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In this study, carpet waste fibers--namely, polypropylene (PP) and polytrimethylene terephthalate (PTT) in the form of mono microfibers and hybrid combinations--were studied. The optimization of mono fiber parameters for fiber content (0.1, 0.3, and 0.5%) and length (6, 12, and 24 mm [0.236, 0.742, and 0.945 in.]) were conducted to achieve the optimum strength properties and minimize drying shrinkage. The microstructure, pore structure, and fiber-matrix interfacial properties of the optimized samples were characterized at 7, 28, and 90 days by means of scanning electron microscopy (SEM), X-ray micro-computed tomography (CT), and nanoindentation. The research data revealed that the inclusion of either the optimized mono PP fiber (υf = 0.5% and l = 12 mm [0.472 in.]) or PTT fiber (υf = 0.1% and l = 12 mm [0.472 in.]) improved the compressive strength of 4.3% and 16.1%, and the flexural strength by 11.5% and 9.2% at 28 days, respectively. Hybrid carpet fibers (0.4% PP + 0.1% PTT) provided a greater enhancement in compressive strength of 6.6%, and flexural strength by 13% at 28 days. Drying shrinkage mitigation of mortar over 120 days was recorded as 18.4, 22.3, and 25.8%, corresponding to the addition of 0.5% PP fibers, 0.1% PTT fibers, and hybrid PP/PTT carpet fibers. A pore-refining effect was also observed for mortars with 0.5% PP and hybrid PP/PTT carpet microfibers. The SEM images indicated that the trilobal cross-sectional shape of PTT carpet fibers had a stronger anchoring effect with cement hydrates than the rounded shape of PP carpet fibers. Nanoindentation identified the thickness of the fiber-matrix interfacial transition zone (ITZ) as approximately 15 µm (5.9 × 10-4 in.) for both mono PP and PTT fibers. Approximately 50% of the phases in the vicinity of the fiber-matrix interface comprised a porous structure at 7 days. However, the hydration of clinker over the 90-day period promoted the formation of calcium-silicate-hydrate (C-S-H) and portlandite to form a dense microstructure. [ABSTRACT FROM AUTHOR]

Fly ash geopolymer concrete is a sustainable green construction material that has outstanding mechanical performance and is a low-energy material with a low carbon footprint. In this study, a detailed investigation of the long-term creep and drying shrinkage of three different 100% fly ash geopolymer concretes was carried out up to 1 year of age. Two geopolymers, produced from Gladstone and Pt. Augusta fly ashes, achieved approximately 700 microstrain at the end of 1 year--equivalent to the total creep strain displayed by portland cement (PC) concrete. Moreover, both geopolymer concretes displayed a lower creep coefficient than PC concrete. Hence, AS 3600 or the CEB-FIP model could be conservatively used to predict creep coefficient for two geopolymers. However, the Tarong fly ash geopolymer concrete differed significantly from the other geopolymers and achieved approximately 1900 microstrain after 1 year. The drying shrinkage of Gladstone and Pt. Augusta geopolymer concretes at 1 year are 175 and 190 microstrain, respectively, while Tarong geopolymer and PC concrete achieved 615 and 475 microstrain, respectively. All the fly ash geopolymer concrete showed lower drying shrinkage than the maximum permitted value recommended by AS3600. Incorporation of calcium-aluminasilicate- hydrate (C-A-S-H) gel with the sodium-alumina-silicatehydrate (N-A-S-H) geopolymeric gel was seen to positively affect the packing density of the gel phase. The degree of uniformity and compactness of aluminosilicate gel matrix together with the macroporosity in the 50 nm to 1 µm range was identified as determining the long-term creep and drying shrinkage of the 100% low-calcium fly ash geopolymer concrete. [ABSTRACT FROM AUTHOR]

This study evaluates the influence of the elemental distribution in the fly ash particles and their impact on phase formation and compressive strength of five low-calcium fly ash geopolymers. The degree of geopolymerization in each geopolymer system was assessed by FT-IR and solid state 27Al MAS-NMR analysis. The corresponding pore volume changes were investigated by mercury intrusion porosimetry (MIP). The uniformity of the distribution of SiO2 and Al2O3 in the fly ash was observed to directly influence the dissolution of the amorphous surface layer in the initial geopolymerization process and control aluminosilicate gel precipitation and gel-phase creation. The results showed that the higher the uniformity of distribution (coupled with the stable conversion of aluminium from octahedral to tetrahedral coordination), the higher the aluminium amalgamation with silicates. The result of this is the production of a three-dimensional (3-D) polysialatesiloxo (Si-O-Al-O-Si) polymeric gel structure with high rigidity and stability, which in turn results in higher compressive strength. It was also observed that an increase of meso-porosity in geopolymer phase formation coupled with a cumulative pore volume below 1000 nm (3.937 x 10-5 in.) is a good indicator of the degree of geopolymerization. [ABSTRACT FROM AUTHOR]

When concrete structures--such as pier supports--are placed in water, they can have a detrimental effect on the surrounding environment by causing the pH to rise. This rise in pH can harm and kill animal and plant life. The concentration of hydroxyl ions leached from concrete can be affected by a number of factors, including cement type, shape of structure, ratio of surface area and volume, and the low of the water. This paper presents the results of a research project that investigated three mixtures: 100% ordinary portland cement (OPC), 30% pulverized fly ash (PVA), and 65% ground-granulated blast-furnace slag (GGBS). Tests were conducted in both stagnant and lowing water using a range of specimen geometries and sizes. The results showed that the mixture, volume/surface area, and geometry of the specimen can affect both the rate of leaching and the cumulative number of moles of hydroxyl ions leached. [ABSTRACT FROM AUTHOR]

This paper reports the results of an experimental program to investigate the changes in the bond characteristics of deformed mild steel reinforcing due to chloride-induced corrosion. The principal parameters investigated are the cover depth, bar diameter, degree of corrosion, and the surface crack width. The results show a strong relationship between the average surface crack width and the average bond strength; the degree of corrosion does not demonstrate such a clear relationship. The bars with a 1 C/Φ (cover/diameter) show an initial increase in bond strength at the first visible crack; no similar initial increase is observed for the bars with 3 C/Φ. The bottom-cast bars display a higher bond strength with no corrosion, but a similar bond strength is observed for both top- and bottom-cast bars once cracking is observed. [ABSTRACT FROM AUTHOR]

Investigates the effect of corrosion attack on the mechanical properties of embedded reinforcement through physical tests on bars with simulated and real corrosion damage and through a simple numerical model. Possible impairment of structural capacity through loss of bar section and loss of bond between reinforcement and concrete as a result of longitudinal cracking; Suggested guidelines on assessment.