Specific Surface Area Of Aggregates Research Articles

Mitigating Stripping in Asphalt Mixtures: Pretreatment of Aggregate by Thermoplastic Polyethylene Powder Coating

Thermoplastic polyethylene (PE) powder coating is proposed as a new technique to pretreat the aggregate of asphalt mixtures and improve the corresponding moisture resistance. In this paper, ethanol solution is investigated as a fluidized bed to disperse the PE powder. The surface tension of the solution, indicating the wettability of the liquid phase, decreases with increasing ethanol concentration and temperature. The PE powder could be stably dispersed into the solution when 15% ethanol solution heated to 40 to 50°C is used to reduce the surface tension of liquid to less than 40 mN/m. The suspension carrying the PE particles could be uniformly sprayed onto a hot aggregate surface (180–190°C) where the liquid phase evaporates fast while the PE powder melts and stays. The powder coating technique could prevent the aggregate from lumping and achieve a high-quality and efficient coating for aggregate. The PE monolayer model considering a hexagonal close packing of PE on aggregate surface is tentatively proposed to determine the theoretical amount of PE required to perfectly coat the aggregate. The predicted PE content was reasonably lower than that determined by the experimental results considering the ideal monolayer coating was hard to achieve. However, the modeling results could be used to determine the lower bound of the required PE content. The optimum PE content significantly increased with increasing particle size of PE and specific surface area of aggregate. The use of high-density polyethylene (HDPE) powder with a smaller particle size was more effective in the coating process. In addition, excessive PE could not further enhance the moisture resistance of asphalt mixtures efficiently. This study can contribute to both the recycling of waste plastic and the construction of durable asphalt pavements.

Study on the mixing process improvement for hot recycled asphalt mixture

Existing studies have shown that the mixing process of hot recycled asphalt mixture has a considerable effect on its performance. The conventional mixing process applied widely in pavement industry, mixed the RAP and virgin aggregate first. Then asphalt binder was added for the second mixing. This conventional mixing process, however, ignored the asphalt-adsorbing capacity of different aggregates, may resulting in the heterogeneity of recycled asphalt mixture after mixing. Adjusting the mixing sequence of RAP, virgin asphalt binders and aggregate is confirmed as an effective way to solve the above-mentioned issue. However, the change in the demand for virgin asphalt binders for each mixing step, which is raised from aggregate gradation and different RAP content, is not taken into consideration in this improved method. In view of this weakness, this study proposed an improved mixing technique for hot recycled asphalt mixture, which comprehensively considered the mixing sequence of materials and determined the amount of asphalt binders added for different RAP content based on the specific surface area of aggregates. And the prediction formula for the amount of virgin asphalt added each step is further proposed from the perspective of aggregate specific surface area. Several laboratory experiments were conducted to verify the feasibility of this improved technique. The results indicated that, the improved mixing technique could contribute to enhancing the water stability, low temperature cracking resistance and fatigue performance of hot recycled asphalt mixtures. And the higher the content of the RAP used in recycled mixture, the stronger the improvement of the improved mixing process.

Normal Concrete Mix Design based on the Isoresponse of Slump as a Function of Specific Surface Area of Aggregate and Cement Paste-Aggregate Ratio

Many methods of normal concrete mix design produce the same proportion of cement and water content of concrete for different specific surface area of aggregate. Therefore, they often produce inappropriate workability of fresh concrete in the f

Establishment of a Shear Strength Prediction Model for Asphalt Mixtures with Raw Materials Properties and Design Parameters

Shear strength is one of the important mechanical properties of asphalt mixtures, which is affected by a combination of various parameters such as asphalt property, gradation, and asphalt content, so it often requires a large number of tests to obtain a satisfactory asphalt mix design result. Thus, a shear strength prediction model considering the effects of various factors is proposed to guide the design of asphalt mixes. Firstly, on the foundation of analyzing the factors affecting the shear strength of asphalt mixtures, composed bulk specific gravity of mineral materials, aggregate surface energy, nonrecoverable creep compliance Jnr3.2, gradation index, aggregate specific surface area, asphalt content, and gyratory compaction number were selected as the input parameters for modeling. Secondly, the effects of modeling parameters on shear strength were analyzed, and an appropriate model was established using the software Origin with 101 sets of test results. In the end, the prediction model was verified using extra 18 sets of test data. The result showed that the correlation coefficient between the predicted and measured value reached 0.8 or more, indicating that the model has satisfactory prediction accuracy. This prediction model proposed in this article can be used to reduce the workload for designing asphalt mixtures and promote the establishment of the performance-based design method of asphalt mixtures.

