Durability, strength, and stiffness of compacted gold tailings – cement mixes

Compaction and Portland cement addition are amongst promising ground improvement procedures for enhancing the mechanical properties of gold tailings. The present investigation intends to compute the impact of Portland cement content and dry density on the properties (durability, stiffness, and strength) of compacted gold tailings – cement mixes. Its main significant addition to knowledge is the quantification of accumulated loss of mass (ALM) after wetting–drying cycles, shear modulus at small strains, and unconfined compressive strength (qu) as a function of the porosity/cement index. In addition, the existence of an exclusive relation connecting ALM divided by the number of wetting–drying cycles and porosity/cement index is revealed empirically. This broadens the applicability of such an index by demonstrating that it controls not only mechanical but also endurance performance of compacted gold tailings – Portland cement mixes.

Download Full-text

Increasing Density and Cement Content in Expansive Soils Stabilization:Conflicting or Complementary Procedures for Reducing Swelling?

Canadian Geotechnical Journal ◽

10.1139/cgj-2019-0855 ◽

2020 ◽

Author(s):

Nilo Cesar Consoli ◽

Mariana Tonini de Araújo ◽

Suéllen Tonatto Ferrazzo ◽

Vinícius de Lima Rodrigues ◽

Cecilia Gravina da Rocha

Keyword(s):

Moisture Content ◽

Portland Cement ◽

Significant Influence ◽

General Equation ◽

Cement Content ◽

Expansive Soils ◽

Dry Density ◽

Loss Of Mass ◽

Porosity Index ◽

Swelling Model

Present study makes three contributions to the literature of expansive soils: (i) it proposes equations to predict soil swelling based on dry density and cement content, (ii) it checks the developed general equation by predicting the swelling of different expansive soils from literature and (iii) it designs experiments that investigate factors that have a significant influence on swelling. An experimental programme was carried out to analyse the expansion of bentonite-kaolin-cement blends. Different proportions of bentonite-kaolin, cement content, dry density and moisture content were evaluated. A unique relation of the cement/porosity index was obtained for cement stabilized expansive soils swelling; this index has been used before to portray strength, stiffness and loss of mass of stabilized soils and is now shown to be applicable to describe swelling of expansive soils treated with Portland cement. In the present research, cement content and dry density are seen as conflicting parameters regarding the swelling of expansive soils, since increasing Portland cement amount reduces swelling and increasing density (through compaction) causes higher expansion. A general swelling model was proposed and successfully checked with data from the literature, being able to predict the swelling of expansive soils with different densities, expansive mineral, moisture and cement contents.

Download Full-text

Impact of Severe Climate Conditions on Loss of Mass, Strength, and Stiffness of Compacted Fine-Grained Soils–Portland Cement Blends

Journal of Materials in Civil Engineering ◽

10.1061/(asce)mt.1943-5533.0002392 ◽

2018 ◽

Vol 30 (8) ◽

pp. 04018174 ◽

Cited By ~ 12

Author(s):

Nilo Cesar Consoli ◽

Rubén Alejandro Quiñónez Samaniego ◽

Luis Enrique González ◽

Eduardo José Bittar ◽

Olivier Cuisinier

Keyword(s):

Portland Cement ◽

Climate Conditions ◽

Fine Grained ◽

Loss Of Mass ◽

Strength And Stiffness

Download Full-text

Efficacy of Popular Diets Applied by Endurance Athletes on Sports Performance: Beneficial or Detrimental? A Narrative Review

Nutrients ◽

10.3390/nu13020491 ◽

2021 ◽

Vol 13 (2) ◽

pp. 491

Author(s):

Aslı Devrim-Lanpir ◽

Lee Hill ◽

Beat Knechtle

Keyword(s):

Gastrointestinal Symptoms ◽

Endurance Performance ◽

Endurance Athletes ◽

Intermittent Fasting ◽

Nutritional Strategy ◽

Current Perspective ◽

Vegetarian Diets ◽

Fat Diets ◽

The Impact ◽

Harsh Conditions

Endurance athletes need a regular and well-detailed nutrition program in order to fill their energy stores before training/racing, to provide nutritional support that will allow them to endure the harsh conditions during training/race, and to provide effective recovery after training/racing. Since exercise-related gastrointestinal symptoms can significantly affect performance, they also need to develop strategies to address these issues. All these factors force endurance athletes to constantly seek a better nutritional strategy. Therefore, several new dietary approaches have gained interest among endurance athletes in recent decades. This review provides a current perspective to five popular diet approaches: (a) vegetarian diets, (b) high-fat diets, (c) intermittent fasting diets, (d) gluten-free diet, and (e) low fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAP) diets. We reviewed scientific studies published from 1983 to January 2021 investigating the impact of these popular diets on the endurance performance and health aspects of endurance athletes. We also discuss all the beneficial and harmful aspects of these diets, and offer key suggestions for endurance athletes to consider when following these diets.

