The Experts below are selected from a list of 147 Experts worldwide ranked by ideXlab platform
Franco Zunino - One of the best experts on this subject based on the ideXlab platform.
-
limestone and silica powder replacements for cement early age performance
Cement & Concrete Composites, 2017Co-Authors: Dale P Entz, Chiara F Ferraris, Sco Z Jones, Didie Lootens, Franco ZuninoAbstract:Developing functional concrete mixtures with less ordinary portland cement (OPC) has been one of the key objectives of the 21st century sustainability movement. While the supplies of many alternatives to OPC (such as fly ash or slag) may be limited, those of limestone and silica powders produced by crushing rocks seem virtually endless. The present study examines the chemical and physical influences of these powders on the rheology, hydration, and Setting of cement-based materials via experiments and three-dimensional microstructural modeling. It is shown that both limestone and silica particle surfaces are active templates (sites) for the nucleation and growth of cement hydration products, while the limestone itself is also somewhat soluble, leading to the formation of carboaluminate hydration products. Because the filler particles are incorporated as active members of the percolated backbone that constitutes Initial Setting of a cement-based system, replacements of up to 50 % of the OPC by either of these powders on a volumetric basis have minimal impact on the Initial Setting Time, and even a paste with only 5 % OPC and 95 % limestone powder by volume achieves Initial set within 24 h. While their influence on Setting is similar, the limestone and silica powders produce pastes with quite different rheological properties, when substituted at the same volume level. When proceeding from Setting to later age strength development, one must also consider the dilution of the system due to cement removal, along with the solubility/reactivity of the filler. However, for applications where controlled (prompt) Setting is more critical than developing high strengths, such as mortar tile adhesives, grouts, and renderings, significant levels of these powder replacements for cement can serve as sustainable, functional alternatives to the oft-employed 100 % OPC products.
Arnon Chaipanich - One of the best experts on this subject based on the ideXlab platform.
-
utilization of fly ash with silica fume and properties of portland cement fly ash silica fume concrete
Fuel, 2010Co-Authors: Thanongsak Nochaiya, Watcharapong Wongkeo, Arnon ChaipanichAbstract:Abstract This paper reports the normal consistency, Setting Time, workability and compressive strength results of Portland cement–fly ash–silica fume systems. The results show that water requirement for normal consistency was found to increase with increasing SF content while a decrease in Initial Setting Time was found. Workability, measured in term of slump, was found to decrease with silica fume content (compared to blends without silica fume). However, it must be noted that despite the reduction in the slump values, the workability of Portland cement–fly ash–silica fume concrete in most cases remained higher than that of the Portland cement control concrete. Furthermore, the utilization of silica fume with fly ash was found to increase the compressive strength of concrete at early ages (pre 28 days) up to 145% with the highest strength obtained when silica fume was used at 10 wt%. Moreover, scanning electron micrographs show that utilization of fly ash with silica fume resulted in a much denser microstructure, thereby leading to an increase in compressive strength.
Navid Ranjbar - One of the best experts on this subject based on the ideXlab platform.
-
dissolution mechanism of fly ash to quantify the reactive aluminosilicates in geopolymerisation
Resources Conservation and Recycling, 2019Co-Authors: Carsten Kuenzel, Navid RanjbarAbstract:Abstract Predicting of fly ash (FA) performance in alkali environment is difficult due to its heterogeneous nature. This paper investigates the dissolution process of FA in NaOH-activated geopolymers toward quantification of its reactivity. Dissolution rates were influenced much more by temperature (25–145 °C) and Time (2–24 h) than by NaOH molarity (8–16 M). Higher temperatures increased the kinetic energy of the system, thus increasing the effectiveness of solute molecular bond breakage by solvent molecules and intermolecular attraction. Analysis by FTIR, ICP, XRD and SEM-EDS implies that FA consists of reactive materials, partially reactive materials, and inert materials. The reactive materials dissolve rapidly during geopolymerisation. The partially reactive materials are cenospheres, whose outer vitreous Si shell dissolves gradually, while the inert materials remain un-reacted. To avoid overestimating or underestimating the reactive material content in FA, it is proposed to modify the dissolution method to match the intended curing temperature and to set the dissolution test duration fitting with the Initial Setting Time of the geopolymer paste at the curing temperature of interest. It is not only the quantity of reactive material that is important but also the Si/Al ratio of the reactive material. Consequently, it is recommended that quantification of reactive material be analysed by ICP dissolution rather than EDS analyses of the undissolved material.
K Sisompho - One of the best experts on this subject based on the ideXlab platform.
-
effect of superplasticizers on workability retention and Initial Setting Time of cement pastes
Construction and Building Materials, 2010Co-Authors: Minhong Zhang, K SisomphoAbstract:Abstract This paper presents an experimental study on the effect of a newly developed modified lignosulphonate (PLS) superplasticizer on the loss of workability and Initial Setting Time of cement pastes in comparison to those of polycarboxylate (PCE) and polynaphthalene (PNS) superplasticizers. The workability loss was monitored by yield stress and effective viscosity of the pastes. The Initial Setting was monitored by heat development, change of rheological parameters with Time, and penetration depth in cement pastes. The relations among these methods were discussed. Different dosages of the superplasticizers were used to obtain cement pastes with yield stress
Thanongsak Nochaiya - One of the best experts on this subject based on the ideXlab platform.
-
utilization of fly ash with silica fume and properties of portland cement fly ash silica fume concrete
Fuel, 2010Co-Authors: Thanongsak Nochaiya, Watcharapong Wongkeo, Arnon ChaipanichAbstract:Abstract This paper reports the normal consistency, Setting Time, workability and compressive strength results of Portland cement–fly ash–silica fume systems. The results show that water requirement for normal consistency was found to increase with increasing SF content while a decrease in Initial Setting Time was found. Workability, measured in term of slump, was found to decrease with silica fume content (compared to blends without silica fume). However, it must be noted that despite the reduction in the slump values, the workability of Portland cement–fly ash–silica fume concrete in most cases remained higher than that of the Portland cement control concrete. Furthermore, the utilization of silica fume with fly ash was found to increase the compressive strength of concrete at early ages (pre 28 days) up to 145% with the highest strength obtained when silica fume was used at 10 wt%. Moreover, scanning electron micrographs show that utilization of fly ash with silica fume resulted in a much denser microstructure, thereby leading to an increase in compressive strength.