Concrete is a widely used construction material, demanding strict quality control to maintain its integrity. The durability and lifespan of concrete structures rely heavily, amongst other factors, on the characteristics of fresh and early age concrete, which are strongly dependent on the curing process. To ensure long-term durability, it is crucial to assess concrete properties throughout construction and verify compliance with design specifications. Currently, electrical resistivity-based sensors are available and used for quality control and monitoring, however, these sensors tend to be costly or only measure at a single location within the concrete cover. This study introduces a printed circuit board (PCB)-based array of electrodes capable of measuring concrete resistivity profiles across the concrete cover, from its fresh state to early age development. In this work, the feasibility of such resistivity PCB-sensors, novel for concrete, is evaluated under laboratory conditions. The sensors exhibit a promising performance in monitoring the efficiency of concrete curing under various conditions. Additionally, they successfully evaluate the effectiveness of internal curing  during the initial stages of hardening. This sensor array provides a valuable tool for monitoring the curing of concrete at early age, and showcases a preliminary solution that could be further developed to ensure long-term performance of concrete infrastructure. Concrete is one of the most widely used building materials in the world and is used in most infrastructure today. Therefore, it is critical to ensure that its quality is maintained during construction . ConcretIn this context, one very important stage in the production process of a concrete structure is the so-called curing, which aims to reduce water loss in the concrete structure at very early ages. One way of accomplishing this is by covering the fresh concrete surface to prevent any evaporation of water . AlternaIn terms of monitoring methods, the electrical resistivity (ER) measurement inside concrete has been used in a few studies as a moisture and durability indicator ,10, and In this study, we present a PCB-based array of resistivity sensors that can measure concrete resistivity from the fresh state of concrete throughout the early age concrete development, and correlate the measurements with the ongoing hydration and hardening of concrete under different curing conditions, simulating real case applications. PCB-based sensors are less expensive than other sensors, as they are manufactured using standard processes that facilitate mass production . Such coThe experimental setup consisted of concrete cubes (side length of 150 mm) of two different mix designs embedded with the PCB-based ER sensors for a period of 7 days while curing under different conditions. In this section, we present details about the concrete mixtures used in the study, about the sensor design, and the experimental setup.Two concrete mixtures were studied: a first mixture  and a second mixture  as an internal curing agent). Superabsorbent polymers consist of a natural and/or synthetic water-insoluble 3D network of polymeric chains crosslinked by chemical or physical bonding . They po50) of 360 µm and absorption capacity of 21 g/g [An overview of concrete mixtures A and B is presented in f 21 g/g ).In the mixing procedure, the dry materials were first mixed for 1 min , then the mixing water was added and mixed for an additional 2 min. When SAPs were present, the additional entrained water was added during the third minute and the mixing proceeded for an additional 2 min. The total mixing time was 3 min for Concrete A and 5 min for Concrete B. For Concrete A, fifteen cubes (150 mm) were produced by pouring the fresh concrete in a cubical mold, and were kept under different curing conditions: (1) room 20/90, (2) room 20/60, and (3) room 32/60. The details of the ambient conditions in these rooms are given in The array of ER electrodes used in this study allowed the monitoring of four different locations over the concrete cover depth, as shown in The sensor was composed of hard-plated gold electrode on a PCB substrate. The fabrication technique was in line with the standard PCB board manufacturing. The levels of the ER sensor in the concrete cover were denoted as level 0, 1, 2 and 3, with respect to the concrete surface. At level 0, the sensing electrodes were positioned at 1 and 5 mm from the concrete surface. Level 1 was defined as a measurement between electrodes at 5 and 11 mm from the surface, level 2 between electrodes at 11 and 25 mm, and finally, level 3 was measured between electrodes at 25 and 42 mm from the concrete surface. These distances were chosen to collect higher spatial resolution of the resistivity measurement close to the concrete surface where the change in resistivity values was higher compared with the innermost depth (50 mm) of the concrete cover depth. The sensor was based on impedance spectroscopy, where an alternating current (AC) excitation voltage was applied between a pair of electrodes, and the resulting current response was measured. Using Ohms law, the impedance was evaluated. The resulting impedance was a combination of real and complex parts with magnitude and phase shift of the output signal depending on the applied frequency. The impedance at which the phase shift of the output response was zero gave the resistance or resistivity of the medium between the electrodes. The details of the electrode design are given in In this section, we discuss the combined effects of curing and drying on the resistivity profiles obtained with the sensors. The results will be presented for each of the curing rooms described in In this room, due to higher ambient RH, evaporation/drying was expected to be minimal, especially in the innermost layers of the concrete cube. Therefore, changes in resistivity in the innermost levels were expected to be almost exclusively related to the ongoing hydration process of the cement. The resistivity values observed in all four levels were similar up to the first 24 h of curing. After that, with the cubes already demolded and with a higher exposure to environmental conditions, the outermost level presented considerably higher values of resistivity, which showcased the influence of drying on the resistivity measurement of the first sensor level (which was only 1–5 mm below the concrete surface). Even at a high relative humidity , there was still an RH gradient between the air in the environment and the concrete specimen, which enabled drying to occur to some extent, especially near the surface.In contrast, for all deeper levels the resistivity values were comparable, with a maximum difference below 0.5 kΩcm between levels 1 and 3, which could be considered as a strong indication that no severe drying was occurring at these levels and the evolution of resistivity was linked almost exclusively to the progressive cement hydration and the changes in the microstructure of the matrix during hardening. It was assumed that the concrete curing was developing in a uniform concrete cover depth covered by sensor levels 1, 2 and 3 (5–42 mm deep). The variation rate depicted in In this room, due to lower ambient RH in comparison with room 20/90, evaporation/drying was expected to be higher, especially near the surface but not limited to it, as in time, the drying front could also reach (some of) the innermost levels, because the fresh concrete had higher internal RH (100%) in the beginning as compared with the ambient condition of room 20/60 (RH of 60%). During the first day of curing, the resistivity values for all levels were very similar, as well as the variation rate of the resistivity. Once the cubes were demolded and exposure to the curing environment increased, the resistivity values recorded at level 0 became significantly higher in comparison with the values registered in the other levels. One day after casting, the resistivity values near the surface of the concrete, i.e., level 0, were already seven to eight times higher than those in the inner levels, and from then onwards, the resistivity of level 0 grew exponentially until it reached a plateau. At day 7, the resistivity values of level 0 reached ca. 50 times the innermost level 3. In contrast, the difference between levels 1 and 3, and between levels 2 and 3, were remarkably lower.The variation rate for level 0 reached a maximum around 3 days after the casting and started to decrease after that. Additionally, for level 1, a noticeable difference in the variation rate was observed in comparison with level 3, indicating that the effects of drying were also affecting the resistivity values, thus the curing, at that level. In The resistivity at level 0 grew exponentially from the very beginning of the monitoring period and reached values above 1000 kΩcm, which were 4, 80 and 300 times higher than those registered for levels 1, 2 and 3, respectively, at the same moment. Level 1 (5–11 mm) reached values of up to 350 kΩcm at 7 days, around 70 times higher than the value recorded in room 20/60 at the same age. A similar trend was also observed for level 2 (11–25 mm). The variation index also reflected such differences. The maximum rate of variation for level 0 was already achieved before 1 day, much earlier than in the other rooms. Additionally, for both levels 1 and 2, no decay in the rate of resistivity was observed. On the contrary, for these levels, an increasing trend was observed from day 2 up to day 7. Based on that, it is clear that the resistivity values and the curing process were significantly affected by the higher temperature, which accelerated the hydration reactions of the cement at the early ages. Furthermore, this acceleration not only meant a faster hardening and strength development, but also a faster water exchange, which, in time, added to the drying caused by the humidity gradient between the inside of the specimen and the atmosphere. Once again, the sensors captured such nuances.With the analysis of the resistivity curves in all rooms, it was observed that in all cases the resistivity curves at the location of level 3 were minimally affected by the drying effect caused by the lower ambient RH of curing rooms 20/60 and 32/60, and the higher temperature of the latter . In a simplified way, it allowed the highlighting of only the effects of curing temperature on the hydration of the cement. Tρ and Trefρ are the resistivity values of concrete (in kΩcm); T is the temperature inside the concrete (in °C); refT is taken as 20 (in °C); a-condE is the activation energy of conduction (here taken as 29.8 kJ/mol); and R is the universal gas constant (here taken as 8314 J/mol·k).The resistivity values from the concrete cube stored in room 32/60 were scaled to the temperature of 20 °C to allow an appropriate comparison with the previous experiments in room 20/60 and room 20/90. The temperature correction method followed Equation (1), as described in . Here, ρUnder the same temperatures, the lower relative humidity affected curing at level 3, but to a very limited extent. In this regard, the curves from room 20/60 and room 20/90 were barely distinguishable up to the first 10–12 h of curing, and even after 7 days, the difference in resistivity value was lower than 1 kΩcm. In the case of the concrete in room 32/60, the scaled resistivity values were significantly higher. After 7 days of measurement, the difference between room 32/60 and room 20/60 reached ca. 5 kΩcm. As mentioned before, at high temperatures the rate of reaction for cement hydration increases, resulting in rapid densification of concrete . Due to 2 is presented. In general, a high correlation between the strength and resistivity was found in all sensor levels in all rooms. For level 0 in room 32/60, there was a slight reduction in the R2 value when compared with all the other rooms and deeper sensor levels in the same room, which was associated with the faster strength development at the earlier ages (from 1 to 3 days) and stabilization right after that. Although there was still a very high correlation of the parameters in this sensor level, this could be an indication that for more extreme curing conditions, the use of data from locations near the surface of the structure could lead to lower correlations between the resistivity and other material properties. The relationship between the compressive strength measured at 1, 3 and 7 days, and the ER values measured with the sensors, is depicted in The sensors were able to capture the internal curing effect of the SAPs in the concrete and provide some insights towards the water release of the polymers in the concrete. Disregarding some small differences during the first hours of monitoring (which could be related to the presence of air bubbles or even the swelling SAP particles in the vicinity of the sensors), the resistivity values of both concrete mixtures at levels 0 and 1 were comparable during the first 12–24 h of measurements. After that, however, the curves started to diverge, which was not so pronounced at levels 2 and 3. The reference concrete reached the higher resistivity values over time. In addition, the moment where the curves started to diverge also shifted to a later time for deeper levels. The explanation for that lies in the kinetics of water sorption and desorption in hardening cementitious materials. During the mixing of the concrete with SAPs, they are added to the dry materials in the form of a dry powder, which is uniformly distributed over the volume of the material. Once water is added to the mixture, the SAPs absorb the amount of water intended for internal curing and become gel-like water-filled reservoirs. Later, once the mixing water is consumed by the cement hydration, and the humidity levels of the hardening concrete start to drop, the water stored in the SAPs starts to progressively be released to maintain the high humidity levels. This water release might be associated with the reduction in the resistivity values observed in levels 0, 1, and 2. As the humidity in room 20/60 was lower than the humidity inside the fresh concrete cube, evaporation also played an important role in the water movement inside the concrete. Not only did the cement hydration consume water, but the humidity gradient also increased due to the water loss to the environment, which accelerated the drying process in the layers of concrete closer to the surface. The drying of the outer layers then forced the release of water from the SAPs prematurely, which is observed in The quality control of concrete during construction is critical for ensuring the long-term durability and service life of concrete infrastructure. Measuring fresh and early age concrete properties, as well as the efficiency of the curing process, can provide valuable information that can help to ensure the quality control of concrete. In this study, we presented a cost-effective PCB-based array of resistivity sensors that can measure concrete resistivity at different depths from the fresh state of concrete through early age development. The sensor was able to detect the effects of drying over different layers in the concrete depth, under different drying conditions, and to characterize the acceleration of the hydration at early ages when the concrete was subjected to higher temperatures. In addition, the sensors were able to distinguish the drying pattern of concrete mixtures with and without superabsorbent polymers used as curing agents, and provided insights allowing for the identification of the water release by superabsorbent polymers when used as internal curing agents. This might represent the possibility of using the sensors as a new testing method when investigating the efficiency of SAPs for use in concrete.When correlating the strength development of the concrete under different curing conditions with the values of resistivity measured at different locations, it was observed that for curing conditions without severe drying or faster hydration, there was a strong correlation between compressive strength and resistivity, regardless of the location where the resistivity was measured. In contrast, when the concrete was subjected to higher curing temperatures and more severe drying conditions, although the correlation between compressive strength and resistivity was still high, it was also slightly lower for the resistivity values measured near the concrete surface in comparison with the rooms with less severe curing conditions. In summary, the solution presented in this exploratory study has the potential to enable the implementation of a network of sensors throughout the structure, providing more representative values and better estimates of strength development and curing conditions, ultimately ensuring the long-term durability of concrete infrastructure.


Soft tissue defects resulting from trauma and musculoskeletal infections cancomplicate surgical treatment. Appropriate temporary coverage of thesedefects is essential to achieve the best outcomes for necessary plastic softtissue defect reconstruction. The antibiotic bead pouch technique is areasonable surgical approach for managing temporary soft tissue defectsfollowing adequate surgical debridement. This technique involves the use ofsmall diameter antibiotic-loaded bone cement beads to fill the dead spacecreated by debridement. By applying antibiotics to the bone cement andcovering the beads with an artificial skin graft, high local dosages ofantibiotics can be achieved, resulting in the creation of a sterile woundthat offers the best starting position for soft tissue and bone defectreconstruction.This narrative review describes the rationale for using this technique,including its advantages and disadvantages, as well as pearls and pitfallsassociated with its use in daily practice. In addition, the article providesa comprehensive overview of the literature that has been published since thetechnique was introduced in surgical practice. In type IIIcfractures, nerve or vessel injuries are also present . Soft tissue damage is a common problem in bone infection,with the extent of soft tissue damage predisposing to the development offracture-related infections (FRIs). The incidence of FRIs varies dependingon the anatomic region, with rates ranging from 1.8 % in Gustilo type Ifractures to 42.9 % in Gustilo type IIIb tibial fractures . When soft tissue defects complicate open fracturemanagement, best possible prophylaxis is required to avoid FRI. When alreadyestablished FRI is present, the goals of therapy are infection eradication and softtissue and bone defect reconstruction. In cases where FRI has already developed, thegoals of therapy are to eradicate infection, reconstruct soft tissue andbone defects, and minimize the socioeconomic and treatment burden forpatients .Chronic osteomyelitis is characterized by infected, dead bone within acompromised soft tissue envelope, according to George Cierny, who paved theway for better understanding and treatment of this condition. Treatment ofchronic osteomyelitis and FRI typically involves adequate bony debridementto remove necrotic bone tissues, as well as resection of compromised softtissues, followed by plastic surgical flap coverage and antibiotictherapy .There are several therapy options available for temporary soft tissuecoverage. Sterile dressings with gauze or towels are a simple andinexpensive option but require regular changes and can be uncomfortable forthe patient. Negative pressure wound therapy (NPWT), also known asvacuum-assisted wound closure, has been widely used in surgical therapysince the early 1990s, particularly in trauma and orthopedic surgery. NPWTimproves local blood supply and simultaneously suctions wound exudate,promoting wound healing Low-quality data indicate that NPWT is beneficialfor wound closure and can reduce hospital-stay time .However, high bacterial loads have been found in foams removed from NPWT. The clinical relevance of this observation is notclear, but it may be one reason why definite soft tissue closure isrecommended within 7 d .The use of an antibiotic bead pouch is a viable option for temporary softtissue coverage. Adequate temporary soft tissue coverage is essential forthe successful treatment of traumatic or posttraumatic soft tissue defects.A healthy soft tissue envelope ensures proper blood supply to the area ofbone healing and protects the healing tissues from bacterial contamination.Furthermore, sufficient blood supply provides ample perfusion of immunecells and systemically administered antibiotics . In contaminated wounds after an open fracture orestablished FRIs, achieving a healthy wound that allows desired healing iscrucial. Thorough debridement and irrigation reduce the bacterial load byremoving necrotic soft tissue. The reduction of the pathogen burden andviable, well-vascularized