Durability improvement, mechanism

Durable concrete is typically characterized by low porosity because the fundamental porosity of concrete influences all of its material properties. For this reason, most of our standard practices for the construction of concrete structures have as their objective the minimization of paste porosity, which consequently increases both strength and durability. Although low water-cement ratio (W/C) is responsible for improved mechanical properties and enhanced durability, attaining a low W/C necessitates either a sacrifice in workability, or the use of high cement content, neither a desirable consequence. A more advantagious alternative is the use of water-reducing admixtures (WRAs). 

Despite improvements in composite durability with certain eement replaeements, little is known as to the mechanism of improved durability. That is, does the eement pore solution play a significant role, or does the permeability of the eomposite Or are durability improvements based on a combination of the two Also, how is eement hydration altered by lowering the pore solution pH These questions must be answered before establishing any criteria or recommendations for improving pulp fiber-eement eomposite durability. 

Fillers affect foams in several ways they induce nucleation of gas bubbles and polymer crystallization, they destabilize liquid foam, they interfere with rate of chemical reactions and gas generation processes, they influence the viscosity of liquid premixes, they improve mechanical properties of foam, and foam durability. Care must be used in the selection of fillers for foams. They are used only sparingly in spite of the potential gains in foam performance which might be expected. 

Several factors are thought to be involved in the mechanism of durability improvement. The objective of this study was to examine compounds which are capable of interacting chemically with the steel surface. In addition, reaction with the epoxide resin is also desirable. The polyfunctional mercaptoester compounds meet both of these requirements in that the mercaptoester moiety provides a means of chelating iron cations and in addition is very reactive towards the epoxide group in the presence of an amine. The polyfunctional nature of this compound enables it to attach to the steel surface at more than one site and provides a group which can chemically attach to the resin. The dramatic improvement in bond durability supports such a hypothesis. 

Highly durable, chemically inert, thermo-stable aromatic polyesters can be produced by interaction of polymers containing links of -oxyben-zoic acid, aromatic dioxy-compounds, for example of hydroquinone and aromatic dicarboxylic acids [40]. Thermo and chemically resistant polyesters of improved mechanical strength can be obtained by the reaction of n-oxybenzoic acid, aromatic dicarboxylic acids, aromatic dioxy-compounds and diaryl carbonates held in solid phase or in high-boiling solvents [41] at temperature 180 °C and lowered pressure, possibly in the presence of catalysts [42], Some characteristics of aromatic polyesters based on n-oxybenzoic acid are gathered in Table 7.1 [20],... 

In this brief review, we have attempted to demonstrate the importance of chemistry to the developments of new (or new forms of) adhesive materials. Much success has been achieved in the syntheses of polymers for aerospace adhesives and sealants. New or modified structural adhesives have been developed with improved mechanical properties and durability. However, there is still room for innovation for developing new adhesive materials for use under severe environments. 

Full impregnation is usually achieved by pressure. The principal reason for full impregnation is to improve the strength and other mechanical properties of concrete. Durability improvement accompanies this. 

Recently, interest was renewed in using PTFE for preparing radiation-grafted PCMs when its radiation resistance was improved by radiation cross-linking at molten temperatures [19-24]. The cross-linked PTFE (RX-PTFE) showed remarkable improvements in radiation resistance, thermal durability, and mechanical properties, compared with those of non—cross-linked PTFE [106-111]. The use of RX-PTFE with its network structure as a base polymer could improve the gas crossover in PEMFC. 

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