Absorption Of Aggregates Research Articles

Multi-pulse laser irradiation of cadmium yellow paint films: The influence of binding medium and particle aggregates

The present work is focused on the study of laser-induced effects that can occur in cadmium yellow paint films. To this aim, samples were prepared with different binders (linseed oil and polyvinylalcohol), mixing methods (manual vs. sonication) and pigment volume concentration (PVC). Laser experiments were performed under a microscope-based setup coupled to a spectrometer, which allowed to study surface and in-depth changes thanks to 2D image processing and 3D reconstructions. The present methodology revealed effective for studying the role that binder, particle-size and density distribution have upon laser irradiation. Results showed the threshold fluences strictly depend on the type of binder and PVC. The damage nucleation is size-dependent with fluence and PVC, and the micro-damaged sites can be ascribed to non-linear absorption of CdS aggregates, whose size is of the order of the incident wavelength. These conclusions were further corroborated by Vis-NIR PL emission and reflection and ESEM-EDX.

Hierarchy of stochastic Schrödinger equation towards the calculation of absorption and circular dichroism spectra.

A theoretically solid and numerically exact method is presented for the calculation of absorption and circular dichroism (CD) spectra of molecular aggregates immersed in a harmonic bath constituted as the combination of some prominent quantized vibrational modes and continuous overdamped Brownian oscillators. The feasibility and the validity of newly proposed method are affirmed in the analytical monomer spectra. To go beyond the independent local bath approximation, all the correlations of site energy fluctuations and excitonic coupling fluctuations are included in our strategy, and their influence on the absorption and CD spectra is investigated based on the Frenkel exciton model of homodimer. In the end, a good fit of the absorption and part of CD spectra for the entire B800-B850 ring in the light-harvesting complexes 2 of purple bacteria to the experimental data is given, and the simulation results suggest that the asymmetry in the 800 nm region of CD spectra is actually an indication of B800-B850 inter-ring coupling.

A new methodology for determining particle density and absorption of lightweight, normal-weight and heavy weight aggregates in aqueous medium

Surface water absorption affects the value of the particle density obtained according to the UNE 1097-6. The aqueous medium absorption according to the standard poses problems as much in coarse fraction as in fine fraction. This new methodology is proposed in order to solve the problems observed in the current standard. The method is validated experimentally applying it to 5 different lightweight aggregates, 2 limestone normal-weight aggregates and a heavyweight aggregate. Different initial water contents and evolution of water absorption up to 28days were analyzed.

Use of carbonate precipitating bacteria to reduce water absorption of aggregates

This paper presents the results of an experimental investigation carried out to evaluate the influence of two types of bacteria, namely Sporosarcina pasteurii and Bacillus subtilis, with different cell concentrations (106, 107, 108cells.ml−1) on the water absorption of four types of concrete aggregates. Surface deposition of calcium carbonate crystals was found to decrease water absorption by 20–30%, depending on the type of bacteria and aggregate porosity. The use of ureolytic gram-positive bacteria S. pasteurii resulted in a more pronounced decrease in the uptake of water by the aggregates. The reduced water absorption observed was possibly due to deposition on the bacteria cell walls in the pores. The results show that the aggregates retained their properties and yielded the same results after about 20days, indicating that the deposits remained over this time period. The XRD and SEM analysis indicated the formation of calcite in bacterial aggregates.

Preparation and Fluorescence Properties of Perylenediimide Nanodispersions Having a One-Dimensional π-Stacked Structure.

We prepared stable nanodispersions of a fluorescent perylenediimide (PDI) derivative having long alkyl chains by nanosecond laser fragmentation of its microcrystalline powder in acetonitrile (ACN). The nanoparticles had cube-like or rod shapes with a mean size of 100 nm, and they dispersed stably for longer than 1 month. The prepared nanobricks exhibited absorption and fluorescence spectra characteristic of one-dimensional aggregates with cofacial stacking of PDI planes. Single-particle fluorescence measurements demonstrated that nanobricks had a well-aligned structure of one-dimensional columns of PDI. The aqueous dispersions were also fabricated by redispersing the prepared nanobricks, utilizing lipophilic interactions of surfactants having long alkyl chains. We examined the fluorescence properties of nanoparticles dispersed in ACN and in water, and observed amplified fluorescence quenching by the surface-adsorbed dye.

