Air Void Ratio Research Articles

Eco-friendly concrete: Combining treated wastewater and recycled aggregates.

The concrete industry is a significant consumer of drinking water and natural aggregates, such as sand and gravel. However, the scarcity of water and aggregate resources and the challenges associated with the disposal of construction and demolition waste prompted the exploration of alternative materials. This study investigates the feasibility of incorporating secondary treated wastewater from UASB reactors followed by trickling filters and mixed recycled aggregates as potential alternatives. To assess the viability of these alternatives, the study considered the replacement of 100% potable water with treated wastewater, as well as varying proportions of recycled gravel (20, 40, 60, 80, and 100%) and recycled sand (10, 20, 30, 40, and 100%). Physical and mechanical properties were negatively affected, but it was possible to reach compressive results over 40 MPa and splitting tensile strength over 4 MPa for almost all mixes. Regarding physical properties, the use of alternative materials caused poorer outcomes for density, water absorption, and air-void ratio. The limited magnitude of these detrimental effects indicates the potential of manufacturing concrete with the addition of combined treated wastewater and recycled aggregate as a viable strategy while enhancing reuse practices.

Verification of The Possibility of Air-void Recovery in RSBS Double-Layer Low-Noise Porous Asphalt Pavement

Radial type styrene-butadiene-styrene double-layer low-noise porous asphalt (RSBS DLPA) pavement is a type of porous asphalt pavement which had high air-void ratio, and well-known to absorb tyre/pavement noise and the rain through the pavement's layer. According to the Korea Meteorological Administration, from July to August in 2022, the daily rain precipitation was more than 100 mm per day and categorized as heavy rain. Due to the high air void ratio in RSBS DLPA pavement, the rainwater will be transferred through the pavement layer. The heavy rain splashing onto the surface pavement is similar to the method using the low water pressure and low-vacuum that our company developed which helps to recover the low-noise porous asphalt pavement. In this study, the CPX method was used to measure the noise level before and after heavy rain to differentiate the noise level. The results showed that the heavy rain had an effect on reducing the noise level. Before heavy rain, the noise level was up to 89.9 dB, while the noise level was decreased to 87.7 dB after heavy rain. It is shown that our cleaning method able to recover the air-void content as same as heavy rain.

The effect of particle shape on the meso-structure of mixture skeleton based on DIP and 3D DEM

Mixture skeleton is the main body bearing the load of asphalt mixture, and particle shape is an important factor affecting the meso-structure of mixture skeleton. Based on the minimum bounding box theory, obtain particles geometry by Digital Image Processing (DIP), and calculate the shape indices: angularity index (A1) and flat-elongated index (F1). By using discrete element method (DEM) software PFC3D, five mixture skeletons were built with different integrated angularity (Am) and flat-elongated particles content (Fm). And analyzed air void, particles distribution and particle angle of mixture skeletons. The results show that Am has no obvious effect on the air void ratio, but increasing Fm can increase the air void ratio. In addition, the index U3D was proposed to evaluate particles distribution on 3D scale, and found that small particles are more likely to have better distribution uniformity. And uniformity of particles distribution in mixture skeleton will increase with the increase of Am. For particles, angle will be increase with the increase of F1. However, if F1 is too large, particle angle will decrease due to the embedding effect. These studies and results analyzed that how can particles shape affect meso-structure of mixture skeleton.

Mechanical Properties of Pervious Recycled Aggregate Concrete Reinforced with Sackcloth Fibers (SF)

The excessive production of construction waste is a significant concern as it requires proper disposal and may become economically unfeasible. Reusing construction waste in producing new concrete can substantially reduce the disposal requirements of construction waste. In addition, this results in a sustainable solution for the rapidly depleting natural resources of concrete. Pervious concrete may contain up to 80% coarse aggregates and could be an exceptional host for reusing construction waste. This study aimed to investigate the mechanical properties of pervious concrete constructed with natural and recycled aggregates. The substandard properties of recycled aggregates were improved by adding natural fibers from sackcloth. This study presents an experimental program on 45 samples of pervious concrete with air void ratios and the size of coarse aggregates as the parameters of interest. The compressive strength of the pervious concrete decreased by increasing the air void ratio regardless of the size of the aggregates. The type of aggregates did not influence the permeability of pervious concrete, and the maximum temperature in pervious concrete increased as the quantity of air void ratios increased. The decrease in compressive strength was 40–60% as the void ratio was increased from 10–30% for all types of concrete mixes, such as natural and recycled aggregates. The permeability of small-size aggregates with 10% designed air void ratios for natural and recycled aggregates with sackcloth was 0.705 cm/s.

