Air Permeability Index Research Articles

Early-Age Index Choosing for Long-Term Quality Evaluation of Concrete Structures

This paper aims to reveal the relationship between typical early-age and long-term properties of concrete structures, in order to select proper early-age indexes to predict or evaluate the long-term performance of concrete structures. Four groups of concrete specimens were prepared in different construction scenarios. Cube compressive strength, air permeability, chloride ion penetration, steel bar corrosion, and porosity of the four groups of concrete specimens were tested at different ages. The test results have confirmed the significant influence of both vibration and curing conditions on concrete qualities. Furthermore, in this study, the 28-day air permeability index has been proved to have good correlation with the tested durability indexes, including the chloride ion diffusion coefficient and corrosion current density of steel bars in concrete. It is recommended in this paper that the 28-day air permeability index, together with the 28-day compressive strength, should be chosen as the early-age property index for long-term quality evaluation or prediction of concrete structures.

Non-formaldehyde, crease-resistant modification of cellulosic material by means of an organotrialkoxysilane and metal alkoxides

Cellulosic material is chemically modified to impart crease-resistant properties to textile products. Due to health considerations formaldehyde-free chemicals are preferred. For this purpose, (3-glycidyloxy)propyltrimethoxysilane (GPTMS) in combination with metal alkoxides aluminium isopropoxide (AIP), titanium tetraisopropoxide (TTP), zircon tetrabutoxide (ZTB) were applied to cotton raw material and cotton fabrics which were pre-treated with butane-1,2,3,4-tetracarboxylic acid (BTCA)/sodium hypophosphite. The as-prepared samples were tested for dry crease recovery angle, tensile strength, tear strength, air permeability, contact angle and whiteness index. The application of GPTMS/AIP resulted in excellent crease resistance values, whereas TTP and ZTB provided a moderate improvement of the wrinkle resistance. The application of the hydrophobic methyltriethoxysilane, octyltriethoxysilane and Dynasylan F8815 (fluoroalkylfunctional water-borne oligosiloxane) caused a significant increase in the contact angle. Fourier-transform-infrared spectroscopy proved the formation of an ester-linkage between BTCA and the cellulose.

Development of functional hybrid cotton fabrics by coating with SiO2and ZrO2/SiO2composites

The silica (SiO2) sol and hybrid zirconia (ZrO2)/SiO2 sol were used to coat cotton fabrics using the pad-dry-cure method to improve their physical and functional properties. The physical properties of coated and uncoated fabrics, such as tensile strength, tear strength, crease recovery angle, air permeability and whiteness index, were tested as per the standard test methods. The wash durability of the coating on the fabric was also analysed after five and 10 wash cycles. The observed results show that the ZrO2/SiO2-coated fabric has better physical properties than SiO2-coated and uncoated fabrics. In addition, an antibacterial activity test confirms that the SiO2-coated fabric possesses higher antibacterial properties against Escherichia coli and Staphylococcus aureus than the ZrO2/SiO2-coated fabrics.

Research on the Correlation between Autoclam Permeability Test and Seepage Height Method

By comparing the permeability test results between the autoclam method introduced by Queens University Belfast and the seepage method specified in China standard, it was found that water permeability index given by autoclam test had a better correlation with seepage value than air permeability index and water absorption index.

Correlation of Elastic Modulus and Permeability in Concrete Subjected to Elevated Temperatures

The laboratory testing of concrete has shown that elevated temperatures cause air permeability index (API) increase and elastic modulus E decrease. Indeed, the API response typically spans several orders of magnitude making it a sensitive indicator of elastic modulus reduction. However, the API versus E data has been historically assumed to be both event and concrete composition specific, thus limiting its applicability for predictive or modeling purposes. In response, a theoretical model is developed here by (1) establishing that the API is equivalent to the Darcy permeability; (2) developing a microcrack flow model accounting for tortuosity, crack density, and microcrack geometry; and (3) interpreting the Giordano and Colombo elastic modulus damage formulas in terms of the corresponding increase in permeability. The resulting general model depends on stress conditions (plane stress versus plane strain) and a single microcrack flow parameter. For materials with small Poisson’s ratios, however, the model becomes independent of stress condition and both equations converge on the same simple solution. The model is verified with both field and laboratory data of concrete response to typical fire elevated temperatures and shown to be comparable in accuracy to previous empirical approaches requiring many more degrees of freedom. Moreover, the data on fire damaged concrete were found to collapse to a single curve suggesting that the microcrack flow parameter is sensitive to elevated temperature but insensitive to concrete composition. The success of the model implies certain limits to microcrack geometry and airflow turbulence in damaged concrete, both of which are discussed.

