Water retaining structures

The three most important properties of concrete used in calculations for load-bearing applications are the compressive strength, the tensile strength and the modulus. However, for certain applications, e.g. water-retaining structures, the permeability or porosity of the concrete will be a relevant design criterion and this is also considered here. 

In water-retaining structures or basement concrete subject to high hydrostatic pressure, materials of this type are generally not beneficial. However, some dampproofing admixtures do contain water-reducing admixtures and will result in a reduction in permeability under an applied hydrostatic head. In addition, the reduced capillary size and quantity will increase the hydrostatic pressure required to enter the concrete surface (see later). 

Polyurethane sealants have taken a good share in today s sealant market. Polysulphide sealants are in greater use for water-retaining structures, and silicone sealants for structural glazing purposes but polyurethanes have a greater market share as construction sealants. These sealants were first introduced to the construction industry in the early 1970s as two-component materials. 

Lee, T, Rees, T. and Wilford, A. (1992) Polysulfide sealants in water-retaining structures, in Science and Technology of Building Seals, Sealants, Glazing and Waterproofing, ASTM STP 1168, American Society of Testing and Materials, Philadelphia, PA, pp. 47-56. 

Apart from determining surface type, the surface conditions have to be considered when selecting primers. For example, different primers may be required for sealing joints in water-retaining structures where- long-term water resistance is required compared to above ground application although both wiU have a concrete surface. 

Performance of primers has been studied both in general construction and water-retaining structures.Further information may be found in articles on Selection of joint sealants. Sealant joint design, Paint primers and Primers for adhesive bonding. 

The failure of such water retaining structures (the probable maximum dam break) due to hydrological, seismic or other causes, such as a landslide into a reservoir or the deterioration of a dam with time, may cause floods in the site area. 

Water retaining structures may fail as a consequence of causes other than those mentioned in the previous subsections. Examples are ... 

Failure of water retaining structures (hydrological, seismic and from faulty operation) ... 

Cullen, M. N. (2005). Tension membrane water retaining structures. Transactions of the Built Environment, 79, 427 36. 

They are applied on roofs, slabs on ground, basements, water-retaining structures, concrete blocks, and clay bricks. Waterproofing admixtures reduce the permeability of concrete. The dampproofing admixtures impart water repellency and reduce moisture migration by a capillary action. Examples of these admixtures are soaps and fatty acids which react with cement, conventional water reducers, methyl siliconates, etc. 

The DSC results do not give information regarding the relative sizes of the phases or the physical blend structure. This information can only be inferred from the mass loss profiles and the amount of water retained in the pores and interconnecting... 

Shapiro and Weiss concluded from their experiments that the structural water retained after degassing at 150° was entirely present in the form of silanol groups. However, Stober (173) pointed out that the observed ratios of Hj/BjHg near 3 would agree well with the assumption of half a molecule of strongly adsorbed water per silanol group. He formulated the reaction with a Ha/BaHg ratio of 3 ... 

With more than 1,200 power stations, the country generates around 57% (=35,000 GWh per year) of electrical energy from hydro power [15]. These power stations are supported by around 1,400 water intake structures [16] and some 200 reservoirs [17]. These artificial storage basins store a total usable volume of almost 4,000 million cubic meters, and are theoretically capable of temporarily retaining around 7% of annual precipitation. 

The most superficial layer of skin is the stratum comeum (SC), which consists of terminally differentiated keratinocytes (comeocytes) that originate from actively proliferating keratinocytes in lower epidermis (basale, spinosum, and granulosum cells), and contain a lamellar lipid layer secreted from lamellar bodies (Fig. 7a). Flydration of the SC is an important determinant of skin appearance and physical properties, and depends on a number of factors including the external humidity, and its structure, lipid/protein composition, barrier properties, and concentration of water-retaining osmolytes (natural moisturizing factors, NMFs) including free amino acids, ions, and other small solutes. 

Ox ocin is a nonapeptide which is structurally related to vasopressin. It stimulates rhythmic uterine contractions and is widely used by intravenous infusion of a diluted solution to induce labour and to treat postpartum bleeding. In large doses, it may cause relaxation of vascular smooth muscle causing hypotension in patients with cardiac disease or who are dehydrated. It has water-retaining properties and when given for prolonged periods to patients whose intake is electrolyte-free it causes overhydration and hyponatraemia. This may result in convulsions in the newborn with the risk of cerebral damage. 

Uterine contractions and fetal heart rate should be monitored during oxytocin administration (SEDA-13, 1310) (1,2). There is no significant increase in uterine complications or in fetal morbidity or mortality in women with a previous cesarean section, although oxytocin-treated patients had a higher rate of failed trial of labor for reasons that are unclear (3). Oxytocin is structurally similar to vasopressin, and like the latter has water-retaining properties when used in pharmacological doses. 

Water retained after D-drying, known as non-evaporable water, has often been wrongly identified with chemically bound water. It excludes much of the interlayer water in C-S-H, AFm and hydrotalcite-type phases and much of the water contained in the crystal structure of AFt phases. It is often used as a measure of the fraction of the cement that has reacted, but can only be approximate in this respect, because the clinker phases react at different rates and yield products containing different amounts of non-evaporable water. Fully hydrated cement pastes typically contain about 23% of non-evaporable water, referred to the ignited weight. Copeland et al. (C38) determined the non-evaporable water contents of a series of mature cement pastes and carried out regression analyses on the cement composition. For pastes of w/c ratio 0.8 and aged 6.5 years, they obtained the approximate expression ... 

BS 5212 1975 Dutch Standard KIWA C-50 Sealants tor water retaining and excluding structures BS 6920 1988 Intumescent sealants ... 

The idea that liquid water retains much of the structure of ice upon melting is very old. It has been used in numerous ways to explain the peculiar properties... 

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