Active additives used in the binder were found to reduce portlandite leaching from concrete exposed to flowing water to significantly increase the resistance of concrete to freezing and thawing cycles and to increase sound absorption, compressive strength and infiltration rate. In addition, industrial waste (FCCCw and PSw) used as active additives significantly reduced the use of clinker in concrete applied in the construction of water pervious systems. The coarse aggregate size distribution had the greatest effect on the density, ultrasound pulse velocity (UPV), porosity, compressive strength and infiltration rate of pervious concrete.Pervious concrete (PCO) has many advantages and applications, such as water pooling reduction, noise attenuation, replenishment of groundwater reserves, etc. However, the use of pervious concrete is limited due to its low compressive strength and durability, especially as a result of portlandite leaching from concrete exposed to flowing water. The effects of active additives (nano SiO Pervious concrete (PCO) is most often used in locations with limited traffic and load: pedestrian areas, bicycle routes, car parks, zoo paving, bridge embankments, solar energy storage systems, tide water control, etc. ,2. The a3). According to [3. A positive correlation was found between water permeability and the ratio of the total pore volume and specific surface area. Passing through the pores with a higher ratio of total pore volume to specific surface area, the water experiences less friction against the pore walls, and permeability is improved. Irrespective of the aggregate particle size, there will always be a significant number of small pores (< 2 mm2) in pervious concrete. The correlation of small pore size with small pore volume will be negative. Pervious concrete mixture is stiff; slump is 10–50 mm [2 [2 has a big particle surface area and high pozzolanic activity, and thus speeds up the reaction with calcium hydroxide, increases the resulting amount of calcium hydrosilicates (CSH) [PCO is coarse-grained concrete usually consisting of coarse aggregates, binder, water and chemical admixtures . Fine agrding to , the porrding to ,26,27. Trding to  found thrding to ,30 also rding to . The paprding to  describe10–50 mm ,34,35 ha10–50 mm . Various50 mm [2 ,38,39,4050 mm [2 , pelleti50 mm [2 , various50 mm [2 ,34,41, a50 mm [2 . Nano Sies (CSH) ,45, and es (CSH) ,47,48. Hes (CSH) ,43.Some results reported in research articles on pervious concrete are shown in The results in 3, and compressive strength between 13.4 and 17.5 MPa at 28 days. With the increase in W/C ratio, the compressive strength decreased, and the binder settled at the bottom of the specimens, thus preventing the flow of water. The authors of [The binder content in concrete mix is also important for the compressive strength and structure of pervious concrete. An excessive amount of the binder can fill voids and reduce porosity, while an insufficient amount of the binder will reduce the binder coating around the aggregate particles and reduce the compressive strength of the mix. The optimum content of cement-based materials depends on aggregate particle size and distribution ,55. Testthors of  determinThe compaction technique and parameters  is another important factor that has had an effect on the properties of pervious concrete. According to , the aimDurability of concrete is one of the most important issues in the design of new structures and assessment of the state of existing structures ,64,65. A2, spent catalyst generated at the fluid catalytic cracking unit (FCCCw), and paper sludge waste burned at 700 °C (PSw)) and the particle size distribution of the coarse aggregate on the properties and durability of pervious concrete.The aim of this research work is to analyse the complex effect of active additives (nano SiO2 (NS) in the form of white powder ; paper industry waste generated at AB Grigeo, Lithuania (PSw).The following materials were used for the tests: cement CEM I 42.5 R manufactured by Heidelberg Cement ; spent catalyst generated at the fluid catalytic cracking unit of oil refinery (FCCCw) ; nano SiOoC are presented in 3S, 16.7% of C2S, 9.0% of C3A, 10.6% of C4AF, and 7.1% of other materials. Physical and mechanical properties of the cement used: density 3.1 g/cm3, initial setting time 180 min., compressive strength at 28 days 55 MPa.Chemical compositions of cement, FCCCw, and PSw fired at 700 3). FCCCw particles are almost spherical with a rough surface. 3), which vary in size, have irregular form and tend to agglomerate.50 is 10.3, 43.1, and 9.1 µm, respectively; particle size d90 is 22.9, 62.5, and 36.0 µm, respectively. The average diameter of cement, FCCCw and PSw particles is 11.7, 40.0, and 14.5 µm, respectively.X-ray diffraction (XRD) patterns of FCCCw and PSw are presented in FCCCw was selected for the composition of pervious concrete for its pozzolanic properties . PSw was2/g; SiO2 purity 99.8%; pH (20% solution) 4.0; density 2.2 g/cm3. Physical–mechanical properties of the coarse aggregate (gravel) are presented in The properties of NS were as follows: size 10–30 nm; surface area 202 m3. The binder content in pervious concrete is quite small, as it is only needed for the adherence of the coarse aggregate. The first two compositions (PCO-C and PCO-1) were used to find out how the application of a combined binder change the properties and durability of pervious concrete. Other compositions were used to evaluate the effect of particle size distribution of the coarse aggregate on the properties of pervious concrete with active additives. The slump of all mixtures was less than 1 cm.Melamine-based superplasticiser (SP) in powder form, pH 9.4 (20% solution) was used. Tap water was used to prepare the specimens. Seven pervious concrete mixes  were mad3 were used to measure sound absorption properties and 100 × 100 × 100 mm3 sizes specimens were used to measure other properties analysed in this paper.Two types of specimens were formed from the mixture compositions given in At first, the binder was mixed with water in a Hobart-type mixer. The binder containing only cement was mixed according to the standard procedure (EN 196-1). When FCCCw and PSw are added to the binder, the additions are first mixed with cement for 90 s and then the mixture is mixed with water according to the standard procedure (EN 196-1). NS was homogenised with one part of water using an ultrasonic disperser and then mixed with the remaining water. The coarse aggregate was added to the binder mixed with water and mixed for 180 s. The mixture was placed into moulds and pressed by placing a 15 kg weight on top of each moulding form. The specimens were cured in metal moulds at 20 °C in 95% humidity for two days. Afterwards, the demoulded specimens were cured in water of 20 °C for 26 days.The density of the specimens in solid state (3 specimens from each batch) was calculated from the specimen’s weight (0.01 g precision) and volume calculated from the specimen’s dimensions (0.01 mm precision). Measurements were taken after 7 and 28 days of curing. Ultrasonic pulse velocity  was calculated according to the literature .The compressive strength of pervious concrete was determined according to EN 12390-3:2003.Water infiltration rate was determined according to reference . The obtThe porosity of pervious concrete was calculated according to two methods: (1) assessment of the density of the material in solid state and in natural state ; (2) calculation of pores in the cross-section of the specimen by means of Cool PHP Tools software.With the aim to determine the effect of active additives on the dissolution of portlandite, cut and polished pieces of the specimens were tested by exposing them to cyclic water flow of 8 h for 15 days, 120 h in total (10 l of circulating water were used). XRD analysis of the specimens and SEM and EDS analyses of the cut and polished pieces were performed before and after the test. Water was also analysed for calcium content, pH and electric conductivity before and after the test. pH Electrode (InLab 410) with the accuracy of 0.01 was used in combination with the conductivity probe with the range of 0.01‒1000 µS/cm (InLab 730) for pH and electrical conductivity measurements, respectively. The measurements were taken at 20 ± 1 °C temperature.The microstructure of the samples was analysed on the scanning electron microscope (SEM) JSM-7600F . The analysis was performed at accelerating voltage 4 or 10 kV, the mode of secondary electrons was used in image formation. Before the investigation, the surface to be investigated was covered with a layer of electrical conductor using a sputtering device QUORUM Q150R ES . X-ray microanalysis was performed by the energy dispersion spectrometer (EDS) Inca Energy 350 , using Silicon Drift type detector X-Max20. The INCA software package (Oxford Instruments) was used.X-ray diffraction (XRD) analysis of the phase composition of materials was performed according to the method described in literature .Freeze–thaw resistance was tested according to LST 1428-17 by measuring the diminishing strength and loss of mass after freezing and thawing cycles. The compressive strength may not decrease more than 5%, and the loss of mass may not exceed 3%.The single-digit value of the sound absorption factor was determined according to EN ISO 10534-1 in the third octave bands. On the basis of these values measured according to ISO 10534-1, a single value of sound absorption was determined according to EN 1793 . The sou3) and UPV (~4180 m/s) values of pervious concrete at 28 days were obtained when equal parts of all gravel fractions were used (3) was obtained in compositions PCO-3 and PCO-4, where the coarse aggregate of either 4/8 or 8/16 was used. Density difference at 7 and 28 days was not significant because a low amount of the binder was used, and the difference was caused by the distribution of the coarse aggregate in the specimen.The highest density  was observed in composition PCO-4 where the aggregates of the biggest fraction 8/16 were used, and the biggest voids formed among the coarsest particles. Active additives, although used in a small amount, also influenced the porosity. The lowest porosity