of measurement, methods of fixing the ends, as well as strain rates ,25,26,27Although international codes have recently started to permit the use of FRP bars in compression members, the lack of research in this area results in an incomplete understanding of the FRP bars’ behavior under compression. Therefore, the first objective of this paper was to provide experimental data on the compressive performance of different sizes of GFRP and BFRP bars. The experimental results were then utilized to numerically investigate the axial performance of concrete columns reinforced with these types and sizes of FRP bars (FRP-RC columns). Nonlinear finite element models were developed to simulate the axial performance of the FRP-RC columns and were validated using experimental tests conducted previously by the authors. The validated models were then used to perform a parametric analysis, considering several column geometries and cross-sections, reinforcement ratios, ties materials, concrete strengths, and loading eccentricities. The FE results were presented and discussed in terms of load vs. displacement curves, interaction diagrams, and ductility indices.In this section, the compressive properties of the GFRP and BFRP bars are experimentally investigated. Commercially produced Φ 8, Φ 12, and Φ 16 GFRP and BFRP bars were selected for this study, as shown in The GFRP and BFRP bars were produced by Galen, a Russian company based in the city of Cheboksary. These GFRP and BFRP bars were manufactured by pultrusion, in which the fibers  are impregnated with a polymer binder, and then run through the system drain bushing.The tensile properties of these bars listed in Several compression test setups were examined, and the test arrangement shown in It was difficult to obtain a perfectly flat end perpendicular to the loading axis with the equipment available. Restraining the ends of the specimens with a recess is illustrated in the test apparatus shown in The FRP bars were tested using a universal testing machine (UTM) with a capacity of 3000 kN under compression, as shown in The compression tests were conducted at a rate of 0.25–0.5 MPa/s. The length of each FRP bar specimen was two times the diameter. Slightly oversized holes in the ends of the testing apparatus allowed some rotation at the ends of the specimens, thereby reducing the moments applied by the apparatus while still providing some end restraint, as shown in Five bar specimens of each size were tested, and the average compressive strength and their standard deviations were reported, as shown in In general, the variation in the compressive strength results between the five specimens were reasonable for all sizes. However, and unlike their tensile strengths, the compressive strengths of both the GFRP and BFRP reported lower values at smaller sizes. In particular, the compressive of the 8 mm GFRP and BFRP bars were reduced by 45% and 12% as compared to 16 mm GFRP and BFRP bars, respectively. On the other hand, the compressive strengths of the BFRP bars were in the range of 35–41% of their tensile strengths. For the case of the GFRP bars, the compressive strengths of the 8, 12, and 16 mm bars were about 32, 51, and 64% of their tensile strengths.One distinct failure mode was observed during the tests. The failure mode was a crushing failure in which the glass and basalt fibers separated from the resin matrix, as shown in In this section, the axial behavior of the rectangular concrete columns reinforced with GFRP and BFRP bars is numerically investigated. Nonlinear finite element (FE) models were developed to predict the axial behavior of the reinforced concrete (RC) columns under concentric and eccentric loading. Different parameters, such as the longitudinal reinforcement ratios, different cross sections, and transverse reinforcement material for the RC columns, were considered. The compressive and tensile properties of the GFRP and BFRP bars investigated in the previous section  were utiThis section presents the development and verification of the FE models for concrete columns reinforced with GFRP bars (GFRP-RC columns) and BFRP bars (GFRP-RC columns). The commercial software package ABAQUS was used to create the nonlinear finite element models in which the axial behavior of the GFRP- and BFRP-RC columns were accurately simulated. The FE model verification was also performed using a set of experimental tests conducted previously by ElMesalami  on similThe material used in the FE models included GFRP, BRFP, steel, and concrete. The concrete material was defined in the elastic zone through the elastic modulus and Poisson’s ratio while the inelastic behavior is defined using the concrete damage plasticity (CDP) model. Utilizing the CDP approach allows defining both the compressive and tensile properties of the concrete material in the FE analysis. −5. The GFRP and BRFP materials are defined using the elastic modulus and ultimate compressive and tensile strengths listed in The plasticity parameters for the CDP model contains the dilation angle of 36, eccentricity of 0.1, an fb0/fc0 ratio of 1.16, parameter K of 0.667, and viscosity parameter of 1.0 × 102 and designed such that they were surrounded by a 27.5 mm concrete cover. The concrete column