Behavior of Concrete Members Containing Lightweight Synthetic Particles.

摘要

The addition of new innovative polymer spheres in the form of Lightweight Synthetic Particles (LSP) to normal weight concrete leads to reduction of the unit weight of the concrete by 10 to 20 percent resulting in concrete with unit weights ranging between 120 and 130 lb/ft3 [1920 and 2080 kg/m3] depending on the amount of LSP added to the concrete mix. In addition to such reduction in unit weight, the addition of the LSP to the concrete enhances the flowability of fresh concrete for pumping purposes, thus reducing the wear and tear of the equipment, and produces durable concrete for freeze/thaw and deicing exposed conditions. It also reduces the thermal conductivity (increases R-value), thus reducing the energy required for heating and cooling of a building.;The objective of the research presented herein is to evaluate the effect of the LSP on the concrete characteristics. Several studies were undertaken to evaluate the effect of the LSP on the basic material characteristics, including the compressive strength, tensile strength, modulus of elasticity and the stress-strain relationship. Results of the experimental program indicate that increasing the amount of LSP in the concrete mix reduces the ultimate compressive strength of the concrete compared to the control mix without LSP, that reduction is also accompanied by a reduction in the tensile strength and the modulus of elasticity; however, the relationships between these values meet the ACI 318-08 equations using the reduced unit weight. Furthermore, the study included the investigation of the internal cracking mechanism by examining concrete disks under a digital microscope to identify the initiation of the microcracks and their propagation throughout the concrete matrix. Results of the research showed that initiation of the microcracks occurs around the particles prior to propagating through the rest of the matrix.;Time dependent behavior was also investigated in the research program concerning creep and shrinkage characteristics of LSP concrete. The results indicate that the measured creep strains are higher than the predictions using the equations proposed by ACI Committee 209 and the AASHTO LRFD Bridge Design Specifications. On the other hand, the measured shrinkage strains were found to be higher than the predicted values using the ACI 209 Committee Report and lower than those predicted using the AASHTO LRFD.;To evaluate the behavior of structural members made with LSP concrete, 27 large scale beams and slabs were fabricated and tested to study the bond and shear behavior. Load-deflection characteristics and crack patterns were similar to typical behavior of normal weight concrete. The results were compared to several available models for bond and shear, and they indicate that the behavior of LSP concrete can be determined by using ACI 318-08 without the need for the lambda factor usually associated with lightweight concrete.