A brief history and review of geopolymer technology is presented with the aim of introducing the technology and the vast categories of materials that may be synthesized by alkali-activation of aluminosilicates. The fundamental chemical and structural characteristics of geopolymers derived from metakaolin, fly ash and slag are explored in terms of the effects of raw material selection on the properties of geopolymer composites. It is shown that the raw materials and processing conditions are critical in determining the setting behavior, workability and chemical and physical properties of geopolymeric products. The structural and chemical characteristics that are common to all geopolymeric materials are presented, as well as those that are determined by the specific interactions occurring in different systems, providing the ability for tailored design of geopolymers to specific applications in terms of both technical and commercial requirements.

Geopolymer technology: the current state of the art

http://www.personal.psu.edu/faculty/g/u/gur/cement%20for%20the%20future.pdf

Alkali-activated fly ashes: A cement for the future

The Role of Inorganic Polymer Technology in the Development of ‘Green Concrete’

Understanding the relationship between geopolymer composition, microstructure and mechanical properties

Carbon dioxide equivalent (CO2-e) emissions: A comparison between geopolymer and OPC cement concrete

Moderately alkaline activators can be used to formulate cementitious binders with a high Supplemetary Cementitious Materials (SCMs) and a low portland cement content (hybrid alkaline cements). This study aimed to prepare hybrid alkaline cements containing large percentages of dehydroxylated bentonite (BT) and small Portland cement (OPC) fractions, with 5% Na2SO4 as a solid alkaline activator. The hydration kinetics of the pastes hydrated in water in the presence and absence of the solid activator were assessed by isothermal conduction calorimetry, whilst the reaction products were characterised with X-Ray Powder Diffraction (XRD) and Fourier-transform Infrared Spectroscopy (FTIR). The presence of the alkaline activator hastened OPC and BT/OPC hydration: more heat of hydration was released, favouring greater initial bentonite reactivity. The portlandite forming during cement hydration reacted readily with the Na2SO4, raising medium alkalinity and enhancing bentonite dissolution and with it reaction product precipitation (primarily (N,C)-A-S-H-like gels that co-exist with C-S-H- or C-A-S-H-like gels). The presence of sulfate ions favoured the formation of AFm-like phases. Preceding aspects accelerated the hydration reactions, with the formation of more reaction product and matrix densification. As a result, the 28 days Na2SO4 activated systems developed greater mechanical strength than the water-hydrated systems, with the 60% BT/40% OPC blends exhibiting higher compressive strength than the 100% OPC pastes.

/pdf/hybrid-alkaline-cements-bentonite-opc-binders-434sons7us.pdf

Hybrid Alkaline Cements: Bentonite-Opc Binders

This article review the state of the art on the effect of the joint incorporation of fluorides and sulfates to the cement crudes. This incorporation may be carried out partially replacing the traditional crudes, thus obtaining a new cement produced with a considerable energy saving and with advantageous characteristics with regard to the traditional cement.
The work presents a study of equilibrium diagrams of interest and mentions some industrial experiences developed by the researchers, authors of this article.

/pdf/influence-of-the-joint-incorporation-of-caf-2-and-caso-4-in-3wh7mascss.pdf

Influence of the joint incorporation of CaF 2 and CaSO 4 in the clinkerization process. Obtainment of new cements

This work analyzes the effect of the presence of 5 wt.% of solid sodium salts (Na2SO4, Na2CO3, and Na2SiO3) on calcium sulfoaluminate cement (CSA) hydration, addresses hydration kinetics; 2-, 28-, and 90-d mechanical strength, and reaction product microstructure (with X-ray diffraction (XRD), and Fourier transform infrared spectroscopy, (FTIR). The findings show that the anions affect primarily the reactions involved. Ettringite and AH3, are the majority hydration products, while monosulfates are absent in all of the samples. All three salts hasten CSA hydration and raise the amount of ettringite formed. Na2SO4 induces cracking in the ≥28-d pastes due to post-hardening gypsum and ettringite formation from the excess SO42– present. Anhydrite dissolves more rapidly in the presence of Na2CO3, prompting carbonation. Na2SiO3 raises compressive strength and exhibits stratlingite as one of its reaction products.

