Unsealed Conditions Research Articles

Improving hydrolysis and acidification by regulating the oxygen status and solid content of lignocellulosic waste: Emphasis on the unsealed environment and harnessing the potential of microbial communities

The recalcitrant nature of lignocellulosic raw materials poses a challenge for current biogas plant operations, where hydrolysis and acidification (HA) are the rate-determining steps. To explore the HA balance and microbial mechanisms according to oxygen status and in conditions with relatively high solid content, we made a simple change to build an unsealed reactor. We found that the hemicellulose degradation rate increased by 149.3 % under unsealed conditions. Under microaerobic conditions (Mi), HA with more than 10 % total solid (TS) content exhibited a carbon loss rate of < 10 % in the first 7 days. In the 15 % TS Mi treatment, the organic acid conversion coefficient was 0.04, and the concentration increased to 7.4 g/L within 2 days. A high solid content was the key factor for ensuring efficient organic acid production in the early stage, whereas Mi affected the middle stage. Multiple methods revealed that abundant Prevotella and Clostridium, as well as rare Bifidobacterium, Sporacetigenium, and specific bacteria, had substantial effects on efficient organic acid production and HA balance. The correlation with Mi was 0.57–0.83. The abundance of hemicellulase genes increased by 18.41 %, and the abundance of pyruvate kinase in Mi increased by 15.55 % compared with the sealed condition, demonstrating that Mi can provide complementary advantages in the HA process. The findings in this study improved the operational quality of conventional HA and anaerobic digestion.

Characterization of hygrothermal, gas pressure and stress characteristics for poplar wood during unilateral surface densification

Unilateral surface compression in wood presents notable benefits, including reduced wood volume loss and energy consumption, rendering a highly promising and extensive utilization. However, shortcomings in compressed wood arise due to unclear gas pressure, temperature, and moisture content distribution within the wood during hot pressing. In this paper, the temperature and pressure distribution were analyzed utilizing an optical fiber temperature and pressure measurement system within the wood during hot pressing. Moreover, the moisture content, stress and strain in each layer at the end of hot pressing were discussed extensively. The results showed that the wood surface layer (SL) and subsurface layer (SSL) maximum temperature values were similar even with different layer thicknesses. Under sealing conditions, SL and SSL temperatures were generally 6 ℃ to 7 ℃ higher compared to unsealing conditions. The gas pressure maximum value exhibited an opposite order, gradually transferring to the core layer (CL) and declining as the processing time extended. During compression treatment, moisture migrated from the hot end to the cold within the wood. The moisture content displayed significant differences between the middle and end parts of the wood under unsealed conditions, with the disparity becoming more pronounced further away from the hot end. The transition region of the compressed wood served as a stress concentration area, experiencing the highest levels of stress. The dense region followed with the second highest stress levels, while the un-densified region exhibited the least amount of stress. Under the same process parameters, the thickness had little influence on the distribution of dense layers.

Internal Curing Utilising Recycled Concrete Aggregate: A Sustainable Approach for Improving High-Strength Concrete’s Performance

AbstractHigh-strength concrete (HSC) makes up the vast majority of materials used in the construction sector due to its exceptional mechanical characteristics and outstanding long-term behaviour. However, in cement-based materials with a low water-to-binder ratio (w/b), excessive autogenous shrinkage has become a prevalent issue. This work suggests the sustainable use of recycled concrete aggregate (RCA) to internally cure HSC in order to reduce autogenous shrinkage during the hydration and curing processes. RCA was employed with various volumetric replacement percentages with natural coarse aggregate as a water storage agent (0%, 8%, 16%, 24%, 32%, 50%, 75%, and 100%) under sealed and unsealed conditions. The efficiency of the adopted materials for internal curing was investigated by determining the autogenous shrinkage in addition to unconfined compressive and flexural strength. The laboratory results reveal that the studied properties significantly improved by incorporating RCA into HSC, and the improvement depends on the substitution rate of the coarse aggregate. A better shrinkage behaviour can be obtained by raising the substitution percentage of coarse aggregate with RCA; in contrast, the strengths decrease with increased RCA. RCA can be utilised as an internal curing material for HSC to alleviate autogenous shrinkage with a percentage of around 40%, with the adopted ambient conditions in the early age of HSC with full replacement of virgin coarse aggregate. It is recommended to use 24% RCA as a substitution for natural coarse aggregate for internal curing to improve the characteristics of HSC and the sustainability advantages and reduce its negative environmental impacts.