Application of ASR tests to recycled concrete aggregates: Influence of water absorption

Concrete is one of the most abundant construction and demolition wastes. It can be crushed to produce Recycled Concrete Aggregates (RCA) that can eventually be recycled for the manufacture of new concrete. However, the presence of adherent cement paste leads to higher alkalis content in these aggregates that could increase the risk to observe Alkali Silica Reaction (ASR). Moreover, the origin of natural aggregates in the RCA is generally unknown and these aggregates can potentially be reactive concerning ASR. Among standards which qualify the risk of ASR for natural aggregates, two main tests are used in this paper to evaluate the risk of ASR of RCA: tests on mortars and tests on microbars. In these tests, the water absorption of aggregates is not taken into consideration for the effective water calculation. However, in the case of absorbing aggregates like RCA, absorption water cannot be neglected. It could change significantly the effective water to cement ratio, and then influence the measured expansion. The first aim of this paper is to study the influences of absorption water and initial saturation state of RCA on the expansion of mortars and microbars. The second objective is to propose a new simple method for the assessment of water absorption coefficient of the fine granular fraction 0.16/0.63mm used for the manufacture of microbars. It is shown that absorption water has a strong influence on the expansion of mortars and microbars made with RCA, and that it has to be taken into account in the composition of the mixes. The initial state of saturation of RCA is less influential. The proposed method for the water absorption coefficient determination of fraction 0.16/0.63mm is based on the correlation between water absorption and cement paste content. The estimation of the latter from the mass loss between 105 and 475°C for two fractions of RCA, allows for an accurate determination of the water absorption coefficient of the fine fraction.

Factors analysis on autogenous volume deformation of MgO concrete and early thermal cracking evaluation

Micro expansive MgO concrete was produced by batching conventional raw materials and expansion agent light-burnt MgO obtained by magnesite decomposition through rotary kiln. Many factors, including calcinations condition, batching method as well as variations in raw materials had been investigated. Results indicated that MgO agent tailored to shrinkage-compensating hydraulic concrete was obtainable by adjusting calcinations condition and uniform distribution of MgO in concrete was gainable by premixing MgO agent with other cementitious materials for 20min and fed in the mixer all at once. Autogenous volume deformation of MgO concrete with reaction time ranging between 50s and 200s tended to stabilize after approximate two years development with no retraction or drop-back, and it exhibited good relationship with long-term water absorption of aggregates while alternative method to accurately quantify the effective periclase in clinker should be explored. Concrete with incorporation of 4% MgO agent with reaction time of 100s was ranked the best in thermal cracking resistance and this solution was adopted for diversion tunnel sealing off in Xiluodu, Xiangjiaba and Baihetan hydropower stations.

Spectral and dynamical properties of a Zr-based MOF.

We report on the spectra and dynamics of a Zr-naphthalene dicarboxylic acid (Zr-NDC) MOF in different diluted solvent suspensions and in a concentrated tetrahydrofuran (THF) one. In a diluted diethyl ether (DE) suspension, we observed intraparticle excimer formation between neighboring naphthalene organic linkers, leading to a red-shifted broad band in the emission spectrum and to a dynamics composed of three components τ1 = 650 ps, τ2 = 3.7 ns and τ3 = 13.9 ns, assigned to the excimer photoproduction, monomer and excimer lifetimes, respectively. Furthermore, both absorption and emission spectra show a blue shift in more polar solvents characterized by the solvent polarity function f(ε,n). We also observed changes in the excimer formation time (490-840 ps) probably due to a variation in the MOF structural fluctuation induced by solvent filling. The global fluorescence quantum yield of these suspensions is around 0.30 ± 0.05. At higher concentrations of the MOF particles, we observed the absorption and emission signals of aggregates having an intercrystal excimer formation in ∼ 5 ps in a THF suspension, ∼ 100 times shorter than that observed in a diluted one. Our results give the spectral and dynamical properties of a Zr-NDC MOF in solvent suspensions, opening the way to further studies of these kinds of MOFs interacting with fluorescent dyes for possible photonic applications.

