Concrete Cutting Cutter Southborough MA Mass Massachusetts

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Southborough Massachusetts Concrete Cutting and Core Drilling

The minimum requirements for tensile strength for concrete one inch square in section, shall be within the following limits, and shall show no retrogression in strength within the periods specified: Pads of neat cement about three inches in diameter, one-half inch thick at the center, and tapering to a thin edge, shall be kept in moist air for a period of twenty-four hours. A pat is then kept in air at normal temperature and observed at intervals for at least 28 days. Another pat is kept in water maintained as near 70� F. as practicable, and observed at intervals for at least 28 days. A third pat is exposed in any convenient way in an atmosphere of steam, above boiling water, in a loosely closed vessel, for five hours. These pats, to pass the requirements satisfactorily, shall remain firm and hard, and show no signs of distortion, checking, cracking, or disintegrating. The cement shall not contain more than 1.75 percent of anhydrous sulfuric acid (SO,), and not more than 4 percent of magnesia. There are many varieties of testing machines on the market. Many engineers have constructed "homemade" machines which serve their purpose with sufficient accuracy.

One very common type of machine is illustrated in Fig. 6. B is a reservoir containing shot; which falls through the pipe I, which is closed with a valve at the bottom. The briquette is carefully placed between the dims as turned until the indicators are inline. The hook lever V is moved SQ that a screw worm is engaged with its gear. Then open the automatic valve J so as to allow the shot to run into the cup. By means of a small valve, the flow of shot into the cup may be regulated. Better results will be obtained by allowing the shot to run slowly into the cup. The crank is then turned with just sufficient speed so that the scale beam is held in position until the briquette is broken. Upon the breaking of the briquette, the scale beam falls, and automatically closes the valve J. The weight of the shot in the cup F then indicates, according to some definite ratio, the stress required to break the briquette. Sand is nearly always a constituent part of concrete mortar and concrete. The strength of the masonry is dependent to a considerable extent on the qualities of the sand, and it is therefore important that the desirable and the defective qualities should be understood. The chief object of the sand is economy. If the joints between stones, especially in rubble masonry, were filled with a paste of neat cement, the cost would be excessive, and the increase in the strength of the masonry, if any, would be utterly disproportionate to the great increase in cost. Secondly, the use of sand is a practical necessity in lime concrete mortar, since neat lime will contract and crack very badly when it hardens.

The word "sand" as used above is intended as a generic term to apply to any finely divided material which will not injuriously affect the cement or lime, and which is not subject to disintegration or decay. Sand is almost the only material that is sufficiently cheap, which will fulfill these requirements, although stone screenings (the finest material coming from a stone crusher), powdered slag, and even coal dust have occasionally been used as substitutes. Specifications usually demand that the sand shall be "sharp, clean, and coarse," and such terms have been repeated so often that they are accepted as standard notwithstanding the frequent demonstration that modifications of these terms are not only desirable but also economical. These words also ignore other qualities which should be considered, especially when deciding between two or more different sources of sand supply. Quartz sand is the most durable and unchangeable Sands which consist largely of grains of feldspar, mica, hornblende, etc., which will decompose upon prolonged exposure to the atmosphere, are less desirable than quartz, although, after being made up into the concrete mortar, they are virtually protected against further decomposition. A mixture of coarse and fine grains, with the coarse grains predominating, is found very satisfactory, as it makes a denser and stronger concrete with a less amount of cement than when coarse-grained sand is used with the same proportion of cement. The small grains of sand fill the voids caused by the coarse grains so that there is not so great a volume of voids to be filled. by the cement.