tissue is essential to enable the host immunesystem to eradicate wound infection-causing pathogens . The debridement of bone and soft tissue usually results ina tissue defect, which is usually filled with a hematoma. This providesnutrients for bacterial growth and can be considered a favorableenvironment for bacterial growth. To avoid bacterial growth by reducing thevolume of dead space and filling it with antibiotics, the management of deadspace has become a cornerstone of septic surgery principles. Differentbiomaterials are available for dead space management, and PMMA beads havebeen used as dead space fillers for more than 40 years . Calcium sulfate is another biomaterial that enables local antibioticapplication and has been historically used as a bone void filler. It is alsobeing studied for dead space management of soft tissues. A concern with itsuse in soft tissues is the induction of heterotopic ossification, which wasnot confirmed in an animal model . Meanwhile, other viableoptions for local application of antibiotics exists in surgical practice. In recent years, application of pure antibiotic powder such as vancomycin hasbeen proven to reduce infection risk in fracture care . In addition, collagen sponges soaked with antibiotics areanother option to apply antibiotics to the surgical site . Both options, collagen sponges and powder, have their limitations fordead space management and wounds that require temporary soft tissue coverage.Sustained release is not provided when powder is administered locally. Bothantibiotic powder and sponges are not able to fill the dead space as adequately as biomaterials with solid consistency, such as PMMA bone cements orcalcium sulfate beads. However, the major drawback of using calcium sulfate beads in an antibiotic bead pouch is its cost. PMMA bone cements are by farless expensive and therefore a more feasible option. Local antibioticcarriers allow for very high local antibiotic concentrations that do notresult in significant negative systemic side effects. Due to the highantibiotic concentrations, biofilms and bacteria initially tested resistantin conventional culture diagnostics can still be eradicated . The preparation of small antibiotic-loaded bone cement beads isparticularly useful, since the increased surface area can significantlyincrease the antibiotic release from the polymethyl methacrylate (PMMA)cement .During the surgical procedure, proper wound irrigation should be performedafter adequate debridement . Additionally, systemicantibiotic prophylaxis or therapy, as well as the application of localantibiotic carriers, is an established standard and should be based on theform of therapy (prophylaxis or therapy) and the soft tissue situation. Foropen fractures with extensive soft tissue involvement (Gustilo type III),3 d of systemic antibiotic therapy should be administered, coveringboth gram-positive and gram-negative bacteria. Recommended antibioticcombinations for infection prophylaxis in open type III Gustilo fracturesinclude ampicillin and sulbactam, piperacillin, and tazobactam, as well asceftriaxone and vancomycin . Typically, 6to 12 weeks of systemic targeted antibiotic therapy is required for boneinfections . Considering this orchestrated approach, theantibiotic bead pouch is a viable surgical method for temporary soft tissuecoverage, adequate dead space management, and reduction of bacterial load toachieve the long-term therapeutic goal of limb reconstruction andrestoration of function, which will be outlined in the following sections.2In the initial treatment of open fractures (Gustilo type IIIb and IIIc), the antibiotic bead pouch technique is a suitable therapy option for infectionprevention. If primary wound closure is achievable , a local antibiotic carrier should be applied to the fracturesite, as it has been shown to reduce reinfection and osteomyelitis rates. In such a scenario, an antibiotic bead pouch isusually not necessary, and primary wound closure is the surgical therapy ofchoice. However, in cases of extensive soft tissue damage (Gustilo type IIIband IIIc), temporary soft tissue coverage is required, and the antibioticbead pouch is a useful means to achieve temporary soft tissue coverage forinfection prevention. If surgical debridement of already establishedinfections such as FRIs and chronic osteomyelitis results in a soft tissuedefect with exposed bone, the antibiotic bead pouch is a suitable therapyoption to fill the dead space around the bone, creating an optimal situationfor plastic coverage. If coverage of the bone by muscle tissue is necessary,NPWT therapy may be useful in conditioning the wound bed early for meshgraft or other plastic procedures. In any case, plastic coverage should beaimed for within 7 d .In the author's experience, pure soft tissue defects without bonyinvolvement do not benefit from antibiotic bead pouch treatment. In case ofisolated soft tissue defects, there is no bony dead space that needs to beantibiotically shielded for subsequent bone reconstruction. NPWT therapy canusually condition the soft tissue for further plastic reconstructiveprocedures with good granulation tendency.3Thorough surgical debridement should be performed in cases like that of the38-year-old patient who suffered a Gustilo type IIIb distal tibial fracture as a result of a motorcycle accident.®; Heraeus, Wehrheim, Germany) with 2 g each of vancomycin and meropenempowder. After a curing time of 2 min, the mass was formed into beadswith the smallest possible diameter and placed into the situs. Theantibiotic-loaded PMMA cement beads were covered, and the wound was sealedwith a temporary skin substitute . Since the artificial skin doesnot cover viable soft tissues directly, it does not require regular changingand can remain in place until definite plastic coverage . In thiscase, the bead pouch remained in place for 3 weeks until free flapcoverage was performed by a microsurgeon.The complete resection of non-viable bone and soft tissue was necessary,followed by the stabilization of the fracture using external or internalosteosynthesis. In this particular case, thorough debridement was achievedthrough extensive wound irrigation with saline via jet lavage, using a totalof 9 L of saline, and treatment of bone and soft tissues withGranudacyn wound irrigation solution . Temporary soft tissue coverage was required untildefinitive plastic restoration could be performed through free flap surgery.For this purpose, an antibiotic bead pouch was utilized. At the instrumenttable, the surgical team mixed 40 g of PMMA cement  to create anantibiotic bead pouch , the reasons for deviating fromthese techniques in the present case are worth explaining for betterunderstanding of its practicability. Mixing different antibiotics providesseveral advantages. First, it allows for optimal empiric local antibiotictherapy, such as vancomycin and meropenem or vancomycin and gentamicin. Whenselecting local antibiotics for empirical therapy in PMMA, it is necessaryto consider the suspected pathogens causing the infection, as well as thetechnical feasibility of mixing antibiotics with bone cement. For thispurpose, antibiotics need to be heat resistant and available in powder form.Our previous investigations have identified several suitable antibioticcombination therapy options for empirical therapy. Among these, vancomycinand meropenem have proven to be useful and practical due to their physicalproperties during preparation with PMMA cement .Additionally, targeted antibiotic therapy can be performed using thistechnique. Although antibiotic combination preparations for bone cements areavailable on the market, they can be quite expensive and are mainly reservedfor revision arthroplasty cases where the aim is to prevent recurrence ofinfection while ensuring optimum stability of the cement and fixation ofrevision implants that will remain in the patient for life. In contrast, inthe case of PMMA bone cement spacers, stability is not of decisiveimportance for the antibiotic bead pouch. The PMMA bone cement primarilyfunctions as an antibiotic carrier and achieves a sterile wound, releasinghigh concentrations of antibiotics to the hematoma around the beads . The amount of antibiotics used in the described technique is based onthe current recommendation of a maximum admixture amount of 10 % (2 gvancomycin and 2 g meropenem is 4 g antibiotics per 40 g PMMA bone cement) .The technique of creating an antibiotic bead pouch involves the use of asynthetic skin substitute and the fabrication of antibiotic-laden beads.While previous publications have described covering bone cement balls withopsite film  or using commercially available gentamicin-loaded chains. The use of syntheticskin substitutes is also preferred, as they can be easily fixed into thewound edges and sealed, allowing for effortless daily dressing changes.Using film to seal the antibiotic beads may result in detachment from theskin and increased wound secretion, and changing the film may alsocontaminate the situs. Changing the antibiotic beads every 48–72 h isnot necessary when synthetic skin substitutes are used, and, with thoroughdebridement, the antibiotic bead pouch can be left in place until plasticreconstruction. The authors do not recommend staged revisions every 48–72 h, as this can result in pathogen changes, unnecessary consumption ofsurgical resources, and added stress for the patient .5Larger defects treated with the antibiotic bead pouch involve the risk ofextensive blood loss. Thorough debridement must nevertheless be performedbecause leaving infected and necrotic tissue in place is contrary to theactual therapeutic goal. However, clinical experience shows that if theclinical findings are not certain, a multi-stage procedure may be useful towait for demarcation of the vital from the avital tissue. In this way,unnecessarily wide, soft tissue resections, which are then again difficult toreconstruct, can be avoided. During debridement, subtle hemostasis ismandatory to prevent postoperative bleeding, and if bleeding occurs from thebone, particularly from the medullary canal, it can be closed with PMMA bonecement. Care should be taken not to apply the cement when it is still veryliquid, as it may be inserted deep into the medullary canal and thecancellous bone, making removal more difficult in a later surgicalprocedure. To avoid small antibiotic beads from disappearing unintentionallyinto the medullary