was modeled as a homogenous three-dimensional solid section using eight-node linear brick elements with reduced integration whereas the longitudinal and transverse reinforcements were modeled using deformable truss elements, which only carries axial load during bending. The transverse reinforcements were defined with cross-sectional areas of 78.5 mmTo simulate the interaction between the reinforcement and the concrete, the ABAQUS built-in constraint “embedment” was used. This constraint restricts the nodes of the reinforcement to the corresponding degrees of freedom of the host domain. As shown in Moreover, normal and tangential surface-to-surface contact defined the interaction between the rigid plates and concrete surfaces using the penalty contact approach. Boundary conditions and displacement were assigned on the plates through reference points defined on the center of each rigid plate.A mesh sensitivity analysis was also conducted to select the appropriate mesh size that provide results accuracy with less computational cost. The model with a mesh size of 20 mm was considered throughout the analysis. The G16-0 model by ElMessalami  was chosThe experimental program conducted by ElMessalami  was partThe column labels represent the reinforcement type and quantity, where the first letter refers to the longitudinal reinforcement type . The first number after the letter refers to the diameter of the longitudinal reinforcement (16 or 20 mm) and the second number refers to the eccentricity value . The comparisons of the load vs. displacement curves a and theA parametric study was conducted to further investigate the response of the GFRP and BFRP bars in RC columns by considering different reinforcement ratios, column shapes and dimensions, concrete compressive strengths, and stirrups types. The effect of changing these parameters on the overall behavior of the RC columns is also presented and discussed. Two different column geometries with rectangular and circular cross-sections were investigated, as shown in The columns in the FE parametric study were divided into ten groups. Each group consisted of a total of 45 short RC columns, including a total of nine load eccentricities with five reinforcement ratios of 1%, 2%, 4%, 6%, and 8% for each load eccentricity, as listed in Each column was labeled with a unique ID in each group. The first letter indicates the column cross-section type ; the second letter refers to the type of reinforcement ; the number after the second letter provides information about the width/diameter of the cross sectional area; the following letter denotes the tie material , followed by the eccentricity in mm; and, finally, the last number provides information about the concrete compressive strength used. As an example, S-G180-S80-40 indicates a square column of 180 mm width, reinforced with GFRP bars and steel ties, has a concrete compressive strength of 40 MPa, and loaded at 80 mm eccentricity.The main objective of considering the 10 groups listed in The results clearly illustrate the transition in the stiffness of the columns as well as ultimate compressive loads over the different eccentricities considered. After obtaining the load vs. displacement results for all groups, interaction diagrams were developed for the five different reinforcement ratios, as shown in The overall response and shape of these interaction diagrams were similar to the graphs presented in the ACI 318  for steecc) was calculated for each column as the difference between the peak load and force carried by the bars, divided by the confined concrete area (Ac) delineated by the centerline of the ties ((Pmax−Pbar)/Ac). Values of the confined concrete strength factor (f’cc) for concentrically loaded columns are shown in The axial load vs. displacement results were also utilized to study the contribution of the GFRP and BFRP bars to the total compressive strength of the concentric FRP-RC columns in all groups. The confined concrete strength factor and ductility indices for the concentric FRP-RC columns were also calculated and compared. The confined concrete strength factor (f’δu) to the yield axial displacement (δy), given by DI = δu/δy. In this method, the yield displacement is estimated to be the axial displacement corresponding to the yield load or to the limit of the linear behavior. The ultimate displacement is assumed to be the axial displacement at 85% of the peak load in the post-peak descending portion of the load vs. displacement curve. The ductility index (DI) for the column is then calculated as the ratio of the displacements obtained for all columns, as shown in Ductility is a desired property in structural design as it protects structures against unpredicted overloading and/or load reversals. It is therefore essential that RC columns possess adequate ductility. A method was developed by Pessiki and Peironi  in whichconcrete), calculated as the difference between the ultimate load (Pmax) and the load carried by the bars (Pbar), are shown in Additionally, values of the force carried by the concrete  models to simulate the axial behavior of concrete columns reinforced with these types of FRP bars. The FE model was initially validated with experimental results on FRP-RC columns and then used to conduct an extended parametric analysis to investigate the overall response of the FRP-RC columns. The parametric analysis included different column geometries and cross-sections, different reinforcement ratios, different ties materials, different concrete strengths, and different loading eccentricities. The main conclusions of this study are summarized below:


A low water-to-binder ratio, i.e., from 0.24, was obtained through application of a polycarboxylate-based superplasticizer. The introduction of up to 10 kg/m3 of basalt fibers to RPC mix was proved to be possible, while keeping the same w/c ratio equal to 0.24, with a slight loss of workability of the concrete mix as the content of fibers increased. It was found that the increase of the fiber content in RPC to 10 kg/m3, despite the w/c ratio was kept the same, caused reduction of the concrete compressive strength by 18.2%, 7.8% and 13.6%, after 2, 7, and 28 days respectively. Whereas, the flexural strength of RPC increased gradually (maximum by 15.9%), along with the fiber quantity increase up to 6 kg/m3, and then it reduced (maximum by 17.7%), as the fiber content in the concrete was further increased. The reduction of RPC compressive strength, along with the increase in basalt fibers content, leads to the increase of the total porosity, as well as the change in pore volume distribution. The reduction of RPC abrasion resistance was demonstrated along with the increase of basalt fibers content, which was explained by the compressive strength reduction of that concrete. A linear relation between the RPC abrasion resistance and the compressive strength involves a high determination coefficient equal to 0.97.The paper presents the test results of basalt fiber impact on a compressive and flexural strength, resistance to abrasion and porosity of Reactive Powder Concrete (RPC). The reasons for testing were interesting mechanical properties of basalt fibers, the significant tensile strength and flexural strength, and in particular the resistance to high temperatures, as well as a relatively small number of RPC tests performed with those fibers and different opinions regarding the impact of those fibers on concrete strength. The composition of the concrete mix was optimized to obtain the highest packing density of particles in the composite, based on the optimum particle size distribution curve acc. to Funk. Admixture of basalt fibers was used in quantity 2, 3, 6, 8 and 10 kg/m Whereas a larger quantity of steel fibers, in amount from 1.5 to 3.0%, assures achievement of the relatively high flexural and tensile strength of this concrete. Steel fibers play an important role in shaping of mechanical properties of this material , dMax—maximum particle diameter [μm], dMin—minimum particle diameter [μm], n—constant value equal to 0.37.Optimization of the concrete mix composition that assured the maximum packing density of particles, was performed based on Funk and Dinger’s curve  Figure  followinFor that purpose, also other computational models are used ,23.3, at the same w/c ratio amounting to 0.24.Composition of RPC mixes is given in The particle size distribution of the concrete was determined by means of the particle size laser analyzer Mastersizer 3000 within the range 0.01–3500 μm.X-ray diffraction (XRD) tests were conducted by means of Philips X’PertSystem diffractometer . The measurement was conducted within a range from 5° to 60° 2θ. CuKα radiation was used.Tests of RPC consistence were performed in line with PN-EN 1015-3 standard (Methods of test for mortar for masonry. Part 3: Determination of consistence of fresh mortar (by flow table)) . ConsistThe tests of compressive strength and flexural strength of RPC specimens were performed in line with PN-EN 1015-11 standard  . Tests wc—section area of specimen [mm2].The compressive strength was calculated according to the following formula:R—specimen density [g/mm3].Resistance to abrasion of RPC specimens was tested in accordance with PN-EN 1338 standard (Concrete paving blocks. Requirements and test methods) . MeasureInfrared Spectra (IR) of basalt fiber specimen in the form of potassium bromide pellets (5 mg/500 mg KBr) recorded on Thermo Nicolet spectrophotometer , Nexus model.The microstructure of RPC was tested by scanning electron microscopy (SEM). Analyses were performed by means of the scanning microscope NOVA NANO SEM 200 . Observations were conducted with magnification from 200 to 10,000. Specimens for testing were prepared by spraying a layer of gold on the surface in high vacuum conditions. Energy Dispersive X-Ray Spectra (EDS) were obtained for selected points.Testing of RPC porosity were performed with the use of a mercury porosimeter PoreMaster 60 , within a pressure range from 1 to 400 MPa. The results of the tests were presented in a form of differential curves and volumetric distribution curves of pores with different size.Identification tests of basalt fibers were conducted by means of XRD test, infrared spectroscopy and scanning electron microscopy.An XRD pattern of basalt fibers specimen is presented in 2 and CH3.IR spectroscopy tests were performed to identify the organic substance. The IR spectra of basalt fibers is presented in 2 and CH3 groups