values were obtained in specimens PCO-C where pure cement was used. The comparison of PCO-C and PCO-1 porosity images revealed a thicker coating of the aggregates by a binder film.The results of water permeability measurement  showed tThe results of physical and mechanical properties of water-permeable concrete show that the size of coarse aggregate particles has the greatest effect on density, UPV, porosity, water permeability and compressive strength, leading to the formation of the porous concrete structure. Active additives have a slight positive effect on the strength and water permeability of concrete. However, further tests showed that active additives play an important role in the durability analysis of pervious concrete.Portlandite dissolution under a long-term exposure to a stream of water is one of the problematic issues in pervious concrete applications. SEM and EDS analyses were performed to evaluate the dissolution of portlandite before and after the exposure of the specimen to water flow .1 and S3 in PCO-C specimens showed that after the exposure to water flow, Ca content decreased 37%, the colour of the area S3 had changed compared to the area S1 prior to the washing, and the layer of cementitious matrix in this area reduced. These results suggest that some portlandite leached out and CASH from a deeper layer was seen in area S3. EDS analysis of areas S2 and S4 in PCO-1 specimens showed that Ca content decreased 17% and the appearance of the area remained the same. These results suggest that less portlandite leached out compared to specimen PCO-C. The active additives used not only reduced the amount of portlandite in the cement matrix, as found in reference sources, but also created a protective layer of calcite, which buffered the negative effect of water flow.EDS analysis of areas SThe results of the XRD analysis (intensities of the main peaks) presented in The results of freeze–thaw resistance tests of the selected characteristic compositions after 50 freeze–thaw cycles in water are given in Sound absorption values at given frequencies for pervious concrete of selected compositions are presented in There was no apparent relationship between the detected values, only that the sound absorption value for the composition PCO-1 was slightly higher than 2.3 dB. The other values were around 2.1 dB . The comA combined binder incorporating NS, FCCCw and PSw used in pervious concrete increased the compressive strength by 6%, while the density and UPV remained the same. The particle size distribution of the aggregate used in the mix of pervious concrete, which also significantly changed the porosity of concrete, had the greatest effect on the physical and mechanical properties of pervious concrete. The highest porosity of pervious concrete (28.4%) was obtained when the coarse aggregate of fraction 8/16 only was used. The mix also produced the highest water permeability of 16000 cm/h, but lower compressive strength of 12 MPa. The use of three fractions  of the aggregate in equal parts increased the compressive strength to 15 MPa and reduced the water permeability to 8500 cm/h with a porosity of 22.7%.After exposure to the flow of water, lower intensities of portlandite, alite and belite were identified in the mineral composition of pervious concrete specimen PCO-C, where only cement was used as a binder, whereas the intensities in the specimen with active additives  remained similar. Water pH after cyclic washing of PCO-C increased by 7.7%, the electric conductivity increased by a factor of 2.2 and the CaO content of the water increased by a factor of 11. In PCO-1 specimens with active additives, the pH of the circulating water increased by 6.4%, the electric conductivity increased by a factor of 1.6, and the CaO content increased by a factor of 8.The assessment of the durability of pervious concrete in terms of freeze–thaw resistance showed that, irrespective of the coarse aggregate particle size distribution, the compressive strength of the specimens with active additives reduced by 4.7%, and actually withstood 50 freeze–thaw cycles. Meanwhile, the compressive strength of PCO-C specimens reduced by 31% after 50 freeze–thaw cycles (6.6 times more compared to the specimen with active additives).The comparison of the results obtained for PCO-C and PCO-1 specimens showed that active additives increased the sound absorption by approx. 10%. The results suggest that, at a similar coarse aggregate particle size distribution, the binder with active additives has a thinner layer and sound propagation is inhibited in the pores.2 was used to keep the cost of permeable concrete low. The low amount of nanosilica was sufficient to obtain the desired effect.Given that a major part of active additives used come from industrial waste (FCCCw) that does not require any additional treatment and that PSw is recycled industrial waste, the use of such materials contributes to the development of circular economy and the reduction of landfill waste. The cement content was reduced by 12.5%, and only 0.02% of SiO


Solid waste silica fume was used to replace fly ash by different ratios to study the early-age hydration reaction and strength formation mechanism of concrete. The change pattern of moisture content in different phases and micro morphological characteristics of concrete at early age were analyzed by low field nuclear magnetic resonance (LF-NMR) and scanning electron microscope (SEM). The results showed that the compressive strength of concrete was enhanced optimally when the replacement ratio of solid waste silica fume was 50%. The results of LF-NMR analysis showed that the water content of modified concrete increased with the increase of solid waste silica fume content. The compressive strength of concrete grew faster within the curing age of 7 d, which means the hydration process of concrete was also faster. The micro morphological characteristics obtained by SEM revealed that the concrete was densest internally when 50% fly ash was replaced by the solid waste silica fume, which was better than the other contents. Silica fume is an ultrafine powder produced during the smelting of ferrosilicon alloy or industrial silicon, and its main component is amorphous silicon dioxide. In 2018, China produced 2 million tons of silica fume, and its utilization rate was less than 60% in that year . Large-sSince the 1990s, silica fume has been utilized in cement, concrete, refractory materials, chemicals, environmental protection and other fields. By studying the role of MgO in the thermal behavior of MgO-silica fume pastes, Li et al.  establisAs a highly effective pozzolanic material, silica fume is the most widely used pozzolan in the field of concrete making. As early as 1982, Norway used silica fume concrete for the construction of the Vonoves Dam . Adding 2 content of the solid waste silica fume used in this paper is 86.3%, while the active ingredient SiO2 content of common silica fume in the market is usually more than 90%. In terms of financial, the solid waste silica fume used in this paper has a lower cost. Predecessors have used a variety of methods to study the process of concrete hydration. However, those studies mainly focused on the hydration products, hydration exotherm, etc. [The physical properties and chemical composition of silica fume are similar to that of fly ash, while silica fume has higher pozzolanic activity than fly ash . The actrm, etc. ,23,24, arm, etc. . In thisIn this study, the cement used was Conch brand P·O 42.5 ordinary Portland cement produced by Liquan Conch Cement Plant in Xianyang City, Shaanxi Province, China, with its physical and mechanical properties as shown in The silica fume originated from the northern part of Shaanxi Province. The Grade I fly ash used was produced by Shaanxi Weihe Power Plant. Using the Bettersize 2600 laser particle size analyzer, the volume-based average particle size of silica fume and fly ash were measured as 12.35 μm and 12.71 μm, respectively. The particle size distribution is presented in 3 and a bulk density of 1480 kg/m3. Limestone with continuous grading between 5 mm and 20 mm was used as coarse aggregate, with an apparent density of 2835 kg/m3 and a bulk density of 1720 kg/m3.Natural river sand with a fineness modulus of 2.66 was used as fine aggregate, with an apparent density of 2630 kg/mThe superplasticizer applied was the Q8086 powder high performance water reducing agent produced by Shaanxi Qinfen Building Materials Co., Ltd.,  with a water reducing rate of 33%, air content of 2.0%, and solid content of 40%. The water reducer comprised 0.5% of the weight of the cementitious material.The water used was ordinary tap water from Xi’an, Shaanxi Province, China.In the experiment, five different composite cementitious material system concretes were prepared, while the external admixture method was used to keep the amount of cement unchanged. The control group without silica fume was designated as group A. In the other four groups, 25%, 50%, 75%, and 100% of fly ash were replaced with silica fume, which were numbered B, C, D, and E, respectively. The water–binder ratio was 0.48, and the mix proportions of concrete were as shown in (1) Prior to preparing the concrete specimens, the raw materials were weighed according to the pre-determined mixing ratios and placed in the test pan. At the same time, the superplasticizer was poured into the water to fully dissolve, the twin-shaft concrete mixer was cleaned, and the mortar with the same water-binder ratio was prepared. The remaining slurry was poured into the wall-hanging slurry in the mixer. Next, coarse aggregate, cement, silica fume, fly ash, and fine aggregate were added in sequence and stirred for 60 s. Finally, the water mixed with superplasticizer was evenly poured into the mixer and stirred for 120 s.(2) After unloading, the slump of fresh concrete was measured according to the Chinese standard “Standard for Test Methods for the Performance of Ordinary Concrete Mixtures” (GB/T50080-2016), and the HC-7L direct-reading concrete air content tester was employed to measure the air content of fresh concrete.