Reduced Water Absorption Research Articles

EFFECT OF RESERVOIR UTILIZATION AND OTHER ANTHROPOGENIC ACTIVITIES ON THE HADEJIA RIVER VALLEY FLOODS: A REVIEW

The unceasing risk perception and socio-economic damages caused by flood disasters have been persistent in Hadejia River Valley (HRV). There is, however, a need to review upstream factors that could exacerbate downstream floods in the valley. The review tends to gain insight from the local and global flood occurrences due to the interplay between upstream reservoir management and other anthropogenic activities and downstream floods. The review underscores the impact of poor upstream reservoir operation, agriculture and other anthropogenic activities in exacerbating the occurrence of floods. These activities alter natural drainage patterns, reduce water absorption, and frequent spills from the major dams and hence, amplify runoff resulting in heightened flood risks. It was observed that reservoirs can serve as flood control facilities (if well-managed) and also exacerbate flooding by releasing large volumes of water too quickly or reaching capacity during intense rainfall events. It is, therefore, essential to consider the location, design, and operation of reservoirs, as well as their role within the HRV management context. In conclusion, the Hadejia-Jama’are River Basin Development Authority (HJRBDA) should adopt the Integrated Water Resource Management (IWRM) approach that combines reservoir management, land use, flood forecasting, and emergency response strategies for minimizing downstream flood risks and maximizing the utilization of the upstream reservoirs.

Polyimide films with ultralow dielectric loss for 5G applications: Influence and mechanism of ester groups in molecular chains

Polyimides are ideal candidates for 5G high-frequency communications due to their good thermal stability, mechanical properties and processability. However, the exploration of how to reduce their high-frequency dissipation factor (Df) remains an urgent and alluring challenge. Inspired by the molecular structure of liquid crystal polyester, which is insensitive to high-frequency electric fields, here we design two series of polyimides derived from diamines with multiple ester groups (AXEB, X = 1, 2 or 3) and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) or p-phenylene bis (trimellitate anhydride) (TA2EB). We investigated the effects of ester number on the aggregation structure, water absorption, dielectric properties, heat resistance and mechanical properties of the polyimides and find that the Df of the multiple ester-containing polyimides decreases rapidly with increasing frequency and number of ester groups. Wide-angle X-ray diffraction analysis, polarized optical microscopy observations and molecular dynamics simulations show that the unique properties of these polyimides benefit from the tight packing of the molecular chain and the strong intermolecular interaction force caused by the ester group, as well as the resulting prolonged dipole relaxation time and the greatly reduced water absorption. Therefore, the polyimide films show extremely low Df values of 0.0030 for AXEB-6FDA and 0.0013 for AXEB-TA2EB. Furthermore, AXEB-TA2EB also shows excellent thermal stability, mechanical properties, electrical properties and permittivity. More importantly, their ultralow moisture rate (<0.83 %) ensures that the high-frequency Df remains stable in different humid environments, even after soaking in water. This method can also be extended to other polymers, thus providing a new strategy for the design of low dielectric loss materials.

RSM-based and environmental assessment of eco-friendly geopolymer mortars containing recycled waste tire constituents

In recent years, there has been a growing emphasis on incorporating recycled materials into the production of eco-friendly construction materials. Additionally, the substantial disposal of end-of-life tires poses significant environmental challenges. Using waste tire constituents in the geopolymer materials as binders a feasible and sustainable alternative to conventional concrete with Portland Cement, effectively resolving environmental problems and promoting the advancement of eco-friendly building material production. This research focuses on producing eco-friendly alternatives to Portland Cement-based products. Moreover, it is aimed to explore the utilization of all components of the end-of-life tires (crumb rubber, textile, and steel fibers) in the mixture and replace Portland Cement with a geopolymer matrix in mortar mixtures. To achieve this, recycled waste tire materials were added to the geopolymer mixtures based on the design of experiments using a central composite design approach. An RSM-based assessment was applied to determine the effect of incorporating recycled materials on the durability and mechanical properties of the geopolymer mixtures. Moreover, the environmental impacts of mixtures were evaluated based on global warming potential and gross energy requirements. The analysis of experimental results revealed that incorporating recycled materials not only substantially mitigated the environmental impact but also improved mixture properties, i.e. reduced water absorption, enhanced resistance to salt scaling, and increased impact resistance. However, there was a slight decrease in compressive strength. Considering all aspects, the final optimized mixture saved 1172.77 MJ/ton energy and reduced 52.33 kg CO2eq/ton per 1 m3 compared to the mixture without recycled materials.