in the spectrum: 2953 cm−1—STR/ASCH3, 2925 cm−1—STR/ASCH2, 2869 cm−1—STR/SCH3, 2855 cm−1—STR/SCH2. These bands are well visible in 3, CH2 groups (1457 cm−1) and scissor vibration of CH3 groups (1377 cm−1). The results of the above testing indicate that the surface of basalt fibers contains a hydrocarbon modifier. It is also supported by results of the SEM testing. EDS spectra made in two different points: 1 . Unfortunately, based on the presence of this band, it cannot be stated definitively whether the silicone oil is the modifier, as basalt fibers also contain Si–O–Si groups. The authors of the paper [The IR spectra shows an intensive, broad band belonging to siloxane groups Si–O–Si STR/AS 16 cm−1. Results of RPC mix consistence tests after 15 min with a flow table test method , are pre3 to 10 kg/m3 in RPC mix, while keeping the same w/c = 0.24, causes reduction of the flow diameter from 240 mm to 180 mm, which indicates a drop in concrete mix flowability. It results from a commonly known fact of a larger water demand of concrete mixes with the addition of fibers, in order to obtain the required workability.As data in The results of compressive strength tests of Reactive Powder Concretes are shown in 3 to 10 kg/m3, while keeping the same w/c ratio, causes a reduction in the compressive strength, which is the higher in value, the higher the fiber content is. The lowest compressive strength values were obtained by concrete with the highest content of fibers (10 kg/m3). The elimination of w/c coefficient influence the compressive strength of RPCs with different amounts of basalt fibers, which indicates that the main factor determining the strength is the amount of fibers. Increasing the amount of fibers in the concrete mix makes their dispersion difficult, which in consequence, does not allow a homogeneous microstructure of the material to be obtained. This can cause an increase in porosity, resulting in a decrease in the compressive strength of the concrete.Based on data given in 3 to 6 kg/m3, increases the RPC flexural strength. Whereas, when the quantity of fibers was higher (8 kg/m3 and 10 kg/m3), a reduction of the concrete flexural strength was observed, but the difference in RPC strength with 8 kg/m3 and 10 kg/m3 content is small  is comparable after 2, 7 and 28 days of curing of specimens. Whereas, the distribution of pore volume is different. RPC with basalt fibers contains definitely more pores with a larger diameter above 20,000 nm, but fewer smaller pores with the diameter from 200 nm to 2000 nm compared to the concrete without fibers, while keeping almost the same total porosity in both concretes. After 2 days of curing, the concrete with fibers showed nearly five times higher amount of pores with diameter above 20,000 nm and about five times lower amount of pores within the range 20–200 nm, compared to the content of those pores in the concrete without fibers. In the later period (7 and 28 days) those differences were smaller. In addition, a reduction in total porosity in time (from 2 to 28 days) can be clearly seen.As shown in 3 and 10 kg/m3, causes a definite growth of RPC total porosity, even by over 10 vol.% along with the increase of the fibers content, but similar to the lower fiber content, the total porosity is reduced over time. A reduction in pore content < 20 nm can be observed, as well as a definite higher amount  of pores within a range 20–200 nm, compared to the content of these pores in the specimen with 2 kg/m3 of basalt fibers. After 7 days, the quantity of these pores is four or even five times higher for RPC specimens with fiber content 6 kg/m3 and 10 kg/m3, respectively. Whereas after 28 days, a visible growth of pores < 20 nm is observed with simultaneous reduction of pores within 20–200 nm. The content of pores > 20,000 nm is generally lower than 10 vol.% for RPC with basalt fiber content 6 kg/m3 and 10 kg/m3 in the time tested, after 2, 7 and 28 days.The addition of basalt fibers to RPC in quantity of 6 kg/mIn general, the content of pores within the ranges 200–2000 nm and 2000–20,000 nm, both in RPC without fibers, as well as with the various content of basalt fibers, is relatively small. In the first case it generally does not exceed 3.0 vol.% and in the second one 2.0 vol.%.3 in RPC, as found in this paper, may contribute to the reduced compressive strength of RPC with the higher fibers content.The change in pore volume distribution in RPC, along with an increase in the basalt fibers content, most probably results from the impediment of fiber dispersion in the concrete mix with a very low w/c ratio, and may have the impact on the concrete strength. Cement pastes compressive strength reduction is related to the growth of pore volume with diameters larger than 20 nm ,29. The Furthermore, the growth of RPC total porosity found along with the increase of basalt fibers content, while keeping the constant water-cement ratio, is one of significant factors having an impact on the reduction of the concrete compressive strength. An increase in porosity, along with the increase in basalt fibers in the concrete, as well as the effect of that phenomenon on its strength, was observed by the authors of the paper . Whereas3 of basalt fibers are presented