Comparative performance Concrete

The difference between the microstructure of cement paste and concrete should be taken into accoimt when the diffusion conditions are compared. The paste (cement matrix in concrete)— aggregate interfacial transition zone is of special importance. This transition zone is formed of the thin layer of cement paste, about 50 pm wide, which has different microstmcture than the bulk cement matrix in this concrete (see Sect. 6.2). The porosity of this interfacial transition zone is significantly higher the portlandite content is higher as well. In the case of high performance concrete with low w/c ratio the microstructural difference between the interfacial region and the matrix is negligible or none. 

The composition of the pore solution is altered in high-performance concrete as compared with concrete mixes with higher w/c and without added microsilica (Sota et al, 1997). The Ca content is higher and increases with time the concentration is strongly reduced, and the Na concentration is increased. 

The values that characterize pervious concrete should be close to the permeability of soil, which is estimated as between approximately 1.2-10 and 10.5 10 m/s for sandy soils and between 5.2-10 and 3.T10 m/s for loam. To compare, the respective value of permeability of ordinary and high performance concretes is usually in the range of 10 - 10 m/s. 

The influence of fly ash and SF was tested by many researchers, and since the 1990s these microfillers have been considered as necessary constituents of high performance concretes (Malier 1992). As an example, tests carried out according to Spanish standards by Sanchez de Rojas and Frias (1995) gave interesting results, which are shown in Figure 4.2. The total amount of heat of OPC mortar is compared with that liberated by mortars with 30% cement replacement with fly ash and SF. The replacement with fly ash decreased the hydration heat due to its slower pozzolanic activity while that... 

In high performance concrete, dispersed fibres are used frequently because of increased brittleness if compared with ordinary concretes and two aims should be addressed strengthening and increase of fracture toughness, and control of cracks. Various fibres (steel, carbon, synthetic) are used, preferably of small dimensions. 

The increased brittleness of high performance concrete compared to ordinary concretes may have no importance in structural applications. Cracks in concrete elements depend not only on the brittleness of the material and its tensile strength, but mostly on tensile forces induced by loads and by constraints imposed on displacements. The main tensions are supported by adequate reinforcement systems and not by the concrete itself. Also, local tensions in external zones of concrete elements due to shrinkage and high rate of drying, thermal stresses and freeze-thaw cycles are reduced in high... 

The superior resistance to a vari ety of degrad i ng effects was reported by Bonneau etal. [59] for RPC freeze-thaw-durability factor equal or greater than 1 scaling-cumulative mass of scaling residue less than 0.03 kg/m (compared with a maximum of 0.80 kg/m allowed in the standards) chloride permeability (ASTM Cl 202) - less than 10 Coulomb (from a practical point of view this is impermeable concrete a range of 500-1000 Coulomb is considered as high performance concrete). The permeability under load conditions, in which cracks are induced, was evaluated by Charron et ai [60] showing that at strains of up to 0.13% the permeability was as low as that of the matrix. This is an indication of the durability potential of such composites under load. 

Since the 1930s, the TP pipe industry continues to expand its use worldwide. It now represents over 30% of the dollar share compared to other materials (iron/steel at 45%, copper at 12%, concrete at 8%, aluminum at 4%, etc.). Although RP TS pipe represents a small portion of the market, it is a product of choice for many special high performance applications. Corrosion resistance, toughness, and strength contribute to its growing acceptance. 

The concrete block walls of the cell housing the generator tube and associated components are 1.7 meters thick. The facility also includes a Kaman Nuclear dual-axis rotator assembly for simultaneous transfer and irradiation of reference and unknown sample, and a dual Na iodide (Nal) scintillation detector system designed for simultaneous counting of activated samples. Automatic transfer of samples between load station to the rotator assembly in front of the target, and back to the count station, is accomplished pneumatically by means of two 1.2cm (i.d.) polyethylene tubes which loop down at both ends of the system and pass underneath the concrete shielding thru a pipe duct. Total one-way traverse distance for the samples is approx 9 meters. In performing quantitative analysis for a particular element by neutron activation, the usual approach is to compare the count rates of an unknown sample with that of a reference standard of known compn irradiated under identical conditions... 