Effects of different conditions tested “in vitro” on the phosphorus runoff potential of livestock manure

This study aimed to investigate the changes of swine and dairy manure characteristics during a long-term storage (150–180 days) under 4 °C, 20 °C, and 37 °C, sealed and unsealed conditions. Water extractable phosphorus (WEP) of both manures rapidly increased during the first 15–30 days and then decreased. At the end of the storage, the WEP reduction was 90%±3% and 71%±5% of the initial concentration for swine manure and dairy manure, respectively. Generally, unsealed storage and higher temperatures led to more WEP reduction. This study suggested that manure stored for less than 30 days had the highest P runoff potential, while a long-term manure storage reduced P runoff potential compared to freshly excreted manure.

Extension of the fib MC 2010 for basic and drying shrinkage of alkali‐activated slag concretes

AbstractAlkali‐activated slag is an alternative to ordinary Portland cement that has been studied for the past 20 years. One of the main challenges for its practical use is understanding and controlling its shrinkage behavior. In this study, new experimental results for two alkali‐activated slag concrete mixes are presented under both sealed and unsealed conditions. The results show that basic shrinkage increases with increased sodium silicate ratio. Under unsealed conditions, the age to exposure to drying has a most significant impact on the final drying shrinkage. Finally, the mechanisms explaining shrinkage of such materials are discussed and thefib Model Code 2010 is extended for alkali‐activated slag concrete using the new experimental results. The extended model consists of four parameters influencing the final values and the speed of both basic shrinkage and drying shrinkage. It is extensively compared with experimental datasets from the literature and improves significantly predictions compared with the original models for both basic and drying shrinkage. This demonstrates clearly the feasibility to extend it for predicting shrinkage of alkali‐activated slag concrete.

Volatile-mediated interactions between Trichoderma harzianum and Acanthoscelides obtectus: A novel in vitro methodology to evaluate the impact of microbial volatile compounds on dry grain storage pests

Biological interactions mediated by Biogenic Volatile Organic Compounds (BVOCs) is a well-established field that has been researched for decades. Although extensive focus is currently given to the control of insect pests using natural molecules, the study of volatile interactions between microorganisms and insects has been largely neglected and has only begun to attract more attention in recent years. In this work, we developed a novel protocol to assess the effects of microbial BVOCs directly produced by growing microbial strains on dry grain insect pests and the seed damage they cause, using VOC Chambers to evaluate both sealed and unsealed conditions. Four Trichoderma harzianum strains were tested against Acanthoscelides obtectus, a wild type and three of its transformants. These had been previously obtained by introducing the tri5 gene and thus overproducing the volatile trichodiene, or by silencing the erg1 gene, which encodes for a squalene epoxidase, therefore reducing ergosterol levels and increasing squalene ones in the fungus. Results demonstrated that ventilation plays a key role in these interactions. All fungal strains significantly increased adult mortality in sealed conditions, while this effect was barely noticeable in unsealed ones. Nevertheless, subsequent insect emergence from bean seeds and bean damage were still significantly reduced in both conditions. The erg1 silenced strains caused significantly higher levels of adult mortality than the rest in sealed conditions and lower insect emergence in both sealed and unsealed ones. Bean damage produced by insects was lower also when exposed to BVOCs from these strains in sealed conditions. Conversely, trichodiene overproduction did not show enhanced toxicity or significant reduction of insect emergence and bean damage in the tested conditions. Therefore, T. harzianum BVOCs, especially those from erg1 silenced strains, should be further researched for their potential use in the biological control of A. obtectus infestation in dry grain storing facilities. VOC Chambers have shown themselves to be a reliable method in the screening of in vitro volatile mediated interactions between growing microbial strains and insect pests.