Download Full-text

Electrically-induced quadriceps fatigue in the contralateral leg impairs ipsilateral knee extensors performance

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00363.2020 ◽

2021 ◽

Author(s):

Fabio Giuseppe Laginestra ◽

Markus Amann ◽

Emine Kirmizi ◽

Gaia Giuriato ◽

Chiara Barbi ◽

...

Keyword(s):

Muscle Activation ◽

Central Fatigue ◽

Endurance Performance ◽

Voluntary Exercise ◽

Peripheral Fatigue ◽

Knee Extensors ◽

Motor Drive ◽

Time To Exhaustion ◽

Crossover Effect ◽

The Impact

Muscle fatigue induced by voluntary exercise, which requires central motor drive, causes central fatigue that impairs endurance performance of a different, non-fatigued muscle. This study investigated the impact of quadriceps fatigue induced by electrically-induced (no central motor drive) contractions on single-leg knee-extension (KE) performance of the subsequently exercising ipsilateral quadriceps. On two separate occasions, eight males completed constant-load (85% of maximal power-output) KE exercise to exhaustion. In a counterbalanced manner, subjects performed the KE exercise with no pre-existing quadriceps fatigue in the contralateral leg on one day (No-PreF), while on the other day, the same KE exercise was repeated following electrically-induced quadriceps fatigue in the contralateral leg (PreF). Quadriceps fatigue was assessed by evaluating pre- to post-exercise changes in potentiated twitch force (ΔQtw,pot; peripheral-fatigue), and voluntary muscle activation (ΔVA; central-fatigue). As reflected by the 57±11% reduction in electrically-evoked pulse force, the electrically-induced fatigue protocol caused significant knee-extensors fatigue. KE endurance time to exhaustion was shorter during PreF compared to No-PreF (4.6±1.2 vs 7.7±2.4 min; p<0.01). While ΔQtw,pot was significantly larger in No-PreF compared to PreF (-60% vs -52%, p<0.05), ΔVA was greater in PreF (-14% vs -10%, p<0.05). Taken together, electrically-induced quadriceps fatigue in the contralateral leg limits KE endurance performance and the development of peripheral fatigue in the ipsilateral leg. These findings support the hypothesis that the crossover-effect of central fatigue is mainly mediated by group III/IV muscle afferent feedback and suggest that impairments associated with central motor drive may only play a minor role in this phenomenon.

Download Full-text

Stiffness and Strength of Stabilized Organic Soils—Part I/II: Experimental Database and Statistical Description for Machine Learning Modelling

Geosciences ◽

10.3390/geosciences11060243 ◽

2021 ◽

Vol 11 (6) ◽

pp. 243

Author(s):

Hernandez-Martinez Francisco G. ◽

Al-Tabbaa Abir ◽

Medina-Cetina Zenon ◽

Yousefpour Negin

Keyword(s):

Machine Learning ◽

Statistical Analysis ◽

Portland Cement ◽

Soil Stabilization ◽

Data Availability ◽

Data Repository ◽

Organic Soils ◽

Experimental Database ◽

Soil Mixing ◽

The Impact

This paper presents the experimental database and corresponding statistical analysis (Part I), which serves as a basis to perform the corresponding parametric analysis and machine learning modelling (Part II) of a comprehensive study on organic soil strength and stiffness, stabilized via the wet soil mixing method. The experimental database includes unconfined compression tests performed under laboratory-controlled conditions to investigate the impact of soil type, the soil’s organic content, the soil’s initial natural water content, binder type, binder quantity, grout to soil ratio, water to binder ratio, curing time, temperature, curing relative humidity and carbon dioxide content on the stabilized organic specimens’ stiffness and strength. A descriptive statistical analysis complements the description of the experimental database, along with a qualitative study on the stabilization hydration process via scanning electron microscopy images. Results confirmed findings on the use of Portland cement alone and a mix of Portland cement with ground granulated blast furnace slag as suitable binders for soil stabilization. Findings on mixes including lime and magnesium oxide cements demonstrated minimal stabilization. Specimen size affected stiffness, but not the strength for mixes of peat and Portland cement. The experimental database, along with all produced data analyses, are available at the Texas Data Repository as indicated in the Data Availability Statement below, to allow for data reproducibility and promote the use of artificial intelligence and machine learning competing modelling techniques as the ones presented in Part II of this paper.