Repeated Uniaxial Compression Test of Permeable Friction Courses Mixtures under Seepage Field and Stress Field Coupling

In order to study the variations of the non-Darcy flow permeability coefficient and the porosity of permeable friction courses (PFCs), as well as the effects of the coupled seepage and stress fields on them, repeated uniaxial compression tests were carried out under the coupled action of water and a load. A set of water and load coupling tests were conducted, and a non-Darcy flow permeability coefficient tester was also made. After the PFC-13 specimen was carried out by the repeated uniaxial compression test under the water and load coupling, the total air void ratio and effective air void ratio were measured by the vacuum sealing method, and the non-Darcy flow permeability coefficients were obtained by a non-Darcy flow permeability coefficient tester. It was found that the coupled action of water and a load caused the total air void ratio, effective air void ratio, and permeability coefficient to sharply increase and reduced the number of repeated uniaxial compression cycles. These results are helpful for the design, construction, and maintenance of PFC mixtures.

Effect of key design parameters on high temperature performance of asphalt mixtures

• Four key design parameters were selected to study their effect on the high temperature performance of asphalt mixtures. • The uniaxial penetration shear test was applied to analyze the variation of high temperature performance of asphalt mixtures. • The multi-way (one way and two-way) ANOVA was adopted to understand the role of factors on the high temperature performance of asphalt mixtures. Rutting is one of the main distresses for asphalt pavements and it has adverse effect on service life. It is associated with the high temperature performance of asphalt mixtures. The paper attempts to investigate the effect of key design parameters on high temperature performance of asphalt mixtures. Initially, the factors consisting of air void ratio, compaction effort, maximum nominal particle size and asphalt binder grade were selected and then the uniaxial penetration shear test was applied to analyze the variation of high temperature performance of asphalt mixtures. Accordingly, the maximum penetration load and the shear strength were used as evaluating indicators. Eventually, the multi-way (one way and two-way) ANOVA was adopted to understand the role of factors on the high temperature performance. The results indicate that the high temperature performance increases an average of 30 % when compaction effort and maximum nominal particle size rise. In contrast, the raise of asphalt grade and air void ratio decrease of 10 %∼30 % of high temperature performance. At the same time, the increase of compaction effort improves the high temperature performance about 20 %∼50 % at two variables condition. In one-way ANOVA, there is no statistically significant difference in the maximum penetration load when changing the air void ratio levels. The compaction effort, maximum nominal particle size, asphalt binder grade significantly influence the change of maximum penetration load. In terms of two-way ANOVA, any combined two factors significantly affect the high temperature results. This provides some guidance for design of asphalt mixtures to elevate high temperature performance.

Pressure and heat treatment of continuous fibre reinforced thermoplastics produced by fused filament fabrication

Fused filament fabrication allows for the additive manufacturing of complex geometries without requiring moulds. However, due to large air voids and poor layer adhesion, the mechanical properties of parts manufactured using fused filament fabrication lag behind those of parts manufactured using conventional techniques. A previous study found that the tensile strength and Young’s modulus of such parts could be increased by a heat-treatment process. However, large air voids were still present after annealing. This study, therefore, investigates the influence of a post-pressure-treatment process on the mechanical performance and the air void ratio of continuous glass fibre-reinforced polyamide 6 in the directions perpendicular to the fibres. Without the treatment, Young’s modulus on the plane parallel to the printing bed is eight times higher than Young’s modulus perpendicular to it. Annealing at 1 MPa homogenises the material and leads to a significant increase of both the tensile strength (55 MPa) and Young’s modulus (5 GPa). Increasing the pressure to 3 MPa only slightly increases the mechanical performance, whereas a further increase to 6 MPa causes no significant changes.

