Effect Of Aggregate Characteristics Research Articles

Effect of Aggregate Characteristics and Distribution on the Mechanical Characteristics of Recycled Concrete

Effect of Aggregate Characteristics and Distribution on the Mechanical Characteristics of Recycled Concrete

Effect of aggregate characteristics on properties of cemented sand and gravel

Abstract To improve the stability of cemented sand and gravel (CSG) dam construction materials, artificial aggregates can be selected to replace missing natural aggregates, and aggregate grading optimization can be carried out to meet the needs of engineering applications. This article uses finite-element analysis software to explore the influence of aggregate characteristics on the performance and destruction characteristics of CSG materials through numerical simulation. The results show that (1) with the increase of circular natural sand gravel aggregates, the peak stress and elastic modulus of the sample increase, while the strength also increases. (2) Compared to circular aggregates, polygonal aggregates have more edges and corners, which exacerbate the deformation disharmony between mortar and aggregates; the phenomenon of stress concentration is more obvious, so under the same loading step, the degree of damage of polygonal aggregates is greater than that of circular aggregates. (3) After the freeze–thaw cycle test, the deterioration of parameters in the CSG resulted in more severe damage and strength loss of the crushed stone aggregate than the circular aggregate sample. This conclusion can provide a reference for the design of CSG mix ratio in engineering sites.

Morphological integrity of insulin amyloid-like aggregates depends on preparation methods and post-production treatments

Protein aggregates are often varying extensively in their morphological characteristics, which may lead to various biological outcomes, such as increased immunogenicity risk. However, isolation of aggregates with a specific morphology within an ensemble is often challenging. To gain vital knowledge on the effects of aggregate characteristics, samples containing a single morphology must be produced by direct control of the aggregation process. Moreover, the formed aggregates need to be in an aqueous solution suitable for biological assays, while keeping their morphology intact. Here we evaluated the dependence of morphology and integrity of amyloid-like fibrils and spherulites on preparation conditions and post-treatment methods. Samples containing either amyloid-like fibrils or spherulites produced from human insulin in acetic acid solutions are dependent on the presence of salt (NaCl). Moreover, mechanical shaking (600 rpm) inhibits spherulite formation, while only affecting the length of the formed fibrils compared to quiescent conditions. Besides shaking, the initial protein concentration in the formulation was found to control fibril length. Surprisingly, exchanging the solution used for aggregate formation to a physiologically relevant buffer, had a striking effect on the morphological integrity of the fibril and spherulite samples. Especially the secondary structure of one of our spherulite samples presented dramatic changes of the aggregated β-sheet content after exchanging the solution, emphasizing the importance of the aggregate stability. These results and considerations have profound implications on the data interpretation and should be implemented in the workflow for both fundamental characterization of aggregates as well as assays for evaluation of their corresponding biological effects.

Conceptual design and performance evaluation of high strength pervious concrete

This study proposes a novel design concept of high strength pervious concrete, aiming at improving its compressive strength with adequate permeability. An ultra-high performance paste was developed and used as the binder of the high strength pervious concrete. The effects of aggregate characteristics and membrane-forming ability of the paste on the performance were investigated and their compatibility was evaluated. The experimental results showed that the use of ultra-high performance paste, improvement of homogeneity and compatibility between the paste and the aggregates by elimination of coarse aggregates could improve the mechanical properties. The combined use of aggregates with two-size ranges also resulted in an increase of compressive strength due to the increase of homogeneity and interlocking effect between the aggregates. The enhancement of the membrane-forming ability could optimize the bonding area and thickness of the cement paste between the aggregates. Therefore, the application of the proposed design concepts was able to produce a high strength pervious concrete with a compressive strength of 60.93 MPa and a water permeability of 0.37 mm/s, which would potentially broaden the scope of application of pervious concrete.

Numerical modelling of elastic modulus and diffusion coefficient of concrete as a three-phase composite material

Concrete is a complex three-phase composite material at a mesoscale, thus its overall elastic and diffusive properties strongly depend on that of each component. However, the effects of aggregate characteristics are little considered, especially the aggregate shape effect. In this study, a set of numerical methods is employed to evaluate the effects of aggregate characteristics on the elastic and diffusive properties of concrete. Firstly, a concrete representative volume element (RVE) is constructed using a pixel-based method by packing aggregates surrounding a soft interlayer as ITZ in a homogeneous mortar matrix. The different aggregate characteristics including morphology, fineness and type, are respectively considered. Subsequently, a set of the finite element-based and finite difference-based numerical method that is designed for the pixel-based concrete structure, is applied to predict the elastic modulus and the diffusion coefficient of concrete. The simulated results indicate that aggregate characteristics apart from aggregate type play a negligible role in the elastic modulus of concrete, while the effects of aggregate characteristics on the diffusion coefficient of concrete are pronounced. The aggregates with less regularity or coarser size can decrease the diffusion coefficient of concrete. Furthermore, the property of ITZ is another pronounced factor for the elastic and diffusive properties of concrete in addition to aggregate area fraction. The weaker ITZ can significantly decrease the stiffness and increase diffusivity of concrete. The modelling results are expected to guide the design of concrete materials from the perspective of aggregate characteristics.

