Fracture properties of geopolymer concrete cured in ambient temperature

Geopolymer concrete (GPC) is a promising alternative of ordinary Portland cement (OPC) concrete. Recent studies indicate potential benefit of heat cured geopolymer concrete in structural applications. This study aimed at the fracture behavior of fly ash based geopolymer concrete cured in ambient temperature. Geopolymer concretes were prepared with mainly fly ash as the binder which was activated by a mixture of sodium hydroxide and sodium silicate solutions. Ground granulated blast furnace slag (GGBFS) was added up to 20% of total binder and amount of alkaline solution was varied to determine the effect on concretes subjected to ambient curing. Notched beam specimens were cast and cured in air at 16-22 oC and 70 ± 10% relative humidity. Three-point bending test was conducted using a closed-loop universal testing machine. The fracture energy values were calculated from the load-deflection curves of the test specimens by using the work of fracture method. The critical stress intensity factors of the specimens were also calculated. The load-deflection curves and the fracture behavior of different geopolymer concretes were compared. Generally, the fracture energy varied with the strength of the concrete. The fracture energy of concrete having slag in addition to fly ash was higher than that having only fly ash. Geopolymer concretes achieved higher fracture energy values as compared to OPC concrete of similar compressive strength

Improvement of Durability and Service Life of Concrete Using Class F Fly Ash

Durability is one of the primary considerations in designing concrete structures, especially when used in aggressive environment. Various supplementary cementitious materials (SCM) can be used to improve durability properties of concrete. However, the degree of improvement is dependent on the type of SCM and the mixture proportions of the concrete. In this study, Class F fly ash sourced from Western Australia was used as 30% and 40% of the total binder. The chloride diffusion properties of concrete containing fly ash were compared with those of control concrete. Fly ash concretes that were designed with adjusted water to binder ratio and total binder content to achieve similar 28-day compressive strength of the control concrete showed less chloride diffusion as compared to the control concrete. Simple deterministic service life estimation technique using the well known Fick’s law was applied to assess the service life of concrete mixes against the corrosion due to chloride diffusion. Early age properties were used along with certain selected parameters to predict the service life of concrete. Fly ash concretes resulted in higher service life than the control concrete when chloride diffusion was considered as the dominant form of attack

Fly ash based geopolymer concrete: A review

Geopolymer binder is an emerging alternative of ordinary Portland cement (OPC) for concrete because of its comparable physical and mechanical properties shown in the recent studies. The current published literature indicates the prospect of geopolymer concrete for structural use. However, the overall performance and functionality under various environmental conditions has not yet been well documented. This paper reviews the works conducted on the fly ash based geopolymer concrete (FGPC) and summarizes its performance as a concrete material. The properties of FGPC are influenced by many factors such as the types and composition of fly ash (aluminosilicate source), final composition of chemical ingredients (alkaline activators), water to solid ratio and curing condition (temperature and relative humidity). Most of the previous studies were based on heat-cured or steam-cured samples. The implications of the current studies were analyzed to identify the critical factors holding back the wide application of FGPC. Further research areas for the improvement of FGPC were identified

Durability of conrete using fly ash as a partial replacement of cement

Utilization of fly ash as a supplementary cementitious material adds sustainability to concrete by reducing the green house gas emission associated with cement production. Fly ash is a by-product of coal fired power stations. The properties of fly ash depend on the type of coal and its burning process. Due to the variation in composition, different fly ash affects the properties of concrete differently. Research data on the performance of concrete containing the Western Australian fly ash is scarce in literature. In this study, mechanical and durability properties of high strength concrete using Class F fly ash from Western Australia were investigated. The ACI 211.4R-08 guidelines were followed to design two series of concretes, each having one control concrete and two fly ash concretes using 30% and 40% fly ash as cement replacement. Fly ash concretes of series A were designed by adjusting the water to binder (w/b) ratio and total binder content to achieve the same strength grade of control concrete. In series B, w/b ratio and total binder content were kept constant in all the three mixtures. Samples were water cured for 7 and 28 days; and were tested at different ages. The mechanical properties were tested by compressive strength, tensile strength and flexural strength test. The investigated durability properties were drying shrinkage, volume of permeable voids, water and air permeability, carbonation and chloride ion penetrability.The 28-day compressive strength of the concrete mixtures varied from 65 to 85 MPa. The fly ash concretes showed lower drying shrinkage than control concrete when designed with adjusted w/b ratio and the total binder content. Inclusion of fly ash reduced sorptivity and water permeability significantly at 28 days. Fly ash showed no adverse affect on air permeability of concrete. Fly ash concretes showed similar carbonation and had less chloride ion penetration as compared to the similar grade control concrete. In general, incorporation of fly ash as partial replacement of cement improved the durability properties of concrete at early age when w/b ratio was adjusted to achieve similar 28-day strength of the control concrete. The durability properties improved with the increase of fly ash content from 30% to 40% of the binder and with the increase of age. Fly ash concretes of series A achieved similar service life of control concrete in carbonation and resulted in higher service life than that of the control concrete, when chloride diffusion was considered as the dominant form of attack

