Nondestructive Evaluation: Structural Performance of Masonry
Masonry is one of the world’s most durable construction materials. Masonry structures can remain in service for hundreds or even thousands of years. Masonry structures often outlive their designers, their original design documents, and their original functions. When historic masonry structures are evaluated for preservation, adaptive use, or additions, there are numerous questions that may arise about the construction and the condition of the brick, stone, concrete block, and mortar. One of the first questions typically asked by the design or investigation team is “How is it performing?” It is important to understand observed distress, such as cracks, corrosion, and surface erosion. Often the cause and/or extent of distress can play a major role in rehabilitation work and in determining what other types of nondestructive evaluation are required. Another common question about masonry is “How strong is it?” In order to conduct a structural evaluation, an engineer must have at least some information about the strength of the masonry. A related question often asked next is “How was it constructed?” Masonry characteristics such as ties, voids, headers, and embedded items are often hidden from view, but these items are critical to understanding how the assembly will perform. Finally, in some cases it is important to ask “What is it doing right now?” It can be vital to understand what types of loads and stresses the masonry is currently experiencing, especially in order predict future performance under new or different loads. Other questions regarding moisture permeability, acoustic properties, or thermal behavior of masonry may also arise. This Practice Point focuses on these fundamental questions by providing a summary of current nondestructive-evaluation tools available for the assessment of historic masonry. While case studies and descriptions of specific nondestructive test methods are fairly common, this article provides an overview of numerous techniques, both listing the technologies available and helping in the selection of an appropriate method. A wide range of evaluation methods are available for use, and many claims are made regarding the accuracy of Practice Points NUMBER 09
Identification of moisture capillarity in masonry using digital impulse radar
The movement of moisture in masonry walls can be particularly problematical, especially in the region of the foundations. Capillary rise can give rise to significant durability problems for the masonry in the structure. In cold climates the action of freeze/thaw cycles in conjunction with capillary rise can result in significant damage. A novel technique of identifying moisture movement in masonry walls using impulse radar is described. Studies have been undertaken on full-scale experimental structures in Milan, Italy. This work illustrates the applicability of digital impulse radar to identifying the zones of fully saturated capillary rise, partially saturated capillary rise and the ‘dry zone’.
Applications of nanocomposite hydrogels for biomedical engineering and environmental protection
Nanocomposite hydrogels are polymeric networks that possess a unique property of hydration. The presence of alcohols, carboxylic acids and amides as hydrophilic moieties in structure of nanocomposite hydrogels enhances their stiffness and water-absorbing capacity. Addition of cross-linker in the synthesis of hydrogels increases their stability under extreme conditions of temperature, pH and pressure. Natural polymer-based nanocomposite hydrogels are biodegradable, highly hydrophilic and possess good mechanical strength. Gelatin, chitin, cellulose, pectin, carrageenan, starch and alginate are natural polymers commonly used to fabricate nanocomposite hydrogels. Nanocomposite hydrogels have special characteristics such as high swelling rate, selectivity and stimuli-sensitive nature. Here we review nanocomposite hydrogels for environmental protection and biomedical engineering. Applications in biomedical engineering include drug delivery agents, wound dressing, tissue engineering and antibacterials. Applications in environmental protection include ion exchangers, adsorption, photocatalysis and soil conditioning. Many nanocomposite hydrogels show excellent adsorption selectivity for heavy metal ions: Cu2+ up to 30.35 mg/g, Pb2+ up to 35.94 mg/g, and Zn2+ and Fe3+ up to 94.34 mg/g. Xanthan gum-based nanocomposite hydrogel has removed 96% dye from industrial effluent as reported. In addition, most of the nanocomposite hydrogels showed better adsorption capacity for pollutants in the pH range from 5 to 7. The nanocomposite hydrogels could also be regenerated and successfully utilized for several times. Nanocomposite hydrogels are therefore good bio-absorbent materials for environmental detoxification.