Concrete Work

For concrete work in cold weather a specially rapid-hardening cement may be made by addition of calcium chloride to the cement. 

Typical uses include the production of non-dispersible underwater concrete and reduction of the accumulation of bleed water in mass concrete placed in deep forms. Consequently, AWAs are useful in mass concrete work because they prevent the formation of laitance on the surface of the concrete and thereby reduce the excessive cleaning between successive lifts. The admixtures also reduce the voids formed under horizontal reinforcing bars. Therefore, bond to steel increases and potential corrosion problems are reduced. The admixtures are also used in conjunction with WRAs in oil-well cementing grouts to reduce pipeline friction and rapid water loss and grouting of pre- and post-tensioned concrete ducts [47]. New valves and control devices under development in Europe and Japan used in conjunction with AWA will likely advance the field on underwater concrete. 

Oligophenylethoxysiloxanes are used as modifiers for various polymers to improve their weather resistance and other technical characteristics, as well as to increase the heat resistance of coatings. E.g., PES-50 is used to modify polyethers, aciylic and epoxy polymers PES-80 is used to modify alkyd and urea-formaldehyde resins. Besides, PES-80 is used as an additive in paints and enamels (to improve their flow properties, gloss and colour), as well as in concrete mixes (to improve the water resistance and durability of concrete works). 

In a study of 1,752 patients considered to have occupational dermatoses, contact dermatitis was the main diagnosis in 1,496 patients (92% women, 83% men). The allergic type, as opposed to the irritant type, was more prevalent in men (73%) than in women (51%). Positive patch tests to chromium (not otherwise specified) occurred in 8% of the women and 29% of the men. Among 280 chromium-sensitized men, 50% were employed in building and concrete work, 17% in metal work, and 12% in tanneries. In the 42 chromium-sensitized women, 20% were in cement work, 19% in metal work, 28% in cleaning, and 15% in laboratory work (Fregert 1975). 

The fineness modulus was developed in an effort to correlate strength of concrete in terms of its component sizes. The fineness modulus is simply the sum of the percentages coarser in a given sieve-analysis divided by 100. In concrete work, fineness modulus is applied to the aggregate and the following Tyler Standard Scale sieves are used 100, 48, 28, 14, 8, 4, and 3/Vin., 3/4-in., and iy2-in. mesh. By using this series of sieves each sieve has a clear width opening double that of the next finest sieve, or one-half that of. the next coarsest sieve. 

Excavation and concrete work in freezing weather can be very expensive and should be avoided. In some instances the construction site may have to be shut down during the winter months. 

Concrete Work Structural Steel Miscellaneous Civil Work... 

Table 19.3 lists the unit hours for the individual operations normally involved in concrete work. These units could be very useful to discuss and negotiate field extras. 

To prevent such leaks in the bottom, the membrane must be continuous down the sides and under the channel pipe. Thus the concrete may be formed to accept the channel pipe, including depressions at the correct locations to accept the bells of the channel pipe, then the membrane applied, and finally the channel pipe installed, making the joints between sections as we fit the sections. By the time all this is done, it is likely that there will have been consumed as much, or even more, labor cost (including some expensive concrete work) than if brick had been laid. 

The scope of the Process Ontology is beyond that of Process Models. Its focus is not only on the support and (semi-)automation of work processes in chemical engineering design, but also on the documentation of concrete work processes and on their analysis and generalization. 

Floating- The next-to-last stage in concrete work, when you smooth off the job and bring water to the surface by using a hand float or bull float. 

The concrete composition and the constituent materials for designed or prescribed concrete are chosen to satisfy the requirements specified for fresh and hardened concrete, taking into account the production process and the intended method of execution of concrete works. A single mix has to be defined that is able to satisfy all the requirements. The procedure used for selection of a concrete mix (type and proportion of cement, water, aggregate, and admixtures) is called the mix design. Several procedures for mix design can be found in the technical literature, which are based on empirical correlations that associate the requirements for concrete to different parameters of its composition, such as the w/c ratio, the water content, etc. [4,10-12]. Some of these parameters are associated with more than one of the requirements. This is the case for the wjc ratio. 

Over the millennia, concrete prepared by the Romans using lime, pozzolana and aggregates has survived the elements, giving proof of its durability. Prestigious concrete works have been handed down to us buildings such as the Pantheon in Rome, whose current structure was completed in 125 A. D. and also structures in marine environments have survived for over two thousand years. This provides a clear demonstration that concrete can be as durable as natural stone, provided that specific causes of degradation, such as acids or sulphates, freeze-thaw cycles, or reactive aggregates, are not present. 

The production of alinite clinker, which has the properties of rapid hardening cement, due to high hydraulic activity of alinite, is, however, linked with two problems. The first one is the HCl emission from the rotary kiln HCl is formed in reaction of chlorine with water vapour, contained in the kiln gases. Nudelman [154] proposed the closed chlorine cycle with the calcittm chloride recovery, in reaction between HCl and CaCOj. However, it wottld complicate seriously the functioning of kiln installation. Another problem relates to the very high chlorine content in alinite clinker and consequently in cement, which will cause the corrosion of reinforcement in concrete. These questions are discussed in Chap. 6. However, the alinite cement can be applied in special cases, in the concreting works at lowered temperature, principally in permafrost area. 

Harvey Slocum was a self-made construction man in the absolute sense of the term. He quit school after the eighth grade to become successively an apprentiee and journeyman carpenter, an ironworker, squad boss on concrete work, and foreman by the time he was 25 years old. Five years later he was eonstruetion superintendant on Lake Hodges Dam, a multiple arch built for the city of San Diego CA. He never left any doubt on his jobs that he was the boss, whieh earned him the affection of his workmen, the fear of his foremen, and the deep respect of his employers. 

Concrete pours and aftercare Can the concrete works be precast and standardised as much as possible to reduce the amount of work undertaken in the exposed environment (Consider impacts on craneage requirements and associated risks) the design be made as simple as possible to avoid complex details/reinforcement fixing in an exposed environment formwork be designed to withstand wave loading reinforcement be deleted to avoid reinforcement fixing requirements ... 

Safety nets are used as protection at rmprotected sides, leading edges, working on the face of formwork or reinforcing steel, overhead or below surface bricklaying, work on roofs, precast concrete work, residential construction, and wall openings. 

Combined influences of endogenous and exogenous factors may lead to the development or to aggravation of hand eczema (Nilsson 1985). Atopic eczema in childhood has been found to be a more important predictive factor for hand eczema than occupational exposure (Meding and Swanbeck 1990). In a population of individuals with atopic dermatitis in childhood, 57% developed sporadic or continuous hand eczema during concrete work (Rystedt 1985). When compared with other occupations, such as the metal industry, cleaning, and even office work, equal prevalences were found. 

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