Cambios volumétricos a edad temprana en el hormigón debido a la retracción química del cemento

Unrestrained early age volume changes due to chemical shrinkage in cement pastes, mortars and concretes have been determined. The measurements were performed on sealed and unsealed samples which were stored under water. The chemical shrinkage of unsealed specimens represents the amount of absorbed water due to the chemical reaction of the cement It depends only on the cement content of the sample and does not lead to changes of the external dimensions. However the chemical shrinkage of sealed specimens is connected with a real volume change due to self-desiccation and the effect of internal pressures. The shrinkage depends in this case on the restraining effect of coarse aggregates as well as the cement content. The chemical shrinkage measured on sealed concretes was much higher than the one expected to ocurr on concretes, because normally an equalization of pressure takes place to some extent in the interior of the concrete. The use of expansive additives showed that they may compensate the chemical shrinkage, but its dosage is very sensitive and should be defined exactly for each case particularly.Se han determinado los cambios volumétricos que ocurren en pastas de cemento, morteros y hormigones a edad temprana debido al efecto de la retracción química. Las mediciones se realizaron en probetas selladas y no selladas sumergidas bajo agua. La retracción química en probetas no selladas representa la cantidad de agua absorbida debido a la reacción química del cemento. Depende solamente del contenido de cemento de la probeta y no produce ningún cambio en las dimensiones de la probeta. Por el contrario, la retracción química en probetas selladas está relacionada con un cambio volumétrico real debido al efecto de la autodesecación y presiones internas. La retracción en este caso depende tanto de la restricción que imponen los áridos, como del contenido de cemento. La retracción química medida en hormigones sellados resultó ser mucho mayor que la que se espera ocurra en el hormigón, dado que en el interior del hormigón ocurre, hasta cierto grado, un equilibrio de las presiones desarrolladas. El uso de aditivos expansivos mostró que sí es posible compensar la retracción química, pero su dosificación es muy sensible y debe definirse exactamente para cada caso en particula

Behaviour of slag cement concrete under restraint conditions

Some constructions built with slag cement concrete exhibit cracking at early age due to restrained shrinkage. To determine the slag effect on cracking, this study focuses on the autogenous deformation evolution of concretes characterized by different percentages of slag (0 and 42% of the binder mass) under free and restraint conditions by means of the TSTM device (Temperature Stress Testing Machine). Despite the fast kinetics of its autogenous deformation, the cracking appears later for the slag cement concrete than for the Portland cement concrete. This behaviour is related to the swelling of its cementitious matrix at early age and its large capacity for relaxing the stresses. © 2011 Lavoisier, Paris.SCOPUS: ar.jSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Jahresmitteilungen 1996

SIGLEAvailable from TIB Hannover: RR 1579(1996,1) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Lehrstuhl fuer Baustoffkunde und Werkstoffpruefung und Pruefamt fuer Bituminoese Baustoffe und Kunststoffe der Technischen Universitaet Muenchen. Jahresmitteilungen 1997

SIGLEAvailable from TIB Hannover: RR 1579(1997,1) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman