Ultra-high performance concrete with one-part alkali-activated slag

Abstract One-part (just-add-water) alkali activated binders are of interest due to their ease in practical applications, particularly in on-site works. This paper focuses on a method to develop ultra-high performance one-part alkali activated concrete using particle packing technology. Modified Andreassen particle packing model is employed to optimize the binder and aggregate content that results in a denser matrix. Two different q-parameter values are used in designing the mixes to evaluate its influence in properties like flowability and compressive strength. Lower q-value leads to higher binder content i.e., it moves towards the finer gradation of particles. Mixes with higher fines content show better workability with high flow percentages measured by the spread table (>120% flow). Variation in water-to-binder ratio (0.25–0.35) affects the flow and compressive strength of alkali activated concrete irrespective of q value used in the design. Compressive strengths over 120 MPa is achieved after 28-day curing. The concept of ultra-high performance concrete with particle packing technology is well established by concrete technologists. However, its application in geopolymer concrete, in specific to one-part alkali activated materials is explored for the first time in this work

Direct carbonation of peat-wood fly ash for carbon capture and utilization in construction application

Abstract Carbon dioxide (CO₂) emissions from industrial processes contribute largely to the greenhouse effect and climate change. One of these industries is the cement industry, which contributes around 8% of CO₂ emissions caused by mankind. Two promising and interesting ways to reduce CO₂ emission are the utilization of alternative cementitious materials and carbon capture and utilization through CO₂ mineralization. In this study, peat-wood fly ashes from fluidized bed combustion were used as a construction material for mineral carbonation. A self-hardening characteristic of this type of fly ash was utilized, and simultaneous carbonation and hydration reactions were studied. The study showed that fly ashes from the fluidized bed combustion of peat and wood could be used to capture and mineralize CO₂ during hydration reactions. At the same time, CO₂ could improve the strength of self-hardened fly ashes. One interesting future possibility is fly ash tile production at energy plants: fly ashes can be used to capture CO₂ from flue gases, thus improving the strength of produced tiles

Sustainable batching water options for one-part alkali-activated slag mortar:sea water and reverse osmosis reject water

Abstract Concrete production is globally a major water consumer, and in general, drinking-quality water is mixed in the binder. In the present study, simulated sea water and reverse osmosis reject water were used as batching water for one-part (dry-mix) alkali-activated blast furnace slag mortar. Alkali-activated materials are low-CO₂ alternative binders gaining world-wide acceptance in construction. However, their production requires approximately similar amount of water as regular Portland cement concrete. The results of the present study revealed that the use of saline water did not hinder strength development, increased setting time, and did not affect workability. The salts incorporated in the binder decreased the total porosity of mortar, but they did not form separate phases detectable with X-ray diffraction or scanning electron microscopy. Leaching tests for monolithic materials revealed only minimal leaching. Furthermore, results for crushed mortars (by a standard two-stage leaching test) were within the limits of non-hazardous waste. Thus, the results indicated that high-salinity waters can be used safely in one-part alkali-activated slag to prepare high-strength mortars. Moreover, alkali-activation technology could be used as a novel stabilization/solidification method for reverse osmosis reject waters, which frequently pose disposal problems

New synthetic glass-based supplementary cementitious materials derived from basalt composition

Abstract The cement industry faces an increasing demand for new supplementary cementitious materials (SCMs) as alternative to slags and ashes, the sources of which are in continuous depletion. This study reports on the characteristics of synthetic aluminosilicate glasses derived from basalt composition (BGs) as new SCMs. The pozzolanic activity of the developed glasses as well as their influence on the hydration kinetics, microstructure, and mechanical properties of blended cements are reported. The obtained results show that pastes containing BGs demonstrated faster hydration rate and higher compressive strength compared to those containing commonly applied granulated blast furnace slag (GBFS). In addition, the developed glasses demonstrated higher pozzolanic activity than GBFS as demonstrated form the measured amount of portlandite and strength activity index. The developed glasses can be obtained from earth abundant carbon-free raw materials as it is similar in composition to basalt. Therefore, this novel approach has potential to provide low-carbon cementitious binders for the concrete industry

Durability of ettringite-based composite reinforced with polypropylene fibers under combined chemical and physical attack

Abstract High-performance fiber reinforced cementitious composites from ettringite-based binders require much understanding of durability before its real-life applications in construction industry. A strain-hardening fiber reinforced ettringite-based composite from the hydration between ladle slag and gypsum with polypropylene (PP) fibers was the object in this study. To investigate the durability of the developed composite under aggressive conditions in cold regions (e.g., the Northern Europe), the material was subjected to a combined sodium sulfate-chloride solution along with freeze-thaw cycling process, which represented the marine environment of cold regions. The experimental study reports the vital role of PP fibers in control crack propagation and, hence, greatly enhanced the durability of the composite. In addition, the developed composite attained good mechanical performance with deflection-hardening behavior and multiple crack even after aging processes. Materials, aged in water, was mainly destructed by volume expansion from water uptake in structural pores, while those, cured in Na2SO4NaCl solution, was mainly spoiled by volume increase from both physical and chemical attacks

Strain-hardening ettringite-based composite with polypropylene fiber reinforced ladle slag:durability under combined chloride and sulfate attack

