Amount Of Calcium Hydroxide Research Articles

ENHANCING CONCRETE DURABILITY

Acid attacks are compromising the durability of concrete more and more, especially in urban and industrial settings. By reducing the amount of calcium hydroxide in the concrete, these attacks have an impact on its mechanical qualities. This study examines the impact of supplemental cementitious materials (SCM) such as rice husk ash (RHA) and cassava peel ash (CPA) on the acid resistance of concrete, given the low resistance of traditional hydraulic cement to such conditions. The goal of the study is to determine the ideal ratio of RHA to CPA in order to improve the durability of concrete in acidic conditions. Ordinary Portland cement and locally available aggregates were used in a methodical experimental approach. In addition to a control mix, concrete mixes with constant CPA percentages of 5% and variable RHA percentages of 0%, 5%, 10%, and 15% were made. Slump tests for workability, density measurements, and compressive strength evaluations of cubes cured in diluted sulfuric acid and plain water were all part of the study. The SCM oxide composition was evaluated by X-ray fluorescence (XRF) analysis, which showed that RHA was more reactive than CPA and that its combined SiO2, Al2O3, and Fe2O3 content was higher than the 70% threshold. The results showed that adding SCM increased durability in acidic environments. According to the study's findings, RHA considerably increases concrete's resistance to acid, indicating that it may be able to increase structural durability under harsh conditions. Future studies should examine how well these SCMs function over the long run in a variety of scenarios and look into other therapies to improve acid resistance even more.

Effects of Post-Fire Rehydration on the Mechanical Properties of Slag-Modified Concrete

Although previous research has examined the mechanical properties of concrete exposed to high temperatures, further investigation is needed into the effects of post-fire curing on the recovery of strength and stiffness of sustainable concretes produced with slag-modified cement. This study conducted an experimental analysis of the residual compressive strength and modulus of elasticity of different types of concrete (20 MPa or 30 MPa) exposed to varying maximum temperature levels (200 °C, 400 °C, 600 °C, 800 °C) and post-fire treatments (with or without rehydration). The concrete specimens were produced using Portland cement CP II-E-32. The rehydration method involved one day of water curing, followed by 14 days of air curing. Statistical analyses revealed potential improvements in the mechanical properties of concretes produced with slag-modified cement due to rehydration processes after exposure to different temperatures levels. The highest values of the relative residual strength factor (Φc) were observed in specimens exposed to a maximum temperature of 600 °C, ranging from 0.862 to 0.905. The highest values of the relative residual elastic modulus factor (ψc) were verified for a maximum temperature of 200 °C, ranging from 0.720 to 0.778. The experimental results were compared with strength and stiffness predictions of design codes. The inclusion of slag in concrete reduced microcracking during the rehydration process due to the reduced amount of calcium hydroxide in the cementitious matrix, increasing the concrete’s relative residual strength and stiffness after post-fire curing.

Preparation and characterization of core-shell structured CaCO3-SiO2 and hollow silica nanoparticles and evaluation of their effects on cement mortar properties

CaCO3-SiO2 particles having a core-shell nanostructure were produced by a modified Stöber process using CTAB as a surfactant. Then, a porous structure composed of a silica shell was formed after the removal of the CaCO3 cores as templates from the nanocomposite. To evaluate phase constitutions and microstructures of prepared nanoparticles, XRD, TEM, and FESEM–EDX techniques were utilized. The main aim of this work was to examine the usability of prepared CaCO3-SiO2 and SiO2 hollow shell nanoparticles instead of OPC in structural applications. In this way, the mixtures of cement mortar were made by partial replacement of 1% of cement mass with prepared nanoparticles. The amounts of calcium hydroxide (CH), bound water, and calcium carbonate for the prepared mortars have been calculated after 7 and 28 days of hydration through thermal analysis of TG/DTG. The results indicated that the CH content decreased by adding prepared nanoparticles as a cement replacement. As CaCO3-SiO2 and hollow SiO2 nanoparticles were used, the compressive strengths of mortars were enhanced by 34 and 59%, respectively, after 28 days, which were higher than the increasing influences on flexural strengths (29 and 55%). The increasing intensity of the XRD peaks related to the C-S-H phases and the decline of the orientation index of CH in a mortar containing silica shell suggest that hydration was further completed, leading to a strength improvement. The SEM micrographs indicated that the addition of prepared nanostructures improved the interface properties inside mortar and caused the microstructure to be denser.