canal, the authors recommend sealing the medullary canalwith PMMA bone cement. Removal of a PMMA bead can be tedious in the course and is avoidable. If one wishes to fill the medullarycanal with local antibiotic carriers, one can either use absorbableantibiotic carriers such as antibiotic fleece or apply antibiotic carrierscontaining calcium sulfate. Optional antibiotic bone-cement-coated rods canalso fill and additionally stabilize the affected bone Commercially available antibiotic bead chains can also be inserted into themedullary canal but are often difficult to remove in the course.The PMMA beads made in the wound bed should be as small as possible, with adiameter of 0.5–1 cm per bead being practical. The number of implanted beadsshould be noted in the surgical report and counterchecked in the subsequentoperation when the beads are removed. To facilitate removal in the follow-upsurgery, an antibiotic bead chain can be made with a nonabsorbable suture.The synthetic skin substitute used in the treatment should be removedcompletely during the follow-up surgery, and moistening is usually notnecessary. The PMMA bone cement beads and the hematoma surrounding themprevent larger granulation and ingrowth of the soft tissue into thesynthetic material.6http://PubMed.gov on 22 March 2023 yielded 24 publications related to “antibiotic bead pouch”. Antibiotic-loaded bonecement was first introduced in arthroplasty by Wilhelm Buchholz, and gentamicin-impregnated antibiotic beads wereintroduced as a local antibiotic carrier in the treatment of osteomyelitisby Klaus Klemm in the 1970s . However, it was not until 1988when two cases involving the use of gentamicin antibiotic beads in thetreatment of pacemaker infections demonstrated the practical clinicalapplication of the antibiotic bead pouch technique . Themost recent publication dedicated to this topic was in February 2023. The relatively rare indications and the heterogeneouspatient population in which the technique is used may explain the limitednumber of publications on the topic. However, the success of NPWT, which hasbeen an integral part of the daily routine of trauma surgery departmentssince the late 1990s, may also explain the low level of interest in theantibiotic bead pouch technique.A literature search conducted on Staphylococcus aureus and surgically treated after 6 h. Another experimental work in a goat model compared thecombination therapy of NPWT with PMMA beads as an antibiotic carrier with achitosan sponge as an antibiotic carrier. The use of an alternative chitosansponge showed higher efficacy than PMMA, but it has not yet been establishedin clinical use analogous to the experimental setup . Recently, Patterson et al. (2023) reported the results of using theantibiotic bead pouch for infection prevention in Gustilo IIIb open tibialshaft fractures and compared the outcome to NPWT treatment. The antibioticbead pouch group had a lower risk for FRI requiring debridement oramputation than the NPWT group .In 1989, the research group led by David Seligson in Louisville, Kentucky,first described the antibiotic bead pouch technique in a series of 21Gustilo II and III tibia fractures. PMMA beads were loaded with tobramycin,opsite film provided temporary soft tissue coverage, and temporary fracturestabilization was performed. Film changes were required every 48–72 h.The advantage of a hematoma in the fracture area with high local antibioticconcentrations was supported by a positive culture rate of only 5 out of 86in 46 procedures . The same research group conducted acomparative study immediately afterwards and demonstrated the positiveeffect of the technique on infection prevention in open Gustilo type IIIband IIIc fractures requiring plastic coverage. With the local application ofantibiotic bead chains in addition to systemic antibiotic prophylaxis, theosteomyelitis rate was significantly lower during the treatment course .Another publication, also from the Louisville group, reported a positiveculture rate of 6.25 % (78 out of 1248) in a series of 204 fractures(Gustilo I–III) in 1993. On average, antibiotic bead pouches were changedtwice (range of 1 to 7). Osteomyelitis developed in 0 % of Gustilo I fractures,2.4 % of Gustilo II fractures, and 5.5 % of Gustilo III fractures . In a subgroup analysis with an expanded group size, the study groupwas also able to demonstrate lower infection rates with earlier soft tissuecoverage after open fractures  . Particularly in severe soft tissue injuries in the setting ofopen fractures (Gustilo type IIIc), the antibiotic bead pouch techniquedemonstrated its positive effect (5 % infection with antibiotic bead pouchvs. 25 % without) . Keating et al. (1996)demonstrated the positive results regarding infection reduction in acomparative analysis of Gustilo II–IIIb tibial fractures (4 % withantibiotic bead pouch vs. 16 % without antibiotic bead pouch). A first comparative study comparing NPWT and theantibiotic bead pouch was published in 2010. More surgical procedures werenecessary when performing NPWT therapy, more MRSA infections occurred, andmore unplanned surgical wound revisions were required. In addition, theauthors demonstrated that in the United States, NPWT was USD 12 000 moreexpensive per patient compared to antibiotic bead pouch therapy. A study investigating the combined use of anantibiotic bead pouch with NPWT in a goat model was first published in 2012.It showed that the additional NPWT significantly reduced the efficiency ofthe antibiotic bead pouch in terms of antiseptic effect. Thus, after 2 d without additional NPWT, 6 times fewer bacteria were found in woundspreviously contaminated with 7The antibiotic bead pouch technique is a valuable, uncomplicated, andcost-effective solution for temporary soft tissue coverage. It allows forthe delivery of high concentrations of antibiotics directly to the affectedarea, effectively reducing bacterial load and treating biofilm infections.This advantage is particularly relevant when compared to alternativetreatments such as negative wound pressure therapy.


While early appropriate antibiotic therapy is a proven means of limiting the progression of infections, especially bacteremia, empirical antibiotic therapy in sepsis is ineffective up to 30%. The aim of this study was to compare early blood culture testing protocols in terms of their ability to shorten the delay between blood sampling and appropriate antibiotic therapy.β-Lacta and oxidase tests (multitest period), or conventional identification and susceptibility tests only (reference period). Conventional identification and susceptibility tests were performed in parallel for all samples, as the gold standard.In this french observational study, we compared three blood culture testing protocols. Positive blood cultures were tested using either GenMark ePlex panels (multiplex PCR period), a combination of MRSA/SA PCR, Among the 270 patients with positive blood cultures included, early and conventional results were in good agreement, especially for the multitest period. The delay between a blood culture positivity and initial results was 3.8 (2.9–6.9) h in the multiplex PCR period, 2.6 (1.3–4.5) h in the multitest period and 3.7 (1.8–8.2) h in the reference period (p<0.01). Antibiotic therapy was initiated or adjusted in 68 patients based on early analysis results. The proportion of patients receiving appropriate antibiotic therapy within 48 h of blood sampling was higher in the multiplex PCR and multitest periods, (respectively 90% and 88%) than in the reference period (71%).These results suggest rapid bacterial identification and antibiotic resistance tests are feasible, efficient and can expedite appropriate antibiotic therapy. Bloodstream infections are associated with high morbidity and mortality and the increase in multidrug resistant pathogens has made them increasingly difficult to treat . IdentifIn this study, we compared in three consecutive periods, three blood culture testing strategies based on m-PCR and multiple rapid tests with conventional Gram staining, to investigate whether the new approaches are feasible and shorten the time to appropriate antibiotic therapy. The main objective of the study was to determine the feasibility and performance of multiple rapid tests and m-PCR tests in clinical practice and compare the effectiveness of the two methods. The secondary objective was to determine whether either approach reduced the delay between blood sampling and appropriate antibiotic therapy.β-Lacta and oxidase tests , blood cultures were tested using GenMark ePlex blood culture identification panels, between 30 April and 21 July 2019 (the reference period), blood cultures were tested by conventional methods, and between 22 July and 20 September 2019 (the multitest period), a combination of rapid MRSA/SA PCR, se tests Figure 1) and Gram staining was immediately performed on positive cultures. Bacterial identification and antimicrobial susceptibility tests were then performed on positive blood cultures by microbiology laboratory staff during working hours  using a VITEK 2 system .All blood samples were immediately incubated on a round-the-clock basis in a BACT/ALERT 3D instrument  . The ePlβ-Lacta tests  for gram negative bacteria, and MRSA/SA tests for clustered gram positive cocci .During the multiple rapid test (multitest) period, blood cultures were tested based on Gram stain results using a combination of three rapid tests with a decision algorithm to select the best possible combination based on Gram-staining results Figure 1During the reference period, the gram stain was considered as the “early analysis” and was communicated to the physicians to help them to adapt empirical antibiotic therapy. The term was also changed in All blood culture results were immediately communicated to the attending physician. Treatment protocols and guidelines were established for each period by a working group of clinical biochemists, infectious diseases specialists, and intensive care physicians .The following data were collected from the patients’ electronic medical records: age, gender, identified pathogens, infection sites, ICU admission, SAPS 2 score, need for vasopressor therapy, invasive mechanical ventilation or renal replacement therapy, length of hospital stay and mortality. All microbiological results were collected. The final results of the conventional identification and susceptibility tests were used as