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

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

Flexural strength and elastic modulus of ambient-cured blended low-calcium fly ash geopolymer concrete

Fly ash geopolymer is an emerging alternative binder with low environmental impact and potential to enhance sustainability of concrete construction. Most previous works examined the properties of fly ash-based geopolymer concrete (GPC) subjected to curing at elevated temperature. To extend the use of GPC in cast-in-situ applications, this paper investigated the properties of blended low-calcium fly ash geopolymer concrete cured in ambient condition. Geopolymer concretes were produced using low-calcium fly ash with a small percentage of additive such as ground granulated blast furnace slag (GGBFS), ordinary Portland cement (OPC) or hydrated lime to enhance early age properties. Samples were cured in room environment (18–23 °C and 70 ± 10% relative humidity) until tested. The results show that, density of hardened GPC mixtures is similar to that of normal-weight OPC concrete. Inclusion of additives enhanced the mechanical strengths significantly as compared to control concrete. For similar compressive strength, flexural strength of ambient cured GPC was higher than that of OPC concrete. Modulus of elasticity of ambient cured GPC tend to be lower than that of OPC concrete of similar grade. Prediction of elastic modulus by Standards and empirical equations for OPC concrete were found not conservative for GPC. Thus, an equation for conservative prediction of elastic modulus of GPC is proposed

Fracture properties of GGBFS-blended fly ash geopolymer concrete cured in ambient temperature

Fracture characteristics are important part of concrete design against brittle failure. Recently, fly ash geopolymer binder is gaining significant interest as a greener alternative to traditional ordinary Portland cement (OPC). Hence it is important to understand the failure behaviour of fly ash based geopolymers for safe design of structures built with such materials. This paper presents the fracture properties of ambient-cured geopolymer concrete (GPC). Notched beam specimens of GPC mixtures based mainly on fly ash and a small percentage of ground granulated blast furnace slag were subjected to three-point bending test to evaluate fracture behaviour. The effect of mixture proportions on the fracture properties were compared with control as well as OPC concrete. The results show that fracture properties are influenced by the mixture compositions. Presence of additional water affected fracture properties adversely. Fracture energy is generally governed by tensile strength which correlates with compressive strength. Critical stress intensity factor varies with the variation of flexural strength. Geopolymer concrete specimens showed similar load–deflection behaviour as OPC concrete specimens. The ambient cured GPC showed relatively more ductility than the previously reported heat cured GPC, which is comparable to the OPC specimens. Fly ash based GPC achieved relatively higher fracture energy and similar values of KIC as compared to those of OPC concrete of similar compressive strength. Thus, fly ash based GPC designed for curing in ambient condition can achieve fracture properties comparable to those of normal OPC concrete

Effect of mixture proportions on the drying shrinkage and permeation properties of high strength concrete containing class F fly ash

Sustainability of concrete can be improved by using large volume of fly ash as a replacement of cement and by ensuring improved durability of concrete. Durability of concrete containing large volume of class F fly ash is dependent on the design of mixture proportions. This paper presents an experimental study on the effect of mixture proportions on the drying shrinkage and permeation properties of high strength concrete containing large volume local class F fly ash. Concrete mixtures were designed with and without adjustments in the water to binder ratio (w/b) and the total binder content to take into account the incorporation of fly ash up to 40% of total binder. Concretes, in which the mixture proportions were adjusted for fly ash inclusion achieved equivalent strength of the control concrete and showed enhanced properties of drying shrinkage, sorptivity, water permeability and chloride penetration as compared to the control concrete. The improvement of durability properties was less significant when no adjustments were made to the w/b ratio and total binder content. The results show the necessity of the adjustments in mixture proportions of concrete to achieve improved durability properties when using class F fly ash as a cement replacement

Value added utilization of by-product electric furnace ferronickel slag as construction materials: A review

This paper reviews the potential use of electric furnace ferronickel slag (FNS) as a fine aggregate and binder in Portland cement and geopolymer concretes. It has been reported that the use of FNS as a fine aggregate can improve the strength and durability properties of concrete. Use of some FNS aggregates containing reactive silica may potentially cause alkali-silica reaction (ASR) in Portland cement concrete. However, the inclusion of supplementary cementitious materials (SCM) such as fly ash and blast furnace slag as partial cement replacement can effectively mitigate the ASR expansion. When finely ground FNS is used with cement, it shows pozzolanic reaction, which is similar to that of other common SCMs such as fly ash. Furthermore, 20% FNS powder blended geopolymer showed greater strength and durability properties as compared to 100% fly ash based geopolymers. The utilization of raw FNS in pavement construction is reported as a useful alternative to natural aggregate. Therefore, the use of by-product FNS in the construction industry will be a valuable step to help conservation of natural resources and add sustainability to infrastructures development. This paper presents a comprehensive review of the available results on the effects of FNS in concrete as aggregate and binder, and provides some recommendations for future research in this field