Effect of Aggregate Characteristics on Texture and Skid Resistance of Asphalt Pavement Surface

Effect of Aggregate Characteristics on Texture and Skid Resistance of Asphalt Pavement Surface

Effect of Aggregate Characteristics on Texture and Skid Resistance of Asphalt Pavement Surface

The skid resistance of asphalt concrete is highly influenced by the microtexture and macrotexture of pavement surface. It is believed that the microtexture and macrotexture are affected by the surface texture of pavement, which refers to the arrangement of aggregates and their aggregates characteristics. The objective of this study is to evaluate the effects of aggregate properties and its orientation on microtexture and macrotexture by using an image analysis technique. Test results reveal that texture values obtained through the use of an image analysis technique is highly sensitive to changes in microtexture. The aggregate types and their related properties which are polished stone value, angularity, and texture of aggregate significantly affect the microtexture whereas the macrotexture is considerably influenced by fineness modulus, angularity and texture.

Effect of aggregate characteristics under different coagulation mechanisms on microfiltration membrane fouling

Effect of particle charge, size and fractal dimension under different pre-coagulation pHs and alum dosages on microfiltration (MF) membrane permeability and removal of humic acids (HAs) were studied. Both aggregates structure and size played important roles in membrane filtration. Under sweep coagulation condition, the insufficient low coagulant dosage of 10 mg/L alum resulted in low removal of HAs and the occurrence of serious membrane pore blocking by some small flocs with size corresponding to membrane pores. However with alum overdosing, the cake layer resistance increased by the direct fouling load from alum hydrolysis Al(OH) 3. Under complexation-charge neutralization coagulation, aggregates with low fractal dimension of loose structure improved permeate flux predominately when particles were near isoelectric point with alum dosages of 20 and 40 mg/L. When alum increased to 60 mg/L and above, although the flocs fractal was much lower, the MF membrane permeability deteriorated severely because more small particles produce higher cake layer specific resistance as a result of a great charge repulsion force. Under the optimum pre-coagulation alum dosages of 20 and 40 mg/L, the membrane fouling was much more alleviative at pH 5 than pH 7 because the more loose aggregates formed under charge neutralization coagulation than sweep coagulation.

Effects of Size and Uncompacted Voids of Aggregate on Mortar Flow Ability

The effects of aggregate characteristics on the flow ability of mortar mixtures were investigated. Two types, five single-sized and three graded fine aggregate were considered. Uncompacted voids of the aggregates were measured. Flow properties of 166 mortar batches made with different aggregates, sand-to-cement ratios (s/c) and water-to-cement ratios (w/c), were evaluated using the modified ASTM C109 flow table test method. The results indicated that in addition to w/c, the content, uncompacted voids, and size of aggregate all significantly affect mortar flow ability. Generally, aggregate having higher uncompacted void content provides its mortar with a lower flow. When aggregate content was low (s/c = 1), aggregate size had little effect on the flow ability of the mortar; when aggregate content was high (s/c = 3), aggregate size significantly influenced the mortar flow ability. The mortar with graded aggregate has better flow ability than the mortar with single-sized particles. River sand provides a mortar with better flow ability when compared to limestone. A statistical model was developed to predict the flow ability of mortar. The model can also be used to study the effect of different parameters on mortar flow properties.

Estimating Potential Aggregate Interlock Load Transfer Based on Measurements of Volumetric Surface Texture of Fracture Plane

The volumetric surface texture (VST) test was developed at the University of Minnesota to provide an estimate of the load transfer potential available through aggregate interlock across a concrete fracture plane. It can also provide an estimate of the abrasion that has taken place since fracture. A study was undertaken to validate the VST concept and test procedures. The factors investigated in this study include the effects of aggregate characteristics on measured surface texture and the effects of measured surface texture on crack and undoweled joint performance, as indicated by deflection-based load transfer efficiency. Deflection, load, and crack width data were collected for both field and laboratory slabs, and VST testing was performed with companion specimens for these slabs. This study has shown that the VST test provides a means of accurately measuring surface texture so that the selection of concrete aggregates can be performed with consideration of potential aggregate interlock at cracks and undoweled joints. Performance prediction equations were developed to provide an early indication of how cracks and undoweled joints will perform before a particular aggregate size, type, gradation, or blend is used in an actual pavement.