reference to assess the results of the m-PCR and rapid tests. The times of blood sampling, positive blood culture alerts, early analysis results and final results were recorded. The timing and choice of antibiotics were recorded and defined for each step: pre-existing antibiotic therapy (started before blood sampling), empirical antibiotic therapy (initiated between the sample collection and antibiogram result) and antibiotic therapy based on early analysis results . We also evaluated the time between blood culture positivity and test results for each approach.The clinical impact of each technique was assessed in terms of the time from blood culture collection to the introduction of appropriate antibiotic therapy. These delays were compared between patients treated in the different periods and for subgroups of patients with confirmed bacteremia and with or without appropriate antibiotic therapy at the release of early analysis results. Patient outcomes were evaluated in terms of ICU admission, length of hospital stay and in-hospital mortality. Duration of exposure to broad-spectrum antibiotics was also considered.Continuous variables were expressed as median (interquartile range), and categorical variables were expressed as numbers and percentages. Between-group comparisons were performed using ANOVA tests  or Kruskal-Wallis tests (if the distribution was skewed) for continuous variables and using chi-square tests for categorical variables. A p-value <0.05 was deemed significant. All analyses were performed with the software SPSS . The diagnostic performance of the rapid tests (sensitivity and specificity) were calculated using the results of the conventional tests as the gold standard . The gram distribution was similar in the three periods (51% of gram-negative bacteria and 47% of gram-positive bacteria). A small proportion of cases (1% in each period) involved fungal infections (p = 0.06)Two hundred and seventy patients were included in total, 90 in each of the three periods, from the medical, geriatric, surgical, emergency, and intensive care units. All patients had a positive blood culture with an unknown pathogenic microorganism in the preceding 48 hours. Patient characteristics and biochemical results are summarized in fections Table 2.The performance of the m-PCR tests was variable with sensitivities for bacterial identification and antibiotic resistance of 93% and 78%, respectively, specificities of 40% and 100%, positive predictive values of 89% and 100%, and negative predictive values of 55% and 98%, respectively see Table 2.Empirical antibiotic therapy was initiated in 229 patients (85%) before early analysis results were available and was inappropriate in 44 of these patients (19%) before early analysis results Figure 2The in-hospital mortality rate was 11.5% overall (31/270) and was slightly lower  in the reference period (7%) than in the m-PCR and multitest periods . The median length of hospital stay was 9 (4–22.5) days and did not differ between periods. Broad-spectrum antibiotic consumption was similar in the three periods  and in-hospital mortality (11%) . Our resThe use of rapid techniques was not associated with reduced morbidity or mortality, possibly because the study was underpowered to detect this. Another limitation of the study may be that the severity of patients’ symptoms differed, but not significantly, between the three periods. This could explain why no significant difference was observed in the consumption of broad-spectrum antibiotics.In these patients with positive blood cultures, the diagnostic performance of multiple rapid tests performed according to a decision algorithm was excellent and superior to that of ePlex assay m-PCR tests. Both rapid techniques were easily incorporated into the laboratory workflow alongside conventional cultures and led to patients receiving appropriate antibiotic therapy sooner. Larger studies with a greater prevalence of resistant pathogens are required to estimate the impact of these tests on length of hospital stay and mortality.The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.The studies involving human participants were reviewed and approved by Declaration of Helsinki. Written consent was not required because of the observational nature of the study. All patients received general information about research activities and data management policies. Written informed consent for participation was not required for this study in accordance with the national legislation and the institutional requirements.P-AC, EV, NR, LP, and CP designed the study. P-AC and NR organized and performed the data collection. P-AC and EV performed the statistical analysis. P-AC, EV, NR, LP, and CP analyzed and interpreted the data. P-AC and EV wrote the manuscript. All authors had full access to the study data, contributed to drafting the manuscript or critically revised its content, approved the final version of the manuscript, and take responsibility for the integrity of the data and the accuracy of the data analysis. EV is the guarantor of the paper. All authors contributed to the article and approved the submitted version.


Rapid multiplex polymerase chain reaction (mPCR) point-of-care tests detect a variety of viral respiratory pathogens. The impact of mPCR results on antibiotic prescribing in the ED or downstream is not well understood. The purpose of this study was to assess the impact of positive viral mPCR results on antibiotic prescribing for patients presenting with respiratory symptomsin the ED.This retrospective cohort study included adult patients presenting to the ED with respiratory symptoms and a positive rapid upper RTI mPCR for a non-SARs-CoV-2 viral pathogen between 11/1/2021 and 10/31/2022. The primary objective was to describe the proportion of patients with appropriate antibiotic management within 24 hours of positive mPCR result. Appropriate management was defined as patients without risk factors for bacterial co-infection who did not receive or continue antibiotic therapy. Those with co-infection risk factors prescribed antibiotic therapy were also considered appropriate. This was determined through independent pharmacist and ID physician review. Secondary objectives compared patient outcomes of those appropriately vs inappropriately managed and admitted vs discharged home from ED. Risk factors for inappropriate antibiotic decisions were also evaluated using logistic regression.250 patients were included, 206 (82.4%) with appropriate management and 44 (17.6%) with inappropriate management. 164 (65.5%) patients were not prescribed empiric or definitive antibiotics. 39 (15.6%) patients empirically received antibiotics prior to mPCR; 9 (23%) were discontinued following positive viral result. Patients discharged home from the ED were more likely to have appropriate antibiotic management than those admitted . Patients with inappropriate antibiotic management were more likely to be readmitted to the hospital within 30 days . Purulent sputum (OR 3.61 [95% CI 1.64-8]) and unilobar infiltrate (OR 3.03 [1.22-7.58]) were independent risk factors for inappropriate antibiotic management.Rapid viral RTI mPCR testing in the ED resulted in a high level of appropriate antibiotic management, with most patients not being prescribed antibiotics.All Authors: No reported disclosures


Treatment for one patient affected by knee Candida albicans PJI in the DACRI group was not successful. In conclusion, DAPRI and DACRI appear to be safe and effective treatments for PJIs. This evidence will encourage the development of new clinical research into local carriers and coatings for use in acute implant-associated infections.Periprosthetic joint infections (PJI) are among the most difficult complications to treat in orthopaedic surgery. Debridement, antibiotics, and implant retention (DAIR) represent an efficient strategy for acute PJI, especially when resorbable local antibiotic carriers and coatings are used. The aim of this pilot study was to evaluate the difference between using antibiotic-loaded hydrogel (ALH) and calcium sulphate (CS) beads in the DAIR procedure. We analysed 16 patients who had been treated since 2018 for acute PJI, namely eight patients with knee PJI (50%), seven with hip PJI (43.7%), and one with shoulder PJI (6.2%). Nine patients were treated with the Debridement, Antibiotic Coating and Retention of the Implant (DACRI) method, while seven were treated with the Debridement, Antibiotic Pearls, Retention of the Implant (DAPRI) method. We found no significant differences between the two groups in terms of age, sex, the American Society of Anesthesiologists risk score, Charlson Comorbidity Index, localisation, days from onset to diagnosis and pathogenesis. Furthermore, no differences were found between the DACRI and DAPRI groups in terms of infection control (15 patients, 93.75% with  Periprosthetic joint infection (PJI) is the most devastating complication in joint replacement surgery, burdened by a high comorbidity and mortality rate ,2. BiofiAntibiotic-loaded hydrogels (ALH) are applied differently than other carrier. Hydrogels are used as a tool to prevent biofilm adhesion in newly implanted hardware with a burst release of the surgeon’s chosen antibiotic, which undergoes complete reabsorption via hydrolytic degradation within 72 h and completely releases the antibiotic contained within it . It is mThese local carriers could be used as an additional weapon in treating acute PJI alongside the standard DAIR procedure. The purpose of this study was to conduct preliminary research to assess whether applying ALH in a DAIR procedure is as effective as CS beads application in treating acute PJI in a single-centre experience. The author’s hypothesis was that local antibiotic delivery was clinically effective regardless of the type of carrier used if targeted to the pathogens.Staphylococcus aureus was the main pathogen  followed by Escherichia coli and Pseudomonas aeruginosa . One patient had culture-negative PJI (6.2%). Patients were divided into two groups: the first group was treated with DACRI  and the second group was treated with DAPRI . There was no significant difference between age, sex, ASA, CCI, localization, or days from onset to diagnosis and aetiology. Among all PJIs treated since 2018, we evaluated 16 cases that fulfilled the inclusion criteria, with a mean age of 67.3 ± 10.8 years. Eight of the patients were female (50%). The mean