Durability of cementitious mortar: Incorporation of highly dispersed superplasticizer modified graphene oxide in fly ash blended mortar

The present study focuses on the utilization of superplasticizer stabilized graphene oxide (GO) as a reinforcing agent in the fly ash blended cement mortar (30–70 ratio of FA/OPC). GO is moderately stable in water solvent medium while, it agglomerates in the alkaline cement pore solution owing to the interference caused by Mg2+, Na+, Ca2+, and OH− etc. So, here an effort has been made to stabilize the GO via superplasticizer's (PCE-SP) steric effect and has further been used as a reinforcing phase in the cement-fly ash-based mortars. The UV–visible (Agilent Pro) spectrometry was used to measure the degree of stabilization via absorbance values. The increased dispersion of GO due to PCE-SP steric stabilization as compared to without PCE-SP has been monitored by UV–Visible spectroscopy. The results have shown that incorporation of 0.08 % PCE-GO (by weight percentage of blend) amended compressive and split-tensile strength of the mortars by 39.85 % and 48.90 % as compared to control-FA specimen at the curing age of 90 days, respectively. Furthermore, the results achieved were equal or even superior than 100 % cement-based mortar (control-OPC). Micro-structural results showed the acceleration of pozzolanic reactions on the nucleation sites supplied by the PCE-GO's functionalities. Mercury Intrusion Porosimeter studies shows that porosity of fly ash-cement mortar was reduced in comparison to control-FA mortar by 51.5 % after 0.08 % PCE-GO incorporation. The cumulative pore volume also contracted from 0.057 to 0.025 cc/g, depicting densification of C–S–H gel network owing to the synergism acting between FA and PCE-GO in cement-FA matrix. Porosity results are also complying with the enhanced electrical resistivity and reduced water absorption values of mortars. In terms of weight loss and compressive strength gain over various exposure periods, mortars incorporating PCE-GO performed better than control samples in all durability-related aspects. PCE-GO incorporation also resulted in improved acid and sulfate attack resistance, owing to the reduced leaching of calcium ions from hydrated cement-FA matrix. This led to lesser deterioration of PCE-GO incorporated mortars owing to reduced ettringite and gypsum formation, as confirmed by XRD and SEM mapping studies. Overall, the incorporation of PCE-GO in mortars has demonstrated significant enhancements in properties. This development holds great promise for the advancement of the construction and infrastructure sectors. The utilization of high-performance mortars has the potential to enhance the strength, durability, and sustainability of structures, thereby making a valuable contribution to the development of safer and more resilient built environments. Furthermore, the utilization of PCE-GO in an innovative manner has the potential to revolutionize construction methodologies and materials in forthcoming times.

CO2-derived microalgae as a biomass filler to fabricate green composite

In this study, protein-rich microalgae (Chlorella sp. HS2) is investigated as a CO2-derived biomass particle to fabricate a sustainable green composite based on the physicochemical characterizations depending on the temperature and its dispersion and mechanical reinforcing effect in a polymer (poly(butylene adipate-co-terephthalate) (PBAT)) are investigated depending on temperature, incorporated with a small amount of reactive additives with peroxide or glycidyl functional groups. When HS2/PBAT is fabricated at a temperature higher than 130 °C, higher than that expected for thermal degradation of the protein in biomass, HS2 particles undergo cell disruption, changing the surface properties of the cells from hydrophilic to neutral and then reducing water absorption. This hydrophilic-neutral surface transition is attributed to the exposure of certain cell components, including proteins, lipids, and others such as amines, due to the disruption of the cells. It causes homogeneous dispersion of HS2 in PBAT during high mixing temperature. Despite the fact that HS2 is disrupted at high temperatures, the HS2 phase shows reactivity to reactive additives with peroxide or glycidyl functional groups, inducing interfacial bonding between PBAT and HS2 cells and enabling the composite to resist stretching deformation, resulting in increased tensile strength, particularly for composite films. This study demonstrates the potential of microalgae cells as a type of sustainability-reinforced biomass filler to fabricate a green composite. Different from natural biomass, microalgae HS2 cells, consisting of complex organic compounds, are disrupted at high mixing temperature and merged as a secondary phase in the polymer matrix. The addition of the CO2-derived microalgal biomass in synthetic polymer serves as the secondary phase and enhances sustainability, CO2 reduction, and cost-effectiveness without a significant sacrifice of mechanical performance.

