Development of ambient cured geopolymer binders based on brick waste and processed glass waste

Effect of phosphogypsum adding on setting kinetics and mechanical strength of geopolymers based on metakaolin or fly ash matrices

Our study aims to highlight the effects of the addition of phosphogypsum on certain fresh and hardened characteristics of geopolymer matrices based on metakaolin or fly ash. In the fresh state, workability and setting were studied by rheology and by the electrical conductivity measurement. The hardened state was characterized by XRD, DTA, SEM, and compressive strength measurement. Workability investigations reveal that the addition of phosphogypsum increases the viscosity, which limited the phosphogypsum addition rate to 15 wt% for metakaolin-based matrices and 12 wt% for fly ash-based matrices, with a setting retarding effect in both cases. Analyses of the matrices show dissolution of gypsum along with formation of sodium sulfate and calcium silicate hydrate. Moreover, the introduction of phosphogypsum to these matrices up to a mass rate of 6% has no significant effect on the mechanical strength. Beyond that rate, the compressive strength drops from a value of 55 MPa for the matrices without addition down to 35 MPa and 25 MPa when the addition rate is 12 wt% for the metakaolin-based and fly ash-based matrix, respectively. This degradation seems to be due to the increase in porosity created by addition of phosphogypsum.

The Obstacles to a Broader Application of Alkali-Activated Binders as a Sustainable Alternative-A Review

This paper aims to raise awareness regarding the obstacles limiting alkali-activated binders' (AABs) application as a sustainable solution in the construction industry. Such an evaluation is essential in this industry, which has been introducing a wide range of alternatives to cement binders yet achieved limited utilisation. It has been recognised that technical, environmental, and economic performance should be investigated for the broader adoption of alternative construction materials. Based on this approach, a state-of-the-art review was conducted to identify the key factors to consider when developing AABs. It was identified that AABs' adverse performance compared to conventional cement-based materials mainly depends on the choice of which precursors and alkali activators to employ and the regionalised practices adopted (i.e., transportation, energy sources, and data on raw materials). In light of the available literature, increasing attention to incorporating alternative alkali activators and precursors by utilising agricultural and industrial by-products and/or waste seems to be a viable option for optimising the balance between AABs' technical, environmental, and economic performance. With regard to improving the circularity practices in this sector, employing construction and demolition waste as raw materials has been acknowledged as a feasible strategy.

Physico-mechanical and durability properties of new eco-material based on blast furnace slag activated by Moroccan diatomite gel

Natural diatomite, an amorphous siliceous rock, was used as a source of silica for the synthesis of a silicate gel to replace commercial sodium silicate gel in the synthesis of geopolymers from blast furnace slag at room temperature. Nine diatomite gels were synthesized by varying the diatomite content in the gel by 0, 10, and 15% and the NaOH molarity by 6 M, 8 M, and 10 M. The chemico-mineralogical and microstructural characterization results of the elaborated geopolymers showed that the blast furnace slag activation by diatomite gel under optimal conditions (8 M NaOH molarity and 10% diatomite) leads to a good dissolution and polycondensation of the precursor by forming amorphous gels of C-A-S-H type, as well as the mineral phase hydrotalcite, which are the same geopolymerization products detected in the case of the use of conventional silicate gel, and consequently, the obtaining of a geopolymer with interesting physical-mechanical characteristics: compressive strength of 42 MPa, density of 1. 61 g/cm³, ultrasonic pulse velocity of 3855 m/s. Thus, this new approach used in this work proved to be successful in reducing the cost and environmental impact of geopolymers.