Effects of rapid electrical curing and internal curing with cellulose microfibers on alkali-activated fly ash mortar

ABSTRACT This study investigates an electrical curing method for the appropriate pre-casting application of alkali-activated fly ash (AAFA) composites, which offer a low-carbon alternative to traditional cement. Cellulose microfibers (CMFs) were incorporated into AAFA mortar to induce internal curing and prevent self-desiccation. The thermal conductivity of hardened AAFA mortar was measured at relatively low 0.461 W/mK. This emphasizes the necessity of an electrical curing method for the proper curing of AAFA mortar. Temperature change and its distribution on the AAFA surface was monitored during 24-hour electrical curing, revealing that electrical curing sufficiently cured AAFA mortar with a spacing of over 10-cm between the electrically conductive cementitious composite (ECCC) elements. Compressive strength tests showed that AAFA mortars with CMFs had greater strength than plain AAFA specimens. Microstructural analyses, including XRD, TG/DTG, and MIP, demonstrated that CMFs promote the formation of C-S-H, while reducing the amounts of calcium hydroxide and calcite, formed from false setting. Furthermore, CMFs effectively reduced pore sizes in the 300–1000 nm range, leading to decreased average pore diameter and enhanced material durability.

Evaluating Alkali Activation in Magnesium Slag Carbonization and Its Mechanism

In recent years, magnesium slag has been used as a raw material for solid waste treatment using the carbonization method and has proven to be promising in reducing carbon emissions. In this study, the alkali activation reaction was introduced to promote the carbonization of magnesium slag. The resulting mechanical properties, microstructural attributes, and carbonization mechanism were studied by varying the sodium hydroxide content, temperature, and carbon dioxide concentration during the reaction process. The results showed that the amounts of calcium hydroxide, C-S-H, and calcium carbonate in the reaction products increased with the sodium hydroxide content, which enhanced the compressive strength of the composite. However, it does not influence the carbonization mechanism with the increasing reaction temperature, which only elevates the reaction rate. With the increase in the carbon dioxide concentration during alkali activation, the carbonization reaction is dominated by the amount of CO2 dissolved in the reaction medium, and the carbonization mechanism is changed. Thus, a significant decrease in the calcium hydroxide content and a sharp increase in the calcium carbonate content in the products occurred, which significantly improved the compressive strength of the resulting magnesium slag composite. Among them, the maximum compressive strength is 6.83 MPa.

Effects of superabsorbent polymer on mechanical properties of cemented paste backfill and its mechanism evolution

Cemented paste backfill (CPB) technology offers advantages in safety, efficiency, environmental protection, and economy, and it has been increasingly applied in mines worldwide. The mechanical properties of CPB are critical indicators of the quality of the backfill. Traditionally, cement is used as the primary binding material; however, its high cost and the resulting inconsistent strength of CPB present challenges. Superabsorbent polymer (SAP) has been extensively used in cement-based materials due to its beneficial effects on mechanical properties, shrinkage, and durability. In this study, SAP is incorporated as an additive, with the unclassified tailings from an iron ore mine used as the research material to prepare SAP-enhanced CPB. The study focuses on SAP content, the cement-to-tailings ratio, and curing time as the main influencing factors. Uniaxial compressive strength (UCS) tests, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM) tests were conducted on CPB specimens to investigate the mechanical characteristics of SAP-enhanced CPB and to explore the influencing mechanisms of SAP on CPB. The results indicate that CPB strength initially increases and then decreases with rising SAP content, reaching a maximum UCS value at 0.2 % SAP content. XRD, TGA, and SEM results show that SAP affects the formation of hydration products and the pore structure of CPB. Specifically, when the SAP content is below 0.2 %, increasing SAP content leads to a denser pore structure and lower porosity, which correlates with higher UCS values. There is an exponential decrease in UCS with increasing porosity. Additionally, a quadratic relationship exists between UCS and the amount of calcium hydroxide, a key hydration product in CPB specimens. These findings provide valuable insights for improving the mechanical properties of CPB and serve as a reference for designing the strength of backfill in similar mining applications.