Charlson Comorbidity Index (CCI) was 3.1 ± 2.8 (range 0–10), and the mean American Society of Anesthesiologists (ASA) risk score was 2.2 ± 0.4. Eight patients had knee PJI (50%), seven were affected by hip PJI (43.7%), and one had shoulder PJI (6.2%). Eight PJI occurred postoperatively (50%), and eight were defined as hematogenous late acute infections. The mean time between the onset of infection and diagnosis was 22.1 ± 9.1 days. Four patients had polymicrobial infections (25%), three of which had postoperative PJI. Streptococcus dysgalactiae PJI and the third had a polymicrobial PJI  isolated preoperatively. In both cases, ALH loaded with vancomycin was used. The third case was a Candida albicans PJI in which ALH was loaded with fluconazole. The mean length of stay was 23 days, in which systemic antibiotic therapy was administered via IV. After discharge, oral antibiotic therapy was administered for 12 weeks postoperatively.Nine patients were treated with DACRI and seven with DAPRI . When feCandida albicans PJI that relapsed after antifungal therapy discontinuation. The patient achieved infection control after a two-stage exchange followed by antifungal suppressive therapy prolonged one year after surgery. The mean C-reactive protein (CRP) at the last follow-up was 3.7 ± 3.7 mg/L. No differences were found between the DACRI and DAPRI groups in terms of infection control (p = 0.3624) and CRP values (p = 0.2680). A statistically significant difference was observed in terms of follow-up between DACRI and DAPRI  with p = 0.0007. After a mean follow-up of 26.1 ± 22.2 months, infection control with no need for further antibiotic therapy was achieved in fifteen patients (93.8%). One patient underwent septic revision surgery in the DACRI group. The patient was affected by a knee Staphylococcus epidermidis has demonstrated successful staining of biofilms over implants in vitro [Debridement, irrigation, local antibiotic delivery, retention of fixed implants, and mobile parts exchange in a setting of a dedicated MDT approach achieved high rates of infection control in acute PJI in this series (93.8%). The DAIR procedure without antibiotic-loaded carriers appeared to have lower rates of infection control , but thein vitro . Its effin vitro . In the Since its proposal, the DAPRI procedure has improved the results achieved by the DAIR procedure by up to 77.5% of infection-free patients at a 2-year minimum follow-up . IndelliFrom the authors’ perspective, its long-lasting activity is not of any further benefit in a debridement procedure setting. After surgery, residual bacteria are exposed to an initial high burst of antibiotic release that decreases for days until its complete resorption. In the immediate aftermath of surgery, hematoma formation requires protection against bacteria colonization and biofilm persistence. After the first few days, what is not already defeated by local and systemic combinations at their highest concentrations cannot be further defeated. p = 0.11) [Bearing in mind this rationale, ALH plays a role in this particular treatment. The present study highlights how the DACRI procedure is non-inferior to the DAPRI procedure in this small series of patients. ALH protects the surfaces of the implant from recolonization and acts as a local burst release of antibiotics during the first few days. Locally administered doses of antibiotics differed significantly when we used DAC hydrogel, specifically 5 cc of hydrogel combined with 125 mg of vancomycin and 100 mg of gentamicin. When Stimulan was used, we added 5 cc of CS beads containing 500 mg of vancomycin and 120 mg of gentamicin. With the same amount of carrier, lower doses of antibiotic could be delivered with ALH but with a completely sudden release. CS beads require more time for resorption. For CS beads, the release rate is size-dependent since small beads resorb faster than large ones. Regarding limitations associated with using CS beads, i.e., hypercalcemia, heterotopic ossifications and prolonged wound discharge , none we = 0.11) . Frances = 0.11) .Clinical results of ALH applied to uncemented hip one-stage revision for PJIs were described in another case series of ten patients, where there was no infection recurrence after 3.1 years of follow-up . AnotherThe present study had several limitations, mostly due to its retrospective nature and not having used randomization to divide the two groups of treated subjects. Another limitation was the small sample size; however, it should be considered that this sample is homogeneous and treated with a systematic multidisciplinary team (MDT) approach. Another limitation was the length of the follow-up, which was done for a minimum of six months and turned out to be a variable with statistically significant differences between the DACRI and DAPRI groups. Debridement usually fails for recurrences , and eveIn conclusion, DAPRI and DACRI appear to be safe and effective treatments for PJIs. The evidence reported here encourages the authors to continue studying hydrogel application as an antibiotic local carrier in acute PJI. A prospective randomized trial is currently under evaluation by our research group. This evidence could also stimulate research in other fields of acute implant-associated infections, such as acute fracture-related infections, where local antibiotic strategies are currently under investigation. A similar study about ALH and CS beads in surgically treating acute and chronic fracture-related infections is already in progress at our institution. Nevertheless, randomized clinical trials with a longer follow-up and a greater sample size are necessary to confirm the data that emerged from our study.We conducted a retrospective single-centre study by reviewing the electronic medical records of our hospital for patients admitted with a diagnosis of acute PJI. The PJI definition was confirmed according to EBJIS criteria . PJIs weAll patients were treated by the same MDT focusing on bone and joint infections. In a multidisciplinary meeting, we discussed treatment strategies on a case-by-case basis and decided to combine them with local and systemic antibiotic therapy. All patients underwent one or multiple attempts of preoperative joint aspiration performed by orthopaedic surgeons where synovial fluid culture was sent in blood culture vials to the microbiology laboratory. Leucocyte count and PMN percentage were investigated in all cases. Whenever feasible, alpha-defensin and leukocyte esterase were performed. Based on the joint aspiration results, antibiotic local treatment was discussed and decided on in the MDT meeting. Preoperative antibiotic treatment was prescribed only if sepsis was present. In the other cases, patients started systemic therapy immediately before surgery. A total of 1 g of tranexamic acid was administered before surgery followed by another 1 g during surgery, immediately after new mobile components were implanted. Total knee debridement was conducted using a tourniquet. All surgeries were conducted by the first and senior authors (DDM and CV) with the same surgical equipment and the same debridement and irrigation protocol, beginning with previous scar excision, especially in postoperative cases. A methylene blue dye injection was performed before capsulotomy directly into the joint space to facilitate debridement . If a siDACRI procedure: In a group of patients, new mobile components and retained implant surfaces were coated with antibiotic-loaded hydrogel  before joint capsule closure. For every procedure, if vancomycin (250 mg) or gentamicin (100 mg) + vancomycin (125 mg) was used, 5 cc of hydrogel was used. If a combination of vancomycin and meropenem was used, 2 vials (5 cc each) containing one antibiotic each were prepared and then mixed together before coating. We also applied 250 mg of vancomycin and 250 mg of meropenem. The technique and the hydrogel used were described in a previous publication [lication .DAPRI procedure: In the other group of patients, new mobile components were inserted, and local antibiotic delivery was applied with the aforementioned technique described by Indelli et al. using 4.8 mm CS beads  [ele, UK) . If a coele, UK) .From 2018 to 2021, the antibiotic ALH was the only antibiotic carrier available in the hospital. Then, antibiotic-loaded CS beads became available in 2022, which we have since used routinely.In both cases, the joint capsule was closed in a water-tight fashion and wound closure was achieved with closed incisional negative pressure wound therapy.p < 0.05.Statistical analysis was performed with R version 3.4.4 (R Core Team (2018); R: A language and environment for statistical computing; R Foundation for Statistical Computing, Vienna, Austria). Categorical data were expressed as a percentage while continuous variables were reported as mean and range. Two sample t was used to compare continuous variables when appropriate. Fisher’s exact test was used to compare categorical variables. The level of significance was set at


