This research evaluates the sulfate attack performance of Portland-limestone cements (PLCs) with varying limestone compositions. Specimens prepared by replacing Type I/II and Type V cement with up to 20% limestone powders and fly ash are examined for their sulfate resistance in sodium and magnesium sulfate solutions at 5 degrees C and 23 degrees C by expansion measurements, an accelerated strength test, visual observations, and X-ray diffraction. For the materials tested, higher calcitic limestone contents increased expansion up to 290% with 20% limestone when added to Type I/II cement but decreased expansion up to 48% with 14.6% limestone (calcitic + dolomitic) when added to Type V cement. Strength loss was not proportional to the percentage of limestone added to the cements. Dolomitic limestone improved sulfate resistance as indicated by increased strength development in magnesium sulfate and reduced expansion in both solutions. Ettringite, thaumasite, gypsum, and brucite were the main sulfate attack phases detected at 5 degrees C.

This paper focuses on the investigation of fresh, mechanical, and durability properties of concrete with the influence of fly ash and polypropylene fiber. In this study, cement was partially replaced by 15 % and 30 % fly ash content in weight, whereas polypropylene fiber was incorporated in concrete mixes at 0.06 %, 0.12 %, and 0.18 % by volume. Twelve concrete mix proportions were developed, and slump, density, ball penetration, and compacting factor tests were conducted to examine the fresh concrete properties. Besides, mechanical characteristics, including the uniaxial compressive and splitting tensile strength of concrete, were evaluated at 7, 28, and 90 days. Further tests of concrete durability, including rapid chloride permeability test, sorptivity, and water penetration, were performed at 90 days. The results exhibited that the incorporation of fly ash developed fresh concrete properties, while polypropylene fiber decreased the fresh characteristics of concrete. Furthermore, the combination of fly ash and polypropylene fiber in concrete was substantially attained to improve the mechanical and durability characteristics compared to the control mix. Mix proportion of 15 % fly ash and 0.12 % polypropylene fiber exhibited a pronounced influence on compressive strength, chloride permeability, sorptivity, and water penetration compared to other concrete mixtures.

This study examined the efficacy of waste glass cullet (WGC) as a substitute for natural fine aggregate in alkali-activated composites when exposed to sulfuric acid and hydrochloric acid solutions for 1year. The physical appearance, surface alkalinity, mass, mechanical strength and microstructure of hardened samples before and after immersion in acid solutions were investigated. The findings this work indicated that physical, mechanical and microstructural damage of the specimens due to acid attack increased with an increase in the percentage of WGC. This was attributed to the smooth surface texture and angularity of the WGC, which affected the bond with the damaged paste matrix at the interfacial transition zone and increased the porosity. However, the acid resistance of the mortars containing up to 50% WGC was found to be satisfactory when compared with the mortar without WGC. Therefore, the use of WGC as a partial replacement (up to 50%) for natural sand is feasible for alkali-activated systems under acid exposure.

Supplementary cementitious materials (SCMs) and ordinary portland cement (OPC) blends have been shown to mitigate external sulfate attack by improving hydrated paste properties. This study provides a comprehensive review of the sulfate attack performance of fly ash, slag, silica fume, and metakaolin. Performance is assessed as the reduction in expansion of SCM - OPC blends with a range of replacement rates compared to an OPC control when exposed to sodium and magnesium sulfate environments. In general, replacement rates of >10% fly ash, >20% slag, 3-20% silica fume, and 5-25% metakaolin were found to improve resistance to sulfate attack in sodium sulfate. Increased dosage rates improved performance in general for all SCMs except silica fume and Class C fly ash. An analysis on correlating fly ash performance to chemical composition indicated that oxide content alone could not be used as the sole indicator of fly ash sulfate attack mitigation potential. In magnesium sulfate at higher replacement rates, the performance was mixed for metakaolin and silica fume as indicated by increased expansion relative to a control. Overall, fly ash, slag, silica fume, and metakaolin can be effective in mitigating sulfate attack, but their performance is dependent on replacement rate, sulfate cation exposure, and their chemical and physical properties. (C) 2021 Elsevier Ltd. All rights reserved.

