CH Content Research Articles

The mechanism of accelerator types on calcium leaching in shotcrete

In regions characterized by abundant water, the surrounding rock exhibits a high water content, which leads to calcium leaching in the shotcrete of the tunnel. This poses a significant hazard to the safe operation of the tunnel. The experimental design focuses on three commonly used accelerators in the market and investigates the leaching process of samples under accelerated leaching conditions. By integrating XRD, TG, and SEM-EDS testing, the calcium leaching mechanism of shotcrete was elucidated. Results revealed that sodium aluminate-based liquid accelerator exhibits the highest detrimental effect on mortar resistance against calcium leaching, followed by fluoroaluminic acid-based liquid accelerator. Additionally, an appropriate amount of aluminum sulfate-based liquid accelerator can effectively mitigate performance degradation during leaching processes in shotcrete. The addition of aluminum sulfate reduces CH content and C-S-H Ca/Si ratio of hydration products, leading to wrapping AFt generated by cement hydration with C-S-H and thereby slowing down solid calcium-containing substance dissolution in hydration products. A moderate accelerator can enhance shotcrete porosity so that corrosive products like CaCl2 accumulate in existing pores first, reducing shotcrete performance deterioration rate.

Microcrystalline cellulose modified chitosan aerogels to enhance Congo Red dye adsorption

Carbohydrate based aerogels were synthesized via a straightforward procedure including freeze-drying of chitosan (Ch) hydrogels of different concentrations cross-linked with glutaraldehyde and incorporating microcrystalline cellulose (MCC) powder to enhance mechanical strength and modify adsorption properties. The increase in Ch content and the incorporation of MCC resulted in samples that exhibited higher densities, lower swelling degrees and accessible porosities while demonstrated improved stabilities. These aerogels were evaluated as adsorbents of the textile dye Congo Red (CR) by isothermal and kinetic studies. Even when relatively simple theoretical models were used to predict these results, in order to eliminate modeling bias, a validation method based on error functions in addition to the more commonly used R2, was applied. Equilibrium adsorption capacities obtained in kinetic studies increased 150 % changing Ch concentration from 4 % to 5 %, and 196 % adding 50 % by weight of MCC. The adsorption tests for initial concentrations of CR below 100 mg/L demonstrated that the aerogels exhibited increased adsorption capacity for higher Ch content or incorporation of MCC. Thermodynamic studies indicated enhanced adsorption at higher temperatures. These environmentally friendly aerogels demonstrated comparable or superior adsorption capacities to other bio-based materials, offering a simple, economical, and effective solution for pollutant removal.

A novel PCM-based foam concrete for heat transfer in buildings -Experimental developments and simulation modelling

Foam concrete is renowned for its lightweight and versatile properties, such as good thermal insulation, airborne sound absorption and adequate compressive strength. Phase change materials are recognized for their heat storage characteristics. The current study investigates the enhancement of building envelope thermal performance by integrating phase change materials in foam concrete composites. The phase change material (PCM) developed using exfoliated vermiculite impregnated with capric acid and absolute ethanol demonstrated optimal thermal stability. Among the various foam concrete mix composites, PCM in addition to the nano silica and coconut fibre (PNC) mix showed improved mechanical and thermal properties. Test results showed that optimum mix (PNC-5 %) possess a compressive strength of 7.96 MPa, with a thermal conductivity of 0.15 W/mK. The nano silica added in the PNC mix reacted with CH rapidly for the formation of C-S-H and filled the pores, which improved the bonding and reduced the brittleness of the samples, which is also evident from the SEM images. The PNC-5 % sample mixture exhibited a melting and freezing point of 31.42 °C and 21.08 °C respectively, with a latent thermal storage 9.72 J/g for freezing and 17.55 J/g melting. Scanning electron microscopy and thermogravimetric analysis confirmed the compatibility and high thermal resistance of PNC-5 %. TGA results confirmed that the mass loss corresponding to CH content was slightly lesser for the PNC-5 % mixture than for the PCM mixture, due to the inclusion of nano silica in the case of PNC-5 %. COMSOL Multiphysics ® software model analysis is implemented for validation of thermal characteristics of the developed PCM-impregnated foam concrete wall panel for insulation in buildings, emphasizing the potential for enhanced thermal comfort compared to that of noninsulated structures. This research proves the efficacy of PNC insulated foam concrete composites for sustainable and energy-efficient building solutions, paving the way for advancements in building applications.