The methodology of the water absorption tests reflected the conditions prevailing in the case of reinforced concrete structures operating below the water table. The microstructure of all materials was also assessed. Based on the conducted studies, it was found that both the fcm of concretes with the addition of CFA and its water absorption depended on the percentage of waste used, whereas both analyzed parameters were closely related to the structure of the cement matrix and interfacial transition zone area between the coarse aggregates and the paste. It should be stated that at the content of 20% CFA in the binder composition, an increase in the fcm of the material is observed, with a simultaneous increase in its water absorption. On the other hand, the addition of 30% CFA results in a significant decrease in both the strength of the composite and its water absorption. Thus, it was found that in the case of concretes with the addition of CFA, the strength of the material is directly proportional to the level of its water absorption. Moreover, the concrete including 30% CFA may increase the durability of reinforced concrete structures subjected to immersion conditions. From an application point of view, the obtained research results may be helpful in understanding the impact of the CFA additive on the level of water absorption in cement concretes with this waste.Studies were carried out to find a relation between the important physical property, i.e., water absorption and the main mechanical parameter, i.e., compressive strength ( Construction is a fast-growing industrial sector that meets the current trends of industrialization and infrastructure development ,2,3. ConUnfortunately, this highly useful construction material is still burdened with negative consequences resulting from the use of cement binders for its production ,9,10. ThTherefore, for many years, various types of measures have been taken to reduce the negative effects associated with the production of binders for the production of concrete ,17,18. OIt should also be noted that concretes made with the participation of SCMs allow not only reducing CO2 emissions generated during the burning of the Portland clinker  but alsoSilica fume (SF) ;Ground-granulated blast furnace slag (GGBS) ;Metakaolin (MK) ;Nanosilica (nS) ;C-S-H nanoseeds ;Waste glass, limestone powder, crumb rubber, and others .The most commonly used SCMs in the cement industry is undoubtedly coal fly ash (CFA) ,34,35. ICoal fly ash is an industrial by-product of hard coal burning in power plants and thermal power plants, and its disposal is a major problem faced by almost all countries in the world . On the On this basis, it was established that the addition of CFA in the range of up to 20% of cement weight improves the strength of the concrete composite and its fracture toughness both in single and complex stress states ,50. It aMoreover, it should be noted that most of the previous research and applications concern mainly concretes with a content of CFA up to 30% by weight of cement, i.e., low-volume fly ash concretes (LVFAC). For this reason, in the presented article, an important physical property affecting the durability of concretes with CFA in relation to LVFAC has been analyzed.This manuscript presents the assessment of water absorption (WA) for concretes modified with various amounts of CFA additives in the context of the durability assessment of this construction material. In addition to the analysis of the specific property of concrete containing CFA, the presented research also addresses the solution to the above-mentioned problems in terms of reducing CO2 emissions in the cement sector. For this reason, a more in-depth understanding of the next characteristic of CFA concrete may enable an increase in the use of this material in concrete technology and a more sustainable development of the construction industry.It should be noted that penetration into the concrete structure in an uncontrolled way of both excess moisture and harmful substances, which results in a decrease in its durability and activation of destructive processes in the material much faster ,57,58. FHowever, durability in the modern approach is considered in a holistic way, and it depends mainly on the microstructure of concrete . AccordiTherefore, water absorption of the hardened concrete is one of its basic qualitative features, which is taken into account already at the stage of designing the composition of the concrete mix . In addiFrom a physical point of view, water absorption is defined as the amount of water that concrete can absorb at atmospheric pressure. In order to ensure proper durability, its value should be within 4–6% , and wheFrom a practical point of view, there is a special group of building structures, which are much more affected by the water absorption problem than other buildings. These structures are primarily hydrotechnical structures, and all other structures occur within their location, e.g., retaining walls.In addition, one should realize that a significant part of hydrotechnical structures, after their completion and commissioning, works below the water table. Often in such situations, there is also a pressure of water on the structural element. Moreover, the flow of water within such structures is turbulent and thus causes intensive soaking of the concrete and its successive destruction .Therefore, it is very important to use a research methodology based on the assessment of this phenomenon for samples subjected to total immersion in water when assessing the water absorption of concrete. The results of such experiments will reflect, at least partially, the actual working conditions of hydrotechnical structures .Moreover, according to , the watHowever, the conditions of testing the water absorption of concrete in the case of soaking samples by contact with water on only one of their surfaces cannot be fully reliable in the assessment of the water absorption of the concretes used in hydrotechnical structures. However, they may concern the assessment of this property in relation to, for example, prefabricated concrete road accessories, e.g., curbs .Capillary porosity;The distribution of the size of capillary pores;The phase composition of the cement matrix.Water absorption of concrete, as well as its other properties, depends on many material and technological factors. However, its level is determined mainly by the microstructure of the cement paste, including primarily:The water/cement or water/binder ratio;The type of cement;The degree of cement hydration;The content of mineral additives.This, in turn, is due to the fact that the matrix in the concrete composite, as its continuous phase, is the basic trajectory for the migration of water and other substances into the concrete element. The degree of homogenization of the matrix is, in turn, related to: It is well-known that the dense microstructure of the cement matrix, with limited porosity, can be obtained by good compaction and curing of the concrete mix and the use of pozzolanic active mineral additives and admixtures as binder modifiers. Therefore, so far, studies have been conducted to analyze the impact of various modifications on the composition of concrete composites in terms of improving their water absorption. 65% GGBFS + 5%SF ;5% and 10% MK ,79;5% MK + 0.5% nylon fibers ;7% and 10% SF ,80;5% nS ;20% CFA + 1.5% glass fibers .On the basis of previous research, it has been found that a significant improvement in the water absorption of concrete is caused by modification of its structure by using: Previous research on the water absorption of modified concretes also included experiments evaluating this property for composites with the addition of CFA and the implementation of various other types of FA. Therefore, The replacement of mineral aggregates in the composition of the concrete mix with recycled aggregates ,89;The substitution of sand by FA + GGBFS and GGBFS + SF mixes ,99;A 5% addition of nS and the application of nanopowders to concretes containing CFA ,101,102.At this point, it should also be noted that a beneficial effect on the level of water absorption of the modified concretes, CFA and GGBFS, has been observed in the case of composites exposed to high temperatures ,89,96,97Analyzing the results of earlier studies on water absorption of concretes—especially those with the addition of CFA in the range of up to 30% of the weight of the cement—it should be stated that the results obtained from various laboratories, using different test methods, do not clearly indicate how the modification of the cement binder composition with this industrial waste affects the water absorption level of concrete composites. Thus, it is also difficult to conclude how such material modification may affect the durability of the concrete in question. It is also ambiguous to associate this physical parameter with the strength of hardened mature concrete. There is also a lack of a thorough analysis and explanation of the results obtained in relation to the microscale of the tested materials. Higher water absorption and, at the same time, reduced compressive strength ,88;Lower water absorption level with obviously still lower compressive strength than in the reference concrete and composites with CFA content below 30% ,91,92,94In some of the previous studies, concretes with the addition of CFA up to 30%, after 28 days, are characterized by: Since the level of water absorption of concrete is influenced by many factors (as mentioned above), and in addition, there is no clear data on the impact of CFA additive on this important physical property in the scope of concretes evaluated under water immersion conditions , extensiEvaluation of the influence of the CFA additive in the amounts of 0%, 20%, and 30% on the level of water absorption of concretes and their compressive strength after 28 days of curing;Analysis of the microstructure of the cement matrix of the tested concretes;Linking the results obtained in the macroscopic tests with observations of the structures of the analyzed composites in order to prepare recommendations helpful in the development of concrete mix compositions with the addition of CFA in an amount of up to 30% with increased durability.Its goals were the following:Locally available natural pit sand with a 2.0 mm maximum size was used as fine aggregate (FA) and natural gravel as a coarse aggregate (CA) with an 8.0 mm maximum size. The properties of both aggregates used were tabulated in OPC CEM I 32.5 R , produceBogue’s method in the case of OPC;Rietvield quantitative analysis in the case of CFA.Moreover, in order to know the mineralogical composition of the binders used, the following measurements methods were introduced: Based on the above studies, In addition, In these studies, tap water (W) was used, which met the requirements of standard provision EN 1008:2002 .3 and a dosing range of 0.1–1.0% of the mass of cement. The plasticizer was used in an amount of 0.6% of the mass of the binder.A calcium lignosulfonate-based plasticizer (P), Basf Liquol BV-18, used in this study had a density of 1.16 g/cmConstant: the total amount of the binder, the amount of coarse and fine aggregate, water, and the water–binder ratio: w/b = 0.4;Different series of concrete containing CFA amounts by weight: 0% (CFA-00), 20% (CFA-20), and 30% (CFA-30).Water absorption tests, WA, as well as compressive strength tests, fcm, were conducted on three types of concrete composites containing different amounts of OPC and CFA. Mix proportions were determined based on the following assumptions:The mix proportions of the concrete composition are shown in A laboratory concrete mixer with a 100 L capacity was utilized in the preparation of all concrete mixtures. The scheme, including all steps in this procedure, is shown in Subsequently, the mixture was