Gradation of limestone-aggregate-based porous asphalt concrete under dynamic crushing test: composition, fragmentation and stability

Aggregate with excellent mechanical properties, like basalt, is always in great demand in porous asphalt concrete (PAC). While in areas where high-quality basalt is insufficient, limestone aggregate with acceptable performance is considered as a potential alternative. This paper analyzed the composition, fragmentation and stability of PAC gradation based on limestone aggregate since its long-term performance and stability under repeated stresses still haven’t been studied. Firstly, dynamic crushing test (DCT) was adopted to simulate the stress characteristics of PAC gradation. Secondly, single size range of aggregate (SSRA) and PAC gradation were used to determine and verify the test conditions. Thirdly, composition, distribution characteristics and stability of formed structural systems were studied. Lastly, more PAC gradations were adopted to further verify the conclusions. Results showing the test samples have reached relative stability by one-cycle test, were not significantly influenced by test temperature. In DCTs, aggregate of 4.75 mm had a critical effect on structural systems stability, while aggregates of 2.36 mm and 9.5 mm also played important roles in improving systems’ stability. Unlike SSRA, which was influenced by its own objective crushing characteristics and contributed to larger air void ratios of newly-formed-systems, aggregates in PAC gradations were affected by objective crushing characteristics as well as structural skeletons. Aggregate particle size distribution of newly-formed-systems of PAC gradations was between those of AC and PAC gradations, more closed to that of AC gradation. Besides, those formed systems have been proved to have better stabilities than control samples of similar air void ratios.

Determining the Void Ratio in Hot-Mix Asphalt Pavements Using Different Methods According to EN 12697

Inaccurate air void ratio based on erroneous bulk density can seriously affect the performance of the roadway and its quality. Therefore, several methods were improved to measure bulk density by using different techniques in the developed countries, while the Saturated Surface Dry (SSD) traditional method has been used in Gaza strip till present days. This study aims at providing a better understanding of the effect of the selected bulk density measurement method on the percentage of voids using four methods namely; Dimensional Method, Dry Method, Surface-Saturated Dry Method, and Paraffin Sealing Method. At Laboratory, sixty-nine specimens were prepared, thirty-three of them were prepared in the Marshal Design System in order to determine the optimum bitumen content of the three different mix types, and thirty-six of the specimens were taken from mixtures design in order to determine bulk density. Laboratory results showed that the SSD method is the best choice for measuring bulk density in dense and mastic mixtures. In addition, there are no differences between SSD and dry methods in mastic mix. The experimental study shows that the dimensional method is the only method suitable for the determination of bulk density (Gmb) in porous mix despite it always gives underestimated results for Gmb in all asphalt mixes. As a result, the dimensional method can be used as an indicator for the upper limit of voids, while the dry method can be used as an indicator to the lowest limit, regardless the type of mix. The study recommended to use new techniques to determine Gmb in open graded mixtures with more accurate methods rather than traditional ones.

Experimental investigation of the permanent deformation and void ratio attenuation of porous asphalt mixtures with hydraulic effects

To investigate the quantitative influence of the material gradation characteristics, saturation degree and loading frequency on the permanent deformation of porous asphalt (PA) mixtures under temperature, loading, and hydraulic coupling conditions, a hydraulic coupling repeated loading test is conducted for five types of PA mixtures with different nominal maximum aggregate sizes, void ratios, saturation degrees and load frequency inputs. The test results indicate that the PA-20 mixture has better anti-deformation performance than the PA-13 and PA-16 mixtures. A larger void ratio corresponds to weaker anti-permanent deformation performance. When the initial void ratio is 24%, the flow number prominently decreases to approximately less than 11% of the initial void ratio of 16%. The results of the loading test with water storage show that the saturation state has a more significant impact on the permanent deformation of PA-13 mixtures than PA-16 and PA-20. When the frequency increases, the cumulative microstrain of the mixture greatly decreases, and the influence degree of frequency on the deformation becomes increasingly obvious when the void ratio increases due to the effect of hydraulic coupling. To easily evaluate the void ratio attenuation of PA, a uniform expression is proposed to characterize the three-stage strain growth, which shows that the permanent deformation curve exhibits nonlinear growth in the second stage of deformation. Then, the minimum permanent deformation growth rate is presented to quantitatively evaluate the deformation resistance performance. Overall, a higher saturation degree of the lower loading frequency corresponds to a smaller PDGRmin. A formula is presented to analyse the effect of permanent deformation on the change in void ratio: the loading frequency, saturation degree and initial void ratio significantly affect the attenuation of the AV ratio. Specifically, the coupling of frequency and water storage slows the decrease in air void ratio.

