Mixing Moisture Content Research Articles

Unconfined Compressive Strength of Cement-Stabilized Qiantang River Silty Clay.

Cement-stabilization of weak and soft soils is an efficient way for ground improvement. Traditional Portland cement remains the most popular cementitious material in practice, and thus, a proper dosage design of cement-stabilized soil is of practical interest to meet the sustainable engineering requirements and to remedy environmental concerns. Based on the unconfined compression test of cement-stabilized Qiantang River silty clay, the effects of cement content, mixing moisture content, mixing-water-to-cement ratio, and curing time on the unconfined compressive strength were investigated. The results show that the mixing-water-to-cement ratio can comprehensively characterize the effects of cement content and water content on the unconfined compressive strength of the cement-stabilized clay. A prediction method for the unconfined compressive strength of cement-stabilized Qiantang River silty clay has been proposed with considerations for mixing-water-to-cement ratio and curing time. By comparing the experimental data of the present study with the existing literature data, it is found that there is a unified relationship between the unconfined compressive strength and the mixing-water-to-cement ratio of cement-stabilized Qiantang River silty clay, kaolin, Singapore marine clay, and Bangkok clay under the same curing time. The prediction method recommended by the standard may overestimate the unconfined compressive strength of cement-stabilized Qiantang River silty clay cured for 90 days.

Investigation of mechanical behavior of sustainable construction materials: Recycled glass sand stabilized with natural binder material — Biopolymers

Presented in this paper is a study on the biopolymer treated recycled glass sand (BRGS). The effect of curing period, temperature, initial mixing moisture content and biopolymer concentration on mechanical behaviors of BRGS were examined through unconfined compaction strength (UCS), consolidated and drained triaxial test and scanning electron microscopy (SEM) analysis. The results revealed that biopolymer had a significant improvement on the soil stability. The mixing moisture content, biopolymer concentration and curing condition had a strong influence on soil strength. The strength of BRGS increased with dehydration, while further addition of biopolymer concentration may result in a decrease in strength. It was found that different types of biopolymers had their own preferences for curing conditions. The strength of agar treated RGS (thermal induced biopolymer) cured at 105 ℃ for 30 days was six times stronger than that cured at room temperature, while the optimal curing temperature of alginate treated RGS (ionic gelation biopolymer) was 50 ℃. The BRGS presented a slight decrease in friction angle but a significant increase in cohesion. The SEM image showing biopolymer uniformly wrapped RGS particles.

The Impact of Moisture and Clay Content on the Unconfined Compressive Strength of Lime Treated Highly Reactive Clays

This study aims to provide a thorough evaluation for the changes in the microstructure and evolution of strength of highly reactive clays that were treated with 7% lime over a period of curing time as a function of the mixing moisture content. Three series of testing were carried out on specimens with 100%, 85% and 75% of bentonite content and prepared with different moisture content of 10, 20, 30 and 40% above the corresponding optimum moisture content. Specimens of 100% bentonite were treated with 7% of lime, compacted to achieve a predetermined dry unit weight and cured at temperatures of 20 °C and 40 °C for up to 28 days whereas the specimens with 85% and 75% of bentonite content were prepared by the addition of sand and were cured at 20 °C for up to 7 days. Unconfined Compressive Strength tests and Scanning Electron Microscopy were conducted to observe the strength and the microstructural changes resulting from increasing mixing moisture content. California Bearing Ratio and Resilient Modulus were correspondingly determined based on correlations with the Unconfined Compressive Strength. The failure pattern was also studied to better understand the ultimate behaviour of lime stabilised clays. The results revealed that the strength of treated bentonite increased with the increase in the moisture content up to 30% above the corresponding optimum moisture content and with increasing the curing time and temperature. Nevertheless, substituting bentonite with sand on the specimen resulted in a significant reduction on the attained strength. Furthermore, the results of California Bearing Ratio and Resilient Modulus showed that values for both parameters are significantly enhanced with lime treatment. The microstructural analysis provided visual evidence to the improved strength in which the pozzolanic reaction was found to be significantly affected by the amount of moisture in the mixture. The results suggested that compacting lime treated expansive clays with moisture content moderately higher than the optimum moisture content would result in a significant enhancement to the attained strength over the period of curing.