(3) The remaining concrete mixture was put into a 100 mm × 100 mm × 100 mm cube mold, placed on a vibrating table for vibrating compaction, and vibrated until the surface continued to produce slurry. Each group of A, B, C, D, E made 28 specimens, totaling 140 specimens.(4) The concrete specimens were demolded 24 h after production, and 25 specimens of each mixing ratio group were naturally cured at a curing temperature of 20 ± 2 °C and relative humidity of 95%. The WAW-1000KN universal testing machine was used to test the compressive strength of concrete cubes with different amounts of substituted silica fume at curing ages of 1 d, 3 d, 7 d, 14 d, and 28 d.2T inversion software. Thus, a spectrum composed of the LF-NMR signal amplitude and relaxation time of different types of water in the concrete test block is obtained [(5) The remaining three specimens in each group of mix proportions were wrapped with a polyethylene film to prevent the entry and evaporation of water, as shown in obtained .In the hardening process of concrete, cement hydration consumes part of the physically bound water, thereby generating chemically bound water. Jehng measured the apparent transverse relaxation time of the chemically bound water in cement paste to be 12 μs . It is g2T spectrum includes three relaxation peaks, which are defined as peak 1, peak 2, and peak 3 from left to right, which correspond to the LF-NMR signals of hydrogen nuclei in adsorbed water, pore water, and free water, respectively [2T spectrum reflects the change in the contents of adsorbed water, pore water and free water in the filler slurry.The ectively . The chax is the total water content, V and A are the volume and signal of the sample, respectively.According to the volume and signal of the sample, a unit volume nuclear magnetic signal can be obtained, as shown in Equation (1). Then, the total water content of the tested sample can be obtained according to the calibration formula in Equation (2) .(1)y=AV(6) The JSM-7610F field emission scanning electron microscope produced by JEOL was utilized to test the surface micromorphology of 28-day-old concrete. Before the test, the sample was sprayed with gold and vacuumed for inspection by the scanning electron microscope imaging system.The working performance of fresh concrete for each mixing ratio is shown in T2 spectra of concrete fluids with different amounts of silica fume substitution at different ages. As seen in the figure, the total water content in the concrete shows a gradual rising trend with the increase of the replacement amount of silica fume. The area of peak 1 shows an increasing trend with more water is adsorbed, indicating that water in the concrete mainly exists in the adsorbed form. The area of peak 2 generally shows an increasing trend with a higher volume of pore water. The area of peak 3 presents a decreasing trend, indicating that the free water in the concrete decreases with the rise of silica fume replacement amount.The graph of different forms of water content and total water content in concrete with different amounts of silica fume replacement is presented in In order to better explore the relationship between the compressive strength of concrete cubes and the change of total water content over time, the least squares method was used for fitting. The correlation equations of the two parameters are as follows:t represents age in days; t; t; a, b, c, and d are constants, and their values are determined by experiment.In the relational equation, The coefficients of the fitting curve equation are shown in It can be seen from the fitting curve that, before 7 days of age, the compressive strength of concrete cubes in each mixture group has a trend of faster growth, while the total moisture content of concrete in each mixture group rapidly decreases. The hydration reaction is the process of converting physically bound water into chemically bound water in concrete . The actFor concrete materials, moisture is not only a guarantee for strength development, but also closely related to performance . In the 2; high-fineness amorphous SiO2 has high pozzolanic activity. The hydration reaction between cement and water yields the hydration product Ca(OH)2, as shown in 2 can quickly undergo a secondary hydration reaction with Ca(OH)2 under the alkaline excitation to form C-S-H gel . Compared with the control group A without silicon powder, the surface of group C is covered by a more irregularly structured C-S-H gel, and the resulting microstructure also denser , the compressive strength of concrete showed a slowed increasing trend. Although the compressive strength of such concrete cubes was higher than that of control group A cubes, it was lower than that of group C. While the D and E groups also contained C-S-H gels, the pores in the surface concrete still existed, and the C group was denser in comparison  at different ages were monitored by LF-NMR. The hydration products of concrete at age of 28 d were analyzed by using SEM. By studying the early-age hydration and strength formation mechanism of silica fume-like solid waste based composite cementitious concrete, the following main conclusions can be drawn:(1) As the amount of solid waste silica fume increased, the slump and expansion of the concrete mixture tended to decrease and its air content firstly decreased and then increased.(2) With the increase of age, the compressive strength of concrete at each replacement ratio of solid waste silica fume showed an increasing trend, which increased faster in the age of 7 d. Besides, the compressive strength of concrete showed an increasing-decreasing-increasing trend with the increase of the amount of solid waste silica fume at each age. The overall comparison showed that the compressive strength of concrete at all ages was enhanced best when the replacement ratio of solid waste silica fume was 50%.(3) With the increase of the amount of solid waste silica fume, the total water content in the concrete showed a general trend of gradual increase. Additionally, with the continuation of hydration reaction, the water content of concrete under each dosage of solid waste silica fume continuously decreased, which was consistent with the change trend of adsorbed water during the curing period. Moreover, the change of the total water content and adsorbed water of concrete under each dosage was more obvious in the age of 7 d, which was shown by the phenomenon that the compressive strength of concrete grew faster in this period.(4) Through the electron microscope analysis, it was found that the concrete was the densest and most effective in improving the internal pore structure when the content of solid waste silica fume was 50% compared to the other contents, and thus its compressive strength was the highest.2 content of solid waste silica fume used in this study is 86.3%. Most studies use high-purity silica fume. In financial terms, the silica fume used in this study has a lower cost, and the cube strength has been greatly improved. In addition, using solid waste silica fume instead of fly ash can greatly increase the early strength of concrete, which also plays an important role in the application of high early-strength concrete engineering.The active ingredient SiO


Streptococcus pneumoniae is limited by prior antibiotic exposure. Immunochromatographic test (ICT) is highly sensitive and specific for pneumococcal antigen detection in the cerebrospinal fluid (CSF) of meningitis cases. We determined the specificity and sensitivity of culture, ICT, and polymerase chain reaction (PCR) and the effect of antibiotic exposure on their performance.Sensitivity of culture for the detection of CSF specimens from suspected meningitis cases admitted to Dhaka Shishu Hospital, Bangladesh, were tested using culture, ICT and PCR. Additionally, 165 specimens collected from 69 pneumococcal cases after antibiotic treatment were tested.Of 1883 specimens tested, culture detected 9, quantitative PCR (qPCR) detected 184, and ICT detected 207 pneumococcal cases . In comparison to ICT, sensitivity of culture was 4.4% and of qPCR was 90.6%; both were 100% specific. After antibiotic exposure, culture sensitivity plummeted rapidly; conventional PCR and qPCR sensitivity disappeared after day 6 and 20, respectively. ICT detected pneumococcal antigen for >10 weeks.While culture provides the most information about bacterial characteristics, in high antibiotic exposure settings, ICT exhibits maximum sensitivity. We recommend culture and ICT as mainstay for pneumococcal diagnosis and surveillance; qPCR can generate additional molecular data where possible. Streptococcus pneumoniae (pneumococcus) is a leading cause of pneumonia, sepsis, and meningitis in children [children . In 2015children . Howeverchildren ; this isS. pneumoniae from blood or cerebrospinal fluid (CSF) samples [Accurate detection and adequate characterization of pneumococcus are key to pneumococcal disease surveillance, but are hampered by a multitude of factors, especially in resource-constrained settings. A large proportion of pneumococcal disease is pneumonia and as most pneumonia cases are nonbacteremic, microbiological diagnosis of pneumococcal cases is specifically difficult . Therefo samples , 8. In g samples , 8–10. T samples , 12 but Several previous studies have shown that sensitivity and specificity of ICT is >95% , 13. HowAll CSF samples used in this study were collected as part of the Invasive Bacterial Vaccine Preventable Disease surveillance study supported by the World Health Organization (WHO) conducted at the Dhaka Shishu Hospital (DSH) . DSH, thAll tests were performed in the DSH microbiology laboratory of the Child Health Research Foundation, which is a high-performing WHO sentinel site . The labcpsA gene of pneumococcus [S. pneumoniae (lytA gene), Haemophilus influenzae (hpd gene), and Neisseria meningitidis (sodC gene) using protocols described elsewhere [lytA gene).All CSF specimens were cultured on blood, chocolate, and MacConkey agar plates for bacterial growth. Pneumococcal antigen testing was performed on CSF specimens with ≥10 white blood cells (WBC)/μL using BinaxNow [mococcus ), irresplsewhere . In addiMicrococcus luteus (American Type Culture Collection 9341). A 10-μL CSF sample was pipetted directly on the disc before incubating the plate overnight at 37°C. Any