Effect of Alkaline Salts on Calcium Sulfoaluminate Cement Hydration.

The objective of this paper was to reproduce the formation of thaumasite due to the reaction of atmospheric SO 2 with hydraulic mortars. The research was carried out on mortars made with ordinary Portland cement (OPC), mineralized white Portland cement, hydraulic lime and a mixture of lime and pozzolana. Mortars underwent sulfation by exposing the samples to 300 ppm SO 2 at 25 °C and 95% RH for 2 days. Subsequently, half of the sulfated samples were kept for 6 and 12 months in a chamber with 0.3 ppm, SO 2 as pollutant (0.50 l min −1 flow gas velocity), 5 °C and 95% RH. The other halves of the sulfated samples were kept partially immersed in water at 5 °C for 4, 9 and 14 months. The process of thaumasite formation in hydraulic mortars due to the interaction of the material with atmospheric SO 2 was reproduced in all the hydraulic mortars kept partially immersed in water at low temperature, except in the lime–pozzolana mixture. Gypsum was the first reaction product formed as a result of that interaction. Subsequently, gypsum reacted with calcium carbonate and C–S–H gel resulting in the formation of thaumasite. The formation of thaumasite was easier and quicker in sulfated samples kept at low temperature partially immersed in water. Only in OPC mortars was thaumasite formation observed in samples exposed to 0.3 ppm of SO 2 for 12 months.

Thaumasite formation due to atmospheric SO2–hydraulic mortar interaction

The binders known as blended or hybrid alkaline cements are obtained by alkali-activating cementitious blends in the Na2O-CaO-SiO2-Al2O3-H2O system. The present paper discusses the results of alkali activating blends prepared were: binder BSLAG = 20 % OPC clinker + 80 % BFS; and binder BFA = 20 % OPC clinker + 80 % FA. The 2-day mechanical strength was over 15 MPa. The main reaction products were gels whose composition varied depending on the initial Ca content. In alkali-activated BSLAG cement they consisted of a mix of C-S-H/C-A-S-H and in activated BFA cement of a mix of C-A-S-H /(N,C)-A-S-H. Lianţii cunoscuţi ca cimenturi amestecate sau cimenturi alcaline hibride, sunt obţinuţi prin activarea alcalina a amestecurilor cimentoide in sistemul Na2O-CaO-SiO2-Al2O3-H2O. In acest articol sunt caracterizate cimenturile amestecate activate alcalin, preparate astfel: liantul pe baza de zgura bazica de furnal (BSLAG) = 20% OPC clincher + 80% zgura (BFS) si liantul pe baza de cenusa zburatoare (BFA) = 20% OPC clincher +80% cenusa zburatoare (FA). Rezistenţa la compresiune la 2 zile a fost de peste 15 MPa. Produsii de reacţie principali, de tip gelic, au avut o compoziţie determinata de conţinutul iniţial de Ca. Compoziţia liantului BSLAG consta din C-S-H si C-A-S-H, iar liantul BFA se caracterizeaza prin C-A-S-H si (N,C)-A-S-H.

/pdf/cimenturi-hibride-alcaline-partea-a-ii-a-factorul-clincher-2phfa006am.pdf

Ángel Palomo

Papers

Hybrid Alkaline Cements: Bentonite-Opc Binders

Influence of the joint incorporation of CaF 2 and CaSO 4 in the clinkerization process. Obtainment of new cements

Effect of Alkaline Salts on Calcium Sulfoaluminate Cement Hydration.

Thaumasite formation due to atmospheric SO2–hydraulic mortar interaction

CIMENTURI HIBRIDE ALCALINE. PARTEA a II-a: FACTORUL CLINCHER ▲ HYBRID ALKALINE CEMENTS. PART II: THE CLINKER FACTOR