Concrete Conduction

Applications. Conduction calorimetry has been widely used for a study ofthe hydration reactions ofvarious cementitious systems. Tricalcium silicate, being the dominant compound in portland cement, determines to a large extent the strength and other properties of concrete. Conduction calorimetric curves of tricalcium silicate and portland cement show five steps during the hydration process (Fig. In the first stage, as soon as... 

Gluconate was found to be a good retarder. Its action is possibly related to its poisoning action on the hydration products of cement. It has also been advocated for controlling slump loss in concrete. Conduction calorimetric curves of cement with gluconate show large hump effects for the hydration of the silicate phase (Fig. 18a). At a dosage of 0.15%, the... 

Residential Construction. Owing to rising energy costs, the cost and low thermal conductivity are of prime importance in wall and ceiling insulation of residential buildings. The combination of insulation efficiency, desirable stmctural properties, ease of appHcation, abiHty to reduce air infiltration, and moisture resistance has led to use of extmded polymeric foam in residential constmction as sheathing, as perimeter and floor insulation under concrete, and as a combined plaster base and insulation for walls. 

Traditional appHcations for latices are adhesives, binders for fibers and particulate matter, protective and decorative coatings (qv), dipped goods, foam, paper coatings, backings for carpet and upholstery, modifiers for bitumens and concrete, and thread and textile modifiers. More recent appHcations include biomedical appHcations as protein immobilizers, visual detectors in immunoassays (qv), as release agents, in electronic appHcations as photoresists for circuit boards, in batteries (qv), conductive paint, copy machines, and as key components in molecular electronic devices. 

The absence of an electron from a covalent bond leaves a hole and the neighboring valence electron can vacate its covalent bond to fill the hole, thereby creating a hole in a new location. The new hole can, in turn, be filled by a valence electron from another covalent bond, and so on. Hence, a mechanism is estabUshed for electrical conduction that involves the motion of valence electrons but not free electrons. Although a hole is a conceptual artifact, it can be described as a concrete physical entity to keep track of the motion of the valence electrons. Because holes and electrons move in opposite directions under the influence of an electric field, a hole has the same magnitude of charge as an electron but is opposite in sign. 

The combination of conductive flooring 7/ia conductive footwear is the preferred method of grounding. Untreated concrete flooring with conductive footwear is usually adequate, but its conductivity should be measured (Fowler and Klein, Static Phenomena and Test Methods for Static Gontrolled Floors, EOS/ESD Symposium Proceedings, pp. 27-38, 1992). Where this method is impractical, personnel grounding devices are available. 

Cable anodes of conducting polymers have an advantage when there are site problems with the installation of other anodes. They are extensively used for the cathodic protection of reinforcing steel in concrete (see Section 19.5.4). 

Nearly all dc railways use the rails to return the operating current. The rails are mounted on wood or concrete sleepers (ties) and have a reasonably good contact with the soil in surface railway installations. The electrolytically conducting soil is... 

Considerable stray currents can, of course, be caused by dc-driven cranes that load and unload ships where the rails act as the return conductor for the current. The rails run parallel to the harbor basin, quay walls of steel-reinforced concrete or steel piling walls. These can take up a large part of the stray current and conduct it further because of their small longitudinal resistance. Noticeable stray current inter-... 

In the first reconstruction [27] of road slabs contaminated with CL, silicon iron anodes were embedded in a layer of coke breeze as shown in Fig. 19-4a or the current connection was achieved with noble metal wires in a conducting mineral bedding material. Slots were ground into the concrete surface for this purpose at spacings of about 0.3 m (see Fig. 19-4b). This system is not suitable for vertical structures. 

There are different concrete replacement systems available for renovating reinforced concrete structures. They range from sprayed concrete without polymer additions to systems containing conducting polymers (PCC-mortar). Since with the latter alkalinity is lower, more rapid carbonization occurs on weathering [59] and the increased electrical resistivity has to be taken into account, so that with cathodic protection only sprayed concrete should be used as a repair mortar. 

