CROSS-SECTIONAL STRENGTH GRADIENTS IN HIGH-STRENGTH CONCRETE COLUMNS

Vertical variations of strength in a structural element is a well-esta blished phenomenon. In large cross-sections, horizontal strength gradi ents can also occur because of local differences in humidity and tempe rature conditions. When the heat of hydration of concrete is free to d issipate from a cross-section, the temperature variations within a cro ss-section imply not only differing rates of strength development but also a fisk of thermal cracking due to high temperature gradients. A s eries of columns of two cross-sectional dimensions were cast in the la boratory for concrete mixes with 28-day compressive strengths ranging from 40 to 115 MPa. Compressive strength results of vertically drilled cores showed the presence of significant cross-sectional strength gra dients. Three-dimensional core strength distributions were constructed from which effective cross-sectional strengths of unreinforced in-sit u concrete were calculated.