Acid Resistance Test Research Articles

Chemical Compound Identification of Lactic Acid Bacteria (LAB) From Porang Tubers Waste (A. muelleri blume) as Probiotic

The production of amylase produced by lactic acid bacteria (LAB) has better stability. The purpose of this study was to utilize and determine the characteristics of LAB isolates from porang skin waste which have the potential as probiotics and the activity of amylase enzymes. Isolation was done by fermentation method for 48 h with the addition of starter Pediococcus acidilactici that had been cultured. The results showed that the number of colonies of N1 isolates was 49 ×108 CFU/mL with regular small round colonies, having a convex elevation, the edges of the colonies were round, yellowish white, and Gram positive bacteria because they produced a purple color on Gram staining. Acid resistance test at pH 2.0; 3.0; 4.0; 5.0 and 6.0, the isolates N1 was able to survive at each pH because it showed turbidity in the growth medium. The antimicrobial activity test showed a strong zone of inhibition on S. aureus and S. pyogenes of 10,33 and 11,17 mm and a moderate zone of inhibition on K. pneumoniae, S. dysentriae, and P. aeruginosa, respectively, which was 6,33; 7,7 and 7,5 mm. The positive N1 isolate contained alkaloids as bioactive compounds from the results of phytochemical screening and the results of the FTIR analysis showed that specific groups of alkaloids were N-H, C-N, and C=O at wave numbers 3423.30 cm-1; 1235.45 cm-1; and 1634.81 cm-1.

Isolation and evaluation of Pediococcus acidilactici YH-15 from cat milk: Potential probiotic effects and antimicrobial properties

The study aimed to screen for the possible presence of lactic acid bacteria (LAB) in cat milk in order to evaluate their probiotic properties. The isolates were characterized by biochemical identification, morphological tests and 16S rDNA sequencing. Afterward, gastrointestinal passage, in vitro safety and probiotic properties were evaluated. The results showed that the isolates had 10 strains of Pediococcus acidilactici permitted in the feed additive catalog. The high survival rate in the acid and bile salt resistance test reflected the good strain tolerance of the isolates to the simulated gastrointestinal conditions of the host in vitro. The mean inhibitory diameters of the 10 strains against chloramphenicol and tetracycline were 23.6 mm and 17.4 mm, respectively; none of the hemolytic tests showed α/β hemolytic ring. The bacteriostatic test showed that P. acidilactici YH-9, YH-14 and YH-15 had inhibitory effects on four common pathogenic bacteria, including Escherichia coli, Salmonella typhimurium, Staphylococcus aureus and Streptococcus. The adhesion test showed that P. acidilactici YH-15 had good adhesion to HT-29 cells. Based on these results, we concluded that P. acidilactici YH-15 extracted from cat milk has potential application as a clinical probiotic therapy and health care product.

Luminescence and spectroscopic studies on Dy3+-Eu3+ doped SiO2-B2O3-ZnO-La2O3-BaO glass for WLED

A series of SiO2-B2O3-ZnO-La2O3-BaO (SBZLBa) glasses doped with Dy3+ and Eu3+ were synthesized using the melt-quenching technique. Their optical characteristics and potential applications in W-LED devices were investigated. The structural effects resulting from doping the glass with Dy3+ and Eu3+ ions were elucidated through infrared spectroscopy and an examination of the physical properties. The variations in emission intensity within the fluorescence spectrum validated the sensitizing effect of Dy3+ on Eu3+ within the glass matrix. By manipulating the transitions of both Dy3+ and Eu3+, the excitation wavelength was altered, enabling the realization of cool white, neutral white, and warm white luminescence, thus accommodating the diverse requirements for white light emission in lighting applications. After incorporating 1.0 mol% of Dy2O3 and 0.8 mol% of Eu2O3, respectively, the glass exhibited CIE coordinates of (0.3332, 0.3535), positioning it within the white light spectrum and in close proximity to the ideal white light coordinates of (0.33, 0.33). The SBZLBa-Dy2O3–0.8Eu2O3 glass exhibited a quantum yield of 5.98 %. It has been demonstrated through acid and alkali resistance tests that this glass possesses excellent chemical stability. Additionally, temperature-dependent emission spectra have revealed that the luminous intensity of the glass maintains over 85 % of its room temperature value at 185 °C, with Eα determined to be 0.2387 eV.

