scholarly journals Clays as SCM – Reactivity of Uncalcined Kaolinite and Bentonite, and Impact on Phase Assemblage and Strength Development of PC Mortars

2019 ◽  
Vol 60 (1) ◽  
pp. 13-30
Author(s):  
Mette Rica Geiker ◽  
Emmanuel Gallucci
Keyword(s):  
Cement Paste ◽  
Chemical Reactivity ◽  
Engineering Properties ◽  
Strength Development ◽  
Phase Assemblage ◽  
Clay Particles ◽  
Compressive Strength Development ◽  
The Impact ◽  
Detrimental Impact ◽  
Porosity Measurements

Abstract The impact of substitution of cement paste with uncalcined clay (bentonite and kaolinite) in the range of 5% by volume of paste on the development of hydration and properties of mortar was investigated. Two issues were addressed, the expected filler effect of the dispersed sub-micron clay particles, and the possible chemical reactivity of the clay. The study indicated that Portland cement paste may be modified by addition of well dispersed clay and that the impact includes accelerated cement hydration as well as altered distribution of products. Compressive strength development was accelerated, but later age strength was reduced, especially for the bentonite mixes. In contrast, microscopic porosity measurements indicated no detrimental impact on the coarse capillary porosity. The investigation indicates that for durability related engineering properties, the application of uncalcined clay might be a potential means for reduction of the clinker factor in concrete in support of sustainability.

scholarly journals Property Analysis of Slag Composite Concrete Using a Kinetic–Thermodynamic Hydration Model

2021 ◽  
Vol 11 (16) ◽  
pp. 7191
Author(s):  
Ki-Bong Park ◽  
Yi-Sheng Wang ◽  
Xiao-Yong Wang
Keyword(s):  
Experimental Study ◽  
Thermodynamic Model ◽  
Experimental Studies ◽  
Hydration Heat ◽  
Strength Development ◽  
Phase Assemblage ◽  
Property Development ◽  
Hydration Model ◽  
Compressive Strength Development ◽  
Reaction Degree

Slag is increasingly unitized for the production of sustainable concrete. This paper presents a procedure with which to analyze the property development of slag composite concrete. Experimental studies of the hydration heat and compressive strength development and simulation studies using a kinetic hydration model and a thermodynamic model were performed. First, we performed an experimental study of the isothermal hydration heat of cement–slag blends. Based on the results of the experimental study on cumulative hydration heat, the reaction degree of slag was determined. We found that the reaction degree of slag decreased as the slag content increased. Second, the reaction degree of slag and cement were used as the input parameters for the Gibbs energy minimization (GEM) thermodynamic equilibrium model. Moreover, the phase assemblage of hydrating cement–slag was determined. The trends of calcium silicate hydrate (CSH) are similar to those of strength. Based on the CSH content, the strength of hardening cement–slag blends was determined. In addition, the calcium hydroxide (CH) content resulting from the thermodynamic model shows good agreement with the experimental results. In summary, the integrated kinetic–thermodynamic model is useful for analyzing the properties of cement–slag blends.

Effects of Different Lithium Admixtures on Ordinary Portland Cement Paste Properties

2014 ◽  
Vol 919-921 ◽  
pp. 1780-1789 ◽  
Author(s):  
Yu Hai Deng ◽  
Chang Qing Zhang ◽  
Hai Qiang Shao ◽  
Han Wu ◽  
Nie Qiang Xie
Keyword(s):  
Compressive Strength ◽  
Cement Paste ◽  
Setting Time ◽  
Lithium Carbonate ◽  
Lithium Hydroxide ◽  
Strength Development ◽  
Lithium Nitrate ◽  
Cement Pastes ◽  
Compressive Strength Development ◽  
Paste Properties

Lithium-based chemicals are known to their signal effect on restraining alkali-silica reaction but uncertain influence on workability and mechanical property in the concrete. The aim of this research is to analyze the effects of three lithium additiveslithium nitrate (LiNO3), lithium hydroxide (LiOH) and lithium carbonate (Li2CO3) at various dosages, with an extensive comparison on fluidities, setting times and compressive strength of cement pastes. The experimental study shows that test results vary with the type of admixture. In general, three conclusions can be made: 1) lithium nitrate and lithium hydroxide can enhance the fluidity of cement paste, but lithium carbonate has opposite effects; 2) all three lithium salts shorten setting time as well as decrease the strength at suitable dosages; 3) the variations in lithium additives dosages have different influence on the cement pastes setting time and compressive strength development.

scholarly journals Review of the relationship between aggregates geology and Los Angeles and micro-Deval tests

2021 ◽  
Vol 80 (3) ◽  
pp. 1963-1980
Author(s):  
Solomon Adomako ◽  
Christian John Engelsen ◽  
Rein Terje Thorstensen ◽  
Diego Maria Barbieri
Keyword(s):  
Los Angeles ◽  
Crystal Size ◽  
Grain Shape ◽  
Mechanical Performance ◽  
Pore Space ◽  
Construction Material ◽  
Engineering Properties ◽  
Coarse Grained ◽  
The Impact ◽  
The Relationship