zone of inhibition around the disc was considered positive for the presence of an antibiotic capable of crossing the blood-brain barrier.CSF samples with ≥10 WBC/μL were tested for the presence of antibiotic following a method described earlier [lytA gene obtained through qPCR. From the cases with known Ct value and exact antibiotic start date, a second-degree polynomial (quadratic) regression model was performed to quantify the relationship between the Ct value of the lytA gene (explanatory variable) and the days of antibiotic treatment (response variable). We found that there was a statistically significant relationship between the explanatory variables, Ct value, and 2, and the response variable, days of antibiotic treatment: F = 26.07, P < .0001, index of goodness of fit = 0.6589. Combined, these 2 explanatory variables accounted for 65.9% of the explained variability in days of antibiotic treatment. The regression equation was as follows: Data on prior antibiotic exposure and antibiotic treatment after hospitalization were recorded for each patient by study physicians. We attempted to collect the exact start date of antibiotic treatment for all pneumococcal-meningitis cases, and from whom longitudinal samples were collected during their hospital stay. Of the 69 pneumococcal cases that provided longitudinal samples, the exact date could be determined for 30 cases, while for the remaining 39 cases, the exact date could not be recalled by the caregivers. For CSF samples that were positive for the presence of an antibiotic (determined by the antibiotic assay described above) but for which the exact start date of antibiotic treatment was not available, we extrapolated the start date based on the cycle threshold (Ct) value of the lytA gene.The above fitted model was used to estimate the days between the start of antibiotic treatment and the first CSF sample that was positive for pneumococcus, using the Ct value of the Considering that (1) previous studies reported sensitivity of ICT to be 95%–100% and specificity to be 99%–100% for detection of pneumococcal meningitis ; (2) ICTAll specimens used in this study were collected from patients as part of routine care at the discretion of the treating physicians. Written consent was obtained from parents or caregivers of all participants for other aspects of the study, including data collection and the use of specimens and isolates for additional laboratory analysis. All protocols were approved by the Ethical Review Committee of the Bangladesh Institute of Child Health, Dhaka, Bangladesh.From January 2014 through June 2018, we processed CSF specimens from 4334 suspected meningitis cases, 1883 of which contained ≥10 WBC/μL . Median S. pneumoniae  were available in sufficient quantity for ICT. Bacterial growth was noted in 32 of the 1883 specimens, 9 of which were eumoniae . ICT detrecorded . Of the In total, 1761 CSF specimens were tested by culture, ICT, and qPCR simultaneously . CultureAmong the 207 cases of pneumococcal meningitis and 68 nonpneumococcal cases, ICT for pneumococcus was negative for all 68 nonpneumococcal cases detected by culture or qPCR, and qPCR for pneumococcus was negative for the 45 nonpneumococcal cases detected by qPCR, indicating 100% specificity of both ICT and qPCR as pneumococcal diagnostics .Among the 207 pneumococcal meningitis cases, longitudinal samples  were available for 69 cases, collected up to 74 days after initiation of antibiotic treatment . For 49 lytA gene from the qPCR (see methods). Sensitivity of detection of pneumococcal cases by the different diagnostic tests after antibiotic exposure is illustrated in The exact date of the start of antimicrobial treatment was known for 30 children; for the remaining 39 children, antibiotic exposure was confirmed by testing for presence of antibiotic in the CSF (see “Methods”), and the treatment start date was estimated based on the Ct value of Only 1 of 165 samples was collected 1 day prior to initiation of antibiotic treatment, and 5 were collected on the day of initiation. Bacteriological culture yielded growth of pneumococcus in 5 of these 6 samples. None of the remaining 159 samples, all of which were collected after antibiotic exposure, were culture positive.All samples collected within 2 days of antibiotic exposure were positive by cPCR (n = 30). By day 3 of antibiotic treatment, cPCR sensitivity decreased to 95% , and by day 6 to 73% . All 102 CSF samples collected after day 6 of treatment were negative by cPCR. All samples were positive by qPCR up to 8 days after antibiotic initiation (n = 75). Sensitivity of qPCR decreased to 87%  by day 12, and to 69%  by day 20. All 19 samples collected after 20 days of treatment were negative.All 165 samples were ICT positive for pneumococcal antigen, including the specimens collected beyond 20 days and up to 74 days.Use of antibiotics prior to seeking care is widespread in many low- and middle-income countries, making it difficult to detect pathogenic bacteria by traditional bacteriological culture , 18. PreIn this study, we conducted a head-to-head comparison of contemporary diagnostics: culture, cPCR, qPCR, and ICT after antibiotic exposure. We compared the sensitivity and specificity of culture, ICT, and qPCR in detection of pneumococcus, using CSF specimens collected from 4334 suspected meningitis cases and elucidated the effect of prior antibiotic exposure on the sensitivity of detection of each method using 165 longitudinal CSF specimens collected from 69 patients during their hospital stay. We did not include the commercial latex agglutination kit as it is expensive, has been shown to lack sensitivity, and has a short shelf life , 19.Bacteriological culture of 1883 meningitis cases with ≥10 WBC/μL yielded growth of pneumococcus in 9 samples. Antibiotic assay of 1674 of these CSF specimens showed that 70% of the cases had antibiotic exposure either prior to seeking care at the hospital or before the lumbar puncture was performed. qPCR detected 184 cases and did not miss any of the culture-positive cases. Use of rapid ICT for pneumococcal antigen yielded 207 cases of pneumococcus and captured all qPCR- and culture-positive cases. Overall, sensitivity of culture in detecting pneumococcus was 4.43%  and that of qPCR was 90.64%  when compared to ICT, respectively. None of the methods yielded any false-negative results when compared to each other, illustrating 100% specificity of all methods.Poor yield from CSF culture within 24 hours of prior antibiotic exposure may be explained by high susceptibility to penicillin and cephalosporins of circulating pneumococcal strains in Bangladesh; over 90% of all pneumococcal isolates are estimated to be susceptible to penicillin and 100% to cephalosporins, which is the most commonly consumed over-the-counter antibiotic in Bangladesh , 20–22. In addition to assessing the overall performance of the diagnostics, this study also illustrated the change in sensitivity with time following antibiotic exposure. This is especially important in settings like Bangladesh, where patients pay for care out of their pockets and sick people often do not come to receive treatment in facilities unless the symptoms are severe. Sometimes, patients come only several days or weeks after manifestation of symptoms , 25. LonThe findings of this study should be considered within the context of some limitations. First, the exact antibiotic and dose received by the child was not known in many cases due to limitations in caregiver recall. Different antibiotics are likely to have different effects on the sensitivity of the diagnostics with time. Second, the time gap between each lumbar puncture varied between patients as this was completely dependent on the treating physicians, and only performed when deemed absolutely necessary. However, the large number of longitudinal specimens (n = 165) from 69 confirmed pneumococcal-meningitis patients collected over a span of 74 days of antibiotic exposure aided in assessment of changes in sensitivity of the diagnostics with time.H. influenzae type b, N. meningitidis, and group B streptococci, need to be additionally tested using latex agglutination test or PCRs. Hence ICT may be cost prohibitive in some settings. However, as noted above, latex agglutination tests have low sensitivity in comparison to other methods [lytA Ct value <35 [Each of the diagnostics examined have their own limitations, and often we may need more than one diagnostic for a comprehensive clinical and epidemiological assessment. Pneumococcal culture can provide data about serotype, antimicrobial resistance patterns, and additional genomic information. However, with exposure to antibiotics, its sensitivity plummets within hours, limiting its utility to a narrow timeframe. ICT is an excellent tool to detect pneumococcus for clinical purposes and burden studies; it can provide results within minutes, it is the most sensitive tool, and can detect pneumococcus for weeks after antibiotic therapy. However, it cannot provide information about the causative serotype or antibiotic sensitivity; serotype information is crucial for epidemiological surveillance and to understand the impact of PCVs on serotype distribution. In addition, the widely used BinaxNOW test for ICT is expensive and can only detect pneumococcus; other common meningeal pathogens,  methods , 19 and alue <35 . Serotypalue <35 . A new value <35 . HoweverUntil we find a diagnostic that is rapid, sensitive, and can identify serotypes and antibiotic susceptibility, we propose that clinical microbiology laboratories or reference laboratories use the diagnostics in the following order: (1) ICT , along with (2) culture  to understand the burden of pneumococcal meningitis in areas where use of prior antibiotic is more common. Finally, qPCR can be used for culture-negative specimens to discern the serotypes for epidemiological data generation; as this will not be required for clinical diagnosis, qPCRs can be performed in batches to lower cost or may be shipped to reference laboratories. If culture, ICT, and qPCR, are conducted optimally, they can aid clinical diagnosis and also elucidate the complete picture of pneumococcal disease in settings with high antibiotic exposures.