Mechanics and Durability of Polyurethane Cement Composite (PUC) Material

In order to investigate the mechanical properties of polyurethane cement (PUC) composite materials, axial tensile test, acid and alkali corrosion resistance test, bond test with concrete, and bond test with steel bars were conducted. The axial tensile results show that the tensile strength of PUC material is 31.11MPa, the stress-strain curve for axial tensile behavior of the material is obtained through fitting. To explore the durability of PUC materials, acid-alkali-salt corrosion resistance test is carried out, the results show that the PUC material has good resistance to acid and alkali corrosion. The failure mode of the bond test between PUC material and concrete is internal cohesion failure of concrete material, indicating good bond performance of PUC material. Axial tensile test of PUC material is carried out at different temperatures (-40℃~60℃). When subjected to temperatures between 40�C and 60�C, the strength of materials does not deteriorate. However, it is noteworthy that the material�s ability to withstand tensile strain significantly increases as temperatures rise to 60�C. The bonding strength between PUC material and steel bar increases with an increase in protective layer thickness, and at a thickness of 70 mm, the maximum bond stress is achieved at 16.38 MPa. On the other hand, the strength of the bond reduces as the anchorage length increases. Smooth round bars demonstrate a significantly lower bond strength compared to deformed bars, as their maximum bond strength is at approximately 47.4% of that of the deformed bars under the same conditions.

Acid resistance of hydroxyapatite dental films fabricated through powder jet deposition

This study proposes a novel dental treatment method using powder jet deposition (PJD). PJD can be employed to fabricate hydroxyapatite (HA) films directly on human enamel by blasting fine HA particles. Acid resistance tests were performed on HA films fabricated with two blast angles (α = 60° and 90° with two samples each) and using human enamel (with one sample) to evaluate the usefulness of the HA films in acidic intraoral environments. All samples were dissolved in acid, and their volume gradually decreased over the test time tacid. Transmission electron microscopy images showed that the grain boundaries near the acid-exposed surface of the HA films were densely modified and prevented acid penetration, whereas the human enamel grains became finer owing to the acid–base reaction. Thus, the HA films lost lesser volume than the human enamel did, indicating higher acid resistance. However, one film fabricated at α = 60° partially peeled off during tacid = 6–9 h. Analysis of the PJD phenomenon through smoothed particle hydrodynamics indicated that the tensile residual stresses promoting crack propagation and delamination increased as α became more acute, causing HA film peeling. Therefore, particles should be blasted in multiple directions to avoid stress bias.

Streptococcus thermophilus and Lactobacillus bulgaricus Attributes as Influenced by Carao (Cassia grandis) Fruit Parts

Carao (Cassia grandis) contains numerous bioactive substances that contribute to gastrointestinal well-being. The present study assessed the potential impacts of carao on the viability and performance of Streptococcus thermophilus and Lactobacillus bulgaricus under various adverse conditions. These conditions included bile, acid, gastric juice, and lysozyme exposure, simulating the digestive process from the mouth to the intestines. The activity of proteases from cultures was monitored to examine their proteolytic capabilities. To achieve this, the cultures were cultivated in a solution containing plant material, and the results were compared against a control sample after an incubation period. Subsequently, the total phenolic content, total carotenoid content, antioxidant activity, sugar profile, and acid profile of the plant materials were analyzed. These analyses were conducted to explore these compounds’ influence on cultures’ survival. Seeds contained the highest total phenols (766.87 ± 11.56 µg GAE/mL), total carotenoid content (7.43 ± 0.31 mg Q/mL), and antioxidant activity (40.76 ± 1.87%). Pulp contained the highest moisture (12.55 ± 0.44%), ash (6.45 ± 0.15%), lipid (0.66 ± 0.07%), protein (16.56 ± 0.21%), sucrose (9.07 ± 0.78 g/100 g), and fructose (3.76 ± 0.06 g/ 100 g). The crust had the highest content of ash (85.14 ± 0.27%) and succinic acid (2.01 ± 0.06 g/100 g). Results indicated that seeds negatively affected cultures’ survival in the bile tolerance test and had positive effects on Lactobacillus bulgaricus in the protease activity test. Otherwise, the other carao tissues could not change the results significantly (p > 0.05) compared to the control in different tests. The carao crust positively affected cultures’ against protease activity, especially in Lactobacillus bulgaricus, and had a negative effect on the growth of S. thermophilus in the lysozyme and gastric acid resistance test.

