Increase In Aggregate Content Research Articles

Effect of key design parameters on the physical / mechanical properties of coarse aggregated UHPC and its structural response subjected to bending

This study experimentally investigates the effect of key design parameters on the physical, mechanical and structural performance of coarse aggregated ultra-high performance concrete (CA-UHPC), with an aim to provide design guidance for on-site engineering applications. The variables of maximum aggregate size, aggregate content, fiber dosage and curing condition are selected for investigation. The results showed that increasing aggregate size does not significantly affect the compressive strength, but somewhat increases the elastic modulus and fracture energy; the increase of aggregate content results in a reasonable increase of compressive strength and elastic modulus. In particular, the 480 kg/m3 coarse aggregated UHPC shows a compressive strength of ∼150 MPa, elastic modulus of ∼50 GPa, autogenous shrinkage of <200 µε, and outstanding durability. The structural specimens fabricated with coarse aggregated UHPC exhibit excellent load-carrying capacity and ductility when subjected to four-point bending. More importantly, it was found that the effect of curing condition on the structural performance is insignificant. The results of this study can provide insights into the development of advanced UHPC materials and structures and promote their applications in practice.

Elucidating the role of 2-methyl imidazolium dihydrogen phosphate in preventing aggregation of Bevacizumab: A biophysical investigation

Evaluating the stability and biological activity of monoclonal antibodies is an essential step during the development process in order to ensure their optimum performance. Monoclonal antibodies (mAbs) are stable against aggregation over a narrow pH range and rapidly aggregate in solutions with pH outside these ranges. The pH of solutions can be controlled by using pH buffers, which determine the surface charge on mAbs and thereby affect their electrostatic interactions. Lower pH may lead to protein cleavage and isomerization, while higher pH may cause deamidation and oxidation reactions, increasing the aggregation potential. Surfactants generally prevent aggregation by reducing the tension at the air–water interface, which reduces the possibility of interactions of mAbs with this interface. Apart from surfactants, salts and sugars are also conventionally added to mAb formulation buffers to prevent aggregation. In this work, we have investigated the role of a biocompatible ionic liquid, 2-methyl imidazolium dihydrogen phosphate (2-MIDHP), to prevent aggregation of Bevacizumab. We employed a pH stress model to study the aggregation behaviour of Bevacizumab. The aggregation behaviour of Bevacizumab was analysed using size exclusion-High performance liquid chromatography (SE-HPLC) dynamic light scattering (DLS), differential scanning calorimetry (DSC), and field flow fractionation (FFF). The aggregation and monomer content were monitored over the pH range of 2 to 6.2 using SE-HPLC. Results indicated that 2-MIDHP was able to control aggregation of Bevacizumab at pH 2, for upto 4 days, as compared to the control sample, which showed an increase in aggregate content for upto 4 days, followed by degradation. These results were further orthogonally confirmed using techniques like DLS, DSC, and FFF. 2-MIDHP was thus found to be a potent, acid-resistant, mAb aggregation controlling agent.

A CT image-driven computational framework for investigating complex 3D fracture in mesoscale concrete

Accurate prediction of fracture in concrete depends on the characterization of real meso-structures. Micro X-ray computed tomography (CT) can fulfil this task but is still too expensive and time-consuming to repetitively generate numerical models, also with massive degrees of freedom (DOFs) that prohibit nonlinear computations. To address such problems, we develop a novel computational framework driven by only one CT image for 3D fracture investigation of realistic mesoscale concrete models. The voxelized CT data of aggregates is first processed to obtain spatially continuous surfaces. A number of aggregates with real shapes from a created library are then randomly packed into containers through compaction and vibration simulated by a dynamic physics engine. In this way, realistic concrete models with various aggregate contents (up to 60%) can be achieved without performing extra CT tests and image processing. To capture potential micro-cracks, cohesive interface elements with zero-thickness are automatically inserted between solid elements. The proposed models with more than 15 million DOFs are well validated through typical uniaxial tension tests, elucidating complex formation mechanisms of micro-cracking, pre-peak nonlinearity, softening behaviour and 3D fracture networks. Quantitative analyses indicate that with the increase of aggregate content, the coupling effect of aggregate blocking and interfacial cracking becomes stronger to make the crack surfaces more tortuous with higher ITZ-mortar area ratios and lower load-carrying capacities, although more aggregates are often required to enhance overall elastic modulus and compressive strength, and reduce carbon footprints of concrete.