An experimental procedure to determine the surface area of fine aggregate particles in fine aggregate matrix mixtures: Development and validation

The specific surface area (SA) of aggregates is a key parameter required to properly design fine aggregate matrices (FAM) based on the volumetric characteristics of corresponding asphalt concrete mixtures. However, SA is often determined based on procedures that adopt simplifying assumptions which may compromise the accuracy of this parameter. This study presents an experimental protocol to determine the SA of FAMs employing the laser diffraction technique. The aggregate SAs were combined with binder film thickness measurements determined with a digital analysis of images obtained in a scanning electron microscope and used to predict the binder content of the FAMs. The comparison between the predicted and the binder content actually adopted in the laboratory demonstrated that the proposed protocol provided reliable results to be incorporated into volumetric-based FAM design procedures.

Influence of light aggregate on structure formation of lightweight concrete

Recycling of glass industry waste is relevant in the world today. It is caused by the increase of environmental problems and devastation of natural resources. One of the option of cullet recycling is production of foamed lightweight glass aggregate. It is energy efficient material with size up to 75 mm, irregular shape and relatively low strength. High specific surface area of aggregate leads to increase the cement consumption to achieve acceptable concrete compaction. This article presents the results of size gradings selection of coarse foamed glass aggregate and its water demand in concrete mix. The determination of structure formation period and water demand of foamed glass aggregate are presented. The influence of particle size distribution of lightweight aggregate on structure formation period of lightweight concrete is established. The density and compressive strength of structural lightweight concrete with foamed lightweight glass aggregate are 1468 kg/m3 and 19 MPa, respectively. The density and strength of insulating lightweight concrete are 1167 kg/m3 and 10 MPa, respectively. The cement consumption of structural and insulating concrete is 260 kg and 254 kg, respectively.

Determination of the stripping process of asphalt mixtures and the effective mix design and SFE parameters on its different phases

Abstract In the present study, attempts were made to determine the process and different phases of stripping by conducting repeated load tests on 24 different asphalt mixtures and specify the effect of thermodynamic (free energy of adhesion, free energy of cohesion, and debonding energy) and mix design parameters (specific surface area of aggregates, asphalt film thickness, and permeability) on different phases of the process. The results revealed that the stripping process consisted of two separate phases with varying intensities and mechanisms. Free energy of cohesion and the debonding energy had the most significant effect on the rise and decline of loading cycles to the initial stripping point, respectively. In the phase after the initial stripping point where the system’s tendency to stripping grew even higher, the specific surface area of aggregates and the debonding energy had the greatest impact on the decrease and increase of the stripping rate respectively.

Impact of tillage intensity on clay loam soil structure

AbstractSoil structure and structural stability are key parameters in sustainable soil management and optimum cropping practices. This study aimed to improve the knowledge of potential precision tillage practices by characterizing the effect of varied tillage intensities on structural properties of a clay loam soil. An experiment with seedbed preparation was conducted using a power take‐off‐driven rotovator equipped to measure torque and angular velocity and with operational speed (OS) and rotational speed (RS) as main factors. Effects of soil coverage prior to tillage and wheeling directly after tillage were measured at one combination of OS and RS. The soil was sampled at 0–80 mm depth. Under slow OS (2.9 km hr−1) compared with fast OS (6.3 km hr−1), specific energy input was greater (116 and 52 J kg−1 on average, respectively), and it increased with RS. Wheeling resulted in larger aggregate diameter right after tillage (at T1; 56 mm as geometric mean compared with 9 mm), with 42 times smaller geometric mean of air permeability 45 days after tillage (at T2) and with greater soil dispersibility at T2. Highly significant correlations were observed between soil dispersibility and energy input, specific surface area of aggregates, fractions of small (<4 mm) and medium (8–16 mm) aggregates, and geometric mean diameter. Slow OS combined with fast RS showed significantly greater air permeability than all other treatments. The results suggest that there is a potential for controlling soil structure in seedbed preparation by minimizing compaction from traffic and adapting site‐specific control of rotovation intensity.