Durability Properties of High-Strength Concrete Containing Fly Ash, Dolomite Powder and Slag Sand

Concrete is the most extensively utilized construction material worldwide. The production and demand for cement have seen significant growth, but this increased demand has raised concerns about its environmental impact within the construction industry. Concrete can be produced using alternative materials or substitutions for cement, fine aggregate and coarse aggregate, often utilizing waste materials. In this study, dolomite powder and fly ash used as a partial replacement for cement and slag sand is used as a 100% replacement to natural sand. Dolomite powder shares certain properties with cement, making it a cost-effective alternative that can enhance the strength of concrete. The disposal of fly ash is becoming a significant environmental concern due to its potential environmental hazards as a waste material. Using fly ash is not only cost-effective but also improves the workability, strength, and durability of concrete. Additionally, the use of slag sand not only contributes to environmental conservation but also enhances the structural strength and durability of concrete. The reason is the high tensile strength of slag. The durability tests on this project are water absorption, acid and alkali resistance tests. In these tests, an acid resistance test involves the use of 5% dilute sulfuric acid (H2SO4) by volume of water, while an alkali resistance test uses 5% sodium hydroxide (NaOH) by weight of water. These tests are conducted using M60 grade concrete mixtures, which incorporate partial replacements of cement with fly ash ranging from 0% to 10% by weight of cement, and dolomite ranging from 0% to 20% by weight of cement. Additionally, fine aggregate is replaced with slag sand in these mixtures.

Isolation of Lactiplantibacillus plantarum producing Extracellular Lipase from Dairy Products and Optimization of the Enzyme Production

Recently, microbial lipases isolated from probiotic bacteria have attracted the attention of many scientists because they have significantly beneficial properties for human health. As a highly nutritious substrate, dairy products possess great potential for probiotic bacteria isolation. The main purpose of this study was to isolate probiotic bacteria in order to search for lipase producing bacteria. The bacteria were isolated from dairy products and purified by repeated sub-culturing on MRS medium at 37°C. The isolates were subjected to primary and secondary screening via fluorometric and colorimetric methods respectively. The isolates showing orange fluorescence under UV light at 350 nm around their colonies were selected for the colorimetric method. In this method, lipase activity was investigated by p-nitrophenyl palmitate. Probiotic characterizations of lipase-producing isolates were performed by acid resistance test, cell surface hydrophobicity assay, auto-aggregation and co-aggregation. The optimization of lipase production was performed by Central Composite Design (CCD). In the present study, 92 isolates were recovered from 71 samples. The results showed that 41 isolates were positive for fluorometric assay. According to the amount of enzyme production, seven strains were selected for probiotic characterizations. Finally, a potential probiotic strain of genus Lactobacillus showed the highest enzyme activity with 3.4 U.ml-1 compared to other isolates. This strain showed 100% similarity to Lactiplantibacillus plantarum. This research indicated that the lipase of Lactiplantibacillus plantarum can be used as a promising enzyme in the food and medicine industries.

Iron ore tailing (IOT) chemical composition and content impact on the physical, mechanical, and durability properties of blended cement