Gradation optimization and strength mechanism of aggregate structure considering macroscopic and mesoscopic aggregate mechanical behaviour in porous asphalt mixture

Porous asphalt mixture (PAM) as a special pavement material with discontinuous gradation has been widely used in pavement engineering because of its versatility caused by high air void content. Aggregate structure plays a significant role in the pavement performance of porous asphalt mixture. In this study, the effects of different size aggregates on the air void ratio and macroscopic aggregate bearing capacity are investigated to put forward an aggregate gradation with a strong aggregate structure. Laboratory tests show that the proposed gradation provides an improved pavement performance for porous asphalt mixture. Moreover, strength mechanisms of aggregate structure in porous asphalt mixture are revealed from a view of the mesoscopic aggregate contact force composition using discrete element method (DEM) simulations considering aggregate irregularity. Finally, the mechanical role of each size aggregate on the aggregate structure is analyzed via mesoscopic aggregate contact force distribution.

Thermal characteristics of porous concrete in a hydronic road heating system

Porous road concrete is an important part of the hydronic road heating system to avoid icing on the road. The thermal characteristics of porous concrete are obtained in the heating process to evaluate the microstructure effects and predict the road conditions. This study applied the Monte Carlo method to generate a two-dimensional heterogeneous porous concrete model. The porous concrete is a mixture of aggregates, bonding interfaces, cement pastes, and air voids. The thermal characteristics (average road surface temperature and road surface temperature distribution) of porous concrete were simulated. The average road surface temperatures were validated with the experiment results. The thermal characteristics of porous concrete as affected by the aggregate areal ratio, air void size, and air void ratio were compared and analyzed. The results indicate that the average road surface temperature at 8 h increased by 1.07 K and the preheating time decreased by 1.05 h when the aggregate areal ratio was increased from 40% to 60%. The road surface temperature fluctuation for the aggregate areal ratio of 50% was the highest (274.34~275.96 K). The average road surface temperature at 8 h decreased by 0.39 K and the preheating time increased by 0.51 h with the air void size changing from 1~3 mm to 1~5 mm. The road surface temperature fluctuation for the air void size of 1~5 mm was the highest (273.80~274.50 K). The average road surface temperature at 8 h decreased by 4.48 K and the preheating time increased by 4.03 h with the air void ratio increasing from 0 to 10%. The road surface temperature fluctuation of none air void was the lowest (277.88~278.12 K), indicating that the air void had a significant impact on the road surface temperature.

Frost Resistance Number to Assess Freeze and Thaw Resistance of Non-Autoclaved Aerated Concretes Containing Ground Granulated Blast-Furnace Slag and Micro-Silica.

Aerated concrete (AC), such as cellular concrete, autoclaved aerated concrete (AAC), and non-autoclaved aerated concrete (NAAC), having excellent insulation properties, is commonly used in buildings located in cold regions, such as Nur-Sultan in Kazakhstan, the second coldest capital city in the world, because it can contribute to a large energy saving. However, when the AC is directly exposed to the repeated freeze and thaw (F-T) cycles, its F-T resistance can be critical because of lower density and scaling resistance of the AC. Moreover, the evaluation of the F-T resistance of the AC based on the durability factor (DF) calculated by using the relative dynamic modulus of elasticity may overestimate the frost resistance of the AC due to the millions of evenly distributed air voids in spite of its weak scaling resistance. In the present study, the F-T resistance of NAAC mixtures with various binary or ternary combinations of ground granulated blast-furnace slag (GGBFS) and micro-silica was assessed mainly using the ASTM C 1262/C1262M-16 Standard Test Method for Evaluating the Freeze-Thaw Durability of Dry-Cast Segmental Retaining Wall Units and Related Concrete Units. Critical parameters to affect the F-T resistance performance of the NAAC mixture such as compressive strength, density, water absorption, air–void ratio (VR), moisture uptake, durability factor (DF), weight loss (Wloss), the degree of saturation (Sd), and residual strength (Sres) were determined. Based on the determined parameter values, frost resistance number (FRN) has been developed to evaluate the F-T resistance of the NAAC mixture. Test results showed that all NAAC mixtures had good F-T resistance when they were evaluated with DF. Binary NAAC mixtures generally showed higher Sd and Wloss and lower DF and Sres than those of ternary NAAC mixtures. It was determined that the Sd was a key factor for the F-T resistance of NAAC mixtures. Finally, the developed FRN could be an appropriate tool to evaluate the F-T resistance of the NAAC mixture.