Two-Dimensional Microstructure-Based Model for Evaluating the Permeability Coefficient of Heterogeneous Construction Materials.

The permeability coefficient of construction materials plays a crucial role in engineering quality and durability. In this study, a microstructure model based on real aggregate shape and digital image technology is proposed to predict the permeability coefficient of concrete. A two-dimensional, three-component finite element model of cement concrete was established considering the interfacial transition zone (ITZ) between aggregate and mortar. The permeability coefficient prediction model was developed by the finite element method. The accuracy of the model was verified by experimental data, and the influence of the water-cement ratio on the permeability coefficient of concrete was analyzed. The results show that this method has good prediction accuracy with a relative error of 1.73%. According to the verified model, the influences of aggregate content, aggregate characteristics, aggregate location, ITZ thickness, and other factors on the permeability of concrete were explored. The higher the water-cement ratio, the higher the permeability coefficient. With the increase in aggregate content, the permeability coefficient decreases. Aggregate permeability has a significant influence on the effective permeability coefficient of concrete within a certain range. The greater the roundness of aggregate, the greater the permeability of concrete. On the contrary, the larger aggregate size causes lower permeability. The permeability coefficient of concrete with segregation is lower than that with uniform distribution. At the same time, the permeability increases with the increase of ITZ thickness.

The use of computerized tomography (CT) and image processing for evaluation of the properties of foam concrete produced with different content of foaming agent and aggregate

This study measures the impact of foaming agent and aggregate content in foam concrete mixes by conducting a series of tests on material properties as well as pore formation by using micro-Computerized Tomography (CT) scanning and image processing technique. This technique allows measuring the porosity fraction of porous materials and foam concretes to comparatively evaluate the experimental versus the image processed porosity of the samples. Based on the results, it is found that the increase in aggregate content can exponentially reduce the pore connectivity of foams and enhance their physical and mechanical properties. Additionally, the proposed CT scanning and image processing approach is a proof-of-concept over the use of 3D modeling. This is done with a specific tool-kit and the results prove suitability of image processing techniques in accurately measuring pore content in foam concrete samples. Suggestions for future studies are also provided and discussed at the end of the manuscript.

Mesoscale synergistic effect mechanism of aggregate grading and specimen size on compressive strength of concrete with large aggregate size

In this paper, a 2D finite element model with a mesoscale level was established. The effects of content, maximum particle size, and shape of aggregate on the strength of concrete were simulated. In addition, five mesoscopic models of aggregate gradation and specimen side length (100–450 mm) were established to investigate the influence law of aggregate grading and model size on the compressive strength of concrete. The simulation results were also compared and verified with four theoretical size-effect models. The results showed that the compressive strength shows a trend of decreasing and then increasing with the increase of aggregate content and falling with the growth of maximum aggregate size dmax. The peak stress of convex polygonal aggregates is higher than that of round and elliptical. In addition, when the ratio of model side length to the maximum aggregate particle size is about 3.5, the compressive strength gradually decreases with the increase of specimen size, up to 27.65 % decreased, showing a pronounced size effect. After comparative analysis, the simulated data in this paper fitted well with the Bažant’s Type-2, Kim’s modified, Jin’s modified, and Carpinteri’s size effect law (SEL). In addition, the data obtained from the simulation of this paper would better reflect the existing test conclusions. The mesoscale model established in this paper can significantly improve the effectiveness and efficiency of full-graded concrete modeling, and better simulate the strength difference between full-graded and wet-screened specimens. The difficulties in the mesoscale numerical simulation are solved to a certain extent.

