Concrete 3D printing is a novel construction method that can bring new horizons to the construction industry. However, there are still many challenges that limit its capabilities. Despite the huge research efforts, to date, there are still no standardized acceptance criteria and guidelines for the evaluation of printing concrete. Therefore, the main objective of this research was to develop 3D printing mixes with different aggregate-to-binder (a/b) ratios  and evaluate it in terms of its fresh printing properties, which include the workability, extrudability, setting time, open time, and buildability. The compressive strengths of cast and printed specimens were also tested to determine the effect of the layering process. The workability was evaluated using commonly used devices in the construction industry (slump and flow table test) and was monitored over time along with the penetration test to indicate the structuration rate of concrete. From the experimental results and observations, the flow test resulted in the best indication of the structuration rate (thixotropy) of concrete, followed by the penetration and slump tests. The a/b ratio affected all the investigated properties of the printing concrete. Higher a/b ratios resulted in increased structuration rate, buildability, and compressive strength of cast specimens. However, for printed specimens, the compressive strength decreased with the increase in a/b ratio due to increased thixotropy. Therefore, from the results of the present investigation, it can be concluded that high a/b ratios (>1.5) are not desirable for printing concrete. In addition to the three main components of concrete—aggregates, cement, and water—other materials such as additives could always be utilized to proportion the concrete to meet specific requirements. However, the use of conventional concrete involves formwork usage and makes the construction industry quite challenging. For example, the construction industry is a high-risk industry that involves the death and injury of many workers. In 2019, the Census of Fatal Occupational Injuries (CFOI) reported that the number of fatal work injuries reached up to 5333 in the United States with a worker dying every 99 min due to work-related injuries [Over the past decades, new innovative technology has been gaining ground, known as additive manufacturing. This technology has the potential to solve many of the problems the construction industry is facing such as those aforementioned. When compared to the conventional process, 3D printing technology may reduce the number of laborers in the construction field, may reduce construction time and materials used, and may eliminate formwork usage ,5,6. ThiAlthough this technology has remarkable benefits, there are still many challenges that restrict its application. In general, the material used for 3D printing should be designed to meet the requirements of the layering process and should be extrudable and buildable with strong interlayer strength. The challenges associated with the printing concrete were recently highlighted in  and inclLe et al.  conducteRheology in general is the science of studying the flow of a matter and its deformation under shear stress . Its basMalaeb et al.  evaluateZhang et al.  investigOn the basis of the available information from the literature, it is conspicuous that there is still no standard method and/or acceptance criteria to evaluate the workability of the printing concrete. Other tests to measure the yield stress as noted in  include In general, conventional test methods such as the slump and flow table test are preferable on-site for their ease of use. Flow test, in particular, may provide a good indication of the rheology of the concrete as it measures the resistance of concrete flow within a specific time interval. In fact, it was previously shown that a relationship exists between the rheological parameters and the flow table test ,24. MostDevelop 3D printing concrete utilizing available construction materials and evaluate its workability using commonly used devices in the construction industry (slump and flow tests) to determine the ranges at which extrudability and buildability are satisfied.Study the structuration rate of concrete using simple devices such as the slump, flow, and penetration tests. The results of the present investigation are expected to encourage researchers to use and explore simple equipment that can facilitate and standardize the evaluation of fresh printing concrete in the future.Study the effect of structuration rate on certain properties of printing concrete such as buildability and compressive strength.Therefore, from the conducted review, the main objectives of the current investigation are as follows: To achieve the main objectives of the study, printing concrete was produced using conventional mixing equipment at normal speeds. The a/b ratio is one of the factors that affects the structuration rate (thixotropy) of concrete and thus three main mixes were developed in this study with different a/b ratios of 1.2, 1.5, and 1.8 to assess its effect. The evaluated properties included the workability, extrudability, setting-time, open time, buildability, and compressive strength of both cast and printing specimens. Pearson correlation analysis was performed to determine which of the above-mentioned devices can best predict the structuration rate.The experimental investigation involved two phases of evaluation. Phase 1 involved mix optimization while phase 2 involved property evaluation of printing concrete. In phase 1 evaluation, two groups of mixes were developed to evaluate the effect of different supplementary cementitious materials (SCM) on the extrudability of the printing concrete as well as the compressive strength of cast specimens. The optimal mix of the two groups was selected and developed with three different aggregate-to-binder (a/b) ratios, and the setting-time of the three mixes were determined. Phase 1 is considered only a preliminary stage and, thus, the mixes were produced on a small scale using a Hobart mixer. For phase 2 evaluation, the main objective was to evaluate the effect of different aggregate to binder (a/b) ratios on the fresh printing properties. The evaluation criteria included the extrudability, setting-time, open-time, workability, and buildability, as well as the compressive strength of cast and printed specimens to indicate the concrete strength. Since this stage involved the evaluation of several properties, a conventional concrete mixer was used for the production of a larger-scale mixing to satisfy volume requirements. 2/kg Blaine fineness, were used in this study. Dune and crushed sand with fineness modulus of 0.48 and 3.2, respectively, were used with a maximum aggregate size of 4.75 mm. Note that these types of sand were selected in the present investigation as these are the commonly used types of fine aggregates in the UAE. The particles size distribution of the aggregates is illustrated in CEM-I 42.5-R0 and GB complying with BS EN 197-1:2011  and EN 1A commercially available superplasticizer (SP) (MasterGlenium SKY 504), complying with ASTM C-494 Type F&G, in addition to a viscosity modifier admixture (VMA) (MasterMatrix 110), were used for the printing concrete production. All mixes were prepared with a constant water-to-binder (w/b) ratio of 0.26. In phase 1 evaluation, the SP and VMA dosage had to be optimized to obtain the best extrudability results. All mixes were prepared using a Hobart mixer and followed the same procedure. First, all dry ingredients were added and mixed at a low speed of 140 ± 10 rpm for 1 min. Water and superplasticizer were then added and mixed at low and medium speeds (285 ± 10 rpm) for 2–3 min. After approximately 4 min, the VMA dosage was added, and mixing continued for 2 min. The Hobart mixer has proven to be very efficient for mixing concrete with a 0.26 w/b ratio. As for the conventional mixer, after the fine aggregates were added to the mixer, additional water was first added to the fine aggregates to account for the water absorption. The mixer was then rotated for 1–3 min, followed by the addition of the rest of the materials. The mixing water was added roughly in around two halves—the first half did not contain any SP, whereas the second half contained all the SP dosage. After achieving a homogenous distribution of all constituents, the VMA dosage was added. The conventional mixer had a speed of 17.5 rpm, and the mixing time to achieve a homogeneous mix was approximately 40 min. It is worth mentioning that the conventional mixer had to be tilted several times to make sure that the water, SP, and VMA had reached all the particles of the mix. This type of mixer was not very efficient for mixing concrete with a 0.26 w/b ratio, and thus it is expected that if the w/b ratio was lower than 0.26, other high-energy mixers would be required. This finding is in line with other studies [A custom-made 3D printer nozzle was manufactured to simulate an extrusion-based 3D printing process. A piston-type extruder was used, and moderate external vibration was applied to ensure that the mixture is adequately compacted inside the extruder. Once the mixture is filled in the 17 cm circular tube manually, the piston is used, and manual extrusion is performed to print the mortar layers. The pressure was kept constant throughout the extrusion process, and the printing rate was approximately 4.2 cm/s. Two nozzles were used, a circle nozzle with a diameter of 17 mm and a square nozzle with dimensions of 20 × 20 mm. This section explains all the conducted tests along with the devices used. Note that all fresh properties were tested once since it is time-sensitive. However, each mix was repeated at least three times to ensure repeatability of the results.The first criteria to be investigated for printing concrete is extrudability, which lies in a smooth grading of materials. Le et al.  and Ma eThe setting time was performed for the optimum mix with a/b ratios of 1.2, 1.5, and 1.8 as per ASTM C191-19 . The setTwo methods were adopted to study the workability of the printing concrete. The first test method involved performing the slump test. The standard slump cone has an internal diameter of 200 mm at the base and 100 mm at the top and a height of 300 mm. These dimensions are suitable for concrete that has an aggregate size of up to 37.5 mm. Since the concrete used in this study has a maximum aggregate size of 4.75 mm and could be considered as mortar, a cone with half the dimensions of the original slump cone was proposed. The base and top diameter and the height of the proposed cone are 100, 50, and 150 mm, respectively, as shown in The second test method selected was the flow of mortar test that was performed as per ASTM C1437-20 . The floThe ability of the printed layers to maintain their shape once extruded and bear the pressure exerted by the upper layers demonstrates the buildability. It is the vertical stacking of layers. Several studies have followed different approaches to assess shape stability (buildability). Some evaluated it by either determining the maximum number of layers that can be printed without noticeable deformation ,12 or byThe compressive strength was performed on all mixes of phase 1 and 2 evaluations. In phase 1, the strength of cast specimens of the two groups was tested at 3 days to have an indication of the concrete compressive strength while choosing the optimum mix. In phase 2, the compressive strength of both cast and printed specimens was performed mainly to indicate the effect of the layering process on the concrete. The compressive strength was performed as per ASTM C109-20 . The casThe results and discussions are organized based on the different phases of the investigation. The results in phase 1 are presented and discussed with respect to the extrudability, compressive strength, and setting time of the mixes using the Hobart mixer. On the other hand, the results in phase 2 are discussed based on the extrudability, setting time, open time, workability, buildability, and