Shape-dependent calculation of specific surface area of aggregates versus X-ray microtomography

The specific surface area (SSA) of constituents in a concrete mixture has a significant effect on its workability in fresh state. Excess layer theories relate the SSA to the flow behaviour of mixtures and can be used as part of an approach to mix design. However, measurement of SSA is complex and includes several issues, and thus is commonly replaced by mathematical estimation of the parameter. The mathematical approximation of surface area is based on the assumption of a spherical shape for the particles, which leads to failure of taking into account the effect of shape and the square–cube law. The article explores the possibility of replacing the assumption of a spherical shape with that of Platonic solids as the representative shape to account for the angularity of aggregates. The calculation was conducted based on information on the particle size distribution (PSD) obtained from dry sieving method. A calculated surface area on the assumption of a dodecahedron shape for natural aggregates and a cubical shape for crushed aggregates showed good agreement with SSA measurements conducted by X-ray microtomography. Furthermore, the effect of changes in PSD on the accuracy of the approach was also studied. It was found that the estimated value of SSA was improved in comparison with the traditional way of calculation on the assumption of a spherical shape.

The study of pervious concrete mix proportion by the method of specific surface area of aggregate

The purpose of this paper is to solve the shortcoming of the mix proportion of pervious concrete. So we have done the research on the measurement of the specific surface area of aggregate, and the research on the volume change of cement after hydration, and the research on the best water-binder ratio and thickness of gelled material package. The experimental results show that the equivalent method is more accurate for measuring the specific surface area of aggregate. It can better reflect the specific surface area of aggregate. Moreover, the calculation method of the mix proportion of the cementing material can improve the utilization ratio of material and the quality of pervious concrete.

Evaluating the Effect of Mix Design and Thermodynamic Parameters on Moisture Sensitivity of Hot Mix Asphalt

AbstractThis study is an attempt to identify the effective mix design and thermodynamic parameters for the moisture damage of hot mix asphalt. In the present study, 24 different combinations of asphalt mixtures were made and evaluated using three types of aggregates with different mineralogical composition, two types of asphalt binders, and three types of additives. The components of surface-free energy of asphalt binders and aggregates are measured to provide thermodynamic parameters using the Wilhelmy Plate and Universal Sorption Device, respectively. To determine the performance of moisture sensitivity, environmental conditions simulation according to the modified Lottman test was used, and an indirect tensile strength test has been conducted on asphalt mixtures. The results of statistical analysis presented show that the free energy of cohesion, free energy of asphalt binder-aggregate adhesion, specific surface area of aggregates, and asphalt binder film thickness on the aggregate surface have a direc...

Shear strength of GMZ07 bentonite and its mixture with sand saturated with saline solution

An experimental study involving direct shear, compression and swelling tests is carried out to investigate the effects of salt solution concentration on mechanical behaviour and microstructural features of a sodium bentonite (GMZ07 bentonite) and its mixture with sand. GMZ07 bentonite is a potential buffer/backfill material for deeply buried geological disposal system to isolate high-level radioactive waste (HLW) in China. Compacted unsaturated GMZ07 bentonite and its mixture with sand saturated with distilled water and sodium chloride solutions at different concentrations (0.2, 0.5 and 1.0mol/L) were first consolidated to a specified stress and then sheared at a constant displacement rate. Test results indicate that shear strength or shear resistance has a noticeable improvement with the increase of salt solution concentration. The test results of GMZ07 bentonite reveal that friction angle increases fairly with the salt solution concentration but the cohesion intercept doesn't. Results of compression tests performed with different salt solution concentrations showed almost the same compressibility for GMZ07 bentonite specimen and its mixture with sand. At last, the microstructure changes associated with variations in the salt solution concentration have been photographed by the Scanning Electron Microscopy (SEM). The photographs show that the increase of salt solution concentration would change the surface roughness and specific surface area of aggregates, which will produce greater interaction among aggregates.

Influence of aggregate absorption and diffusion properties on moisture damage in asphalt mixtures

An experimental study was undertaken to characterise moisture sensitivity of asphalt mixtures by comparing certain physico-chemical properties of selected aggregates of different mineralogies to the moisture-induced strength degradation of the aggregate–mastic bonds. The aim of the study was to evaluate the effect of using different aggregate types (as substrates) with a single mastic type that had shown severe moisture sensitivity in the past when combined with a susceptible aggregate substrate. Four different aggregate types and an asphalt mastic (made with a 40/60 pen base bitumen) were used. Aggregate moisture sorption at ambient temperature was characterised using gravimetric techniques. Aggregate specific surface area was determined by octane adsorption using a dynamic vapour sorption device. Dynamic mechanical analysis techniques based on data from a dynamic shear rheometer were used to characterise the rheological properties of the asphalt mastic. Aggregate–mastic bond strength as a function of moisture conditioning time was determined using a tensile pull-off test set-up. The results were used to estimate equilibrium moisture uptake, diffusion coefficient, characteristic diffusion time, and aggregate ‘porosity’. The effect of moisture on bond strength was aggregate substrate-type-dependent with three out of the four aggregates performing well and the fourth performing poorly. The moisture absorption and diffusion properties of the poorly performing aggregates were worse than the ‘good’ performing aggregates. Susceptible aggregate–mastic bonds had high porosity, high moisture absorption, high diffusion coefficient and contained granite as substrates. Results of statistical analyses suggested that the differences in moisture sensitivity of the other three aggregates were not significant. Therefore, two unique damage models, one for ‘good’ performing and another for ‘poor’ performing were proposed to characterise moisture damage sensitivity of asphalt. The influence of aggregate moisture absorption and diffusion on asphalt mixture moisture damage was found to be aggregate-type-dependent. The results also suggested that in a susceptible mixture, the effect of the substrate aggregate may be more influential than the effect of mastic. The results have important implications for the selection of coarse aggregate for asphalt mix design.