Enhancing the Performance of Hemihydrate Phosphogypsum by the Collaborative Effects of Calcium Hydroxide and Carbonation.

Normally, the acidic impurities in hemihydrate phosphogypsum (HPG) must be neutralized when HPG is utilized, and a little amount of calcium hydroxide (CH) is the best choice. In this paper, the effects of excessive CH (5 wt.%, 10 wt.%, 15 wt.% and 20 wt.% of HPG) for carbonation curing on the performance of hardened HPG paste were studied. According to the results of macro tests and microanalyses of XRD, TG, SEM-EDS, MIP and N2 physisorption, it could be verified that CaF2, Ca3(PO4)2 and a large amount of nanoscale CaCO3 crystals were produced as a result of neutralization and carbonation, and the compressive strength and the water resistance of carbonated HPG + CH paste were significantly improved due to the effects of nanoscale CaCO3 crystals on pore refinement and the coverage on the surfaces of gypsum crystals of the hardened paste. Therefore, this study suggests a feasible and green method for recycling HPG/PG, with the collaborative effects of neutralization, performance enhancement and reductions in CO2 emissions.

Drying Shrinkage and Mechanical Strength of Cementitious Composites with Alkali-Treated Makino Bamboo Fibers

ABSTRACT Alkali-treated bamboo fibers (AFs) treated with different NaOH concentrations (5 and 10%) and treatment times (1, 12, and 24 h) were used as fillers to fabricate cementitious composites with AFs (CAFs) in the present study. The results demonstrated that alkali treatment caused the partial decomposition of hemicellulose and lignin and an increase in the surface roughness of bamboo fibers. Additionally, the amounts of calcium hydroxide in alkali-treated CAFs were higher than in untreated CAFs, and they increased with increasing NaOH concentration and treatment time. For drying shrinkage (DS) under 75% relative humidity (RH), the DS values of the CAFs significantly decreased after adding AFs compared to the DS values of untreated CAFs. Compared to untreated CAFs, the density of the 5% and 10% NaOH-treated CAFs with longer treatment times decreased by 2.9% and 5.1%, respectively. Furthermore, the tensile strength of all alkali-treated CAFs exhibited no significant differences when compared with that of untreated CAFs, while the modulus of rupture and compressive strength were significantly decreased by NaOH treatment. These results indicated that the AFs significantly improved the drying shrinkage of the CAFs and hydration retardation effect of cement pastes, while the density and mechanical strength of the CAFs decreased.

Long-Term Performance of Soybean-Based Concrete Surface Protectant under Laboratory Accelerated Aging Conditions

Soy methyl ester-polystyrene (SME-PS) is an organic material derived from soybeans, which has proven to be an effective protectant for concrete surfaces. This study investigated the long-term performance of cement paste samples treated with SME-PS under laboratory accelerated aging conditions (AAC). The specimens were subjected to cyclic conditions: 8 h of UVA radiation (simulating solar radiation), followed by 6 h of darkness with water condensation and a high temperature of 40°C for 28 days. After the AAC exposure, the samples were immersed in a deicing salt solution, specifically a 29.8 wt. % calcium chloride solution, for 7 days. To evaluate the long-term behavior of SME-PS, a series of experiments, including visual observation, thermogravimetric analysis (TGA), and low-temperature differential scanning calorimetry (LT-DSC) was conducted. Visual observations revealed slight damage in SME-PS-treated samples after AAC exposure, while control samples experienced microcrack formations. SME-PS chemical compositions remained unaffected by AAC, in contrast to the control samples where a decrease in the quantity of calcium hydroxide and an increase in calcium carbonate content were observed as a result of carbonation during AAC exposure. LT-DSC results indicated that SME-PS-treated samples showed a significant reduction in the enthalpy of fusion associated with calcium oxychloride (CAOXY) formation, indicating that the SME-PS remained effective after AAC exposure, while control samples exhibited higher CAOXY enthalpy of fusion.