compressive strength of the mixes with different aggregate to binder (a/b) ratios  using the conventional mixer. The extrudability of the D-CM and D-GB mixes was the most difficult to adjust. Several trials were performed to achieve acceptable extrudability of the control mix (D-CM). VMA was initially not used in the control mixes to prevent additional costs. This mix failed as it was too stiff to extrude through the nozzle. Additional superplasticizer was added to adjust this mix; however, segregation occurred as a result and the mix became too flowable which led to blockage. Most of the mixes segregated or became unstable when either the water-to-binder ratio or the SP were increased; however, when VMA was used, segregation did not occur and extrudability was achieved, as shown in The use of a low w/b ratio in either the control mix or the D-GB mix caused the mix to be too stiff and pumpability and extrudability could not be achieved, and hence it was necessary to increase its flowability. The increase in flowability for extrusion can either be achieved by increasing the w/b ratio or SP dosage. This, in turn, may either cause the mix to segregate or result in unstable filaments. Therefore, the use of VMA is essential with the increase in w/b ratio or SP to adjust the viscosity of the mix and to account for the excessive water, which may increase the chances of blockage. As expected, the D-SF mix was much easier to extrude than the D-CM and D-GB mixes. The use of SF is well known to increase the cohesiveness of the mix which consequently improves the pumpability of the concrete and enhances its extrudability. To obtain the combined benefit of each of the GB and SF, a mix containing both materials was developed (D-GBSF).Similar to Group I, the use of GB and SF had the same effect on Group II mixes. The DC-CM and DC-GB mixes were the most difficult mixes to adjust for extrusion as compared to the DC-SF and DC-GBSF. The use of crushed sand along with dune sand facilitated the extrusion process for the four mixes as compared to the mixes of Group I. This is mainly attributed to the production of a smoother gradation curve, which thereby enhanced the extrusion performance. In this phase, all fresh properties in addition to the compressive strength of the mixes produced using the conventional mixer are discussed. As previously mentioned, the mixing speed for the conventional mixer was 17.5 rpm, which is considered relatively slow compared to the Hobart mixer. The mixing speed is one of the factors that affect mixing time, and thus several trials were first conducted to achieve the optimal mixing time while utilizing the conventional mixer. During the first trial, the mixing time was approximately around 20 min, and the mix was too stiff to extrude. Therefore, the mix required an increase in workability that could easily be achieved by increasing the SP dosage and/or the w/b ratio. However, to avoid any changes in the mix proportions, other factors were optimized such as the mixing time to account for the change in mixing speed/technique. The results show that when the mixing time was increased to 40 min, the mix was extrudable and the setting-time results were analogous to that of the Hobart mixer (≤15 min. difference), as illustrated in The workability results of the conventional mixer of the 1.2, 1.5, and 1.8 mixes are shown in Slump test: From Concrete with higher slump values (>90 mm) led to unstable filaments. As for the 0 slump, there were times at which the 0 slump provided acceptable extrudability and times at which the filaments were discontinuous and difficult to extrude. Hence, it can be concluded from the slump results that the slump only provides an indication of the extrudability, consistency, and homogeneity of the concrete, and cannot be completely relied on to evaluate the workability of the printing concrete. Extrudability has to be within a slump ranging from 85 to 9 mm; however, it is worth noting that these values will not always necessarily cause the concrete to pass the extrudability criteria, and hence other test methods should be proposed to evaluate the workability of the printing concrete. Mortar flow test: From the mortar flow test results, when the flow was around 56.4% and lower, the extrudability was affected. Results also showed that when the flow was beyond 95%, the filaments were unstable and inconsistent. In Structuration rate: The slopes of the curves shown in This method was adopted to find the relationship strength between each of the workability indicators with time as well as their mutual relationships to confirm the findings of the study. Since extrudability is a time-dependent factor, it is critical for the workability indicators to have a very strong relationship with time. When comparing each of the variables with time, all the coefficients had a negative value, indicating that as time increased, there was a loss in workability. Flow had the strongest relationship with time as the mixes had coefficients ranging from 0.98 to 0.99, followed by the penetration and slump, which had coefficients ranging from 0.87 to 0.91 and 0.76 to 0.89, respectively. Slump had the lowest relationship strength with time as compared to penetration and flow.From the slopes of the penetration and flow b,c, the This property was evaluated for the three mixes using both the circular and square nozzle. Buildability is dependent on all the factors that affect the structuration rate as well as the shape of the layers, which plays a role in providing stability to the structure. The factors that affect the structuration rate are the mix proportions, a/b ratio, w/b ratio, and materials used. Each of these has a significant impact on buildability. For example, it was shown in  that an From the results of this study, it was observed that as the a/b ratio increased, the buildability also increased, regardless of the shape of the nozzle. It is logical that if the mixes had similar flow (green strength) initially, the difference in buildability would not be detected during the first couple of minutes. However, as time increases beyond a few 10s of minutes, the rate of structuration (thixotropy) will play a role, and the layers of the mixes with lower a/b ratio will lose their shape stability upon extrusion as they have lower structuration rates and therefore would not have enough time to gain sufficient strength. For this study, within the first 15 min, all mixes had the same number of layers (10 layers) using the square nozzle. After approximately 15 min, the buildability for each mix varied. As previously stated, from the penetration and flow results, the structuration rate was highest for the 1.8 mix, followed by the 1.5 and 1.2 mixes. Thus, it was expected for the 1.8 mix to have the highest number of layers within the shortest time since it had the highest structuration rate. It is important to mention that the filaments were extruded from the same batch continuously with a time gap of approximately 1.5 min. The 1.8 mix showed the best performance, followed by the 1.5 and 1.2 mixes. The maximum number of layers reached by the circular nozzle was 10 layers for the 1.8 mix. External supports were required to go beyond 10 layers, which is because circular nozzles, in general, do not provide good shape stability and have a low area of contact compared to square and rectangular nozzles. The buildability of the circular nozzle of each of the 1.2, 1.5, and 1.8 mixes is demonstrated in The 20 × 20 mm square nozzle produced more stable filaments compared to the 17 mm circular nozzle. The buildability of the square nozzle for the three mixes is shown in It is worth mentioning that the workability of the mixes had to be adjusted to satisfy the buildability requirement. The computed slump and flow range to maintain printability were found to be within the ranges of 85 to 9 mm and 90.6 to 56%, respectively. These values provide good extrudability performance but do not satisfy the buildability requirement. The buildability demonstrated in The strength of the cast specimens of the 1.2, 1.5, and 1.8 mixes were 33, 34, and 34.5 MPa at 3 days, and 44.3, 52, and 53.8 MPa at 28 days, respectively. The results show that the compressive strength increased with the increase in a/b ratio. In For the printed specimens, the compressive strength decreased with the increase in a/b ratio. These results are contrary to the cast specimen results. Although high thixotropy is usually preferred for printing concrete for buildability purposes, as previously shown, several studies have reported that increased thixotropy can also lead to weak bonding between the layers and cause cold joints ,40. In fThe results also show that the printed specimens exhibited lower strength than that of the cast specimens, which is in line with previous studies ,42,43,44Moreover, enhancing the buildability of the 1.2 mix is more controllable as opposed to enhancing the interlayer strength of the 1.5 and 1.8 mixes. It can visually be seen from Mixing using the conventional mixer requires more time as compared to the Hobart mixer. The mixing time was significantly increased from 5 min on the Hobart mixer to 40 min on the conventional mixer as a result of changes in mixing speed/technique. This emphasizes the importance of optimizing the mixing time when using different concrete mixers. Overall, the conventional mixer was adequate to prepare mixes with 0.26 water-to-binder (w/b) ratio; however, for lower ratios, other high-energy mixers may be required.The workability results suggest that the optimal ranges to satisfy the extrudability are in the ranges of 85–9 mm and 90–56%, respectively. However, the lower limit may differ from one study to another, depending on the properties of the printer used.The structuration rate was indicated by the loss of each of the flow, slump, and penetration with time. From the Pearson correlation analysis results, it is suggested that flow and penetration provide the best indication of the structuration rate of concrete as compared to slump, and thus it is recommended to correlate these results with the rheological properties.The higher aggregate-to-binder (a/b) ratio increased both the buildability and compressive strength of cast specimens. However, for the printed specimens, the strength decreased with the increase in a/b ratio. The decrease was mainly due to an increase in thixotropy. This suggests that the optimal mix in this study was the 1.2 mix, and higher a/b ratios are not preferred for 3D printing or have to be used alongside other materials that lower the thixotropy to avoid the formation of weak interfaces.The main goal of the present investigation was to develop 3D-printing concrete using local construction materials and study its workability and structuration rate through employing commonly used devices. The critical early age properties studied included the extrudability, setting time, open time, workability, and buildability of printing concrete in addition to the compressive strength. The following conclusions are drawn from the study: From this study, it is concluded that flow and penetration show a good indication of the workability of printing concrete, and thus future research will be devoted to studying the correlation between each of these tests with the rheological parameters . The results of the present investigation show that simple devices can be used to describe some of the rheological properties of concrete, and therefore this can encourage researchers to evaluate the rheological properties using simpler devices that are currently needed due to the complexities associated with concrete rheometers. Additionally, from the lab observations, it is clear that the interlayer strength is also affected by different workability results, and the open time should not only be selected as the time that maintains acceptable extrudability, but also as the time that maintains adequate interlayer strength. Therefore, future research will be focused to study the effect of different factors on the interlayer strength of printing concrete.