Quantification of Specific Surface Area of Aggregates Using an Imaging Technique

An imaging method is proposed to quantify the specific surface area of aggregates of different sieve sizes. The procedure for determining the specific surface areas of aggregate particles by the proposed method includes the following steps: (1) separating the aggregates into different standard sieve sizes, (2) placing the aggregate particles in a container and injecting a resin to bind them, (3) sawing the aggregate/resin specimen to obtain one to four cut planes, (4) using an image analyzer to take the aggregate particles images from the cut planes, (5) determining the specific surface areas and other aggregate particle properties, such as the slenderness ratio and the roughness from the images. The proposed method was used to determine the specific surface area of a crushed granite aggregate sample with the particle size ranging from passing 19mm to #50 sieve. The results were compared with the approximate specific surface areas for different aggregate sizes commonly used by the aggregate industry. The approximate specific surface areas were based on the average specific surface areas of the spheres having the diameters equal to the corresponding passing and retaining sieve opening sizes. The specific surface areas determined by the proposed method are higher, particularly for the aggregates passing #16, #30, and #50 sieve sizes, than those of the approximate values. The reason for the higher specific surface areas determined by the proposed method was primarily due to the irregular shapes and the rough textures of the crushed aggregate particles. The proposed method can be used for quantifying the aggregate properties, including the specific surface area, roundness, slenderness ratio, and roughness in the laboratory for the quality control of aggregate properties.

Damköhler number design method to avoid clogging of subsurface flow constructed wetlands by heterotrophic biofilms

Clogging of subsurface flow (SSF) treatment wetlands from excess biofilm growth is a design problem for which only empirical guidelines exist. A method is proposed to systematically analyse this type of clogging as a design tool. In recognition of the physical reality that most SSF treatment wetland processes are a function of biofilm surface area, a Damköhler number (Da) definition based on aggregate specific surface area is used to investigate a method of predicting clogging induced by heterotrophic biofilms growing on treatment media.

Specific surface area of aggregate and its relation to concrete drying shrinkage

This paper deals with the influence of aggregate properties on the shrinkage of concrete during drying. The drying shrinkage strains of concretes with various types of aggregates were measured and their influences on the fundamental properties of the different types of aggregates were investigated. Furthermore, the specific surface areas (SSAs) of aggregates were obtained by the BET method using both nitrogen (N2) and water vapour (H2O). The SSAs determined by using H2O exhibited higher values than those by using N2. The drying shrinkage strains of concretes increased with the H2O SSAs of the aggregates used. Our results suggest that the SSA determined by using H2O is an effective index for evaluating the influence of the aggregate type on the drying shrinkage of concrete.

硬化モルタル及びコンクリート中の遷移帯厚さの評価並びに遷移帯厚さと強度との関係の検討

A method for estimation of the thickness of transition zone is proposed by calculating the coarse pore volume in transition zone from discrepancy between pore size distribution of hardened mortar and concrete and hardened cement paste using specific surface area of aggregate. Thickness of layer of coarse pore in transition zone of mortar and concrete at the age of 28 days is calculated at 14.6μm and 12.3μm, respectively, and average thickness of transition zone in mortar and concrete is estimated at 30μm and 25μm, respectively by the method proposed. These values coincide well with those determined by SEM observation. Transition zone in mortar and concrete is generally formed at 3 days after placing mortar and concrete and increases in its thickness reaching the maximum value at 7 days and gradually decreases in its thickness with age although the change is not remarkable especially in concrete. Estimation of development strength and explanation of the difference of strength development between cement paste, mortar and concrete can be obtained from the time dependency of thickness and pore structure of transition zone.