An important goal to achieve sustainable development is to use raw materials that are easily recyclable and renewable, locally available, and eco-friendly. Sheep wool, composed of 60% animal protein fibers, 10% fat, 15% moisture, 10% sheep sweat, and 5% contaminants on average, is an easily recyclable, easily renewable, and environmentally friendly source of raw material. In this study, slump testing, compressive and flexural strengths, ultrasonic pulse velocity, sorptivity, and chloride penetration tests were investigated to assess the influence of wool fibers on the strength and transport properties of concrete composites. Ordinary Portland cement was used to make five concrete mixes incorporating conventional wool fibers (WFs) ranging from 0.5 to 2.5% and a length of 70 mm. The wool fibers were modified (MWFs) via a pre-treatment technique, resulting in five different concrete compositions with the same fiber content. The addition of WF and MWF to fresh concrete mixes resulted in a decrease in slump values. The compressive strength of concrete was reduced when wool fibers were added to the mix. The MWF mixes, however, achieved compressive strength values of more than 30 MPa after a 90-day curing period. Furthermore, by including both WF and MWF, the flexural strength was higher than that of plain concrete. In addition, adding fibers with volume fractions of up to 2% reduced the concrete composite’s sorptivity rate and chloride penetration depths for both WF and MWF content mixes. Consequently, biomass waste like sheep wool could be recycled and returned to the field following the circular economy and waste valorization principles. The circular economy is becoming a driving force behind the development of new technologies and the modernization of old production cycles. As is well known, the circular economy is built on utilizing prospective waste materials in new productive chains and procedures, such as energy generation or the development of novel materials. The main goals are to avoid exploiting non-renewable raw resources and avoid the cost and effect of waste disposal. This technique can effectively address some of the most pressing social and environmental issues we face today; for example, climate change, the rise in produced wastes resulting from rapid population growth, and resource shortages ,2,3,4. NSheep wool is another notable example of a product tied to farming. Sheep are notable for food security because they are proficient and can adapt to a wide range of climates, from the frigidity of Iceland to the wastelands of Africa, Asia, and Australia . SeveralFiber-reinforced concrete (FRC) is a conventional concrete mix that comprises cement, coarse and fine aggregates, and a random dispersion of discontinuous short fibers. The fibers enhance the concrete mixture’s ductility, energy absorption, and tensile and flexural strengths. Many types of fibers, either polymeric or metallic, are commonly used in concrete mixtures for their benefits. Glass, steel, synthetic, and natural fibers, and fibers from pre-and post-consumer wastes, recycled carbon fibers, and recycled tire textures are the most prevalent fibers used in FRC ,13. FibrNatural fibers include lignocellulosic, mineral, and protein fibers; using protein fibers such as sheep wool and animal hair is limited in concrete production . FurtherDespite the advantages mentioned above, the long-term durability of cement-based composite materials containing waste sheep wool fibers limits large-scale production ,25. HoweAlthough this research includes an investigation of waste sheep wool fibers available, the conducted experiments and analyses are based on one single type of fiber. The work has been focused on the performance of concrete containing conventional and modified wool fibers, but it is believed that technical issues have to be understood and corrected before utilizing any type of waste fibers in concrete. Furthermore, effective pre-treatment can increase the physical properties of wool fibers, hence improving the mechanical properties and durability of concrete composites. In addition to conventional concrete, the use of discarded natural fibers in fiber-reinforced concrete is increasingly being studied in specific applications. To date, and to the authors’ best knowledge, there are limited studies on the strength and transport characteristics of concrete containing waste sheep wool fibers. Consequently, due to the local availability of waste sheep wool, these fibers are used to produce concrete composites to examine their influences on the mechanical and transport properties.In this study, type I ordinary Portland cement (OPC) was used in accordance with the specifications of ASTM C150-07. For fine aggregates, clean and dry natural river sand was used, which was passed through a 4.75 mm sieve, had a specific weight of 2.6, fineness modulus of 2.3, and water absorption of 0.70%. Crushed granite with a specific weight of 2.7, 0.5% water absorption, and a maximum size of 20 mm was employed as coarse aggregate. Furthermore, the waste sheep wool fibers (WFs) used in this investigation were obtained from local sources in Saudi Arabia. In this work, WF with a length of 70 mm was employed, as illustrated in The ACI-211-19 standard was used for proportioning concrete mixtures. The concrete mixes were divided into two groups of regular wool fiber (WF) concrete mixes and modified wool fiber (MWF) concrete mixes with fiber volume fractions of 0.5%, 1%, 1.5%, 2%, and 2.5%, respectively, based on the total volume of concrete mix referred to as WF1–WF5 and MWF1–MWF5. Additionally, a batch of concrete without any fiber was made as a control mix (C). This range of fiber dosages was chosen based on the available literature and a series of preliminary experimental studies conducted prior to the main work. However, fiber additions greater than 2.5% have a detrimental effect on the performance of concrete. Following the existing literature ,7,8 and The process of mixing ingredients into fiber-reinforced concrete is somewhat different from that of normal concrete. Cement binders were added to the dry mix of fine and coarse aggregates in the first step. Then, water was added and mixed for approximately two minutes. Finally, the required volume of fiber was added to the mixture, and the mixing process was continued for another two minutes to ensure that the fibers were evenly dispersed in the mix. The workability test was performed on plain and reinforced concrete mixtures following ASTM C143-03 to determine the slump values. Compressive strength tests were conducted on cylindrical specimens of size 150 mm in diameter and 300 mm in height in accordance with ASTM C39-19. The ultrasonic pulse velocity (UPV) test was performed before the compressive strength test. Prism beam samples with a size of 150 mm × 150 mm × 700 mm were prepared according to ASTM C78-18 to conduct the flexural strength test. Cylindrical samples of size 100 mm × 200 mm were used for the chloride penetration and sorptivity tests. The sorptivity test of concrete specimens reinforced with wool fibers was determined according to ASTM C1585-13 requirements, as illustrated in 3) solution to determine the chloride penetration depth. After spraying the AgNO3 solution onto the concrete specimens, the outer portion was brighter due to the silvery deposit of silver chloride (AgCl), which indicated the depth of chloride penetration, whereas the innermost part was darker owing to the occurrence and consequence of silver hydroxide (AgOH), as shown in A solution with 5% sodium chloride (NaCl) was prepared to imitate harsh conditions in which concrete members can deteriorate significantly when exposed to seawater, and the concrete samples were immersed in it to test the chloride penetration depth. After the exposure periods of 7, 28, and 90 days had been completed, the cylindrical specimens were cut diagonally down the length of the concrete cylinders into two parts. The concrete samples’ split surface was then sprayed with 0.1 N silver nitrate  of 0.783 and 0.577 for all samples.cf and ff are the compressive and flexural strengths (MPa), respectively, and V is the UPV (m/s).Additionally, some factors such as type of aggregates, curing period, W/C ratio, size of specimens, and the testing procedures can influence the UPV values of concrete specimens in the same way as compressive and flexural strength might. Other factors, such as the types and shape, the aspect ratio, and the dosage of wool fibers, could affect the strength of concrete in addition to the considerations mentioned above. The velocity of compression waves is affected by the strength and other mechanical parameters of concrete in the UPV technique. The density and elasticity of the material also affect the velocity of these waves. As a result, the UPV is useful for determining concrete quality and uniformity, estimating static and dynamic modulus of elasticity, and measuring time-dependent concrete behavior . In addip-values were greater than 0.05 for all tests according to the statistical analysis and findings. At the 0.05 level of significance, this result verifies the null hypothesis. Consequently, the mechanical characteristics and UPV of concrete mixtures are distributed normally. The current study’s findings are comparable to those reported by Mastali et al. [The compressive and flexural strengths and UPV values of concrete mixtures comprising WF and MWF were examined, as well as their probability distribution and analytical investigation. The mechanical properties of polypropylene and steel-fiber-reinforced concrete are the subjects of most statistical data analysis in the literature. However, no statistical research has been performed on the mechanical characteristics and UPV of concrete reinforced using sheep wool fibers. As a result, statistical analysis is required to understand better the properties of concrete based on the experimental results. The impact of fiber content on the statistical considerations and distributions of flexural and compressive strengths and UPV is substantial and deserves to be discussed. Therefore, the statistical software SPSS was used to statistically calculate the mechanical characteristics and UPV. The compressive strength, flexural strength, and UPV values for sheep wool fiber-reinforced concrete mixes are revealed in i et al. .Exploitation circumstances and external factors determine the durability of wool-fiber-reinforced concrete composites. The quality and developments that appear at the fiber/matrix interface determine the bonding amongst fibers and the cement matrix, which is a critical factor. Their high proclivity limits natural fibers’ utility in cement-based composites for degrading in an alkaline environment. When fibers are utilized as reinforcement in concrete subjected to harsh environments, they frequently lose strength . The resWhen fiber dosages of more than 1% and 2% for WF and MWF, respectively, were added, water absorption increased slightly. The results showed that the water absorption rate in reinforced specimens was lower than in their conventional equivalent mix, up to a specific fiber dose. Lower water absorption in reinforced specimens indicates lower environmental harm, confirming the matrices’ lower permeability. With the addition of fibers beyond 2%, due to the uneven distribution of fibers in the concrete matrix, the volume of pores increased, consequently reducing the concrete density and providing more space in the matrix to absorb water and a higher water absorption rate ,42. The Although sheep wool fibers can withstand almost any solvent, alkalis can cause them to disintegrate even in diluted