Aged Concrete

Many studies have been carried out on old concretes to determine the reactions that could be responsible for deterioration. Sarkar, et al.,1 examined a seventy-five year old stone building containing mortar that had shown signs of distress. The presence of g5q)sum (endothermic effect at 133°C), quartz (endothermal peak 573°C), calcium carbonate (endother-mal effect at 900°C), and thamdite (endotherm at 880°C) could be identified. It was concluded that one of the main causes of deterioration was the interaction of SO2 from the atmosphere with mortar and sandstone. In another study,a fifty year old concrete was subjected to examination 

Ramachandran, V. S., Applications of Differential Thermal Analysis in Cement Chemistry, p. 308, Chemical Publication Co., New York (1969) 

Ramachandran, V. S., and Garg, S. P., Differential Thermal Analysis as Applied to Building Science (with an annotated bibliography), p. 182, Central Building Research Institute, India (1959) 

Mackenzie, R. C., (ed.), Differential Thermal Analysis, 2 607, Academic Press, London (1972) 

Advances in Cement Technology, p. 804, Pergamon Press, London (1983) 

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Most latex-modified mortars and concretes have good adhesion to most substrates (tile, stone, brick, steel and aged concrete) compared to conventional mortar and concrete. In general, bond strength in tension and flexure increases with an increase in the polymer-cement ratio,... 

A migrating corrosion inhibitor decreases somewhat the early-age concrete strength, while the ultimate compressive strength seems to be improved. However, in combination with BFS cement, a decrease in the ultimate compressive strength might be obtained. 

Mori, V. Ellingwood, B. 1993. Reliability based service-life assessment of aging concrete stmctures. Journal of Structural Engineering, ASCE,Vol. 119,No5 1600-1621. 

As discussed in the previous chapter, advanced FRP composites have a key role to play in the repair and construction of bridge stmctures. They have been used in the rehabilitation of both ageing concrete and metallic bridge structures. The unique in-service and mechanical properties, viz. durability, high specific stiffness and strength, etc., of advanced FRP composites for the civil infrastructure suggest their suitability for integration in hybrid structural systems as well as the development of all advanced FRP composite structures. 

The reological parameters of concrete materials in the whole history of (concrete mix) - (flesh concrete) - (hardened concrete) - (aged concrete) - (failure) reflect the variation of stage of c-s-f on different levels in the cause of time. This is another important approach to establish the relationship between the c-s-f and mechanical behaviour which could run through from technology of processing and service performance to durability. 

The modulus of elasticity can also influence the adhesion lifetime. Some sealants may harden with age as a result of plasticizer loss or continued cross-linking. As a sealant hardens, the modulus increases and more stress is placed on the substrate—sealant adhesive bond. If modulus forces become too high, the bond may faH adhesively or the substrate may faH cohesively, such as in concrete or asphalt. In either case the result is a faHed joint that wHl leak. 

The specific electrical resistance of concrete can be measured by the method described in Section 3.5. Its value depends on the water/cement value, the type of cement (blast furnace, portland cement), the cement content, additives (flue ash), additional materials (polymers), the moisture content, salt content (chloride), the temperature and the age of the concrete. Comparisons are only meaningful for the... 

The ordn uses for polypropylene are varied. It is used in the fabrication of personnel body armor (Refs 6 7) in slurry-type expls for the demolition of concrete structures (Ref 11) as a microporous hydrazine-air (cathode) separator in fuel cells (Ref 9) as a propint binder matl, particularly in caseless ammo, (Refs 5 8) and as a candidate to act as a proplnt aging inhibitor for the 155mm RAP round (Ref 10) Refs 1) Beil 1, 196, (82), [167], 677 and (725) 2) A.V. Topchiev V.A. Krentsel,... 

Plastic is forever.Whether future archaeologists will find our plastics neatly arranged in dump sites or scattered everywhere across the globe, find them they will. They will still be there long after the wood has rotted, the concrete crumbled and the iron rusted away. This will be known as the Plastic Age". 

Time of setting of concrete mixtures by penetration resistance Change in height at early ages of cylindrical specimens from cementitious mixtures... 

The gas permeability of the constructive materials after treatment by chemicals was examined. Influence of types of concrete, cement and gypsum, preliminary treatment by different chemicals, time between treatments by organic compounds, humidity of constructive materials, time between preparation of chemicals and treatment of materials (aging of chemicals), time between treatment of materials and testing (aging of treated materials) were investigated. 

For calculation of flow in fire main systems, the design engineer should use the Hazen-Williams friction coefficient of C = 100 in the design of bare steel and concrete steel lined pipingforfire water systemsto allow for future deterioration as the system ages. A friction coefficient of C = 140 may be used for plastic pipe, such as fiber reinforced plastic (FRP) or polyvinyl chloride (PVC). 

By the addition of the admixture with a reduction in the water-cement ratio, a concrete having the same workability as the control concrete can be obtained, with unconfined compressive strengths at all ages which exceed those of the control. 

The major physical attributes of concrete as a construction material are a high compressive strength and stiffness, an ability to protect and restrain steel and, most important of all, to retain these properties over a considerable period of time. The effects that water-reducing admixtures have on these properties can be considered from the point of view of design parameters, i.e. those properties of concrete at a relatively early age (usually 28 days) which are used for structural calculations, and longer-term aspects or durability. 

The heat evolution of concrete mixes containing no admixture, 1.5% calcium chloride and 3.0% calcium formate is shown in Fig. 5.18. The heat evolution of calcium chloride and calcium formate are approximately equal at 24 h, which is reflected in similar compressive strengths at this age of 10.0 and 12.5 N mm i. 

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