in Results of abrasion tests of RPC without fibers and containing 2, 6 and 10 kg/m3, which showed the highest compressive strength. Whereas, as the content of basalt fibers in RPC grows, the resistance to abrasion is reduced, which is associated with reduction of the compressive strength of this concrete. No linear relation was found between the abrasion resistance of RPC with basalt fibers and the flexural strength  for abrasion dependence on the compressive strength (2 = 0.13) for abrasion dependence on the flexural strength . A reduction of RPC compressive strength is caused by the presence of a larger quantity of pores along with the increase of the fiber content in this concrete. Whereas, the clear reduction of the total porosity of specimens over time (from 2 to 28 days), due to the increase of cement hydration products formed, weakens the impact of fiber quantity on reduction of RPC compressive strength.While keeping the same w/c ratio equal to 0.24, the compressive strength of RPC containing basalt fibers reduces along with the increase of the fiber content in the concrete. The highest drop of the compressive strength from 15.5% to 18.2% with the fiber content increase from 2 kg/m3 causes a slight gradual growth in the flexural strength (maximum by 15.9%). Whereas, with the higher content of fibers (8 and 10 kg/m3), reduction of the flexural strength occurs (maximum by 17.7%), but the differences in flexural strength of RPC specimen with the content 8 kg/m3 and 10 kg/m3 are minimal and they are from 0.1 MPa to 0.4 MPa. The increase of the flexural strength along with the increase of the fiber content up to 6 kg/m3 goes up over time and after 2, 7 and 28 days it amounts to: 4.4%, 15.9%, and 12.3%, respectively. The higher content of basalt fibers in the RPC mix at the lower w/c ratio used (0.24), deteriorates their dispersion, which in consequence, may cause a reduction of the flexural strength.Introduction of basalt fibers to RPC in quantity up to 6 kg/m2 for this relationship is 0.97. Whereas, there was no significant relationship between the resistance to abrasion and the flexural strength (R2 = 0.13). The compressive strength is generally recognized as the most important factor that affects the concrete resistance to abrasion. The results abrasion resistance tests of RPC with basalt fibers also confirmed this relationship.The reduced resistance to abrasion resistance of RPC along with the increase of basalt fibers content is caused by the reduction of the concrete compressive strength. A strong relationship was found between the RPC resistance to abrasion and its compressive strength. The determination coefficient R3, the content of larger pores > 20,000 nm grows, and the content of 20–200 nm pores goes down. Whereas at the higher content of fibers (6 kg/m3 and 10 kg/m3), reduction of pores below 20 nm occurs, as well as the increase of pores within a range 200–2000 nm, but the content of pores above 20,000 nm goes down. The above changes in the total quantity of pores and their distribution correspond well with the reduction of RPC compressive strength, as the content of basalt fibers in that concrete increases.The introduction of basalt fibers to RPC causes the increase of the total porosity, as well as the change in distribution of pores as the content of basalt fibers grows. At the fiber content of 2 kg/m


The main objectives of this study are to investigate the variations of the dielectric constant of concrete on Korean expressways by using a 1 GHz air-coupled Ground Penetrating Radar (GPR) system and to develop a practical approach to the condition assessment of concrete bridge decks with asphalt overlay on Korean expressways by dielectric constant measurements. A total of 684 GPR investigations of 601 actual concrete bridge decks, which are in service between 2 and 43 years, were carried out during the period between 1999 and 2013. Statistical analysis revealed that the dielectric constant of asphalt-covered concrete bridge decks reduced with service age and this trend continued until service age of over 40 years. As a result, this study provides a practical dielectric constant curve that could be used for condition evaluation of top concrete in asphalt-covered bridge decks with consideration of concrete age. Based on regression analyses of the GPR field survey data and experiences through the field survey, a double cut-off dielectric constant criterion was proposed for condition assessment of asphalt-covered concrete bridge decks on Korean expressways. In addition, a GPR field survey was performed at an actual bridge on the Yeongdong expressway in Korea to test the proposed GPR signal interpretation method. The field survey results provide fundamental data to better understand the variation of the dielectric constant of concrete in actual bridges with asphalt overlay and to develop a practical approach to condition assessment of asphalt-covered concrete bridge decks on Korean expressways by dielectric constant measurements using air-coupled GPR.  