solutions. Temperature increases accelerate the dissolution reaction, which damages fibers when the pH is above 11. Wool fibers can be damaged by both acids and alkalis ,45,46. WWool fiber reinforcing of concrete mixtures up to 1.5% generated a grid and dense structure in the concrete matrix that substantially influenced reducing chloride diffusion into specimens and the formation of microcracks. According to the test results, the penetration depth in those mixtures containing WF and MWF at doses of 0.5%, 1%, and 1.5% was significantly decreased. The lowest depth of chloride penetration was 10.5 mm for concrete reinforced with 1% MWF at 90 days, roughly 44% lower than the noted value of 18.9 mm for the plain concrete mix. However, increasing the fiber content raised the permeability of the matrix, which increased the penetration depth. When relating the penetration depths for concrete mixes, it can be seen that pre-treatment and modification of wool fibers resulted in a better performance in preventing the entry of chemicals into the concrete matrix, resulting in the formation of a grid structure and a decrease in the chloride penetration rate when compared to mixes comprising normal wool fibers. The characterization of the interface, which plays a vital role in the durability of concrete components, is critical for service life modeling and prediction. Generally, fiber-reinforced concrete with high dosages of fibers has porous interfaces with lower strength. Increased binding strength and loss of flexibility of fiber bundles are directly linked to the durability of natural fibers such as wool fibers ,48. Pre-The addition of wool fibers and increased fiber dosages remarkably reduced the workability of concrete mixtures, at which the slump values dropped to about zero at a fiber content of 2.5%.When sheep wool fibers were added, the compressive strength was slightly reduced. Nevertheless, pre-treatment wool fibers resulted in higher strength values than normal wool fibers. The obtained compressive strength values ranged between 28 and 35 MPa for the mixes containing 0.5% to 2.5% MWF at the age of 90 days, which signifies the sufficient strength that can be utilized for various applications.Despite the reduction in compressive strength of concrete mixtures, considerable increases in flexural strength of all concrete mixes were recorded. All reinforced mixes obtained greater flexural strength values than plain concrete mixes. The maximum flexural strength of 5.3 MPa was obtained for the concrete mix containing 1.5% MWF at the age of 90 days, which is about 28% higher than that of 4.15 MPa recorded for the plain control mix.The addition of wool fibers did not significantly affect the UPV values. However, the obtained UPV values of higher than 3300 m/s classified the concrete as good quality concrete.Pre-treatment of sheep wool fibers with saltwater resulted in significantly improved fiber characteristics and better adherence to cement paste. In addition, a lesser percentage of modified sheep wool fibers improves mechanical qualities, whereas the same improvement in strength can be achieved with a higher rate of untreated wool.The addition of wool fibers up to a specific dosage reduced the water absorption rate of concrete mixtures and resulted in a lower rate of chloride penetration in reinforced specimens. This was owing to the fiber’s bridging action and providing a rigid network, which prevents the entrance of liquids into the concrete matrix. In addition, wool fibers can absorb up to 28% of their weight in water without feeling wet, which significantly interacts with the concrete matrix in reducing the water absorption rate.The overall performance of concrete mixtures may be improved by a particular treatment of sheep wool fibers. Consequently, concrete composites comprising modified waste sheep wool fibers are regarded as one of the most promising sustainable building materials for environmentally friendly construction with comparatively lower cost.Sheep wool fibers are one of the most sustainable natural resources owing to ease of recyclability, low carbon impact, biodegradability, and energy-efficient properties. Therefore, the current study determined the feasibility of reinforcing the concrete mixtures with conventional and modified waste sheep wool fibers, and proposed novel concrete composites. The mechanical and transport properties of concrete specimens comprising various dosages of normal and modified wool fibers were investigated. Based on the experimental and analytical results, the following conclusions can be drawn:


In this study, the effects of heating rate and compressive strength on the spalling behavior of single-sided heated ring-restrained concrete with compressive strengths of 60 and 100 MPa were investigated. The vapor pressure and restrained stress inside the concrete were evaluated under fast- and slow-heating conditions. Regardless of the heating rate, the concrete vapor pressure and restrained stress increased as the temperature increased, and it was confirmed that spalling occurred in the 100-MPa concrete. Specifically, it was found that moisture migration and restrained stress inside the concrete varied depending on the heating rate. Under fast heating, moisture clogging and restrained stress occurred across the concrete surface, causing continuous surface spalling for the 100-MPa concrete. Under slow heating, moisture clogging occurred, and restrained stress continuously increased in the deep area of the concrete cross-section owing to the small internal temperature difference, resulting in explosive spalling for the 100-MPa concrete with a dense internal structure. Additionally, while the tensile strength of concrete is reduced by heating, stress in the heated surface direction is generated by restrained stress. The combination of stress in the heated concrete surface and the internal vapor pressure generates spalling. The experimental results confirm that heating rate has a significant influence on moisture migration and restrained stress occurrence inside concrete, which are important factors that determine the type of spalling. The internal structure of high-strength concrete is denser than that of normal-strength concrete. This increases the likelihood of spalling in high-strength concrete when it is exposed to high temperatures, such as temperatures caused by fire. Concrete spalling is difficult to predict owing to its irregular nature and may lead to strength degradation by causing cross-sectional loss of concrete members. It has been reported that vapor pressure, thermal stress, and a combination of the two are the main causes of concrete spalling ,2,3,4,5.In addition, the mechanical properties of concrete exposed to high temperatures are negatively affected. Concrete spalling and mechanical property degradation can have a significant effect on the structural stability of buildings. Various studies have been conducted to compensate for this phenomenon ,7,8.During heating, moisture migration occurs inside concrete, and the moisture is released outwards or condensed as it moves inwards. For high-strength concrete, the likelihood of spalling is high owing to low internal moisture migration and high vapor pressure on the surface ,10,11. THertz  stated tAlgourdin et al.  heated cPhan et al. ,24 appliIn addition, Choe et al.  examinedRecently, Ozawa et al. ,27 devisConcrete spalling is significantly affected by the heating condition and compressive strength. In particular, to improve the fire safety performance of concrete structures, it is necessary to examine the concrete spalling behavior considering the heating condition and compressive strength. Previous studies focused on the spalling of concrete specimens by vapor pressure under heating; however, stress due to thermal expansion of concrete should be considered simultaneously. In addition, when concrete is subjected to single-sided heating, as shown in In this study, ring-restrained concrete subjected to single-sided heating was used to investigate the concrete spalling behavior according to heating rate. When concrete with compressive strengths of 60 and 100 MPa were subjected to single-sided heating, the vapor pressure due to the temperature difference inside the concrete was measured, and the restrained stress by the ring-restrained condition was calculated to examine the influence of thermal stress.Restrained stress in concrete was calculated based on the research of Ozawa et al. ,27, who t, R: thickness and inside radius of the steel ring (mm)x- and y-axis stress that corresponds to restrained stress occurs in concrete during heating, and the biaxial stress may generate stress in a new axis, as shown in z-axis stress, which occurs in the direction of the heated surface of the ring-restrained concrete specimens, may cause cracks inside the concrete, as shown in z-axis stress in this study is a value estimated using the restrained stress and may be different from the actual stress in concrete; however, z-axis stress may occur and may affect the spalling. Therefore, z-axis stress can be calculated as follows:x-y coordinate (MPa)In concrete exposed to high temperatures, stress is generated by thermal expansion regardless of the axis. The x-y coordinateHowever, under slow heating, the 100-MPa concrete specimen exhibited explosive spalling that caused a large internal fracture, resulting in a maximum spalling depth of approximately 42 mm. In addition, the maximum debris size differed depending on the spalling type. The debris size was approximately 50 × 40 × 4 mm for surface spalling and 160 × 140 × 20 mm for explosive spalling, showing that explosive spalling had a larger debris size.For the spalling depth distribution of the 100-MPa concrete specimen for different spalling types, the spalling depth was measured in the form of a grid on the heated surface of the concrete specimen. Under fast heating, concrete was peeled off from the center of the heated surface owing to surface spalling, but the concrete close to the steel ring exhibited a narrow and deep shape without spalling. This appears to be because spalling occurred in the center of the concrete specimen where the temperature rapidly increased, and thus the expansion force of the concrete close to the steel ring was relieved. Under slow heating, explosive spalling temporarily occurred, but a wide and shallow shape was observed compared to surface spalling. In addition, the weight loss of the concrete was found to be approximately 25.40% and 21.25% for surface and explosive spalling, respectively. It was confirmed that explosive spalling can exhibit a similar amount of weight loss to that of surface spalling, which occurs continuously despite being a one-time phenomenon.Under slow heating, the temperature difference inside the concrete was smaller than that under fast heating. For the 60-MPa concrete specimen that did not exhibit spalling, a temperature difference of approximately 130 °C was observed between the depths of 5 and 40 mm at the end of heating. In addition, the 100-MPa concrete specimen exhibited explosive spalling at approximately 8 h and 41 min after the start of heating. Because of this spalling, the thermocouples at the depths of 5, 10, and 25 mm were exposed simultaneously, thereby exhibiting sharp temperature changes.Under slow heating, the vapor pressure inside the concrete slowly increased. In particular, for the 100-MPa concrete specimen, the vapor pressure at the depths of 5 and 10 mm was released, but the vapor pressure at 40 mm increased to 7.6 MPa. The vapor pressure decreased after explosive spalling.Meanwhile, as shown in Under fast heating, the vapor pressure was similar to