Numerical investigation and ANN-based prediction on compressive strength and size effect using the concrete mesoscale concretization model

The concrete mesoscale concretization model (CMCM) is proposed using the statistical distribution and local spatial correlation theory to describe the randomization, continuum, and correlation of the material properties of mesoscale components. The distribution of material properties was obtained by stochastic discretization, spatial correlation correction, and remapping operations. The hypotheses of elastic modulus control (EMC) and characteristic deformation control (CDC) are used to describe the variation of mechanical parameters in the concrete damage plasticity model. The uniaxial compression behavior and size effect of concrete with different side lengths, aspect ratios, aggregate contents, air contents, and contact frictions are simulated using the above model. Without the contact frictions, the size effect of the sample’s side length is apparent, while the size effect of aspect ratio is not observed. The increase of size effect degree is contributed by the increase of air content rather than aggregate content. When the loading boundaries are constrained by friction, both the side length and aspect ratio of samples show the size effect. The increase of aggregate content leads to the increase of size effect degree, while the increase of air content leads to a minor increase of size effect degree. The developed CMCM can capture the mechanical responses, and the ANN-based prediction model is applicable to explore the relationship between compressive strength and sample parameters.

Investigation on triaxial numerical test method and dilatancy behavior of asphalt mixture

To investigate factors affecting the dilatancy behavior of asphalt mixture, more accurate prediction and reduction of rutting are required. The dilatancy law of asphalt mixture was studied using an indoor triaxial test. Based on the triaxial numerical test, the effect of meso-model parameters on the test results was studied, and relevant model parameters were determined. Then, the effects of the loading speed, confining pressure levels, and pore and aggregate characteristics on the dilatancy performance of asphalt mixture were studied. The results show that the constructed triaxial numerical simulation method correlates well with the indoor triaxial test. Increasing the loading speed and confining pressure levels can improve the dilatancy resistance of the asphalt mixture numerical model. When pores are uniformly distributed, the dilatancy deformation of the numerical model decreases as the porosity increases; the dilatancy angle increases with the increase of aggregate content; and the rougher the surface of the coarse aggregate, the larger the dilatancy angle of the specimen; when the aggregate distribution characteristics are different, the corresponding dilatancy characteristics are also different.

Analytical Solution for Chloride Diffusivity of Concrete with Aggregate Shape Effect.

In view of the key role of chloride diffusivity in evaluating concrete durability, it is very important to determine this parameter accurately by an effective approach. This paper establishes an analytical solution for chloride diffusivity of concrete that can consider the aggregate shape. In this approach, the aggregate shape is simulated as an ellipse and the equivalent model is applied to calculate the chloride diffusivity of equivalent aggregate composed of interface transition zone (ITZ) and aggregate. With resort to this model, at the meso scale, the concrete can be reduced from the original three-phase composition to the two-phase one (i.e., equivalent aggregates and cement paste). Based on the mesostructure of concrete that consisted of randomly dispersed equivalent elliptical aggregates and cement paste, the generalized Maxwell’s approach is formed to determine the chloride diffusivity of concrete. The corresponding chloride diffusion test is conducted and the thickness of ITZ is reasonably determined as 0.04 mm by SEM test. By comparing with the experimental data, the accuracy of the analytical solution is confirmed. Finally, the impact of aggregate shape on chloride diffusivity is discussed. The analytical results show that the chloride diffusivity has a reduction with the increase of aggregate content or decrease of aspect ratio.

Compressive and flexural properties of ultra-high performance fiber-reinforced cementitious composite: The effect of coarse aggregate

The inclusion of coarse aggregate in the cementitious composite can improve the mechanical property and simultaneously curb the cement demand thus lowering the production cost in concrete built infrastructure. This study investigates the effects of different coarse aggregate types and contents on the compressive and flexural properties of ultra-high performance fiber-reinforced cementitious composite (UHPFRC). Four types of coarse aggregates (granite, basalt, limestone and steel slag) and four contents denoted by the volume of mortar replacement (0%, 15%, 30% and 40%) are the main variables. The test results have shown a significant increase in compressive strength and elastic modulus of UHPFRC after moderate addition of coarse aggregate with only an expense of a slight reduction in the flexural strength and post-peak ductility. The aggregate types having different stiffness can be effective in either increasing the compressive strength or enhancing the post-peak ductility, which is also true for the increase in aggregate content. With respect to the flexural behavior, it is found that coarse aggregate type significantly affects the flexural strength and equivalent flexural strength ratio, whilst no considerable variations in the first crack strength is observed. Furthermore, an analytical model is proposed to generate the complete compressive stress-strain curves of UHPFRC.