The effect of specimen size on autogenous and total shrinkage of ultra-high performance concrete (UHPC)

Unlike normal strength concretes, in which drying is the dominant form of shrinkage, in concretes with very low water to cement ratios autogenous and chemical shrinkage mechanisms can dominate. While the impact of specimen size and shape on drying shrinkage is well understood, the same is not true for autogenous and chemical shrinkage, and this lack of understanding may limit model precision and accuracy. To address this issue, this paper presents the results of a series of experiments conducted to measure the dependency of shrinkage of UPHC on specimen size. Results, recorded from 2 days after water addition, demonstrate a strong specimen size dependency when tested under both sealed and unsealed conditions, thereby indicating that the underlying mechanism is fundamentally different from normal strength concrete, with autogenous shrinkage exhibiting a large influence. Existing shrinkage models (AS3600, B4, CEB-FIP, GL2000 and ACI209) are evaluated for their potential calibration and/or extension to low water to binder ratio concretes and it is shown that commonly used parameters to account for size dependency in normal strength concrete (volume to surface area ratio and hypothetical thickness) do not capture size dependency in UHPC.

Plastic and early-age shrinkage of ultra-high performance concrete (UHPC): Experimental study of the effect of water to binder ratios, silica fume dosages under controlled curing conditions

The magnitude of early age shrinkage of Ultra High Performance Concrete (UHPC) is markedly different from normal and high strength concretes. A series of experiments were performed to determine the influence of water to binder ratio and silica fume content on the rate of hydration, stiffness development, chemical and external shrinkage under both sealed and unsealed conditions. Experimental apparatus, designed for shrinkage in normal strength concretes, were adapted to accommodate the larger volume changes and minimise the influence of boundary restraint. Continuously monitored internal temperature, and relative humidity conditions, along with periodic measurements of hydration degree and stiffness are used to elucidate the volumetric deformation mechanisms. Results, from as early as three hours after water addition demonstrate significant volumetric changes occurring in the early plastic state of the material.

Air seal performance of personalized and statistically shaped 3D-printed face masks compared with market-available surgical and FFP2 masks

The ongoing COVID-19 pandemic has revealed alarming shortages of personal protective equipment for frontline healthcare professionals and the general public. Therefore, a 3D-printable mask frame was developed, and its air seal performance was evaluated and compared. Personalized masks (PM) based on individual face scans (n = 8) and a statistically shaped mask (SSM) based on a standardized facial soft tissue shape computed from 190 face scans were designed. Subsequently, the masks were additively manufactured, and in a second step, the PM and SSM were compared to surgical masks (SM) and FFP2 masks (FFP2) in terms of air seal performance. 3D-printed face models allowed for air leakage evaluation by measuring the pressure inside the mask in sealed and unsealed conditions during a breathing simulation. The PM demonstrated the lowest leak flow (p < 0.01) of inspired or expired unfiltered air of approximately 10.4 ± 16.4%, whereas the SM showed the highest (p < 0.01) leakage with 84.9 ± 7.7%. The FFP2 and SSM had similar values of 34.9 ± 18.5% leakage (p > 0.68). The developed framework allows for the time- and resource-efficient, on-demand, and in-house production of masks. For the best seal performance, an individually personalized mask design might be recommended.

Evaluation of a Filtering Facepiece Respirator and a Pleated Particulate Respirator in Filtering Ultrafine Particles and Submicron Particles in Welding and Asphalt Plant Work Environments.

Manufacturing sites, such as welding, casting, and asphalt production (fumes), generate vast numbers of ultrafine particles of <0.1 µm in size and submicron particles close to the ultrafine range (0.1–0.5 µm). Although cumulative masses of these particles are negligible in comparison to the larger particles, the health effects are more severe due to the higher penetration in the human lower respiratory tract, other body parts crossing the respiratory epithelial layers, and the larger surface area. This research investigates the effectiveness of two common commercially available N95 filtering facepieces and N95 pleated particulate respirator models against ultrafine and submicron particles. Two specific types of respirators, the N95 filtering facepiece and the N95 pleated particulate models, in both sealed and unsealed conditions to the manikin face, were tested at various commercial and academic manufacturing sites, a welding and foundry site, and an asphalt production plant. Two TSI Nanoscan SMPS nanoparticle counters were used simultaneously to collect data for particles of 10–420 nm in size from inside and outside of the respirators. While one of them represented the workplace exposure levels, the other one accounted for the exposure upon filtration through the respiratory surfaces. The results showed the particles generated by these manufacturing operations were mostly within the range of from 40 to 200 nm. Results also indicated that while the percentage of filtration levels varied based on the particle size, it remained mostly within the desired protection level of 95% for both of the N95 respirator models in sealed conditions and even for the N95 pleated particulate model in the unsealed condition. However, in the case of the N95 filtering facepiece model, unsealed respirators showed that the percentage of penetration was very high, decreasing the protection levels to 60% in some cases. Although the number of workplace airborne particle levels varied considerably, the filtration percentages were relatively consistent.