The IOT addition in cement prevents the construction of new tailings dams and reduces carbon dioxide emission in the atmosphere as the need for clinker in Portland cement decreases. This paper aims to evaluate the use of IOT as supplementary cementitious material and to investigate the impact of IOT chemical composition and Fe content on the physical, mechanical, and durability properties of cement blended with IOT. The motivation for this paper is that the literature presents chemical compositions of IOT with different percentages of Fe and Si, and the influence of this variation is still unknown, mainly with regard to high levels of Fe2O3 in the IOT. Basically, the IOT was benefited by magnetic separation, producing three materials: (i) IOT N (as collected), (ii) IOT S (low Fe content), and (iii) IOT F (high Fe content). IOT N, S, and F were processed by milling and characterized using XRF, XRD, and granulometry techniques. Pastes and mortars were produced to carry out isothermal calorimetry, thermogravimetry, compressive strength, water absorption, porosity, and sulfuric acid resistance tests. The accumulated heat of hydration, chemically bound water, remaining portlandite, and calcium carbonate were reduced for IOT cement. Regarding the compressive strength, 10 % IOT cement could be classified, according to the Brazilian standard, as CP–II–Z 40 while 20 % IOT cement as CP-IV 32. A small increase of less than 1 % for water absorption and IOT improved the resistance to sulfuric acid in the cement. The reference mortar (REF) showed 8.87 % mass loss during acid attack and the mortar with IOT F20 cement showed 6.81 % mass loss during acid attack, demonstrating greater durability under severe attack conditions. ANOVA verified that the IOT chemical composition and content statistically impacted all the results of the hardened cement blended with IOT. Hence, IOT as a partial replacement for clinker in Portland cement proved environmentally and commercially viable.

STRENGTH-DURABILITY PROPERTIES AND MICROSTRUCTURAL ANALYSIS OF CONCRETE CONTAINING COW BONE ASH AND BENTONITE

One of the major agricultural wastes discarded from abattoirs in large quantities is the cow bone. Thus, there is need to find alternative means of promoting cleaner environment which is critical for environmental sustainability. This study aims to establish the viability of using cow bone ash and bentonite as partial replacement for cement improve the properties of concrete. Chemical composition examined on the CBA and BT showed that the materials have potential to serve as supplementary cementing material in concrete. In this study cement was partially replaced with cow bone ash and bentonite at 5% interval from 5 – 20%. Mix with 10% CBA/BT had the highest compressive strength across all curing ages. At 7, 14, 21, 28 and 56days 10% CBA/BT replacement recorded a 1, 49, 23, 14 and 8% increase in compressive strength respectively, similar flexural and split tensile strength examined also showed increase in strength. Water absorption test recorded a decrease in water absorption as the CBA/BT content increased. Acid resistance test showed that the concrete specimen reduced in compressive strength of at an average of 39%. The microstructure analysis of the concrete specimen revealed an improved micro packing of aggregate resulting in a denser and increased strength of concrete. The study finds that at optimal dosage of 10% CBA/BT, the concrete had an improved mechanical strength, lower water absorption ability and a better interlocking particle arrangement at microstructural level.

Slippery surface with ternary coupled structures for improving lubricant-storage capacity

A slippery surface has the capability to protect the substrate surface, which can prevent substrate corrosion in a harsh environment. However, existing slippery surfaces have the limitation of insufficient oil-locking capability for rough structures, which limits their practical application. To solve the aforementioned limitation, the authors developed a slippery surface with a good oil-locking capability. First, a wire-cutting machine tool was used to fabricate ternary coupled grooved structures on an aluminum (Al) substrate, which could increase the lubricant-storage capacity of the microstructures, and the substrate was named slippery porous surface with groove-textured aluminum (Slips-G-Al). Then, a surface durability test was performed involving lubricant shear, sandpaper wear and water impact. The chemical stability test involved acid, alkali, salt corrosion and weather resistance tests, which showed that Slips-G-Al had a good lubricant-storage capacity compared with the traditional Slips surface. In addition, the self-cleaning performance and the fog collection capability of Slips-G-Al were also studied. Finally, an electrochemical corrosion test of Slips-G-Al was carried out. The findings showed remarkable application prospects in the aerospace and shipbuilding fields.

Mechanical properties of polyolefin and polypropylene fibers-reinforced concrete–An experimental study

