Air Permeability Coefficient Research Articles

Durability index for quality classification of cover concrete based on water intentional spraying tests

This study proposes a new durability indicator for classifying cover concrete quality through the total amount of sprayed water index (rW) using the water intentional spraying test (WIST). The usability of four WIST apparatuses was first verified through strong positive correlations between the previously proposed “repetition number of water spraying” index (rN) and the coefficient of air permeability, kT, (using a Torrent tester) that were individually measured on specimens produced with different cement types, water-to-binder ratios, and curing periods. Subsequently, a new equation was established showing the correlation between WIST apparatuses using rN and the amount of water for each spraying, W, in order to establish a generalized approach. A suggested range of rW indexes for quality classification of cover concrete was thereafter formulated and verified on the basis of good correlation between rW and kT. In addition, an innovative technique for expanding the usability of WIST was presented.

Investigating the effect of raising on the sound absorption behavior of polyester woven fabrics

This work presents the results of efforts focused on the development of sound absorptive woven fabrics by the raising process. Four woven fabrics with rib and basket weave patterns were produced for the raising process. Micro-fiber-based polyester weft yarns were used in one set of rib and basket weave fabrics, while weft yarns comprising regular polyester fibers were used in the other set. Fabrics were subjected to dyeing and heat setting prior to the raising process. Fabrics were then passed one to three times through the raising unit in order to obtain fabrics with different voluminous characteristics and different quantities of fiber ends on the fabric surface. The mass per unit area, thickness, air permeability, and sound absorption coefficient of the fabrics were measured and surface images of the fabrics were taken. The solid volume fraction and airflow resistivity of the fabrics decreased significantly after the first and second raising passes. Increasing the number of raising passes up to two passes resulted in higher sound absorption (average increment of 20% at 5 kHz) in the higher frequencies at the expense of that in the lower frequencies. Sound absorption change beyond two passes was insignificant, though. The results demonstrated that raised fabrics having a lower solid volume fraction and airflow resistivity had better acoustical properties in the higher frequency region.

Correlations between air permeability coefficients and pore structure indicators of cementitious materials

Abstract Correlations between the air permeability coefficient and various pore structure indicators in cementitious materials were examined to determine the pore structure indicator that best evaluated air permeability using data from previous studies. In this study, the air permeability data from sufficiently dried specimens were selected and the effect of pressure on the air permeability was ignored. Among five pore structure indicators, the median and new threshold pore diameters obtained by percolation theory showed higher determination coefficients. The regression equation using the new threshold pore diameter better estimated the air permeability coefficient than the Katz–Thompson equation.

Validation of simple nondestructive method for evaluation of cover concrete quality

The Water Intentional Spraying Test (WIST) was originally proposed as a simple nondestructive method for evaluating the cover concrete quality based on the “repetition number of water spraying,” rN. The validity of the test was verified in the present study by comparing rN with the coefficient of air permeability, kT, determined by the Torrent test. Both tests were conducted on three-month-old concrete specimens produced with different cement types, water-to-cement ratios, and curing periods, using different measurement heights. A good relationship was observed between kT and rN, with the WIST also found to be sensitive for the detection of poor-quality concrete.

Long-term permeability measurements on site-cast concrete box culverts

This study investigated the effect of age on transport property measurements of concrete cover. Changes in moisture contents, air permeability, and water sorptivity were monitored for three years by conducting non-destructive tests on surfaces of site-cast concrete box culverts and mock-up specimens. Furthermore, carbonation rates in the specimens were measured. The results revealed that transport properties measured by non-destructive tests were effective at detecting effects of cement types and curing periods on the carbonation progress. In particular, the air permeability coefficients of specimens with lower moisture contents at later ages showed high correlation with the carbonation rates.

Design of a steady-state in situ test to determine the air permeability coefficient of covercrete

An in situ air permeability test method that does not require assumptions for the often-difficult unidirectional flow has been developed to calculate the air permeability coefficient of the near surface concrete. The proposed method involves applying a constant pressure head to a surface mounted ring and measuring the steady state air flow rates. The analysis is based on modification of the flownet theory, which needs a calibration factor accounting for the influence of specimen and ring geometries. Effects of test area, width of seal, depth and width of test specimen were investigated using numerical simulation of the air flow. The repeatability of the proposed test method was assessed by the signal noise ratio (SNR) and discrimination ratio (DR). A new formula is offered and it only requires the steady state air flow rate to calculate the coefficient of air permeability, thus assisting engineers and researchers to quickly determine this property of structural concretes.

