Paste-Reinforcement Bond

The construction of interfacial transition zone aroiuid the reinforcement in concrete is very similar to the aggregate paste interface. This is presumably the consequence of locally occurring higher w/c ratio, promoting dissolution of cement components and crystallization of cement hydration products from the liquid phase. This interfacial transition zone reveals also higher porosity and lower strength than the bulk cement matrix. 

This interfacial transition zone is enriched with portlandite crystals of hexagonal shape, with the c axis perpendicular to the surface of aggregate [49]. This layer is not continuous and there are in the formed pockets the C-S-H particles, surrounding sometimes the portlandite crystals [50, 51], as well as the ettringite is present too [52]. In Fig. 6.9 the construction of paste—reinforcement interface is shown [50]. The three zones can be noticed  

The thickness of interfadal transition zone is determined by the range of oriented portlandite crystals and equals 50-100 pm [16]. However, only a 10-20 pm thick layer of this zone shows clearly different mechanical properties, as compared to the bulk cement matrix. The microstmcture of interfacial transition zone is variable and depends on the type and properties of cement and reinforcement, presence of admixtures, concrete maturing regime, as well as the other factors (Fig. 6.19). 

There are no chemical reactions between the reinforcing steel and cement paste however, they can occur in the case of copper, brass and zinc. As a consequence, the bonding forces between the paste and a reinforcement are increasing [49, 53], In Fig. 6.20 the strength of bonds between cement paste and different metals are shown, according to A1 Khalaf and Page [51]. 

The chemical reactions of cement paste with zinc (galvanized steel) result in the release of zinc to the solution and the formation of calcium zincate, CaZn2(OH)g 2H2O, covering the surface of metal [49], Simultaneously, there is no portlandite crystals in this transition zone because in the presence of zinc alite hydration is delayed (see Sect. 4.1.3.2). The coating of hydrated calcium zincate crystals on the surface of metal increases the bonding forces between paste and reinforcement by the roughness formation on its surface. 

---

There is also a shortage of data on the impact of the transition zones both paste-aggregate and paste-reinforcement on concrete properties. The correlation between concrete durability and strength of bond has not been foimd as yet. Mindess et al. [54] propose some methods of paste with aggregate or reinforcement bond strengthening. The silica fume addition can be apphed very easily. 

In the past, many failures occurred cOTiceming mainly side effects due to invasive retrofitting interventions on the MHS ensembles. The current evolution in this field focuses on the development of compatible grouts, fiowable mortars, and repointing mortars for irreversible type consolidation of the mass of the masonry corpus. Besides, steel and other fiber reinforcement bonded on the surface of masonry with materials of polymeric- or cement-based matrix are used as reversible interventions. 

Proper reinforcement of rubber matrix using hllers can be achieved only if there exists adequate adhesion between the hller and the mbber. Rubber-mbber adhesion and rubber-hller adhesion both without and with adhesion promoters have been studied extensively [125-127]. Fiber-matrix adhesion in short fiber-rubber composites is always a field of extensive research. If the fibers are not bonded properly with the rubber matrix, fibers will shde past each other under tension deforming the matrix, thereby reducing the strength properties. In the case of short fiber-reinforced rubber composites, loads are not directly applied to the fibers, but are apphed to the matrix. To obtain a high-performance composite, the load must be effectively transferred to the fibers, which is possible only when the fiber-matrix interphase is sufficiently strong. In addition, the adhesion between the fiber and the matrix should be such that the failure occurs in the matrix rather than at the interphase [92]. 

Fig. 6.20 Strength of cement paste bond with different metal reinforcement, (according to [51]) 1—brass, 2—copper, 3—soft steel, 4— stainless steel...

The steel-paste bond is deteriorated progressively under the repeated cycles of reinforced concrete loatlmg the mechanism of load transfer is destroyed arrd the strength of composite decreases [41]. 

The bonding force of paste with reinforcing steel depends on temperature and decreases at increasing temperature [55]. Reduction of steel-paste bond is clearer in the case of polished steel than of msted or ribbed bars (Fig. 6.21). The steel-paste bond weakening in the case of ribbed bars vs. temperature is equivalent to the decrease of concrete flexural strength. 

The general public s traditional perception of textile factories is that the social standards within these facilities are poor. Events over the past few years with the tragic loss of life due to factory fires or building collapses have reinforced this perception. Beyond the terrible fatalities that have occurred, other social problans associated with the apparel industry include child labor, gender inequality, poor health and safety, exposure to harmful chemical and bonded labor. 

Indirect Contact. Direct contact was more popular in the past, when none of the common construction metals was resistant to chlorine. Typical materials of construction were thermosets (such as a phenolic resin reinforced with asbestos) for vessels and stoneware or glass for piping. This situation changed with improvements in fiber-reinforced plastic fabrication and the commercial advent of titanium. The indirect-contact approach has now become a standard. The typical chlorine cooler today is a single-pass vertical shell-and-tube exchanger with titanium tubes and tube sheets and a carbon steel shell (or perhaps FRF in smaller units). Construction of tube sheets may be of solid titanium, or they may be clad or explosion-bonded with titanium. The inlet channel to the primary cooler also may be of titanium the other channels usually are of FRR... 

Fiber-resin interface (fiber-matrix interface). The surfaces shared by the fibers and the resin in a fiber-reinforced plastic structure. This interface, and the effects of various sizes and chemical treatments on the interfacial bond, are subjects of many past and ongoing studies. Because of the pretreatment of fibers with sizes, the interface has a small but finite thickness. 

Reinforced thermoplastic (RTP) n. A reinforced structure in which the bonding resin is a thermoplastic rather than a thermoset. Over the past two decades, apphcations for RTP have grown rapidly, mainly based on nylons, polycarbonates, acetal resins. 

---