Expressway bridges are essential elements to connect road segments on various terrain conditions and to constitute the expressway as a single network. It has been reported that the physical life of a bridge could extend to over 100 years when cared with by a systematic maintenance and management program . In Korea, the service life of a concrete structure was first defined in 2004 [Infrastructure management agencies in many countries have used Ground Penetrating Radar (GPR) as a tool for evaluating concrete bridge decks because of its capability of visualizing the sub-surface condition of asphalt-overlaid concrete bridge decks and rapid operation at a traffic speed. American Society for Testing and Materials (ASTM) first established the standard test method for condition assessment of bridge decks using GPR in 1997 . SeveralIn Korea, the evaluation of concrete bridge decks with asphalts overlay is mainly based on the relative permittivity (or dielectric constant) of the top concrete of bridge decks ,14. GoodThere have been many previous studies investigating the effects of influencing factors on the variation of relative permittivity of concrete. Zhang et al.  found ouThe primary objectives of this study are to investigate the variations of relative permittivity of concrete under asphalt-covered concrete bridge decks on Korean expressways by using a 1 GHz air-coupled Ground Penetrating Radar (GPR) and, based on statistical analyses of long-term GPR field survey data, to develop a practical GPR signal interpretation method for reliable condition assessment of actual concrete bridge decks with asphalt overlay on Korea expressways. For these purposes, this study carried out the following four main tasks: (1) investigation on influencing factors of concrete relative permittivity, using GPR equipment, for asphalt-covered bridge decks in Korean expressways that are in service from 1999 to 2013, (2) establishment of a practical formula describing the age-related variations of concrete relative permittivity, (3) proposal of a practical GPR signal interpretation method for condition assessment of asphalt covered concrete bridge decks based on the practical relative permittivity formula and double cut-off relative permittivity criterion and (4) test of the practical GPR signal interpretation method by applying to an actual bridge on the Yeongdong expressway in Korea. The results of this research would provide fundamental data to better understand the variation of relative permittivity of concrete in actual bridges on Korean expressways and to develop a practical GPR signal interpretation method for more reliable condition assessment of concrete bridge decks with asphalt overlay.The electromagnetic properties of a material can be generally expressed in terms of complex permittivity and complex permeability. Concrete is a dielectric and nonmetallic material, and most dielectric materials are nonmagnetic. Since permeability of a nonmagnetic material is almost the same as the permeability in a vacuum  indicates the capability of a dielectric material to accumulate energy from outside the electric field. It has a value greater than one in most cases of solid or liquid state. Moreover, the imaginary part (or loss factor) indicates the energy loss of a dielectric material against outside the electric field and generally has a value much smaller than the dielectric constant. For relatively dry and low conductivity materials, this will be much less than one, and the loss factor can then be ignored. In this study, the relative permittivity of concrete is simply referred to as the real part of the relative complex permittivity (or dielectric constant) εVm in a material can be calculated by dividing the EM wave velocity in air Cair about 300 mm/ns by the square root of relative permittivity value as follows [The propagation velocity of an electromagnetic (EM) wave  follows : (3)Vm=Cd in a material is calculated from the following equationT is the two-way travel time (TWTT) of an EM wave in a material. Therefore, a reliable dielectric constant value of a material is necessary to accurately assess the condition of the targets embedded in the media. Subsequently, the depth of a reflector ectively . Note thA total of 684 GPR surveys were performed from a total of 601 bridges on Korean expressways from 1999 to 2013. This study includes bridges with a wide range of ages from 2 years–43 years at the time of survey. All the bridges had concrete decks with asphalts overlay. The GPR survey should be conducted at least 24 h after the precipitations,The investigation should not be conducted on sunrise or sunset when the relative humidity and moisture on the road change rapidly, andReference GPR signals from a steel plate for GPR signal calibration should be collected immediately before or after GPR surveying.The GPR survey system used was Sir Series of Geophysical Survey Systems Inc. (GSSI) and it used 4-channel 1 GHz air-coupled antennas. The 4-channel antennas were installed at the back of a vehicle that had the distance measuring instrument (DMI) on one of the rear wheels. The GPR system was operated on each traffic lane, including the road shoulder, at the speed of 80–100 km/h for collecting the GPR survey data . The surFurthermore, the survey was only conducted after confirming that the air-dried surface of an asphalt concrete layer had no standing water on the pavement surface and had no considerable debris that would