Insight into the Mechanical Properties and Microstructure of Recycled Aggregate Concrete Containing Carbon Fibers and Nano-SiO2.

This study aimed to improve the mechanical properties and microstructure of recycled aggregate concrete (RAC) by incorporating carbon fibers (CFs) and nano-SiO2 (NS) to promote the optimal utilization of RAC. The mechanical properties of the RAC were enhanced by both single and hybrid additions of CFs and NS, and the hybrid addition had a better strengthening effect. From the experimental results, it was found that the addition of CFs could increase the 28 d compressive strength and splitting strength of the RAC by 9.05% and 22.36%, respectively. The hybrid CFs and NS were more conducive to improving the mechanical properties of the RAC, and the enhancement effect increased first and then decreased with an increase in the NS content. The optimal content of NS was 0.8 wt%, which increased the 28 d compressive strength and splitting strength of the RAC by 20.51% and 14.53%, respectively. The microstructure results indicated that the addition of CFs had little effect on the optimized pore structure of the RAC, but the crack inhibition action of the CFs could improve the mechanical properties of the RAC. The addition of NS reduced the content of CH and facilitated the formation of more (C-S-H) gel. The hydrated calcium silicate (C-S-H) gel significantly decreased the porosity and transformed harmful capillary pores and harmful pores into harmless capillary pores and gel pores, thus improving the mechanical properties of the RAC. Therefore, the use of hybrid CFs and NS was more conducive to enhancing the performance of RAC for building materials.

Rice husk ash and recycled sand as synergistic substitutes in ultra-high performance concrete: Microstructural, mechanical performance, and eco-economic analysis

Quartz sand and silica fume (SF), commonly used in UHPC production, are costly and contribute to dust pollution and significant carbon emissions. In this work, we explored the preparation of an environmentally friendly ultra-high performance concrete (e-UHPC) by substituting SF and quartz sand with rice husk ash (RHA) in ratios of 10 %, 20 %, and 30 %, and recycled building sand (RS) in ratios of 25 %, 50 %, and 75 %. We assessed the impact of these substitutions on workability, mechanical strength, hydration products, and the micromechanical characteristics of the interfacial transition zone. In addition, an environmental and economic assessment index for e-UHPC was introduced. Results showed that while RHA and RS reduced the flowability of e-UHPC, RHA helped mitigate the compressive strength loss due to RS (3.9 %-9.7 %). RHA accelerated early hydration, and improved densification in the transition zone, enhancing late hydration and refining the pore structure of e-UHPC. Notably, a 10 % RHA replacement rate optimally improved early hydration efficiency and minimized CH content. The combination of 10 % RHA and 25 % RS proved most effective in optimizing the interfacial transition zone and improving the pore structure of e-UHPC. Importantly, e-UHPC reduces the carbon footprint at a lower cost and offers significant environmental and economic advantages over traditional UHPC. The results of this study will promote the incorporation of construction and agricultural wastes into concrete.

Phase evolution and microstructure changes induced by accelerated carbonation in natural hydraulic lime paste with GGBFS addition

Carbonation is a primary factor driving the continuous improvement of the long-term performance of natural hydraulic lime (NHL). This research systematically examines the impact of accelerated carbonation (3 % CO2) on the carbonation depth, phase composition, microstructure, and compressive strength of hardened natural hydraulic lime (NHL) pastes mixed with different amounts of ground granulated blast furnace slag (GGBFS), termed as S-NHL. The findings show that the hydration reaction products of GGBFS and Ca(OH)2 (CH), such as C3AH10, C4AĈH11, and C-S-H, densify the microstructure of S-NHL, resulting in a decrease in carbonation depth with increasing GGBFS content. Accelerated carbonation (AC) promotes the rapid transformation of a significant quantity of CH into calcite in S-NHL, with the carbonation of CH occurring more readily than the carbonation of hydration reaction products. Throughout the AC process, NHL contains only calcite-type calcium carbonate. In contrast, after 28 days of AC, the carbonation of hydration reaction products such as C3AH10 and C-S-H in S-NHL produces a minor amount of aragonite and vaterite. AC continuously reduces the total pore volume and porosity of S-NHL, but the average pore diameter and most probable pore diameter initially decrease and then slightly increase. AC significantly reduces the large pores in S-NHL, ultimately resulting in pores predominantly composed of capillary pores (50–1000 nm). AC facilitates the development of compressive strength in S-NHL paste, with the increase in compressive strength being positively correlated with its CH content.