A Study of Optical Properties of Soot Aggregates Composed of Poly-Disperse Monomers Using the Superposition T-Matrix Method

The diameters of soot monomers may not be constant in the single fractal aggregated soot particle. The optical properties of light absorbing soot particles aggregated with poly-disperse monomers were studied using the superposition T-matrix method. Soot aggregates were generated with different log-normal probability distribution functions (PDF) of soot monomer diameter, according to the same soot volumes and monomer numbers. The single scattering properties of soot particles were calculated at a wavelength of 550 nm, assuming a soot refractive index of 1.95 + 0.79i and a mass density of 1.8 g/cm3. The random-orientation averaging results indicated that the optical properties of soot aggregates were fairly varied for the different distributions of the monomer diameters. In these simulations, the extinction and absorption of soot aggregates were slightly (<10%) affected by the monomer poly-dispersity. The simulated mass absorption cross-sections (MAC) of fresh dry soot particles aggregated with poly-disperse monomers reached up to 6.62 ± 0.07 m2/g, which was closer to the measurement (7.5 ± 1.2 m2/g) than the assumption of volume-equivalent mono-disperse monomer (6.36 ± 0.06 m2/g). Moreover, the optical properties of soot coated with an organic shell were calculated, and the optical results showed that the absorption cross-sections of the internally mixed soot particles were also slightly (<8%) influenced by the monomer poly-dispersity. We found that the effect of the monomer poly-dispersity on the light scattering and the single scattering albedo may be considerably large (up to ˜50% in extreme cases) for fresh dry soot aggregates. This effect on light scattering should be taken into account for those aggregates composed of monomers with widely distributed diameters.Copyright 2015 American Association for Aerosol Research

A time domain two-particle approximation to calculate the absorption and circular dichroism line shapes of molecular aggregates.

The hierarchical equations of motion (HEOM) method has recently emerged as an effective approach to simulate linear and nonlinear spectroscopic signals of molecular aggregates in the intermediate coupling regime. However, its application to large systems is still limited when there are a large number of molecules in the molecular aggregate. In this work, we propose a time domain two-particle approximation (TPA) in combination with the HEOM method to calculate the absorption and circular dichroism line shapes of molecular aggregates. The new method is shown to reduce the number of auxiliary density operators (ADOs) significantly for large systems, and a further truncation of the two-bath-set excited terms based on geometric considerations can lead to a linear increase of the number of ADOs with the system size. The validity of the HEOM-TPA method is first tested on one-dimensional model systems. The new method is then applied to calculate the absorption and circular dichroism line shapes of the Photosystem I core complex, as well as the population evolution of the Fenna-Matthews-Olson complex to demonstrate its effectiveness.

Two-photon absorption of polyfluorene aggregates stabilized by insulin amyloid fibrils

We report on the photophysical and optical properties of a polyfluorene derivative (PFO) and its binding to the amyloid-forming protein insulin.

Influence of hardened cement paste content on the water absorption of fine recycled concrete aggregates

A linear relationship was found between the mean size of four granular classes (0/0.63, 0.63/1.25, 1.25/2.5, 2.5/5 mm) of different laboratory-made fine recycled concrete aggregates (FRCA) and their hardened cement paste content (CPC). A method based on salicylic acid dissolution was specifically developed for the measurement of CPC. Results showed that bound water and density of FRCA were strongly correlated with their CPC. Identically, the water absorption coefficient also followed a linear trend as a function of the CPC but only for the three coarser granular classes. Indeed, the water absorption coefficient of the finer fraction of FRCA (0/0.63 mm) cannot be correctly measured using European standard method EN 1097-6 or method no. 78 of IFSTTAR; but it can be obtained by extrapolation from the previous linear trend. As a consequence, the accurate total water absorption of FRCA (fraction 0/5 mm) can be estimated.

Investigation of Absorption and Scattering Properties of Soot Aggregates of Different Fractal Dimension at 532 nm Using RDG and GMM

Radiative properties of numerically generated fractal soot aggregates of different fractal dimensions were studied using the numerically accurate generalized Mie-solution method (GMM) and the Rayleigh-Debye-Gans (RDG) approximate theory. Fractal aggregates of identical prefactor but different fractal dimensions, namely, 1.4, 1.78, and 2.1, were generated numerically using a tunable algorithm of cluster–cluster aggregation for aggregates containing up to 800 primary particles. Radiative properties of these aggregates were calculated at a wavelength of 532 nm assuming a soot refractive index of 1.6 + 0.6i. Four commonly used structure factors in the RDG approximation were used to investigate the effect of structure factor on the differential and total scattering cross-sections and the asymmetry factor. The differential and total scattering properties calculated using the RDG approximation become increasingly sensitive to the structure factor with increasing the fractal dimension. Primary particle interactions are the fundamental mechanism for the aggregate absorption enhancement for small aggregates and the shielding effect for larger aggregates. The extent of these two competing factors is dependent on the fractal dimension and aggregate size. RDG reasonably predicts the effect of fractal dimension on the scattering properties, but fails to account for the effect of aggregation or fractal morphology on the absorption property of fractal soot aggregates, though the error is in general less than 15%.Copyright 2013 American Association for Aerosol Research

