Stronger Concrete BRYANT MATHER, U. S. Army Engineer Waterways Experiment Station, Jackson, Miss. The most frequently encountered difficulty with any particular quantity of concrete is that the test specimens representing it fail to develop a high enough apparent compressive strength. In many cases the concrete rep- resented by the specimens is actually strong enough for its intended use, since the test results are incorrect or the specified strength is in excess of that needed. In other cases the concrete represented is actually not strong enough. There are many factors that affect concrete strength and many ways of making stronger concrete. For example, the practical routine production of portland cement concrete having a compressive strength consistently above 10, 000 psi after 90 days moist-curing can be accomplished by care- ful selection of materials; mixture proportions; and mixing, placing, con- solidating, and curing procedures. The most important single factor in the successful production of strong concrete is the maintenance consistently of an adequately low water-cement ratio. Concrete with a strength of 10, 000 psi cannot be obtained from mixtures having water-cement ratios higher than 0. 45 by weight; and in order to provide adequate workability, it will usually be necessary to use at least 7 bags of cement per cubic yard of mixed concrete. Similar methods to those thatmay be used to make strong concrete stronger may .also be used to make weak concrete stronger. eOUR understanding of compressive strength of concrete would be facilitated if a theory of strength or a theory of failure existed that would adequately deal with this phenome- non. Siess (48) stated in 1958 that the most important need appeared to be for theories based on mechanical models which in turn are based on fundamental knowledge regard- ing the character and properties of the cement paste. He noted that phenomenological theories of failure are not capable of predicting deformation characteristics and sug- gested that the goal should be the development of hypotheses or theories capable of predicting both deformation and failure. Three years later the question of the origin and nature of strength of concrete was again considered. The unsatisfactoriness of theories based on the assumption that con- crete can be considered as ideal, continuous, and isotropic was noted, and considera- tion was directed to those theories based on the assumption that matter consists of particles held at certain spacings by fields of force. It appeared that knowledge of the kinds and numbers of bonds, their strength, and the time and condition of their forma- tion is requisite to an understanding of the nature and origin of strength and the mech- anism of fracture and failure of concrete (30). In the absence of a theoretical backgro\ind, including either an adequate theory of strength or an adequate theory of failure, and also a developed technology for the production and utilization of high-strength concrete, it is necessary to assume both that high-strength concrete may represent simple extrapolation from concretes of normal strength, for which there are abundant data, and that unusually high-strength concrete may involve relations that are other than simple extrapolations. The available data can be interpreted either way. Some of the data suggest that at- tempts to produce unusually high-strength concrete will involve encountering a Paper sponsored by Committee on Mechanical Properties of Concrete and presented at the 46th Annual Meeting.
Stronger Concrete
May 10, 2023
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Related Documents