Concrete, a widely used construction material, exhibits inherent brittleness and limited tensile strength. To address these shortcomings, the incorporation of fibers has gained prominence, with polyolefin and polypropylene fibers emerging as promising reinforcements. This study experimentally conducted and examined the mechanical characteristics of polyolefin and polypropylene fibers-reinforced concrete. The study involved conducting compressive strength tests and durability tests, including sulfate resistance, acid resistance, chloride ion penetration resistance, and abrasion tests. The results demonstrated a notable enhancement in the compressive strength of both cubic and cylindrical specimens with varying dimensions, owing to the inclusion of polyolefin fibers. Polyolefin fibers exhibited a greater reinforcing effect compared to polypropylene fibers, especially in larger cubic specimens and cylindrical specimens. The quantitative results show that specimens with polypropylene fibers exhibited a 9.67 % improvement in compressive strength, while those with polyolefin fibers showed a 30.47 % enhancement compared to specimens without fibers. The acid resistance test revealed that both types of fiber-reinforced specimens exhibited higher compressive strength in acidic environments compared to plain concrete specimens. In the chloride ion penetration resistance test, the polyolefin fiber-reinforced specimen demonstrated the highest resistance to degradation, while the plain concrete specimen exhibited the lowest resistance. Polyolefin demonstrated superior reinforcement compared to polypropylene, with a 35 % increase in acid resistance and better chloride ion resistance. In contrast, specimens without fibers weakened by 35.36 % in a chloride environment. The sulfate resistance test showed that the polyolefin fiber-reinforced specimen had the highest compressive strength in a sulfate environment, while the plain concrete specimen had the lowest. In sulfate and abrasion tests, polyolefin-fiber-reinforced specimens displayed the highest resistance and the lowest abrasion rate of 34.6 %. These findings highlight the potential of polyolefin fiber-reinforced concrete for enhancing mechanical properties and durability in various applications.

Retracted: A study on the strength and durability characteristics of fiber-reinforced recycled aggregate concrete modified with supplementary cementitious material

Recycled aggregate (RA) made from waste concrete is an environmentally friendly alternative to natural aggregate (NA) for concrete manufacturing. However, compared to NA concrete, concrete produced with recycled aggregates has poor characteristics. Supplementary cementitious materials (SCMs) can be used to enhance the poor properties of recycled aggregate concrete (RAC). Silica fume and fly ash are commonly used SCMs in the World, but their high usage led to a shortage of silica fume and fly ash. Still, the deficiency of these materials in large parts of the world is a challenge that requires exploring alternative feedstock materials for the construction industry in the coming years. Wheat straw ash (WSA) is an agricultural waste product that could be used as an alternative SCM due to its pozzolanic behavior to enhance the properties of RAC. In addition, concrete is brittle and needs reinforcement, for which polypropylene fibers (PPFs) can be used. The current research examines the mechanical characteristics of fiber-reinforced RAC, including compressive strength, splitting tensile strength, and ductility performance. Durability indicators, such as chloride diffusion, chloride penetration, acid resistance, and water absorption test, were also assessed. The results showed that concrete samples with 10% WSA, 50% RA and 1.5% PPFs had the highest compressive and splitting tensile strength, 60.2 MPa and 7.25 MPa, respectively, representing increases of 24.75% and 30.65%, as compared to plain samples at 56 days. In these samples, water absorption was reduced by 13% due to the finer WSA particles resulting in the lowest reduction in strength and mass recorded when exposing concrete samples to acidic media. The statistical analysis also validated that irrespective of WSA and PPFs, the concrete with 0% RA had the highest performance in strength and durability behavior. The study showed that WSA and PPFs might be employed in tandem to offset the poor behavior of RA, enhance the bond between fibers and concrete, and improve the mechanical strength and durability performance of RAC, thus demonstrating its suitability as a sustainable and economical construction material.

Durability performance of low calcium Flyash-Based geopolymer concrete

This investigation aims to systematically evaluate the durability performance of 30 MPa grade of low calcium fly ash-based geopolymer concrete. The geopolymer concrete with fly ash as binder is manufactured using an alkaline activator solution (of 14 Molar and Na2Sio3/NaOH ratio of 2.5). The results were also compared with the Portland cement concrete of similar grade. The concrete samples were subjected to water absorption, water permeability, sorptivity, acid resistance, sulphate resistance, and rapid chloride penetration tests. Water absorption study findings revealed less water absorption by low calcium fly ash-based geopolymer concrete than Portland cement concrete. Also, the water permeability tests on geopolymer concrete indicated lower water penetration depth compared to Portland cement concrete. Sorptivity test results depict lower sorptivity by geopolymer concrete over ordinary Portland cement concrete. Geopolymer concrete shows better acid resistance and sulphate resistance performance than Portland cement concrete in terms of residual compressive strength. Rapid chloride penetration test results indicated moderate chloride penetrability of geopolymer concrete and low chloride penetrability by Portland cement concrete. In general, low calcium fly ash based geopolymer concrete outperformed Portland cement concrete in most durability indices, which led to the conclusion that low calcium fly ash based geopolymer concrete durability performance was superior to that of concrete of a similar grade made of Portland cement concrete.