affect the GPR radar signal interpretations. The GPR signals were acquired with the sampling rate to 12–14 scans/m  in the longitudinal direction. A typical GPR B-scan image obtained on asphalt-covered concrete decks in one of the survey bridges in this study is shown in ® [p-values of all the bridge decks were greater than 0.05, which indicates the validity of the normality assumption. In this study, the means of concrete dielectric constant were assumed to represent those of concrete decks with asphalt overlay in Korean expressways.The received signals were stored for the determination of the concrete dielectric constant and location (depth). In this study, a commercially available software, RADAN® , was useThis study used atmospheric relative humidity in order to indirectly investigate the seasonal variation of concrete dielectric constant in asphalt covered concrete bridge decks during the GPR survey. Korea Meteorological Administration (KMA) offers the atmospheric relative humidity data through its website . The atmt-test  showed that the dielectric constant of concrete is related to each parameter  was established by using linear regression to investigate the influence of each variable, as follows,Equation (7) indicates that the relative humidity of air  has only little influence on the dielectric constant of concrete with asphalt overlay. The change of atmospheric relative humidity of 10% results in the change of dielectric constant of top concrete inside the pavement of about 0.11. The ratio of change is only 12% of the case of the bare concrete bridge decks in Korean expressways . Furtherp-value < 0.001), which means that the relationship in Equation (8) is considered statistically significant at the confidence level greater than 99%. Standard errors of the coefficient of p-value < 0.001) and 0.296 , respectively. Therefore, it can be said that the coefficient of p-value = 0.003 at the significance level of 0.05  and the group with RH greater than 70% (Group R4).In addition, the influence of relative humidity on the relationship between concrete age (service performance period of the bridge) and dielectric constant of concrete was investigated. The research survey bridges were classified into four groups according to relative humidity: RH ≤30% (Group R1), 30% < RH ≤ 50% (Group R2), 50% < RH ≤ 70% (Group R3), 70% < RH (Group R4). 0.05 see . In addiThe best-fit curve for the relationship between the dielectric constant and age of concrete for the relative humidity less than or equal to 70% was found from nonlinear regression analysesp-value < 0.001), which means that the relationship in Equation (9) is considered statistically significant at the confidence level greater than 99%. Standard errors of the coefficient of p-value < 0.001) and 0.332 , respectively. Therefore, the coefficient of RH and the intercept in Equation (9) are statistically significant at the confidence level greater than 99%. F-statistics of the nonlinear regression model is 63.349  and (9) result in very similar dielectric constant values, with a mean absolute error of 0.05. However, Group R4 (relative humidity greater than 70%) shows a slightly greater dielectric constant for the same ages compared to the other three groups with an approximate equation,p-value < 0.001), which means that the relationship in Equation (10) is considered statistically significant at the confidence level greater than 99%. Standard errors of the coefficient of p-value< 0.001) and 0.90 , respectively. These statistical analysis results indicate that the coefficient of F-statistic of the nonlinear regression model is 28.225 , for the relative humidity less than or equal to 70%, is proposed to be a practical curve describing the age-related variation of the dielectric constant of concrete bridge decks with asphalt overlay on Korean Expressways for the 1 GHz air-coupled GPR system. A calibration factor is proposed to suppress the effect of relative humidity on the dielectric constant of concrete as follows,t(α/2),n−21− is the t-distributed variate at the probability of (1 − α/2) with (n − 2) degree-of-freedom; n is the number of samples (in this study n = 573); and i is the measured value and Based on the field experiences and the data analyses in this study, a dual cut-off dielectric constant criterion is proposed to determine the severity of concrete deterioration in concrete bridge decks with asphalt overlay. Note that the upper and lower bounds were suggested as criteria to evaluate the deteriorated concrete in the relatively wet and dry conditions, respectively. The concrete can be interpreted as nearly sound (not significantly deteriorated) with a confidence level of (1 − α) when the relative permittivity of concrete in bridge deck is within the upper and the lower boundaries as follows ,(12)εr,The target ‘J’ bridge is a steel box girder bridge constructed in 1999 with an extension of 600 m, a width of 12.15 m, and offers three traffic lanes including the road shoulder . The cony = 0.4, 0.9, 1.4, 1.9, 2.4, 2.9, 3.4, 3.9 m: whereas for section B, GPR antennas were located at y = 5.4, 5.9, 6.4, 6.9, 7.3, 7.8, 8.3, 8.8, 9.3, 9.8, 10.3, 10.8 m . A traffic lane was blocked during the survey time for a more accurate survey. To