Download Full-text

Study on Impact Compaction of Aeolian Sand Subgrade and its Effect Evaluation

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.378-379.370 ◽

2011 ◽

Vol 378-379 ◽

pp. 370-373

Author(s):

Yu Qing Yuan ◽

Xuan Cang Wang ◽

Hui Jun Shao

Keyword(s):

Rayleigh Wave ◽

Impact Force ◽

Engineering Practice ◽

Effect Evaluation ◽

Aeolian Sand ◽

Field Compaction ◽

Vibratory Compaction ◽

Strength And Stiffness ◽

The Impact ◽

Elastic Stage

In order to solve the problem of aeolian sand subgrade compaction, we studied the technology of impact compaction, applied it to the engineering practice and analyzed its effect with Rayleigh wave. The technology of impact compaction can combine the compaction of potential energy and kinetic energy and make it easier for the materials to reach their elastic stage. With the combined function of "knead-roll-impact", the impact compaction road roller can compact the soil body and offer 6～10 times impact force and 3～4 times the depth of influence more than the vibratory roller. The impact compaction methods of aeolian sand subgrade were put forward. The comparative field compaction tests between impact and vibratory compaction are carried through, which are detected by Rayleigh wave. The results show that the impact compaction can make the density of the aeolian sand subgrade 2～5% higher than the vibratory compaction, and reach the influence depth of 7 metres. To sum up, the impact compaction can clearly increases the strength and stiffness of aeolian sand subgrade with a dynamic elastic modulus of 202.63MPa.

Download Full-text

The impact of coarse aggregate shape on the behavior of self-compacting high-performance concrete

E3S Web of Conferences ◽

10.1051/e3sconf/20184900079 ◽

2018 ◽

Vol 49 ◽

pp. 00079

Author(s):

Krzysztof Ostrowski

Keyword(s):

High Performance ◽

Coarse Aggregate ◽

High Performance Concrete ◽

Significant Proportion ◽

Rheological Parameters ◽

Concrete Technology ◽

Binder Ratio ◽

Strength And Stiffness ◽

Aggregate Shape ◽

The Impact

Self-Compacting High Performance Concrete (SCHPC) presents a crucial step in the development of concrete technology. The most important features of self-consolidating concrete are flowability, segregation resistance and passing ability. Generally, the rheological properties are modified by effective superplasticisers and water to binder ratio. The aim of this study is to focus on the important aspect of the impact of shape of the coarse aggregate on fresh concrete mixture properties, strength and deformability of SCHPC. Coarse aggregate is a significant proportion of the concrete volume and therefore has a meaningful influence on its quality. By appropriate selection of the shape of the grain aggregate, it is possible to affect the rheological parameters of concrete. The results presented in this study indicated that the shape of the grains of coarse aggregate has an impact on the strength and stiffness of SCHPC. Moreover, the occurrence of irregular grains of coarse aggregate causes lower slump flow and higher plastic viscosity in comparison to concrete mixtures with regular grains only. The research presented in this article is part of the author's wider research devoted to this issue.

Download Full-text

Life Cycle Assessment of Railway Ground-Borne Noise and Vibration Mitigation Methods Using Geosynthetics, Metamaterials and Ground Improvement

Sustainability ◽

10.3390/su10103753 ◽

2018 ◽

Vol 10 (10) ◽

pp. 3753 ◽

Cited By ~ 14

Author(s):

Sakdirat Kaewunruen ◽

Victor Martin

Keyword(s):