Changes in Fluid Penetrability and Mechanical Properties of Concrete due to High Temperature Exposure

Abstract This paper examines the relationship between changes in mechanical properties and fluid penetrability of a conventional and a high strength concrete mixture resulting from exposure to temperatures of 150°C, 300°C, or both, using a unique experimental technique. Measurements were taken before and after exposure on 100 mm diameter disks, approximately 25 mm thick. The dynamic modulus of elasticity (Ed) was measured using resonant frequency techniques. Fluid penetrability of the disks was characterized by air permeability index (API) and rate of water absorption (sorptivity). The nondestructive nature of these tests allowed multiple testing on the same samples. The changes in API and Ed of high strength concrete disks were greater than those of conventional strength. Damaged high strength concrete was found to have a lower residual rate of water absorption than damaged conventional strength concrete. However, the rate of water absorption of high strength concrete did not show as large an increase as was found with air permeability. The API identified differences between high strength concrete specimens exposed to both 150°C and 300°C compared to similar specimens exposed to 300°C only. This difference was also identified by changes in Ed, but was not identified using the rate of water absorption. The test methods for API and Ed described in this paper are simple and easy to conduct, and appear to provide useful information in studying changes in microstructure of concrete exposed to elevated temperatures.

Influence of Nano Silica Coating on the Functional Properties of Cotton Fabrics

Coating of nanoparticles on fabrics provides huge potential applications in textile industry. The microencapsulation process is used to encapsulate the nanosilica particles which is used to coat on the surface of fabrics and to observe the special properties such as anti-bacterial, wrinkle resistance, etc. The amorphous nano silica particles were prepared from the natural resources through chemical route. The encapsulated nano silica was prepared using sodium alginate as a wall material by the coacervation method. The prepared sample was coated on the surface of the fabrics by pad-dry-cure method. The anti-bacterial studies were carried out for the nano silica coated and uncoated fabrics and the results would demonstrate the antibacterial effectiveness of treated cotton fabrics. The basic properties like tensile strength, tear strength, air permeability, crease recovery and whiteness index have been analysed for the coated and uncoated fabrics.

Elastic Dynamic Young’s Modulus and Permeability of Concrete in Fire Damaged Structural Members

This article reviews the results of two studies examining the effects of exposure to elevated temperatures on the dynamic elastic (Young’s) modulus (Ed) and air permeability index (API) of concrete. The relationship between Ed and API in fire damaged concrete, and the use of Ed and API to determine both the extent of damage due to exposure to fire and the presence and extent of damage gradients are reviewed. Cores were removed from a precast, prestressed concrete beam containing lightweight aggregate and from a reinforced concrete structural wall containing conventional mineral aggregates. Both of these structures were exposed to intense fires and the laboratory investigation of cores was part of a forensic engineering evaluation to determine the extent of damage to the structure and the necessary repairs prior to returning to service. The Ed and API were determined using 25mm thick disks sawn from the cores. The findings of the study suggest that Ed and API are linearly related for a given set of raw materials until damage is significant and permeability increases nonlinearly when significant damage is sustained for both types of concrete that were evaluated. The findings also suggest that permeability of lightweight aggregate concrete increases more rapidly than conventional mineral aggregate concrete per unit change in Young’s modulus, under exposure to fire. Analyzing Ed and API of concrete disks at 25mm(1in.) depths provided insight into damage gradients and was found to be an effective tool in the assessment of damage gradients. API was found to be particularly sensitive to fire damage.

Assessment of Fire Damage to a Reinforced Concrete Structure during Construction

This article summarizes an engineering evaluation of the extent of fire damage to a concrete structure under construction. The fire occurred in a portion of the reinforced concrete structure and visibly damaged a load bearing exterior foundation wall. The purpose of the assessment was to promptly evaluate the in situ condition of the wall and recommend necessary repair or replacement options prior to commencement of backfilling and the concrete construction to be supported by the subject wall. The engineering assessment of the damaged wall included a nondestructive evaluation phase consisting of ultrasonic pulse velocity testing and a laboratory testing phase on the concrete cores removed from the damaged wall. Dynamic Young’s modulus of elasticity and an air permeability index of 25mm(1in.) thick disks sawed from the cores were determined. Analysis of properties of 25mm(1in.) concrete specimens permitted assessment of the presence and degree of any damage in smaller depth increments compared to the size of a compressive strength core. Significant differences were not indicated by compressive strength of cores, however, the in situ nondestructive testing and laboratory testing of the disks were effective in determining the depth of damage, as a result of the fire. The results of the nondestructive and laboratory evaluation indicated that the distressed zone of the concrete was limited to a near-surface layer. Repair recommendations were based on removal and replacement of the affected concrete sections identified by the testing program.

