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This paper studies the use of municipal solid waste incinerator bottom ash as a supplementary cementitious material in concrete products using an innovative chemical treatment approach. The primary objective is to address emissions associated with waste-to-energy facilities and the heavy reliance on ordinary Portland cement as the primary binder in concrete. The proposed method involves the removal of metallic aluminium from the bottom ash and the subsequent use of the treated bottom ash as a partial cement replacement to produce concrete. Concrete specimens were produced with varying proportions of treated or untreated municipal solid waste incinerator bottom ash, replacing 20%, 35%, and 55% of ordinary Portland cement according to EN 197 European standard for common cement. Moreover, class F fly ash was incorporated in equivalent percentages as a reference supplementary cementitious material, and a control mix was prepared using solely Portland cement. The evaluation encompassed multiple visual and analytical techniques, including scanning electron microscopy, X-ray diffraction, X-ray fluorescence, and setting time analyses on pastes made with Portland cement, fly ash, and bottom ash. All specimens were evaluated in terms of mechanical performance, namely compressive strength. The chemical treatment process facilitated the release of a significant quantity of hydrogen, a by-product of aluminium oxidization. Consequently, this resulted in significantly reduced formation of gas bubbles in concrete in the fresh state and, therefore, diminished expansion during the setting process. As the proportion of cement replacement with bottom ash increased, a decline in strength was observed. However, this decline was less pronounced when using treated bottom ash, particularly with lower levels of incorporation. • Municipal solid waste incinerator bottom ashes as partial cement replacement. • Novel NaOH-based chemical treatment for incinerator bottom ashes. • Mixes with untreated ashes present extensive expansion due to aluminium oxidization. • Treatment led to overall performance enhancement due to lower gas generation. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) members are subject to map cracking owing to the delayed ettringite formation (DEF) by excessive core temperature during the first few days of hydration. Studies on the mechanical properties of concrete with DEF expansion have been conducted to identify the variation in moduli and strength of the material. This paper provides a comprehensive review of the mechanical properties of plain concrete with DEF expansion to examine the degradation characteristics compared to the experimental conditions. The dynamic moduli, static moduli, and compressive strength of the plain concrete decreased up to 60%, 85%, and 65%, respectively, owing to large swelling, where the damage process showed colossal expansion. The reduction amount depends on the aggregate-to-cement ratio, chemical composition of the cement, aggregate type, water-to-cement ratio, and the mix. The static moduli is more sensitive to expansion in the initial expansion stage than other mechanical properties. The structural performance of DEF-affected RC members was also investigated, reviewing the relevant studies to include the structural performance of alkali-silica reaction (ASR) affected structures. The structural performance cannot be appraised using the mechanical properties of plain concrete. It was indicated that the DEF expansion of concrete core can be significantly confined by surrounding reinforcement in RC members. This inhibits the reduction in mechanical properties of concrete and results in maintaining the load-carrying capacity of RC members. Chemical prestress developed in concrete due to the swelling restraint by reinforcement, and anisotropic damage improves the stiffness of the RC members. • Comprehensive review of mechanical properties of DEF-affected plain concrete. • Structural performance of DEF-deteriorated RC members was studied. • Structural performance depends on DEF- induced stress in reinforced concrete. • DEF expansion confinement should be considered to assess structural performance. [ABSTRACT FROM AUTHOR]

Cementitious concrete is considered potentially the largest avenue to utilize the captured carbon dioxide (CO 2). Its capacity is significantly influenced by various parameters, including the CO 2 introduction method for sequestration. This paper attempted to study the variation in carbon sequestration potential of ordinary Portland cement (OPC) based concrete and paste when the CO 2 is introduced to the samples during mixing, curing and both. The carbonated samples obtained using the abovementioned methods have been compared in terms of CO 2 uptake capacity, microstructural densification, porosity reduction, and strength variations. A maximum CO 2 Uptake Capacity of about 25% was achieved under Standard Ambient Temperature and Pressure (SATP) conditions, with a maximum CO 2 Conversion of 70.35% and 93.80% obtained at the surface for CO 2 Mixing and CO 2 Curing, respectively. Further, carbon-sequestered concrete (CSC) resulted in enhanced compressive strength, and reduced the size of pores in addition to making them uniform in size. • A CO 2 Uptake Capacity of 13.9% was obtained using the CO 2 Mixing regime. • A CO2 Uptake Capacity of 19.75% was achieved using the CO 2 Curing regime. • A CO 2 uptake of 25.17% was observed using the CO 2 mixing + CO 2 curing regime. • A maximum CO 2 Conversion rate of 70.35% was achieved in the CO 2 Mixing case. • A maximum CO 2 Conversion rate of 93.80% was achieved for the CO 2 Curing case. [ABSTRACT FROM AUTHOR]