Influence of sea polymer removal on sound absorption behavior of islands-in-the-sea spunbonded nonwovens

This work presents the results of efforts focused on the development of relatively lightweight and fibrous acoustic webs. For this objective, nonwoven webs that contain bicomponent filaments with islands-in-the-sea cross sections were produced by spunbonding, which involves the extrusion of sea and island polymer melts through dies, cooling and attenuating the bicomponent filaments by high-velocity air streams. Nylon 6 and polyethylene were used as the island and sea polymers, respectively. Webs were hydroentangled with high-pressure water jets prior to the dissolving process to obtain fiber entanglement. Sea polymer was removed from the spunbonded nonwovens by using a reflux dissolution setup. Weight, thickness, air permeability, pore size and sound absorption coefficients of the nonwoven samples were measured before and after the sea polymer removal. Results demonstrated that sea polymer removal led to further bicomponent filament fibrillation, which affected sound absorption positively. The structure with the higher number of island fibers had better acoustical properties. Lightweight and fibrous acoustic nonwovens can be obtained with the method given in this study.

A novel process for preparing fireproofing materials from various industrial wastes

In the current study, the possibility of incorporating various industrial wastes into fireproofing materials was investigated. It was found that the newly developed materials showed excellent air sealing and fireproofing performance, with air permeability coefficients 3 to 4 orders of magnitude smaller than traditional fire prevention materials. The influence of different parameters on the air permeability was investigated, and the air sealing mechanisms were clarified through microstructure analysis. In addition, the workability and mechanical properties of the fireproofing materials for practical application in coal mine were studied. The new materials derived from industrial wastes had a compact and monolithic structure, and the excellent air tightness could be attributed to the pozzolanic activity of the industrial wastes and the film-forming property of organic polymers. Among the industrial wastes examined, a special coal fly ash with high pozzolanic activity and little free calcium oxide derived the best product with air permeability coefficient, tensile strength and breaking elongation of 4.17 × 10−8 m2/s, 2.14 MPa and 48.90%, respectively. This study provides an economical, environmentally friendly and promising approach for industrial wastes recycling.

Laboratory test investigations on soil water characteristic curve and air permeability of municipal solid waste.

The air permeability coefficient has a high correlation with the water content of municipal solid waste. In this study, continuous drying methodology using a tension meter was employed to construct the soil water characteristic curve of municipal solid waste (M-SWCC). The municipal solid waste air permeability test was conducted by a newly designed apparatus. The measured M-SWCC was well reproduced by the van Genuchten (V-G) model and was used to predict the parameters of typical points in M-SWCC, including saturated water content, field capacity, residual water content and water content at the inflection point. It was found that the M-SWCC was significantly influenced by void ratio. The final evaporation and test period of M-SWCC increase with the increase in void ratio of municipal solid waste. The evolution of air permeability coefficient with water content of municipal solid waste depicted three distinct characteristic stages. It was observed that the water contents that corresponded to the two cut-off points of the three stages were residual water content and water content at the inflection point, respectively. The air permeability coefficient of municipal solid waste decreased with the increase of the water content from zero to the residual water content. The air permeability coefficient was almost invariable when the water content increased from residual water content to the water content at the inflection point. When the water content of municipal solid waste exceeded the water content at the inflection point, the air permeability coefficient sharply decreased with the increase of water content.

Durability Assessment of Blended Concrete by Air Permeability

Assessment of concrete cover quality is necessary for proper maintenance of concrete structures. Concrete durability is evaluated primarily based on chloride penetrability, neutralization and other external factors. The present study attempts to analyze concrete quality and its mass transfer resistance performance by measuring the air permeability and its relation with concrete durability indicators like chloride diffusion and neutralization. The applicability of air permeability as a durability indicator is validated using concrete with different materials, parameters and curing conditions. The tests are conducted on laboratory prepared concrete as well as for concrete exposed to actual marine conditions. From the experimental results, it is found that air permeability coefficient, neutralization coefficient and chloride ion diffusion coefficient have high correlation. It is suggested that air permeability could be considered as an alternative to estimate mass transfer resistance of concrete and as a concrete durability indicator.

Air Permeability of Renovation Plasters Evaluated with Torrent’s Method

The aim of research was to determine the air permeability of the renovation plasters, using Torrent’s method. The scope of this research included three renovation plaster systems. Each of them was applied on experimental, masonry element and had a different rendering coat. Permeability measurements were performed after 28 days of curing in a natural state. In order to calculate the coefficient of air permeability (kT), the partial data was registered during the measurements. The test results indicate the possibility of determination the coefficient of air permeability kT in relation to the renovation plasters. At the same time results confirm the high porosity of the renovation plasters.