The contractors SSAHPs at Sites I and K required that safety and health program inspections be conducted however, these requirements were not effectively implemented at either of these sites. Both Site K contractors required the HSO to conduct daily inspections, and both stated in their written plans that hazards would be immediately corrected. Neither contractor, however, had established hazard abatement procedures to ensure the prompt correction of hazards, and site records for both contractors indicated that hazard abatement activities were either not documented or not completed. For example, the subcontractor s daily safety log contained several notations of safety hazards, including an unstable concrete well and storage of diesel cans near the propane tank however, later log entries and site records did not track the abatement of these hazards. 

Another aspect of epoxy resin mortar floorings which needs careful attention is that their coefficients of thermal expansion are approximately three times that of concrete. This, coupled with the relative low thermal conductivity of epoxy mortar, can cause stresses to be induced at the resin mortar/concrete interface under conditions of thermal shock (e.g. thermal cleaning), resulting in break-up of the flooring due to initial failure in the concrete. Two approaches have been tried to overcome this problem ... 

Schutt reported that the coke breeze specification and conditions in which the mix is prepared are important factors in determining the optimum operation of the conductive cement mix, whilst further details on the coke breeze asphalt mix composition are given by AndersonConductive concrete mixes, with a polymer binder have also been developed as an anode system specifically for reinforced concrete cathodic protection systems . 

Conductive overlay systems are not practical propositions on vertical surfaces or surfaces where weight restrictions are important. However, they are proven cathodic protection systems, and should be considered in conjunction with other reinforced concrete cathodic protection system anodes. 

A conductive polymer electrode has been designed specifically for the cathodic protection of steel reinforcing bars in concrete and is marketed under the trade name Ferex . The anode consists of a 16 AWG stranded copper conductor surrounded by a carbon-loaded polymeric coating similar to that used on the Anodeflex system ) to provide a nominal anode diameter of 8 mm The manufacturer claims that at the maximum recommended current density of 0 08 Am the anode life in concrete will be 32 years with a proportionately longer life at lower current densities. 

These consist of a number of parallel slots cut into the concrete surface. Each slot is then filled with a secondary anode of carbon/graphite fibres embedded in a conductive polymer grout. The current to each of these secondary anode systems is provided by a primary anode of platinised niobium wire placed in slots filled with conductive polymer which acts as the primary anode, these slots intersecting each slot of graphite fibre/conductive polymer at right angles. 

Conductive paints (resins) have recently been used for the cathodic protection of steel reinforcing bars in concrete, but they are always used in conjunction with a primary anode material, e.g. platinised-niobium or platinised-titanium wire or a conductive polymer rod. 

Brown and Fessler have conducted a laboratory evaluation of conductive mastics that can be brushed or sprayed onto the concrete surface to achieve the necessary thickness. However, the most extensive study on conductive paints for cathodic protection purposes has been undertaken by the Federal Highway AuthorityA total of nine commercially available resins were evaluated in this work. It was shown that neither thermal cycling, freeze thawing nor the application of cathodic protection currents... 

The advantages of conductive paints are that they are easy to apply and a concrete overlay is not required. They can be applied to complex shapes and are not a problem where weight restrictions are imposed. 

Any columns passing through coldrooms would be insulated, at least partially, to reduce conduction along the heat bridge and the build-up of condensation and ice. Floors would have a layer of hard concrete on the floor insulation. Ceilings were stuck to a concrete ceiling or fixed to a false timber ceiling. 

For a fully developed fire, conduction commonly overshadows convection and radiation therefore, a limiting approximation is that h hk, which implies Tw T. This result applies to structural and boundary elements that are insulated, or even to concrete structural elements. This boundary condition is conservative in that it gives the maximum possible compartment temperature. 

A fire occurs in a 3 m cubical compartment made of 2 cm thick. Assume steady state heat loss through the concrete whose thermal conductivity is 0.2 W/m2 K. By experiments, it is found that the mass loss rate, m, of the fuel depends on the gas temperature rise, AT, of the compartment upper smoke layer ... 

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