Development and Characterization of Green Composites from Agro Waste Aloe Vera and Pineapple Leaf Fiber

Natural fibers possess the advantage of low cost, abundant in quantity and biodegradability. Rising awareness about green products and supportive government regulations are likely to propel the growth in the field of green composite. In this current research, a comparative study of mechanical characteristics and water absorption behaviour of green composites incorporating Aloe Vera and pineapple leaf fibers in biodegradable matrix (polylactic acid) has been experimentally examined. Composite has been developed using compression molding technique. The effect of surface modification of fibers on mechanical properties and water absorption behaviour of developed composite was investigated. Surface treatment was done using alkaline solution of sodium hydroxide having concentration of 5%. Treatment of fiber enhanced tensile, flexural, microhardness and impact properties of developed green composite and reduces water absorption capacity. Moreover, experimental results show that Aloe Vera reinforced composites have better mechanical properties in comparison to Pineapple leaf fiber reinforced composites. Thereby having potential to be used in various engineering applications

Influence Substitution of Tabas Stone Waste which Coated Polyester Resin to Concrete Compressive Strength

The need for the use of concrete raw materials is increasing in line with the increase in the use of concrete in construction. The availability of concrete raw materials is dominated by the exploitation of natural resources, namely components of cement, sand and crushed stone or gravel. If the availability of this material is exploited in excess, it will have an impact on environmental damage. On the other hand, many stone crafts for decoration and building ornaments in Bali also utilize tabas stone which is also exploited from nature, where the processed rock leaves a lot of waste that is disposed of without any wise processing actions. Tabas stone waste management is expected to maximize the utilization of natural resources and also reduce environmental pollution caused by the disposal of tabas stone waste that is not managed properly. This research is expected to provide an alternative to maximize the use of tabas waste as a partial substitution of crushed stone or gravel as coarse aggregate in concrete mixtures. The porous structure of tabas stone and the high level of water absorption in the concrete mix can reduce the compressive strength of the concrete. Steps to reduce water absorption in tabas stone are carried out by maximally closing the pores using a polyester resin coating. The study was carried out by making normal concrete mixture objects according to SNI 03-2834-2000. The percentage of substitution of crushed stone with waste stone that is coated with polyester resin is 0%, 25%, 50%, 75%, 100% of the required weight of coarse aggregate. The compressive strength of the concrete will be tested at the age of 7 and 28 days using a cylindrical specimen measuring 150x300mm. Test results in the laboratory showed that the coating of tabas stone using polyester resin was able to reduce the level of water absorption from 9.96% to 3.24% or 67.5% compared to tabas stone that was not coated with polyester resin. The optimum compressive strength of coarse aggregate substitution using tabas was obtained at variations of 50% crushed stone 50% tabas stone at the age of 7 days and 28 days, respectively, reaching 15.06 MPa and 21.55 MPa.

Effect of moisture absorption on the flexural strength of phenolic matrix composites reinforced with glass fibers and aluminum oxide nanoparticles