Workability, Mechanical Properties, and Microstructure Analysis of Bottom Ash Mortar Reinforced with Recycled Tire Steel Fiber

Recycled tire steel fiber (RTSF) is added to mortar with pre-wetted bottom ash (BA) to enhance the mechanical properties of the mortar, in addition to providing an internal curing effect. This work investigated the mechanical properties of BA mortar, such as the compressive strength, splitting tensile strength, and flexural strength, including the heat of reactions and the total shrinkage, considering different contents of BA (i.e., 10%, 20%, and 30% replacements by volume of fine aggregate) and recycled steel fiber (RSF, i.e., 0.5% and 1.0% by volume). The results showed that BA reduced all mechanical properties; however, it increased the degree of hydration by raising the heat peak of hydration in the first 7 days, increasing the amount of calcium hydroxide at 28 days, and significantly refining the pore structure during the curing period. Regarding the effects of RTSF, the bridging effect positively affected the compressive strength, splitting tensile strength, and flexural strength of the mortar with 30% BA when 1% RTSF was added, increasing them by 25%, 46%, and 40%, respectively. Moreover, adding 1% RTSF reduced the total porosity of the mortar with 30% BA from 17.2% to 14.8%.

THE INFLUENCE OF MINERAL ADDITIVES ON THE PROPERTIES OF ULTRA-HIGH STRENGTH CONCRETE

The article presents the results of a study of the influence of highly active mineral additives on the physical and mechanical properties of ultra-high strength concrete. Currently, according to the classical concept of making ultra-high strength concrete, a significant amount of ultradispersed microsilica is introduced, which determines the increased cost of its preparation. In order to obtain cost-effective ultra-high-strength concrete, the composition of mixtures was evaluated according to the criteria of strength and economy by replacing microsilica with technologically optimized highly dispersed zeolite (SSA=1200 m2/kg), which belongs to the class of superzeolite. It is shown that for modified concrete with the addition of microsilica, the compressive strength after 2 days is 88.8 MPa, after 28 days ‒ 161.0 MPa. When microsilica is partially replaced by superzeolite, sufficiently high mechanical parameters are achieved: after 2 days the compressive strength is 75.8 MPa, after 28 days the strength increases by 2.1 times and is 163.2 MPa, in this case a flexural strength of 12.1 MPa is achieved. The microsilica has a positive effect due to increased reactivity, especially at an early age. Similarly, the fine fraction of superzeolite is characterized by the acceleration of the pozzolanic reaction, while the coarser fraction contributes to increasing the degree of hydration of the Portland cement due to the desorption of water molecules from micropores and provides internal care for concrete. The cementitious matrix is compacted by filling the intergranular space due to the formation of nanodispersed C-S-H phases. Thermal analysis showed that the amount of calcium hydroxide in the superzeolite cementitious system is 2.75% or 66 kg/m3, which meets the requirements for ultra-high strength concrete. The synergistic combination of microsilica and superzeolite with high surface activity and polycarboxylate superplasticizer provides high packing density and the necessary strength characteristics of ultra-high strength concretes, as well as contributes to their cost-efficiency, which opens the prerequisites for a large-scale engineering application of such concrete in construction.

Removal of Calcium Hydroxide Paste Leaked Into the Maxillary Sinus.

Calcium hydroxide is a widely used endodontic medicament with antibacterial activity. When excessive pressure is applied during injection of calcium hydroxide paste or apical perforation occurs, calcium hydroxide can leak into the maxillary sinus and is adsorbed onto the sinus membrane. Although a leakage of calcium hydroxide may not usually cause clinical symptoms, when a large amount of leakage occurs, it can cause degeneration of adjacent tissue and functional disorder, requiring immediate surgical removal. However, due to adsorption to the sinus membrane, calcium hydroxide leaked into the maxillary sinus is difficult to remove completely. Here, we describe the case of a 47-year-old patient in whom a large amount of calcium hydroxide leaked into the maxillary sinus and was successfully removed using modified endoscopic-assisted sinus surgery, and favorable bone regeneration and sinus membrane regeneration were achieved. In addition, histological and ultrastructural changes of the membrane resulted from the calcium hydroxide were presented.

Analysis of the Microstructure and Porosity of Cement Pastes with Functionalized Nanosilica with Different Contents of Aminosilane.