Thus, it demonstrated that the positive effect of incorporation of PSBE in foamed concrete is linked to the pozzolanic effect whereby more calcium silicate hydrate (CSH) produces denser foamed concrete, which leads to higher strength, and it is less pore connected. In addition, the regression analysis shows strong correlation between density and compressive strength of the foamed concrete due to the R2 being closer to one. Thus, production of foamed concrete incorporating 30% PSBE might have potential for sustainable building materials.This study aims to obtain the relationship between density and compressive strength of foamed concrete. Foamed concrete is a preferred building material due to the low density of its concrete. In foamed concrete, the compressive strength reduces with decreasing density. Generally, a denser foamed concrete produces higher compressive strength and lower volume of voids. In the present study, the tests were carried out in stages in order to investigate the effect of sand–cement ratio, water to cement ratio, foam dosage, and dilution ratio on workability, density, and compressive strength of the control foamed concrete specimen. Next, the test obtained the optimum content of processed spent bleaching earth (PSBE) as partial cement replacement in the foamed concrete. Based on the experimental results, the use of 1:1.5 cement to sand ratio for the mortar mix specified the best performance for density, workability, and 28-day compressive strength. Increasing the sand to cement ratio increased the density and compressive strength of the mortar specimen. In addition, in the production of control foamed concrete, increasing the foam dosage reduced the density and compressive strength of the control specimen. Similarly with the dilution ratio, the compressive strength of the control foamed concrete decreased with an increasing dilution ratio. The employment of PSBE significantly influenced the density and compressive strength of the foamed concrete. An increase in the percentage of PSBE reduced the density of the foamed concrete. The compressive strength of the foamed concrete that incorporated PSBE increased with increasing PSBE content up to 30% PSBE. In conclusion, the compressive strength of foamed concrete depends on its density. It was revealed that the use of 30% PSBE as a replacement for cement meets the desired density of 1600 kg/m In recent years, the world has moved in a new direction by looking for lighter, durable, practical, economical, and environmentally sustainable materials to cater to the demands of modern construction. It is well known that concrete is a massive substance, and it is the main component used for construction. As a result, lightweight concrete has been introduced in the construction industry owing to its lower density, ease of handling, and most importantly, cost savings. Foamed concrete (FC) is a type of lightweight concrete which is produced through the combination of cement paste and preformed foams that cause the foam concrete to be lighter than normal concrete Brandt, 2009]. The best thing about foamed concrete is that it can be placed easily by pumping, if necessary, and does not require compaction, vibration, or levelling. It can be a highly workable concrete. Due to its porous or cellular make up, it provides significant benefit to the construction industry through its unique properties of being of a low density, flowing and self-compacting ,2, therm009. The 2). The incorporation of waste or industrial by-products, such as fly ash [Recently, a concrete containing pozzolanic material used as a cement replacement as a building material for the construction industry has been another approach for reducing greenhouse gases (GHG) emissions including carbon dioxide  as a partial cement replacement on the workability, density, and compressive strength of FC.In FC, the compressive strength reduces with decreasing the density . DransfiMcCarthy , and ShaMcCarthy  point ouMcCarthy , with deMcCarthy ,24,25,26McCarthy ,29,30,31McCarthy  reportedMcCarthy  said tha2 emission by delivering green technology and green living.PSBE is derived from waste material known as SBE from the palm oil industry, which causes environmental pollution as it is disposed at landfill. Globally, an estimated 2 million tons or more of SBE are utilized worldwide in the refining process based on worldwide production of more than 200 million tons of oils, which is equivalent to 1% mass of SBE being produced relative to the amount oil produced yearly . There aIn general, the properties of concrete depend on the properties of its constituent materials. However, the method used to design normal concrete mix cannot be used for designing a FC mix since it contains no coarse aggregate . The foa3. ASTM C796-19 [3), cement content , water , and sand . While, the compressive strength can be increased based on altering the constituents materials for a given density even though the strength of foamed concrete depends on its density. Usually, the mixture design strategy of the mortar or base mix  defines the strength of the FC. The target density, water and sand are calculated from the Equation (1) to Equation (2) [According to previous studies ,57,58,59 C796-19  and ACI  C796-19  stated ttion (2) .Target plastic density,w/c) represent water to cement ratio, (C) cement content, (Rc) any cement replacement and (Rs) any sand replacement.Water content,Furthermore, curing condition is one of the factors that influence the strength of FC. Curing is defined as the process of controlling the moisture and temperature during the cement hydration. James et al. ,63 studiAccording to Brady et al. , the wat2 emissions, and conserve energy and resources.All the reviewed above found that the properties of foamed concrete were influenced by the mix proportion components such as sand to cement ratio, water to cement ratio, foam volume, and binder and filler content. In addition, the employment of pozzolan in foamed concrete has demonstrated significant influence in improving the workability, compressive strength, and durability due to the ability of silica in the pozzolan material to convert the CH to CSH depends on the amorphous state, the amount of silica content and specific surface area. The pozzolanic reaction improves the properties of FC through the formation of additional CSH gel. The microstructure of the hardened paste of FC became denser because the larger spaces had been filled with CSH gel, and the capillary voids decreased and reduced in size. The denser structure leads to improve the strength and durability of FC. However, the effect of PSBE as partial cement replacement on the properties of FC is not yet available. Therefore, this research attempts to fill the gaps of knowledge by studying the effect of PSBE as partial cement replacement in FC on its workability, density, and compressive strength. This study aims to obtain the relationship between density and compressive strength of foamed concrete. Finally, the incorporation of PSBE as cement replacement can promote the use of waste materials and lead to reduce the COThe materials used to prepare specimens in this research are cement, water, silica sand, foaming agent, and pozzolan material known as processed spent bleaching earth (PSBE). Ordinary Portland cement (OPC) produced by YTL Cement Sdn. Bhd was used throughout the experimental work conforms to BS EN 197-1:2000 Type I. Tap water was used for mixing and curing purposes. The hydrolyzed protein foaming agent was manufactured by LCM Technology Sdn. Bhd. Kuantan is conforming to ASTM C796-19  The chems/c) ranging from 0.5 to 2.0, with an interval of 0.5. 3. According to Kavitha and Mallikarjunrao [w/c) for mortar or paste lies between 0.5 and 0.6, but with superplasticizer the w/c ratio lies between 0.17 and 0.19. In the mix design recommended by ACI 523.3R-14 [s/c ratio ranged from 0.29 to 3.66 with densities ranges from 800 to 1920 kg/m3. Further, the cement content for the common strength FC with a density range of 1100 to 1500 kg/m3 were adopted at 920 to 1260 kg/m3. For this reason, this study chose the s/c ratio from 0.5 to 2.0 and w/c ratio at 0.5 to produce a stable mix and achieve the design density and strength. Then, the selected mortar mix was used to produce a control FC, which was based on the results of density, workability, and average 28-day compressive strength.In this study, the trial mix was proportioned by volume due to ACI 523.3R-14  with sinarjunrao , several23.3R-14 , the s/c3) were produced by adjusting the dosage of pre-formed foam added into mortar paste. In general, the stability and consistency of FC were affected by foam volume and quality of foam, which was also affected by its density. Hence, it is important that the foam stability is maintained. According to ASTM C796 [3. From the previous study, the quality of the foam is affected by its density, dilution ratio, and mixing process with the mortar. The foam should be stable and not collapse during processing and placement. However, most of the studies on FC are concentrated on the effect of admixtures on its strength and other properties of FC but seldom on the effect of foam dosage [3 where the maximum average can be 55 kg/m3. According to Maldonado-valderrama, Martı, Martı, and Cabrerizo-vı [3 compared to synthetics. Based on previous study, the compressive strength drops sharply with an increased in foam volume ranging from 20% to 80%. It can be seen that the compressive strength of FC is influenced by foam volume. For FC with the foam volume ranging from 20% to 50%, it can reach a density of 65% to 35% of mortar and its strength within 30 to 10 MPa [w/c ratio and dilution ratio used being 0.5 and 1:33, respectively, as recommended by the manufacturer of foaming agent. Then, the best percentage of the foam dosage was selected to produce the control FC mix, which was based on the results of density, workability, and average 28-day compressive strength.Secondly, the control FC mix was prepared with different percentages of foam dosage to determine the best portion of foam used in the ranges of 20 to 35% with an interval of 5 from the mortar volume. As reported by Zhao et al. , the widSTM C796 , the denm dosage . Therefoerizo-vı  and Paneerizo-vı  the densw/c) within the range of 0.4 to 0.6 with an interval of 0.05. The s/c ratio, dilution ratio, and percentage of foam dosage in this trial mix were kept constant throughout at 1.5, 1:33, and 25%, respectively, based on previous trial mix recommendations. Kearsley [w/c ratio that the control FC was studied to produce is based on the results of density, workability, and average 28-day compressive strength.Thirdly, a trial mix was designed to determine the optimal water to cement ratio . Based on the previous trial mix, the nd Hilal ,79,80, i3. The next stage combines the foam in the cement slurry after the flow table test has been tested. Foam is added into the cement slurry and mixed continuously until the foam is homogeneously mixed with the slurry. After that, the fresh FC density was recorded by measuring 1 L of the mix and weighing it until 1600 kg/m3 is achieved. The fresh mix is poured into the cube specimen size 100 × 100 × 100 mm. Then, the specimens were removed from the mold after 24 h. All the equipment, materials, and procedures in producing foamed concrete have been implemented were in accordance with ASTM C796.The preparation of the specimens is divided into the mixing process, casting of specimens, and curing condition were reported as follows. The mixing process is presented in The present study was conducted to investigate the fresh properties of foamed