AbstractIn this research, the effect of adding aluminum oxide nanoparticles on the flexural strength of glass/phenolic composites that were exposed to water environment was experimentally investigated. To make glass/phenolic composites, IL‐800 phenolic resin, H002 hardener, T400 bidirectional glass fibers and Al2O3 nanoparticles were used. Four‐layer composite plates were made by hand layup method. Beam‐shaped samples were extracted from the plates with the help of laser cutting method. Rectangular composite beams made of glass/phenolic and Al2O3/glass/phenolic were subjected to three‐point flexural test. The moisture absorption test was continued until the amount of water absorption reached a constant level. Bending test was performed on the samples before and after immersion in water. Based on the results, the average flexural strength of the samples after water absorption shows a decrease of about 15%. This parameter is equal to 118.96 MPa for glass/phenolic composite samples immersed in water, and by adding 0.25 wt% of Al2O3 nanoparticles into the matrix material of glass/phenolic composite samples, the flexural strength reaches 142.54 MPa, which shows an increase of 19.82% compared to samples without nanoparticles. Furthermore, the amount of flexural modulus decreases after water absorption, and the addition of nanoparticles in the base material can compensate this reduction. Scanning electron microscopy images illustrate that the addition of Al2O3 nanoparticles into the phenolic resin can enhance the strength of matrix material and improve the adhesion of glass fibers to the resin.Highlights Addition of nano Al2O3 reduces water absorption of glass/phenolic composites. Nano Al2O3 improves composite flexural strength after water absorption. Addition of nano Al2O3 increases the adhesion between the layers of the specimens.

The Use of a Friction Separator to Increase the Strength and Reduce Water Absorption of the Road-construction Slag Aggregate

The purpose of the study is to assess the influence of the parameters of the working process of a laboratory friction separator on the physical and mechanical characteristics of the enriched material (slag aggregate). To achieve the purpose, the methods of laboratory experiment (enrichment on a friction separator), physical-mechanical tests of road-building materials, mathematical processing of experimental data were used. The design of a friction separator for the enrichment of the slag aggregate is considered, the principle of its operation is described. The results of an experiment to assess the effect of the enrichment of the slag aggregate on a friction separator on its strength and water absorption are presented. The authors also established the dependencies interrelating the physical-mechanical characteristics of the slag aggregate and the parameters of the friction separator operation. A quantitative assessment of reducing water absorption and increasing the strength of road-construction slag aggregate after enrichment on a friction separator was obtained

Synergic effect of polyester fiber and nano silica on chemical resistance of geopolymer mortar.

The aim of this study is to evaluate the synergistic effect of polyester fiber-reinforced and nanoslica on the technical performance and durability of geopolymer mortar in terms of the chemical resistance. The study examined how the addition of polyester fiber and nanosilica affects the short-term severe durability of geopolymer mortar specimens made with fly ash (type F). The specimens were cured under ambient conditions. Different percentages (0.6%, 1.2%, and 1.8%) of polyester fiber were used, both with and without nanosilica. Additionally, a reference mixture containing only nanosilica was prepared.All mixtures had a liquid to binder ratio of 0.50, and the ratio of NaOH to Na2SiO3 solution was kept at 2.5:1 by weight. The produced mixes, after 28 days of ambient curing, were immersed for another 28 days in solutions containing 3.5%, 5%, and 5% of sodium chloride, magnesium sulphate and sulfuric acid, respectively. For comparison, control specimens which were not exposed to chemical attacks were tested at the same age of 56 days. Moreover, water absorption and sorptivity tests were conducted to explain the durability performance in a more detailed way. The test results express that the combination of both materials showed a synergistic effect and resulted in greater improvements in compressive and flexural strengths. Both materials can reduce the reduction in compressive strength caused by sulfuric acid exposure, but polyester fiber can increase mass loss. The presence of magnesium sulfate and sodium chloride can lead to a reduction in strength, but the addition of both polyester fiber and nanosilica can mitigate these effects. The addition of fibers creates a network of pores that can limit water absorption, and nanosilica can further enhance the microstructure and reduce water absorption. However, using polyester fiber beyond 1.2 percent can adversely affect the rate of water absorption.

Investigation of the effects of red clay on the structural properties of chamotted clay bodies