This research aims to analyze the effect of functionalized nanosilica (NSF) with different levels of amine groups in the formation of hydration products. Four cement pastes were investigated, one reference with Portland cement and three replacing 1% of Portland cement by nanosilica (NS), NSF with a low content of amine groups, and NSF with a high content of amine groups. The heat of hydration of the pastes was evaluated up to 7 days of hydration, the amount of calcium hydroxide (CH) and hydrated phases by means of the thermogravimetric analysis (TGA) test and compressive strength at 2, 7, and 28 days, and porosity through tests of mercury intrusion porosimetry and computed tomography at 28 days of hydration. It was possible to observe that the NSF directly influenced the hydration kinetics of the pastes, delaying the hydration of the Portland cement; however, it demonstrated a similar mechanical performance to the paste with NS at 2 days of hydration and an increase of 10% at 28 days of hydration due to the improvement in the hydration process. Thus, it is possible to conclude that the functionalization of NSF with a low 3-aminopropyltriethoxysilane (APTES) content is promising for use in cementitious materials and may improve hydration and mechanical performance at more advanced ages compared to NS.

Wood sawdust waste-derived nano-cellulose as a versatile reinforcing agent for nano silica cement composites: a systematic study on its characterization and performance

The development of sustainable construction materials is a pressing concern for researchers worldwide, as the cement industry is a major contributor to environmental degradation. The incorporation of nano-materials with cement composites has emerged as a promising solution to sustainable materials production. In this study, the effect of the addition of nano cellulose produced from wood sawdust waste on the performance of cement-based nano-silica composite was investigated. The nano-materials were incorporated at low concentrations and in gel form to eliminate the need for any advanced dispersion techniques. The results indicated that the addition of even low concentrations of nano cellulose significantly enhanced the compactness and mechanical properties of the cement matrix. The crack propagation was observed to be arrested with better adherence to the cement hydration product, which resulted from the presence of nano-silica. The nano cellulose fibers were found to bridge the calcium silicate hydrate products, arresting the propagation of cracks at their initial condition. The high pozzolanic reactivity of nano-silica ensured a minimal amount of calcium hydroxide, which is a significant contributor to the carbon footprint of cement production. Overall, the findings of this study suggest that the incorporation of nano cellulose from wood sawdust waste with cement-based nano-silica composite can lead to the development of sustainable and high-performance building materials with improved mechanical properties and reduced environmental impact.

Effect of polyvinyl alcohol on the performance of carbon fixation foam concrete

The introduction of carbon fixation components (calcium hydroxide) can improve the carbon fixation performance of foam concrete, however, it will reduce its mechanical properties. In order to solve the adverse effects of carbon fixation components on the mechanical properties and optimize carbon absorption properties, a specific amount of polyvinyl alcohol (PVA) is incorporated. In this study, a serial of test was employed to study the production process of nano-modified foam, and some basic properties of the foam concrete of interest. Further, the micromorphology and pore structure of the samples were analyzed by scanning electron microscope and mercury injection test. The evolution of mineral phases was examined by X-ray diffraction and thermogravimetric analysis. The results show that the carbon sequestration efficiency of foam concrete increases significantly as the amount of calcium hydroxide is increased, however, the cementitious properties of materials deteriorate, resulting in a decrease in strength. When PVA is added as a water-soluble admixture, it can enhance the mechanical properties of test blocks. It can also strengthen the bubble film of nano stabilized foam, increase bubble stability, and refine the internal pore structure of carbon fixation foam concrete. In addition, PVA can modify the calcium hydroxide morphology from a laminar structure to a smaller volume edge corrosion structure, which improves the reaction activity of calcium hydroxide with CO2 and boosts the efficiency of carbon sequestration.