Research on the effect of tuff powder on the properties of moderate-heat portland cement-based materials and the methods for evaluating pozzolanic activity

Tuff powder (TP) has attracted significant attention due to its abundant resources, low carbon emissions, and potential enhancements in concrete property. This study investigates the effect of TP on the mechanical properties, hydration behavior, pore structure, microstructure morphology, economic and environmental analysis of moderate-heat portland cement (MHPC), comparing it with MHPC-based materials containing fly ash (FA). The synergistic morphological effect and micro-aggregate filling action of FA and TP result in higher early strength in the fly ash-tuff powder (FT) group mortar. The CH content and chemically bounded water content of TP paste are higher, showing a better early hydration promotion effect. The pore structure of the composite cement mortar is changed due to the addition of the admixture. Furthermore, the multi-factor response strength and strength activity index (SAI) model were developed based on response surface methodology (RSM), linking to TP specific surface area, dosage, and specimen curing age. This provides a reference for more accurate and comprehensive prediction of cement mortar property, quantification of effects, optimization of mix proportions, and evaluation methods for the activity of pozzolanic materials.

Bionic repair protective coatings with high toughness and bond strength based on anionic waterborne polyurethane-modified cement

Protection and repair of surface cracks play pivotal roles in enhancing their effective service life. Inspired by the bionic shell principle, an anionic waterborne polyurethane (WPU) was designed. The Synthetic WPU was applied to sulphoaluminate (SAC) and ordinary Portland (OPC) cements to prepare composite coatings. The results showed that with the increase in polymer-to-cement ratio (P/C), attributable to the electrostatic adsorption and complexation of R-COO-, the content of CH, AH3 and AFm increased, while the content of AFt decreased due to the inhibitory effect of WPU on hydration reactions. The molecular dynamics model indicated that the oxygen atoms in WPU can not only form ion pairs with Ca2+ in AFt but also form strong hydrogen bonds with the H in the hydroxyl group of AFt and the H in water molecules. Hence, for P/C exceeding 10 %, combined with Flory-Huggins theory, a continuous interpenetration polymer network (IPN) comprising multiphase composites was successfully demonstrated, bolstered by the macromolecular structure composed of —OH, —COOH, Ca2+ and Al3+ serving as a bridge. The network was more pronounced in coatings with SAC than in those with OPC due to synergistic effects caused by rapid hydration reactions. Due to the presence of IPN and the Si-O-Si bonds caused by the hydrolysis condensation reaction of silane coupling agent, the tensile and bond strengths exhibited an upward trend with increasing P/C, surging by up to 326 % and 180 %, respectively. The value reached 6.81 MPa and 2.2 MPa. And the addition of WPU enhanced crack resistance.

Modeling of effect of fly ash amount on microstructure and chloride diffusivity of blended fly ash-cement systems

Reasonable utilization of industrial fly-ash wastage in concrete engineering has been regarded as an effective way to reduce carbon emissions. By adding the reasonable dosage of fly ash to cement paste, the compactness and microstructure characteristics of the blended cement systems can be significantly improved, thereby effectively enhancing the durability of concrete structures. The vector hydration model of blended fly ash-cement systems with the interference effects of different hydration layers of fly ash and cement particles, the solubility equilibrium of solid phases and the electrical neutrality of the pore solution involved is established. By fully comparing with the experimental data of hydration degree, capillary porosity and CH content, the accuracy of the developed hydration model is verified. Based on the hydration model, the effect of fly ash content on the concentration of different ions and pH in the pore solution with curing time is discussed. Additionally, the evolution characteristic of hydration degree, capillary porosity and CH content with curing time at different fly ash content is also analyzed. Based on the reconstructed microstructure of blended systems, the rolling sweep (RS) technique is used to determine the pore size distribution of capillary pores. The effect of fly ash content on cumulative pore size distribution and differential pore size distribution at different curing time is quantitatively evaluated and discussed. By utilizing the first-passage cube, the dual-probability-Brownian motion method is constructed to predict the chloride diffusivity of blended cement systems. After diffusion model is verified by multi-group experimental data, the optimal dosage of fly ash at different water-binder ratio is calculated, which can provide theoretical guidance for practical applications in concrete engineering.