Evolution of the quality of forest biomass for energy generation in a cogeneration plant

This study aimed to analyse the evolution of the quality of different types of forest residues and wood waste used for energy generation in a cogeneration plant, located in the city of Lages, Santa Catarina, Brazil. 4937 samples were analysed belonging to a database coming from a historical series, since the beginning of plant operation (2005–2015). The evaluated properties were moisture content, ash content and calorific value of the biomass. The results showed the there was a gradual and steady increase in the use biomass for energy generation in the study region. The three types of forest biomass purchased and used for energy generation in higher amounts in a cogeneration plant were the industrial chip, the bark and the sawdust. The mix analyses enabled the perception that there was an improvement in the quality of fuel supplied to company, evidenced by the decrease in moisture and ash content and consequent increase in the net calorific value (mean value 6612.84 kJ/kg). The moisture content of mix is also below (mean of 56.60%) the threshold value (60%) and it has been declining over the plant operation period, indicating progress in the processing and treatment of biomass for energy generation.

Using the calculation method for low-melting clay assessment

Low-melting polymineral clays are widely used in building ceramics production. The properties of ceramic products depend on many factors. The paper describes properties of low-melting clay from Belebey deposit, Bashkiria. Using mathematical statistics methods, researchers make statistical analysis of grain size composition of clay raw material on Belebey brick factory and also analyze amount of sand additives and mixing moisture content. The study of general and technological properties of clay raw materials, and materials obtained from this raw material, was carried out in accordance with existing regulations using chemical, differential-thermal and non-standard methods. According to chemical analysis, non-standard assessment of clay raw materials was carried out by means of computer program "Assessment", developed at the Department of Building Materials Production and Engineering Structures. The method of calculating quantity and composition of melted material, formed in ceramic masses during firing, using known diagrams of aluminosilicate systems state is used. The assessment made it possible to determine maximum firing temperature and firing range and additives improving clinker formation. The studies show that calculation indicators are consistent with experimental data. They can be used for quick assessment of raw materials properties when changing its composition, and in adjustment of technological parameters of production.

The influence of material related parameters on the mechanical properties of foamed asphalt mix

By indirect tensile strength (ITS) test and unconfined compressive strength (UCS) test, the influence of various material related parameters, including asphalt foamability, aggregate temperature, mixing moisture content (MMC) and foamed asphalt (FA) content, on the mechanical properties of FA mixes was studied. The results indicated that both asphalt foamability and aggregate temperature greatly affected ITS of FA mixes. Too low aggregate temperature was unfavorable for mechanical properties of FA mixes. Foamed index alone was unfit for the evaluation of asphalt foamability. Compared with half-life, expansion ratio had more prominent influence on ITS of FA mixes. MMC had significant impact on the mechanical properties of FA mixes and should be optimized by trial and test in FA mix design. The mechanical properties of FA mix were sensitive to the change of FA content. Compared with the ITS determined with standard Marshall specimens, both the ITS and UCS determined with static compressed specimens by 15 cm diameter were more effective in terms of choosing the optimal asphalt content for FA mixes.

Study on the optimization design of mixing moisture content in foamed asphalt mix

This research discussed the rational mixing moisture content (MMC) in foamed asphalt (FA) mix design. Sieve analysis was firstly used to study the bitumen dispersion and bitumen-aggregate coating and bonding action in FA mixes with three levels of MMC. Then, through variance analysis, the impacts of MMC, bitumen content and their interaction effect on the mechanical properties of FA mixes were studied. Indirect tensile strength test and dry density determination were carried out on FA mixes consisting of different gradings and material types to explore the rational MMC. On base of that, monotonic triaxial test was performed on two types FA mixes with various filler contents to further investigate the rational MMC for FA mix. The research results indicated that improper MMC led to bitumen clots and affected cohesion of FA mix. MMC and bitumen content had important impacts on mechanical properties of FA mix, while their interaction effect could be ignored in mix design. Optimal MMC increased to a certain extent with the increase of fine aggregates content, especially filler content in the grading. 70–80% of the optimum moisture content (OMC) was recommended as rational range of MMC for FA mix with 5–15% filler content and 75–85% of OMC for mix with 15–20% filler content, which offered a reference for easy and simplified MMC design for FA mix.