concrete in terms of workability, consistency, and stability in the performance of flow behaviour derived from the mix design compositions. These tests were conducted to assess whether the calculated and actual water–cement ratios and foam required are sufficient. The workability of the FC was measured by using the flow table test. The flow table test consists of a flow table with a diameter of 255 mm and flows molds with a diameter of 100 mm. The flow table test was carried out by following the procedure of ASTM C1437-15 .In this study, density of FC was measured in three ways: fresh density, hardened density (air density), and oven dry density (dry density). The present investigation has followed the procedure of ASTM C796-19  for dete2.In this study, the cube specimens with dimension 100 mm × 100 mm × 100 mm were prepared and tested to determine the compressive strength of FC. The present investigation followed the procedure of ASTM C513-11  for dete3 to set a baseline to produce a control FC mix. s/c ratios. Increasing s/c ratios will increase the flow spread of fresh mortar. From the results, the flow spread value for s/c 0.5, 1.0, 1.5, and 2.0 was 190 mm, 195 mm, 210 mm, and 215 mm, respectively. The higher the flow spread value, the higher the workability of fresh mortar. The flow spread value increases when the sand to cement ratio increases. However, the number of the drop of flow table decreases for the same reason. According to the results, the s/c = 1.5 meets the required flow spread for type M mortar as stated in ASTM C109-16 [s/c ratios increases, the design and fresh density of mortar increases with increasing sand content. The design density of mortar for s/c 0.5, 1.0, 1.5, and 2.0 was 1981 kg/m3, 2088 kg/m3, 2167 kg/m3, and 2227 kg/m3, respectively. Nevertheless, the fresh density of mortar was slightly lower than design density in the range of 120 kg/m3. According to the literature review, this condition shows the comparable results that increasing s/c ratios will increase the density of mortar [s/c = 1.5 produces the acceptable density by 2167 kg/m3, which is close to desired density for mortar of 2100 kg/m3.The fresh density, flow table spread, number of the drop, stability, and consistency of different mortar mixes were studied. This study aimed to obtain the desired density for mortar 2100 kg/m C109-16 . Then, if mortar . Moreoves/c ratios. The 28-day compressive strength with s/c of 0.5, 1.0, 1.5, and 2.0 was 20 MPa, 23 MPa, 28 MPa, and 34 MPa, respectively. It is observed that the 28-day compressive strength and s/c ratios have a directly proportional relationship. When the sand to cement ratio increases, the compressive strength of mortar increases with the increase in the sand content. The s/c = 2.0 mix achieved the highest compressive strength value as compared to others. It indicates that the 28-day compressive strength at four different s/c ratios was found to be higher than 25 MPa. On the other hand, the dry density of mortar for s/c 0.5, 1.0, 1.5, and 2.0 was 1955 kg/m3, 2056 kg/m3, 2130 kg/m3, and 2200 kg/m3, respectively. According to data, the dry density of mortar was slightly higher than fresh density in ranges below 100 kg/m3. There is a directly proportional relationship between the dry density and compressive strength of mortar. The compressive strength of mortar increases with the increase in density.The result of dry density and 28-day compressive strength of mortar specimens are shown in 3 has to remain with acceptable strength. The relationship between compressive strength and dry density, as well as the effect of sand cement ratio, are shown in s/c = 2.0 mix achieved the highest compressive strength of 34 MPa as compared to others. In this study, optimal sand to cement ratio is chosen based on the target density of 2100 kg/m3. In most mixtures, s/c = 1.5 mixes show an acceptable density range of 2130 kg/m3 within the target density of 2100 kg/m3, which gives a compressive strength of 28 MPa.Here, the relationship between compressive strength and dry density of mortar was studied. The target mortar density of 2100 kg/m3 in order to set a baseline to produce a control FC mix. The fresh density, flow spread, number of drops, stability, and consistency of different percentages of foam dosage mixes were studied. The aim of this study is to obtain the desired density for the control mix 1600 kg/m3, 1875 kg/m3, 1817 kg/m3, and 1758 kg/m3, respectively. The fresh density of FC at foam dosages of 20%, 25%, 30%, and 35% was 1684 kg/m3, 1575 kg/m3, 1463 kg/m3, and 1355 kg/m3, respectively. There is a good relationship between design density and fresh density, whereby the fresh density of control FC mixes were decreased as higher percentages of foam dosage were added. This condition has a similar agreement with previous researchers by Bing et al. [Furthermore, it is clear that when the percentage of the foam dosage increases, the design and fresh density of the control FC mixes decreases, with increasing foam dosage. This indicates that density and foam dosage have an inversely proportional relationship. The design density of FC at foam dosages of 20%, 25%, 30%, and 35% was 1934 kg/ms/c = 1.5 mixes was 69% higher than the compressive strength of control FC at 28 days. It is concluded that compressive strength and foam dosage have an inversely proportional relationship. Furthermore, the dry density and fresh density of the control FC were way below that of the control mortar. Based on data, the dry density of 35% foam dosage was lowest with 1409 kg/m3, followed by 30% (1517 kg/m3), 25% (1625 kg/m3), and 20% (1734 kg/m3). However, the control FC shared the similar trend in mortar where the dry density was slightly higher than fresh density in ranges below 100 kg/m3. Additionally, this condition has a similar agreement with previous researchers Bing et al. [The dry density and 28-day compressive strength of the control FC specimens were investigated as shown in g et al. , found t3 has to be maintained with acceptable strength. The relationship between compressive strength and density, as well as the effect of percentage of foam dosage, was shown in 3. Thus, 25% of foam dosage was recommended due to its reasonable in density (1625 kg/m3), workability (205 mm), and 28-day compressive strength of the control FC (7.5 MPa).Here, the relationship between compressive strength and density of FC was studied. The target control FC density of 1600 kg/m3 to set a baseline to produce a control FC mix. w/c mix and the minimum flow was 200 mm on the 0.4 w/c mix. Although the flow spread diameter increased and the water–cement ratio increased and became more fluid, the number of the drop of flow table decreased due to the same factor. According to Zhao et al. [w/c ratio increased from 0.54 to 0.64. It shows that the amount of water affects the slurryness of FC, which achieves the target density. In addition, the flowability of fresh mix is related with the compressive strength of FC.The fresh density, flow spread, number of the drop, stability, and consistency of different water–cement ratio mixes were studied. This study aims to obtain the desired density for control mix 1600 kg/mo et al. , the flo3, 1660 kg/m3, 1620 kg/m3, 1580 kg/m3, and 1530 kg/m3, respectively. This condition has a similar agreement with Risdanareni et al. [w/c mix was equal to one and produced the density 1620 kg/m3 that was close to the desired density of 1600 kg/m3.Additionally, it clearly shown that when the water–cement ratio increases, the fresh density of control FC mixes increase. This indicating that the fresh density and water–cement ratio has a directly proportional relationship. The fresh density of FC at water–cement ratio of 0.4, 0.45, 0.5, 0.55, and 0.6 was 1690 kg/mi et al.  who repow/c of 0.50 mix. This condition has a similar agreement with Liu, Zhao, Hu, and Tang [The dry density and 28-day compressive strength of control FC specimens were studied, as shown in and Tang  who repoand Tang  and Risdand Tang , reportew/c) ratio is shown in w/c ratio and density. According to Mugahed et al. [w/c ratio leads to a decrease in the compressive strength of FC [w/c ratios produced different air void size, air void frequency, and spacing factor. Hence, air void size of FC increases with the increase in air content due to increasing the w/c ratio. Therefore, any variations in air void affect density, which significantly affects the compressive strength of FC. In this study, the highest compressive strength of FC was 7.5 MPa with the w/c of 0.50 mix as compared to others. Risdanareni et al. [w/c of 0.50 was higher than FC with w/c of 0.4. In most mixtures, the 0.5 w/c mix shows a stable and consistent density range of 1620 to 1630 kg/m3 within the target density of 1600 kg/m3 that gives a compressive strength of 7.5 MPa.Here, the relationship between compressive strength and density of foamed concrete was studied. The relationship between compressive strength and density, as well the effect of the water to cement , 1:30 (1540 kg/m3), 1:25 . Additionally, this condition has a similar agreement with previous research which found that increasing the dilution ratio results in the decreasing of density and the compressive strength of foamed concrete [The dry density and 28-day compressive strength of control FC specimens were studied as shown in concrete .3.At this point, the relationship between compressive strength and density of foamed concrete is studied. The relationship between compressive strength and density, as well as the effect of dilution is shown in The fresh density, flow table spread, number of the drop, stability, and consistency of different percentage of PSBE mixes were studied. This study aims to obtain the best mix proportions of FC containing PSBE (PFC). 3, produced by PFC5 mix, and followed by 1620 kg/m3 (PFC4), 1641 kg/m3 (PFC3), 1632 kg/m3 (PFC2), and 1630 kg/m3 (PFC1). It was a similar trend with control FC mix where the dry density was slightly higher than fresh density in the range of below 100 kg/m3. In this study, the higher the PSBE content in the mixture, the lower is the density due to the specific gravity of the cement, which is more than PSBE. According to Nambiar and Ramamurthy [The dry density and 28-day compressive strength of control FC and five different percentages of PSBE (PFC 1 to PFC5) were studied as shown in mamurthy , the denmamurthy . Other tmamurthy . The avemamurthy  and loadmamurthy  at 4.1 M2) and alumina (Al2O3) in an active form which reacts with the calcium hydroxide (CH) that was produced during hydration of cement to generate more calcium silicate hydrate (CSH) gel in the presence of water. Pozzolanic reaction contributes to more CH being removed from the paste by reaction with PSBE depending on the curing condition, particularly at the early stage of curing. Furthermore, the reduction of voids in PFC is linked to an increase in strength that is evident from the pozzolanic effect by which more CSH produces denser specimens since FC is a porous structure. A similar influence of pozzolan material on the strength of foamed concrete was reported by [The presence of PSBE in the foamed concrete is the principal reason for the compressive strength of PFC higher than FC. It contains silica  ratio for mortar mix specified the best performance for density, workability, and 28-day compressive strength.3 with 205 mm workability and 28-day compressive strength of 7.5 MPa. Similarly, the increasing of water cement ratio led to a decrease in compressive strength of FC. It was reported that the compressive strength of FC increased first and then decreased when the water cement ratio increased because the air void size of FC increases with the increase in air content due to increasing w/c ratio. In most mixture, the 0.5 w/c mix produced consistent results with density being 1630 kg/m3, 204 mm workability, and compressive strength of 7.5 MPa. Additionally, this condition has a similar trend in the increasing dilution ratio resulting in the decreasing of density and compressive strength of FC. The results showed that the optimal dilution ratio is 1:25 (1 L of foaming agent:25 L water) where the desired density for control FC 1630 kg/m3 with compressive strength of 10 MPa are met.For the production of the control FC, there is an inversely proportional relationship between the foam dosage, water to cement ratio, and dilution ratio with density and compressive strength. Referring to the results, the increase in the percentage of foam dosage decreases the density and compressive strength of FC. It was noticed that the compressive strength decreases when the density of FC decreases. In this study, the use of a 25% foam dosage achieved the desired density of 1625 kg/m3 as compared to others. This finding fulfils the requirement for strength of structural bearing load, whose requirement is more than 17 MPa by ASTM C 330-17a [The incorporation of PSBE significantly influences the density and compressive strength of foamed concrete. Based on the relationship, the compressive strength of FC increases with increasing PSBE content up to 30% PSBE. However, beyond that the foamed concrete experiences strength reduction. It was revealed that the optimal mix of 30% PSBE as replacement of cement achieved the highest compressive strength of 23 MPa with 1641 kg/m 330-17a . On the