Effect of calcium hydroxide on pasting, thermal, and water‐adsorption behavior, and the flow properties of nixtamalized corn flour

AbstractNixtamalized corn flour (NCF) has gained favor worldwide due to the growing popularity of Mexican cuisine. This research evaluates the effect of the amount of calcium hydroxide (Ca(OH)2) employed during the nixtamalization on the water‐adsorption, thermodynamic, and flow properties of NCF. In addition, NCF pasting and thermal properties were evaluated to relate bulk‐powder properties to wet‐dispersion conditions. Ca(OH)2 amounts of 1.5 and 2.0% induced higher ash and calcium content as well as lower fat and protein content. Also, pasting properties and gelatinization enthalpy (ΔHgel) values, in addition to yellowish NCF, were related to Ca(OH)2 concentration. With the independence of the Ca(OH)2 amounts employed, no important differences in the equilibrium's moisture content, as well as a negligible effect of temperature on adsorption behavior, were observed. For prepared NCF, the moisture content corresponding to minimum integral entropy was not observed within the range of the aw analyzed; thus, GAB parameters are more reliable for suggesting the storage conditions. NCF with a low amount of Ca(OH)2 exhibited higher values of mean caking strength (≈1.81 N) and cohesiveness index (≈13.99 × 10−5 N m g−1), in addition to higher resistance to flow. Therefore, the amount of Ca(OH)2 positively influenced flow properties, whereas wet‐dispersion properties such as lower maximal peak viscosity and ΔHgel values were obtained.Practical applicationsThis study contributes useful information to the manufacturers of NCF concerning the amount of Ca(OH)2 needed to obtain NCF with desirable physical properties while attempting to affect thermal and pasting properties to a lesser extent. In addition, this study characterizes and provides the adequate amount of Ca(OH)2 employed the during the nixtamalization process to improve the flowability of NCF in industry during handling. Finally, the absence of a moisture content corresponding to minimum integral‐adsorption entropy provides clarification for NCF producers regarding the long‐term storage stability of NCF.

Ultra-high-performance fiber-reinforced sustainable concrete modified with silica fume and wheat straw ash

Developing ultra-high fiber-reinforced concrete (UHPFRC) demands an immense quantity of ordinary Portland cement (OPC). Using a high percentage of cement in UHPFRC leads to uneconomic concrete and significant release of CO2 into the atmosphere. Therefore, it is critical to address this issue by substituting the part of cement with a sustainable material. The current research has tried to tackle this issue by assessing the impact of adding wheat straw ash (WSA) and silica fume (SF) as a partial substitute of cement on the properties of UHPFRC on the static and dynamic compressive strength test, among other strength and durability characteristics. Two different batches of mixes were developed. The OPC was substituted for up to 40% in the first batch, with combined WSA plus SF at 10% intervals. In the second batch, OPC was replaced up to 40% with only WSA at an interval of 10%. Polypropylene fibers (PPFs) at 2% (by vol.) were added to modified samples to improve the ductility of concrete. The dynamic compression strength was evaluated utilizing a Split Hopkinson pressure bar, and quasi-static compression strength was determined using the compression machine. Moreover, splitting and flexural strength were also assessed, and water permeability and sorptivity tests were carried out for durability. The test outcome showed that the sample with 15% WSA plus 15% SF had higher compressive strength (174.8 MPa at 90 days) and improved durability than the sample with only 30% WSA (170.2 MPa at 90 days) and the control sample. The assessed properties tend to decline at 40% of WSA and 20% WSA with 20% SF. In dynamic compression strength, it was observed that the WSA and SF, and fibers samples performed similarly to the control sample, and these modified samples were not sensitive to strain rates. Adding 15% plus 15% SF had an optimal effect in improving the durability properties of UHPFRC. Also, the thermogravimetric analysis (TGA) confirms the role of WSA and SF in densifying the matrix of UHPFRC, decreasing the porous pores and amount of calcium-hydroxide and developing additional gels of calcium-silicate-hydrate, which enhances the strength and durability of UHPFRC. The current study revealed that the modified samples (with WSA and SF) had a low embedded CO2 for the sustainability features compared to the control sample.