Role of Curing Conditions and Precursor on the Microstructure and Phase Chemistry of Alkali-Activated Fly Ash and Slag Pastes.

Understanding the role of curing conditions on the microstructure and phase chemistry of alkali-activated materials (AAMs) is essential for the evaluation of the long-term performance as well as the optimization of the processing methods for achieving more durable AAMs-based concretes. However, this information cannot be obtained with the common material characterization techniques as they often deliver limited information on the chemical domains and proportions of reaction products. This paper presents the use of PhAse Recognition and Characterization (PARC) software to overcome this obstacle for the first time. A single precursor (ground granulated blast-furnace slag (GBFS)) and a binary precursor (50% GBFS–50% fly ash) alkali-activated paste are investigated. The pastes are prepared and then cured in sealed and unsealed conditions for up to one year. The development of the microstructure and phase chemistry are investigated with PARC, and the obtained results are compared with independent bulk analytical techniques X-ray Powder Fluorescence and X-ray Powder Diffraction. PARC allowed the determination of the type of reaction products and GBFS and FA’s spatial distribution and degree of reaction at different curing ages and conditions. The results showed that the pastes react at different rates with the dominant reaction products of Mg-rich gel around GBFS particles, i.e., Ca-Mg-Na-Al-Si, and with Ca-Na-Al-Si gel, in the bulk paste. The microstructure evolution was significantly affected in the unsealed curing conditions due to the Na+ loss. The effect of the curing conditions was more pronounced in the binary system.

Effect of silica fume on the hardened and durability properties of concrete

AbstractThis paper involves the study on the hardened and durability properties of the concrete at two different grades containing silica fume (SF) with various replacement percentages. Investigation on the performance of the SF was performed for M25 and M40 grades concrete with 0, 5, 10, and 15 % replacement levels at 7, 14, 28, and 90 days. The behavior of SF on the autogenous shrinkage of the concrete was studied for both the grades of concrete in the sealed (SC) and unsealed conditions (USC). The workability of the SF concrete was examined at various levels of replacement by the slump cone test. The hardened properties of the SF concrete were investigated through the estimation of compressive strength (CS) and elastic modulus (EM) at 7, 14, 28, and 90 days, respectively. Acid attack was conducted at 28 days and autogenous shrinkage of the SF concrete was investigated using length comparator at 28 day in SC and USC. Results indicate that upon increase in the percentage of SF, the hardened properties of the concrete increases at higher ages of curing and the shrinkage of the concrete tends to increase for both the grades of concrete.

Experimental study on sulfate resistance of concrete with recycled aggregate modified with polyvinyl alcohol (PVA)

Using the wastes as a recycled concrete aggregate (RCA) is a promising technology to reduce the impact of construction and demolition wastes on the environment and the shortage of natural resources. However, higher permeability of RCA leads to greater absorption, affecting the RCA concrete's long-term performance. In general, the soil in Iraq contains a high sulfate level, accelerating concrete deterioration reducing concrete strength, and increasing concrete spalling and cracking. The aim of this study is to investigate the impact of sulfate environment on the mechanical properties of pretreated RCA concrete using a PVA agent. The normal aggregate was replaced in four portions of 8 %, 16 %, 24 %, and 32 % RCA, with the same grading and max size as normal aggregate. Two w/c ratios of 0.50 and 0.3 were used with two curing systems, namely sealed and unsealed conditions. The RCAs were socked in 0.5 % PVA of the water volume. The durability of RCA concrete was also experienced by sulfate attack immersing the concrete cubes in magnesium sulfate heptahydrate (MgSo4.nH2O) solution for 150 days after 28 days from casting with the wetting and drying cycle. The compressive strength results showed that the mixes with RCA pre-soaked in PVA have higher strength than the reference mix. For durability, the concrete mix with 32 % RCA exhibited the best durability. When the increased amount of RCA pre-soaked in PVA, the hydration increased, and internal voids decreased. Using 24 % RCA replacement with the sealed curing condition gives a 1.2 % increase in absorption, which is less than the unsealed curing condition of a 1.8 % increase in absorption.