There are two major views toward the role of antibiotics in microbial social interactions. The classical view is that antibiotics serve as weapons, produced by a bacterial species, at a significant cost, to inhibit the growth of its competitors. This view is supported by observations that antibiotics are usually upregulated by stress responses that infer the intensity of ecological competition, such as nutrient limitation and cellular damage, which point out to a competitive role for antibiotics. The other ecological function frequently assigned to antibiotics is that they serve as signaling molecules which regulate the collective behavior of a microbial community. Here, we investigate the conditions at which a weapon can serve as a signal in the context of microbial competition. We propose that an antibiotic will serve as a signal whenever a potential alteration of the growth behavior of the signal receiver, in response to a subinhibitory concentration (SIC) of the antibiotic, reduces the competitive pressure on the signal producer. This in turn would lead to avoiding triggering the stress mechanisms of the signal producer responsible for further antibiotics production. We show using individual-based modeling that this reduction of competitive pressure on the signal producer can happen through two main classes of responses by the signal recipient: competition tolerance, where the recipient reduces its competitive impact on the signal producer by switching to a low growth rate/ high yield strategy, and niche segregation, where the recipient reduces the competitive pressure on the signal producer by reducing their niche overlap. Our hypothesis proposes that antibiotics serve as signals out of their original function as weapons in order to reduce the chances of engaging in fights that would be costly to both the antibiotic producer as well as to its competitors. When antibiotics were first discovered it was widely assumed that their ecological function in nature is similar to their observed effect in the laboratory settings, a “weapon” used by bacterial species to fight its competitors  variability in mixing conditions between the native species of a microbiome, which can bring the resident species into competition with different members of its community, and (ii) migration; new species, among them are antibiotic producing species, can migrate to the microbiome. The migrating species could or could not have the ability to inflict harm on the resident species by producing an antibiotic.The optimal growth strategy of the resident species would differ depending on whether the invader species is or is not a antibiotic producer.Escherichia coli can respond to an initial attack by an antibiotic producer with a counterattack that targets its opponent  metabolic cost, the energy invested in antibiotic production which could have been allocated to growth, (ii) the antibiotic itself could be partly harmful to the invader species, (iii) conflict escalation with the resident species, an example is when the resident species is also capable of harming the invader species.I can be a useful signal whenever R can alternate it growth strategy to avoid triggering the stress responses responsible for further antibiotic production by I. The change in growth strategy of R when an invader species signaling its antibiotic production capability comes into its niche will be classified into two general categories: competition tolerance and niche segregation.Hence, an antibiotic produced by Niche segregation happens by reducing the niche overlap with the antibiotic producer. This can happen via spatial segregation, through microbial motility. When sensing the antibiotic, some bacterial species can move away from dangerous conditions  and R (mg bacteria/l) as the concentrations of the invader and the resident species, respectively. I produces an antibiotic A (mg/l) by investing a fraction of its metabolic energy, f, in its production, and both I and R consume nutrient N (mg/l). The antibiotic A has a killing rate of KA (l/mg antibiotic/h) and a decay rate that is denoted by βA (/h). The growth dynamics are modeled after Monod dynamics with μ (/h), μmax (/h), and KN (mg/l) as the growth rate, maximum growth rate, and half saturation constant of the Monod equation, respectively. Finally, the production of the antibiotic is regulated by a stress response such that it is only initiated when the nutrient concentration is lower than a certain threshold Nth (mg/l), this condition is expressed by the Heaviside step function H(Nth−N), which is equal to one only when N < Nth.With fs, in its production. Correspondingly, the resident species can perform a set of actions, utilizing alternative growth strategies, depending on whether a signal has been received or not. For the competition tolerance response, R switches from high growth rate/ low yield strategy to low growth rate/ high yield strategy based on the existence of a threat. This means that the growth dynamics of I and R will be expressed as follows:To model a signaling game, the invader's equation is modified such that it always produces a signal of its capability of antibiotic production by investing a small fraction of its metabolic energy, max, Y), characterizing the metabolic configuration of a certain strain. For the resident species,  can take values out of possible set of actions A = {, }, with μmax, 1 and Y1 as the maximum growth rate and yield abstracting the high growth rate/ low yield strategy, μmax, 2 and Y2 on the other hand describe the low growth rate/ high yield, metabolically efficient, strategy.Following Kreft , we abstTo simulate a non-efficient antibiotic producer, the stoichiometric coefficient for antibiotic production by the non-efficient, cheater strain is set to α = 0.4 (mg antibiotic/mg bacteria) instead of the nominal value.For the niche segregation response, the basic model is modified as follows:Nhigh (mg/l) is the high value substrate, which can support a maximum growth rate of μmax,high (1/h), while Nlow (mg/l) is the low value substrate, with a corresponding maximum growth rate of μmax,low (1/h). Hence, depending on the existence of a signal, the set of possible actions of R can be expressed as A = {μlow, maxμhigh, μlow}. In absence of a signal, R consumes the nutrient which provides it with higher growth rate. If a signal of a nutrient stress regulated antibiotic producer is received, R switches to exclusively consume the low value nutrient, growing with a rate of μlow (1/h).with m grid, seeded with uniformly distributed 100 cells of each strain and carried out till the biofilm height reached 150 μm. The nominal values of all the parameters are provided in All individual-based modeling simulations were carried out using MICRODIMS, an in-house IbM platform that has been developed at BioTeC+ and applied for modeling spatial microbial growth phenomena as colonies and biofilms , instead of the nominal value, α = 4 (mg antibiotic/mg bacteria). In how can a weapon turn into a signal. Explaining the evolution of a communication system in nature is not straightforward, and it has been described as a chicken and an egg problem as signals and responses are mutually dependent on each other , by the ERA-NET FACCESurPlus FLEXIBI Project, co-funded by VLAIO project HBC.2017.0176, by the Fund for Scientific Research-Flanders (projects G.0863.18 and G.0B41.21N), and by the European Union's Horizon 2020 Research and Innovation Programme (Marie Sklodowska-Curie grant agreement numbers 813329 and 956126).The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


We found that the use of 50% uncarbonated RCA improved the properties of concretes produced with FA with respect to using natural aggregates. The concrete made of 25% FA plus RCA was considered the most eco-efficient based on the tests of compressive, carbonation and chloride properties with the values of 4.1 kg CO2 m−3 MPa−1, 76.3 kg CO2 m−3 mm−1 year0.5 and 0.079 kg CO2 m−3 C−1, respectively. The uncarbonated RCA improved carbonation resistance, and FA improved chloride resistance. It can be concluded that the use of 50% un-carbonated RCA combined with FA considerably enhanced the properties of hardened concrete and their eco-efficiency with respect to concretes produced with natural aggregates.The fabrication of conventional concrete, as well as remains from demolition, has a high environmental impact. This paper assessed the eco-efficiency of concrete made with uncarbonated recycled concrete aggregates (RCA) and fly ash (FA). Two concrete series were produced with an effective water/cement ratio of 0.50 (Series 1) and 0.40 (Series 2). In both series, concretes were produced using 0% and 50% of RCA with 0%, 25% and 50% FA. After analysing the compressive strength, and carbonation and chloride resistance of those concretes, their eco-efficiency based on the binder intensity and CO In mosphere . Adequatmosphere . It can mosphere . In thismosphere ,9,10.RCA has been proven to be suitable for concrete production . In addiHowever, certain researchers ,20 have Today, the use of FA in proportions of up to 15–30% ,24 in coThe concrete produced with a combination of FA and RCA (CRAFA) could improve durability and eco-efficiency required for new sustainable concretes . AccordiHowever, the CRAFA mixtures were prepared with a lower water/binder ratio ; as a re2-eq intensity (Ci) of the concrete. The Bi value measures the amount of binder necessary to deliver a unit of strength and, consequently, the efficiency of the employed binder. It has been suggested that the minimum stabilised Bi value at 28 days after production is 5 kg m−3 MPa−1 for concretes of >60 MPa. Research suggests that this value will be an achievable goal for normal strength concrete (<50 MPa) in the near future and the ready-mix concretes <40 MPa consume the most cement, having a Bi value of 10–12 kg m−3 MPa−1. For 20 MPa concretes, the minimum Bi value is approximately 13 kg m−3 MPa−1 [−3 