Direct electric curing of alkali-activated fly ash concretes: a tool for wider utilization of fly ashes

Abstract

Utilization of the fly ashes is a major problem in many developing countries and in South Africa only about 7% of the fly ash produced annually by coal-fired power stations, has being utilized. Although, fly ashes can be used as an alternative binder in alkali-activated concretes, strength development of these concretes at room temperature is slow limiting application of the material. Direct electric curing is proposed for heat curing of alkali-activated fly ash concrete which will open new opportunities for in-situ applications of these concretes in the construction industry thus increasing the amount of beneficially utilized fly ash. Alkaliactivated fly ash concretes containing unclassified low calcium fly ash, sodium hydroxide and sodium silicate solutions were cured at 60 ºC by means of direct electric curing. The electric resistivity and compressive strength development of the concretes were investigated. The resistivity strongly depends on the type of activator used. Compressive strength up to 33.8 MPa and 48.5 MPa at 2 and 28 days respectively, can be achieved after a short period of 2 direct electric curing. This opens new opportunities for wider application of alkali-activated fly ash concretes and for more extensive utilization of fly ash.

Confined-Direct Electric Curing of NaOH-activated fly ash based brick mixtures under free drainage conditions: Part 1. Factorial experimental design

“…Bakharev (2005) [28] observed that fly ashes activated with NaOH had more stable strength properties at later ages than fly ashes activated with sodium silicate. Previous work revealed that the NaOH present in the alkali activator provided an adequate conductive medium for generating heat in accelerated curing of NaOH-activated fly ash concretes [29].…”

“…The electric current will induce the heating mechanism (Joule heating [29] and taking part in the alkali activation of fly ash [35]. There is a critical range for the conductivity of the alkaline solution in order for Joule heating to be effective.…”

Effect of slag content and activator dosage on the resistance of fly ash geopolymer binders to sulfuric acid attack

“…Fly ash is a by-product from coal combustion, however the demand for fly ash as a construction material is increasing. Nonetheless, there are still many countries where efficient utilisation of fly ash is a major problem with as little as 7% being used effectively [25]. Slag is a by-product of steel manufacture and is produced when blast furnace slag is cooled rapidly in water resulting in glassy granules, these are then ground to form a fine powder [26].…”

Resistance of geopolymer and Portland cement based systems to silage effluent attack

“…In 2014, 70% of the PFA produced in the UK was used in the manufacture of construction materials [21]. Nonetheless there are approximately 114 million tonnes of PFA stockpiled accessibly in the UK [22] and in many countries around the world utilisation of PFA is a major problem with as little as 7% being utilised effectively [23].…”