THE EFFECTS OF MOISTURE ON THE PHYSICAL PROPERTIES OF HARDENED CONCRETE AND MORTAR (TESTING, STRENGTH, ELASTICITY).

摘要

The Strength and Elastic Modulus of concrete and mortar are functions of moisture content and moisture distribution. In essence, "wet" concrete behaves differently than "dry" concrete. This has been recognized (to various degrees) by researchers for many years, but the impact of this moisture dependency has not been recognized in full by the design/construction industry.; The optimum strength of a 6" x 12" concrete cylinder is obtained by removing the cylinder from moist storage at some time prior to the 28th day, and allowing drying to occur prior to test. The modulus of rupture of high strength concrete varies from 8 times the square root of the compressive strength to 16 times, as a result of modifying the moisture conditions at test. The increase in compressive strength with drying is accompanied by a decrease in elastic modulus which significantly alters the relationship between these parameters as a function of moisture condition.; Previous explanations have generally focused on individual causitive factors. The purpose of this research has been to construct a synthesis which allows for the combination of factors. This has been done by analyzing the proposed theories in the light of an experimental program which measured strength and elastic modulus as functions of moisture content and distribution for both mortar and concrete specimens.; It is proposed that the behavioral changes which result from modifications to the moisture conditions are caused by a combination of the following factors: (1) The extent and uniformity of hydration at the time of removal from moist-storage. (2) The stress/strain state imposed by wetting or drying. (3). The physical changes caused by wetting or drying. (4) The effects of moisture gradients in specimens which are not at hygral equilibrium. (5) The moisture dependency of the physico-chemical properties of the internal microstructure.; Applications of this work include a re-examination of "standard" testing procedures, improvement in the correlation between field and laboratory test results, and recognition of the effects of in-service moisture conditions on structural behavior. Properties of concrete can be enhanced by proper moisture conditioning, while construction measures which inadvertently reduce strength and/or elastic modulus may be avoided.