Study of the development of hydration of ternary cement pastes using X-ray computed microtomography, XRD-Rietveld method, TG/DTG, DSC, calorimetry and FTIR techniques

This paper analyzes and discusses in depth the development of hydration of ternary cement pastes with silica fume (8%) and nano-silica (3%), with water/binder (w/b) ratios of 0.4 and 0.6 up the age of 28 days. The study was based on parameters obtained from X-ray computed microtomography (μCT), XRD-Rietveld Method, TG/DTG/DSC analysis, calorimetry and FTIR techniques. As expected, a reduction in porosity and a densification of the microstructure were observed in these cementitious systems modified with mineral additions. This was potentiated by a complex system made up of multidimensional binding particles (from the nanoscale to the microscale – particles of nano-silica, silica fume and Portland cement), which provided an acceleration of hydration and pozzolanic reactions at all ages. As a result, especially from the pozzolanic activities, it was verified a significant reduction in the amount of calcium hydroxide (CH) followed by increasing in the amount of C-S-H. This work showed the role of the mineral additions used in this research (under ternary condition) at early ages for pastes and its effect on the hydration kinetics. Besides that, the effect of water on later ages on pastes studied was presented. Finally, the positive impact on concrete durability properties was discussed in terms of scientific arguments.

Evaluation of the microstructure and micromechanics properties of structural mortars with addition of iron ore tailings

The Interfacial Transition Zone (ITZ) between the cement paste and aggregates is a region of great interest for concretes because it is the composites' weakest region. ITZ presents a great amount of large calcium hydroxide and ettringite crystals, with the porosity being able to be up to 2.5 greater than that the rest of the paste. The microstructure, and consequently the ITZ, can be improved by mineral addition. These materials fill the pores in the composite, influence the hydration process and densify the matrix. Therefore, mineral additions, such as iron ore tailings (IOT), can modify microstructure of composites. There are few studies on the assessment of IOT heterogeneity on the microstructure and hardness of structural mortar. Thus, the present study analyzes the properties influences of four IOT types on the microstructure, porosity, and thickness of the structural mortars' Interfacial Transition Zone (ITZ) with IOT addition, by different evaluation methods. The composites were characterized through the Scanning Electron Microscope by backscattered electrons (SEM-BSE), line scan by Energy Dispersive Spectroscopy and nanoindentation. Results presented that IOT improved particle packing and tended to reduce the ITZ. The IOT improved nucleation since it reduces the amount of anhydrous cement particles and increases the amount of calcium hydroxide particles in the cement matrix. The nanoindentation showed that IOT-added matrix presented greater hardness and indentation module. It can be concluded that the IOT heterogeneity may affect microstructural properties and that the methods presented can be good ways to evaluate the parameters.

Heterogeneous Catalyzed Synthesis of Biodiesel from Crude Sunflower Oil

Biodiesel is the fatty acid alkyl esters that are used as the substitute for petro-diesel. The aim of the present work is to optimize biodiesel production from plant based non-edible crude oils with methanol using heterogeneous catalyst by transesterification for its commercialization. The factors affecting the biodiesel production from plant oils are volume of feedstock (oil), volume of alcohol (excess reactant), quantity of calcium hydroxide (catalyst), reaction time, temperature, and agitation speed. Transesterification is the reaction between acid and alcohol to produce ester in the presence of alkali catalyst. In this work, transesterification was carried out between crude sunflower oil and methanol in the presence of calcium hydroxide as catalyst. Finally, the maximum conversion of 85.6% was achieved at the optimum process parameters of 2 L of crude sunflower oil, 0.3 L methanol, 23 g of calcium hydroxide, reaction time of 24 h, temperature of 65 °C, and agitation speed of 100 rpm. The results showed that crude sunflower oil could serve as potential renewable substrate for biodiesel commercialization.Biodiesel is the fatty acid alkyl esters that are used as the substitute for petro-diesel. The aim of the present work is to optimize biodiesel production from plant based non-edible crude oils with methanol using heterogeneous catalyst by transesterification for its commercialization. The factors affecting the biodiesel production from plant oils are volume of feedstock (oil), volume of alcohol (excess reactant), quantity of calcium hydroxide (catalyst), reaction time, temperature, and agitation speed. Transesterification is the reaction between acid and alcohol to produce ester in the presence of alkali catalyst. In this work, transesterification was carried out between crude sunflower oil and methanol in the presence of calcium hydroxide as catalyst. Finally, the maximum conversion of 85.6% was achieved at the optimum process parameters of 2 L of crude sunflower oil, 0.3 L methanol, 23 g of calcium hydroxide, reaction time of 24 h, temperature of 65 ?C, and agitation speed of 100 rpm. The results showed that crude sunflower oil could serve as potential renewable substrate for biodiesel commercialization.