Pozzolanic Index and lime requirement of low calcium fly ashes in high volume fly ash mortar

The major drawback for High Volume Fly Ash Concrete (HVFAC) is low strength development. It is because of the production of less lime by the hydration due to less cement present. However, the exact amount of the lime required for HVFAC system is an unsolved problem so far due to the complexity of hydration and pozzolanic reactions. This paper presents the application of the theory of a logical Pozzolanic Index proposed by Dunstan R Edwin in 2006 for three fly ashes of different chemical and physical properties. Based on the procedure used to find the Strength Activity Index proposed by ASTM C 618, an experimental analysis is conducted on mortar compressive strength, whose results are used to determine the Pozzolanic Index. Thereby calculates the required lime for each replacement of cement with fly ash ranging from 0 to 80% for the three fly ashes. It also concludes that the finer the fly ash the more reactive and consumes more lime at certain age of concrete

Durability of basalt fibers in concrete medium

This study investigates the durability of basalt fiber following immersion in a range of chemical solutions representative of the concrete medium. The tests were conducted over a 62-day period and the solutions were sodium hydroxide, sodium chloride, sodium sulfate and combinations of the three. Weight loss was observed in all alkali solutions, with the worst being the combination of sodium hydroxide with sodium sulfate. The impact of chloride was minimal in the alkaline environment and reduced the impact of the sulfate when both were present. Microstructure analysis using a Scanning Electron Microscope (SEM) found that the silica structure present in basalt fibers was degraded by the OH- from an alkaline medium. The study suggests the need for modification or treatment of basalt fibers before use as fiber reinforcement in concrete

Development of high volume fly ash concrete using ultra-fine fly ash

Given one ton of cement is producing nearly one ton of CO2, there is need to reduce the cement production worldwide to make the concrete sustainable. On the other hand, fly ash (FA) production levels worldwide have increased. Therefore, there is a need to examine the issue of increasing FA levels in concrete. High Volume Fly Ash Concrete (HVFAC), which is defined as the FA replacements above 50 % partly addresses this issue. The replacements can be up to 85%. But, unlike geopolymer concrete with 100% fly ash, HVFAC does not require heat curing which is an advantage over geopolymer concrete to be accepted by the construction industry. This research is aimed to produce high volume high performance fly ash concrete by reducing the drawback of low early strength of HVFAC. To achieve this, few key factors are considered in mix design and investigated studying microstructure of HVFAC. The factors being the w/b ratio, fineness of fly ash added, type of mixing water and dosage of super plasticizer. The experimental results of 50% replacement of cement with ultra-fine fly ash, raw fly ash with tap water and lime water as mixing water are presented in this paper

Design and synthesis of Troger's base ditopic receptors: host–guest interactions, a combined theoretical and experimental study

Two flexible Tröger's base ditopic receptors C4TB and C5TB incorporating monoaza crown ether were designed and synthesized for bisammonium ion complexation. A comprehensive study of host–guest interactions was established by <SUP>1</SUP>H NMR spectroscopy and DFT calculations. Bisammonium chloride (A1) with a shorter alkyl chain spacer showed the highest affinity for the receptors. M06-2X/cc-pVTZ calculations including the solvent effects on host–guest complexes were employed to explain and rationalize the experimental trends. The short N–H⋯O or N–H⋯N hydrogen-bond distances observed in the range of 1.71–1.98 Å indicate the existence of a strong charge assisted hydrogen bonding between the host and the guest. The unusual behaviour (higher binding constant) of A5 in <SUP>1</SUP>H NMR titration is traced to the conformational folding of the guest