Waste glass powder as a high temperature stabilizer in blended oil well cement pastes: Hydration, microstructure and mechanical properties

Recycling waste glass for diversified utilization has received increasing attention in recent years. This work aimed to reuse waste glass powder (GP) as a high temperature stabilizer to replace silica flour (SF) in blended G class oil well cement (GOWC) pastes. Blended pastes containing 40 % and 66.7 % GP were prepared and compared to pure GOWC paste and blended paste containing 40 % SF commonly used in the oil industry. Under simulated field conditions in a steam injection well, these pastes were cured at 50 °C for seven days, followed by three rounds of thermal cycling curing at high temperature and high pressure (HTHP, 300 °C/13 MPa) conditions. The effects of GP on the hydration kinetics, hydration products, microstructure, and mechanical properties of hardened pastes were evaluated. The results demonstrated that the addition of GP or SF reduced the compressive strength of the pastes at 50 °C due to dilution effect. Compared with SF, GP exhibited higher pozzolanic activity, prolonged the induction period, and promoted the formation of more C-(N)-S-H gels with lower Ca/Si ratios, which led to an increase in the gel pores content of the matrix and partially compensated for the loss of compressive strength due to the dilution effect. Additionally, due to the pozzolanic reaction of GP, the content of CH in the matrix decreased and its crystal size became smaller. After three rounds of thermal cycling curing, the incorporation of GP significantly increased the compressive strength of the hardened pastes. The compressive strengths of the hardened pastes with 40 % and 66.7 % GP were 20.33 MPa and 22.25 MPa, respectively, which were 7.62 % and 17.79 % higher than those of the hardened paste containing 40 % SF. In addition, the compressive strengths of hardened pastes containing 40 % and 66.7 % GP after three rounds of thermal cycling curing decreased by 22.49 % and 5.52 %, respectively, compared to the pastes at the low-temperature stage, while that of the pure GOWC pastes decreased by 83.8 %. Characterization analyses indicated that GP could further reduce the Ca/Si ratio of the system, modulate the crystallization of the gels at high temperatures, and generate foshagite or xonotlite phases with high polymerization structure and thermal stability, instead of reinhardbraunsite. These products effectively refined pore structure and enhanced microstructure densification. Furthermore, the precipitation of Na+ ions during hydration did not affect the microstructure of the matrix. This study offers some guidelines for recycling waste glass, conserving raw materials, and producing sustainable blended cement pastes.

Study on the microscopic transmission characteristics and coupled erosion depth of tailings recycled concrete under the coupling effect of carbonization and salt-fog

In ocean and salt-lake district, especially in some industrial areas, concrete structures suffer from the coupling erosion of carbonation and salt-fog. As an eco-friendly material, tailings recycled concrete(TRC) has been used to its alleviate the deterioration of living environment. Based on series of physical and chemical equations of hydration, carbonization and salt-fog erosion, this paper introduces parameters such as hydration rate, carbonization rate and Friedel salt degradation coefficient. Then，a comprehensive analysis method that can reflect the erosion performance of TRC quantitatively is established, and the microscopic transmission characteristics and erosion depth calculation method under coupling effect are studied. The results indicate that aggregates have a “blocking effect” on the diffusion of corrosive substances, resulting in higher concentration around the front edge of aggregates, and the erosion of salt-fog plays a leading role under the coupling effect. Overall, the CO2 concentration decays faster than that of Cl−. The longer the erosion age, the higher the CaCO3 content, while the content of CH and CSH is approximately inversely proportional to that of CaCO3. In addition, the method for determining the depth of carbonation and salt-fog erosion under coupling effect is studied, and the calculated values are in good agreement with the experimental values. It shows that the coupling erosion depth is greater than that under single erosion, which leads to the salt-fog erosion depth increased by about 30 %, the longer the erosion age, the greater the erosion depth. The effect of iron ore tailings(IOT) on coupled erosion depth is similar to that of single erosion. The results also show that the coupled erosion performance of TRC can be analyzed by using the model proposed in the paper.

