Journal of Advanced Concrete Technology最新文献

Although engineered cementitious composites (ECC) exhibit tensile strain hardening and multiple microcracking characteristics, whether the performance of ECC changes obviously under freezing-thawing conditions is important for the design and maintenance of buildings in the areas with freeze-thaw exposure. Results indicates that, as the number of freeze-thawing cycles increase, the PVA fiber/matrix interfacial bonding strength decreases, more fibers can be pulled out, thereby resulting in an increasing deformation on ECC. The results of water capillary absorption, chloride penetration and carbonation on ECC reveal that the frost damage has little effect on ECC. In addition, the steel bar-normal concrete interfacial ultimate bonding strength decreases linearly with the increase in the number of freeze-thawing cycles, the specimen splits failure. However, for the ECC, the steel bar-ECC interfacial ultimate bonding strength decreases with the increase in the number of freeze-thawing cycles, the pull-out failure occurs.

This paper investigates the mechanism of the corrosion pattern of wires on the prestressing forces of prestressed concrete (PC) strands. A rigid frame testing machine combined with an electrically accelerated corrosion device was used to test 16 steel strands. Specimens subjected to the tensile load of 50% of the tensile strength were divided into three groups according to the target corrosion level (mass loss). The rigid frame testing machine can remain the prestressing force, and the force and deformation were measured continuously during the corrosion test. The prestress was degraded in two stages; the beginning and development of the second stage being related to the maximum cross-sectional area loss and fracture type of the wires, respectively. The prestress loss of the strands was the result of the internal force balance after the deterioration of the tensile properties. It was found that the deterioration process of the ultimate tensile capacity related to the fracture type of the wire. The fracture type of PC strand was influenced by the shape and the distribution of the cross-sectional area loss of corroded wires.

Red mud (RM) is a hazardous waste generated by aluminum production. It is difficult to utilize due to its high aluminum and iron oxide contents, high alkalinity, and large specific surface. Still, extensive research is underway to explore its potential as partial replacement for cement in concrete. Due to the differences in the physical, chemical, and mineralogical characteristics of bauxites from different sources, the associated RMs are also different. Some studies have reported that unless calcined, RM produced by the Bayer process has negligible pozzolanicity. However, the appropriate calcination temperature is not unique as it will depend on the RM mineralogical composition. Here, the calcination mineralogical composition nexus and its effect on RM pozzolanicity are investigated in three types of RM produced by Bayer’s process. The RMs were calcined at 600, 800, and 1000°C for 2 hours, and were used as 15 wt.% replacement for Portland cement in mortar mixes. One of the RMs exhibited pozzolanicity without calcination while another showed increased reactivity after calcination at 800°C. The underlying mechanisms are discussed, and it is concluded that no specific calcination temperature(s) can be recommended to activate every RM. Contrary to the findings of previous studies, one of the investigated RMs, used in its virgin form at 15 wt.% replacement for cement, exhibited noticeable pozzolanic activity and achieved over 94% of the compressive strength of the control specimen at 91 days. The calcination of the same RM, irrespective of the calcination temperature, reduced its pozzolanicity.

Capturing atmospheric CO₂ into cement-based materials is a way to set off the CO₂ emissions of concrete production. This study proposes an experimental method to track the origin of cement paste that fixes CO₂ directly from the air under natural conditions. By exposing powders of well-hydrated cement paste to air, carbonated cement paste powders are obtained with different carbonation degrees. The inorganic carbon of these carbonated samples is extracted by dissolution in phosphoric acid, and the isotopic characteristics related to ¹³C and ¹⁴C are measured. The experimental results show that the ¹⁴C value of carbonated cement paste can be used as an indicator for tracing the origin of carbon.

The aging and damage of concrete buildings and structures is a problem in modern society. This is especially true for nuclear power plant buildings, which are required to have high safety standards. In this study, molecular dynamics simulations were performed to obtain mechanical properties for silicate minerals, including quartz, which is used as an aggregate in concrete. We also attempted to clarify phenomena including mechanical fracture. Mechanical properties of each mineral (Young's modulus, Poisson's ratio, and maximum stress) were obtained by performing tensile simulations on 10 silicate minerals which are α-quartz, Orthoclase, Microcline, Albite, Oligoclase, Andesine, Labradorite, Augite, Diopside and Forsterite. Minerals other than α-quartz were highly anisotropic with respect to Young's modulus. The maximum stress was highest for α-quartz, but once a fracture started, the development of large fractures progressed at once and the stress relaxed rapidly. Deformation and fracture of the mineral in response to strain were analyzed by extracting the non-affine component of the local displacement of atoms in tensile simulations. This analysis was able to explain the behavior of the stress-strain curve for each mineral. We also investigated how the composition of a mineral affects its mechanical fracture.

The usage of supplementary cementitious materials often alters the chemical composition of the main binding phase in modern concrete, i.e., C-S-H. The consequent influence on the mechanical properties is not completely clear, due to the lack of study on the inter-particle interaction of C-S-H. Recent papers published by the authors have provided experimental evidence, and in this work, a subsequent numerical study based on discrete element method (DEM) is provided. Models of compacted C-S-H were established with various surface interaction parameters between particles, e.g., surface energy and friction coefficient, and subjected to simulated triaxial load. The results revealed that increased surface energy and friction coefficient enhance the stiffness of C-S-H and densifies its microstructure. The work may inspire methods to design stronger cementitious composite materials.

The purpose of this study is to clarify the bond behavior between rebar and concrete during DEF expansion and pullout testing. The details of the expansion test and the influence of reinforcing bar on DEF expansion have been precisely described in Part I. In Part II, the data related to the bond test is described. The change in bond behavior due to DEF expansion is investigated via the one-end pullout test and the influence of DEF expansion on the bond behavior is discussed. The local bond behavior (slip and bond stress) during the pullout test of the specimens without stirrups is observed to be dramatically changed by DEF expansion. Regarding the specimens with stirrups, failure did not occur during the pullout test and the local bond behavior slightly changed as in the case without stirrups. From the experimental results, a conceptual diagram is proposed to explain the bond behavior during DEF expansion and the pullout test based on the general conceptual understanding of the bond. It can be considered that the direction of local slip and local bond stress during the pullout test is opposite to that during the expansion process. This results in the observed complex local bond behavior during DEF expansion and the pullout test and the effect of stirrups on DEF expansion.