Reinforcement of steel-slag asphalt concrete using polypropylene fibers

Steel-slag asphalt concrete (SSAC) is a type of asphalt mixture that uses slag particles instead of conventional aggregates. It has been proven that replacement of course aggregates by steel-slag particles is the best composition of SSAC mixtures. Despite benefits derived from SSAC, like higher resistance to rutting, the mixture has some disadvantages. Higher optimized asphalt content is the major disadvantage of SSAC compared to ordinary AC mixtures. In order to solve this problem, it is necessary to decrease the bitumen absorption of slag aggregates. One approach that can be taken to increase the viscosity of the bitumen and/or to decrease the effective surface of slag aggregates is reinforcement of asphalt mixtures by using polypropylene (PP) fibers. The main aim of this paper is, therefore, to introduce a novel AC mixture, i.e. PP fiber-reinforced steel-slag asphalt concrete. In this respect, the optimized asphalt content was identified by using Marshall method. Analysis of results shows that the treatment reinforced with 2% of 19 mm PP fibers experiences a decrease in optimized asphalt content about 15% in comparison with the neat mixture, i.e. SSAC sample. Moreover, indirect tensile strength and resilient modulus (MR) have increased.

Influence of Aggregates on Cracking Sensitivity of Concrete

Upon large demands from southwest of China where a large number of hydropower stations are schemed or under construction with presence of a variety of aggregates, it is of necessity to launch a comprehensive investigation on influence of aggregates on properties of concrete which was rarely reported before. Four types of aggregates selected from different construction sites were used to conduct tests, and results indicated that water absorption of aggregates exhibited a consistent rising tendency over 180 days and it had close relationship with autogenously shrinkage of concrete which varied in the manner that high water absorption of aggregates produced more obvious shrinkage. With employment of advanced temperature and stress machine, concrete made with diorite and basalt was rated better than limestone and natural granite concrete in crack resistance based on comparison of cracking temperature and thermal impact according to RILEM TC119.

Cement paste content and water absorption of recycled concrete coarse aggregates

In this paper, we first show that the amount of residual cement paste in recycled concrete aggregates (RCA) depends on the initial paste content, on the mechanical properties of the initial cement paste and on the mechanical quality of the transition zone at the interface between the initial natural aggregates and cement paste. Our results suggest that water absorption of RCA at 24 h can be seen as the simple sum of the capillary absorption of both residual cement paste and initial natural aggregates. The absorption kinetics is similar to the capillary absorption of traditional uncrushed concretes but, on the industrial time scale of interest, is strongly affected by the size and configuration of the residual cement paste patches at the surface of the initial natural aggregates. We finally propose a tentative frame for a classification of RCA based on water absorption rate and water absorption capacity at 24 h.

폐유리가 첨가된 석탄바닥재-준설토 계 인공골재의 특성

본 연구에서는 석탄 바닥재와 준설토(7 : 3, 무게비율)로 제조된 인공골재의 물성에 미치는 폐촉매 유리질 슬래그(이하 폐유리로 칭함) 첨가 영향을 평가하였다. 특히 인공골재의 비중 및 흡수율 결과를 미세구조와 연계하여 그 발포특성을 고찰하였다. <TEX>$1050{\sim}1150^{\circ}C$</TEX> 범위 내에서 인공골재 비중은 소성온도와 함께 약간 증가되었으나 그 이상의 소성온도에서는 감소하여 발포경향을 나타내었다. 폐유리 첨가량이 증가할수록 인공골재의 발포특성은 억제되었으며, 비중은 증가하는 경향을 보였다. 한편 인공골재 흡수율은 소성온도의 증가와 함께 감소하였다. <TEX>$1200^{\circ}C$</TEX> 이상의 소성온도에서 표면에 균열이 발생함과 동시에 다량의 액상이 형성되었으나, 이러한 현상들은 폐유리를 첨가함으로서 제어할 수 있었다. 본 연구에서 제조된 인공골재의 비중은 1.1~1.6, 흡수율은 8~22 % 범위값을 나타내어 인공경량골재의 KS 기준을 만족하였다. In this study, the effect of addition of waste glassy slag produced from recycling of spent catalyst (denoted as waste glass hereafter) on the physical properties of artificial aggregates made of coal bottom ash and dredged soil (7 : 3 by weight base) was evaluated. Especially, the bloating behavior of artificial aggregates was analyzed by performing the relation study between the apparent density, water absorption and microstructure. The apparent density of artificial aggregates increased slightly with sintering temperature at <TEX>$1050{\sim}1150^{\circ}C$</TEX>, but decreased above <TEX>$1150^{\circ}C$</TEX> showing bloating phenomenon. The bloating behavior of artificial aggregates was decreased so the apparent density increased with amount of waste glass added. Also, the water absorption of artificial aggregates decreased with sintering temperature. Above <TEX>$1200^{\circ}C$</TEX>, big fissure and much liquid were formed at the surface of artificial aggregates and these phenomena could be suppressed by increasing amount of waste glass added. The artificial aggregates fabricated in this study had an apparent density of 1.1~1.6 and water absorption of 8~22 % which meet KS requirements for the artificial lightweight aggregates.