Effects of coarse aggregate content on the paste rheological thresholds of fresh self-compacting concrete

Abstract This work studies the effects of coarse aggregate content on the paste rheological thresholds of fresh self-compacting concrete (SCC). A new mechanical model for highly flowable SCC was established, and a coefficient in the plastic viscosity threshold formula was modified after conducting experimental tests on Wu’s model. The threshold of the paste yield stress decreases while the threshold of the paste plastic viscosity increases with the increase of aggregate content. The bilinear interpolation method was used to process the paste and SCC results. Prediction accuracy formulae based on figure area were introduced to assess the predictive effect of the new model. The relative accuracies of the new model are greater than 70%, whereas the relative accuracies of Wu’s model are no greater than 45%. At last, Two types of cement were used to conduct the verification experiments and high prediction accuracies were obtained. The results show that the application of this method is independent of the type of cement used.

Effects of the size and content of protein aggregates on the rheological and structural properties of soy protein isolate emulsion gels induced by CaSO4.

The effects of the size and content of soy protein isolate (SPI) aggregates on the rheological and textural properties of CaSO4-induced SPI emulsion gels were investigated. Considerable differences in the rheological, water-holding, and micro-structural properties were observed. The gels with larger and/or more SPI aggregates showed substantial increase in the elastic modulus and had lower gelation temperatures. Creep data suggested that the size of the SPI aggregates contributed more to the elastic modulus, whereas the increase of aggregate content enhanced the elastic modulus and viscous component of the gels. The water-holding capacity was markedly enhanced (p<0.05) with the increase in both the size and content of SPI aggregates. Confocal laser scanning microscopy and scanning electron microscopy showed that larger and/or more SPI aggregates resulted in more homogeneous networks with smaller oil droplets. These insights provide important information for the product development in relation to soy protein-stabilized emulsions and emulsion gels.

Forskolin and phorbol ester stimulation of neuropeptide Y (NPY) production and secretion by aggregating fetal brain cells in culture: evidence for regulation of NPY biosynthesis at transcriptional and posttranscriptional levels.

Using fetal brain cells in culture, we have previously shown that activation of the cAMP pathway by forskolin induces the production and secretion of neuropeptide Y (NPY). In this study we wished to ascertain 1) if activation of the protein kinase C pathway induces NPY production and/or secretion and if there is synergism between the pathways, and 2) the role of protein/RNA synthesis and influx of extracellular calcium. Aggregates, formed from dissociated cells obtained from the hypothalamus-olfactory tubercle area of 17-day-old rat fetuses, were cultured in serum-free medium for 12 days. The NPY content of aggregates incubated for 24 h with solvent (control) was 4.4 ng/flask, and the medium content was 7.6 ng. Forskolin (10 microM) or phorbol 12-myristate 13-acetate (PMA; 20 nM) marginally affected aggregate content, but each increased medium content 2- to 3-fold; forskolin and PMA were additive. When cycloheximide (75 microM) was included along with forskolin, PMA, or forskolin plus PMA for a period of 10 h, the increase in NPY medium content was abolished. Actinomycin D (Act-D; 5 micrograms/ml) inhibited the response to each secretagogue in a time-dependent manner. When Act-D was included along with forskolin, PMA, or forskolin plus PMA for a total period of 12 or 24 h, the 12 h increase in content was not affected, whereas the 24 h increase was abolished. When the presence of Act-D was limited to 0-24, 6-24, or 12-24 h, and forskolin plus PMA were included for the entire 24-h period, the increase in NPY content was inhibited by 94%, 57%, and 12%, respectively. Verapamil (100 microM) totally inhibited the 24 h response to forskolin and partially (40-50%) inhibited the response to PMA or forskolin plus PMA. In none of these conditions was the inhibition of the increase in medium NPY content accompanied by an increase in aggregate content, nor was the NPY content of aggregate/medium of control cultures affected.(ABSTRACT TRUNCATED AT 400 WORDS)