With increasing advancement in military aircraft technology, concrete pavements at Australian airbases have been experiencing premature degradation as manifested by scaling. It occurs progressively on the surface of concrete and causes higher maintenance cost and disruption to aircraft operation. This study elucidates the underlying mechanisms of scaling and recommends some low-cost alternative cementitious composites resilient to the airbase operating conditions. To prepare those cement composites, Portland cement (PC) was treated with epoxy resin, acrylic emulsion (AE) and silica fume (SF). Moreover, fly ash (FA) based geopolymer was fabricated and used as another candidate. The resilience of geopolymer, epoxy-SF-cement, AE-SF-cement, and plain PC mortar (control) are examined after prolonged exposure to reproduced airfield environmental conditions. The exposures conditions are applied cyclically until surface scaling is formed. XRD (X-ray diffraction) and FTIR (Fourier transform infrared spectroscopy) analysis are performed to detect the decomposition of crystal lattices of mineral compounds and the degradation of covalent bonds in the cement composites. Also, changes in microstructures, loss of mass and percentages of decreases in the strength of the cement composites are determined. Scaling is developed on the plain PC mortars at the end of 2 months of exposure. However, no scaling is observed on the geopolymer, epoxy-SF-cement, and AE-SF-cement mortars even after 5 months of exposure. In comparison with all cement composites used in this study, the epoxy-SF-cement mortar retained the highest percentage of the strength and exhibited substantially better resistance to the exposure conditions used. Thus, this study recommends the epoxy-SF-cement composite to repair and rehabilitate scale concrete at military airbases. Besides, geopolymer can be used for regular construction at army airbases to combat the saponification problem noticed at an early age of exposures. Crown Copyright (C) 2021 Published by Elsevier Ltd. All rights reserved.

Sulfate optimisation of the aluminate phase (C3A) in Portland–limestone cements (PLCs) is critical for improving their hydration performance. This study investigates the changes in the sulfate attack performance of an undersulfated interground PLC (14.6% limestone) through the addition of gypsum. Isothermal calorimetry is used to measure the early-age hydration kinetics to optimise the sulfur trioxide content of the PLC. Sulfate expansion and strength loss of the undersulfated and optimised PLC in combination with fly ash is measured in both sodium sulfate and magnesium sulfate solutions. Sulfate optimisation of the PLC reduced its expansion to a greater extent in magnesium sulfate and improved strength at later ages to a greater extent in sodium sulfate. Less physical deterioration was also observed for the optimised PLC samples. Fly-ash incorporation resulted in improved expansion and strength performance for certain mixtures. Optimised samples underwent less sulfate attack as indicated by their higher calcium hydroxide contents measured by thermogravimetric analysis at later ages. The improved sulfate attack performance can be attributed in part to the formation of carboaluminate hydrates as determined by X-ray diffraction in the optimised PLC. This research study highlights the importance of sulfate optimisation in achieving PLCs with greater sulfate attack resistance.

This study has investigated the strength development of alkali-activated binders (AAB) fabricated from slag, fly ash (FA), rice husk ash (RHA), and palm oil fuel ash (POFA). Materials being used as singular, binary and ternary compositions while Ca(OH)(2), KOH and NaOH were used separately as a chemical activator. All the test results of AAB for 10 numbers of different mixes have been compared to ordinary Portland cement (OPC) mortar. Test result reveals that compressive strength of slag activated mortar with 5% NaOH (by weight of binder) achieves 88.2% compressive strength of OPC at 28 days. Among the 10 mixes, AAB4 containing 40% slag, 30% POFA and 30% RHA with 5% NaOH shows a significant compressive strength of 41.7 MPa at 28 days. Flexural strength of alkali-activated mortar with 5% NaOH seems to be acceptable compared with that of OPC mortar at 28 days. It is clearly observed that the strength development of AAB-mortar is greatly influenced by the types and fineness of materials and blending of materials. In contrast, the compressive strength of AAB-mortar is comparatively less influenced by employing different curing methods like water, wetted jute bag and air curing.