Effects of culture media and physical factors on the mycelial growth of the three wild strains of Volvariella volvacea from Ecuador

Optimization of physical parameters for the growth and lipid production in Nannochloropsis gaditana (Lubian, 1982)Shyni MarKose, Ajan Chellappan, Praba Thangamani, Subilal George, Selvaraj Thangaswamy, Citarasu Thavasimuthu, Michaelbabu Mariavincent

Effects of curing environment on strength and microstructure of alkali-activated fly ash-slag binder

This paper delineates the influence of curing environment on strength and microstructural growth in alkali-activation of fly ash-slag. The strength properties of fly ash-slag binder cured under different temperatures and humid conditions were evaluated. Further, the development of strength in autoclave and microwave cured specimens were studied. An investigation was done to understand the strength development in short and long duration curing. Microstructural analysis was also made to correlate the reaction products with the observed strength. Results revealed that a higher curing temperature favored a better strength development in fly ash rich samples whereas slag rich samples developed micro cracks; particularly for unsealed conditions in dry curing environment. Autoclaving pressure and microwave radiation curing showed high strength development in the early stages of curing due to the faster development of reaction products. The major reaction products were the hydrates of calcium/sodium based alumino-silicates.

Predicting relative humidity of early-age concrete under sealed and unsealed conditions

The decrease of internal relative humidity (IRH) in early-age concrete induces autogenous shrinkage. Autogenous shrinkage usually increases the risk of cracking if the concrete is restrained from shrinking freely at an early age. Predicting autogenous shrinkage of early-age concrete requires knowledge of IRH. Therefore, investigation of IRH is fundamental to evaluate cracking resistance. Although investigations of IRH in hardened concrete have been conducted, a prediction model for IRH in early-age concrete that considers the water/cement ratio (w/c) is still lacking. Therefore, experimental studies and analysis of IRH in early-age concrete with different values of w/c were conducted. Results showed that: (i) the IRH in concrete at 28 d after casting increased with increasing w/c under sealed and unsealed conditions; (ii) the average rate of IRH decrease in early-age concrete decreased with increasing w/c; (iii) the critical time of IRH (the length of the water-vapour saturated stage with 100% IRH) in early-age concrete increased with increasing w/c. Models for early-age IRH are proposed in consideration of w/c, critical time and age of concrete under sealed and unsealed conditions.

Effect of novel superabsorbent polymer composites on the fresh and hardened properties of alkali-activated slag

In this work, the poly(sodium-acrylate acrylamide) superabsorbent polymer (SAP) composites reinforced with micro silica and kaolin clay particles are evaluated as novel additives to control and improve the fresh and hardened properties of alkali-activated slag (AAS). The water swelling and retention capacity of plain and modified SAPs in various solutions pertinent to AAS binder systems (including deionized water, saturated Ca(OH)2, 1.0 M NaOH, 0.5 M Na2CO3, and 0.5 M Na2SO4) are studied using the gravimetric ‘tea bag’ and thermogravimetric methods, together with molecular analysis. The results show that the use of micro silica and kaolin clay-reinforced SAP composites slightly alleviates the negative influence of conventional SAP counterparts on the flowability, setting, and early-age compressive strength of AAS pastes. Nevertheless, the addition of SAP composites merely postpones the early-stage drying shrinkage development but tends to increase the long-term deformation of hardened AAS in unsealed conditions, likely due to the reduced bulk stiffness with enlarged porosity.