Microstructural investigation of thermo-mechanically processed lithium slag for geopolymer precursor using various characterization techniques

Lithium slag is an emerging industrial waste due to the increasing demand for lithium rechargeable batteries attributed to the recent boom in the automobile industry and space exploration. It is extracted as a powder residue in sedimentary tanks after the refining process of lithium extraction. In this study, the effect of thermo-mechanical processing on the chemical reactivity of lithium slag is assessed by TESCAN Integrated Mineral Analyzer (TIMA), X-ray Fluorescence (XRF), Rietveld quantitative refinement techniques. The chemical, mineral, and crystallographic phase composition of processed lithium slag specimens were assessed and compared by XRF, TIMA, and Rietveld quantitative refinement techniques, respectively. The results of thermo-mechanical processing indicated that the mineral and crystallographic transformation of Spodumene to feldspars (Anorthite, Muscovite, Albite) occurred by crystallite agglomeration. The chemical reactivity of lithium slag is gauged in terms of amorphous alumino-silicates present in feldspars and unidentified phases. Characterization of unidentified phase is evident that it majorly contains micro-nano sized alumino-silicate rich particles with similar spectral signatures to that of feldspar, some fraction of it is aggregated into other phases due to its reactivity. The concentration of the amorphous phase is proportionate with the thermo-mechanical processing energy. However, the thermo-mechanical processing energy is also optimized based on the generation of amorphous phase and reduction in particle size. Therefore, the G1C700 processed regime resulted in one of the maximum amounts of amorphous phase (52.60%). The mineral phase transformation of Spodumene to Anorthite (+10.46%) and unidentified phase (+8.24%) along with D50 value of 13.26 µm, consequently releasing 0.45 kg of carbon emissions upon thermo-mechanical processing. Hence, G1C700 lithium slag is recommended for its use as a geopolymer precursor

Bond strength of reinforcing steel embedded in fly ash-based geopolymer concrete

Geopolymer concrete (GPC) is an emerging construction material that uses a by-product material such as fly ash as a complete substitute for cement. This paper evaluates the bond strength of fly ash based geopolymer concrete with reinforcing steel. Pull-out test in accordance with the ASTM A944 Standard was carried out on 24 geopolymer concrete and 24 ordinary Portland cement (OPC) concrete beam-end specimens, and the bond strengths of the two types of concrete were compared. The compressive strength of geopolymer concrete varied from 25 to 39 MPa. The other test parameters were concrete cover and bar diameter. The reinforcing steel was 20 mm and 24 mm diameter 500 MPa steel deformed bars. The concrete cover to bar diameter ratio varied from 1.71 to 3.62. Failure occurred with the splitting of concrete in the region bonded with the steel bar, in both geopolymer and OPC concrete specimens. Comparison of the test results shows that geopolymer concrete has higher bond strength than OPC concrete. This is because of the higher splitting tensile strength of geopolymer concrete than of OPC concrete of the same compressive strength. A comparison between the splitting tensile strengths of OPC and geopolymer concrete of compressive strengths ranging from 25 to 89 MPa shows that geopolymer concrete has higher splitting tensile strength than OPC concrete. This suggests that the existing analytical expressions for bond strength of OPC concrete can be conservatively used for calculation of bond strength of geopolymer concrete with reinforcing steel

Thermal properties and residual strength after high temperature exposure of cement mortar using ferronickel slag aggregate

This study evaluates the thermal properties of cement mortar using by-product ferronickel slag (FNS) fine aggregate and its residual strength after high temperature exposure. Compressive strength of mortar increased when FNS was used up to 50% replacement of sand and then reduced with further increase of FNS. Volume of permeable voids (VPV) increased by 4% and 7% respectively for using 50% and 100% FNS fine aggregate. Thermal conductivity of mortar decreased from 2.34 W/m.K for using 100% sand to 1.65 W/m.K and 1.16 W/m.K for 50% and 100% FNS, respectively. Similarly, specific heat increased from 2.18 MJ/m3.K to 2.43 MJ/m3.K for 100% replacement of sand by FNS. These changes of VPV and thermal properties are attributed to the cavity of FNS particles, and their larger size and angular shape. Residual strengths of mortar after exposure to 800 °C were found marginally less for using FNS aggregate. This is attributed to the decrease of thermal conductivity of mortar by FNS. Overall, FNS aggregate showed improved thermal insulating properties and thermal mass of mortar without compromising compressive strength. Therefore, FNS can be considered for use as an energy efficient sustainable building material