Evaluating engineering properties and environmental impact of pervious concrete with fly ash and slag

Abstract This study evaluated engineering properties, cost, and energy and environmental impacts of three pervious concrete mixtures: pervious concrete with regular Portland cement (PC-Regular); with fly ash (PC-FA); and with blast furnace slag (PC–BFS). Laboratory tests were conducted to measure mechanical strength, hydraulic conductivity, and freezing-thaw resistance of mixtures. Life-cycle assessment (LCA) approach was used to quantify greenhouse gas (GHG) emission and energy consumption of pervious concrete mixtures with different material compositions. Mass and economic allocation methods were applied to quantify the effects of allocation on impact assessment of fly ash and slag. Laboratory test results show that as compared to the regular pervious concrete, pervious concrete mixtures with slag or fly ash had the similar freeze-thaw resistance but the lower mechanical strength, especially in tensile or flexural strength. The hydraulic conductivity of pervious concrete mixtures with fly ash and slag was found slightly higher due to the larger air void ratios. The choice of allocation methods was found to have significant effect on the assessment results. The adoption of economic allocation method showed 6–9% lower energy saving and 11–19% GHG emission reduction as compared to the mixture with Portland cement. The overall performance of each pervious concrete mixtures was quantified through internal normalization and the area covered in the radar diagram. The pervious concrete with fly ash exhibited the highest overall performance considering the balance of multiple-criteria in engineering properties, cost saving, energy and GHG reduction.

A grain moisture model based on capacitive sensor

This study starts with the principles of the variable dielectric-type cylindrical capacitive sensor, conducts the theoretical analysis after dielectric is divided into three phases (solid, liquid and gas), determines the relation between dielectric constant and other influence factors through the least squares fitting method, makes compensation for such factors as temperature, grain variety and air void ratio, builds the mathematical model of grain moisture content(GMC) through the variable dielectric-type cylindrical capacitive sensor, and suggests the capacitance measurement method based on pulse-width modulation. The experiment result shows that the suggested capacitance measurement method can accurately measure micro-(pF-class) capacitance, and the theoretical value of GMC as produced by this mathematical model falls within an allowable error range when compared to actual value, so this model proves to be rational.

Importance of controlling the degree of saturation in soil compaction linked to soil structure design

Abstract In the typical conventional fill compaction, the dry density, ρd, and the water content, w, are controlled in relation to reference values, (ρd)max and wopt, determined by standard laboratory compaction tests using a representative sample at a certain compaction energy level, CEL. Although CEL and soil type affect significantly (ρd)max and wopt, they change inevitably, sometimes largely, in a given earthwork project while field CEL may not match the value used in the laboratory compaction tests. Compaction control based on only an index of strength/ stiffness of compacted soil has such a drawback that, for a fixed value of ρd, the index may increase significantly as the degree of saturation, Sr, of compacted soil becomes lower than the optimum degree of saturation (Sr)opt defined as Sr when (ρd)max is obtained for a given CEL. In comparison, the value of (Sr)opt and the unified compaction curve in terms of ρd/(ρd)max vs. Sr − (Sr)opt relation of compacted soil are rather insensitive to variations in CEL and soil type. Besides, CBR (unsoaked and soaked), the unconfined compression strength, the elastic shear modulus and the collapse upon submerging of compacted soil and the cyclic undrained shear strength and the coefficient of hydraulic conductivity of saturated soil are all controlled by ρd and “Sr at the end of compaction”. As a standard method, it is proposed to control the values of w and ρd in such that Sr becomes (Sr)opt while ρd becomes large enough to ensue soil properties required in design fully taking advantage of available CEL. It is argued that the compaction control keeping Sr larger than a certain value (or the air void ratio va lower than a certain value) without controlling ρd is relevant as a simplified method only if Sr is controlled to become (Sr)opt while always keeping CEL high enough to ensure the soil properties required in design.

