In the recent past, there is growing interest to study the two modes of cementing of materials - i.e., conventional cement concrete and geopolymers in the same investigation to bring about their merits and demerits. As a complement to such studies, in this investigation, the analysis and assessment of strength development within the basic framework of Abrams’ Law are examined. It is interesting to note that the generalized Abrams’ Law holds valid both in the case of chemically bonded OPC and thermally bonded geopolymers in the analysis and assessment of strength development for the data generated by independent researchers. The pattern of strength development in conventional concrete and geo-polymers is the same. This is useful in re-proportioning cementitious composites irrespective of the binder.
The objective of this study is to propose a rheological model for a self-compacting concrete (SCC) on a reduced scale in which a mobile (with 4 vanes) rotating at an imposed speed is immersed. This model allows to describe the rheological behaviour of concrete (at full scale) and to acquire its intrinsic parameters, namely the yield stress and the plastic viscosity. The validation of this approach is established first of all from the realization of six self-compacting concretes (at the real scale). The intrinsic rheological parameters given by their reduced concretes confirm their self plasticity by referring to the rheological results obtained with three other rheometers of international references. Indeed, a very good correlation is obtained between the slump flow of these six SCC and the yield stress of their reduced concretes. Moreover, a design of experiments with three variables is used to demonstrate that this approach is suitable for providing a mathematical model of the intrinsic rheological parameters (yield stress and viscosity) of SCC. The results showed that the yield stress is governed by the interactions (paste-superplasticizer) and (paste-aggregate) while the viscosity is exclusively governed by the paste.
In this study, 150 and 200 MPa ultrahigh-strength concrete (UHSC) specimens were mixed with polypropylene and nylon fibers and heated according to the ISO 834 heating curve. The effects of mass loss of each organic fiber on moisture migration and water vapor pressure reduction in concrete were assessed. Spalling was controlled when 0.15 to 0.25 vol% fiber was added to the specimens. The mass loss of the organic fibers effect on the pore network formation in UHSC. The nylon fiber formed pores below melting temperature via drying and allowed for moisture movement, whereas the propylene fiber effectively reduced the vapor pressure because of rapid mass loss above the melting temperature.
Pumping is the most common technique used to transport fresh concrete in construction sites. The large-scale use of concrete all over the world makes the pumping increasingly important. A wide variety of additives and admixtures are incorporated into modern concrete in order for sustainable development. The performance of modern concrete is rather complex and its pumping behavior differs significantly from that of conventional concrete, especially in the fresh stage. This paper presents a comprehensive overview on the state of the art of concrete pumping. The models and methods used for characterizing the concrete pumpability and lubrication layer are described. The factors influencing the pumping behavior are discussed. A couple of ultra-high pumping engineering of concrete conducted in China are introduced.