Strength and permeation properties of slag blended fly ash based geopolymer concrete

Geopolymer is a binder that can act as an alternative of Portland cement. Geopolymers use by-product substances such as fly ash, and can help reduce carbon dioxide emission of concrete production. This paper presents the results of a study on the fly ash based geopolymer concrete suitable for curing at ambient temperature. To activate the fly ash, a combination of sodium hydroxide and sodium silicate solutions was used. The setting and hardening of geopolymer concrete were obtained by blending blast furnace slag with fly ash instead of using heat curing. Ground granulated blast furnace slag (GGBFS) was used at the rate of 10% or 20 % of the total binder. The tests conducted include compressive strength, tensile strength, flexure strength, sorptivity and volume of permeable voids (VPV) test. The geopolymer concrete compressive strength at 28 days varied from 27 to 47 MPa. Results indicated that the strength increased and water absorption decreased with the increase of the slag content in the geopolymer concrete. In general, blending of slag with fly ash in geopolymer concrete improved strength and permeation properties when cured in ambient temperature

The effects of ground granulated blast-furnace slag blending with fly ash and activator content on the workability and strength properties of geopolymer concrete cured at ambient temperature

Inclusion of ground granulated blast-furnace slag (GGBFS) with class F fly-ash can have a significant effect on the setting and strength development of geopolymer binders when cured in ambient temperature. This paper evaluates the effect of different proportions of GGBFS and activator content on the workability and strength properties of fly ash based geopolymer concrete. In this study, GGBFS was added as 0%, 10% and 20% of the total binder with variable activator content (40% and 35%) and sodium silicate to sodium hydroxide ratio (1.5–2.5). Significant increase in strength and some decrease in the workability were observed in geopolymer concretes with higher GGBFS and lower sodium silicate to sodium hydroxide ratio in the mixtures. Similar to OPC concrete, development of tensile strength correlated well with the compressive strength of ambient-cured geopolymer concrete. The predictions of tensile strength from compressive strength of ambient-cured geopolymer concrete using the ACI 318 and AS 3600 codes tend to be similar to that for OPC concrete. The predictions are more conservative for heat-cured geopolymer concrete than for ambient-cured geopolymer concrete

Properties of fly ash and slag blended geopolymer concrete cured at ambient temperature

The properties of concrete using fly ash based geopolymer as the binder were shown in recent studies. However, most of the previous studies focused on the properties of geopolymer concrete samples cured at high temperature. In this study, fly ash based geopolymer concrete suitable for curing at ambient temperature was designed and some durability properties were investigated. Geopolymer mixtures were prepared with fly ash as the primary binder which was activated by a mixture of sodium silicate and sodium hydroxide solutions. Ground granulated blast furnace slag (GGBFS) was added as 0%, 10% and 20 % of the total binder. Samples were also cast from an ordinary Portland cement (OPC) concrete mixture in order to compare with the properties of geopolymer and OPC concretes. All the concrete samples were ambient-cured (15-20°C) after casting until tested. The tests conducted include compressive strength, drying shrinkage, sorptivity and volume of permeable voids (VPV) test. The strength of the geopolymer concretes enhanced from the early age and continued to develop in similar trend as OPC concrete. Strength increased with the increase of slag in the mixture. The geopolymer concretes showed drying shrinkage, sorptivity and VPV values comparable to those of the control OPC concrete. In general, the results show that it is possible to design fly ash and slag blended geopolymer concrete suitable for ambient curing with similar or better durability properties of conventional OPC concrete