Chamotte means fired clay. It is also called Grog and it can have many particle sizes, from fine to coarse. The composition formed by the addition of chamotte to various clay compositions is called chamotte mud (CM). The most preferred and widely used muds in the production of artistic ceramic products are chamotte mud and red pottery mud (R-PM). The sintering, linear shrinkage, water absorption, and color properties of these muds vary depending on their components and firing temperatures. Chamotte mud has properties that make it suitable for use at high temperatures (1150-1200 oC). The obtained products, however, have a high-water absorption value, because it deforms in high-temperature firings, the red Kınık pottery mud used in the study is typically used for artistic productions at low temperatures such as 900-1000 oC. Ceramic artists may prefer to combine and use both types of mud to enhance the color effects and shaping properties in their works. &#x0D; The aim of this study is to reduce water absorption of the body while increasing firing shrinkage, in other words, increasing shrinkage during sintering by adding red pottery mud to chamotte mud and also to optimize the tendency of the R-PM to undergo deformation with temperature. As a result, the products obtained, particularly those produced for artistic outdoor use, will have a longer lifetime. In experimental studies, 6 recipes were produced by combining chamotte and red mud in specific ratios, and the changes in properties such as water absorption, linear shrinkage, color, gloss, microstructure, and sintering behavior of ceramic bodies as a result of firing at 1160 oC were investigated.

The Influence of Chitosan on Water Absorption and Solubility of Calcium Phosphate Cement

Calcium phosphate cements are widely used biomaterials for bone regeneration due to their biological properties, such as biocompatibility, biodegradability, and bioactivity. The presence of chitosan in cement composition influences the resorption rate of the material and its mechanical properties. In the present work, the water absorption and solubility of a tricalcium phosphate bone cement, prepared with and without chitosan addition, was comparatively evaluated. The absorption and solubility properties were monitored for 21 days by immersing the samples in water at room temperature and then weighing them. A morphological analysis of the samples was carried out via scanning electron microscopy (SEM). The absorption dynamics and pore evolution were investigated with low-field nuclear magnetic resonance (NMR) relaxometry. It was demonstrated that the presence of chitosan accelerates the hardening dynamics, reduces water absorption, and influences the solubility and degradation behavior of the cement. It was also observed that, independent of the presence of chitosan, the polymerization process is not completed even after one hour, which influences the solubility process. It was also shown that the presence of chitosan reduces the amount of microcracks and improves the functional properties of the hardened cement.

Properties of abaca/epoxy composites modified by activated carbon particles for orthosis application

Abaca fiber (AF), epoxy (EP), and activated carbon particle (ACPs) incorporated composites have been previously studied to improve their mechanical properties. A study on integrating AF and ACPs to reinforce EP has not been done for comparison. The current study investigates the mechanical (tensile and flexural) and physical (water absorption) properties of AF/EP composites with 20 vol% AF modified by ACPs at 1% to 10% levels, and ACPs/EP composite with 20 vol% ACPs. Optical and scanning electron microscopy examined ACPs and the composite’s fracture surface morphologies. X-ray diffraction was used to identify the ACPs’ phase. The results showed that adding 5 vol% ACPs to AF/EP led to an optimum tensile strength of 42.50 MPa, which was slightly lower than AF/EP (43.00 MPa), and an optimum flexural strength of 62.10 MPa, which was slightly higher than AF/EP (60.50 MPa). Besides, adding 20% ACPs to EP resulted in a tensile strength of 31.93 MPa, higher than the previous result of ACPs/EP (26.34 MPa), also by adding 20% ACPs. Introducing ACPs to AF/EP could reduce water absorption in the composite by 6.52%. The measured flexural modulus of AF/EP added with 5 vol% ACPs was selected as the best material used in the simulation of ankle-foot orthosis (AFO) by Autodesk Inventor integrated with ANSYS Workbench 2019 R1. Applying a load of 27 N resulted in a von Misses stress of 54.018 MPa and a deformation of 44.675 mm.

New insights into the effects of nanosilica on transmission properties and pore structure in high-volume blast furnace slag cementitious materials

This study investigated the effect of nanosilica (NS) on the properties of high-volume blast furnace slag (HVS) cementitious materials. Results showed that HVS led to inadequate early-age development of properties, such as reduced strength and transmission properties, due to increased total porosity and porosity of pore size greater than 100 nm (P100). However, the addition of 2 wt% NS increased the hydration products and decreased the P100 of HVS containing cementitious materials. NS also increased compressive strength and decreased transmission properties of water absorption, especially at higher dosages. The reduction in water absorption was mainly due to the decrease in P100 rather than overall porosity, as shown by the strong correlation between water absorption and P100. NS was an effective additive for enhancing the properties of HVS-cementitious materials by reducing the porosity of pores larger than 100 nm, while increasing the porosity of pores smaller than 100 nm, without significant effect on total porosity.