poured into the molds. Mechanical vibration was applied for casting and compacting the fresh specimens. Cubes with a dimension of 150 × 150 × 150 mm were prepared from each mixture to determine compressive strength parameters and water absorption properties.After preparing specimens, they were stored in the casting room for 48 h. Specimens were covered by wet burlap to prevent water loss. After demolding the specimens, they were taken to a moist curing chamber and maintained at 20 ± 2 °C and more than 95% relative humidity for the first 14 days. Next, for the following two weeks until testing, the specimens were maintained under laboratory conditions.fcm, was tested in accordance with the European Standard EN 12390-3:2011 + AC:2012 [The compressive strength of concrete,  AC:2012  on 150 mConcrete absorption tests were carried out on cubic specimens with a side length of 150 mm (6 with each series of concrete) and were cured for 28 days by completely immersing the dried cubes see . During Soaking the samples with water a;Drying them to a constant mass b.The complete experiments of measuring the water absorption of the concrete containing CFA consisted of two basic stages shown in Initially, the samples were placed in a bath vessel on washers with a thickness of about 10 mm so that the distance between the samples was at least 15 mm;The bath was filled with water at a temperature of 18 ± 2 °C to half the height of the samples;After 24 h, water was added to the bath to a level 10 mm higher than the level of the samples; this level was maintained until the end of sample saturation;After another 24 h, the samples were removed from the water, dried to remove excess water, and weighed with an accuracy of 0.2%;The saturation of the samples lasted for the following days until two subsequent weighings showed no increase in mass a;After the samples were completely saturated, their mass was recorded, and then samples were placed in a dryer with hot air circulation in a Pol-Eko SLW 400 at 105 ± 5 °C b.Both in the process of saturating the samples with water and their drying, a number of samples did not exceed twelve pieces during one experiment . HoweverThe basic essential parameters of the dryer applied are summarized in In the dryer, the samples were dried to a constant weight and the result was recorded again. Measurements of the weight of the samples were made daily, with an accuracy of 1.0 g. PN-88/B-06250 , i.e., tEN 13369 , i.e., tAfter this stage, the determination of the water absorption levels in all materials was started. Calculations of water absorption were carried out according to the provisions of two standards:It should be noted that the water absorption test according to both standards looks the same. The differences in the provisions of both standards consisted in adopting a different percentage level of the difference in the weight of the samples subjected to subsequent drying, after which it was possible to determine the level of their water absorption. In the case of , the cham1 is the mass of the sample saturated with water to a constant mass (g), and m2 is the mass of the sample dried to a constant mass (g).After determining the moment at which, after two consecutive weighings of the samples, the recommendations of both standards were met, the level of water absorption in the samples was determined. Thus, the water absorption of the concrete specimens was calculated according to Equation (1):Find the influence of the effect of CFA particles on the water absorption of the analyzed composites;Evaluate the air voids of the cement matrixes including CFA;Determine the degree of the homogenization of individual materials;Assess the degree of reaction of CFA grains;Evaluate the Interfacial Transition Zone (ITZ) areas between the coarse aggregate and the paste.A microstructural structure analysis was performed in order to:Thanks to this information, it was possible to link the results of the water absorption research with the morphology of the matrixes of individual composites and draw conclusions about their possible susceptibility to penetration of water and other substances into the structure of the analyzed concretes in the context of their durability.The shape of the samples—rectangular concrete cube;Sample dimensions—10 × 10 × 3 mm;Preparation of the samples—taken as raw, i.e., the samples before the test were not polished or prepared in any other way;Number of samples—6 for each series of concrete;Number of photos per sample—30 photos were taken for each sample, from which the representative photos were selected;Magnifications used—200 to 80,000 times;Presentations—significant observed details like phases, pores, microcrack width in the ITZ area, and unreacted CFA particles were marked on the selected representative photos.A Quanta FEG 250 Scanning Electron Microscope (SEM) equipped with an energy dispersive spectroscopy (EDS EDAX) was used in this experiment. The procedure and crucial parameters related to the sample preparation process for SEM tests were as follows:fcm and WA were 47.51 MPa, 5.0%; 48.96 MPa, 5.3%, and 45.10 MPa, 4.6% for test concrete specimens CFA-00, CFA-20, and CFA-30, respectively. Therefore, it can be concluded that:The highest compressive strength had concrete CFA-20, while the lowest had CFA-30;When the content of CFA increased, the eater absorption of the composites with this waste clearly decreased ;The compressive strength behaved proportionally to the absorption by immersion , which wBased on the results in The obtained results can be explained by the different nature of the phenomena affecting the destructive processes in concrete, which differs from the factors determining the level of its permeability. This is especially true for concrete with the addition of CFA because in such materials CFA grains clearly modify both the ITZ area and the basic structure of the cement paste .It should be noted that the mechanism of transporting media and moisture deep into the concrete structure is mainly based on its migration through the system of large capillary pores in the area of the continuous phase of concrete, which is the cement matrix. However, the mechanism of concrete destruction is different and based on the development and propagation of microcracks through the contact zones of aggregate grains with cement paste.Although the ITZ area occupies as much as 1/3 to 1/2 of the entire volume of the hardened cement paste in concrete, it is known that it has a microstructure different from the microstructure of the paste inside the concrete composite. Since it is also the place where the first microcracks in concrete occur, it would seem that it may also have a significant share in the permeability of concrete, and thus affect the level of its water absorption. However, Ref.  shows thThe differences in both physical phenomena are shown in the example of the structure of the loaded concrete sample in In turn, water absorption is directly related to the structure of the continuous phase of concrete, i.e., the cement matrix. The greater tightness of this phase of the composite reduces the level of material water absorption. As mentioned above and demonstrated in , the ITZSuch a phenomenon has been observed among others in the case of composites with the addition of CFA, which do not contain coarse aggregate grains in their composition, i.e., mortars. In these composites, due to the limitation or even complete absence of weak points in the form of ITZ in the area of large aggregate grains, the strength of such materials shows convergence with the levels of their water absorption . A similTherefore, in order to determine the exact mechanism affecting the obtained test results, including primarily the water absorption, microstructural analyses of pieces of cement matrixes separated from the structures of all concretes have been carried out. In addition, the ITZ areas of all composites have been also studied. Association of observations of the microstructures of both zones of the composite—determining both the strength of the concrete and the level of its water absorption—was supposed to give an answer to the question of how the modification of the cement binder composition by the addition of CFA affects the change in the analyzed parameters in the concrete in question.The SEM photos for the three types of analyzed concrete samples with the same magnification  are shown in Presented the typical microstructure of unmodified concrete and contained mainly the continuously developing phases of calcium silicate hydrate (C-S-H) and calcium hydroxide (CH);Contained both the fibrous phase of the C-S-H and C-S-H structures that look like honeycombs  Compressive strength increased in concrete containing 20% CFA, i.e., in CFA-20, and decreased with an increase in CFA content up to 30%, i.e., in CFA-30;(2)Coal fly ash concrete made with up to a 30% replacement level showed better absorption behavior than reference concrete;(3)Both the compressive strength of concrete with the addition of CFA and its water absorption depend on the percentage of waste used, whereas both analyzed parameters are closely related to the structure of the cement matrix and ITZ areas between the coarse aggregate grains and paste;(4)At a content of 20% CFA in the binder composition, an increase in the compressive strength of the material is observed, with a simultaneous increase in its water absorption. On the other hand, the addition of 30% CFA results in a significant decrease in both the strength of the composite and its water absorption. Therefore, the compressive strength in concretes containing CFA behaved proportionally to the absorption by immersion;(5)The hydration products of concrete mixed with 20% CFA showed a loose and porous microstructure, and its water absorption increased accordingly;(6)The concrete composites including 30% CFA may increase the durability of reinforced concrete structures subjected to immersion conditions;(7)Finally, more investigations are needed on other parameters such as porosity, permeability, and depth of water penetration aspects of concrete made with CFA in order to better understand the influence of this waste on these specific and significant properties of concrete affecting the durability of these composites. The results of these studies will be the subject of subsequent publications.The idea behind this research was to produce concrete with improved durability and reduced CO