Water absorption and frost heaving of recycled aggregates

Water absorption and frost heaving of aggregates have a strong influence on the performance of a highway pavement. This is because several mechanical properties of aggregates change in direct response to water ingress and ground freezing. Recycled aggregates of different types are increasingly being used in pavements; however, their frost heaving and water absorption potential has not been fully investigated and documented. In the present study the opportunity was taken to study the water absorption and freeze–thaw properties of three different aggregates: (i) 100% recycled concrete aggregate, (ii) 100% natural aggregate from limestone rock, and (iii) 50% recycled concrete aggregate + 50% reclaimed asphalt pavement. For different particle size ranges, extensive tests were carried out for each of the above materials ((i)–(iii)) using the pyknometer and wire basket methods as well as simulation in a self-refrigerated unit. The following three kinds of density were measured: (a) over-dry, (b) saturated and surface dry, and (c) apparent particle density. The 100% natural aggregate had the lowest water absorption and highest densities ((a)–(c)) whereas the 100% recycled concrete aggregate had the highest water absorption. In contrast to the above findings, the frost heave potential was found to be much less sensitive to the aggregate type and particle size. Water absorption of recycled concrete aggregate decreased with increasing mean particle size. The measured relationships between density, grading and water absorption led to increased understanding of the behaviour of materials containing different fractions of recycled concrete aggregate and reclaimed asphalt pavement.

A new method to determine the density and water absorption of fine recycled aggregates

The construction industry keeps on demanding huge quantities of natural resources, mainly minerals for mortars and concrete production. The depletion of many quarries and environmental concerns about reducing the dumping of construction and demolition waste in quarries have led to an increase in the procuring and use of recycled aggregates from this type of waste. If they are to be incorporated in concrete and mortars it is essential to know their properties to guarantee the adequate performance of the end products, in both mechanical and durability-related terms. Existing regulated tests were developed for natural aggregates, however, and several problems arise when they are applied to recycled aggregates, especially fine recycled aggregates (FRA). This paper describes the main problems encountered with these tests and proposes an alternative method to determine the density and water absorption of FRA that removes them. The use of sodium hexametaphosphate solutions in the water absorption test has proven to improve its efficiency, minimizing cohesion between particles and helping to release entrained air.

Protochlorophyllide in model systems — An approach to in vivo conditions

Absorption and fluorescence properties of protochlorophyllide (Pchlide) monomers and aggregates in various model systems are presented in this study. The absorption and fluorescence maxima, and fluorescence lifetimes of Pchlide monomers were not dependent on liposome composition. Fluorescence quenching experiments using KI and SASLs as fluorescence quenchers, revealed that Pchlide molecules entered a lipid bilayer and were localized close to the polar lipid headgroup area. The process of Pchlide aggregation was evident for high (i.e. at least 9mol%) Pchlide content in liposomes prepared from galactolipids. To our knowledge, this is the first study of Pchlide aggregation in membrane-mimicking model systems. The aggregates showed absorption maxima at 480 and 650nm. Fluorescence of the aggregates measured for excitation at 480nm had a maximum at 656nm and was characterized with two fluorescence lifetime components, i.e. 0.1 and 1–2ns. Pchlide aggregates observed in the buffer had similar position of absorption and fluorescence bands to those observed in liposomes, although the overall fluorescence intensity was considerably lower. Some differences in the relative intensity of Soret absorption bands were observed. These results showed that the presence of liposomes decreased the efficiency of the process of Pchlide aggregation. Water bound at the interface region of AOT/isooctane/water reversed micelles induced disaggregation of the Pchlide aggregates indicating that Pchlide aggregates are buried into hydrophilic core of micelles. The results are discussed with respect to the role of lipids in Pchlide aggregation found in plant etioplasts and their significance for light-induced Pchlide photoreduction.