Effects and mechanisms of capric acid/silica capsule on water absorption reduction of cement paste

Inspired by the structure design on biomaterials for drug delivery, the encapsulation of hydrophobic capric acid (CA) core with a hydrophilic silica shell was proposed and demonstrated in a cement paste system for improving the resistance to water absorption. Firstly the fabrication of CA/silica capsule by interfacial polymerization reaction was reported. Subsequently, the effects of CA/silica capsule and mono-doped CA-hollow silica as hydrophobic admixtures on the compressive strength, water absorption, hydration process and pore structure of 28-day cement pastes were studied. Compared with the mono-doped one, the cement paste incorporated with the capsule exhibited an increased compressive strength and hydrophobicity with reduced water absorption. The increment in the compressive strength and the resistance to water absorption of capsule/cement paste was further ascribed to the improved dispersion and possible sustained release of CA/silica capsule in water, resulting in the improved hydration degree with refined pore structures and the hydrophobicity of the cement paste matrix. The study based on prepared capsule materials suggested a simple but effective approach to the fabrication of hydrophobic cement-based materials with reduced water absorption and extended service life.

Improvement of the Dimensional Stability of Rubber Wood Based on the Synergies of Sucrose and Tung Oil Impregnation

Rubber wood often exhibits dimensional instability during use, which seriously hinders its widespread application. In order to enhance the dimensional stability of rubber wood, a two-step method was employed in this study to modify rubber wood using two plant-derived compounds, namely sucrose and tung oil. Samples treated alone with sucrose or tung oil were also prepared. The water absorption, dimensional stability, and thermal stability of modified and untreated wood were evaluated. The results show that wood samples treated with 30% sucrose and tung oil had excellent water resistance and dimensional stability based on the synergistic effect of sucrose and tung oil. After 384 h of immersion, the 30% sucrose and tung oil group presented a reduction in water absorption by 76.7% compared to the control group, and the anti-swelling efficiency was 57.85%, which was 66.81% higher than that of the tung oil treatment alone. Additionally, the leaching rate of the 30% sucrose and tung oil group decreased by 81.27% compared to the sample modified with the 30% sucrose solution alone. Simultaneously, the 30% sucrose and tung oil group showed better thermal stability. Therefore, this study demonstrates that the synergistic treatment of modified rubber wood by sucrose and tung oil is an eco-friendly, economical, and highly efficient approach with the potential to expand the range of applications of rubber wood products.

High-performance artificial aggregate prepared with recycled concrete powder and its impact on concrete properties

Given the pollution of waste concrete powder, low utilization rate, sand and stone resources shortage, and poor performance of artificial aggregate, the high-performance artificial aggregate was prepared by high dosage recycled concrete powder (RCP). The effects of curing methods, RCP grinding time, RCP:slag ratio, Na2O dosage, and Na2SiO3 modulus on the properties of the aggregate were studied. The results show that natural curing is the most effective, and the best-performing aggregate was obtained with an RCP grinding time of 40 min. The particle size coefficient of the aggregate was around 1.3, and increasing the proportion of slag increased the content of large particles. The amounts of slag and Na2O had a significant impact on the aggregate. As the amounts of slag and Na2O increased, the amount of C-(A)-S-H gel increased, the microstructure improved, and the macroscopic manifestations increased apparent density and strength and reduced water absorption. The maximum strength of the aggregate reached 8.59 MPa, and water absorption was 12.67% at this point. Concrete was prepared using the aggregate above, and the effects of aggregate curing time, aggregate pre-wetting time, and aggregate material ratios on the properties of the concrete were studied. The results show that the density of RCP artificial aggregate concrete is low, between 2030 kg/m3-2220 kg/m3. The compressive strength and splitting tensile strength of concrete increase with the increase of aggregate curing time, prewetting time, and the dosage of aggregate Slag and Na2O, which reach 59 MPa and 4.5 MPa, respectively. The aggregate strength increased, leading to interfacial failure inside the concrete, while larger aggregate particle size tended to cause aggregate failure inside the concrete.