the SVP curve or exhibited a supersaturated state regardless of the compressive strength of the concrete. Owing to the fast heating, the vapor generated from the heated surface is discharged outwards or moves inwards, and the moisture that moves inwards forms moisture clogging by causing the supersaturated state ,33. BecaUnder slow heating, the 60-MPa concrete specimen exhibited a saturation state similar to the SVP curve, whereas the 100-MPa concrete specimen showed the unsaturated state except for the vapor pressure at 40 mm. The vapor pressure slowly increased under slow heating regardless of the compressive strength of concrete. This delayed the time of the vapor pressure release, and moisture moved to a deep location away from the heated surface of the concrete specimen. The migrated moisture formed moisture clogging by causing a supersaturated state at a depth of 40 mm in the 100-MPa concrete specimen, and the vapor pressure was more than twice as high as that under fast heating. Explosive spalling occurred owing to the vapor condensing inside the concrete.Under slow heating, restrained stress tended to slowly increase regardless of the compressive strength of the concrete because the temperature difference inside the concrete was small compared to that under fast heating. As the strain gauges of the steel ring could only be used for temperatures of up to approximately 80 °C, the expansion deformation could only be measured for approximately 6 h. However, it can be estimated that the restrained stress continued to increase afterwards.z-axis stress) may occur as the restrained stress of the heated surface increases, as explained in z-axis stress may cause cracks inside the concrete, and it acts as a force that pushes the concrete surface in the direction of the heated surface. Spalling occurs owing to a combination of the z-axis stress and vapor pressure, and it appears that the influence of the z-axis stress is different depending on the spalling type.For the 100-MPa concrete specimen that exhibited spalling, stress in the direction of the heated surface (z-axis stress of concrete according to heating rate. The values at a depth of 5 mm were compared for fast heating that caused surface spalling, while those at a depth of 40 mm were compared for slow heating that led to explosive spalling. Eurocode was used for the residual tensile strength of concrete exposed to high temperature [z-axis stress in the concrete increased [perature , and Poiperature . As the ncreased .z-axis stress in the concrete rapidly increased and was higher for the 100-MPa concrete specimen than for the 60-MPa one. As the heating temperature increased, the z-axis stress and vapor pressure in the concrete increased, and they exceeded the residual tensile strength of concrete. This phenomenon occurred earlier in the 100-MPa concrete specimen that exhibited spalling than in the 60-MPa concrete specimen that did not exhibit spalling. For the 100-MPa concrete specimen, surface spalling began at approximately 8 min 30 s. Then, the sum of the z-axis stress and vapor pressure at a depth of 5 mm significantly exceeded the residual tensile strength of concrete, thereby causing surface spalling. It appears that the 100-MPa concrete specimen exhibited continuous surface spalling by repeating the above phenomenon. For the 60-MPa concrete specimen, spalling did not occur because the vapor was discharged without being expanded to the supersaturated state, even though the sum of the z-axis stress and vapor pressure exceeded the residual tensile strength of the concrete.Under fast heating, z-axis stresses in the concrete were found to be similar regardless of the compressive strength. As the heating temperature increased, the z-axis stress and vapor pressure in the concrete increased and exceeded the residual tensile strength of the concrete. This phenomenon occurred earlier in the 60-MPa concrete specimen than in the 100-MPa one. However, the 60-MPa concrete specimen did not exhibit spalling because the vapor was released before being expanded to the supersaturated state as in fast heating. For the 100-MPa concrete specimen, the residual tensile strength of the concrete was significantly exceeded owing to a rapid increase in the supersaturated vapor at a depth of 40 mm, resulting in explosive spalling at approximately 8 h 41 min.Under slow heating, the z-axis stress. It was confirmed that the supersaturated vapor and restrained stress in concrete are the main factors of spalling, and that surface or explosive spalling may occur in concrete depending on the heating rate and compressive strength.As shown in In this study, single-sided heating was applied to ring-restrained concrete to evaluate its vapor pressure and restrained stress, which are the main causes of spalling. Spalling was significantly affected by the compressive strength and heating rate of the concrete. Based on our experimental results, the following conclusions were drawn.Because concrete has a low thermal conductivity, an internal temperature difference occurs depending on the heating rate. In particular, the temperature gradient of concrete may increase under a single-sided heating condition. The temperature difference inside concrete affects the formation of vapor pressure and restrained stress, which are important factors that determine the spalling type. The temperature difference inside concrete is large and continuous surface spalling occurs under fast heating, whereas the temperature difference inside concrete is small and explosive spalling occurs under slow heating.Under fast heating, the heated surface of concrete is continuously peeled off and small concrete debris is generated in large quantities owing to the surface spalling of concrete. However, under slow heating, explosive spalling of concrete involves an impact and generates a very large concrete fracture. In particular, explosive spalling may cause rapid strength degradation because it may lead to a rapid cross-sectional loss. It was confirmed that the spalling type of concrete has a significant influence on the cross-sectional loss pattern.For high-strength concrete with a dense internal structure, moisture migration occurs when the internal temperature increases, and the inward-migrated moisture forms moisture clogging in the supersaturated state. Under fast heating, the temperature difference in concrete between the surface and the inside was large, therefore, repeated surface spalling occurred owing to the moisture clogging formed on the heated surface of the concrete and the rapidly increasing restrained stress. Under slow heating, moisture migration was not active because the temperature was evenly distributed from the surface to the inside of the concrete, but explosive spalling occurred owing to the moisture clogging forming in a deep area of the concrete and the restrained stress slowly increased. The moisture clogging and restrained stress formed by the temperature distribution in high-strength concrete significantly affect the spalling type.Concrete exhibited surface or explosive spalling depending on the heating condition and compressive strength. The cross-sectional loss pattern varies depending on the spalling type and can affect the strength degradation of concrete. For surface spalling, the strength of concrete can be conserved if part of the cross-sectional loss is inhibited. However, the occurrence of explosive spalling may cause a rapid strength degradation of concrete. As the strength degradation of concrete affects the structural stability of concrete structures, it is necessary to control concrete spalling considering the heating condition and compressive strength.In future work, spalling control methods according to heating rate should be investigated. In addition to previous methods, new methods and materials for explosion control should be considered. Furthermore, there is also a need to study the effectiveness of concrete members.


Human mitochondrial chaperonin mHsp60 is essential for mitochondrial function by assisting folding of mitochondrial proteins. Unlike the double-ring bacterial GroEL, mHsp60 exists as a heptameric ring that is unstable and dissociates to subunits. The structural dynamics has been implicated for a unique mechanism of mHsp60. We purified active heptameric mHsp60, and determined a cryo-EM structure of mHsp60 heptamer at 3.4 Å. Of the three domains, the equatorial domains contribute most to the inter-subunit interactions, which include a four-stranded β sheet. Our structural comparison with GroEL shows that mHsp60 contains several unique sequences that directly decrease the sidechain interactions around the β sheet and indirectly shorten β strands by disengaging the backbones of the flanking residues from hydrogen bonding in the β strand conformation. The decreased inter-subunit interactions result in a small inter-subunit interface in mHsp60 compared to GroEL, providing a structural basis for the dynamics of mHsp60 subunit association. Importantly, the unique sequences are conserved among higher eukaryotic mitochondrial chaperonins, suggesting the importance of structural dynamics for eukaryotic chaperonins. Our structural comparison with the single-ring mHsp60-mHsp10 shows that upon mHsp10 binding the shortened inter-subunit β sheet is restored and the overall inter-subunit interface of mHsp60 increases drastically. Our structural basis for the mHsp10 induced stabilization of mHsp60 subunit interaction is consistent with the literature that mHsp10 stabilizes mHsp60 quaternary structure. Together, our studies provide structural bases for structural dynamics of the mHsp60 heptamer and for the stabilizing effect of mHsp10 on mHsp60 subunit association. Due to its roles in human health, mHsp60 has been proposed as potential biomarkers and drug targets8. mHsp60 belongs to an essential protein family called chaperonin that are conserved among the three kingdoms of life9. The main function of chaperonins is to mediate folding of cellular proteins. Detailed molecular mechanism of chaperonins has been extensively investigated using the E. coli chaperonin GroEL and its cochaperonin GroES14. GroEL consists of 14 subunits assembled in two heptameric rings forming two central cavities, and each subunit consists of three domains, apical, intermediate and equatorial domains. Proteins in non-native conformations bind to the central cavity, and in an ATP-dependent mechanism they are sequestered into the cavity upon GroES binding to the end of the substrate-loaded cis heptameric ring. The enclosed GroEL-GroES chamber provides the substrate protein an isolated environment favorable for folding. Binding of ATP to a second GroEL ring, trans to the substrate-loaded GroEL-GroES chamber, trigger dissociation of the GroEL-GroES folding chamber, releasing the substrate protein. In support of the essential role of the second ring in GroEL, a single-ring GroEL, GroELSR, where conserved inter-ring contacts including a conserved salt bridge are disrupted, is nonfunctional with GroES in vivo15, because the GroELSR-GroES complex does not dissociate16.Human mitochondrial mHsp60 is essential for mitochondria as it is required for mitochondrial protein transport, folding and assembly17, and mHsp60 lacks the two pairs of salt bridge found in the inter-ring interface in the double-ring GroEL18, suggesting that mHsp60 and its cochaperonin mHsp10 may function in a single-ring mechanism other than the double-ring mechanism of GroEL-GroES. In support of the single-ring mechanism, mHsp60 interacts transiently with mHsp1019, thus the dissociation of the mHsp60-mHsp10 chamber does not require the action from a second ring. However, an