Alkali-activated binders (AAB) have been extensively researched as a potential replacement of ordinary portland cement (OPC) concrete to minimize carbon emissions released during OPC production while reusing a significant amount of industrial waste by-products. This paper provides a comprehensive review on the materials composition and the fresh properties of AAB. The chemical, physical, and mineralogical properties of a suite of pozzolans used to make AAB are analysed including fly ash, slag, metakaolin, silica fume, rice husk ash, palm oil fuel ash, and others. Sodium and potassium based alkaline activator solutions are also highlighted. The influence of AAB properties on workability (namely consistency, flow, and slump), setting time, reaction kinetics (as measured by isothermal calorimetry), and temperature are synthesized from past literature. The findings show that fresh properties of AAB can be tailored for specific applications based on mix design and processing conditions.

This study examined the crucial durability properties of cementitious materials named water absorption and sorpitivity of two alkali-activated binders (AAB) namely AAB-1 and AAB-2, which incorporated a different composition of pozzolans including rice husk ash, fly ash, palm oil fuel ash, and slag. NaOH with a concentration of 2.5 M was used to activate these binders. While the water absorption was measured at 28, 90, 180, and 270 days the sorptivity test was performed at 90, 180, and 270 days on mortar specimens. The test result indicates the AABs absorbed more water than OPC, especially at the initial period, which reduced over the curing period. Porous microstructure and consequential lower compressive strength of AABs has been considered responsible for this. Similarly, the sorptivity value was higher for both AAB than OPC. The higher water absorption and lower strength of AABs lead to a higher sorptivity. The water transport properties can be improved through increasing the strength and making a dense microstructure by optimizing the properties of pozzolans and the mixture composition of AAB.

This study has investigated the chloride ion penetration, carbonation, corrosion resistance, and drying shrinkage of alkali-activated binders (AABs) that include: (i) AAB-1 being produced from slag, palm oil fuel ash, and rice husk ash while (ii) AAB-2 is composed of slag, fly ash, and rice husk ash, both being activated by 2.5 M sodium hydroxide solution. Chloride ion penetration result revealed a slightly higher value in AAB-1 and AAB-2 mortars than the reference ordinary Portland cement (OPC) mortar when tested in NaCl solution for 270 days. Carbonation depth of AAB mortar was found more than 4.3 times higher than the OPC mortar exposed to accelerated carbonation for 540 h. Half-cell potential readings revealed a similar corrosion resistance for all the mortars after 270 days. However, AAB-1, AAB-2 and OPC mortars showed a shrinkage value of 833, 782 and 474 microstrain, respectively, after 270 days. Therefore, above-mentioned pozzolans with NaOH cannot be recommended to use (solely) as an alternative to OPC in terms of the durability aspects investigated in this study. (C) 2020 Elsevier Ltd. All rights reserved.

For portland-limestone cements (PLCs), sulfate optimization is critical for improving their hydration performance.This study investigated the changes in the sulfate attack performance of an undersulfated interground PLC (14.6% limestone) through the addition of gypsum.Isothermal calorimetry was used to measure the early-age hydration kinetics to optimize the SO3 content of the PLC.Sulfate expansion and strength loss of the undersulfated and optimized PLC was measured in both sodium sulfate and magnesium sulfate solutions.Sulfate optimization of the PLC reduced its expansion to a greater extent in sodium sulfate.Strength loss was also marginally improved at later ages to a greater extent in magnesium sulfate.The improved sulfate attack performance can be attributed in part to the formation of carboaluminate hydrates instead of monosulfate in the optimized PLC.This research highlights the importance of sulfate optimization in achieving PLCs with greater sulfate attack resistance.