Comparison of Pulse Velocity and Impact-Echo Findings to Properties of Thin Disks from a Fire Damaged Slab

The engineering assessment of fire damage to a concrete slab provided the opportunity to compare the results of in situ, nondestructive evaluation (NDE) techniques and laboratory testing of specimens taken from cores extracted from the fire damaged slab. This paper discusses and compares results of in situ pulse velocity and impact-echo testing with dynamic elastic modulus and air permeability index test results of 25 mm (1 in.) thick disks sawed from concrete cores removed from selected areas of the damaged slab. Both the NDE techniques and the laboratory testing of thin disks identified the presence of damage as a result of the fire. Analysis of the relatively thin concrete specimens permitted assessment of the presence and degree of damage in thin layers, and provided important and useful data on concrete properties for engineering assessment which was not available from NDE alone. Compressive strength results were consistent with the results of other tests but largely inconclusive by themselves. Impact-echo testing was able to identify the presence of a severely deteriorated concrete layer but could not identify the extent or depth of damage or clearly identify less damaged areas. A distressed layer of concrete was found by subsequent laboratory testing to be limited to a near-surface zone in some areas as suggested by the pulse velocity evaluation, but pulse velocity based analysis resulted in an overestimate of the depth of the damage. The findings highlighted a shortcoming of using conventional strength testing alone on investigations involving relatively thin layers of damage and pointed out several key limitations in the use and interpretation of nondestructive evaluation and associated analysis in a field assessment project.

Nondestructive and Laboratory Evaluation of Damage Gradients in Concrete Structure Exposed to Cryogenic Temperatures

This paper discusses the use of pulse velocity, dynamic Young’s modulus of elasticity, and air permeability of concrete to evaluate the extent of damage and damage gradients to a concrete structure exposed to thermal shock and subsequent cryogenic temperatures. Liquefied natural gas (LNG) is maintained in liquid form at cryogenic temperatures typically below −160°C(−260°F). The elevated concrete pedestal and precast concrete piles supporting a LNG storage tank were exposed to cryogenic temperatures following a leak of the LNG. The engineering assessment of the concrete structure consisted of a nondestructive evaluation phase using ultrasonic pulse velocity and a subsequent laboratory phase based on concrete cores. Dynamic Young’s modulus of elasticity and air permeability index of 25mm(1in.) thick disks sawed from the cores were determined. Analyzing concrete disks at 25mm(1in.) increments permitted assessment of changes in these properties with depth and enabled evaluation of depth of damage and damage gradients. The laboratory study confirmed that the distressed zone was limited to a near-surface area of concrete as suggested by the results of pulse velocity testing.

Evaluation of Fire Damage to a Precast Concrete Structure Nondestructive, Laboratory, and Load Testing

This article discusses the use of nondestructive and laboratory testing techniques and load testing in evaluation of fire damage to precast prestressed concrete members in a parking structure. The in situ evaluation phase consisted of nondestructive testing of concrete using ultrasonic pulse velocity and radiographic exposures to locate tendons prior to the removal of cores. Flexural strength of concrete and dynamic Young's modulus of elasticity and air permeability index of 25 mm (1 in.) thick disks sawed from the cores were determined in the subsequent laboratory testing phase. Analysis of concrete properties at small depth increments permitted assessment of whether a damage gradient was present and the nature of any gradient found, as expressed by changes in these properties. Based on the compromise in material properties indicated by nondestructive and laboratory testing, two affected double-tees were load tested. The deflection pattern observed during load testing confirmed the compromise indicated by the findings of the testing program.

Relationship Between Elastic Modulus and Permeability of Damaged Concrete

The study examined the effects of selected damage mechanisms on the dynamic elastic (Young's) modulus (Ed) and air permeability index (API) of concrete. The relationship between Ed and API in damaged concrete and the use of Ed and API to determine both the extent of damage due to various exposures and the presence and extent of damage gradients are reviewed. The Ed and API were determined by using 25-mm-thick disks sawed from high-strength and conventional- strength concrete cylinders, before and after static fatigue damage; from cores removed from a lightweight, precast, prestressed concrete beam after exposure to intense fire; and from cores removed from an elevated concrete slab after exposure to thermal shock and subsequent cryogenic temperatures. The findings of the study suggested that Ed and API were linearly related for a given set of raw materials until damage was significant, that analyzing concrete disks at 25-mm (1-in.) depths provided insight into damage gradients, and that the durability of high-strength concrete in service may have been better than conventional-strength concrete under similar stress conditions. Ed and API were found to be effective tools in the assessment of damaged concrete and gradients of damage. API was found to be particularly sensitive to fire damage and associated severe drying.