Alkali Activated Fly Ash Concrete Research Articles

Aspects of the deformational behaviour of alkali activated fly ash concrete at elevated temperatures

As a result of tightening of environmental legislation, there is a renewed interest in the technology of alkali activated concrete also known as geopolymer concrete (GPC). Yet, for GPC to assume its own niche in the construction market, it must display equal or better properties at elevated temperatures than Ordinary Portland Cement (OPC) concrete. Currently there is sufficient evidence that GPC has a better resistance to fire; however not all of its behavioural aspects at high temperatures have been investigated. The aim of this research therefore is to investigate its deformational behaviour, in particular the existence or lack of transient creep, which OPC is known to undergo under first time heating when subject to compressive stresses. It was found that not only GPC undergoes transient creep, but also exhibits both expansive and contractive volume changes during heating. It was also found that GPC maintains its structural integrity at 1000°C.

Structural behavior of alkali activated fly ash concrete. Part 2: structural testing and experimental findings

Alkali activated fly ash concrete (AAFAC) is an alternative form of concrete that uses coal fly ash as a 100 % replacement for ordinary portland cement (OPC). In this paper structural testing of nine steel reinforced AAFAC beams is explored. The test matrix included three over-reinforced, three under-reinforced, and three shear critical AAFAC beam samples, all tested in four point monotonic bending. For control purposes, an identical set of OPC concrete (OPCC) beams was fabricated and tested under identical conditions. Data collection during testing included load, deflection, top and side fiber concrete strains, and crack width. Test results show that AAFAC beams have very similar behavior to companion OPCC beams. This applies to load induced crack pattern, crack width magnitude, neutral axis location, flexural stiffness, and ultimate flexural and ultimate shear strengths. The research concludes that AAFAC flexural members can be designed using existing ACI 318-08 methods developed for OPCC, and that this applies to both the service and ultimate limit states.

Material Properties of Structurally Viable Alkali-Activated Fly Ash Concrete

AbstractAs the concern for the environment and need for sustainable construction practices continues to grow, development of portland cement–free binders is gaining wide interest in the concrete research and engineering community responsible for design and construction of civil infrastructure. In this work, microstructural (as determined by quantitative X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy techniques) and material properties of alkali-activated fly ash concrete were evaluated to verify the material’s performance and structural viability. Results show that the heat-cured products of reaction of fly ash in an aqueous alkaline solution form a concrete binder with adequate design properties and promising durability aspects.

Structural behavior of alkali activated fly ash concrete. Part 1: mixture design, material properties and sample fabrication

Alkali Activated Fly Ash Concrete (AAFAC) is an alternative form of concrete that uses fly ash as a 100 % replacement for ordinary portland cement. In producing AAFAC, fly ash is combined with alkali activators that chemically react to form a binder. When combined further with fine and coarse aggregates and often cured at elevated temperature, a concrete material is produced with strength and stiffness properties similar to ordinary portland cement concrete (OPCC). In this paper fabrication of full scale steel reinforced AAFAC beams is presented. The research scope includes: development of an AAFAC mixture design, fabrication of nine AAFAC beam samples, development of an elevated temperature curing system, temperature measurement during curing, and investigation of hardened AAFAC material properties. Results show AAFAC can be manufactured in the same way as OPCC, and that it has a self consolidating consistency in the fresh state. Curing at 60 °C for 24 h produced very rapid strength gain. Compression strengths at 1 day ranged between 47 and 53 MPa, with 28 days compression strengths ranging from 48 to 55 MPa. Material test results show AAFAC is a brittle material with an approximately linear stress–strain response, and an elastic modulus slightly less than that predicted by ACI 318.

FACTORS AFFECTING THE WORKABILITY AND STRENGTH OF ALKALI-ACTIVATED HIGH CALCIUM FLY ASH CONCRETE

The effects of several parameters on the workability and strength of alkali-activated high calcium fly ash (AAHCFA) concrete were investigated in this study. The AAHCFA concretes were activated with alkali sodium hydroxide solution (NaOH), sodium silicate solution (Na2SiO3) and heat. Three alkali liquid to fly ash (L/S) ratios of 0.55, 0.60 and 0.65, three NaOH concentrations of 10, 15 and 20 molars (M) and three Na2SiO3/NaOH ratios of 1.0, 1.5 and 2.0 were used. The workability was obtained by measuring the slump and the compressive strength was tested to gauge the strength of concrete. The results revealed that the workability of AAHCFA concrete was related to the molar ratio of H2O/Na2O in activator, the NaOH concentration, and the L/S ratio. The improvement in compressive strength was mainly related to the increase in the NaOH concentrations. The strength was, however, reduced with the increase in the Na2SiO3/NaOH ratio. The obtained slumps were in the range of 70 to 260 mm and the 28-day compressive strength ranged from 9.0 to 47.5 MPa. The influence of delay time (the time taken from the completion of specimen casting to the start of heat curing), curing temperature and curing duration on compressive strength were also presented.

Propiedades y aplicaciones de los cementos alcalinos

In this paper are presented some of the technologic properties of cementitious material elaborated by alkali activation of aluminosilicates are presented. More specifically it is about the properties of alkali activated fly ash concrete and mortar (without Portland cement). So depending on the type of alkali activator that is used and after a previous thermal curing, the resulting material will show an interesting list of properties and features that includes: high initial mechanical strengths (under flexure and compression), low drying shrinkage, and a very good matrix-steel bonding, as well as an excellent strength to acid attack and an excellent behaviour when is exposed to fire. That is the reason why these new cements, due to their magnificent and durable technologic features as well as its easy adaptability to the existing installations in the precast industry, can be used in a variety of applications, for example: elaboration of railroad cross ties, blocks for building or paving, and so others.

Railway sleepers made of alkali activated fly ash concrete

Actualmente se estima que las vias de ferrocarril a nivel mundial contienen aproximadamente tres billones de durmientes, de los cuales 400 millones son de hormigon. Conjuntamente, sobre el 50% de la demanda mundial por durmientes (estimada en 20 millones anualmente) fue por durmientes de hormigon; ademas, entre el 2% y 5% de los durmientes de hormigon son utilizados en reemplazar elementos danados. La durabilidad del hormigon, sin embargo, depende de muchos factores. En este contexto se debe hacer notar que el proceso de prefabricacion de elementos de hormigon industrial en planta difiere de la fabricacion in-situ, lo que les da a los primeros caracteristicas que los hacen destacar en terminos de durabilidad. En general, se sabe que el proceso de activacion de cenizas volantes permite obtener un material con caracteristicas cementantes similares a aquellas del cemento Portland. En realidad, las cenizas volantes activadas con alcalis es un procedimiento singular en el cual el residuo resultante de la combustion de carbon en plantas termoelectricas es mezclado con disoluciones alcalinas que curadas bajo ciertas temperaturas generan materiales resistentes. A diferencia del hormigon tradicional, este nuevo tipo de hormigon puede alcanzar altas resistencias en un periodo muy corto de tiempo (1 dia) ademas de desarrollar una durabilidad excelente