Immediate induction of labor in premature rupture of membranes at term (PROMT)-vaginal Misoprostol tablet versus PGE2 gel: a randomized comparative study

Background: The aim of the study is to compare immediate induction with vaginal misoprostol tablet and immediate induction with vaginal PGE2 gel in women with premature rupture of membranes at term (PROMT).Methods: Nine hundred thirty-two women with PROM at term were assigned randomly to receive intravaginal 25μg misoprostol tablet, 4 hourly with a maximum of 5 doses or 0.5 mg vaginal PGE2 gel 6 hourly with a maximum of 2 doses. The primary outcome measures were cesarean section rate, admission to delivery interval and induction to delivery interval. Secondary outcomes included, mode of delivery, and maternal and neonatal safety outcome. Results were calculated applying Fisher Exact Test, Chi square test, t test and calculating the P-value using an alpha level of 0.05 for Type I error.Results: The mean time from admission to delivery was 13.16 hours in the misoprostol group and 13.56 hours in the PGE2 group (P= 0.3014). Induction to delivery interval was also comparable between the groups (10.23 h versus 10.18 h).Caesarean section rate did not differ significantly between groups (12.13% versus 15.74% ,P=0.135 RR 0.783 95% CI 0.568-1.079).More women in misoprostol group had instrumental delivery (7.57% versus 4.25%, P=0.031, RR 1.089 95% CI 1.04-3.03).The  neonatal outcomes were comparable between the groups . Maternal outcomes were not significantly different except incidence of analgesic use (P=0.009 RR 1.62 95% CI 1.03-1.30), meconium stained liquor (P=.0096 RR 2.03 CI 1.17-3.53) and   number of digital vaginal examinations (P<.0001) in misoprostol group.Conclusions: Vaginal misoprostol is equally efficacious in labor induction and demonstrates a similar fetal and maternal safety profile to PGE2 gel

Early age properties of low-calcium fly ash geopolymer concrete suitable for ambient curing

Geopolymer is a promising alternative binder to Portland cement. It is produced mostly from by-product materials such as fly ash and blast furnace slag; hence recognised as a low-emission alternative binder for concrete. Recent studies have shown that the properties of geopolymers are similar or superior to those of the OPC binder that is traditionally used for concrete. Most of the previous studies employed heat curing for setting and hardening of fly ash geopolymer mixtures. Heat curing process requires special arrangements which is energy-consuming and may not be feasible to apply in cast-in-situ concreting. Therefore, development of geopolymer mixtures suitable for curing at normal temperature will widen its application. This paper presents a study on low calcium fly ash based geopolymer concrete cured in ambient temperature (23oC) without additional heat. Small amount of additives were added with fly ash to accelerate the early-age reaction. Setting times of geopolymer pastes, and workability and compressive strength of geopolymer mortar were studied. The effects of the additives and binder content in the mixtures were determined from experimental results. The results show that inclusion of additives with fly ash significantly enhanced the early age properties. Setting time reduced to reasonable values and compressive strength increased to enable early de-moulding of specimens. Compressive strength increased with the increase of binder content. However, workability results showed an optimum binder content for the fly ash geopolymer blended with the additives. The results suggest that suitable geopolymer mixtures can be designed for ambient curing with low calcium fly ash and the additives as partial replacement

Drying Shrinkage of slag blended fly ash geopolymer concrete cured at room temperature

Recent studies have shown that blending of ground granulated blast furnace slag (GGBFS) with low-calcium fly ash can have significant effects on the setting and early strength development of geopolymers cured at room temperature. This paper presents the shrinkage behaviour of geopolymer concrete mixtures in which class F fly ash was replaced with 10% or 20% GGBFS and the sodium silicate to sodium hydroxide (SS/SH) ratio was either 1.5 or 2.5. Shrinkage of 4 geopolymer and 1 ordinary Portland cement (OPC) concrete mixtures cured at room temperature were studied. Comparisons are made between the shrinkage behaviours of geopolymer concretes with different mixture proportions and those of the OPC concrete. It was found that shrinkage decreased with the increase of slag content and decrease of SS/SH ratio in geopolymer concrete cured at room temperature. The shrinkage of geopolymer concrete up to the age of 180 days was found to be comparable to that of OPC concrete of similar compressive strength. Thus, shrinkage of geopolymer concrete could be reduced to values within the limit recommended in the Australian Standards for normal OPC concrete