Experimental investigation on the reversibility of concrete creep under repeating loads

So far, creep reversibility of concrete has been tested either under single unloading or stepwise (“staircase”) stress histories. However, these investigations do not provide a complete understanding of the creep behavior under repeating stress histories, similar to variable live load histories in usual concrete structures. Typical examples are parking garages, bridges or storage buildings with frequent but still longer-term loadings and unloadings. Therefore, the paper attempts to extend the knowledge on the creep under frequently repeated stresses by testing concrete specimens under various loading and drying conditions. The creep-recovery versus creep ratio over time, considered here as a measure of creep reversibility, was studied within two separate experiments. The first experiment aims to assess the influence of different service stress levels with 30% and 45% of the concrete compressive strength fc as well as different unloading levels of full and partial unloading. The second one focuses on the influence of different hygral conditions of the specimens, namely sealed and unsealed conditions. Regardless of the stress level, the creep-recovery versus creep ratio tends to approach unity after a sufficient number of loading and unloading cycles. Drying conditions show negligible effects on the creep recovery. On the other hand, they have remarkable influence on the proportion of the creep reversible in each loading cycle. Moreover, the basic creep component shows high reversibility under repeating stress histories. The results demonstrate that the recovery behavior under repeating stresses pronouncedly differs from the ones under just sustained stresses.

Effect of shrinkage reducing admixture on early expansion and strength evolution of calcium sulfoaluminate blended cement

This research examines the influence of presence of shrinkage reducing admixture (SRA) on expansion, hydration, and strength evolution of calcium sulfoaluminate-based expansive agent (CSA-based EX) blended with ordinary portland cement (OPC) in the absence of initial moist curing. The performance of inclusion of SRA in OPC-CSA system and without moist curing was compared to the moist-cured OPC-CSA system made without any SRA. The investigation uses the measurements of cement hydration from isothermal calorimetry, autogenous and drying volume changes, internal relative humidity, X-ray diffraction (XRD), and thermogravimetry, as well as compressive strength to characterize the expansion and hydration of OPC-CSA mortar systems. The results indicate that under unsealed conditions, the expansion and strength evolution of OPC-CSA system is significantly sensitive to the presence of moist curing. Mortar containing 15% CSA-based EX resulted in no expansion and had comparable magnitude of total deformation to that of the plain OPC system when no moist curing was adopted. This is linked to the: (i) reduced ettringite formation; and (ii) decreased stiffness which translates to the lower resistance to deformation. Analysis of calorimetry, XRD pattern, and thermogravimetry indicates the synergistic effect of using SRA in OPC-CSA system, which contributes towards higher early-age expansion and increased later-age strength compared to the similar system made without any SRA. In the absence of moist curing, the OPC-CSA system containing SRA exhibited 20% higher non-evaporable water content than OPC-CSA system alone, confirming the effect of SRA addition on hydration reaction progress of OPC-CSA system. The outcomes of this research provide insights into formulation of CSA-based suspensions with the aim of reduced shrinkage, when insufficient initial moist curing is applied.

Structural and Thermal Properties of Air‐Stable [Mg(1‐methylimidazole)6][N(SO2CF3)2]2

An air‐stable Mg salt, [Mg(MIm)6][TFSA]2 [MIm = 1‐methylimidazole; TFSA = bis(trifluoromethylsulfonyl)amide], was obtained by recrystallization from the MIm solution of Mg[TFSA]2. This compound melts at 481 K under sealed conditions, whereas it loses MIm at elevated temperatures (448 K, 5 % weight loss) under unsealed conditions. The crystal structure of [Mg(MIm)6][TFSA]2 was determined by X‐ray diffraction. The compound crystallizes in the monoclinic system (space group P21/c) with a = 8.2062(7) Å, b = 11.3185(10) Å, c = 24.454(2) Å, β = 90.229(2)°, V = 2271.3(3) Å3, and Z = 2. The Mg2+ cation is octahedrally surrounded by six non‐methylated N atoms of MIm ligands to form the [Mg(MIm)6]2+ complex cation, in which three imidazolium rings are crystallographically independent. The interplanar angles between two imidazolium rings, which are close to 90° in an ideal model, are 64.01(14), 72.86(18), and 81.91(17)° owing to the interaction of the [Mg(MIm)6]2+ cations with the TFSA– anions. The TFSA anion is completely isolated from the Mg2+ core and adopts the energetically favorable trans conformation. Raman spectroscopic measurements revealed the octahedral coordination of MIm to Mg2+ in crystalline [Mg(MIm)6][TFSA]2 and MIm solutions of Mg[TFSA]2.