The geometric tortuosity of pores is a critical parameter for assessing the transport characteristics of eroding agents in concrete. Based on the porous, multiphase, and multiscale features of concrete composite materials, this paper establishes a model for geometric tortuosity of pores in concrete composite materials, correlating it with water-cement ratio, volume fraction and shape factor of aggregates, and quantitative analysis is conducted on the influencing factors of tortuosity. The results demonstrate a close alignment between the developed geometric model and experimental results obtained through Mercury Intrusion Porosimetry (MIP). The quantitative analysis reveals that the geometric tortuosity of pores in concrete composite materials increases with an increase in aggregate shape factor and aggregate volume fraction, while it decreases with an increase in water-cement ratio. For instance, as the aggregate shape factor increases from 1.0 to 3.0, the tortuosity of mortar increases from 8.42 to 25.28, and the tortuosity of concrete rises from 10.41 to 93.69. Similarly, as the water-cement ratio rises from 0.2 to 0.6, the tortuosity of hardened cement paste, mortar, and concrete decreases from 13.68, 18.22, and 29.33 to 7.23, 9.42, and 14.76, respectively. Furthermore, an increase in aggregate volume fraction from 0.1 to 0.5 leads to an increase in the tortuosity of mortar from 12.29 to 13.79 and the tortuosity of concrete from 18.08 to 22.76. • A model proposed for the geometric tortuosity of concrete. • A model reflected the time-varying characteristics of concrete microstructure. • A close alignment between the developed geometric model and MIP test results. [ABSTRACT FROM AUTHOR]

This paper presents an investigation into the potential of recycling fly ash - based geopolymer concrete, to produce a recycled binder for circular re – use as starting material. The aforementioned would be a significant advantage over Portland cement which is non – recyclable, owing to its irreversible hydration. The experiment conducted involved crushing and sieving old parent fly ash – based geopolymer concrete, to separate out the paste from aggregate. The paste was then pulverized using a ball – mill to produce the recycled aluminosilicate starting material, herein referred to as recycled geopolymer cement (RGPC). Fly ash was blended with 0 to 100% RGPC, then used to prepare fresh geopolymer paste and mortar mixtures activated using a binary alkali activator consisting of sodium hydroxide and sodium silicate. Samples were cast then cured at 23 or 80 °C. The various tests done were workability, setting time, compressive strength, splitting tensile strength, drying shrinkage, water absorption, and volume of permeable pores. Analytical studies were done using X – ray diffraction, scanning electron microscopy and Fourier – transform infrared spectroscopy. Results showed that incorporation of RGPC into geopolymer mixtures generally led to reduction of workability and setting time, reduction of compressive and tensile strength, along with increase in drying shrinkage. It was, however, found that up to 60% RGPC can be incorporated into geopolymer mixtures while maintaining adequate performance suitable for structural applications. Unlike Portland cement, hardened geopolymer concrete is evidently recyclable to produce a circularly re – usable binder. [Display omitted] • FA–GPC is fly ash geopolymer cement, RGPC is recycled geopolymer cement. • FA-GPC concrete is recyclable to produce a circularly re - usable binder. • RGPC effectively underwent geopolymerisation to form the binder phase. • RGPC incorporation led to reduction of mortar strength and workability. • Mortars containing ≤ 60% RGPC gave strengths > 50 MPa suited for structural uses. [ABSTRACT FROM AUTHOR]

Proper bonding between different layers of a composite pavement is a major factor in ensuring that the entire structure acts as a monolithic layer under load. This paper studies the bonding between hot mix asphalt (HMA) overlay and Portland cement concrete (PCC) pavement using tack coats. An in-situ pull-off test method was developed for use on project sites on a routine basis to screen and test the quality of bond between asphalt layer and concrete layer. This test replaces the arduous process of coring through often times very thick concrete layer with steel rebars, transporting the core to a lab, trimming the concrete side of the core to fit the shear jig, and finally conducting a shear test. Results show that the in-situ pull-off test method developed in this study is strongly correlated to the laboratory based direct shear test. Limits were also suggested to indicate an adequate bond strength in the PCC–HMA interlayer on the basis of laboratory and field testing. This study also evaluates the influence of various factors on the performance of the interlayer bond in laboratory. These factors include the type of tack coat, application rate, the texture of the concrete pavement surface, the surface cleanliness and the surface moisture. Results indicate that sandblasting and hydro-demolition textures offer the best interlayer bond strength, the influence of application rate is not significant on the interlayer bond strength and the influence of surface moisture and cleanliness are dependent on the type PCC surface texture. • The study develops a pull-off test method to test the HMA–PCC interlayer bond. • This test has a potential to replace the direct shear test performed in laboratory. • This test is performed on-site which requires only 1.5 h to test four replicates. • Pull-off strength strongly correlates with the direct shear strength. [ABSTRACT FROM AUTHOR]