Life Cycle ◽

Life Cycle Cost ◽

Ground Improvement ◽

Cycle Performance ◽

Vibration Mitigation ◽

Noise And Vibration ◽

Climate Conditions ◽

Extreme Climate ◽

Mitigation Methods ◽

The Impact

Significant increase in the demand for freight and passenger transports by trains pushes the railway authorities and train companies to increase the speed, the axle load and the number of train carriages/wagons. All of these actions increase ground-borne noise and vibrations that negatively affect people who work, stay, or reside nearby the railway lines. In order to mitigate these phenomena, many techniques have been developed and studied but there is a serious lack of life-cycle information regarding such the methods in order to make a well-informed and sustainable decision. The aim of this study is to evaluate the life-cycle performance of mitigation methods that can enhance sustainability and efficacy in the railway industry. The emphasis of this study is placed on new methods for ground-borne noise and vibration mitigation including metamaterials, geosynthetics, and ground improvement. To benchmark all of these methods, identical baseline assumptions and the life-cycle analysis over 50 years have been adopted where relevant. This study also evaluates and highlights the impact of extreme climate conditions on the life-cycle cost of each method. It is found that the anti-resonator method is the most expensive methods compared with the others whilst the use of geogrids (for subgrade stiffening) is relatively reliable when used in combination with ground improvements. The adverse climate has also played a significant role in all of the methods. However, it was found that sustainable methods, which are less sensitive to extreme climate, are associated with the applications of geosynthetic materials such as geogrids, composites, etc.

Download Full-text

Calorimetric determination of the effect of additives on cement hydration process

Chemical Papers ◽

10.2478/s11696-012-0256-x ◽

2013 ◽

Vol 67 (2) ◽

Cited By ~ 16

Author(s):

Pavel Šiler ◽

Josef Krátký ◽

Iva Kolářová ◽

Jaromír Havlica ◽

Jiří Brandštetr

Keyword(s):

Portland Cement ◽

Silica Fume ◽

Maximum Temperature ◽

Granulated Blast Furnace Slag ◽

Mineral Components ◽

Maximum Temperatures ◽

The Impact ◽

Furnace Slag ◽

Calorimetric Determination

AbstractPossibilities of a multicell isoperibolic-semiadiabatic calorimeter application for the measurement of hydration heat and maximum temperature reached in mixtures of various compositions during their setting and early stages of hardening are presented. Measurements were aimed to determine the impact of selected components’ content on the course of ordinary Portland cement (OPC) hydration. The following components were selected for the determination of the hydration behaviour in mixtures: very finely ground granulated blast furnace slag (GBFS), silica fume (microsilica, SF), finely ground quartz sand (FGQ), and calcined bauxite (CB). A commercial polycarboxylate type superplasticizer was also added to the selected mixtures. All maximum temperatures measured for selected mineral components were lower than that reached for cement. The maximum temperature increased with the decreasing amount of components in the mixture for all components except for silica fume. For all components, except for CB, the values of total released heat were higher than those for pure Portland cement samples.

Download Full-text

Influence of Aluminous Cement on the Hardening Rate of Cement-Based Stucco Mortars

Materials Science Forum ◽

10.4028/www.scientific.net/msf.865.57 ◽

2016 ◽

Vol 865 ◽

pp. 57-61 ◽

Cited By ~ 1

Author(s):

Wojciech Siemiński ◽

Marcin Kaczmarczyk

Keyword(s):

Portland Cement ◽

Setting Time ◽

Experimental Studies ◽

Cellulose Ether ◽

Hydrophobic Properties ◽

Content Ratio ◽

Flow Table ◽

Aluminous Cement ◽

Hydrophobic Nature ◽

The Impact

Renovation mortars used to restore damaged stucco elements are materials with special physical properties due to the nature of the work and environment in which they are applied. They must be characterized by low shrinkage, relatively short setting time, appropriate working properties and hydrophobic nature of hardened mortar. This paper analyzes the impact of mortar stucco ingredients on these parameters. The analysis was performed by experimental studies. The effect of the content ratio of aluminate cement to Portland cement on the change in mortar setting time was studied. Suitable workability of fresh mortar is achieved by the use of consistence-modifying additives. To assess this parameter, flow table method was applied in accordance with PN-EN 1015-3: 2000. The additives used were a system of thickeners, which included: cellulose ether in the form of hydroxyethylmethylcellulose and modified starch ether (starch 2-hydroxypropyl ether). Hydrophobic properties were obtained by the addition of triethoxyoctylsilane. The results were presented as graphs and tables. It was found that the ratio of aluminous cement to Portland cement most beneficial in terms of the setting rate of the resulting stucco mortar is 25% (m/m). This amount accelerates the end of setting time to 2 hours, the beginning of the setting time being 20 minutes. Suitable working characteristics were obtained by the addition of 0.080% of hydroxyethylmethylcellulose and 0.025% (m/m in dry mix) of starch 2-hydroxypropyl ether. Best hydrophobic properties of the hardened mortar was obtained by the addition of 0.075% (m/m in dry mix) of triethoxyoctylsilane.

Download Full-text