A high reliability super hydrophobic silicone rubber

Superhydrophobic surface is extensive used in aerospace, biomedicine and everyday life because of its excellent hydrophobicity. In order to verify the durability and stability of superhydrophobic silicone rubber composite (MVQ/screen mesh/spray) prepared by template method and spraying technology, dry heat aging test, acid and alkali salt resistance test, extrusion resistance test, steel ball resistance test and sandpaper wear test were carried out. The results showed that the surface contact angle of the prepared MVQ/screen mesh/spray was 160.88 ± 0.78°, and the rolling angle was 1°. After a series of durability tests, because of the regular concave-convex structure of the rubber surface, the abrasion of the rubber surface was slowed down, and when the liquid drops fell on the surface of MVQ/screen mesh/spray, it can provide great support and kept good hydrophobic effect on the rubber surface. The mechanism of rubber surface wettability was expounded, and the influence of chemical and physical factors on superhydrophobic surface was analyzed.

Experimental studies on mechanical and durability properties of high performance concrete with partial replacement of fine aggregate with crushed Quartzite and binding material by fly ash and silica fume

The high performances concrete’s demand growing day by day due to its mechanical properties like compressive strength and it’s durability characteristics therefore the Research on high performance concrete on its verge. The availability of natural fine aggregates are diminishing day by day there by it is the time to search for alternative. Many researches are using utilizing industrial waste in High performance Concrete. In the present study, M60 grade of the concrete was used and designed as per the mix design standards of American Concrete Institute (ACI, 234R-96). The mechanical properties of HPC, such as compressive strength, split tensile strength, and modulus of elasticity, as well as durability properties, such as acid resistance test, sulphate resistance test, chloride resistance test, ultrasonic pulse velocity test, and alternate wet and dry test, were determined using specimens of regular concrete mix and modified Crushed Quartzite concrete mixes. According to the experimental findings, HPC has good mechanical and durability features when 30% crushed quartzite is substituted for fine aggregate, and the amount of binder is determined by the compressive strength of concrete when varied amounts of fly ash and silica fume are used. Optimization of admixture arrived as Fly ash 15% and silica fume 10% to the weight of cement content.

Strength and durability characteristics of concrete blended with micro level fibres

Concrete is among the most used building materials, which is often produced using materials that are readily available locally. To fulfill the demands of modern building, the current trend in concrete technology is to make concrete stronger and more durable. The primary goal of this research is to examine the comparative analysis of mechanical parameters of different size cubes and to determine the durability parameters of concrete of grade M40 incorporated with various dosages of glass fibre and steel fibre in a micro size level. Concrete's durability and brittleness are both improved with the inclusion of fibres for a dosage of 0.1 to 1% of concrete volume. In this investigation we researched the compressive strength variations of 150 mm size cubes and 100 mm size cubes cast with 0.5% & 1% addition of glass and steel fibre. The ultimate compressive strength of concrete cubes with 1% addition of glass fibre at 28 days of curing is 49 MPa and 51 MPa for 150 mm size and 100 mm size cubes respectively. The various mix proportions are tested for different durability tests like acid resistance test, sulphate attack test, alkalinity of concrete and water absorption. The strength loss of mix with 0.5% addition of glass and steel fibres due to acid attack are 19% and 19.2% which is low compared to control concrete. Also the average strength loss of mix with 1% addition of glass fibre is low when compared to other mixes in a sulphate environment. The water absorption percentage is low for concrete mixes blended with glass fibres. The alkalinity of concrete varies with pH of 10.5 to 9.5 for various mixes. Through this experiment, it was discovered that glass fibre blended concrete outperformed control mix and mixes with steel fibres in terms of all strength and durability metrics.