MPa−1) is necessary when large volumes of weak or low elastic modulus waste materials are employed in concrete production. To achieve a moderate Bi value, needed for higher concrete strengths, the binder consumption per unit of MPa should always be low [The eco-efficiency of the cement used in concrete production was first analysed by Damineli et al. . The opt2-eq in kg per m3 of concrete by its compressive strength at 28 days, and it is expressed as kg CO2 m−3 MPa−1. The Ci value considers the contribution of concrete mixtures to the global warming potential (GWP) per unit volume and strength, and it has been analysed intensively during recent years [2 m−3 MPa−1. All Ci values > 13 kg CO2 m−3 MPa−1 presented a high Bi value and no clinker replacement [2 m−3 MPa−1 to a minimum of 1.5 kg CO2 m−3 MPa−1. The minimum estimated Ci value was 1.5–2 kg CO2 m−3 MPa−1. According to de Matos et al. [2 m−3 MPa−1 are in the range of 70–80 MPa, while for the range of 50–60 MPa, the average Ci value is 6.2 kg CO2 m−3 MPa−1. Similar values have been obtained by Celic et al. [The Ci value of concretes is determined by dividing the emitted COnt years ,42. Damis et al. , all conc et al. . Randl eThis paper analyses the beneficial application of 50% of uncarbonated RCA as a substitution for natural aggregates together with 0%, 25% and 50% of FA in the replacement of cement for adequate properties of CRAFA concrete production. The compressive strength and durability properties of carbonation and chloride resistance were determined and compared with conventional concrete. The eco-efficiency of the produced concretes was assessed by measuring Bi and Ci values with respect to those obtained for compressive strength, carbonation coefficient and chloride resistance. The results guaranteed that CRAFA concrete (produced with FA and RCA) could maintain high strength and durability properties. Consequently, CRAFA achieved a higher level of eco-efficiency than the concretes made with Portland cement and natural aggregates.3. The coal-FA produced by a Spanish coal-fired power plant had a density of 2.16 kg/dm3. The CEM II A-L 42.5R cement  was employed in the concrete production. Class F coal-fly ash was used at 0%, 25% and 50% to replace CEM II. The CEM I 52.5R cement  was used, replaced by FA by 50%. CEM II and CEM I were produced by the same cement producer using the same type of clinker for their manufacture. The density of both types of cement was 3.1 kg/dm3, 2.64 kg/dm3 and 2.66 kg/dm3, respectively. The absorption capacity was 1.79%, 0.69% and 0.57%, respectively. The dry density and absorption capacity were determined following the EN 1097-6 specifications.Three fractions of natural limestone aggregates were used to produce concrete: fine natural aggregates (NS of 0/4 mm) and two natural coarse aggregates (CA1 of 5/10 mm and CA2 of 8/20 mm). The grading distribution of the aggregates  was dete2 component is shown. The grading distribution of RCA was a 5/20 mm fraction .The RCA aggregates were produced by crushing a one-year-old parent concrete, specifically, 30 MPa cylindrical concrete samples (150 mm Ø and 300 mm long) obtained from a concrete manufacturing company. The component of the parent concrete was CEM II A-L 42.5R cement and limestone aggregates. RCA was used for concrete production immediately after the parent concrete was crushed. The parent concrete presented a carbonation depth of 3–4 mm. In consequence, the RCA aggregates were uncarbonated. fraction . Its dryTwo series of concrete production were carried out, employing an effective water/cement ratio of 0.50 for Series 1 and 0.40 for Series 2 . Each coIn each series, eight different concretes were produced. Four types of binders were employed: (1) 100% CEM II cement; (2) 75% CEM II cement plus 25% FA (FA25); (3) 50% CEM II cement plus 50% FA (FA50); and (4) 50% CEM I cement plus 50% of FA (FA50.2). Those binders were mixed with two types of aggregate fractions: (1) 100% of natural aggregates and (2) 50% of RCA in replacement (in volume) of natural coarse aggregates. All the concretes were produced employing natural sand. The grading distribution of the different aggregate fraction mixtures is described in Following Neville’s  definitiA superplasticiser based on modified polycarboxylates was employed in all mixtures, at 0.50% with respect to the cement’s weight in all the concrete mixtures produced in Series 1  to achie2 concentration of 400 ppm, 21 ± 1 °C and 50–55% humidity before then being placed in the CO2 chamber.The concrete samples were produced and cured following UNE-EN 12390-2:2001 regulations  and manuThe compressive strength of concretes was determined using a compression machine with a loading capacity of 3000 kN. The compressive strength was measured at the ages of 7, 28 and 90 days following the EN 12390-3:2009 specifications . Three c2 control for the accelerated carbonation test at 20% CO2, 20 °C and 60% humidity, following GB T50082-2009 standards [Concretes’ carbonation resistance was determined by analysing the carbonation depth presented by concrete specimens after being submitted to accelerated carbonation for 0, 7 and 14 days. Six cylindrical samples of 100 mm Ø and 100 mm long and six cubic samples of 100 × 100 × 100 mm were analysed for each concrete. All the samples were cured in the humidity room for 28 days and were later exposed to a pre-conditioning period of 2 weeks under laboratory conditions (21 ± 1 °C and 50–55% humidity) before their exposure to accelerated carbonation. After the pre-conditioning period (0 day), the carbonation depth and compressive strength of the first concrete samples, two cylindrical samples of 100 mm Ø and 100 mm long and two cubic samples of 100 × 100 × 100 mm of each concrete mixture were tested, respectively. The carbonation depth was determined by spraying a colour indicator solution on a freshly broken surface. A solution composed of 1 g of phenolphthalein indicator in 70 mL of ethanol and 30 mL of demineralised water was applied following EN specifications. The four cylindrical samples of 100 mm Ø and 100 mm long and four cubic samples (100 × 100 × 100 mm) of each concrete mixture were placed in a climate chamber with COtandards . After 72 concentration was found to be excessive. It is known that the carbonation coefficient increases with increased CO2 concentration [2 cause modifications in the microstructure of the cement paste when compared to samples subjected to natural exposure only [2 over short periods of testing (for 14 days in this study) allows for the determining of the concrete’s resistance to carbonation [The 20% COntration . Moreoveure only . Howeverbonation .The chloride penetrability of the concrete was determined following the American Standard Test Method, ASTM C1202 standards , using a3 of concrete production to deliver one unit of performance, compressive strength (Bi-comp), performance of carbonation coefficient (Bi-carb) and chloride resistance (Bi-chlor), were determined for each concrete. For each type of concrete, three Ci values were also determined, as the amount of CO2 emitted per unit of compressive strength (Ci-comp), per carbonation coefficient (Ci-carb) and per chloride resistance (Ci-chlor).Bi and Ci values were used to assess the concretes’ eco-efficiency as defined by Damineli et al. . Three B2 emissions (kg) per weight of CEM II and CEM I were adapted from existing data provided by the cement production company, “Cement Molins Industrial (CMI)”, located in Barcelona. The Ci values of CEM I and CEM II were 0.753 kg CO2-I and 0.674 kg CO2-II, respectively. The supply and transport of raw materials and cement production have been included in the given values. The CO2 emissions per kg of FA were considered as 0.023 kg CO2-FA (including transportation), a similar value considered by Matos et al. [2-eq m−3) [2 emissions. The use of recycled aggregates significantly reduces the consumption of natural resources [2 during concrete carbonation was also not considered. Consequently, the Ci results probably underestimate the impact on global warming. However, the obtained data are still helpful in analysing the potential detrimental effect on the environment.The COs et al. . Natural-eq m−3) , a valueesources ; however2 emissions per m3 of concrete are determined by Equation (1).The CO2 emission (in kg) per m3 of concrete by its unit of performance. Compressive strength was expressed as kg CO2·m−3 MPa−1, carbonation as kg CO2 m−3 mm−1 year0.5 and chloride resistance performance as kg CO2 m−3 C−1.Finally, the concretes’ Ci value was determined by dividing the COThe lower Bi-comp and Ci-comp values obtained guarantee a higher efficiency of required strength in the concrete. Whereas, a higher Bi and Ci for carbonation and chloride resistance guarantee a higher efficiency in achieving required durability values within the concrete. Moreover, only the concrete that achieved the durability property values (carbonation and chloride resistance) defined by the Spanish Structural Code  for XC3 The compressive strength and the standard deviation of all concretes at 7, 28 and 90 days are shown in The concretes produced with FA had a lower initial strength than the CC concretes. In Series 1 a, at 28 In addition, the CFA50-1 and CFA50-2 concretes with FA replacing CEM II were found to have lower strength values than the CFA50.2-1 and CFA50.2-2 concretes, when FA was the replacement of CEM I. While it was determined that in Series 2, the CFA50.2-2 concrete achieved a <10% reduction of the compressive strength compared to the CC-2 concrete at 90 days, the CFA50.2-1 concretes produced in Series 1 achieved a decrease of 15% with respect to the CC-1 concrete.According to the results obtained from the concretes produced with RCA, the CRA-1 and CRA-2 concretes achieved compressive strength levels similar to CC-1 and CC-2, respectively, at all ages. While the CRA-1 achieved a maximum reduction of 6% with respect to CC-1 concrete at 7 days, the CRA-2 achieved a maximum reduction of 9.5% with respect to CC-2 at 28 days. In Series 1, FA in the production of RAC led to a lower reduction of the compressive strength compared to that of the FA concretes produced with natural aggregates at 7 days of curing. Probably, this difference was due to a reaction to the FA caused by the presence of a slightly higher amount of portlandite in the concretes produced with uncarbonated RCA  achieved the lowest carbonation depth in both Series. In addition, the CC-2 and CRA-2 concretes achieved 0 mm of carbonation after 7 days of the carbonation process . Furthernt paste , a resulnt paste ,38,59.reacted [In Series 1, the concretes produced with RCA suffered lower carbonation depth than those with natural aggregates, probably because RCA concretes had higher amounts of CaOreacted . This lokacc) of each concrete. The kacc (cX is the carbonation depth (mm), kacc is the carbonation coefficient and t is the time (day).The kacc  was deteknat, of each concrete was determined  and the natural carbonation process , respectively.In addition, the natural carbonation coefficient, termined  assuming defined ,61 and ikacc value (5.6 mm/day0.5), followed by the CFA25-1 concrete. The CC-1 concrete achieved the lowest kacc (2.3 mm/day0.5). However, the use of 50% RCA in concrete production caused a reduction of the kacc coefficient compared to those employing the same binder type and natural aggregates. This effect was more evident in concretes produced with FA.2, thus causing an increased carbonation resistance. Previous research [kacc coefficient by 8.3%, 22.1% and 18.7% compared to the CC-1, CFA25-1, and CFA50.2-1 concretes, respectively.Here, the