Experimental analysis on light weight concrete utilizing compost and Ground Granulated Blast Furnace Slag (GGBS): Insights into elevated temperature properties through TGA

AbstractWhenever a new material is replaced in concrete, some other tests other than strength and durability need to be carried out to validate the viability of the material replaced. This study aims to investigate the sustaining capacity of the light weight concrete manufactured with compost and Ground Granulated Blast Furnace Slag (GGBS) for M sand and cement respectively subjected to high temperature. Four concrete samples are tested, which includes the control specimen and three specimens are opted based on the optimum mix arrived from the strength and durability studies. Thermogravimetric Analysis (TGA) is done on the samples and they are heated up to 1,000 °C. For the specimens tested, the loss in mass with respect to the temperature is obtained. It is noted that the mass loss of the concrete samples with 15% GGBS along with compost at 0 & 10% is found lower than the control specimen. Also, from the loss in mass, the loss of chemically bound water and free CH content can be found, which aids in contributing strength to the concrete. For the concrete to be sustainable, compost can be replaced at 10% and GGBS at 15%.

The Influence of the Frequency of Ultrasound on the Exhaust Gas Purification Process in a Diesel Car Muffler

This research aimed to analyze the possibility of installing an ultrasonic emitter in an already manufactured car and to prove the possibility of cleaning the exhaust gases of an internal combustion engine through the action of an ultrasonic wave due to coagulation and examining the optimal regimes of its work. The existing theoretical solution to describe the proposed process was analyzed. A Mercedes-Benz M-Class ML 270 CDI MT car with the OM 612 DE 27 LA Diesel engine was used for the experiment. An ultrasound generator and an ultrasound emitter were connected to the muffler. The stand was connected to the car via the inlet with a rubber hose that directs the exhaust gases out of the car. The crankshaft speed of the engine was changed in the range of 750 to 1250 rpm, which corresponds to urban conditions when cars are moving in heavy traffic jams. The content of CH, CO, CO2, and O2 in the exhaust gas of the vehicle was determined as a function of the crankshaft speed without ultrasonic exposure and with ultrasonic exposure at an ultrasound frequency of 25, 28, and 40 kHz. The results of the experiment showed that the introduction of an ultrasonic emitter into the muffler reduced the smoke content of the gas, increased the oxygen content, and reduced the amount of carbon dioxide in the exhaust gases. With an increase in the ratio between the ultrasonic frequency and the angular velocity of the engine crankshaft (f/ω), the smoke content of the gas also decreased. At the maximum values of ultrasonic frequency and angular velocity of the engine crankshaft selected in the experimental studies, the minimum value of the ratio of gas smoke indicators was achieved, and the degree of purification was 10–13%. Such results correspond to the condition of optimal operation of the ultrasonic muffler, where the ratio of gas to smoke values should tend to a minimum. These results confirm the potential of using ultrasound as a method for cleaning exhaust gases and underline the need for further research in this area.

Steam gasification of lime dried sewage sludge: Effects of temperature and addition of lime

Gasification shows great potential as an alternative method for energy utilization from sewage sludge. Lime (CaO) is a cheap and commonly used dewatering conditioner for sewage sludge. The calcium hydroxide (Ca(OH)2) generated during the drying process with lime can enhance the pH level of the sludge, thereby providing disinfection properties. This paper investigated enhancement mechanism of Ca(OH)2 on hydrogen gas generation and the effect on gas product yield during the steam gasification process of lime-dried sludge. The experiments were conducted in an electrically heated reactor at 500–800 °C. The forms of calcium present in the gasified sludge char samples were analyzed using X-ray diffraction (XRD) analysis to investigate their transformation process. Fourier transform infrared spectroscopy (FTIR) was utilized to obtain information regarding the chemical structure in the gasified sludge char samples, with the aim of exploring the mechanism behind hydrogen production from lime-dried sludge. The results indicate that the CaO generated from Ca(OH)2 dehydration acts both CO2 adsorbent and catalyst during the gasification process. The addition of Ca(OH)2 during the sewage sludge gasification process leads to a reduction in the aromatic CH content in the organic matter, while significantly increasing the content of reactive CH3-chains. It also promotes the ring-opening and rearrangement reactions of aromatic hydrocarbons and nitrogen-containing heterocycles and steam reforming reaction of tar. The combined effects of these factors contribute to an overall increase in hydrogen gas yield.