Abstract Ladle slag, an industrial waste from steel manufacturing processes, is an interesting raw material for sustainable inorganic binders. In earlier work, we have developed an ettringite-based binder (LSG) from the hydration between ladle slag and gypsum. In addition, polypropylene (PP) fiber was employed to attain a strain-hardening cementitious composite from LSG. To investigate the durability of PP fiber reinforced LSG, the composite was exposed to a combined chloride and sulfate environment under freeze-thaw cycling. The compressive and flexural behavior of PP fiber reinforced LSG after up to 180 freeze-thaw cycles was experimentally characterized. The experimental results confirm the durability of LSG under Na₂SO₄-NaCl environment. Furthermore, the PP fibers generally enhance the mechanical properties and durability of the reinforced composite. Since there is a lack of study on the durability of ettringite-based binders from industrial wastes under harsh environments, this experimental study reveals the feasibility of using fiber reinforced ettringite-based composite as an alternative construction material

Peat-wood fly ash as cold-region supplementary cementitious material:air content and freeze–thaw resistance of air-entrained mortars

Abstract Fluidized bed combustion fly ash (FBCFA) is a promising industrial side stream to be used as a partial cement replacement material. Untreated and milled FBCFAs from cocombustion of peat and wood were used to replace 20% of portland cement in air-entrained and non-air-entrained mortars. Additionally, equivalent mortars containing fly ash from pulverized coal combustion (CFA) were prepared to compare FBCFAs with more conventional standardized cement replacement material. The study found that both FBCFAs produced mortars with similar compressive strengths compared to a reference, indicating that milling did not affect reactivity of ashes. Air-entrained FBCFA-containing mortars had about the same amount of entrained air compared to the reference mortar. FBCFAs outperformed CFA as a cement replacement material, which produced lower compressive strengths and reduced the amount of entrained air. Non-air-entrained mortar containing CFA suffered severe damage during the freeze–thaw (FT) experiment, unlike non-air-entrained mortars containing untreated or milled FBCFA. The addition of an air-entrainment agent improved FT resistance of all mortars, except those that contained milled FBCFA, which nevertheless had good FT resistance. This first-of-its-kind investigation of the suitability of peat-wood FBCFAs as a supplementary cementitious material in air-entrained mortars suggests a potential use of FBCFAs in cold-region concreting

Effect of green liquor dregs as an alkali source for alkali-activated blast furnace slag mortar

Abstract Sodium-rich green liquor dregs (GLD) are one of the main landfilled residues generated in pulp mills, and to date, no economically profitable ways to utilise GLD has been identified. In this study, GLD have been studied to be used as an alternative alkali source together with alkali-activator, sodium metasilicate (Na₂SiO₃), for blast furnace slag (BFS) mortar. Microsilica was used as an additional silica source to ensure steady Na₂O:SiO₂-ratio (0.16). In purpose to remove the remaining organic carbon and increase the suitability of GLD to be used in alkali-activated materials, it has been first thermally treated in 525 °C. The amount of GLD in the recipes varied from 0 to 45 wt%. Calorimetry measurements showed that increasing the amount of GLD reduced the hydration heat and postponed the reaction. With thermogravimetric analysis, X-ray diffractometry and scanning electron microscopy it was found that hydrated samples with more GLD contained more carbonate phases, which indicated that the reactivity of GLD was lower in comparison with that of other raw materials. Compressive and flexural strength measurements showed that increasing the amount of GLD affected the early strength gain (2 and 7 days) of the samples, but at the age of 29 days, the difference was not as high. The compressive strength of the reference sample at 29 days was 59 MPa, while the compressive strength of four sample recipes containing GLD (up to 36 wt%) was higher than 49 MPa. According to the results, green liquor dregs have potential to be used as a secondary alkali source in alkali-activated materials, but more detailed study should be conducted for the recipe in the future

Partial replacement of Portland-composite cement by fluidized bed combustion fly ash

Abstract Fly ash from fluidized bed combustion differs greatly from that of pulverized coal firing. The most noticeable differences are in morphology, reactivity, and chemical composition. The use of biomass fly ash from fluidized bed combustion as a cement replacement material could be a promising method for both minimizing the amount of landfilled fly ash and reducing CO2 emissions in the concrete and cement industry. In this study, fly ash from fluidized bed combustion of peat and forest industry residue was used as a supplementary cementitious material for portland-composite cement (CEM II) containing clinker, blast furnace slag, and limestone. Even with a 40% cement replacement ratio, the compressive strengths of the mortar samples were still as high as 88% of the control sample’s strength. Comparison with unreactive replacement material revealed that moderate hydraulic properties of the studied fly ash explained the positive effects on strength rather than filler or nucleation effects

Cementitious phase quantification using deep learning

Abstract This study investigates deep learning-based backscattered electron (BSE) image segmentation as a novel approach to automatise phase quantification of cementitious materials and estimate their degree of hydration and porosity. The case study was on Portland cement paste that hydrated from 1 day to 2 years. The initial findings suggest that using arbitrary thresholds for phase segmentation, a strong correlation can be established between the results from BSE image analysis, quantitative XRD, and EDS/BSE, particularly for samples with a hydration age >28 days. The second part demonstrates the success of automated image segmentation that relies on learning the material composition from a meticulously analysed image database, which can then predict the content of numerous other images within seconds. This novel approach can turn the analysis of cementitious materials’ phase composition from a tedious process that requires specialised equipment and expertise into a routine test for quality control