Assessment of some incipient caries risk factors in adolescents

Relevance. Risk assessment of carious lesion onset remains relevant due to the high incidence rate. The article presents the data on the impact of permanent dental enamel functional condition and microbial factor on incipient caries onset in adolescents.Purpose: The study aimed to investigate the etiology and pathogenesis risk characteristics of incipient caries onset in adolescents.Material and methods. The study included 90 adolescents aged 11-17 y.o. from Penza city. At the clinical stage, we studied adolescents’ permanent teeth vulnerability to caries; then, we formed the study groups according to WHO criteria (Group 1 – moderate, Group 2 – high, Group 3 – the very high intensity of caries) and Group 4 included children of the same age without caries. Vital staining and electric pulp testing with the “DentEst” device (Geosoft, Russia) detected white spot lesions. The OHI-S and enamel acid resistance test (TER-test) evaluated the level of oral hygiene. The laboratory stage determined the number of mixed saliva cells contaminated with bacterial microflora (microflora contamination coefficient) to define the bacterial load in the mixed saliva of the examined adolescents.Results. Besides high clinical rate of white spot lesions (intensity rate 3.10 ± 0.05 and demineralization degree 5.90 ± 0.08 μA) linked to poor oral hygiene level according to OHI-S (2.80 ± 0.13), the examined children of Group 3 (very high caries intensity) revealed a decrease in enamel acid resistance (TER-test 6.50 ± 0.22) and increased bacterial load of mixed saliva – microflora contamination coefficient (48.12 ± 0.80%). Differences with the same parameters in Group 4 (without caries) were statistically significant (P < 0.05). The study of the statistical relationship between enamel demineralization degree and the level of mixed saliva bacterial load (microflora contamination coefficient) detected a positive correlation between the studied parameters of moderate and high power and received the following correlation coefficient values in Group 1 (R = 0.46), 2 and 3 (R = 0.73 and R = 0.78) respectively.Conclusion. Assessment of some risk factors for white spot lesion onset and monitoring of changes may include the analysis of clinical and laboratory data on the hard-dental-tissue condition and mixed saliva bacterial load determination (microflora contamination coefficient).

Experimental investigation on compressive strength and acid resistance of autoclaved aerated concrete using GGBS

The objective of this paper is to produce Autoclaved aerated Concrete (AAC) by using Ground Granulated Blast Furnace Slag (GGBS) as the partial replacement of the fly ash. AAC has emerged as one of the most prominent sustainable material because of its benefits such as fire resistance, light weight and high workability etc. Proportioning the mix components for AAC is a most important step in generating high-strength AAC block. The GGBS have been replaced at 24%, 30% and 36% of the total weight and have been tested for compressive strength, water absorption and acid resistance. The experimental results have shown that there has been an increase in compressive strength by 28–44% when compared to conventional AAC block and in acid resistance tests, the ratio of weight reduction and compressive strength declined as GGBS increased. It is been found that the block is eco-friendly as it contains non-toxic materials and the waste generated from industries. It can be used for constructing low load bearing structures and as the block is light weight material, it decreases the dead load of the structure.

Assessment of Natural Additives Modified Lime Mortars for Repair of Historic Structures with Strength, Durability and Microstructural Parameters

The contemporary building material despite the significance of cement in construction industry is the lime mortars because of its usage as a structural repair material around the ancient heritage structures. Though the significance of lime mortars lies in the fact of compatibility towards the existing ancient lime-based structures, the method of construction and material preparations are still undisclosed. In such a case, it is necessary for the researchers to analyze scientifically, the influences of various additives towards the performance of lime mortars. This paper tries to attempt two natural additives viz., gallnut (Terminalia chebula) and palm jaggery (Saccharam officinarum) as modifiers of mixing water in the preparation of class B hydraulic lime-based mortars through the process of fermentation. Based upon the trials, 39 mixes were considered with varying water to lime ratios and dosages of additives. Experimental tests such as workability, compressive strength, water absorption, acid resistance and NaCl cyclic tests were conducted along with SEM and XRD microstructural assessments. The maximum compressive strength achieved was about 4.3 MPa which is 200% that of conventional lime mortars. Jaggery and gallnut-based additives were efficient in various durability studies however the performance of jaggery is superior to gallnut in various aspects.