uncarbonated RCA aggregates were carbonated during their contact with COresearch ,20 has vresearch ,21,22,30kacc value, followed by the CRA-2 concrete. The CRA-2 concrete achieved a higher carbonation coefficient, probably because the quality of the new cement paste was superior to that of RCA, thus causing an increase in the carbonation coefficient [R-squared value of 0.53, much lower than any other concrete, is probably due to the high CO2 concentration resulting in an acceleration of the carbonation process from 7 to 14 days. However, testing the lower CO2 concentration would be required to verify the carbonation coefficient value. The R-squared value of all the other concrete mixtures was >0.80 (the majority achieving R = 0.99), guaranteeing that at 7 and 14 days, the relationship between carbonation depth and time was constant.In Series 2 b, the CCfficient . The facThe results for Series 2 were similar to those for Series 1 b. In gen0.5 for XC3 and 50 mm/year0.5 for XC4 for a service life of 50 years. Consequently, the results obtained in the present paper estimated that the Series 1 CC-1, CRA-1 and CRAFA25-1 concrete mixtures would be adequate for use only in an XC4 environment with the kacc values of 45, 41 and 49 mm/year0.5, respectively. The XC3 environment, being less restrictive, also allowed a smaller cover width of the concrete structure. In addition, the Series 2 CC-2 and CRA-2 concretes were adequate for employment in both XC3 and XC4 environments, and the CFA25-2 and CRAFA25-2 concretes would also be suitable for use in an XC4 environment.According to Silva et al. , to avoiknat, determined by Equation (3) and described in 2 concentration.According to the Spanish Structural Concrete Code , the minAt 90 days, the 50% FA concretes (CFA50.2-1 and CRAFA50.2-1) achieved the lowest values, followed by the CRAFA25-1 concrete. The concretes produced using 25% FA and RCA reduced the corrosion risk with respect to concretes produced with FA and natural aggregates. However, the CRA-1 concrete was found to still have a high corrosion risk level after 90 days of curing. While the reduction of the total passed charge from 28 to 90 days for the CFA50.2-1, CFA25-1 and CC-1 concrete mixtures was 53%, 25% and 19%, respectively, the reduction rate of CRAFA50.2-1, CRAFA25-1 and CRA-1 was 24%, 41% and 9%, respectively. CFA50.2-1 achieved the highest decrease, followed by the CRAFA25-1 and CRAFA50.2-1 concretes.In contrast, the Series 2 concrete samples b after 23 of concrete was used for all the produced concretes. As for the Ci values, three binder mixtures were considered: 100% CEM II, 75% CEM II plus 25% FA and 50% CEM I plus 50% FA.The eco-efficiency of concretes was assessed by measuring the Bi and Ci values, taking into account the mechanical and durability performance. To evaluate the Bi values, 350 kg of binder per mThe obtained Bi-comp values at 28 and 90 days are illustrated in −3 MPa−1 and 8.5 kg m−3 MPa−1, respectively, whereas, to the contrary, the 50% FA concretes CFA50.2-1 and CRAFA50.2-1 achieved the highest values of 10.7 and 11.5 kg m−3 MPa−1, respectively. These results are acceptable considering that FA replaced 50% of the cement, and Damineli et al. [−3 MPa−1. It was also determined that the effect of RCA on the Bi-comp value was almost negligible in concretes produced with 0% and 25% FA, as RCA did not affect the reduction of compressive strength. After 90 days of curing, the concretes produced with 50% FA achieved the highest reduction of Bi-comp compared to the values at 28 days. The CFA50.2-1 and CRAFA50.2-1 concretes achieved the value of 8.2 kg m−3 MPa−1. In addition, the CFA25-1 and CRAFA25-1 concretes achieved a similar Bi-comp value to that of the CC or CRA concrete (7.0 kg m−3 MPa−1).In Series 1, at 28 days, the CC-1 and CRA-1 concrete mixtures achieved the lowest Bi-comp values of 8.3 kg mi et al.  stated t−3 MPa−1, respectively). The Bi-comp value was slightly higher when RCA was employed. The concretes CFA50.2-2 and CRAFA50.2-2 achieved the highest values with 8.5 and 8.6 kg m−3 MPa−1, respectively, because of lower compressive strength. After 90 days of curing, all the Series 2 concretes achieved a similar Bi-comp value, approximately 6 kg m−3 MPa−1, regardless of the type of binder or aggregates. According to various researchers [In Series 2 concretes, the binder achieved higher effectiveness due to the use of a lower water/binder ratio than in Series 1 concretes. This also occurred in Series 1, at 28 days, where it was determined that the CC-2 and CRA-2 concretes achieved the most moderate Bi-comp values  as they achieved compressive strengths similar to CC-1 and CRA-1 concretes. The concrete produced employing 50% FA achieved the lowest Ci values due to the upper range of the FA’s cement replacement [2 m−3 MPa−1). It was determined that the 50% FA concretes were the most efficient concretes. The CRAFA50.2-2 concrete achieved the lowest value with 2.7 kg CO2 m−3 MPa−1 followed by the CFA50.2-2 concrete with the value of 3.0 kg CO2 m−3 MPa−1, representing concretes that were considered very efficient [lacement . Howeverlacement ,62, as afficient .2 m−3 MPa−1, which is considered to be efficient [2 m−3 MPa−1 with a compressive strength of 56 MPa (7% lower than that of CC-2). The concretes produced with RCA, 25% and 50% of FA, achieved similar values to those with natural aggregates.At 90 days of curing b, the cofficient . In Seri2-eq intensity in carbonation resistance in Series 1, the concrete with the highest efficiency was CRA-1, followed by the CC-1, CRAFA25-1 and CFA25-1 concretes. In Series 2, due to the lack of positive influence of RCA, the CC-2 concrete had the highest efficiency, followed by the CRA-2, CRAFA25-2 and CFA25-2 concretes.According to the durability performance, higher values of Bi and Ci define a higher eco-efficiency of the concretes. The concretes produced with the lowest Bi-comp and Ci-comp values were considered the most eco-efficient. −3·mm−1·year0.5. Similarly, the optimum Ci-carb values were determined as the maximum kg CO2-eq emissions of each concrete made with a specific binder and are presented in To assess the concrete’s eco-efficiency for carbonation resistance, it was considered that the reinforced concrete should be exposed to an XC4 environment for 100-year service life. According to the Spanish Structural Concrete Code , the rei2 emissions proved to be unnecessarily high. The CFA25-1 and CRAFA25-1 concretes were considered the most efficient concretes with values of 1.17 and 1.49, respectively, achieving a value >1, durable enough for this defined environment exposure. In addition, the employment of RCA increased the eco-efficiency using the same amount and type of binder. In contrast, the CFA50.2-1 and CRAFA50.2-1 concretes achieved a ratio value < 1 and these concretes, which cannot be considered durable, do not guarantee the uncarbonation of the cover, thus causing corrosion of the reinforced bars.The Series 1 CC-1 and CRA-1 concretes achieved the highest ratio values. Consequently, they were considered to be the most durable concretes; however, their CO2-eq emissions were too high and inadequate for an XC4 environment.All Series 2 concretes were considered durable even though they achieved a ratio value > 1. However, the CFA50.2-2 and CRAFA50.2-2 concretes had the highest eco-efficiency since their ratio value was the closest to 1. Furthermore, due to the reduction of the water/cement ratio, the CC-2 and RCA-2 concretes achieved very high ratio values and excellent durability properties. Still, the kg CO2-eq emitted from concretes produced with a specific binder in order to achieve a moderate corrosion risk. The analysis was carried out at 28 days of curing as the values were more critical at this age than at 90 days.In order to assess the eco-efficiency of the concretes with respect to the chloride ion resistance, it was necessary to achieve a moderate corrosion risk (a maximum charge of 4000 C). Therefore, the optimum Ci-chlor  was defiIn Series 2, similar to Series 1, the durability and eco-efficiency increased with increasing levels of FA. The CFA50.2-2 achieved the highest value, followed by CRAFA50.2-2. Considering the use of RCA, the CRAFA50.2-1 and the CRAFA50.2-2 concretes had the highest eco-efficiency in Series 1 and Series 2, respectively, making their application possible in this context.In concretes produced with a water/cement ratio of 0.50, the use of 50% uncarbonated RCA together with Portland cement did not influence the reduction of compressive strength. In addition, when the concrete was produced with FA, the use of RCA improved the compressive strength of 41.8 MPa compared to concrete employing natural aggregates.In concretes produced with a water/cement ratio of 0.40, RCA negatively affected the compressive strength when Portland cement was used for concrete production. However, combining it with FA resulted in the concrete achieving similar compressive strength of 56 MPa to conventional concrete at 90 days.Concretes with higher compressive strength achieved higher carbonation resistance. While the use of RCA in concrete production increased the carbonation resistance, it was determined that the employment of FA reduced it. Additionally, the carbonation resistance of concretes produced with FA increased when RCA was used in their fabrication.The employment of FA improved the chloride ion penetration resistance of the concrete. In addition, the use of RCA together with FA improved the resistance to chloride ion penetration compared to that of the concretes produced with natural aggregates, even more evidently at 90 days of curing.Considering the eco-efficiency analysis:Based on the mechanical performance at 28 days, the concretes produced with 25% FA and 50% RCA (CRAFA25) achieved the highest eco-efficiency when an effective water/cement ratio of 0.50 and 0.40 was employed. At 90 days of curing, the CRAFA25-1 and CRAFA50.2-2 concretes achieved the highest eco-efficiency.Based on the conclusions of carbonation resistance, the CC and CRA concretes achieved the highest durability and the highest value of eco-efficient values. However, for reinforced concrete exposed to the XC4 environment for 100 years of service life (required 35 mm of cover), the CRAFA25-1 and CRAFA50.2-2 concretes also achieved the minimum durability required according to standards and consequently the highest eco-efficiency.Based on the results of minimum chloride resistance where the concretes were required to achieve a moderate corrosion risk: the CRAFA50.2-1 and CRAFA50.2-2 concretes, produced with an effective water/cement ratio of 0.50 and 0.40, respectively, had the highest eco-efficiency. The eco-efficiency of the CRAFA25-1 and CRAFA25-2 concretes was also considered valid.The following conclusions can be drawn based on the results presented above:It can be concluded that the use of 50% uncarbonated RCA as a replacement for natural aggregates combined with FA not only considerably improved the properties of concrete but also their eco-efficiency with respect to concretes produced with natural aggregates. The concrete produced with 50% RCA and 25% FA (CRAFA25) achieved the highest eco-efficiency in accordance with the mechanical performance and carbonation resistance of the concretes. Furthermore, the concrete produced with 50% RCA and 50% FA  had the highest eco-efficiency concerning chloride resistance. All the concretes produced with an effective water/cement ratio of 0.40 were considered durable with respect to carbonation and chloride resistance, independently of the type of binder and aggregates, and met the required standard specifications.