Study on the compressive mechanical properties of mixed recycled aggregate concrete with silane modified

This study used a 10% silane solution to strengthen recycled brick aggregates (RBA). Subsequently, mixed recycled aggregate concrete (MRAC) was prepared by using recycled concrete aggregate (RCA) and RBA modified with silane (Si-RBA). The properties of RBA and RCA were compared. The effects of the Si-RBA/RCA ratio on the failure modes, compressive strengths, and characteristics of the compressive stress strain curves under monotonic loading and cyclic loading were tested. The microstructures of the RBA, Si-RBA, and MRAC were analyzed by scanning electron microscopy (SEM). The test results showed that RBA modified with silane reduced water absorption by 51.61% and improved the crushing index by 14% compared to RBA. When the Si-RBA/RCA ratio changed from 0:10 to 10:0, the failure mode of MRAC transformed from interfacial transition zone (ITZ) failure to aggregated failure, while the compressive strength decreased. The MRAC specimens exhibited similar failure phenomena, regardless of monotonic or cyclic loading. The peak stress and elastic modulus decreased as the Si-RBA/RCA ratio increased, whereas the peak strain showed a fluctuating growth trend, and the plastic strain increased. In addition, SEM images showed that the reaction products of silane filled the pores of the RBA, and the silane solution made the ITZs of the RBA much denser. Based on the test data, a constitutive model for MRAC under monotonic and cyclic loadings was proposed, which showed good accuracy in predicting the response of MRAC under a compressive load.

A19-saponin–modified polymethyl methacrylate base denture composites: antimicrobial, mechanical and water absorption potentials

Abstract The increased growth of Candida albicans (C. albicans) with allergy reaction of MMA remains an issue of concern among denture wearers. C. albicans growth inhibition, mechanical and water absorption potentials of extracted A19-saponin–commingled PMMA denture base composites were investigated. Soxhlet extraction technique for defatting of Dialium guineense (D. guineense) stem powder was used with ethanol to extract A19-saponin. Fungicidal inhibition concentration of A19-saponin extract of D. guineense was determined. PMMA denture base was prepared with incorporation of A19-saponin at different concentrations of obtained 23.2 % yield. The mechanical and water absorption properties were determined. The minimum and maximum fungicidal inhibition concentrations and susceptibility of 25 and 100 % for extracted A19-saponin were obtained, respectively. PMMA, MMA and extracted A19-saponin of ratio of 30 g: 5 ml: 5 ml denture was optimally fabricated. A19-saponin increased the impact strength and hardness by 352.94 and 11.54 % with reduced water absorption by 82.85 %. Thus, A19-saponin as an additive improved quality of denture.

Effect of regulating urease activity on the properties of bio-CaCO3 precipitated on recycled aggregates

The high porosity of attached mortar on recycled aggregates leads to high water absorption and low strength, which hinders its application efficiency in concrete production. Microbial induced carbonate precipitation is a promising approach for enhancing recycled aggregates. The difficulty at present is that the low bonding between biogenic CaCO3 and aggregates leads to low strengthening efficiency. The cohesion among CaCO3 and its bonding with aggregates have been found to be closely influenced by the precipitation rate. While in the ureolytic process, urease activity is the key to control the precipitation process. In this study, the precipitation process was controlled by regulating the release rate of urease activity and its effect on the mechanical properties of the deposited CaCO3 was studied. The results showed that controlling the initiation time of induced bacterial urease and the concentration of precipitated precursors (calcium and urea) could effectively slow down the release rate of initial urease activity, thus regulating the precipitation rate. It was found that the bacteria cultivated without substrate urea can slowly release urease activity, and the urea decomposed process can be sustained until 14 d, and the best cohesion of biogenic CaCO3 could be obtained at 0.5 M of calcium and urea. The aggregates treated by the bacteria cultivated with urea showed a mass loss of 1.88% and water absorption reduction of 8.9%. While the ones treated by the bacteria cultivated without urea showed a mass loss of 1.70% and water absorption reduction of 29.83%, and the ones treated by the pellets centrifuged by the bacteria cultivated without urea showed a mass loss of 1.44% and water absorption reduction of 22.46%. It proved that the method of bacterial cultivation without urea can efficiently enhance the bonding strength between biogenic CaCO3 and aggregates, thus further improving the properties of aggregates, which was of great significance to improve the application efficiency of recycled aggregate in concrete.