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Metakaolin (MK) and ground granulated blast furnace slag (GGBS) based geopolymers have been utilised as materials for concrete road repair. However, their early-stage performance and bonding mechanism as rapid repairs are not well understood. This research investigated the workability, early strength development and bonding mechanism of geopolymer repair mortars with different GGBS contents. The reaction kinetics and reaction products of the geopolymer repairs were analyzed through reaction heat evolution and FTIR, and the microstructure of the bonding interface was examined using BSE-EDS. Results showed that geopolymer repair mortars with higher GGBS content exhibited shorter setting times, higher flowability, and higher compressive strength. Geopolymers demonstrated a one-dimensional rod-shaped nucleation pattern during hardening, and the crystallization rate decreased with GGBS addition. GGBS increased the formation of C-A-S-H gels and accelerated the geopolymerization process. However, excessive GGBS reduced bond strength due to the introduction of microcracks. A GGBS content of 60 wt.% is recommended in this investigation. The study also revealed that the cement substrate could absorb alkali activator, leading to the formation of high-Ca gels and strengthening the interface. [ABSTRACT FROM AUTHOR]

By harnessing the benefits of lowering cost and reducing CO 2 emission, employing geopolymer as the repair materials have been gaining interest. This article investigated the bond strength and degradation of metakaolin-based geopolymer mortar subjected to rapid efflorescence exposure, acid attack, freeze-thaw cycles, wet-dry cycles, and heat-cool cycles. The slant shear strength tests evaluated the new-old mortar bond strength. FTIR, XRD, and TGA were conducted to monitor the deterioration of geopolymers. Visual observation and ICP-OES tests were performed to quantify the efflorescence risk. Results showed that acid exposure mainly reduces bond strength by degrading the geopolymer framework. In aggressive environments involving moisture and temperature changes, i.e., freeze-thaw, wet-dry and heat-cool cycles, geopolymers exhibit negligible deterioration. However, the shrinkage induced by water migration and the volume expansion caused by elevated temperatures significantly decrease (up to 90%) the bond strength of geopolymer repair mortar. The negative effect imposed by the efflorescence should not be neglected. A significant bond strength reduction (up to 20%) was observed for geopolymer repair mortar suffering from efflorescence. Samples with higher granulated blast furnace slag (GGBS) addition show lower strength loss, benefiting from their lower efflorescence extent. Stoichiometrically designing the geopolymer repair binder to avoid efflorescence is recommended. [ABSTRACT FROM AUTHOR]

[Display omitted] • The properties of ITZ in geopolymer-stabilized RAP were investigated. • A model representing the interaction between geopolymer, aged asphalt, and aggregate was developed. • The impacts of RAP aging degrees on interfacial bonding were examined. • The simulation findings were corroborated by SEM-EDS results. Geopolymer technology offers significant advantages in stabilizing recycled asphalt pavement (RAP), allowing its repurposing as road construction materials. This study employs a combination of molecular dynamics simulations and experimental characterization to investigate the properties of the interfacial transition zone (ITZ) in geopolymer-stabilized RAP. A composite model of geopolymer-aged asphalt-aggregate was established using molecular dynamics (MD) to access the effects of aging degrees of RAP on the interfacial bonding. The findings revealed that aging asphalt molecules on the RAP surface exhibit an affinity for Na+ present in geopolymers. Na+ ions migrate to the interfacial region, forming electrostatic interactions with double-bonded oxygen atoms in the aging asphalt molecules. The interfacial interaction energy and nanomechanical performance grow up and then reduced with the aging degree of RAP. SEM-EDS results verified these simulation findings, indicating that C(N)-A-S-H might grow at the interface, leading to a strong affinity and external chemical bonding. [ABSTRACT FROM AUTHOR]

Using construction and demolition waste (CDW) as the geopolymer precursor is gaining increasing interest. The milling process is required in the production of CDW-based precursor. This paper aims to investigate the impacts of milling duration on CDW-based precursors and resulting geopolymer paste. Results show that prolonged milling enhances the reactivity of CDW precursors by changing the particle size, crystal structures and surface group. A longer milling duration promotes the formation of the Si-rich gel, resulting in a higher reaction degree and a more densely packed structure of CDW-based geopolymer. Benefiting from the higher strength, geopolymer derived from CDW with longer milling can achieve a lower CO 2 emission per unit strength. However, the reactivity enhancement of CDW became less apparent with the increasing milling duration since the particle aggregation and activated phases on the surface could prevent further activation. The milling for CDW-based precursor production is suggested to be appropriately prolonged but not exceed 2 h. [Display omitted] [ABSTRACT FROM AUTHOR]