earlier model23, supported by the crystal structure of an inactive mHsp60 variant24 complexed with mHsp10 in a double-ring football-shaped conformation25, assumes that mHsp60 functions via a GroEL-like double-ring mechanism. In the recent revised model, the single-ring mechanism has been incorporated in addition to the double-ring mechanism26. In the studies, cryo-EM shows that mHsp60 forms both the single- and double-ring mHsp60-mHsp10 complexes in the presence of ADP. Structure-based mHsp60 variants of single-ring only and covalent bonded double-ring are shown active in folding of a substrate protein and in substituting GroEL-GroES to support E. coli cell growth. Thus, it is proposed that mHsp60-mHsp10 can function as either single- or double-ring mechanisms based on the specific mitochondrial substrates.Unlike GroEL, mHsp60 exists as single ring27, and mHsp60 has been purified as a double-ring conformation that when in the presence of mHsp10 cannot hydrolyze ATP without the substrate protein21, highlighting the difficulties in mHsp60 preparation. In this report, we purified active mHsp60 in single-ring conformation, and determined mHsp60 structure using cryo-EM. We found that mHsp60 contains several unique residues that decease inter-subunit sidechain interactions and shorten the inter-subunit β sheet, resulting in reduced inter-subunit interface when compared with GroEL. These residues are conserved among higher eukaryotic mitochondrial chaperonins. Our structural analysis with the reported single-ring mHsp60-mHsp10 shows that the mHsp60 subunit interface is increased as a result of mHsp10 binding. Note that a cryo-EM structure of mHsp6028 was reported during our manuscript submission, however, without structural analysis on inter-subunit interactions and discussion on their roles on the structural dynamics of mHsp60.Detailed mechanistic investigations on mHsp60-mHsp10 had been hindered by difficulties in preparing mHsp60 until recently. Purified mHsp60 dissociates readily to nonfunctional monomersSR. As shown in Fig. SR, but later than that of the double-ring GroEL. Also, mHsp60 existed as a particle with a size similar to that of GroELSR, but smaller than that of GroEL  and dynamic light scattering (DLS) to compare mHsp60 with the double-ring GroEL and single-ring GroELoEL Fig. . All throEL Fig. .Figure 129. The intrinsic ATPase rate of mHsp60 was decreased by ~ 50% in the presence of mHsp10: the cochaperonin inhibition on the ATPase of the chaperonin is a property found in the chaperonin systems. Moreover, mHsp60-mHsp10 was as effective as GroEL-GroES in mediating folding of malate dehydrogenase (MDH)  is well resolved with clear sidechain information —the diameter of the chaperonin ring is determined by the equatorial domains. Since the apical domains contribute to the height of the chaperonin ring, their lower resolution regional map in mHsp60 may not estimate the height of the mHsp60 ring (74.4 Å) accurately compared to that of the GroEL ring (69.1 Å); however, mHsp60 appears taller than the GroEL ring Fig.  of mHsp6Between mHsp60 and GroEL, the three domains, apical, intermediate and equatorial domains, are arranged similarly but differ in their conformations. While conformations of the equatorial domains overlay well, those of the apical domains deviate Fig. b. Overal2 versus ~ 1674 Å2. In the following, we compare the molecular interactions on the inter-subunit interface between mHsp60 and GroEL. We focus on the equatorial domains because they contribute most of the inter-subunit interactions and their regional maps are well resolved with clear sidechain information.The equatorial domains contribute most of the inter-subunit interactions, accounting for ~ 75% of the total inter-subunit interface and 44 residues involved in inter-subunit interactions. The apical domains contribute nine residues for the inter-subunit interactions, while the intermediate domains contribute six residues. Overall, mHsp60 has a much smaller inter-subunit interface than GroEL, ~ 1258 ÅCenter on the inter-subunit interface is a four-stranded β-sheet: β1 and β18 from one subunit connected with β2 and β3 from the other subunit  and is proximity with T517 4.5 Å); both T516 and T517 are from the other GroEL subunit . The K4-D523 sidechain interaction brings the backbones of K4 and D523 close to form hydrogen bonding, adding twisted ends to β1 and β18, respectively  of mHsp60 is lower than GroELSR , both solved via cryo-EM , increasing their contribution to the inter-subunit interaction from 25 to 35%. Overall, the inter-subunit interface of the mHsp60 heptamer increases drastically by ~ 49% from 1258 Å2 in the mHsp60 alone structure to 1871 Å2 in the mHsp60-mHsp10 structure. The mHsp10-induced drastic increase in inter-subunit interface in mHsp60 heptamer is consistent with the observation that the presence of mHsp10 (and ATP) prevents mHsp60 from dissociation20.The mHsp60 subunit interactions are enhanced upon mHsp10 binding. We compared our structure of single-ring mHsp60 (3.4 Å) with the structure of single-ring mHsp60-mHsp10-ADP-EM Fig. a,b. We f-EM Fig. . Moreove-EM Fig. c,d. As a34, both the apical and the intermediate domains of mHsp60 undergo large domain movements upon mHsp10 binding  and after (1594 Å2) GroES binding . In addition, the contributions from individual domains to the inter-subunit interface remain largely the same. For example, the equatorial domains contribute 62% and 64% of the total interface before and after GroES binding, respectively. Moreover, structure of the inter-subunit β1-β18-β2-β3 sheet remains the same after GroES binding. This structural analysis suggests that the subunit association in the GroEL ring, i.e., the stability of the GroEL ring, is not affected by GroES binding. In a striking contrast, mHsp10 binding affects inter-subunit interaction in mHsp60 drastically. Upon mHsp10 binding, the overall inter-subunit interface in mHsp60 increases by 49%, and the contributions from the equatorial domains and the apical/intermediate domains increase by 29% and 105%, respectively. In addition, the shortened inter-subunit β1-β18-β2-β3 sheet of mHsp60 is restored to the same as in GroEL or the GroEL-GroES complex  and lyzed via sonication. After centrifugation, ammoniate sulfate was added to the clear lysate to a final concentration of 20%. The solution was centrifuged, and the supernatant was loaded onto a butyl column, preequilibrated with 20% (NH4)2SO4 ammoniate sulfate in Buffer A. After extensive wash including with 20% methanol, 20% ammoniate sulfate in Buffer A, the bound protein was eluted with a linear gradient of 20–0% (NH4)2SO4. The mHsp60 containing fractions were combined and (NH4)2SO4 was added to a final 60% to precipitate mHsp60. The precipitated mHsp60 was dissolved in 100 mM NaCl in Buffer A, and the solution was subjected to gel filtration purification using a Superdex 200 column . Fractions containing single ring mHsp60 were concentrated to a desired concentration, and the freshly concentrated mHsp60 was frozen on the EM grids or used within the same day for analysis. mHsp60D3G was generated using QuickChange (Qiagen), and purified as above. GroEL and GroELSR were purified as before37.Gene encoding the mature mHsp60 sequence  was synthesized with codons optimized for protein expression in SR were subjected to DLS analysis using a Zetasizer Nano-S dynamic light scattering instrument . Samples were in 100 mM NaCl, 10 mM KHepes, 1 mM EDTA, 1 mM DTT and 5% glycerol, and the temperature was 25 °C. DLS data were collected within few hours of purification and for the next six days. Measurements were repeated more than once for each sample.Freshly purified mHsp60, GroEL and GroEL37. mHsp60, GroEL or GroELSR was added to TEA buffer  to a final concentration of 0.25 uM (heptameric mHsp60 or GroELSR) or 0.125 uM (tetradecameric GroEL). The final concentration of mHsp60 or GroES was 0.3 uM. The solution was incubated at 25 °C for 10 min. The hydrolysis was initiated by addition of 100 mM pH 7.0 ATP to a final concentration of 2 mM and followed every 3 min for 21 min using the malachite green assay. Measurements were repeated more than once for each sample.The steady-state ATP hydrolysis rate was measured using the malachite green assay, as described in our previous work+, as described in our previous work37. MDH was unfolded in TEA buffer including 3 M GdmHCl to a final concentration of 36.7 uM (monomeric MDH). To refold MDH, 2.75 ul of unfolded MDH was diluted at 1:100 (v/v) to a final volume of 275 ul of refolding solution (at 30 °C) containing 50 mM TEA, pH 7.4, 50 mM KCl, 1 mM ATP, and 2 uM heptameric mHsp60 or GroELSR or 2 uM tetradecameric GroEL) with 4 uM or without mHsp10 or GroES. At desired time intervals, 20 ul of reaction solution was removed and mixed with 1 ml of NADH assay solution , and absorption at 340 nm was taken to monitor the decrease of NADH. As a positive control, activity of 367 nM native MDH (monomeric concentration) was measured at the same time intervals and was taken as 100% activity. Measurements were repeated more than once for each sample.Refolded MDH was assayed by measuring its ability to convert NADH to NAD38:yN and yD are the derived signals for the native and denatured samples, and mN and mD are the derived baseline slopes for the native and denatured samples, T is the temperature, ΔHvh is the van’ Hoff enthalpy, R is the gas constant and Tm is the temperature of the transition midpoint. The free energy of unfolding at specific temperature is estimated from a modified Gibbs–Helmholtz equation, assuming no heat capacity change between the denature and native conformations: ΔCp = Cp(denatured) − Cp(native) = 0Protein stocks were in 100 mM NaF, 10 mM KHEPES, pH 7.4, 1 mM EDTA, 1 mM DDT and 5% glycerol. Proteins were tenfold diluted to 100 mM NaF, 10 mM KHEPES, pH 7.4, 1 mM EDTA and 1 mM TCEP. Samples were heated from 20 to 86 °C with a heating rate of 2.0 °C/min by a Jasco Peltier thermo control device. The CD signal at 222 nm was recorded by a J-715 CD spectrometer every 2 °C with a 4-s averaging time. Measurements were repeated more than once for each sample. Thermal denaturation was analyzed by fitting the data to a two-state model according to the following equation39 with (at 30 eV) or without energy filter. Initial data quality assessment was done by RELION and Appion40. Dose weighted motion corrected was done by MotionCor241 and CTF estimation was done by ctffind442 and Gctf43. Particles were semi-manually picked by e2boxer.py in EMAN244. Reference-free 2D classification, initial model building, 3D classification, 3D refinement, and CTF refinement were performed in RELION45. A total number of 182,600 particles were used to build the final 3D reconstruction at a resolution of 3.5 Å for NCCAT data and a total number of 196,060 particles were used in the final 3D reconstructions at a resolution of 3.5 Å for PSU COM data (Table 46. Atomic model for mHsp60 was built using GroEL coordinate (PDB 1PCQ) as a template. Mutation and real space refinement were performed in Coot47 and Phenix48.Protein sample prepared in the same batch were submitted to two facilities PSU COM and NCCAT for cryo-EM data collection. Detailed methods for cryo-EM are described in the supplementary method section. In general, approximate 4 µl of mHsp60 in ~ 9 mg/ml were applied to Quantifoil™ holey carbon grids. Vitrification was performed using Thermo Fisher Scientific (TFS) Vitrobot Mark IV under 100% humidity. Frozen-hydrated specimens were loaded into Thermo Fisher Scientific Titan Krios operated at 300 kV equipped with Gatan K3 camera. Data collection was done by using TFS EPU or LeginonSupplementary Information.