avoid traffic interruption, the bridge was divided into two sections . The atmospheric relative humidity measured at this time was 51%, which was below the critical relative humidity value of 70%, requiring no calibration. In addition, the lower limit and upper limit of dielectric constant value based on Equation (12) and x,y),x,y). Note that the x coordinate was read from the GPR B-scan image  [The average and standard deviation of measured dielectric constant of concrete were 9.6 and 2.4, respectively. The dielectric constant of concrete in the GPR field survey was calculated by Equations (5) and (6). The measured average was a little greater than that of the predicted value, 8.7. According to the field experiences from KEC, this discrepancy is attributed to water penetration into concrete of bridge decks from the rain before the survey date through the damaged area of pavement and deteriorated part of waterproofing . Figure mage see  and the Surfer®) .  efflorescence,  map cracking,  patching, in the same figure. The part of bridge decks where efflorescence was observed (marked with ‘’) exhibited high dielectric constant values. It is expected that continuous water penetration and deterioration of the inside is developing there. One interesting finding is that some damaged (or solid) regions determined from concrete dielectric constant were interpreted as solid (or damaged) regions by visual inspection on the surface. For example, the deteriorated areas according to the dielectric constant are mostly located near the median barrier and shoulder, where no obvious deterioration is observed by visual inspection on the surface. In contrast, the dielectric constant values in most of the traffic lanes are between the cut-off values, while there are many surface-breaking cracks in the traffic lanes.In Core samples were extracted from four locations near the shoulder and the median barrier to examine the actual condition of concrete decks under asphalt overlay see . Two cor2 and 13%, respectively. The dual cut-off criterion resulted in 1038 m2 (51 m2 + 987 m2) and 15%, respectively. Consequently, these results demonstrated two important conclusions in this study: (1) the practical GPR interpretation method based on concrete dielectric constant is effective for evaluating the condition of concrete under asphalt overlay, which could not be directly estimated by visual inspection on the surface and (2) the double cut-off criteria for dielectric constant could further improve the capability of the practical GPR interpretation method in asphalt-covered concrete bridge decks in the relatively dry conditions, which could be not effectively estimated by the conventional single cut-off dielectric constant criterion. In addition, the actual conditions of larger areas of concrete bridge decks under asphalt overlay were examined by visual inspection after removing the asphalt overlay and the deteriorated parts of concrete using high pressure water jetting. (1)The influence of atmospheric relative humidity  on asphalt-covered concrete bridge decks of 2–43 years of service performance was investigated. As relative humidity changed to 10%, the dielectric constant of concrete changed to about 0.11. This is about 12% of the bare concrete bridge deck, indicating that the influence of relative humidity (air) is blocked by asphalt overlay and a waterproof layer on the concrete bridge deck.(2)Dielectric constant of concrete was found to be influenced by the service age of the bridges in most expressway routes based on the observed values of the dielectric constant of concrete in the bridges with 2–43 years of service. This pattern was similar to the bare concrete bridge decks. This study proposed a practical curve describing the variation of the dielectric constant of the top concrete of bridge decks with asphalts overlay in consideration of service life with a confidence level of 85%. Based on the proposed model and field survey experiences on Korean expressways, a double cut-off dielectric constant criterion was newly proposed for condition assessment of asphalt-covered concrete bridge decks on Korean expressways. (3)A case study of GPR application at an actual bridge on the Yeongdong expressway in Korea demonstrated that the proposed GPR signal interpretation method, based on the double cut-off dielectric constant criterion, is useful for better interpretation of concrete dielectrics and beneficial for reliable condition assessment of asphalt-covered concrete bridge decks in Korean expressways. However, the validation was obtained from only a single target bridge in Korea. Therefore, more studies are still needed to verify the validity of the practical curve and the methodology described in this study by systematic comparison researches using the data from other bridges in the field. This study carried out GPR tests of asphalt-covered bridge decks currently in service to investigate the age-related variations of the dielectric constant of concrete in asphalt-covered bridges on Korean expressways. As a result, a standard curve of the dielectric constant of top concrete of asphalt-covered bridge decks with mid-to long-term service age was established. The following conclusions are derived in this study.