In 1964, Shell Canada conducted full scale paving trials in Oakville, Ontario and St. Boniface, Manitoba in which the in-service performance of SAS systems were compared with conventional asphaltic concrete using both well graded aggregates and poorly graded sands. The results of these trials are summarized below ... 

A characteristic of single sized sands is their comparatively high air void contents which usually exceed 30 percent. Since sulfur s role in SAS mixtures is to fill these air voids without the aid of mechanical densification, both economic and performance considerations would require analysis of the maximum permissible air void content the mixture may possess and still be relatively impermeable to water without sacrificing structural integrity. Figure 4 [15] shows the relationship between air voids content and permeability for both SAS and asphaltic concretes as determined... 

So far we have considered memory from the point of view of recognition and identification. There is yet another side to memory that is concerned with recall and mental imagery. Here the perfumer is at a natural disadvantage when compared to the artist or musician. Most of us have more or less well developed senses of visual and auditory recall. The ability to see familiar objects in our mind s eye is one that we put to constant use, and the trained artist can reproduce on paper realistic images from memory. Similarly a musician can be trained to know precisely the sound that will be produced from the notes of a musical score, as might be heard in an actual performance. However, the ability to recall smell is usually much less developed. Can we really recall the smell of a rose in the same way that we can recall a color or a melody We may be able to describe the smell and recapture all the associations that go with it, but can we experience a concrete olfactory image of it in our minds ... 

This chapter discusses current research on the use of sulfur in recycled asphaltic concrete pavements. In addition, it describes the results of laboratory tests and theoretical predictions using the latest linear viscoelastic layered pavement analysis methods (15,16) to compare the performance of various sulfur-asphalt concrete pavements with conventional asphalt concrete pavements in a variety of climates. The relationship between pavement distress and performance used in the computer program was established at the AASHTO road test (17). Finally, the results of domestic field tests of sulfur-asphalt pavements are presented along with a discussion of future trends for the utilization of sulfur in the construction of highway pavement materials. 

Much of the remainder of the pool was covered with the SAPER-T tiles. These were comparatively cheap ( 50/sq.ft.) but contributed only 4 to 5 dB ER, as shown in figure 9. These tiles were used in this application primarily as an inexpensive low frequency reverberation reduction coating. (The reduced performance measured for these tiles in this application is a consequence of the unfavorable backing impedance presented by the thick concrete walls and method of attachment which used double stick tape instead of a rigid adhesive bond.)... 

This report contains the results of one study of long-term performance of recycled HMA pavement. The study in question is a 15 year follow-up survey of one of Japan s earlier (1978) full-scale applications of recycled pavement using recycled HMA to pave municipal roads in Nagoya City. In this pavement test, new HMA was applied at the same time so as to compare it with to the recycled pavement. Both the new and recycled pavements are in good condition even to date, and serve as a source of valuable information about pavement durability. We will also report on the results of our investigation of recycled and re-recycled HMA using asphalt concrete lumps collected at a study site. 

Figure 19.29 shows the comparative shielding efficiency data for various materials. Rubber filled with lead oxides comes very close in performance to lead and is superior to concrete and aluminum. Exposure of these shields to radiation causes degradation of mechanical properties (hardness, in particular, is increased) but it does not affect shielding efficiency. 

This report deals with dynamic processes of the deterioration of polymers often used as paints and finishes in housing, and also refers to their influence as the reduction in protective performance on the durability of reinforced concrete. The deterioration processes of polymers by the simiiltaneous action of ultraviolet (UV) light and diffusive oxygen is explained theoretically based upon unsteady state dynamics. The parabolic law (/t" law) is derived for a typical path for the progress of the deterioration of polymers inwards from the surface (l), and compared with some experimental data. The same parabolic law involving a constant term was also derived for the carbonation of concrete, which well explains the retardation effects of finishes on the carbonation (2). 

Recent developments in this field seem to suggest that both epoxy or polyester resins are often times used for similar applications with no apparent difference in the performance of the materials. Ohama and co-workers (15) compared the resistance of polymer concretes to boiling water for periods of up to 12 months and found that epoxy resins were more resistant than orthopthalate based... 

---