Effects of wetting-drying cycles on the air permeability of compacted Téguline clay

Due to their low permeability and self-sealing ability, compacted clays are often considered as barrier materials in waste disposal. In most disposal cases these materials are exposed to atmosphere and thus subjected to wetting-drying cycles. As a result, their microstructures might significantly change and sometimes cracks can occur, giving rise to changes in hydro-mechanical properties. It is expected that this microstructure change can be evidenced through changes in air permeability since any growth of micro-cracks can greatly affect the air permeability. In this study, the air permeability evolution of Téguline clay compacted at 12.7% and 16.0% water content during wetting-drying was investigated. The results show that the final water content, void ratio and degree of saturation decreased with the increase of wetting-drying cycles. Cracks occurred in the radial direction on the sample surface rather than in the axial direction after 4–5 wetting-drying cycles. The coefficient of air permeability of the compacted samples is larger than those of the samples subjected to wetting-drying cycles. It also appears that the coefficient of air permeability increases with wetting-drying cycles and the initial water content has insignificant effects on the wetting-drying behaviour and air permeability characteristics. Furthermore, the coefficient of air permeability in the axial direction is larger than the one in the radial direction after the initial 2 wetting-drying cycles, suggesting an anisotropic behaviour with larger shrinkage in the axial direction. These findings show clearly that the effects of wetting-drying cycles on soil microstructure can be effectively investigated through air permeability measurements.

Semi-analytical solutions to one-dimensional consolidation for unsaturated soils with semi-permeable drainage boundary

The semi-analytical solutions to Fredlund and Hasan’s one-dimensional (1D) consolidation for unsaturated soils with a semi-permeable drainage boundary are presented. Two variables are introduced to transform the two coupled governing equations of pore-water and pore-air pressures into an equivalent set of partial differential equations (PDFs), which are easily solved by the Laplace transform method. Then, the pore-water pressure, pore-air pressure, and soil settlement are obtained in the Laplace domain. The Crump method is adopted to perform the inverse Laplace transform in order to obtain the semi-analytical solutions in the time domain. It is shown that the proposed solutions are more applicable to various types of boundary conditions and agree well with the existing solutions from the literature. Several numerical examples are provided to investigate the consolidation behavior of an unsaturated single-layer soil with single, double, mixed, and semi-permeable drainage boundaries. The changes in the pore-air and pore-water pressures and the soil settlement with the time factor at different values of the semi-permeable drainage boundary parameters are illustrated. In addition, parametric studies are con- ducted on the pore-air and pore-water pressures at different ratios (the air permeability coefficient to the water permeability coefficient) and depths.

Effect of styrene–butadiene rubber latex on the properties of modified porous cement-stabilised aggregate

As road base materials, porous cement-stabilised aggregates (PCSA) can reduce the erosion damage caused by the water inside pavement structure. However, due to the reduced deformation resistance and anti-cracking ability associated with the high porosity, the application of PCSA has been held back. A laboratory experiment was conducted in this study to improve the cracking properties of PCSA through the incorporation of the styrene–butadiene rubber (SBR) latex. The effects of the SBR latex usage on permeability, compressive strength, flexural strength and anti-freezing ability (AFA) of PCSA were investigated. In addition, the modification mechanisms of the SBR latex on the PCSA properties were analysed. Test results indicated that the air voids and permeability coefficient decreased with the increase in the SBR latex dosages. The flexural strength and AFA were improved when the SBR latex dosages are between 10% and 15%. 7 d compressive strength has a slight decrease, while the 28 d compressive strength is increased. The significant increase in flexural strength and AFA can be attributed to the interpenetrating matrices formation, stretching effect as well as flexibility enhancement after adding the SBR latex.

