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The development and modification of high volume fly ash (HVFA) concrete using nanomaterials to enhance the strength has advanced significantly of late. However, the long-term behavior of HVFA concrete with nanomaterials, including permeation and durability characteristics, have yet to be studied in detail. This study reports the long-term permeation and diffusion characteristics and the carbonation of nanoengineered HVFA concretes utilizing up to 80% cement replacement with fly ash, hydrated lime, and nanosilica. The 450-day compressive strength of the HVFA concrete was 73 MPa. The air and water permeability indices of HVFA-65 and HVFA-80 concretes (65% and 80% cement replaced) decreased from 0.058 to 0.039 Ln(mbar)/min and 0.3–0.1(×10−7 m3/min0.5) between 28 and 450 days, and 0.078–0.043 Ln(mbar)/min and 0.5–0.2(×10−7 m3/min0.5) , respectively. These permeation values were significantly lower than the specified indices for low permeability concretes. The presence of pores, ranging from 30 μm to 1 mm, was observed to be the principal influence on the permeability properties. The pore size and the quantity of pores decreased significantly in the HVFA composites over time. The C─ A─ S─ H gel products formed [ Ca/Si=0.43 and Ca/(Si+Al)=0.25 ] increased both pore discontinuity and the strength of the interfacial transmission zone (ITZ). This increased the packing density in the gel matrix correlated with enhanced durability. The chloride diffusion coefficients of HVFA-65 and HVFA-80 decreased from 3.88 to 0.60(×10−12 m2/s) and from 4.06 to 1.61(×10−12 m2/s) , respectively, between 28 and 450 days. Furthermore, both HVFA-65 and HVFA-80 composites displayed low carbonation coefficients, 2.93 and 4.73 mm/month0.5 , respectively. Calcite was observed at 28 days and was attributed to the carbonation of the hydrated lime. Calcite intensity in the HVFA concretes was observed to decrease up to 90 days; this was attributed to dissolution in pore water to form the more soluble calcium bicarbonate. However, from 90 to 450 days, carbonation led to the accumulating of additional undissolved calcite (calcium carbonate) within the HVFA composites over the long term. [ABSTRACT FROM AUTHOR]

Three types of textile fabric waste, namely Kevlar, Nomex, and Cordura Nylon, were investigated in this study. The effects of the fiber parameters: volume fraction (0.1%, 0.3%, and 0.5%), length (6, 12, and 24 mm), and use of 1D fiber (width of 0) versus 2D woven fabric fiber (width of 3 and 6 mm) on strength properties, flowability, and shrinkage were studied to determine the optimum textile parameters. The pore structure, microstructure, and fiber-matrix interfacial properties of the optimised mixtures were then characterized by means of X-ray micro-CT, SEM, and nanoindentation at 7, 28, and 90 days. Results showed that the optimized parameters for three types of fabric fibers are 1D fiber (width of 0), length of 12 mm, and volume fraction of 0.3%. This optimized design provided an enhancement of strength and shrinkage resistance. Pore refinement was pronounced in the case of hydrophilic Kevlar and Nomex fibers. However, this also correlates to inferior performance in shrinkage resistance of mortar compared to hydrophobic Cordura Nylon. The fiber-matrix ITZ thickness was dependent on fiber size, while the wettability of fibers (i.e., hydrophobicity or hydrophilicity) was observed to affect the phase distribution in the vicinity of the fiber surface. Furthermore, a large volumetric proportion of the structure is porous in nature (more than 50%) in the region of the fiber-matrix interface after 7 days. With the increment of curing age, the microstructure at the fiber interface becomes denser due to the hydration of the clinker phase facilitating the growth of CSH and CH phases. [ABSTRACT FROM AUTHOR]

Production of alkali-activated binders is a developing research field that utilizes industrial/agricultural by-products and solid waste for the development of sustainable concrete. This paper comprehensively reviews the literature relating to rice husk ash (RHA)–based alkali-activated binders incorporating fly ash (low/high calcium) and blast furnace slag. The literature demonstrates that the properties of raw material significantly influence the formation of the alkali-activated gel matrix. Every precursor (low/high calcium fly ash and slag) that is used to develop alkali-activated binders with RHA have their own reaction mechanism dependant on their specific chemical composition. Hence the incorporation of RHA influences each binder in a unique way depending upon the alkali activation process and reaction mechanisms. The incorporation of RHA, in the range 5%–15%, with blended slag alkali activated binders, yields better compressive strength, when compared with RHA blended with fly ash (low/high calcium). The review presented in this paper is very useful to understand the behavior of alkali-activated binders incorporating RHA and in advancing the research into the successful application of RHA as a binder for alkali-activated materials. [ABSTRACT FROM AUTHOR]