Antimicrobial resistance occurs due to the propensity of microbial pathogens to develop resistance to antibiotics over time. Antimicrobial stewardship programs (ASPs) have been developed in response to this growing crisis, to limit unnecessary antibiotic prescription through initiatives such as education-based seminars, prescribing guidelines, and rapid respiratory pathogen (RRP) testing. Paediatric patients who present to the emergency setting with respiratory symptoms are a particularly high-risk population susceptible to inappropriate antibiotic prescribing behaviours and are therefore an ideal cohort for focused ASPs. The purpose of this systematic review was to assess the efficacy and safety of ASPs in this clinical context. A systematic search of PubMed, Medline, EMBASE and the Cochrane Database of Systematic Reviews was conducted to review the current evidence. Thirteen studies were included in the review and these studies assessed a range of stewardship interventions and outcome measures. Overall, ASPs reduced the rates of antibiotic prescription, increased the prescription of narrow-spectrum antibiotics, and shortened the duration of antibiotic therapy. Multimodal interventions that were education-based and those that used RRP testing were found to be the most effective. Whilst we found strong evidence that ASPs are effective in reducing antibiotic prescribing, further studies are required to assess whether they translate to equivalent clinical outcomes. Streptococcus pneumoniae pose a moderate to high risk, especially to vulnerable populations including preterm infants, those that are immunocompromised and the elderly [Antimicrobial resistance (AMR) continues to present a growing public health challenge in an era of widespread antibiotic availability . As resi elderly ,5,6.The paediatric population in particular has become recognized as a nidus for the propagation of AMR in recent times . InapproHaemophilus influenzae Type B have had a greater effect in reducing the incidence of bacterial infections that cause severe morbidity in comparison to antibiotics [Acute respiratory tract infections (ARTIs) are among the most common in children and account for a significant proportion of the antibiotics prescribed in paediatric emergency departments . Studiesibiotics . Furtheribiotics . These fAntimicrobial stewardship programs (ASPs) were introduced in healthcare settings to guide antibiotic prescribing by encouraging the use of narrow-spectrum antibiotics, optimizing dosages, and shortening the duration of antibiotics prescribed . The conIt is important to assess how effective these programs are at addressing these concerns in order to make the necessary adjustments and continue to implement these strategies to help control the global burden of AMR. There are no current systematic reviews addressing the use of ASPs in the paediatric emergency department, with regards to respiratory infections. Our review will address this topic to support improvements in the delivery and quality of future paediatric ASPs.The purpose of this systematic review was to assess the efficacy of ASPs in addressing suboptimal antibiotic prescribing for respiratory infections in the paediatric emergency setting. The primary outcome of the study was to determine whether the implementation of ASPs in paediatric emergency settings translated to judicious antibiotic prescribing in the form of narrow spectrum antibiotics, shorter courses, and reduced dosing. The secondary outcome was to determine whether the implementation of ASPs resulted in comparable clinical outcomes when compared to usual prescribing practices.A systematic review of the literature was performed to identify primary journal articles that assessed the efficacy and safety of ASPs in guiding appropriate antibiotic prescribing. The Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines were followed when performing the review.Are antimicrobial stewardship programs for acute respiratory presentations in the paediatric emergency setting effective in narrowing antibiotic spectrum, reducing dosage, and shortening duration of antibiotic prescription?P (population): paediatric patients (aged 3 months–18 years old) presenting to the emergency department with respiratory symptoms; I (intervention): implementation of antibiotic stewardship programs; C (comparison): usual care;O (outcome): changes in antibiotic prescribing behaviours whilst maintaining patient outcomes.The review was performed on 28 August 2021 and included PubMed, MEDLINE, EMBASE and the Cochrane Database of Systematic Reviews for publications from 1 August 2001 to 31 July 2021 to include studies from the last twenty years. Briefly, specific search terms included ‘antimicrobial stewardship’, ‘antimicrobial control’, ‘paediatric’, ‘respiratory tract infection’ and ‘emergency department’. The complete search strategy used for MEDLINE is shown in Inclusion criteria: all primary research articles that included children aged between 1 month–18 years who presented to an emergency department due to respiratory infections. Studies that implemented an ASP as an intervention and reported outcomes pertaining to efficacy or safety were included.Exclusion criteria: articles were excluded if they were case series, letters, notes, conference abstracts, policy statements or opinion articles. ASPs implemented in paediatric settings other than emergency departments were excluded. For studies that included both adult and paediatric patients and the paediatric data was not available, the corresponding author was contacted, and the data requested. Studies reporting on antiviral and antifungal drugs were also excluded ,22.The titles and abstracts of studies that were identified by the search were screened and studies that were deemed relevant were further assessed using the full texts and reviewed in lieu of the inclusion and exclusion criteria. Additionally, reference lists of eligible studies and of relevant systematic reviews were examined to identify further studies. The search and study selection was conducted independently by two authors (KW and PM) and disagreements were resolved by consensus.The quality of included articles was assessed using the Integrated Quality Criteria for Systematic Review of Multiple Study Designs (ICROMS) tool . Only stData was extracted by KW from all eligible studies using a standardized data collection form that was constructed a priori. Variables of interest included study design, location and setting, details of ASP-implemented prescribing practices and patient outcomes.In total, 228 articles were identified using the search strategy, with a filter limiting to titles published in English between 2001 and 2021. After removing 66 duplicates, the abstracts of the remaining 162 were screened and 120 were excluded for a variety of reasons including being a non-primary article, not having an ASP or QI intervention, not focusing on the paediatric population, not addressing respiratory tract presentations and for not being conducted in the emergency setting. Following the title and abstract screening, a total of 42 full-text articles were reviewed. Thirteen articles were eligible for final analysis .A summary of the included studies is provided in The nature of ASP interventions varied greatly between included studies. Eight of these studies reported outcomes from education-based interventions which provided clinical decision tools and aids with current guidelines regarding appropriate antibiotic prescription ,31,33,34The primary outcomes reported in the included studies are heterogeneous, ranging from antibiotic prescription rate  to susceOf the studies based on education-based interventions with clinical decision tools, a significant reduction of overall antibiotic use and inappropriate antibiotic prescription was reported by six studies ,30,33,34p = 0.01 decrease in antibiotic prescription rate and with an estimated cumulative effect of intervention of −30.9%  [Study interventions which provided ongoing feedback to participants throughout the study period showed a significant increase in appropriate antibiotic use. Ouldali et al., provided feedback during the first year of intervention and observed a −15.5%, , −20.1) . It is h, −20.1) .p < 0.001) in discharge antibiotic prescriptions between the number of patients testing positive with RRP in comparison to patients who were not tested [Of the two studies based on RRP testing interventions, both reported a decrease in antibiotic use ,35. HoweH. influenzae however, decreased in susceptibility throughout the study period. Further, the enhanced antibiotic strategy, including an education-based ASP towards the end of the study only showed a significant improvement of drug resistance in nosocomial pathogens and not community-associated pathogens [Huang et al., reported a significant reduction in the resistance of antibiotics in response to the pneumococcal vaccination program across Taiwan. Certain pathogens such as athogens .p = 0.01) was observed following intervention [Pernica et al., observed the effects of a short-course high-dose antibiotic (intervention) in comparison to a long course of high-dose antibiotics (control) on clinical cure between 14–21 days . Clinicarvention .All included studies were assessed for bias using the ICROMS tool. All studies met the mandatory criteria and minimum score required to be deemed of fair quality and therefore were included for review Clostridioides difficile infection in patients admitted from ED [The global burden of AMR, particularly in the context of increased antibiotic use is rapidly increasing. ASPs were developed in response to this growing public health issue and are aimed at optimising antibiotic prescription, whilst maintaining patient care . The eme from ED . May et  from ED . This st from ED .There is limited evidence surrounding the use of ASPs in the ED setting for the paediatric population, in particular with regard to ARTIs. This systematic review looking at the effectiveness of ASPs for respiratory presentations in the paediatric emergency setting shows that multiple methods of delivering education-based ASPs translate to improved antibiotic prescribing and equivalent or improved clinical outcomes and safety, which are sustainable. Further, the availability of diagnostic tools such as RRP testing facilities shows promise in increasing the rate of appropriate antibiotic prescribing.When evaluating the efficacy of ASPs, the most commonly used measures included proportion of appropriate first-line antibiotic use and broad-spectrum antibiotics. The effects of overall antibiotic use were well reported by the included studies, and the postintervention difference was statistically significant in nine of thirteen studies ,33,34,35Further, two other included studies although implementing education-based clinical tools, reported a decrease in antibiotic use, however, these results did not reach statistical significance ,31. RutmThere is conflicting evidence regarding the use of feedback techniques when delivering an ASP, with some studies reporting a significant change in the prescription of targeted antibiotics , and othp < 0.0001) after the utilisation of RRP has been reported [p = 0.06) that was larger in the paediatric patients  in age-stratified post hoc analysis [p < 0.001) [p < 0.001) [In the adult population, a significant reduction in inappropriate antibiotic prescription  . However< 0.001) . Zhu et < 0.001) .Although there is evidence for the use of RRP testing, there is limited evidence on the use of other diagnostic testing methods, such as chest radiographs and blood tests, as a method for antimicrobial stewardship. McDaniel et al., assessed adherence to diagnostic measures within an intervention including complete blood count, blood cultures, acute-phase reactants, and chest radiographs as an intervention to improve rates of appropriate antibiotic prescription and associated an increase in adherence  with an increase in narrow-spectrum antibiotic prescription . Although there is a significant increase in both measures, there was no clear analysis conducted to ensure a correlation. Therefore, an RCT directly assessing the effect of diagnostic testing methods on antibiotic stewardship would be beneficial.The success of an ASP cannot be completely appreciated without the clinical outcomes of the patients included in the study population. The majority of current literature focuses on the stewardship measures such antibiotic use and cost, however, more recently the literature is encouraging a shift in focus towards the clinical impact of ASPs . Only twThis study has many advantages. The inclusion of only studies meeting the mandatory criteria and minimum score requirements from the ICROMS risk of bias tool, ensured only good-quality papers were reviewed. Further, a variety of ASP interventions were reviewed, providing an overview and opportunity for comparison. This provides a strong basis for future ASP development and implementation.Our study has some limitations. Firstly, only four databases were searched, and some references may have been missed. Further, the search was restricted to papers published in English, which may have led to some relevant papers being overlooked. It should also be noted that with the high volume of observational studies included in this review, a risk of reporting bias is present however, this was minimised by the inclusion of only high-quality studies. Lastly, the phrase ‘antibiotic stewardship’, as a relatively new term, may not have applied to all studies exploring this concept which may have resulted in relevant papers being missed.We conclude that most ASPs are effective in addressing suboptimal antibiotic prescription for respiratory infection in the paediatric emergency setting. Successful delivery of both education-based ASPs, as well as clinical tools such as RRP testing, translated to judicious antibiotic prescribing with a reduction in overall antibiotic prescribing and increased the proportion of narrow-spectrum antibiotics and short-course antibiotic therapies. As many included papers were not RCTs, there are many factors in the delivery of ASPs that further research can shed some light on. We recommend further research into the effectiveness of ASPs for respiratory infections in the paediatric ED setting. Such studies should aim to identify focused strategies to improve the adherence to and efficacy of ASPs and strive to include clinical outcomes as a primary measure of success.


Although testicle tumor markers and soluble interleukin‐2 were not elevated, the patient underwent orchidectomy because magnetic resonance imaging findings highly suspected seminoma or malignant lymphoma. After the diagnosis of IgG4‐RD, high levels of serum IgG4 was observed. These findings indicate that clinicians should consider the possibility of IgG4‐RD and check the level of serum IgG4 when examining patients with the atypical clinical course.In this case report, the mass in the right seminal vesicle was reduced after left orchidectomy without further treatment. Based on the International Consensus Guidance Statement on the Management and Treatment of IgG4‐RD, “watchful waiting” may be appropriate in patients with no symptoms.The authors declare no conflict of interest.