Study on infrared differential thermal non-destructive testing technology of the permeability of hot mix asphalt pavements

In order to non-destructive test (NDT) the permeability coefficient of hot mix asphalt (HMA) pavements fast, A methodology for assessing the permeability coefficient was proposed by infrared differential thermal testing of pavement after rain. The relationship between permeability coefficient and air voids of HMA specimen deter-mined. Finite element method (FEM) models were built to calculate the surface temperature difference with different exposure time after precipitation. Simulated solar radiation source and fully saturated plate specimens were set in laboratory, tests verify that the different exposure time the specimen surface temperature difference. Infrared differential thermal detection permeable pavement hardware and corresponding software developed. Based on many test results, the evaluation index and criteria of permeability coefficient of HMA pavements tested by infrared differential thermal were developed. The results showed that: There is correlation between air voids and permeability coefficient of HMA specimen. Permeability coefficient of HMA pavements can be determined by different surface temperature at different exposure time. 9:00 am - 14:00 pm is the best time to detect permeability coefficient by infrared differential thermal NDT. Permeable asphalt pavement permeability can be achieved by infrared detector quickly and continuously, a lane testing; Per the permeable assessment criteria, in-place pavements permeability coefficients can be accurately evaluated.

Experimental Determination of the Longitudinal Component of the Coefficient of Air Permeability of Textile Materials

A technique of calculating the air permeability of a packet of textile materials is proposed. A plant for use in the investigation of the longitudinal component of the coefficient of air permeability for experimental verification of the component is developed.

Influence of combined carbonation and chloride ingress regimes on rate of ingress and redistribution of chlorides in concretes

In majority of exposure environments for concrete structures, there is a high probability of the cyclic occurence of both chloride ingress and carbonation. This paper reports a detailed investigation on the influence of carbonation on both the ingress and distribution of chlorides in three different types of concretes, by comparing results from exposure to chlorides, chlorides before carbonation and chlorides after carbonation. Concretes studied were of 0.55 water-binder ratio with 100% Portland Cement (PC), 70% PC+30% pulverized fuel ash (PFA) and 85% PC+10% PFA+5% microsilica (MS) as binders. Chloride profiles were compared to assess the effects of all variables studied in this research. The effect of carbonation was quantified by measuring the consumption of hydroxyl ions (OH−), air permeability and chloride migration coefficient. The results indicated that carbonation of concrete increases chloride transport, but the precise nature of this is dependent on the combined regime as well as the type of binder. In general, it was found that carbonation of chloride contaminated concretes results in a decrease of their chloride binding capacity, that is it releases the bound Cl− in concretes and pushes chlorides inwards, as has been established previously by other researchers. However, it is established in this research that the combined regimes detrimentally affect the service life of concrete structures, particularly when chloride induced corrosion is a concern.

Ceramic microfiltration membranes based on natural silica

The physicochemical features of preparation of macroporous ceramics and multilayer ceramic materials based on natural silica—quartz sand—from the Republic of Belarus, Qatar, Saudi Arabia, Mongolia, Azerbaijan, Turkmenistan, and Vietnam have been studied. It has been shown that the properties and structure of macroporous ceramic substrates are mostly determined by the phase composition of the natural sand and its quartz content. Membrane layers on the macroporous ceramic surface have been formed by the deposition of a suspension of fine natural silica in an aqueous solution of an aluminosilicate binder. The resulting microfiltration membranes with an average pore size of 3–5 μm, an air permeability coefficient of 10–12–10–13 m2, a water permeability of 10–50 m3/(m2 h bar), and a tensile strength of up to 10 bar are promising for wide practical use in the microfiltration of liquid media.

VERIFICATION OF MECHANISM ON IMPROVEMENT OF DRYING SHRINKAGE OR AIR PERMEABILITY ON CONCRETE USING BLAST FURNACE SLAG SAND BASED ON PORE STRUCTURE

In this study, the differences in the pore structures densified by the blast furnace slag (BFS) sand and powder were investigated by using the mercury intrusion test and removing the fine particles contained in the sand. By using BFS sand, the pores with a diameter of 400 nm or higher were densified. The characteristics of the transition zone detected in natural sand were not observed with the elemental analysis around the BFS sand. A strong correlation was found between the volume of the pores densified by mercury intrusion method and drying shrinkage and the air permeability coefficient. It was verified that the densification and adhesion strengthening of cement paste and sand by BFS sand improve the drying shrinkage and air permeation resistance. Using BFS sand, concrete infrastructures can be more durable.

各種結合材を用いたコンクリート模擬壁部材の透気性および中性化に関する実験研究

This research examined air-permeability of concrete mock test piece uses various kinds of binding material. The parameter of the experiment was various kinds of binding material, water binding material ratio, and an age of demold. When the water-cement ratio is small and the hydration is slow, the air-permeability is small. Influence of the age of demold was admitted only by the rapid air-permeation speed. The relation between the depth of neutralization and the air-permeability coefficient was able respectively to be shown by Portland cement, Portland blast-furnace slag cement, and Portland fly-ash cement in one line. However, coefficients of determination were smaller than the researches in the past.