The influence and mechanism analysis of aluminum sulfate as an environmentally friendly early strength agent on the properties of cement-based materials

Environmentally friendly chemical admixtures are becoming important in the cement industry. The research objective of this paper is to use aluminum sulfate as an early-strengthening agent to achieve the goals of a large increase in early strength and a reduction in CO2 emissions. The experimental design was as follows: The macroscopic properties and microscopic characteristics of aluminum sulfate were experimentally investigated on five different replacement ratios of 0%, 1%, 2%, 3%, and 4% paste specimens of cement at different ages. The results show that (1) AS4 demonstrated a notable enhancement in early strength, while AS2 and AS3 contributed to increased late-stage strength. Over time, the Ultrasonic Pulse Velocity (UPV) of all samples exhibited a steady rise. Additionally, aluminum sulfate was found to reduce the electrical resistivity of the samples. (2) aluminum sulfate increased the rate of exothermic heat release of samples at induction and acceleration phases, advanced the accumulated heat was high in the samples with high aluminum sulfate content, and the accumulated heat was strongly correlated with the compressive strength. FT-IR and XRD results show that aluminum sulfate promoted the formation of AFt while depleting the CH content, and the TGA results show the content of bound water in the samples increased from Day 1 to Day 28, which had a positive effect on the compressive strength. UHR-SEM results show that increasing aluminum sulfate substitution results in the formation of a denser microstructure. (3) for all the various mixtures, AS2 has the lowest CO2 emissions per unit strength.

Surfactant-free synthesis of highly monodispersed in situ grown nano-silica on modified fly ash and its impact on the properties of cement pastes

This paper introduces a novel approach to synthesize highly mono-dispersed in situ grown NS (INS) on Fly Ash (FA). The uniform particle size (41 ± 3.5 nm) and mitigation of the agglomerations tendency of INS were accomplished without any surfactant by utilizing the surface properties of acid-treated FA. INS's growth and adsorption mechanisms were proposed by employing the findings of FTIR and zeta potential investigations. SEM and TEM were used to evaluate the structure and INS dispersion. The impacts of synthesized INS and commercial NS (CNS) on cement pastes' cementitious properties were comparatively investigated using equal dosages of INS & CNS (0.5%, 1.0%, 1.5%). The experimental results revealed that even the highest dosage (1.5%) of INS exhibited better fluidity and rheological behavior than the lowest dosage (0.5%) of CNS in cement pastes. Moreover, compared to CNS, excellent dispersion of INS engendered prominent hydration kinetics of cement pastes and showed more efficient early and long-term strength development. QXRD cement pastes' findings further endorsed INS's prominence over CNS by indicating a significant increase in amorphous content and a notable reduction in CH content. Furthermore, INS refined the pores in the hardened cement pastes efficiently by decreasing the porosity more remarkably.

Effect of surface activity of recycled fine aggregates from clay bricks on the hydration, microstructure and chloride transport of concrete

Use of recycled fine aggregates from clay bricks (RFCB) in the preparation of eco-friendly concrete was proposed to tackle the river sand (RS) shortage and satisfy the construction demand. This study explored the surface activity of RFCB influenced by additional water and particle size distribution (PSD) on the hydration, microstructure and chloride transport of concrete. Compared to the RS, more silica and alumina released from RFCB depending on its PSD under alkaline environment was noted, which verified its appreciable surface activity. Overall, the presence of RFCB could hinder early hydration process because of the higher additional water, while the surface activity and nucleation effect supplied from finer RFCB were beneficial for the improvement of the hydration kinetics. Furthermore, inclusion of RFCB increased the total pore volume and porosity but performed better in refining the pore size distribution, thus decreased the average pore diameter. The surface activity of RFCB decreased CH content while increased chemical bond water and additional hydrates, thereby leading to enhancement of the compactness of interface, cement matrix and surface rim. More importantly, RFCB helped to decrease the chloride migration coefficient and electric flux. Though the surface activity of RFCB was beneficial in the strength development, it could not offset a deteriorated influence of porous RFCB with a higher replacement.

ОПРЕДЕЛЕНИЕ КОНЦЕНТРАЦИЙ ПОЛЛЮТАНТОВ В ОТРАБОТАВШИХ ГАЗАХ ПОДВЕСНОГО ЛОДОЧНОГО МОТОРА HANGKAI T6 ПРИ ОБКАТКЕ И В ПОВСЕДНЕВНОЙ ЭКСПЛУАТАЦИИ

Active development of water recreation market leads to a noticeable increase in the number of motorized recreational boats and, as a consequence, to an aggravation of their technogenic impact on the environment. New outboard motors should go through a fairly long break-in period to allow the moving parts to better break in. During the mode, on average, twice as much engine oil is added to the fuel as during daily operation, and this affects the concentration of pollutants in the exhausts. The results of the experimental study of the HANGKAI T6 2-stroke gasoline outboard motor, have shown that the content of CO, CO2 and CH in the exhausts has increased, respectively, by 19,0–62,8 %, 32,3–60,7 % and 18,1–64,7 % in the break-in mode with a fuel-oil ratio 25:1 compared to daily operation mode with a fuel-oil ratio 50:1.

Study on hydration process of alkali-activated slag cement activated by weakly alkaline components

Alkali-Activated Slag Cement (AASC) activated by weak alkaline components has good workability and safety. Sodium carbonate (Na2CO3, SC), sodium sulfate (Na2SO4, SS), reactive magnesium oxide (R-MgO), and calcium hydroxide (Ca(OH)2, CH) were used to prepare the AASC. The hydration process, phase composition and hydration kinetics of AASC were studied. The results showed that the pH value of AASC slurry activated by weak alkaline components ranging from 10.8 to 13.2. CH could significantly affect the pH of AASC slurry. When the dosage reached more than 5%, the pH value of AASC slurry reached more than 12.0. The hydration heat release of AASC activated by weak alkaline components was mainly concentrated in 1 day. Two hydration heat release peaks appeared. The initial hydration peak appeared within 0.5 h-1 h, and the acceleration hydration peak appeared within 1 h-8 h. When the content of CH was 5%, and the content of SS and SC was 7% and 4%, the acceleration peak of AASC was much higher than that of others. At the same time, the Krstulovic-Dabic model was used to study the hydration kinetics of AASC. The increase of SS content prolonged the NG-I and I-D processes. CH accelerated the hydration rate of AASC and shortened the hydration process of AASC. The main hydration products of AASC activated by weakly alkaline components were C-(A)-S-H gel, calcite, ettringite, hydrotalcite and gaylussite. R-MgO was favorable for the formation of hydrotalcite, while SS was favorable for the formation of ettringite.

Study of the transition zone of concretes prepared with metakaolin using sem/eds-associated nanoindentation technique

The instrumented nanoindentation technique using significantly small loads is a viable alternative for specific studies in the interfacial transition zone (ITZ) of concrete. This study analyses the properties of the transition zone of concretes prepared with metakaolin (MK) using the nanoindentation technique and SEM/EDS. The response variables adopted were the thickness of the transition zone, nano-hardness and modulus of elasticity, and the formation of high- and low-density C-S-H in the transition zone. Incorporating MK and decreasing porosity and CH content in concretes can increase the percentage of frequency of CSH in the cementitious matrix. Reduced ITZ is a direct consequence of these reported effects. However, this beneficial effect of MK on ITZ is more pronounced in concretes with poorer cement consumption. The incorporation of MK has a more discreet influence on concretes with high cement consumption − C60, with 512 kg/m³ , for example, had a similar behavior to C60 8% MK. The analysis of the ITZ thickness by nanomechanics and nanoindentation techniques presented results very similar to those of the chemical analysis (EDS).