AbstractRock aggregates constitute the enormous volume of inert construction material used around the globe. The petrologic description as igneous, sedimentary, and metamorphic types establishes the intrinsic formation pattern of the parent rock. The engineering properties of these rocks vary due to the differences in the transformation process (e.g. hydrothermal deposits) and weathering effect. The two most common mechanical tests used to investigate the performance of aggregates are the Los Angeles (LA) and micro-Deval (MD) tests. This study reviewed the geological parameters (including mineralogy, grain and crystal size, grain shape, and porosity) and the relationship to Los Angeles and micro-Deval tests. It was found that high content of primary minerals in rocks (e.g. quartz and feldspar) is a significant parameter for performance evaluation. Traces of secondary and accessory minerals also affect the performance of rocks, although in many cases it is based on the percentage. Furthermore, some studies showed that the effect of mineralogic composition on mechanical strength is not sufficient to draw final conclusions of mechanical performance; therefore, the impact of other textural characteristics should be considered. The disposition of grain size and crystal size (e.g. as result of lithification) showed that rocks composed of fine-grain textural composition of ≤ 1 mm enhanced fragmentation and wear resistance than medium and coarse grained (≥ 1 mm). The effect of grain shape was based on convex and concave shapes and flat and elongated apexes of tested samples. The equidimensional form descriptor of rocks somehow improved resistance to impact from LA than highly flat and elongated particles. Lastly, the distribution of pore space investigated by means of the saturation method mostly showed moderate (R = 0.50) to strong (R = 0.90) and positive correlations to LA and MD tests.

scholarly journals The potential use of pumice in mine backfill

2020 ◽  
Vol 1 ◽  
Author(s):  
Mohammed A. Hefni
Keyword(s):  
Compressive Strength ◽  
Portland Cement ◽  
Mining Industry ◽  
Strength Development ◽  
Natural Pozzolan ◽  
Mine Backfill ◽  
Natural Pozzolans ◽  
Cemented Backfill ◽  
Compressive Strength Development ◽  
Potential Use

Abstract The use of natural pozzolans in concrete applications is gaining more attention because of the associated environmental, economic, and technical benefits. In this study, reference cemented mine backfill samples were prepared using Portland cement, and experimental samples were prepared by partially replacing Portland cement with 10 or 20 wt.% fly ash as a byproduct (artificial) pozzolan or pumice as a natural pozzolan. Samples were cured for 7, 14, and 28 days to investigate uniaxial compressive strength development. Backfill samples containing 10 wt.% pumice had almost a similar compressive strength as reference samples. There is strong potential for pumice to be used in cemented backfill to minimize costs, improve backfill properties, and promote the sustainability of the mining industry.

scholarly journals The contribution of changes to tax and social security to stalled life expectancy trends in Scotland: a modelling study

2020 ◽  
pp. jech-2020-214770
Author(s):  
Elizabeth Richardson ◽  
Martin Taulbut ◽  
Mark Robinson ◽  
Andrew Pulford ◽  
Gerry McCartney
Keyword(s):  
Life Expectancy ◽  
Social Security ◽  
Tax Credits ◽  
The Difference ◽  
Group Sex ◽  
The Uk ◽  
Social Security Benefits ◽  
The Impact ◽  
Welfare Reforms ◽  
Detrimental Impact

BackgroundLife expectancy (LE) improvements have stalled, and UK tax and welfare ‘reforms’ have been proposed as a cause. We estimated the effects of tax and welfare reforms from 2010/2011 to 2021/2022 on LE and inequalities in LE in Scotland.MethodsWe applied a published estimate of the cumulative income impact of the reforms to the households within Scottish Index of Multiple Deprivation (SIMD) quintiles. We estimated the impact on LE by applying a rate ratio for the impact of income on mortality rates (by age group, sex and SIMD quintile) and calculating the difference between inflation-only changes in benefits and the reforms.ResultsWe estimated that changes to household income resulting from the reforms would result in an additional 1041 (+3.7%) female deaths and 1013 (+3.8%) male deaths. These deaths represent an estimated reduction of female LE from 81.6 years to 81.2 years (−20 weeks), and male LE from 77.6 years to 77.2 years (−23 weeks). Cuts to benefits and tax credits were modelled to have the most detrimental impact on LE, and these were estimated to be most severe in the most deprived areas. The modelled impact on inequalities in LE was widening of the gap between the most and least deprived 20% of areas by a further 21 weeks for females and 23 weeks for males.InterpretationThis study provides further evidence that austerity, in the form of cuts to social security benefits, is likely to be an important cause of stalled LE across the UK.

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