Optimization of the physico-chemical processes occuring during the preparation of glass mix and evaluation of the effect of the mix moisture content on the efficiency of the glass-making process

The physico-chemical processes and individual factors affecting the uniformity of the mix both when the mix components are being mixed in a mixer in a sectional line and when the mix is transported and loaded into a glass-making furnace are analyzed. The effect of moistening on mix quality in obtaining glass mix and transporting and loading the mix into the furnace by means of mix loaders is determined. The temperature factors ensuring that the mix temperature when the mix is loaded into the furnace is no lower than 35 – 40°C are determined. The degree to which mix is removed with respect to both quantity and individual components on the loading hopper and regenerators along the glass-making furnace is determined. The direction for further research on optimizing the mix preparation process in order to increase the operational efficiency of a glass-making furnace is proposed on the basis of the results obtained in the present work.

Micromechanics of the Effects of Mixing Moisture on Foamed Asphalt Mix Properties

The mixing moisture content (MMC) is an important mix design variable in pavement full-depth reclamation (FDR) with foamed asphalt. It has been known for many decades that MMC in the granular material subjected to foamed asphalt treatment can affect asphalt dispersion. This paper investigates the micromechanics of this phenomenon by combining direct microstructure observations and conventional laboratory testing. It was found that for a typical loose moist granular material with a considerable amount of fine particles, the agglomeration state evolves through a series of states as the MMC increases. If the MMC is high, the fine particles become saturated and form a pastelike substance that coats larger aggregate particles, creating large agglomerations with low surface area to volume ratios. Inferior asphalt dispersion is resulted for mixes in this state. Theories for wet agglomeration processes are used to explain the observations on the basis of thermodynamic equilibrium. Fracture face image analysis for tested indirect tensile strength specimens confirmed this observation. Laboratory tests also found that mixes with inferior asphalt dispersion due to suboptimal MMC yield low strength and low stiffness. These effects are particularly significant for granular materials with higher fines content. The main practical implication of the findings is that relatively dry loose granular mixes are preferred for foamed asphalt dispersion, and a balance should be sought between asphalt dispersion and mix compactability. The existing postulation that high MMC aids foamed asphalt dispersion is therefore dismissed.

A Case Study on Optimization of Biomass Flow During Single-Screw Extrusion Cooking Using Genetic Algorithm (GA) and Response Surface Method (RSM)

In the present study, response surface method (RSM) and genetic algorithm (GA) were used to study the effects of process variables like screw speed, rpm (x1), L/D ratio (x2), barrel temperature (°C; x3), and feed mix moisture content (%; x4), on flow rate of biomass during single-screw extrusion cooking. A second-order regression equation was developed for flow rate in terms of the process variables. The significance of the process variables based on Pareto chart indicated that screw speed and feed mix moisture content had the most influence followed by L/D ratio and barrel temperature on the flow rate. RSM analysis indicated that a screw speed > 80 rpm, L/D ratio > 12, barrel temperature > 80 °C, and feed mix moisture content > 20% resulted in maximum flow rate. Increase in screw speed and L/D ratio increased the drag flow and also the path of traverse of the feed mix inside the extruder resulting in more shear. The presence of lipids of about 35% in the biomass feed mix might have induced a lubrication effect and has significantly influenced the flow rate. The second-order regression equations were further used as the objective function for optimization using genetic algorithm. A population of 100 and iterations of 100 have successfully led to convergence the optimum. The maximum and minimum flow rates obtained using GA were 13.19 × 10−7 m3/s (x1 = 139.08 rpm, x2 = 15.90, x3 = 99.56 °C, and x4 = 59.72%) and 0.53 × 10−7 m3/s (x1 = 59.65 rpm, x2 = 11.93, x3 = 68.98 °C, and x4 = 20.04%).

Influence of curing on cold mix mechanical performance

Cold mixes are evolutive materials, especially in their early life. Their initial cohesion is low and builds up gradually. The materials characteristics have to be evaluated at different states: fresh, mature, aged. An evaluation method is already available for fresh cold mixes. Ageing issues have been addressed elsewhere and are not dealt with here. Different curing procedures have been assessed and compared. Their goals are: laboratory curing must be related to field curing, the binder film must not be brought to an artificial state, no binder ageing must be caused by curing. Diverse curing sequences have been applied to grave-emulsion and dense wearing course mix. The effects of temperature, relative humidity and time have been evaluated. During each curing span, the mix moisture content has been monitored. The mechanical behaviour has been characterized by compressive strength and stiffness modulus (measured by indirect tensile testing). At the end of the varied curing periods, the bitumen was extracted and characterized. Special care has been taken in selecting the extraction method, to prevent any alteration of the bitumen. To establish a relationship between laboratory and field, the above results have been compared to those obtained on cores taken from similar mixes laid on roads. Finally, a new curing method has been selected and is proposed to road engineers.