Every year, substantial amount of waste materials containing toxic substances is produced throughout the world, which causes serious damage to the environment and poses threat to human health. Among available techniques of immobilisation of toxic elements in harmful by-products, geopolymerisation is considered as an effective approach to deal with many environmental issues. Geopolymer binders have long been recognised to have great potential in immobilisation of hazardous wastes due to its advantages over Portland cement based binders. A profound knowledge of how hazardous elements are immobilised by geopolymer binders is necessary for achieving effective waste management strategies. This paper provides some important aspects of geopolymer materials regarding the immobilisation mechanisms and factors influencing the immobilisation efficiency, which are necessary to carry out further research on addressing the hazardous waste immobilisation.
Notion of “activation energy of structure formation” of the cement-concrete compositions has been introduced and substantiated. Methods of its definition have been developed based upon the results of direct electrical resistivity’s measurements in the process of concrete hardening.
Apparent activation energy of structure formation is being defined by common laws of evolution of the structural-moisture state of the hardening cement-concrete compositions.
Excursions of the activation energy of structure formation during hardening strictly correspond to the regularities of concrete strengthening: correlation coefficients of the “Strength – Activation energy” linear dependences for diverse types of concrete are close to 1.
Notions of specific energy and energy efficiency of strengthening during hardening of the cement-concrete composi-tions have been introduced and substantiated.
In this paper results of an experimental investigation on the bearing stiffness (Kf) of Ultra-High Performance Concrete (UHPC) under dowel bars are summarized. The effect of concrete strength, bar diameter, and location of the bar in concrete were investigated. By considering these parameters as input variables, several linear and nonlinear regressions and also Support Vector Regressions (SVRs) by incorporating different kernels are constructed, trained and tested to predict the Kf of UHPC. Comparing the results show that in the regression models, quadratic polynomial is more feasi-ble in predicting the Kf of UHPC than other proposed functions and among the various kernels, SVR with radial basis function (RBF) kernel exhibits better results than other kernels.
This paper reports the analytical and the experimental results of changes in the performance of PVA fiber reinforced concrete (FRC) exposed for 10 years to seawater spray. In this study, the specimens were FRC prisms with a corroded rebar and cracks in some areas, after having been maintained in a saline environment. In addition, a push-out test of the rebar in the specimens was conducted to examine changes in push-out load and crack width at surface in FRC. Furthermore, the salinity analysis, the measurement of initial crack widths, and the measurement of the corrosion amount of the rebar were performed.
As a result of the salinity analysis, it was confirmed that the chloride ion density of the concrete increased to around 9-12 kg/m3 by exposure to a seawater spray environment for 10 years. As a result of the chemical analysis of short fibers, the quality of the fibers in this study had not changed after the exposure.
As a result of the rebar push-out test, it was confirmed that fibers mixed into the concrete suppressed the enlarging of cracks immediately below the rebar. By this bridging effect of fiber, there was a tendency for new cracks to develop. The addition of fibers increased the load at the displacement of 2mm based on the rebar push-out test, and the load was proportional to the remaining tensile strength of FRC.