Thermo-optic characteristics of hybrid polymer/silica microstructured optical fiber: An analytical approach

Microstructured optical fibers (MOFs) allow a variety of advanced materials to be infiltrated in their air-voids for obtaining the increased fiber functionality, and offering a new versatile platform for developing the compact sensors devices. We aim to investigate the thermal characteristics of high-index core triangular hybrid polymer/silica MOFs with circular air-voids infused with polymer by using the analytical field model [1]. We demonstrate that infiltration of air-voids with polymer, e.g., polydimethylsiloxane (PDMS) can facilitate to tune the fundamental modal properties of MOF such as effective index of the mode, near and the far-field profiles, effective mode area and the numerical aperture over the temperature ranging from 0 °C to 100 °C, for different values of relative air-void ratios. The evolution of the mode shape for a given temperature has been investigated in transition from near-field to far-field regime. We have studied the thermal dependence of splice losses between hybrid MOF and the standard step-index single-mode optical fiber in combination with Fresnel losses. For enhancing the evanescent field interactions, we have evaluated fraction of power associated with fundamental mode of hybrid MOF. We have compared the accuracy of our results with those based on full-vector finite-difference (FD) method, as available in the literature.

Composting physics: A degradation process-determining tool for industrial sludge

Management of industrial sludge is a big challenge for developing countries. Composting is an economical and viable option to manage and treat an industrial sludge. However, efficient compost production requires nature of materials involved, process understanding and physics behind the process. We investigated the physical parameters during composting of solid pulp and paper mill sludge in 550 L rotary drum composter. Variation in physical parameters such as bulk density, volatile solids, moisture content, free air space, void ratio, ash content and particle density were analyzed over the period of composting. Bulk density was observed increasing, whereas free air space was showed declining trend and observed 52% in end compost. The particle density was observed to be increasing from 610 to 680 kg m−3. End compost was analyzed for nutritional parameters and seen to be increasing over the period of composting. A strong relationship was found between various physical parameters. Pearson’s correlation coefficient matrix was formed between free air space, bulk density, moisture content and particle density.

A study on fatigue damage of asphalt mixture under different compaction using 3D-microstructural characteristics

The aim of this paper is investigating the microstructural characteristics of asphalt mixture under different compaction powers. In order to achieve this aim, a test track was built to provide asphalt mixture specimens and X-ray computed tomography (XCT) device was used to scan the internal structure. The aggregate particles and air-voids were extracted using Digital Image Processing (DIP), so the relationship between compaction and air-voids was determined at first, and then, the effect of aggregate particles on the morphology of air-voids can be evaluated, finally, fatigue properties of asphalt mixture with different air-void ratio were measured by indirect tensile fatigue test as well. The research results release the distribution of microstructures in asphalt pavement. 3D fractal dimension is an effective indicator to quantize the complexity of aggregate particles and air-voids; suffering the same compaction power, aggregates cause different constitutions of air-voids in asphalt mixture; investigation in this paper can present the essential relationship between microstructures and fatigue properties.

Laboratory investigation of the characteristics of SMA mixtures under freeze–thaw cycles

In this study, the effects of freeze–thaw cycles on the characteristics of Stone Mastic Asphalt (SMA) mixtures, containing cement 30% or lime 20%, are investigated under different freeze–thaw cycles. SMA mixtures were produced in a laboratory environment. Specimens containing different additives were prepared with different air void ratios ranging from 2.5% to 6.0% based on the calculated optimum bitumen amount. The volumetric properties, Marshall Stability (MS), flow and freeze–thaw split tensile strengths were experimentally determined for each specimen at the end of the 1st, 3rd, 5th, 8th, 10th, 15th, 20th cycles. Test results indicate that initial air void ratio plays an important role in the performance of SMA under freeze–thaw cycles; freeze–thaw resistance of SMA mixtures with lime was better than those with cement. The MS values of SMA decrease between 24.4% and 56.5%, 26.5% and 45.5% and 17.9% and 14.1% for samples without additives, samples with cement, and samples with lime after 20 freeze–thaw cycles, respectively. SMA mixtures exhibit brilliant performance on the resistance to freeze–thaw damage.